ATMOSPHERIC OZONE RESEARCH AND ITS POLICY IMPLICATIONS
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Studies in Environmental Science 35
ATMOSPHERIC OZONE RESEARCH AND ITS POLICY IMPLICATIONS Proceedings of the 3rd US-Dutch International Symposium, Nijmegen, The Netherlands, May 9- 13 , 1 9 8 8
Organized by the EnvironmentalProtectionAgency, United States of America, and the Ministry of Housing, Physical Planning and Environment, The Netherlands Edited by
T. Schneider National Institute of Public Health and Environmental Protection, 3 7 2 0 BA Bilthoven, The Netherlands
S.D. Lee Harvard University, Energy and Environmental Policy Center, Cambridge, M A 02 138, U.S.A. G.J.R. Wolters Ministry of Housing, Physical Planning and Environment, 2260 MB Leidschendam, The Netherlands L.D. Grant US Environmental Protection Agency, Research TrianglePark, NC 2 7 7 1 1, U.S.A.
ELSEVlEH Amsterdam - Oxford - New York -Tokyo
1989
ELSEVIER SCIENCE PUBLISHERS B.V. Sara Burgerhartstraat25 P.O. Box 21 1, 1000 AE Amsterdam, The Netherlands
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First edition 1989 Second impression 1990
ISBN 0-444-87266-3
0 Elsevier Science Publishers B.V., 1989 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science Publishers B . V . 1 Physical Sciences & EngineeringDivision, P.O. Box 330, 1000 AH Amsterdam, The Netherlands.
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Other volumes in this series
1 Atmospheric Pollution 1978 edited by M.M. Benarie
2 Air Pollution Reference Measurement Methods and Systems edited by T. Schneider, H.W. de Koning and L.J. Brasser
3 Biogeochemical Cycling of Mineral- Forming Elements edited by P.A. Trudinger and D.J. Swaine
4 Potential Industrial Carcinogens and Mutagens by L. Fishbein
5 Industrial Waste Management by S.E. Jprrgensen 6 Trade and Environment: A Theoretical Enquiry by H. Siebert, J. Eichberger, R. Gronych and R. Pethig 7
Field Worker Exposure during Pesticide Application edited by W.F. Tordoir and E.A.H. van Heemstra-Lequin
8 Atmospheric Pollution 1980 edited by M.M. Benarie 9 Energetics and Technology of Biological Elimination of Wastes edited by G. Milazzo 10 Bioengineering, Thermal Physiology and Comfort edited by K. Cena and J.A. Clark 11 Atmospheric Chemistry. Fundamental Aspects by E. M6szBros
12 Water Supply and Health edited by H. van Lelyveld and B.C.J. Zoeteman 13 Man under Vibration. Suffering and Protection edited by G. Bianchi, K.V. Frolov and A. Oledzki 14 Principles of Environmental Science and Technology by S.E. Jprrgensen and I. Johnsen
15 Disposal of Radioactive Wastes by Z. Dlouhi, 16 Mankind and Energy edited by A. Blanc-Lapierre 17 Quality of Groundwater edited by W. van Duijvenbooden, P. Glasbergen and H. van Lelyveld
18 Education and Safe Handling in Pesticide Application edited by E.A.H. van Heemstra-Lequinand W.F. Tordoir 19 Physicochemical Methods for Water and Wastewater Treatment edited by L. Pawlowski 20 Atmospheric Pollution 1982 edited by M.M. Benarie 21 Air Pollution by Nitrogen Oxides edited by T. Schneider and L. Grant 22 Environmental Radioanalysisby H.A. Das, A. Faanhof and H.A. van der Sloot 23 Chemistry for Protection of the Environment edited by L. Pawlowski, A.J. Verdier and W.J. Lacy
vr 24 Determination and Assessment of Pesticide Exposure edited by M . Siewierski 25 The Biosphere: Problems and Solutions edited by T.N. Veziroglu 26 Chemical Events in the Atmosphere and their Impact on the Environment edited by G.B. Marini-Bettblo 27 Fluoride Research 1985 edited by H. Tsunoda and Ming-Ho Yu 28 Algal Biofouling edited by L.V. Evans and K.D. Hoagland 29 Chemistry for Protection of the Environment 1985 edited by L. Pawlowski, G. Alaerts and W.J. Lacy 30 Acidification and its Policy Implications edited by T. Schneider 31 Teratogens: Chemicals which Cause Birth Defects edited by V. Kolb Meyers 32 Pesticide Chemistry by G. Matolcsy, M. Nhdasy and V. Andriska
33 Principles of Environmental Science and Technology (second revised edition) by S.E. Jargensen 34 Chemistry for Protection of the Environment 1987 edited by L. Pawlowski, E. Mentasti, C. Sarzanini and W.J. Lacy
VII CONTENTS
Foreword The E d i t o r s
SESSION I
............................................
XVII
PLENARY SESSION: WELCOME AND OVERVIEW PAPERS
Opening Address P.J.Verkerk
............................................
3
Keynote Address V.A.Newil1
.............................................
11
Ozone Health E f f e c t s and emerging Issues i n Relation t o Standards s e t t i n g M.Lippmann
21
Photochemical Oxidant Formation: Overview o f c u r r e n t Knowledge and emerging Issues 6.Dimitriades
..........................................
35
Current Knowledge o f Ozone on Vegetation/Forest E f f e c t s and emerging Issues G.H.M.Krause and B.Prinz
45
Global elemental Cycles and Ozone J.van Ham
57
Changes i n atmospheric Composition and C1 imate C.J.E.Schuurmans
73
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SESSION II
TROPOSPHERIC OZONE, OXIDANTS AND PRECURSORS: SOURCES AND LEVELS
Motor Vehicles as Sources o f Compounds important t o tropospheric and stratospheric Ozone F.M.Black
..............................................
85
VIII
Emission Inventories for Europe C.Veldt ................................................
111
Sources and Levels of Background Ozone and its Precursors and Impact at Ground Level A.P.Altshuller .........................................
127
Trends in atmospheric Trace Gases S.A.Penkett ............................................
159
Concentrations and Patterns of Ozone in Western Europe R.Guicherit ............................................
167
Concentrations and Patterns of photochemical Oxidants in the United States B.E.Tilton and S.A.Meeks ...............................
177
Trends in ambient Ozone and Precursor Emissions in U.S. urban Areas T.C.Curran .............................................
195
Relationships among Ozone Exposure Indicators in the United States T.McCurdy ..............................................
205
SESSION I I I
EFFECTS ON VEGETATION AND ECOSYSTEMS
Analysis of Crop Loss for alternative Ozone Exposure Indices D.T.Tingey, W.E.Hogsett and E.H.Lee
219
Effects of Ozone on agricultural Crops S.V.Krupa and M.Nosa1
229
....................
..................................
Effects of Ozone and Ozone-acidic Precipitation Interaction on Forest Trees in North America W.J.Manning 239
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Evaluation of Ozone Effects on Vegetation in The Nether1 ands A.E.G.Tonnei jck
........................................
251
IX
Consequences of decreased atmospheric Ozone: Effects o f ultraviolet Radiation on Plants L.O.Bj8rn ..............................................
261
What are the Effects of UV-B Radiation on Marine Organisms? 269 R.C.Worrest ............................................
SESSION IV
EMERGING HEALTH STUDY METHODOLOGIES AND ISSUES
Critical Issues in Intra- and Interspecies Dosimetry of Ozone F. J .Mi 11 er and J .H.Overton .............................
281
Do functional Changes in Humans correlate with the Airway
Removal Efficiency of Ozone? T. R.Gerri ty and W. F .McDonnel 1
..........................
293
Extrapulmonary Effects of low Level Ozone Exposure E.Yokoyama, 1.Uchiyama and H.Ari to .....................
301
Responses of selected reactive and nonreactive Volunteers to Ozone Exposure in high and low Pollution Seasons J.D.Hackney, W.S.Linn, D.A.Shamoo and E.L.Avo1 ......... 311 Dosimetric Model of acute health Effects of Ozone and Acid Aerosols in Children M.E.Raizenne and J.D.Spengler ..........................
319
Is there a Threshold for human health Risk from Ozone? D.B.Menze1 and R.L.Wolpert .............................
331
Ozone-induced Changes in the Pulmonary Clearance of 99?c-DTPA in Man H.R.Kehr1, L.M.Vincent, R.J.Kowalsky, D.H.Horstman. J. J.O-Nei1, W.H.McCartney and P.A.Bromberg ............. 343
X SESSION V
GLOBAL ATMOSPHERIC CIRCULATION AND MODELING
Chemistry o f stratospheric Ozone Depletion i n c l u d i n g possible Mechanisms underlying the A n t a r c t i c Ozone Hole G.D.Hayman
.............................................
355
P o t e n t i a l E f f e c t s o f stratospheric Ozone Depletion and global Temperature Rise on urban Photochemistry M.W.Gery, R.D.Edmond and G.Z.Whitten
365
A Scenario Study o f t h e Greenhouse E f f e c t J.Rotmans
377
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SESSION V I
MOBILE SOURCE CONTROL TECHNOLOGIES
Motor Vehicle Contribution t o global and transported A i r Pol 1u t i o n M.P.Walsh and C.A.Moore
................................
387
Evaporative and r e f u e l i n g Emissions: Options f o r Control i n the U.S.A. R.A.Rykowski and J.F.Anderson 405
..........................
Evaporation and r e f u e l i n g Losses: Options f o r Control i n Europe A.Friedrich
423
Heavy Duty Diesel Emissions Control: I m p l i c a t i o n s f o r Fuel Consumption H.D.Freeman
431
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............................................
Effectiveness o f Control Technology i n Use and I m p l i c a t i o n s f o r a P o l i c y on T r a f f i c Emissions 443 L.C.van Beckhoven and Y.J.Zwalve
.......................
Overall P r o g r a m f o r Monitoring t h e Emission Behaviour o f new and I n - t r a f f i c Motor Vehicles K.Becker
455
Mobile Source Control Strategies i n The Netherlands M.Kroon
467
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................................................
XI
SESSION VII
MECHANISMS OF HEALTH EFFECTS
Persistence of Ozone-induced Changes in Lung Function and Ai m a y Responsiveness L. J.Fol i nsbee and M. J.Hazucha ..........................
483
Ozone-induced Lung Function Changes in normal and asthmatic Subjects and the Effect of Indomethacin W.L.Eschenbacher, R.L.Ying, J.W.Kreit and K.B.Gross .... 493 Effects of Ozone on the Production of active bactericidal Species by A1 veol ar Macrophages M.A.Amoruso, J. E. Ryer-Powder, J .Warren, G. W i tz and B.D.Goldstein ..........................................
501
Impact Mechanisms of Ozone at Cell Level I.Rientjens, L.van Bree, A.Konings, P.Rombout and G.Alink ................................................
513
Ozone-induced structural Changes in Monkey Respiratory System D.M.Hyde, C .G. P1 opper, J .R.Harkema, J .A. St .George, W.S.Tyler and 0.L.Dungworth ............................
523
SESSION VIII CHRONIC OZONE EXPOSURE HEALTH EFFECTS The Impact of a 12-Month Exposure to a diurnal Pattern of Ozone on pulmonary Function, antioxidant Biochemistry and Immunology E.C.Grose, M.A.Stevens, G.E.Hatch, R.H. Jaskot, M. J.K.Selgrade, A.G.Stead, D.L.Costa and J.A.Graham .... 535 Effects of repeated Exposure to 0.15 ppm O3 for four Months on bronchial Reactivity in Guinea Pigs (4 hrs/day; 5 days/wk) J.Kagawa, M.Haga and M.Miyazaki ........................ 545 Respiratory Tract Dosimetry of [18]O-labeled Ozone in Rats: Implications for a Rat-human Extrapolation of Ozone Dose 6.E.Hatch, M. J.Wiester, J .H.Overton and M.Aissa ........ 553
XI1
SESSION I X
ATMOSPHERIC CHEMISTRY AND MODELING
The Use o f Ozone Modeling i n t h e Design o f Control St r at eg ies E. L.Meyer Jr.
563
Ozone and Oxidants i n t h e planetary boundary Layer R.M.van A a l s t
573
Comparison o f chemical Mechanisms i n photochemical Models R.G.Dement and A.M.Hough
589
I n t e r a c t i o n o f planetary boundary Layer and f r e e Troposphere P J H Bui1tj e s
605
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...
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Development and Evaluation o f the regional Oxidant Model f o r the Northeastern United States 613 K. L. Schere and R.A.Way1 and
.............................
Evaluation o f Ozone Control Strategies i n t h e Northeastern Region o f the United States N.C. Possiel , J.A.Ti kvart, J.H.Novak, K.L.Schere and E. 1.Meyer
..............................................
623
Photochemical Oxidant Model A p p l i c a t i o n w i t h i n t h e Framework o f Control Strategy Development i n t h e Dutch/ German P r o g r a m PHOXA J.Pankrath
.............................................
633
C a l c u l a t i o n o f Long Term averaged Ozone Concentrations F.A.A.M.de Leeuw, H.J.van Rheineck Leyssius and P.J.H.Builtjes
.........................................
647
Model Calculations o f Ozone i n t h e atmospheric boundary Layer over Europe j3.Hov
657
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XI11
SESSION X
STATIONARY SOURCE CONTROL TECHNOLOGIES
Hydrocarbons 2000 N.Stenstra
667
VOC Control i n Storage and Process Industry J. J.Verhoog
675
NOx Control Technology f o r large Combustion I n s t a l l a t i o n s J.van der Kooij
681
Perspectives f o r 1ow-solvent Pal nts J.C.den Hartog
691
............................................. ............................................ ........................................
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SESSION X I
RECENT STUDIES ASSESSING THE NEED FOR AN ADDITIONAL LONG-TERM OZONE STANDARD
The Need f o r an eight Hour Ozone Standard P. J .A. Rombout , L. van Bree, S .H. Hei sterkamp and M.Marra
701
The Dynamics o f human Exposure t o tropospheric Ozone P.J.Lioy and R.V.Dyba
711
Pathobiochemical Effects i n Rat Lung related t o episodic Ozone Exposure L .van Bree, P. J .A. Rombout* I.M.C .M. Rientjens J.A.M.A.Donnans and M.Marra
723
Pulmonary Function Studies i n the Rat addressing Concentration versus Time Relationships o f Ozone D. L.Costa, G. E.Hatch, J.Highf 111, M.A.Stevens and J.S.Tepper
733
The i n f l a m a t o r y Response i n human Lung exposed t o ambient l e v e l s o f Ozone H.S.Koren, R.B.Dev1 in, D. E.Graham, R.Mann and W. F.McDonnel1
745
................................................ ..................................
............................
.............................................
..........................................
XIV
Changes i n pulmonary Function and Airway Reactivity due t o prolonged Exposure t o t y p i c a l ambient Ozone Levels D.Horstman, W.McDonnel1, L.Folinsbee, S.Abdu1-Salaam and 755 P.Ives
.................................................
SESSION XI1
SOURCE CONTROL FOR STRATOSPHERIC OZONE PROTECTION
Overview o f Controls f o r Chlorofluorocarbons D.L.Hamn and W.J.Rhodes
765
Moving Forward: Key Implications o f the Montreal Protocol D.Dul1, S.Seide1 and J.Wells
775
Prevention o f stratospheric Modification L.Rei jnders
785
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SESSION X I I I
HEALTH EFFECTS OF STRATOSPHERIC MODIFICATION
Health Effects o f stratospheric Ozone Depletion: An Overview M.L.Kripke
795
Effects o f increased UV-B on human Health J.C.van der Leun
803
Ozone Change and Melanoma F.R.de Grui j l
813
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SESSION X I V
RISK EVALUATION, CONTROL COSTS
AND ASSESSMENT
Application o f the NAAQS Exposure Model t o Ozone T.McCurdy and R.A.Pau1
825
Risk Analysis and Evaluation f o r Development o f an Ozone Control Strategy K.R.Kri jgsheld and S.Zwerver
837
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xv A health Risk primary Ozone S.R.Hayes, R.L.Winkler
Assessment f o r Use i n s e t t i n g the U.S. Standard A.S.Rosenbaum, T.S.Wallsten, R.G.Whitfield, and H.Richmond
.............................
851
Estimated economic Consequences o f Ozone on Agriculture: Some Evidence from the U.S. R.M.Adams
869
Estimating t h e Costs o f c o n t r o l l i n g ambient Ozone i n the United States T.McCurdy, W.Battye, M.Smith and M.Deese
881
Estimated Costs and Benefits o f c o n t r o l l i n g Chlorofluorocarbons D.Du11. S.Seide1 and J.Wells
891
Cost-effectiveness o f s p e c i f i c Control Options f o r VOC Emissions - A European O i l Industry Assessment R.J.Ellis
901
Options f o r VOC-Reduction i n t h e mechanical and e l e c t r i c a l engi neeri ng Industry J.Nobe1
911
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SESSION XV
POLICY ISSUES AND CONTROL STATEGIES
Emerging U.S. Pol i c y regarding stratospheric and Ground Level Ozone D.Clay
919
Ozone Control P o l i c y i n The Netherlands 6. J.R.Wo1 t e r s , S.Zwerver and K.R.Krijgsheld
931
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............
Conrnent on P o l i c y Issues and Control Strategies o f U.S. EPA, Ozone NAAQS M.A.Mehlman
943
The Ozone Layer Depletion and European P o l i c i e s M. J . Scoul 10s
949
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xv I Chairman-s concluding Remarks L.D.Grant
..............................................
953
POSTER SESSION Ozone Aggravates H i stopathology due t o a r e s p i r a t o r y I n f e c t i o n i n t h e Rat H.van Loveren, P. J.A.Rombout and J.G.Vos
967
Adaptation upon Ozone Exposure i n Mice and Rats T.S.Veninga
............................................
975
..............................................
981
......................................
983
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1009
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ORGANIZATION
LIST OF PARTICIPANTS
SUBJECT INDEX
PAPERS RECEIVED LATE
...................................... 1013
Stationary Source Characterization and c o n t r o l S t r a t e g i e s f o r r e a c t i v e v o l a t i l e organic Compounds G.B.Martin
.............................................
1015
Global Modeling o f Ozone and Trace Gases W.L.Grose, R.S.Eckman, R.E.Turner and W.T. Blackshear
... 1021
C a t a l y t i c Control o f Hydrocarbons i n autornative Exhaust H.S.Gandhi and M.Shelef
1037
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XVII
FOREWORD
The t h i r d US-Dutch I n t e r n a t i o n a l Symposium on Ozone Research and i t s P o l i c y Implications was h e l d i n Nijmegen, The Netherlands, from May 9-13, 1988, as one o f the a c t i v i t i e s under the Memorandum o f Understanding between t h e United States o f America and The Netherlands. The f i r s t Symposium i n t h i s series dealing with a i r p o l l u t i o n was held i n Maastricht, The Netherlands, May 1982 and addressed problems associated w i t h n i t r o g e n oxides p o l l u t i o n . The f o l l o w i n g Symposium held i n Williamsburg, V i r g i n i a USA, i n May 1985 discussed issues concerning a i r p o l l u t i o n by aerosols. The present Symposium covers the wide range o f issues concerning ozone p o l l u t i o n both i n t h e troposphere as w e l l as i n t h e stratosphere. Recent research r e s u l t s as w e l l as p o l i c y measures t o reduce t h e impact o f ozone o r secondary e f f e c t s caused by UV-B r a d i a t i o n , were discussed. These proceedings contain the t e x t s o f t h e opening statements made by US and Dutch Government o f f i c i a l s , t h e keynote sddress given by Dr.Vaun Newill, Assistant Administrator o f the United States Environmental Protection Agency and the technical papers presented a t t h e Symposium. I n a d d i t i o n t o the technical papers a number o f poster presentation were made during t h e Symposium. The successful conduct o f an i n t e r n a t i o n a l conference o f t h i s magnitude, depends on the cooperation and dedication o f numerous i n d i v i d u a l s and groups t o whom the e d i t o r s o f t h i s Symposium are deeply indebted. The organization o f t h e Ozone Symposium, e s p e c i a l l y t h e preparation o f the f i n a l p r o g r a m was made possible w i t h the a i d o f t h e members o f t h e US and Dutch Advisory C o n i t t e e s l i s t e d i n t h e present volume, t h e sessions' chairmen and i t s rapporteurs. The invaluable h e l p o f Mr.David S t r o t h e r o f the O f f i c e o f I n t e r n a t i o n a l A f f a i r s o f t h e US Environmental Protection Agency i s g r e a t l y appreciated as w e l l . It would be impossible t o acknowledge here a l l those i n d i v i d u a l s who have c o n t r i b u t e d i n many ways t o the organization o f t h e Symposium and i t s associated events as w e l l as t o the subsequent preparation f o r p u b l i c a t i o n o f t h e present proceedings. However, we would l i k e t o express our sincere appreciation t o a number o f s p e c i f i c i n d i v i d u a l s whose very hard work and cooperation contributed i n such a l a r g e way t o t h e f i n a l success o f t h e conference. We would l i k e t o recognize t h e e x c e l l e n t work p e r f o m d by J.van Ham o f TNO Study and Information Centre f o r Environmental Research who served as i n t e r n a t i o n a l secretary t o the Symposium, by S.Zwerver o f t h e M i n i s t r y o f Housing, Physical Planning and Environment and O t t e l i e n van Steenis o f t h e National I n s t i t u t e o f Public Health and Environmental P r o t e c t i o n as a c t i v e members o f t h e Organizing C o n i t t e e , t o Nel Venis-Pols from TNO Study and
XVIII
Information Centre for Environmental Research and Hanneke Brosi -Heymans from the National I n s t i t u t e of Public Health and Environmental Protection as members o f the Symposium Bureau, without whom the organization o f the Symposium and i t s successful conduct would not have been possible. We are also grateful f o r the excellent organization and conduct by Mrs.M.Schneider o f the partners programne. This programne involved not only the excursions during the conference week but also two well attended weekends before and the a f t e r the conference. Not only s i t e s i n Nijmegen and i t s surroundings were v i s i t e d but also other i n t e r e s t i n g parts o f The Netherlands. Especially the weekend t r i p t o the south-western p a r t o f the country was highly appreciated by the foreign guests. There were during the Symposium week also numerous social events, including the Symposium dinner and several receptions associated with the meeting. Thanks are due t o the M i n i s t r y o f Housing, Physical Planning and Environment, the Council o f the City o f Nijmegen and the Board o f Directors o f the National I n s t i t u t e o f Public Health and Environmental Protection for hosting the receptions during the conference. O f great value t o the Organizing Comittee was also the excellent help given by representatives o f the symposium hotels, Hotel Erica and Hotel Val Monte, both i n Berg en Dal near Nijmegen, Nessrs. Van V l i e t and t h e i r coworkers offered a very high standard o f Dutch h o s p i t a l i t y t o a l l our hosts a t the Symposium. F i n a l l y a special word o f thanks i s due t o O t t e l i e n van Steenis who took also care o f the preparations f o r these proceedings including corrections and adjustments i n the prepared papers, i n time t o meet the deadline f o r pub1ication. We hope t h a t these proceedings from the International Symposium on Ozone Research and i t s Policy Implications, w i l l be h e l p f u l as a reference volume, both f o r research s c i e n t i s t s and policymakers i n the environmental field. Preparations are already under way f o r the f o u r t h US-Dutch international symposium, which i s t o be hosted by the United States o f America i n 1991.
The Editors
T
SESSION I
PLENARY SESSION: WELCOME AND OVERVIEW PAPERS
Chairmen
G.J.R. Wolters L. Grant
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T. Schneider et aL (Editors),Atmospheric Ozone Research and ite Policy Zmplicotiona 1989 Elsevier Science Publishers B.V., Ameterdam Printed in The Netherlands
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3
OPENING ADDRESS
P. J. VEFMERK Ministry of Housing, Physical Planning and Environm8nt, P.O. Box 450, 2260 ME Leidschendam (The Netherlands)
INTRODUCTION On behalf of Minister Nijpels, the Dutch Minister of Housing, Physical Planning and Environment, it is my pleasure to welcome you here in Nijmegen on the ozone-symposium. Minister Nijpels regrets not being here. He has to accompany her majesty Queen Beatrix on a state visit to Canada. In particular I would like to welcome Mr. Newill, Assistant Administrator for Research and Development and Mr.Clay, Acting Assistant Administrator for Air and Radiation from the Environmental Protection Agency in the United States of America. This ozone symposium has been organized by the Environmental Protection Agency of the United States of America and the Ministry of Housing, Physical Planning and Environment of the Netherlands. The close co-operation between these two organizations stems from an agreement between our two countries regarding co-operation on environmental matters. A Memorandum of Understanding to this end was signed in 1980 by Dr. L. Ginjaar, former Dutch Minister of Health and Environmental Protection, and Mr. D.M. Costle, former Administrator of the U.S. Environmental Protection Agency. The first joint symposium, which dealt with air pollution caused by nitrogen oxides (NO,), was held by in Maastricht in 1982. It was one of the most important scientific events of the Dutch-American bicentennial, which celebrated 200 years of unbroken friendly relations between our two nations. Her majesty Queen Beatrix, who attended the opening of the first symposium, attaches great importance to a clean environment. She would most likely have attended this opening too, were it not for the fact that she is currently making a state visit to Canada. Bilateral co-operation between countries offers an opportunity to acquire and deepen knowledge together and to support one
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another in dealing with problems. The fruits of such co-operation can, in turn, provide an impulse for the broader international cooperation which is sorely needed. The problems associated with air pollution from ozone are a good illustration of the fact that environmental protection, preservation and management cannot be the business of one nation alone. This has been made painfully clear to us by the large scale ambient ozone pollution and especially by the damage being done to the ozone layer by CFC's in the stratosphere. A topic like this one, which does not stop at any national boundary but affects the whole world, is very appropriate to the co-operation between our countries in the context of the Memorandum of Understanding. This symposium, like the two earlier ones, is being held in the framework of the Memorandum of Understanding. The first symposium, which was held in Maastricht in 1982, was devoted to nitrogen oxides and was a great success. Since then, there has also been movement in NO, abatement policy internationally. Effective NO, control measures are starting to take shape. Hopefully, many countries will be ready to sign the NO, Protocol to the ECE Convention on Long Range Transboundary Air Pollution late this year; this Protocol will promote the reduction of NO, emissions. Standards are also being prepared for the European Community, including ones pertaining to NOI in vehicle exhaust. The Netherlands, together with the Federal Republic of Germany, Denmark, Portugal and Greece, is striving after stringent EC standards, comparable to those in force in the U.S. The second symposium in the series took place in Williamsburg in 1985 and dealt with the problem of aerosols. I had the opportunity to attend this aerosolsymposium and it is a great pleasure to recognize so many good friends among the audience today. This second symposium was also a succes. New particulate norms, based on the PM-10 standard, are now in effect in the U.S.. The World Health Organization Air Quality Guidelines, brought out late last year, also speak out for the PM-10 standard as the relevant health parameter. The Netherlands is trying to get the PM-10 standard accepted in Europe through the intended revision of the EC Directive on Sulfur Dioxide and Suspended Particulates. This would introduce harmonization on at least a trans-Atlantic, though not a worldwide, scale.
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The major focus of this third symposium, is both to address the problems of tropospheric pollution caused by ozone and other photochemical oxidants and to examine the possible consequences of projected changes in stratospheric ozone resulting from anthropogenic activities. The choice of ozone for this international symposium reflects the need for an international approach to evaluating and dealing with these problems. Air pollution, and especially the ozone problem, is a topic which is receiving a great deal of attention, certainly in the Netherlands. Environmental pollution in general, and air pollution in particular, have international dimensions. That is why the Netherlands considers international co-operation on environmental matters so vitally important. In addition to our existing bilateral agreements, with Poland and the U.S. among other, our country is also entering into an agreement with Canada for co-operation in the environmental field. Minister Nijpels of Environment and his Canadian colleague, Mr. T. MacMillan, will sign a Memorandum of Understanding this week, during Queen matrix's state visit to Canada. The EPA has also organized a workshop on polar ozone this week in Colorado. It is, of course, regrettable that various experts have had to choose between attending that workshop or this ozone symposium. But the fact of these two meetings occurring simultaneously does illustrate the enormous attention for the ozone problem which currently exists. EPA Administrator Lee Thomas underlined this once again most emphatically in a conversation that I had with him several weeks ago. Ozone will also be an important topic in the World Conference on "The Changing Atmosphere Implications for Global Security" to be held in Toronto late next month. In short, ozone is receiving ample international attention. But these events also illustrate the general recognition of the fact that environmental problems do not stop at national borders and that environmental management cannot be allowed to, either. SCALES OF ENVIRONMENTAL PROBLEMS Only 15 or 20 years ago, it was chiefly the local impact of pollution that was recognized. But today's environmental problems are presenting themselves on different scales.
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The lowest level of scale is that of local ecosystems like urban and industrial areas where man has disconnected himself from nature and the ecosystem is governed by technology and its buildings. The indoor environment is also part of this. The small-scale ecosystems of landscapes operate at the regional level. The processes occurring in the soil are the most distinctive ones of regional ecology. The fluvial scale has to do with river basins like those of the Rhine in Europe and the Mississippi in North America. The water cycle is characteristic of fluvial ecosystems: they are fed by moist air currents originating over the oceans to which the water ultimately returns. The continental scale, consisting of continents and oceans, comes above the fluvial scale. The prevailing air and ocean currents - such as the Atlantic Ocean's Gulf Stream - are salient features in these ecosystems. These, in turn, are determinant in the functioning of the smaller-scale ecysystems on the continents and in the oceans. At the global level, it is primarily the flows of energy and radiation which determine the earth's ecosystem. The ozone layer in the stratosphere protects the earth f r o m the harmful effects of the sun's ultraviolet. R6ntgen rays and radiant heat plays a major role in the troposphere. The lowest level of scale - that of local ecosystems - usually falls within the borders of a single country. The political and administrative structure for handling problems on this scale is the most well developed. Because of our country's small size, we in the Netherlands were rather rapidly confronted with the
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necessity of seeking political and administrative frameworks outside our borders. Frameworks which are suitable for dealing with the environmental problems occurring at the various higher levels of scale. Political and administrative structures like the Benelux, EC, OECD, ECE and UN can serve as platforms for solving problems occurring at the various higher levels of scale. New Structures have also been created where they used to be lacking. This has been the case, for example, at the fluvial scale of the Rhine. The International Rhine Commission, which is composed of representatives from the countries through which the Rhine flows, recently drew up the Rhine Action Plan and the environmental ministers of the countries involved formalized the plan on October la', 1987. Discharges of most priority substances will have to be reduced to 50 percent of their 1985 levels in 1995. It is just an exemple. Similar initiatives have been taken in relation to the pollution of the North Sea and the Mediterranean Sea.
A common feature of the environmental problems occurring at the various levels is that they make it painfully clear that the relationship between man and his environment has been distorted and that the resilience of the environment puts limits on our activities. In the highly developed, very densely populated Netherlands, it appears that we may have exhausted environmental resilience. The harmful effects of our activities are becoming manifest in scores of places. Damage to our forests, heathlands and fens, disintegration of our cultural heritage and threats to our drinking water from acidification and eutrophication, the waste problem and the wide diffusion of toxic substances into the food chain are all problems facing the Netherlands. These problems, but also higher scale problems such as climate impacts and damage to the ozone layer, require that measures to control pollution be taken internationally. A symposium like this one can be of great significance in this connection. In the early 19701s, the report of the Club of Rome confronted the world with limits to growth as a consequence of raw material shortage and environmental pollution. Nowadays, the report of the Brundtland Commission, "Our Common Future', is receiving a great deal of attention. This report, like that of the Club of Rome, also observes that equilibria continue to be threatened at various
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levels nearly twenty years later. The Commission concludes that the days of shifting environmental problems to future generations must be ended. Growth must be based on development that meets the needs of the present without compromising the ability of future generations to meet their own needs. They summarize this notion under the term "Sustainable development". The Commission recognizes, and the Netherlands agrees completely, that environmental management has to encompass more than just bailing out the boat to keep it from sinking. We must start now to plug the existing leaks and, more importantly, to ensure that no new ones develop. If we want to pass on a seaworthy boat, if we want to hand the world over to our children and grandchildren in good shape, we must take care that our activities do not lead to consequences which exceed the carrying capacity of our ecosystems. This will only be possible if there is a fundamental change in our attitude about the environment and if this changed attitude carries over into our behavior. SOCIETAL SUPPORT FOR ENVIRONMENTAL PROTECTION The desirability of sustainable development is not something that many people would refute: even stronger, all thoughtful people would endorse the notion that humanity should live in harmony with its surroundings. In short, such a general pronouncement about the environment is one which many people would be ready to make. But, as we all know, "talk is cheap". Even unanimous agreement with this statement worldwide will not mean much in the long run if behavior is not adjusted in a way which reflects this concern. Ultimately, the goal of our policies must be to change both attitudes and behavior. In fact, we are imposing a change in behavior when we promulgate regulations. Regulation is a logical and necessary step given the seriousness of the environmental problems confronting us. But regulations will not change attitudes in the long term. what we ultimately must have, if we are to achieve the goals of sustainable development, is environmentally favorable behavior which springs from personal conviction, not which is imposed from above. One of the things we can do to encourage a move in the direction of sustainable development is to use the price mechanism to reward environmentally favorable behavior. When push comes to
9 SOCIETAL SUPPORT FOR ENVIRONMENTAL PROTECTION
PUBLIC INFORMATION CAMPAIGNS
EDUCATION
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MEDIA
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ENVIRONMENTAL AWARENESS
PRICE MECHANISM
ENVIRONMENTALLY FAVOURABLE BEHAVIOUR
shove, the immediate effect on our pocketbook usually weighs more heavily in our decision-making than our awareness that our activities may affect the environment in a harmful way. For example, most Dutchmen are aware that driving a car is bad for the environment, but that knowledge doesn't seem to inhibit their behavior. There are currently about 5 million automobiles in our small country and we expect that this number will increase to 7 million before the year 2000. But, on the other hand, we have seen that we can achieve results by rewarding certain kinds of behavior financially. Lead free gasoline was introduced in the Netherlands through a government-induced price differential which led the oil companies to voluntarily withdraw normal octane, leaded gasoline from the market. We have also used fiscal measures to accelerate the introduction of "clean" cars. The result is that two out of three newly purchased cars already satisfy the EC standards which have not even entered into force yet.One out of four is equipped with a catalytic converter. But the price mechanism alone will not stimulate the fundamental change in attitude that is needed in the longer term. At least equally important is the diffusion of information. People must be made aware of the consequences that a failure to change behavior will have and of the alternative behavior possibilities open to them. This can be done via the schools, the media and public information campaigns initiated by the government and by environmental organizations. Public information is a policy tool which the Dutch government has used extensively in the past to stimulate changes in attitude and behavior with respect to various environmental issues. The
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role of cars in acidification and the possibilities for disposing responsibly of household items of chemical waste are just two exemples of this. Public information is a policy tool which we must also develop in our approach to dealing with the ozone problem in all its facets. But in order to do this, we must have access to good information. SIGNIFICANCE OF THE OZONE SYMPOSIUM This symposium can support the development of policy especially by providing well-ordered information about the ozone problem and what we can do about it. There are two aspects to the problem. Excessively high tropospheric ozone concentrations occur at the regional and continental scales, while in the stratosphere, we are threatened with an ozone shortage on a global scale. Neither of these problems can be solved at a national level any more, regardless of the size of the nation involved. The solutions will have to be found internationally. The Montreal CFC Protocol is an encouraging sign in this respect, but we in the Netherlands consider it far from adequate. Hopefully, an ECE protocol on NO, will be realized in the near future. But no matter what, the question of whether the emission reductions we are currently aiming at will be enough to prevent further damage to the environment, will be with us for a while. This ozone symposium will contribute to increasing our knowledge about this. And with prior knowledge, we will be able to increase support for the necessary measures through public information. It is important - although towards the end of the symposiumthat policy is also coming into the picture. Both scientists and policy-makers are grappeling with the ozone problem at this symposium. Scientists and policy-makers sometimes look at things somewhat differently, but hopefully these differences will generate interaction which will yield fruit that can lead to a good approach to the ozone problem in the future. I wish you a successful symposium. And I hope that this third symposium will live up to the high expectations that past experience with the previous US-Dutch air symposia has shown to be warranted.
T. Schneider et aL (Editors),Atmospheric Ozow Research and its Policy Implkatwns 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
KEYNOTE ADDRESS
Vaun A.Newil1 Assistant Administrator, Office o f Research and Development (RD-672), United States Environmental Protection Agency, 410 M Street SY, WASHINGTON DC 20460, USA
On behalf o f the United States Protection Agency, a cosponsor o f t h i s a l l o f you t o beautiful Nijmegen policy issues related t o ground level ozone.
delegation and the U.S.Environmenta1 Symposium, I am pleased t o welcome t o discuss new research findings and ozone p o l l u t i o n and stratospheric
EPA Administrator Lee Thomas has asked me t o express h i s best wishes f o r the success o f t h i s Symposium. He also sends h i s greetings t o the many individuals he enjoyed meeting a t the second U.S.-Dutch Syrpposium three years ago i n Williamsburg. The Williamsburg Symposium, which addressed a wide range o f issues concerning aerosols, followed an equally impressive f i r s t Symposium - held i n Maastricht i n 1982 - which focused on nitrogen oxides. Both o f these e a r l i e r symposia resulted i n proceedings that have been widely read and frequently cited. I n view o f these past successes, I am especially pleased t o help open this, the t h i r d Symposium i n the series. Here we w i l l focus on both tropospheric and stratospheric ozone. Tropospheric ozone, which i s sometimes referred t o as ambient o r "bad' ozone, r e f e r s t o ozone formed near the grounds as a r e s u l t o f photochemical oxidation. It i s a major component o f urban smog and presents a threat t o both human health and the environment
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I n contrast, stratospheric o r "good" ozone i s contained i n a t h i n layer w i t h i n the outer reaches o f the atmosphere, and i t benefits human health and environment. Many would argue t h a t t h i s t h i n layer o f stratospheric ozone has been essential i n the evolution o f l i f e as we know i t on earth, and t h a t i t s disruption o r depletion may have very serious consequences. This Symposium w i l l a r t i c u l a t e the s c i e n t i f i c bases f o r recent public concerns about these two types o f ozone. I would l i k e t o begin the process by i d e n t i f y i n g some o f the technical and p o l i c y issues we w i l l consider throughout t h i s meeting. The p o t e n t i a l l y serious human health e f f e c t s t h a t can be caused by tropospheric ozone have l e d the United States t o set a one-hour standard o f 0.12 ppm. As required by the U.S. Clean A i r Act, we p e r i o d i c a l l y reassess that standard i n l i g h t o f the most recent s c i e n t i f i c data. For example, recent studies indicate t h a t healthy exercising individuals breathing ozone concentrations a t o r s l i g h l y above the U.S. standard can experience reduced lung function, chest pain, and pulmonary congestion. New animal studies show that short- and long-term exposure t o high concentrations o f ozone can cause permanent structural damage t o animal lungs and/or impair lung inmune defense systems. Some o f these recent data have been generated by U.S.Dutch collaborative studies t h a t w i l l be reported l a t e r i n t h i s Symposium. O f p a r t i c u l a r note are new findings t h a t suggest changes i n lung function with more prolonged (6 - 8 hr) exposures t o ozone a t concentrations below the current 0.12 ppm one-hour standard. We are presently evaluating such new health data t o determine whether the e x i s t i n g ozone standard needs t o be adjusted e i t h e r i n terms o f allowable concentration o r averaging time. Any future adjustment w i l l depend l a r g e l y on what i s determined t o be an gdverse decrement i n lung function, as well as the relationship between transient acute e f f e c t s and more serious e f f e c t s frm chronic exposure. Our a b i l i t y t o define t h i s relationship i s closely l i n k e d t o dosimetry and health e f f e c t s modeling, by which we extrapolate from animals t o humans. This topic, which i s being researched a t EPA i n cooperation with researchers o f the National I n s t i t u t e o f Public Health and Environmental Protection (RIVM), Bilthoven, w i l l be addressed a t t h i s conference. I n addition t o health effects, we share w i t h our colleagues i n the Netherlands and many other countries concern about possible ozone damage t o crops, forests, and man-made materials. High ozone l e v e l s can a f f e c t not only c i t i e s , but r u r a l areas as w e l l , due t o large-scale regional d i s t r i b u t i o n o f a i r masses polluted with photochemical oxidants. Episodic accumulations o f such pollutants t h a t are formed over urban centers and then transported t o r u r a l areas have the potential t o reduce crop y i e l d s and t o seriously damage sensitive forest lands, including conmercially
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important plants. The U.S. experience with forest dieback in the Appalachian Mountains and recent European experiences with forest damage represent but two examples where ozone is suspected as a major contributor to forest damage. International cooperation is clearly needed to study and control such ozone damage. Because polluted air masses do not respect international boundaries, they have the potential to cause economic damage in neighbouring countries. In less developed countries, transboundary ozone could further exacerbate existing problems of deforestation and inadequate food production. Control1 ing tropospheric ozone adequately will not be easy, whether through domestic or international action. For example, many o f the major population centers in the United States do not meet the national ozone standard. A few cities experience ozone peaks twice as high as the current standard. Although the U.S. Clean Air Act called for national attainment of the standard by the end of 1987, EPA estimates that about 70 areas have not attained it, and that about 40 of those areas will not attain it in the near future. Some of the areas probably will require many years to achieve the standard, even if extraordinary control measures are taken. Nonattainment of the ozone standard presents one of the most difficult air pollution problems that we now face in the United States. Don Clay, EPA*s Acting Assistant Administrator for Air and Radiation, will discuss U.S. policies and strategies on the ozone non-attainment issue in the last session of this Symposium. Our failure to achieve widespread attainment of the ozone standard is especially disturbing in view of significant efforts undertaken to reduce ozone precursor emissions from both mobile and stationary sources in the United States. A number of factors contribute to the non-attainment experience in many U.S. urban areas, and those factors vary from area to area. Some of the possible reasons for non-attainment include: 1. incomplete implementation of state control strategies; 2. overly optimistic assumptions in state control strategies; 3. higher emissions of volatile organic compounds (VOC's) than assumed in state control strategies; 4. underestimates of VOC-control requirements due to inaccuracies in computer models used to plan control strategies; or 5. combination of all these factors. EPA research efforts that address these different factors, including improvement and validation of the regional oxidant model (ROM) and urban AIRSHED model, will be discussed later in this Symposium. EPA will be presenting recent data concerning hydrocarbon emissions inventories that will allow models to be adjusted for evaporative hydrocarbon emissions and
14 seasonal variations i n temperature. International cooperation t o improve these types o f models and inventories i s very important t o the control o f ground-level ozone. I shall conclude my coments on tropospheric ozone by noting t h a t the severity o f the ozone problem i n many c i t i e s i n the United States and elsewhere w i l l l i k e l y necessitate the implementation o f more stringent a i r p o l l u t i o n control programs. These new programs are expected t o be both c o s t l y and controversial. Unlike many other a i r p o l l u t i o n problems, ozone i s not caused by a few large and well-defined sources. Small, widely dispersed sources w i l l have t o be controlled i n order t o reduce ozone concentrations i n many areas. F o r example, everyday human a c t i v i t i e s such as d r i v i n g automobiles, refueling a t gas stations, drycleaning clothes, and using household products such as paints and cleansers a l l contribute t o the formation o f ozone. Reducing those kinds o f a c t i v i t i e s , o r f i n d i n g substitutes f o r those kinds o f products, may require substantial changes i n 1if e s t y l e. Now l e t me h i g h l i g h t several major points about stratospheric ozone depletion and the i n t e r r e l a t e d problem o f global warming, o r the so-called "greenhouse effect". These two problems are c l e a r l y international i n nature, both i n regard t o t h e i r sources and the scope o f t h e i r potential impacts on human health and the environment. Increased i n d u s t r i a l and agricultural a c t i v i t y during the past two centuries has resulted i n substantial atmospheric loadings o f c e r t a i n gases, such as carbon monoxide, methane, and chlorofluorocarbons (CFC-s) These and many other chemicals are causing important changes i n the chemical composition o f the atmosphere. O f p a r t i c u l a r concern i s the f a c t t h a t the continued o r increased use o f CFC-s may lead t o a substantial net depletion o f stratospheric ozone - an environmental degradation t h a t nay be more advanced than previously be1 ieved. Any s i g n i f i c a n t reduction o f ozone i n the upper atmosphere could mean long-term increases i n the frequency o f skin cancer and cataracts worldwide. It could also have s i g n i f i c a n t impacts on our t e r r e s t r i a l and aquatic ecosystems. In addition, the gases a f f e c t i n g ozone e x h i b i t greenhouse properties; because they t r a p solar energy i n the atmosphere, they could contribute t o future warming o f the earth. The adverse e f f e c t s o f global warming over the long-term extend well beyond higher temperatures. The greenhouse e f f e c t could also r e s u l t i n substantially altered r a i n f a l l patterns, increases i n sea level, l o s s o f s o i l moisture, and changes i n the movement o f storms. These s h i f t s could a l t e r agriculture, forests, wetlands, water resources, and coastal c i t i e s .
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As we look for solutions, we must recognize the unuasual nature of these
new challanges. Both the causes and effects of ozone depletion and global warming are distributed unevenly throughout the world - not just between two countries or within one region. Furthermore, in most cases the adverse environmental impacts in a particular country will not be proportional to its emissions of harmful air pollutants. Thus, traditional approaches to problem solving - domestic legislation, rulemaking, and enforcement - are inadequate to deal with these new problems. The United States has already taken some important domestic regulatory steps to control CFC’s, beginning with a ban on their use in aerosols in 1978. The United States Senate has ratified the Montreal Protocol. Even so, more needs to be done. More research is needed to delineate the full scope of expected impacts due to stratospheric ozone depletion and global warming, along with considerable international cooperation to develop and implement effective control strategies. There is good reason for all of us to be pleased with the Montreal Protocol on Substances that Deplete the Ozone Layer. That protocol was signed by the United States and 23 other nations in Montreal, Canada, on September 16, 1987. The signing of the Montreal Protocol was an historic event in both international relations and environmental protection. For the first time, concerted action has been taken by a group o f nations in anticipation of what could be a major global environmental problem. The Montreal Protocol is a truly international agreement. Signed initially by 24 nations, including Japan and the member countries of the European Community, it has since been signed by an additional seven countries, including the Sovjet Union. Together, these countries account for well over three-quarter of current global production of CFC-s and halons, two of the chemical compound families believed to cause depletion of the ozone layer. The protocol was also signed by many developing countries that do not now produce or use CFC’s and halons in significant quantities, but would be expected to increase use o f these chemicals as their economies develop. The fact that such nations are joining this effort to protect the environment should contribute greatly to the international community‘s ability to address this problem. The protocol would freeze the consumption of CFC*s 11, 12, 113, 114, and 115 at 1986 levels beginning in mid-1989 or six months after entry into force. Beginning in mid-1993, consumption would be reduced to 80% o f 1986 levels, followed by a reduction to 50% of the 1986 level in mid-1998. The protocol would also freeze the consumption of halons 1211, 1301 and 2402 at 1986 levels starting three years after entry into force.
16 I n addition, t h e protoqol contains special provisions t h a t apply t o developing countries. They are allowed an a d d i t i o n a l ten years before they must comply w i t h t h e same reduction schedule. It i s widely believed t h a t s u b s t i t u t e chemicals and technologies w i l l be a v a i l a b l e w i t h i n 10 years, and the protocol encourages major producing and consuming nations t o f a c i l i t a t e t h e access o f developing countries t o safe a l t e r n a t i v e s . The protocol a l s o provides a mechanism f o r change i n t h e reduction schedule. The p a r t i e s t o t h e protocol w i l l p e r i o d i c a l l y review t h e s c i e n t i f i c , technological, and economic data and then meet f o r m a l l y t o decide i f f u r t h e r o r d i f f e r e n t steps t o p r o t e c t the ozone l a y e r are required. The incorporation o f s c i e n t i f i c assessments i n t o the r i s k management process a t an i n t e r n a t i o n a l l e v e l i s a very p o s i t i v e step, and i t should be encouraged i n other areas o f i n t e r n a t i o n a l environmental concern where s c i e n t i f i c understanding can be a n t i c i p a t e d t o evolve. Other s i g n i f i c a n t provisions are also contained i n t h e protocol, b u t I w i l l defer t o Don Clay t o cover these and other aspects o f U.S. p o l i c y f o r addressing stratospheric ozone. I n t e r n a t i o n a l cooperation i s c r i t i c a l t o t h e long-term success o f t h e agreement. The world must now move forward t o implement t h e Montreal Protocol. EPA hopes t h a t meetings such as t h i s Symposium w i l l help f o s t e r r e g u l a t o r y programs t h a t support t h e goals o f t h e Montreal agreement. EPA urges favourable a c t i o n by a l l nations i n implementing i t as q u i c k l y as possible. Crucial t o e f f e c t i v e implementations o f t h e Montreal Protocol are c e r t a i n important research e f f o r t s , some o f which I would l i k e t o h i g h l i g h t today. Based on the r e p o r t from an Ozone Trends Panel f o n d by serveral U.S. and i n t e r n a t i o n a l organizations, t h e r e i s undisputed evidence t h a t t h e atmospheric concentrations o f source gases important i n c o n t r o l 1 i n g stratospheric ozone l e v e l s continue t o increase on a g l o b a l scale. A key challenge f o r EPA-s Stratospheric Ozone Research Progranne i s t o focus i t s e f f o r t s on those s c i e n t i f i c issues o f most concern t o policymakers. The Montreal Protocol can be successful on a g l o i a l scale o n l y i f t h e s c i e n t i f i c comnunity helps inform t h e p o l i t i c a l leaders i n developing and newly i n d u s t r i a l i z e d countries. Although we cannont acheve these r e s u l t s on our own, t h e Netherlands, t h e United States, and o t h e r nations, and other nations represented here can p l a y a c r u c i a l r o l e i n generating s c i e n t i f i c information t h a t i s c r e d i b l e and h e l p f u l t o various nations i n a r r i v i n g a t t h e i r own p o l i c y decisions.
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In the United States, EPA acts as the lead federal agency to: 1. set research goals in response to policy issues regarding stratospheric ozone; 2. coordinate "effects" research to accomplish those goals; 3. synthesize the results of the research which will take place within a number of agencies. For this part, EPA will continue to develop its international resources and research effort as necessary to fulfill its responsibilities under the Montreal Protocol and the U.S. Clean Air Act. According to the protocol, in 1990, again in 1994, and periodically thereafter, major risk assessments are scheduled to determine: 1. whether additional chemicals should be included in the protocol; 2. whether a faster or slower regulatory schedule is appropriate; and 3. whether current controls on chemicals regulated under the protocol are adequate. In light of the Ozone Trends report, EPA Administrator Lee Thomas has written Dr. Mustafa Tolba, Executive Director of UNEP, urging him to expedite the assessment and review process. For these risk assessments, we need to know the likely growth in the concentrations of gases that influence the column density of stratospheric ozone, and we need to understand the relationships between emissions and the potential impact on humans and the environment. EPA will compile and analyze data from both national and international sources to assess the effects of continued release of gases that deplete stratospheric ozone. These will include health effects, ecological effects, and welfare effects such as degradation of natural resources and materials damage. The data currently available for this assessment are incomplete and of highly variable quality. The cooperation of other national and international organizations is essential. EPA risk characterization and scientific assessment will address: 1. Predictions regarding the quantities and impact of continued release of ozone influencing substances into the stratosphere, and the concomitant increase in UV-B irradiation at the surface of the earth; 2. Trends in emissions of ozone influencing gases in the United States and around the world; and 3. The nature, extent, and severity of environmental impacts o f continued release of ozone depleting substances on the United States and other countries. Such impacts will be expressed in socially, institutionally, and economically relevant terms. These assesments will allow EPA to evaluate overall policy implications as new scientific information is developed.
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Five areas of further research or assessment are particularly important to understanding stratospheric ozone depletion. These include research on: 1. terrestrial ecosystems 2. aquatic ecosystems 3. human health 4. tropospheric oxidants and 5. mitigative solutions. As part of its terrestrial ecosystems research program, EPA is coordinating with the U.S. Department of Agriculture to provide preliminary dose-response data on important food crops and associated ecosystem processes. The integrated study will examine the effects o f UV-B radiation on interspecies competition and plant pathogen and pest interactions, the interaction between UV-B radiation and other stresses such as water and nutrient deficiency, and widespread anthrophogenic factors such as global climatic change and tropospheric ozone. These data will allow such factors to be considered in the overall risk assessment process. Little information currently exists regarding the effect of increased levels of UV-B radiation on long-lived or perennial species such as trees. These species are important from an economic as well as an ecological standpoint. EPA research has been initiated to study the effects of UV-B radiation on one commercial species of tree (Loblolly pine), but the impact of UV-B radiation on fores s in the United States and elsewhere also needs to be addressed. For aquatic ecosystems many of the projected results of increased levels of UV-B radiation are of acute concern. For coastal marine ecosystems in particular, where ecological impacts could be of consequence to many important fisheries, there is a pressing need to evaluate likely ecological change due to increased exposure to UV-B radiation. This issue is important not only for the United States and the Netherlands, but for most other seaboard nations as well. Using facilities already at its disposal, EPA will study the effects of UV-B radiation on one Atlantic coast and one Pacific coast fisheries ecosystem. Using fisheries models and food-web dynamics data generated in both areas, EPA will quantitatively'project the needs of UV-B radiation on select fisheries. * Also to be addressed among those critical aquatic ecosystems of recent concern is the Antarctic marine ecosystem. In the area of human health research, recent findings suggest that human exposure to UV-B radiation can lead to inmunological alterations and innnunosuppression, which implies an increased incidence of disease in people of all ethnic backgrounds. Research is needed to: 1. investigate the mechanisms of immunosuppression in animals and humans;
19 2. i d e n t i f y the i n f e c t i o u s diseases t h a t include a stage o r process t h a t could be worsened by exposure t o UV-B r a d i a t i o n and t o develop models t o
explain these diseases;
3 . i n v e s t i g a t e wavelength dependence and develop dose-response information f o r humans concerning the e f f e c t s o f UV-B exposure on t h e incidence o f i n f e c t i o u s diseases; and 4. determine the impact o f UV-B imnunosuppression on vaccination e f f i c a c y . I n addition, cataracts occur i n a l l societies, b u t because o f t h e l i m i t e d access t o surgical f a c i l i t i e s i n many countries, t h e r e are a major cause o f blindness i n l e s s developed countries. Additional EPA funded research on the biology and epidemiology o f cataracts and on methods t o reduce the r i s k o f eye diseases w i l l be pursued. Currently, only a preliminary assessment has been made r e l a t i n g UV-B i r r a d i a t i o n t o possible changes i n concentrations o f ozone p o l l u t i o n a t t h e surface o f the earth. Several f a c t o r s could increase tropospheric ozone p o l l u t i o n , including increased l e v e l s o f UV-B r a d i a t i o n and increased emissions o f methane and other hydrocarbons. This area o f research w i l l address the 1inkages between UV-B r a d i a t i o n and tropospheric ozone production, as w e l l as the s y n e r g i s t i c e f f e c t s o f oxidants and a c i d deposition. From t h i s , EPA w i l l determine some o f the i n d i r e c t e f f e c t s o f UV-B r a d i a t i o n on people, materials and ecosystems i n urban, r u r a l , and wilderness areas. While EPA w i l l conduct research o r assessments i n t h e f o u r areas I j u s t mentioned, a f i f t h area i s o f special i n t e r e s t . As w i t h tropospheric ozone, f i n d i n g new technologies t o m i t i g a t e t h e depletion o f stratospheric ozone i s a major challenge we a l l take. Many o f the p o t e n t i a l a l t e r n a t i v e s t o the current us o f CFC’s involve new o r modified technologies t h a t promise a v a r i e t y o f benefits. I f the claims are true, these a l t e r n a t i v e s would help reduce the upward pressure on p r i c e s t h a t r e s u l t from inadequate supplies o f CFC-s i n the future. Furthermore, new technologies have t o be s p e c i f i c t o t h e needs o f developing countries. The United States would l i k e t o be i n a p o s i t i o n t o present unbiased t e s t i n g data on new technologies i n order t o support f u t u r e negotiations and t o provide technology t r a n s f e r t o such nations. A t a minimum, EPA w i l l provide q u a l i t y assurance regarding these technologies, which w i l l allow the United States t o propose v i a b l e a l t e r n a t i v e s . These evaluations may even lead t o new i n s i g h t s i n t o b e t t e r ways t o achieve reduced dependency on e x i s t i n g CFC-s. It i s expected t h a t t h i s e f f o r t w i l l lead t o the f u t u r e t r a n s f e r o f engineering systems t h a t i s essential t o achieving worldwide solutions. We i n v i t e a l l nations t o j o i n in implementing so1utio;s f o r t h i s global problem, and we hope t h a t t h e present Symposium contributes movement toward t h e goal.
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Before closing, I wish t o thank the many people who have been involved i n t h e organization of an e x c e l l e n t technical program, and our Dutch hosts f o r t h e i r f i n e l o g i s t i c a l arrangements. The e f f o r t s o f t h e Organizing and Advisory Comittees, Session Chairmen and Rapporteurs, the Conference Secretariat, and other who are c o n t r i b u t i n g d u r i n g the next several days are a l l very much appreciated. I a l s o wish t o extend special r e c o g n i t i o n t o several key i n d i v i d u a l s who have l e d the organizational e f f o r t n o t o n l y f o r t h i s Symposium b u t a l s o f o r the previous two successful meetings i n Maastricht and Williamsburg. The e f f o r t s o f Drs.Toni Schneider and Joop van Ham from the Netherlands and Drs.Lester Grand and S i Duk Lee from the United States, along w i t h David S t r o t h e r and other s t a f f h e r s o f t h e i n t e r n a t i o n a l o f f i c e s from each country, are e s p e c i a l l y appreciated. Congratulations t o you a l l f o r p u l l i n g together what promises t o be y e t another superb Symposium.
T. Schneider et 01. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science PublishersB.V.. Amsterdam - Printed in The Netherlands
21
OZONE HEALTH EFFEepS AND EMEDGING ISSUES IN REXATICN TO STANDARDS SETTING
m r t o n LipFsMnn, Ph.D. I n s t i t u t e of Environmental W c i n e , Nar York University Medical Center, NY 10987 USA
TUX&,
ABSTRACT Our current knowledge of 0 exposure and health effects is growing rapidly. Transient respiratory functian effects accumulate throughout an exposure day, and ambient exposures have broad daily peaks. 0 exposures a l s o produce changes i n airway inflamation and p e m a b i l i t y . & l a y adults engaged f o r 1/2 hr i n outdoor exercise show greater responses than those observed i n chamber studies involving 1 o r 2 h r of exposure, indicating potentiation of
-
the 0 response by other environmental exposures. Acute animal studies show bioch&cal and structural responses t o O3 are potentiated by co-exposure t o NO and Chronic animal studies show that 0 effects on lung structure ac&mla2Y&d several recent epidemiological s t u h e s suggest that cumulative functional e f f e c t s are occurring in people. Recent research has a l s o shown: 1) a seasonal variation in functional responsiveness i n humans; 2) that a seasonal pattern of daily exposure in monkeys produces greater changes i n the lung than a continuous pattern of daily exposures at the same concentration; and 3) that transient exposures produce persistent responses.
OZONE HEALTH EFFECTS Ozone (03)exposure a f f e c t s the structure and function of the respiratory t r a c t i n a variety of ways. mst of the research on humans has focussed on its e f f e c t s on respiratory function, especially on transient responses t o acute exposures. Other lung functional responses t o acute and subacute exposures which have been studied, largely in animals, include m c o c i l i a r y and early alveolar zone particle clearance, functional responses in macrophages and e p i t h e l i a l cells, and changes i n lung cell secretions. Structural changes in the v i c i n i t y of the respiratory acinus have been associated with subchronic and chronic animal exposure protocols. However, the health significance of localized structural changes, and t h e roles of the transient functional and cellular responses, i f any, i n the pathogenesis of lung disease, remain speculative. The responses i n animals suggest possible links between O3 exposure and aggravation of asthma, bronchitis, and lung f i b r o s i s i n humans, but do not provide clear evidence f o r such ties. The following sunanarizes current knowledge on transient and chronic health effects produced by the inhalation of 03, and i d e n t i f i e s critical knowledge gaps i n the relationships between the observed e f f e c t s and lung disease.
22
Transient Effeds on Respiratory Function It is well established that the inhalation of O3 causes concentration dependent mean decrements in volumes and flow rates during forced expiratory maneuvers, and that the mean decrements increase with increasing minute ventilation [ref. 11, that there is a wide range of reproducible responsiveness among healthy subjects [ref. 21 , and that functional responsiveness to O3 is no greater, and usually lower, m n g cigarette smokers [refs. 3,4], older adults [refs. 5,6], asthmatics [refs. 7,81, and patients with allergic rhinitis [ref. 91 or chronic obstructive pulmonary disease (COPD) [refs. 10,111. It is also well established that repetitive daily exposures, at a level which produces a functional response upon single expcsure, results in an enhanced response on the second day but diminishing responses on days 3 and 4, with virtually no response by day 5 [refs. 12-141. This functional adaptation disappears about a week after exposure ceases [refs. 15,163. The current U.S. National Ambient Air Quality Standard ( W S ) for O3 uses a 1 hr averaging time, based primarily on a report of respiratory function inpainrent for exercising persons exposed for 1 hr at 0.15 ppn [ref. 171, and the expectation that ambient exposures are characterized by relatively sharp afternoon peaks. However, it has recently been shown that ambient O3 concentrations in the Netherlands and New Jersey often have broad daytime peaks, with maximum 8 hr averages close to 90% of peak 1 hr levels [ref. 181. In the ambient air in the U.S. as a whole, a 1 hr O3 peak at 0.12 ppn is, on average, associated with a maximum 8 hr average concentration of 0.10 p ~ m . Approximately half of the U.S. population lives in comnunities w h i c h exceed the current O3 NAAQS at least twice annually, and many comnunities in California frequently have concentrations exceeding 0.2 ppn [ref. 191. The first indications that the effects of O3 on respiratory function accumulate over more than 1 hr were the observations of M.3onnell et al. [ref. 201 and Kulle et al. [ref. 211 in chamber exposures to O3 in purified air for 2 hr. Significant function decrements observed after 2 hr of exposure were not present at measurements made after 1 hr. Spektor et al. noted that children at sumner camps with active outdoor recreation programs had greater lung function decrements than children exposed to O3 at comparable concentrations in chambers for 1 or 2 hr [ref. 221. Furthermore, their activity levels, although not measured, were known to be considerably lower than those of the children exposed in the chamber studies. Since it is well established that functional responses to O3 increase with levels of physical activity and ventilation [ref. 11, the greater responses in the carp children had to be caused by other factors, such as greater m l a tive exposure, or to the potentiation of the response to O3 by other pllu-
23 t a n t s in the ambient a i r . cumulative daily exposures t o O3 e r e generally greater for the camp children exposed all day long than for the children exposed i n chambers for a 1 or 2 hr period preceded and follow& by clean a i r exposure. Similar considerations apply t o the recent study of M e y et al. [refs. 23,241 of schml children i n Kingston and Harrirnan, TN whose lung function was measured i n school on up t o s i x occasions during a 2 mo period in the l a t e winter
and early spring.
Child specific regressions of function versus mix 1
hr O3 during the previous day indicated significant
associations between O3 and function, with Coefficients similar t o those seen i n the sumner camp studies of L i p p M n n et a l . [ref. 251 and -or et a l . [ref. 221. Since children i n school m y be expected t o have relatively low a c t i v i t y levels, the relatively high response coefficients m y be due t o potentiation by other p l l u -
or t o a low-level of seasonal adaptation. As shown by Spmgler et al. [ref. 261 , Kingston-Harrhan has higher annual average and peak acid aerosol concentrations than other cities studied, i.e., Steubemrille, OH, St. Louis, tants,
Alternatively, the relatively high response coefficients could have been due t o the fact that the W m t s were made i n the l a t e winter and early spring. Hackney [ref. 271 has shown evidence f o r a seasonal
M3, and Portage, W I .
adaptation, and children studied during the s~nrmermay not be a s responsive as children measured earlier in the year. In the study by Hackney [ref. 271 a t Rancho Los Amigos Hospital in Southern California, a group of subjects selected for their relatively high functional responsiveness t o O3 had much greater functional decrements following 2 hr of exposure t o O3 a t 0.18 p p n w i t h intermittent exercise in a chamber in the spring than t h e y did in the following autunm or winter, while their responses i n the
following spring were equivalent t o those in the preceding spring.
These findings suggest that some of the variability in response coefficients reported for earlier controlled human expsures t o O3 i n charr33ers could have been due t o seasonal variations i n responsiveness which, in turn, may be re-
l a t e d t o a long-term adaptation t o chronic O3 exposure. The observations from the f i e l d studies in the children's camps stimulated Folinsbee et a l . [ref. 281 a t the EPA Clinical Studies Laboratory i n chapel e of adult volunteers involving Kill, NC t o undertake a chamber e x ~ ~ s u rstudy
of O3 exposure @ 0.12 p. bbderate exercise was performed for 50 min/hr for 3 hr i n the morning, and again in the afternoon. They found that the function decrements become progressively greater a f t e r each hour of exposure, reaching average values of 400 mL for forced Vital capacity (EW) and 540 mL for forced expiratory volume i n one second (W1) by the end of the day. The effects were transient, w i t h no residual function decrements on the 6.6
-
hr
-
24
following day. The functional decrements after 6.6 hrs of exposure at 0.12 ppn were caparable to those seen previously in the same laboratory on similar subjects following 2 hr of intermittent heavier exercise at an interpolated concentration of 0.22 ppn. The total m u n t of O3 inhaled during 2 hr of intermittent heavy exercise @ 0.22 ppn would be 2.0 q 03. The corresponding amount of O3 inhaled during 6.6 hr of intermittent moderate exercise @ 0.12 ppn was 3.0 mg 03. Thus, the effect accumulates w i t h time, but there appears t o be a concurmt tanporal decay of effect. Follow-up studies in the same laboratory at 0.08, 0.10, and 0.12 ppn confirmed the previous findings, with the 0.08 and 0.10 ppn exposures producing lesser changes which also became progressively greater after each hour of exposure [ref. 291. Thus, it is now clear that the appropriate averaging time for transient functional decrements caused by O3 is 2 6 hr, and there is no scientific basis for a 1 hr health based exposure limit. Since O3 exposures in ambient air can have broad peaks with 8 hr averages equal to 90% of the peak 1 hr averages, the functional decrements associated with ambient concentrations are likely to be much greater than those predicted on the basis of the responses in the chamber studies following 1-2 hr exposures. To the extent that transient changes in respiratory function influence the selection of a W S , the case for a longer tern acute exposure standard is quite clear. The remaining question now has becaane whether there is any scientific rationale for retaining a 1 hr standard to supplement the clearly needed new standard with an averaging time on the order of 8 hr. A study which addressed the issue of the potentiation of the characteristic functional response to inhaled O3 by other e n v i r m t a l cofactors was performed at the NYU bdical Center in Tuxedo, NY on healthy adult nonsmkers engaged in a daily program of outdoor exercise. The ambient mixture contained low concentrations of acidic aerosols and No2 as well as 03. Each subject did the same exercise each day, but exercise intensity and duration varied widely between subjects. Spirametry was perfomid imnediately before and after each exercise period. O3 concentrations during exercise ranged fran 0.021 to 0.124
-
-
-
-
All measured functional indices showxi significant (~0.01)O3 associated man decrements. The functional decrenwts were sMlar, in praportion to lung velum, to those seen in children engaged in supervised recreational programs in sumnez camps, and about twice as large as those seen in controlled 1 and 2 hr exposures in chambers. Since the anbient exposures of the adults exercising out of doors were for 1/2 hr, it was concluded that ambient cofactors potentiate the responses to O3 [ref. 301. Thus, the results of the exposures in thankers to O3 in purified air can underestimate the O3 associated responses which occur among ppulations engaged in n o d outdoor recreational
ppn.
-
25
activity and exposedto O3 i n ambient a i r . The NYU study on exercising adults, and earlier studies on children a t sum-
mer camps [refs. 22,24,31] were not able t o demonstrate the specific effect of any of the measured environmental variables, including heat stress and acid aerosol concentration, on the 03-associated responses. The i n a b i l i t y t o show the individual effects of other environmental cofactors on the response t o ambient O3 m y be due t o inadequate knowledge on the apprapriate biological averaging t h e for these other factors. However, i n the study of functional responses of children t o ambient pollution in Mendham, NJ, a weeklong baselhe shift in PEFR was associated with both O3 and %SO4 exposures during a four day pollution episode which preceded it [ref. 311. A similar response t o a brief episode with elevated O3 and a mch higher peak 4 hr concentration of H2S04 (46 pg/m3) was seen among g i r l s attending a m r canp in 1986 a t Dunnv i l l e , Ontario, Canada, on the northeast shore of Lake Erie [ref. 321. Controlled human exposure studies i n chambers have not demonstrated synergism i n functional response &ween O3 and No2 or %SO4, although Stacy et a l . [ref. 331 reported m responses t o 0.40 ppn O3 and 100 pg/m 3 €$SO4 a f t e r 2 h r of exposure of -9.0% for FVC and -11.5% for E W l , carpared t o -5.7 and -7.7% for O3 alone, -1.4, and -1.2% f o r sham exposure, and t0.9 and +O.% for H2S04 alone. These mean differences, which appear t o indicate an e n h a n m t of the O3 response by %SO4, were not s t a t i s t i c a l l y significant because of the very high variability of the sham exposure results. Pollutant interactions w h i c h potentiate the characteristic O3 response have been reported for other effects, i n controlled exposure studies i n animals, as w i l l be discussed l a t e r i n the sections on lung defenses and lung structure. Exposure t o O3 can also alter the respansiveness of the airways t o other bronchoconstrictive challenges as measured by changes in respiratory mechanics. For example, Folinsbee et al. [ref. 281 reported that airway reactivity t o methacholine for the group of subjects as a whole was approximately doubled following 6.6 hr expsures t o 0.12 ppn 03. Airway hyperresponsiveness ( t o histamine) had previously been demonstrated, but only a t O3 concentrations 2 0.4 ppn [refs. 34,351. On an individual basis, Folinsbee et al. found no apparent relationship betwen the 03-associated changes in methacholine reae t i v i t y and those in FVC o r Wl. TNs d i f f e r s fran resporlSes t o inhaled €$SO4 aerosol, where changes in function correlated closely t o changes in reactivity t o carbachol aerosol [ref. 361. Perhaps the O3 associated changes in bronchia l reactivity predispose individuals t o bronchospasm f m other environmental agents such as acid aerosol and naturally cxxurring aeroallergens. Effects -- on Lung Defenses and Lung Structure Practical and ethical cansiderations limit the amoLlIlts and kinds of data
26
that can be collected on the effects of O3 on lung defenses and lung struc-
ture. Mst of the limited body of data on humans that are available relate t o the rate of particle clearance fmn the lungs and t o a l t e r a t i o n s i n the con: s t i t u e n t s of bronchoalveolar lavage (=) Foster et al. [ref. 371 s t d e d the effect of 2 h r exposures t o 0.2 o r 0.4 ppn O3 with intermittent light exercise on the r a t e s of tracheobronckial m a c i l i a r y particle clearance in seven healthy adult males, using y-tagged i n e r t p a r t i c l e s and external detection w i t h a )'-camera. The 0.4 ppn O3 exposure prcduced a marked acceleration in particle clearance from both central and peripheral airways, as ell as a 12% drop i n E'VC. The 0.2 ppn O3 exposure prcduced a significant acceleration of particle clearance only i n peripheral airways, and a small and nonsignificant reduction i n E'VC. The e f f e c t s of O3 on mucociliary particle clearance have a l s o been studied i n animals. Rats exposed f o r 4 h r t o O3 at 0.4 t o 1.2 ppn exhibited slowed clearance a t 1 0.8 ppn, but not a t 0.4 ppn [refs. 38,391 Rabbits exposed f o r 2 hr at 0.1, 0.25 and 0.6 ppn O3 showed a concentration dependent trend of reduced clearance rate with increasing concentrations, with the change at 0.6 ppn being 50%and significantly different from control [ref. 401 It is not known why t h e animal tests show only retarded mccciliary clearance i n response t o O3 exposure, while the human tests show accelerated clearance. In corresponding tests with other i r r i t a n t s , i.e., %SO4 aerosol and c i g a r e t t e smoke, both humans and animals have exhibited accelerated clearance a t lower exposures and retarded clearance a t higher exposures [ r e f . 411. Studies of the effects of O3 on alveolar macrophage mediated particle clearance during the f i r s t f e w weeks have a l s o been performed in rats and rabb i t s . Rats exposed f o r 4 h r t o 0.8 ppn O3 had accelerated particle clearance [refs. 38,391. Rabbits exposed t o 0.1, 0.6, o r 1.2 ppn O3 once f o r 2 hr had accelerated clearance a t 0.1 p%m and retarded clearance at 1.2 p ~ a n . Rabbits exposed f o r 2 hr/d f o r 13 days at 0.1 o r 0.6 ppn O3 had accelerated clearance for the f i r s t 1 0 days, with a greater e f f e c t at 0.6 ppn [ref. 421. The permeability of the respiratory epithelium can be determined by measuring the plasma concentration of horseradish peroxidase (HRP) a f t e r intratracheal i n s t i l l a t i o n [ r e f . 431. Miller et al. [ref. 441 showed that 2 hr exposures @ 1 ppn O3 affected permeability i n the guinea pigs using this technique. Permeability can a l s o be determined from the externally measured r a t e % ' diethylenetriminepntaacetate of clearance from the lung of Y-emitting c ('%c-DFA), inhaled a s a droplet aerosol o r i n s t i l l e d via the trachea. Bhalla et al. [refs. 45,461 reported increased t r a n s f e r of instilled tracers from the bronchoalveolar lumen t o blood following 2 hr exposure of r a t s t o 0.6 and 0.8 ppn 03. Bhalla et a l . [ref. 461 also examined the e f f e c t s of exercise
.
-
.
27
and -sure
t o other pollutants on tracheal and bronchoalveolar permeabil-
ity. Atmospheric mixtures inclukd: O3 + No2 at 0.6 ppn and 2.5 ppn, respec tively; and a 7-canponent particle and gas mixture (capla atmosphere) The effects representing urban air pollution in a photochemical.environment. of exercise during exposure w e r e evaluated by exposing additional groups in an
enclosed treahill. -sure of resting r a t s t o 0.8 ~ p O3 n increased tracheal permeability t o DTPA and bmnchoalveolar permeability t o DTPA and bovine serum allnrmin (BSA) a t 1 hr after the exposure. B r a n c h o a l v e o l ~ ,but not tracheal, permeability remained elevated a t 24 h r a f t e r the exposure.
Exercise during
exposure t o O3 increased permeability t o both t r a c e r s i n the tracheal and the bronchoalveolar zones, and prolonged the duration of increased permeability in
the tracheal zone from 1 h r t o 24 hr, and i n the bronchoalveolar zone fm 24 h r t o 48 hr. Exposure a t rest t o 0.6 ppn O3 plus 2.5 ppn NO2 significantly increased bronchoalveolar permeability a t 1 and 24 h r a f t e r exposure although exposure a t rest t o 0.6 ppn O3 alone increased branchoalveolar permeability only a t 1 h r a f t e r exposure. Fxposure t o O3 and No2 during exercise led t o significantly greater permeability t o DTPA than did exercising exposure t o O3 alone. Resting r a t s exposed t o the wnplex gas/aerosol atmosphere had increased permeability a t 1 and 24 hr a f t e r exposure. N i t r i c acid vapor was formed i n both the O3 + M2 a m s p h e r e and the ccrrplex gas/aerosol atmosphere. The particles in the l a t t e r also contained hydrogen ions equivalent in mcentration t o about 100 g/m3 of NI-I~HSO~,suggesting that acidic canponents in the atmospheres produced effects that were additive upon the e f f e c t of O3 i n prducing both increase and prolongation of permeability i n tracheal and bronchoalveolar zones of the respiratory tract. Intravenous injection of tracer molecules and xemvery of the label in lung lavage fluid can also be used t o identify lung injury and loss of integrity of air-blood barrier a f t e r expsures t o low levels of toxic agents [refs. 47,481. The increase in permeability fran blood t o air was carparable t o the haease
.
from a i r t o blood [ref. 451 Autoradiography by electron micrOscapy identified multiple pathways for BSA transfer frun blood t o the alveolar space. Although defects in t i g h t junctions of dlveolar type I cells were observed in lungs of r a t s exposed t o 03, autoradiographic grains also aFpeared i n intercellular spaces, with the intercellular junctions reMinFng intact. ry
Kehrl et a l . [ref. 491 have studied the effects of inhaled O3 on respiratoepithelial permeability in hunam. Perosolized '%C-DTPA was inhaled by
eight healthy, nonsnoking males following exposure f o r 2 hr t o purified air or 0.4 ppn O3 while performing intermittent high i n t a i t y exercise (minute ven-
.
t i l a t i o n = 66.8 L) Specific airway resistance ( S R A and Fvc Were measured before and a t the end of exgmsures. The pllmanary clearance of '%eDTPA was
28
measured 75 min after the q s u r e s by lung imaging with a Y-camera. O3 exposure caused respiratory symptans in all 8 subjects and was associated w i t h a 1 4 2 2.8% (mean 2 S.E.) decrement in Fvc (p < 0.001) and a 71 5 22% increase (p = 0.04). ccnpared w i t h the air exposure day, 7 of the 8 subjects i n saw showedincreasedg%c-mAclearanceafterthe o3 exposure w i t h the mean value increasing fran 0.59 2 0.08 t o 1.75 2 0.43%/& (p = 0.03). Thus, O3 exposure sufficient t o produce decrenwts in the respiratory function of human subjects a l s o caused increased '%c-D'FA clearance. The Overton and M i l l e r [ref. 501 model of O3 dosimetry w i t h i n the lungs predicts similar airway deposition patterns f o r O3 i n rats and humans, w i t h the greatest deposition in the Vicinity of the respiratory acinus. A recent extension of t h i s work, based upon differences i n O3 removdL i n the upper respiratory tract and fraction exhaled, suggests t h a t humans have about t w i c e the deposition rate at the respiratory a c b as rats [ref. 511. Thus, the e f f e c t s seen in the chronic animal inhalation studies are l i k e l y t o be conservative estimates of the effects that OCCUT i n humans i n areas w i t h high chronic exposure, such as Southern California. Mst of the inhaled O3 penetrates beyond the sites i n the airways which trigger the functional responses and produces e f f e c t s w h i c h are concentrated on the region at and j u s t beyond the terminal bronchioles. These include changes i n biochemical indices and lung structure. In this region, the eff e c t s of O3 exposure in terms of progressive epithelial damage and inflamnatory changes appear t o be cumdative and persistent, even in animals t h a t have adapted t o the exposure i n tenns of respiratory mecham'cs [ref. 521. In groups of mice exposed t o 0.2 ppn O3 f o r 1, 3, o r 6 hr, superoxide anion radical production decreased 8, 18, and 35%respebively, indicating a pro-
gressive decrease i n bacteriocidal capacity w i t h increasing duration of exposure [ref. 531. In inhalation studies in rats involving O3 exposures a t constant concentrations of 0.12 and 0.25 ppn f o r 12 hr/d f o r 6 and 12 wk, Barry et al. [ref. 541 found that hyperplasia of Type I alveolar cells i n the proxim a l alveoli was l i n e a r l y related t o the clnrmlative lifetime O3 q s u r e . For s aw chronic effects, intermittent e.qmsures can prcduce greater eff e c t s than those produced by a continuous exposure w h i c h results i n higher currmlative e.xpsures. For exanple, Tyler et al. [ref. 551 exposed two groups of 7 mo o l d male Rlonkeys t o 0.25 ppn O3 f o r 8 hr/d either daily or, i n the seasonal model, on days of alternate mths during a t o t a l exposure period of 18 mo. A control group breathed only f i l t e r e d air. W e y s fran the' seasonal exposure model, bA not those exposed daily, had significantly increased t o t a l lung collagen content, chest wall carpliance, and inspiratory capacity. A l l mankeys exposed t o O3 had respiratory bronchiolitis w i t h significant in-
29 creases i n related morphanetric parameters. The only significant moqhamtric difference between seasanal and daily groups was in the volume fraction of macrophages. Even though the seasonally exposed Inonkeys here exp3sed t o the s a m concentration of O3 for only half as many days, they had larger biochemical and physiological alterations and equivalent morphcmetric changes as those exposed daily. bng growth was not ccnpletely no& in either expsed group. Thus, long-term effects of oxidant air pollutants may be more dependent upon the sequence of polluted and clean air than on the t o t a l nLnrS3er of days of pollution, and estimations of the risks of hman exposure t o seasonal air pollutants frm effects observed in animals exposeddailymayunderestimate long-term pulmonary damage. Epidemiologic studies of popllations living in Southern California suggest that chronic oxidant exposures do affect baseline respiratory function. Detels et a l . [ref. 561 canpared respiratory function a t two times 5 yr apart in Glendora (a high oxidant ccmmity) andinLancaster (a lower oxidant comrmulity-but not low by M t i d standards). Baseline function was lower in Glendora, and there was a greater r a t e of decline Over 5 yr. Kilburn et a l . [ref. 571 reported that nonsnokhg and exgpokcng w i v e s of Long Beach shipyard workers had significantly lower values of FEvll mid expiratory flow, tenninal expiratory flow, and carbon monoxide diffusing Capacity than those in a matched population frcm Michigan. The oxidant exposures i n Long Beach and Michigan are not known, but those in Longeeach and Lancaster are similar, while those in Michigan are qenerallymch lower. Bothstudieshave scme serious methodologic deficiencies, but &serve citation because they suggest effects which are consistent with the chronic animal exposure findings. A variety of pollutant interactions which potentiate other characteristic O3 responses have been reported in studies i n animals. Last [ref. 581 reported significant synergistic interaction in rats, i n terms of increased lung 3 protein content, a f t e r 9 d exposures a t 0.2 ppn O3 with 20 or 40 m/m €$SO4, 3 and a non-significant increase for 9 d at 0.2 p p ~ l O3 with 5 pg/m €$So4. Kleinman e t al. [ref. 591 reported that 03-i"h"d lesions i n the lung parenchyma w e r e greater in s i z e in r a t s also exposedto either €$SO4 o r NO2. Graham et a l . [ref. 601 reported a synergistic interaction between O3 and NO2 i n terms of mortality i n mice challenged with streptococcal infection either hmediately or 18 h r a f t e r pollutant exposure. Pinkerton et al. [ref. 611 reported that asbestos fiber clearance fran the lungs of r a t s was reduced when the r a t s were also exposed t o 03. "his increased fiber retention could increase the fibrogenic and carcinogenic risks of asbestos. The a b i l i t y of O3 and other toxicants t o act synergistically indicates that exposure limits for O3 should include an extra w i n of safety t o acknowledge
30 that co-exposures m n g ubiquitous pollutants such a s 03, NO2, %SO4,
and as-
bestos are l i k e l y t o occur in anbient air and many work e n v i r o m t s .
EMERGING ISSUES I N RELATION TO STANDARDS SETTING The r e s u l t s of recent research have substantially expanded our knowledge of exposure-response f o r many of the various e f f e c t s of O3 on the respiratory t r a c t . They have a l s o provided a basis f o r e n h a n d appreciation of the fact o r s affecting delivered dose, t h e duration and progression of effects, and the variations i n responsiveness m n g individuals. A t the same t h , it is important t o recognize that we s t i l l have a primitive understanding of t h e biological mechanisms f o r most of the e f f e c t s of concern, and that we lack a consensus on the health significance and importance in the pathogenesis of disease of even the more completely described effects, such a s transient changes i n respiratory function. While the absence of an adequate mechanistic framework is unfortunate, there is still a need f o r public action on standards and measures t o protect the public health based on current knowledge. The issues related t o exposure standards which should and can be addressed effect i v e l y i n the next few years with carefully conceived and well executed exposure-response studies are:
on
The influence of patterns of g3 exposure patterns of response- extending from transient changes & respiratory and particle clearance functions through airway inflamnation, lung permeability, c e l l u l a r changes a t the respiratory acinus, t o persistent changes in lung architecture associated w i t h lung f i b r o s i s and enphysema. The influence of other environmental factors on responses tog3. We need t o know more about the influence of temperature, h d d i F y , and coexposures t o NO2, SO2, HN03, acidic aerosols, inert aerosols and other widespread components of ambient a i r on responses t o 03, and the extent t o which the sequence of the exposures a f f e c t the responses. -~ Host factors affecting responsiveness.
We need t o identify the host fac-
t o r s responsible f o r the very w i d e range of responsiveness t o O3 exposure among humm and animals. Specifically, we need a better appreciation of how factors such as airway s i z e and structure and respiratory patterns affect O3 uptake, and how biochemical and genetic variations m n g viduals affect the responses of exposed tissues and cells. Interspecies v a r i a b i l i t y jg responses.
indi-
W e need t o have a better appreci-
ation of the similarities and differences in responses between humans and laboratory animals, and the ventilatory,
structural,
biochemical and
31
studies i n animals can be i n t e r p r e t e d f o r their inplications t o human health, e s p e c i a l l y for the genetic factors which control them, so t h a t the results of
chronic changes resulting fran repetitive exposures. A(JK"TS
This research was supported by Coaperative Agreement No. CR 811563 between t h e U.S. Environmental Protection Agency and New York University Medical Center. It was p r f o r m d as part of a Center program a t NYU supported by the National I n s t i t u t e of Enviromental Health Sciences - Grant ES 00260 and as part of a Center program a t NYU supported by the National Cancer Institute G r a n t CA 13343. The research described i n t h i s report has not been reviewed by the Health Effects Research Laboratory of the Emrironmental Protection Agency and the contents do not necessarily r e f l e c t the views of the Agency. REFERENCES 1 M.J. Hazucha, J. -1. Physiol., 62 (1987) 1671-80. 2 W.F. WDomell, D.H. Horstman, S. Abdul-Salaam, D.E. House, Am. Rev. R e p . D i s . . 131 (1985) 36-40. 3 R.J..Shephard, B. U r c h , F. Silverman, P.N. Corey, Environ. Res., 31 (1983)
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52 J.S. Tepper, D.L. C o s t a , M.F. Weber, M.J. Wiester, G.E. Hatch, M.J.K. Selgrade, Amer. Rev. Resp. D i s . , 135 (1987) A283. 53 M.A. AmDruso, B.D. Goldstein, T o x i c o l o g i s t , 8 (1988) 197. 54 B.E. Barry, F.J. Miller, J.D. C r a p O r Lab. IIlvest., 53 (1985) 692. 55 W.S. Tyler, N.K. T y l e r , J.A. Last, M.J. G i l l e s p i e , T.J. Barstow, T o x i c o l o g y (in press). 56 R. Detels, D.P. Tashkin, J.W. S a p , S.N. Rokaw, A.H. Coulson, F.J. msey, D.H. m,Chest., 92 (1987) 594-603. 57 K.H. Kilburn, R. Warshaw, J.C. Thronton, Am. J. M., 79 (1985) 23-28. Health P e r s p e c t . ( i n press). 58 J.A. Last, &iron. 59 M.T. Kleinman, R.F. P h a l m , W.J. mutz, R.C. m, T.R. M X 3 r e , T.T. Crocker, Environ. Health P e r s p e c t . ( i n press). 60 J.A. Graham, D.E. Gardner, E.J. Blarmer, D.E. House, M.G. &ma&, F.J. Miller, J. T o x i c o l . Emriron. Wth, 21 (1987) 113-125. 61 K.E. P i n k e r t o n , A.R. Brody, F.J. M i l l e r , J.D. Crapo, Am. Rev. Resp. D i s . , 137 (1988) A b s t r a c t .
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T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Zmplicatwns 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlande
PHOTOCHEMICAL OXIDANT FORMATION:
35
OVERVIEW OF CURRENT KNOWLEDGE AND EMERGING
ISSUES
Basil Dimitriades Atmospheric Sciences Research L a b o r a t o r y , U. S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, N o r t h C a r o l i n a 27711 (USA)
ABSTRACT D e s p i t e 1-1/2 decades o f c o n t r o l e f f o r t , t h e photochemical ozone p r o b l e m One reason a l l e g e d c o n t i n u e s t o p l a g u e human s o c i e t y and e c o l o g y i n t h e US. f o r t h e d i f f i c u l t y i n a c h i e v i n g t h e e s t a b l i s h e d ozone a i r q u a l i t y s t a n d a r d i s t h a t current understanding o f t h e science underlying t h e problem i s s t i l l insufficient S c r u t i n y o f e x i s t i n g empi r i c a l and theoretical/experimental evidence r e v e a l e d i m p e r f e c t i o n s i n ozone a i r q u a l i t y models and model a p p l i c a t i o n procedures. L a t e s t chemical mechanism developments e s t a b l i s h e d t h e CBM and CALL mechanisms as s u p e r i o r t o o t h e r s b u t s t i l l l a c k i n g i n some r e s p e c t s . P r e c u r s o r r e l a t e d u n c e r t a i n t i e s a r e o f consequence b o t h f o r models r e q u i r i n g e m i s s i o n r a t e i n p u t and f o r models r e q u i r i n g ambient c o n c e n t r a t i o n i n p u t . O t h e r f a c t o r s a f f e c t i n g model p r e d i c t i o n s a r e t h e c o m p o s i t i o n o f VOC e m i s s i o n s and t h e amount and makeup o f p o l l u t a n t s t r a n s p o r t e d i n t o t h e modeled atmosphere. Regional ozone a i r q u a l i t y models a r e now a v a i l a b l e and procedures a r e b e i n g developed f o r use o f such models i n f o r m u l a t i n g r e g i o n a l ozone c o n t r o l s t r a t e g i e s . The r e l a t i v e importances o f "hydrocarbons" (VOC) and n i t r o g e n o x i d e s (NO,) d i f f e r i n t h e urban and t h e r e g i o n a l ozone f o r m a t i o n phenomena.
.
INTRODUCTION I t has been some 3 1/2 decades s i n c e Haagen-Smit and co-workers
(ref.
1)
dernonstrated t h a t t h e smog symptoms e x p e r i e n c e d t y p i c a l l y i n Los Angeles and o t h e r urban areas a r e p r o d u c t s o f photochemical r e a c t i o n s o f o r g a n i c (VOC) and i n o r g a n i c (NO,)
pollutants.
Since then,
several
n o t a b l e developments have
taken place:
--
The s p e c i f i c chemical species r e s p o n s i b l e f o r t h e smog e f f e c t s (eye-
i r r i t a t i o n , p l a n t / m a t e r i a l s damage, etc.) aldehydes, H202, e t c . )
-
have been i d e n t i f i e d (e.g.
03, PAN,
(ref. 2).
Oryan'ic emissions, have been found t o d i f f e r w i d e l y i n ozone-forming
p o t e n t i a l , a f i n d i n g t h a t l e d t o t h e concept o f d i s c r i m i n a t e VOC c o n t r o l f o r ozone r e d u c t i o n ( r e f . 3).
-
Ozone and o t h e r p o l l u t i o n p r o b l e m have been f o u n d t o be a r e g i o n a l
r a t h e r t h a n an urban s c a l e phenomenon as a r e s u l t o f m u l t i - d a y p o l l u t a n t t r a n s p o r t ( r e f . 4).
36
-
The mechanism o f t h e atmospheric chemical process t h a t produces ozone
has been e l u c i d a t e d i n great d e t a i l ; i t now takes hundreds of elementary chemic a l r e a c t i o n steps t o describe t h e mechanism as now understood ( r e f s .
-
5-7).
Urban scale and regional scale ozone a i r q u a l i t y models capable of
p r e d i c t i n g s p a t i a l and temporal occurrence of ozone have been developed and are now i n use ( r e f . 8 ) . These remarkable advancements and t h e f a c t t h a t they r e q u i r e d more than 35 years of focused research e f f o r t appear t o suggest t h a t c u r r e n t understanding of t h e photochemical ozone problem i s adequate and a t t e n t i o n n a t u r a l l y s h i f t s t o " n e w ~ r " emerging a i r p o l l u t i o n problems (e.g.
t o x i c p o l l u t i o n , a c i d r a i n and
p r o b l e m a r i s i n g from changes i n stratosphere and global climate).
However,
t h e l a t e s t e f f o r t s t o evaluate mechanistic models and t h e d i s a p p o i n t i n g e x p e r i ences i n t h e US from a p p l i c a t i o n o f 33-related c o n t r o l s have a l l i n d i c a t e d t h a t t h e r e are s t i l l serious gaps i n our understanding o f the ozone problem.
Ozone
resedrch, and f u r t h e r advancement o f t h e theory u n d e r l y i n g t h e ozone problem, c l e a r l y , must
continue u n t i l t h e r e i s convincing evidence t h a t t h e o r e t i c a l
p r e d i c t i o n s agree w i t h r e a l world observations.
I n t h e discussion t h a t f o l l o w s ,
an attempt w i l l be made t o summarize t h e state-of-science i n t h e ozone problem area and t o i d e n t i f y and discuss outstanding s c i e n t i f i c issues. STATE-OF-SCIENCE AND ISSUES
I t i s now accepted t h a t t h e main reason f o r not having solved t h e ozone problem a f t e r 35 years o f research i s the enormous complexity o f t h e problem. This complexity stems from t h e f a c t s t h a t 03 i s an extremely r e a c t i v e p o l l u t a n t and t h a t i t can be scavenged by t h e very same p o l l u t a n t s t h a t produce i t .
It
i s f o r t h i s l a t t e r reason t h a t t h e ozone concentrations do not respond l i n e a r l y t o precursor
controls
or t o dilution.
Therefore,
the
key p r e r e q u i s i t e t o
s o l v i t i g t h e ozone problem i s a good, q u a n t i t a t i v e understanding o f t h e ozone-toprecursor r e l a t i o n s h i p s , which, i n t u r n , requires a good, d e t a i l e d understanding o f t h e atmospheric ozone-forming process. Ozone t o precursor r e l a t i o n s h i p s (ref.
2) a r e derived from basic labora-
t o r y , smog chamber, and modeling evidence, and t o a l e s s e r e x t e n t from empirical, f i e l d monitoring studies also.
U n l i k e i n past years, smog chamber data today
are n o t used d i r e c t l y t o d e r l v e such r e l a t i o n s h i p s .
Instead, such data a r e
used only f o r t h e purpose o f developing o r e v a l u a t i n g chemical mechanisms. t h i s reason,
For
smog chamber data, along w i t h l a b o r a t o r y k i n e t i c and mechanistic
data are now viewed as p a r t o f what i s commonly r e f e r r e d t o as modeling evidence, i n d i s t i n c t i o n t o empirical,
f i e l d monitoring evidence.
How do t h e modeling
evidence and empirical evidence r a t e r e l a t i v e t o each other?
37 Recent studies by t h e State of C a l i f o r n i a i l l u s t r a t e t h e t y p e and u t i l i t y of empirical evidence p e r t a i n i n g t o t h e ozone problem (ref. 9).
Notwithstanding
i t s non-causative nature and other l i m i t a t i o n s , such evidence i s believed by many t o have i n d i s p u t a b l e m e r i t because o f t h e i n t r i n s i c v a l i d i t y associated w i t h real world data.
For t h e evidence t o be conclusive, however, t h e r e must be an
abundance of data, and meteorology,
e.g.
multi-year h i s t o r i c a l data on emissions,
a i r quality
and t h e data must be o f documented r e l i a b i l i t y .
Based on
experiences t o date, these conditions o n l y r a r e l y can be met; f o r t h a t reason t h e amount o f acceptable empirical evidence i n existence i s r a t h e r l i m i t e d and can only be of suggestive nature.
I n contrast, t h e modeling evidence i s abun-
dant and extremely useful f o r d e r i v i n g q u a n t i t a t i v e ozone-to-precursor r e l a t i o n ships.
I n f a c t , t h e r e l a t i o n s h i p s we c u r r e n t l y accept and use have been derived
e n t i r e l y from modeling evidence and f o r t h a t reason, t h e next l o g i c a l question i s how r e l i a b l e and complete t h i s evidence i s . I n judging the r e l i a b i l i t y and completeness o f t h e modeling evidence, s p e c i f i c items of
i n t e r e s t are the accuracy o f t h e chemical and t r a n s p o r t /
dispersion mechanisms f o r t h e atmospheric ozone formation process, t h e accuracy of the r e q u i s i t e chemical k i n e t i c data, t h e accuracy of t h e precursor (ambient) concentration and emission inventory data, t h e d i s t i n c t i o n between " r e a c t i v e " versus "non-reactive"
VOC's, and the r o l e o f p o l l u t a n t transport.
I n 1981, we learned from s e n s i t i v i t y studies t h a t d i f f e r e n t chemical mechanisms appearing t o have equally good credentials,
when used t o compute VOC
c o n t r o l requirements, could g i v e widely d i f f e r e n t r e s u l t s ( r e f . 10).
This was
d i s t u r b i n g and underlined t h e need t o develop more r e l i a b l e methods f o r evaluat i n g chemical mechanisms. chamber data o r f i e l d data,
Such methods--e.g.
checking mechanisms against smog
o r against theory--do
e x i s t and,
i n concept can
give useful evaluations provided t h e r e q u i s i t e data and theory a r e s u f f i c i e n t l y accurate and comprehensive.
I n a 1986 workshop i n USA on Evaluation o f Chemical
Mechanisms, t h e p a r t i c i p a n t s agreed t h a t , despite c u r r e n t shortcomings o f smog chamber data, t e s t i n g o f a chemical mechanism against such data i s s t i l l t h e most r e l i a b l e and indispensable method f o r e v a l u a t i n g mechanisms ( r e f . Smog chamber data are not without shortcomings.
11).
The most important, w e l l known
shortcoming i s t h a t smog chambers e x h i b i t erroneously h i g h r e a c t i v i t y because o f chamber w a l l e f f e c t s . The question o f how t h e chamber w a l l s generate t h i s e x t r a r e a c t i v i t y has not been f u l l y and s a t i s f a c t o r i l y answered yet. r e c e n t l y (1987), Dr. Akimoto and h i s co-workers
Very
a t t h e Japanese I n s t i t u t e f o r
Environmental Studies reported evidence suggesting t h a t t h e e x t r a r e a c t i v i t y i s due t o a photoenhanced surface reaction between NO2 and H20 which r e s u l t s i n production o f n i t r o u s a c i d some 2-6 times more than o r i g i n a l l y thought ( r e f . 12). It would be very useful i f other smog chamber researchers would r e a c t t o o r
38 t e s t t h i s explanation so t h a t i t can be determined whether t h e Japanese theory has broad v a l i d i t y . From e f f o r t s t o date i n t h e US, two mechanisms have emerged as having t h e best c r e d e n t i a l s because o f t h e i r long h i s t o r y o f development and t e s t i n g . These are:
SAI's Carbon Bond Mechanism (CBM) ( r e f . 5), and t h e Carter-Atkinson-
Lurmann-Lloyd (CALL) mechanism developed by U. ( r e f . 6).
C a l i f o r n i a and ERT researchers
Ozone p r e d i c t i o n s by t h e two mechanisms agree w e l l w i t h each other
and they a l s o agree e q u a l l y well--or e q u a l l y badly--with e x i s t i n g smog chamber data.
The two mechanisms have undisputed strengths but they a l s o have imper-
f e c t i o n s ( r e f . 11).
For example, t h e p o r t i o n s o f t h e mechanisms t h a t describe
t h e r e a c t i o n o f OH w i t h most p a r a f f i n s , o l e f i n s and aldehydes have been shown t o be accurate.
The mechanisms, however, have u n c e r t a i n t i e s i n t h e areas of
aromatic hydrocarbon chemistry, t h e chemistry of heavy alkanes, and t h e ozoneo l e f i n r e a c t i o n chemistry.
U n c e r t a i n t i e s are a l s o caused by t h e lack o f photo-
l y t i c data f o r several carbonyl compounds, e.g. glyoxal, and methylglyoxal.
MEK, propionaldehyde, acetone,
One piece o f evidence a t t e s t i n g t o presence o f
imperfections i s t h e f a c t t h a t t h e 03 p r e d i c t i o n s o f t h e 2 mechanisms respond d i f f e r e n t l y t o changes i n VOC composition. One f a c t o r t h a t has been drawing i n c r e a s i n g a t t e n t i o n i n modeling s t u d i e s o f t h e ozone problem i s t h e precursor emissions o r ambient concentrations t h a t are i n p u t t o t h e models.
Use o f e x i s t i n g emission inventory data i n a i r q u a l i t y
models t o compare model-computed ambient VOC concentrations w i t h observations
o r t o compare VOC-to-NO,
emission r a t i o s t o respective ambient concentration
r a t i o s o r t o compare anthropogenic-to-biogenic VOC emission r a t i o s t o respective ambient r a t i o s r e s u l t e d i n inconsistencies t h a t suggest erroneously low emission i n v e n t o r i e s f o r anthropogenic VOC's ( r e f s .
13,14).
heretofore ignored anthropogenic VOC emissions ( r e f s .
More recent evidence on 15,16)
[e.g.
POTW's, f u g i t i v e emissions, higher evaporative auto emissions, etc.]
from TSDF, has v e r i -
f i e d t h i s emission problem and has cast a greater doubt on t h e accuracy o f model p r e d i c t i o n s regarding c o n t r o l requirements f o r ozone.
Another emission-
r e l a t e d problem i s t h e l a c k o f r e l i a b l e VOC emission composition data w i t h d e t a i l consistent w l t h t h e model ' s requirements.
Given t h e s e n s i t i v i t y o f model
p r e d i c t i o n s t o VOC composition, t h i s problem i s n o t i n s i g n i f i c a n t . Problems a l s o e x i s t
i n t h e cases f o r which the main precursor-related
i n p u t s t o t h e model are ambient concentrations. i s the 6:00-to-9:00-am presently measured--i .e. validity.
VOC-to-NOx
A key i n p u t t o t h e EKMA model
concentration r a t i o ,
an e n t i t y which,
as
a t c e n t e r - c i t y s i t e s d u r i n g 6-9 AM--is o f questionable
To explain, such r a t i o s vary widely from l o c a t i o n t o l o c a t i o n ( w i t h i n
t h e c e n t e r - c i t y area) and from day t o day both because o f measurement e r r o r and because of normal v a r i a b i l i t y o f t h e source and meteorology f a c t o r s . Because o f t h e l a t t e r reason, s e l e c t i n g t h e average o r mean r a t i o value (as i s c u r r e n t l y
39 done) f o r i n p u t i n g t o t h e EKMA model may o r may n o t be j u s t i f i e d .
In efforts
t o t e s t t h e v a l i d i t y o f t h e c u r r e n t method and t o s e a r c h f o r more v a l i d a l t e r n a t i v e s , a f i e l d s t u d y i s b e i n g c u r r e n t l y conducted b y USEPA i n w h i c h measurements o f VOC and NO,
a r e made i n t h e same a i r mass where t h e d a y ' s peak 03 Such VOC and NO,
c o n c e n t r a t i o n occurred.
measurements,
r e p r e s e n t t h e 6-9-AM concentrations--some VOC and NO,
of
course,
do n o t
must have r e a c t e d o u t and
must have mixed i n d u r i n g t h e t i m e i n which ozone reached
some f r e s h VOC and NO, i t s peak
concentration.
possible.
For example,
Some adjustment measurement
b a s i s f o r a d j u s t i n g t h e VOC/NO,
of
for
NO,
these
effects,
however,
are
r e a c t i o n p r o d u c t s can p r o v i d e a
r a t i o f o r reaction.
The d a t a f r o m t h i s s t u d y
w i l l be examined f o r e v i d e n c e on t h e m e r i t s o f t h i s method f o r o b t a i n i n g t h e r e q u i s i t e VOC/NO,
value.
The d i s t i n c t i o n between r e a c t i v e and n o n - r e a c t i v e VOC's has s i g n i f i c a n c e because o n l y r e a c t i v e VOC emissions a r e r e q u i r e d t o b e i n v e n t o r i e d and because r e a c t i v i t y must be c o n s i d e r e d i n j u d g i n g impacts o f VOC e m i s s i o n t r a d e - o f f s (e.9.
emissions
autos).
f r o m alcohol-powered
autos
versus
emissions
from
gasoline
Several r e a c t i v i t y c l a s s i f i c a t i o n schemes have been c o n c e i v e d t o date,
ranging from t h e simplest scheme t o a t e d XIS
b u t l e a s t e f f e c t i v e 2-Class
(reactive-unreactive)
t o use b u t more e f f e c t i v e 5-Class scheme ( r e f . 2).
Current
t h i n k i n g i n t h e US f a v o r s a 2-Class scheme t h a t uses t h e r e a c t i v i t y o f ethane
as t h e "border1 ne" s e p a r a t i n g r e a c t i v e f r o m n o n - r e a c t i v e VOC's. n o t a1 1--cases,
a VOC
measurement o f
t s r a t e o f r e a c t i o n w i t h t h e OH r a d i c a l ( r e f .
VOC's, however,
(e.g.
can
I n most--but
be r e a c t i v i t y - c h a r a c t e r i z e d t h r o u g h e x p e r i m e n t a l
17).
F o r some
h i g h m o l e c u l a r w e i g h t a l i p h a t i c s ) t h e OH r e a c t i o n r a t e
c o n s t a n t i s n o t a v a l i d i n d e x o f ozone-forming p o t e n t i a l ( r e f . 18). and use of more complex e x p e r i m e n t a l / m o d e l i n g t e c h n i q u e s i s r e q u i r e d . With respect t o p o l l u t a n t transport,
t h e phenomenon has been s t u d i e d t o
t h e p o i n t t h a t r e g i o n a l 03 a i r q u a l i t y models a r e now a v a i l a b l e . established t h a t
l o n g range ( i .e.
t h e 03-to-precursor transport conditions, formation ( r e f .
NO,
multi-day)
relationships drastically. f o r example,
It has been
pollutant transport
increasing
Under r e g i o n a l NOx
influences
o r multi-day
c o n s i s t e n t l y enhances
03
19) whereas under s i n g l e day t r a n s p o r t c o n d i t i o n s i n c r e a s i n g
may e i t h e r enhance o r i n h i b i t 03 f o r m a t i o n (depending on VOC/NO,
conditions ) ( r e f s
. 20.21).
and o t h e r
Regional 03 models have been developed ( r e f . 8) b u t have n o t been f u l l y evaluated yet.
I n f a c t , t h e modelers have n o t d e v i s e d y e t a t o t a l l y s a t i s f a c -
t o r y method f o r e v a l u a t i n g r e g i o n a l models.
Comparing r e g i o n a l model p r e d i c -
t i o n s and o b s e r v a t i o n s i n p a i r s , as commonly done w i t h u r b a n s c a l e models, i s much l e s s m e a n i n g f u l because o f t h e more s t r o n g l y s t o c h a s t i c n a t u r e o f t h e
40 r e g i o n a l model p r e d i c t i o n s .
S t a t i s t i c a l comparison of p r e d i c t i o n s and observa-
t i o n s ( r e f . 221, although somewhat l e s s u s e f u l , i s more r a t i o n a l and appears t o be t h e p r e f e r r e d e v a l u a t i o n approach a t t h i s time. While most o f t h e ozone i n problem areas o r i g i n a t e s from photochemistry of urban emissions, s i g n i f i c a n t c o n t r i b u t i o n s can a r i s e a l s o from s t r a t o s p h e r e troposphere exchanges,
from background t r o p o s p h e r i c chemistry,
from b i o g e n i c
emissions, and from photochemistry o f d i f f u s e anthropogenic emissions i n r u r a l areas ( r e f .
23).
ground ozone",
The sum t o t a l o f these c o n t r i b u t i o n s , r e f e r r e d t o as "backcan reach s i g n i f i c a n t
reason i t warrants
attention.
levels
i n c e r t a i n areas and f o r t h a t
Tropospheric chemistry has been r e p o r t e d t o
r e s u l t i n ozone formation only when t r o p o s p h e r i c NOx c o n c e n t r a t i o n s exceed a c e r t a i n t h r e s h o l d value;
otherwise,
destruction of
ozone occurs
(ref.
24).
Biogenic VOCls have been s t u d i e d and found t o be both p o t e n t producers and extremely e f f e c t i v e scavengers o f ozone ( r e f .
24).
There have been s t u d i e s
suggesting t h a t b i o g e n i c VOC's have an i n s i g n i f i c a n t r o l e i n urban ozone problems ( r e f . 24).
They may c o n t r i b u t e ,
however, t o r u r a l ozone--an e f f e c t which i s
supported by some b u t not enough evidence ( r e f . 25).
F i n a l l y , e x i s t i n g evidence
on t h e s i g n i f i c a n c e o f r u r a l anthropogenic emissions as a source o f background
ozone i s l i m i t e d and somewhat unclear.
Modeling estimates vary depending on
NO, assumptions and/or c a l c u l a t i o n techniques used ( r e f . 25). t i o n s o f magnitude,
Thus, t h e ques-
o r i g i n s and c o n t r o l l a b i l i t y o f background ozone a r e open
and important and c a l l f o r a d d i t i o n a l research. Next, t h e discussion w i l l address t h e c o n t r o l i m p l i c a t i o n s o f t h e recent advances i n 03 chemistry and modeling, and some c o n t r o l - r e l a t e d questions t h a t remain unanwered due t o unresolved s c i e n t i f i c issues. Recent modeling s t u d i e s have e s t a b l i s h e d t h a t t h e r e l a t i v e r o l e s o f VOC and NO,
i n urban 03 f o r m a t i o n vary considerably from c i t y t o c i t y depending on
a host o f f a c t o r s t h e most important o f which i s t h e VOC-to-NO, The r e l a t i v e m e r i t s o f VOC c o n t r o l and NO,
r a t i o ( r e f . 20).
c o n t r o l depend a l s o on whether t h e
c o n t r o l goal i s an immediate and modest r e d u c t i o n o f peak 03 c o n c e n t r a t i o n s o r t h e d r a s t i c 03 r e d u c t i o n r e q u i r e d t o meet t h e 03 a i r q u a l i t y standard. example, NO,
For
c o n t r o l can b r i n g about an immediate modest r e d u c t i o n o f peak 03
c o n c e n t r a t i o n i n urban areas b u t i t may also, under some, n o t uncommon condit i o n s , make i t more d i f f i c u l t t o u l t i m a t e l y achieve t h e 03 a i r q u a l i t y standard ( r e f . 20).
F i n a l l y , t h e evidence i n d i c a t e s t h a t whereas VOC c o n t r o l i s never
d e t r i m e n t a l , NO,
c o n t r o l can be d e t r i m e n t a l , p a r t i c u l a r l y ,
p a r t s o f the urban areas ( r e f . 20).
i n the center-city
U n l i k e urban 03, t h e r e l a t i v e e f f e c t s o f
NO, c o n t r o l s on r e g i o n a l 03 have n o t been w e l l s t u d i e d y e t . There i s suggestive evidence t h a t c o n t r o l o f NO, i n urban and r u r a l areas would reduce VOC and
r e g i o n a l 03 b u t more complete s t u d i e s are necessary b e f o r e such an e f f e c t can be a s c e r t a i n e d and q u a n t i f i e d .
41 The f i n a l
comnents p e r t a i n t o t h e modeling t o o l s c u r r e n t l y available.
From t h e discussion thus far, i t can be seen t h a t t h e 03 problem i s t o o complex f o r t h e c o n t r o l agencles t o design ozone c o n t r o l s t r a t e g i e s based on "comnon sense" o r on empirical evidence alone. Notwithstanding t h e i r imperfections and l i m i t a t i o n s , state-of-the-art physicochemical 03 a i r q u a l i t y models are t h e superior t o o l ,
indispensable i n 03 a i r q u a l i t y management p r a c t i c e s .
For t h e
urban 03 problem case, t h e r e are now a v a i l a b l e simple, EKMA-type models ( r e f s . 26,271 as w e l l as more sophisticated--but c o s t l i e r - - E u l e r i a n models ( r e f . 28). t h a t can be used by the s c i e n t i f i c comnunity w i t h i n t h e a i r p o l l u t i o n c o n t r o l agencies i n t h e US.
The EKMA models a r e acceptable f o r small,
i s o l a t e d urban
areas w i t h m i l d 03 problems whereas use o f t h e g r i d models i s g e n e r a l l y p r e f e r able i n t h e cases o f severe 03 problems i n urban areas w i t h i n densely populated regions.
I n e i t h e r case, t h e i n p u t information r e q u i r e d by t h e models i s a v a i l -
able o r can be measured, except f o r f u t u r e boundary conditions. The r e q u i s i t e data on t h i s l a t t e r i n p u t can be estimated only through use of p r e d i c t i v e regional models and t h i s i s one reason why regional 03 models have been developed.
Regional models are now a v a i l a b l e i n t h e US and Europe but, u n l i k e t h e
urban scale models, t h e i r use i s s t i l l q u i t e l i m i t e d .
Thus,
i n t h e US,
for
example, EPA's ROM has not been f u l l y evaluated y e t , t h e p r o b a b i l i s t i c nature o f i t s p r e d i c t i o n s complicates t h e use o f t h e model f o r 03 s t r a t e g y development, and l a s t l y but most importantly, i t s complexity and c o s t o f a p p l i c a t i o n make t h e model accessible t o only a few.
The model i s extremely demanding i n quan-
t i t y and q u a l i t y o f i n p u t and i n ADP resources. For example, t h e r e q u i s i t e emission inventory i n p u t should include biogenic emissions data, and t h e s t r o n g s e n s i t i v i t y o f model p r e d i c t i o n s t o the NOx emission f a c t o r makes i t c r u c i a l t h a t the NO, emission inventory i n p u t be extremely accurate.
Finally, there are
imperfections i n the chemistry and dispersion components o f t h e model. For example, the model ' s chemical mechanism does n o t i n c l u d e aerosol-related steps and, therefore,
sink processes such as l o s s o f H202 and o f N0,derived
products
on l i q u i d / s o l i d p a r t i c l e s , are ignored, and, as a r e s u l t , model-predictions f o r H202 and some NO,
species may be erroneously high.
While i t may t a k e several
years t o remove a l l o f these imperfections, i t i s expected t h a t i n a year o r so t h e current version o f USEPA's ROM w i l l be f u l l y evaluated and ready t o be used f o r development o f ozone c o n t r o l strategies. REFERENCES
1 Haagen-Smit, A. J. Ind. Eng. Chem., 44:1342 (1952). 2 U.S. Environmental Protection Agency. " A i r Qua1i t y C r i t e r i a f o r Ozone and Other Photochemical Oxidants", EPA-600/8-78-004, A p r i l 1978. EPA, C r i t e r i a and Assessment Office, Research T r i a n g l e Park, NC 27711.
42 3
4
5 6
7 8
9 10 11
12 13
14 15
16
17
18
19
U.S. Environmental P r o t e c t i o n Agency. " R e a c t i v i t y and I t s Use i n OxidantRelated Control". I n : Proceedings o f international Conference on Photochemical Oxidant P o l l u t i o n and I t s Control". EPA-600/3-77-001a, b, January 1977. E d i t o r , 8. Dimitriades, EPA, Environmental Sciences Research Laborat o r y , Research T r i a n g l e Park, NC 27711. Wolff, 6. T., P. J. Lioy, G. D. Wright, R. E. Meyers, and R. T. Cederwall. "An I n v e s t i g a t i o n o f Long Range Transport o f Ozone Across t h e Midwestern and Eastern United States". I n : Proceedings o f I n t e r n a t i o n a l Conference on Photochemical Oxidant P o l l u t i o n and I t s Control". EPA-600/3-77-001a, January 1977. E d i t o r , B. Dimitriades, EPA, Environmental Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. Whitten, 6. 2 . and M. W. Gery. EPA r e p o r t EPA-600/3-86;12, 1986. EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. Carter, W. P. L., F. W. Lurmann, R. Atkinson and A. C. Lloyd. EPA r e p o r t EPA-600/3-86-031, 1986, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. Graedel, T. E., L. A. Farrow, and T. A. Weber. Atmospheric Environment, 10: 1095 (1976). Lamb, R. G. EPA reports EPA-600/3-83-035, September 1982, EPA-600/384-085, May 1984, and EPA/600-3-85-037, Apri 1 1985. EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. C a l i f o r n i a A i r Resources Board. "The E f f e c t s o f Oxides o f Nitrogen on C a l i f o r n i a A i r Q u a l i t y " . Report Number TSD-85-01, March 1986. State of C a l i f o r n i a , A i r Resources Board, 1102 Q Street, Sacramento, CA 95814. J e f f r i e s , H. E., K. G. Sexton, and C. N. Salmi. EPA report, EPA-450/481-034, November 1981, EPA, O f f i c e o f A i r Q u a l i t y Planning and Standards, Research T r i a n g l e Park, NC 27711. Atkinson, R., H. J e f f r i e s , G. Whitten, and F. Lurmann. Proceedings of Workshop on Evaluation/Documentation o f Chemical Mechanisms. E d i t o r , 6. Dimitriades. EPA-600/9-87-024, October 1987. EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. Akimoto, H., H. Tagagi, and F. Sakamaki. I n t . J. Chem. Kinet., 19:539 (1987). Ching, J. K. S., J. H. Novak, K. L. Schere, and F. A. Schiermeier. "Reconc i l i a t i o n o f Urban Emissions and Corresponding Ambient A i r Concentrations I n t e r n a l document. EPA, Atmospheric Using A Mass Flow Rate Technique". Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. EPA-600/3-85-013, 1985. EPA, Atmospheric Westberg, H. and B. Lamb. Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. "Area Source Documentation f o r t h e 1985 National Acid P r e c i p i t a Pahl, 0. t i o n Assessment Program Inventory". I n t e r n a l EPA Report, September 1986. EPA, A i r and Energy Engineering Research Laboratory, Research T r i a n g l e Park, NC 27711. "Motor Vehicles as Sources o f Compounds Important t o TropoBlack, F. spheric and Stratospheric Ozone". T h i r d US-Dutch I n t e r n a t i o n a l Symposium on Atmospheric Ozone Research and I t s P o l i c y I m p l i c a t i o n s , May 9-13, 1988, N i jmegen, Nether1ands. Proceedings i n press (1988). P i t t s , J. N., Jr., A. M. Winer, S. M. Aschmann, W. P. L. Carter, and R. Atkinson. "Experimental Protocol f o r Determining Hydroxyl Radical Reaction Rate Constants f o r Organic Compounds--Estimation of Atmospheric R e a c t i v i t y " . EPA Report 600/3-85-058, June 1985, EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. B u f a l i n i , J . J. and R. R. Arnts. "Review o f t h e UCR Protocol f o r Determinat i o n o f OH Rate Constants w i t h VOC's and I t s A p p l i c a b i l i t y t o P r e d i c t Photochemical Ozone Formati on". EPA Report 600/3-87-046, November 1987. EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. Carter, W. P. L., M. C. Oodd, W. D. Long, and R. Atkinson. EPA r e p o r t EPA-600/3-84-115, March 1985, EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711.
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Dimitriades, B. "The Role o f NOx i n t h e Urban Ozone Problem. Recent Developments i n Atmospheric Photochemistry". (Presented a t EPA-CARB ConferTiburon, CA., June 3-4, 1987). I n t e r n a l document, 1987, EPA, ence on NO, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. P i t t s , J. N., Jr., A. M. Winer, R. Atkinson, and W. L. Carter. Env. Sci. Technol. 17:54 (1983). Schere, K. "Development and V a l i d a t i o n o f t h e Regional Ozone Model f o r t h e Northeastern United States". T h i r d US-Dutch I n t e r n a t i o n a l Symposium on Atmospheric Ozone Research and I t s P o l i c y Implications, May 9-13, 1988, N i jmegen, Netherlands. Proceedings i n press (1988). A l t s h u l l e r , A. P. JAPCA 37:1409 (1987). Dimitriades, B. JAPCA. 34:729 (1981). Trainer, M., E. J. Williams, 0. 0. Parrish, M. P. Buhr, E. J. Allwine, H. H. Westberg, F. C. Fehsenfeld, and S. C. Liu. Nature, 329:705 (1987). Dimitriades, B. "An A l t e r n a t i v e t o t h e Appendix J Method f o r C a l c u l a t i n g Oxidant and NO2 Related Control Requirements". In: " I n t e r n a t i o n a l Conference on Photochemical Oxidant P o l l u t i o n and I t s Control: Proceedings, Volume 11". Editor, B. Dimitriades. EPA-600/3-77-016, January 1977. EPA, Atmospheric Sciences Research Laboratory, Research T r i a n g l e Park, NC 27711. U.S. Environmental P r o t e c t i o n Agency. "Guideline f o r Use of C i t y - S p e c i f i c EKMA i n Preparing Post-1987 Ozone S I P ' S " . November 1987. I n t e r n a l OAQPS document. EPA, O f f i c e o f A i r Quality Planning and Standards, Research Triangle Park, NC 27711. U.S. Environmental P r o t e c t i o n Agency. "Guidelines f o r Applying t h e Airshed Model t o Urban Areas." NTIS P u b l i c a t i o n Number PB81-200529, 1980. U.S. National Technical Information Service, 5285 Port Royal Road, S p r i n g f i e l d , VA 22161.
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T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science PublishersB.V.,Amsterdam - Printed in The Netherlands
CURRENT KNOWLEDGE EMERGING ISSUES
OF
OZONE
ON
VEGETATIONfFOREST
EFFECTS
AND
G.H.M. KRAUSE and 8. PRINZ Landesanstalt ftr Immissionsschutz des Landes NRW, Wallneyer Strape 6, 4300 Essen 1, FRG
ABSTRACT In consequence of increased emissions of nitrogen oxides and reactive hydrocarbons as precursor substances as well as in respect of phytotoxicity, range of concentration and spatial distribution, ozone is today the most important phytotoxic component among photochemical oxidants and besides sulfur dioxide probably the most important air pollutant in Europe today. M i l e its importance to forest decline was first discovered in California 25 years ago, new impetus in effects research was caused by the appearance of novel forest decline in Europe and United States of America. Former research was emphasising more the acute effects, especially in connection with agricultural and horticultural crops. Now, the central point of discussion are chronic effects. By this, the problem has become increasingly difficult, since other environmental stresses, such as pathogenes, soil, and climate very often mimic ozone effects under field conditions.
INTRODUCTION Impact of air pollutants on vegetation and ecosystems is a well documented phenomenon, which has been observed for over 100 years in case of sulfur dioxide as shown by one of the first reviews prepared by Yislicenus (ref.1). With increasing efforts to reduce the air pollution burden, the pollution environment has changed considerably during the last decade. While sulfur dioxide emissions have stayed more or less constant and will be markedly reduced in the near future, secondary air pollutants such as photochemical oxidants have gained importance with respect to vegetation effects, due to increased emissions of nitrogen oxides and organic compounds as precursor substances and the long range transport of these pollutants. Effects of photochemical oxidants and their potential phytotoxicity though were discovered rather lately and observed first on vegetation during the fourties in the Los Angeles basin
(ref.2). Meanwhile, origins of ozone as the most prevalent com-
pounds within the group of photochemical oxidants have been subject to many
46
reviews in the past in respect to atmospheric chemistry, health effects, impact on vegetation, animals and materials as well as control strategies (refs.3-6). Especially recent decline phenomena observed in many forests throughout Europe, being first primarily related to 'acid rain' alone, are currently discussed to be associated with the impact of ozone in one or another way (refs.7-8), and recent research activities were focussed very effectively on this matter (ref.9). In the following, principle mechanisms of ozone impact on plants are discussed under consideration of external and internal growth factors. Special attention is given to the role of ozone in respect to novel forest decline and reference made to combinatory effects with other pollutants as well as dose-response relationships.
EFFECTS OF OZONE ON PLANT METABOLISM
The effects of
on plant metabolism can be described as follows: tree response to ozone starts with the diffusion of the gas from the atmosphere into the leaf through the stomata. Uptake is controlled by leaf resistances (ref.10) as well as stomatal density and conductance (refs.l1,12), and is generally dependent on physical, chemical, or biological factors involving the transition between gas phase and liquid phase movement into the cells (ref.13). In the liquid phase, ozone will readily undergo transformation, yielding a variety of free radicals which will then react with cellular components (ref.13). Sensitivity of plants is modified, therefore, by any factors influencing stomatal aperture such as light (refs.l4,15), relative humidity (ref.16), and soil moisture (ref.17). Besides genetic (refs.18,19) or developmental factors (ref. 2 0 ) , soil fertility (ref.21) or chemicals such as herbicides, fungicides (ref-22) etc. can also influence stomatal aperature. When plants are unable to repair or compensate oxidant induced perturbations, injury on above-ground plant parts occurs and.can be characterized for gymnosperms as destruction of the mesophyll cells leading to chlorotic bleaching of the needle tip or mottling of the youngest needles (ref.231, frequently accompanied by an unspecific needle cast (ref.24,25). Ozone injury in angiosperms starts with the decay of chlorophyll and the destruction of the palisade parenchyma cells, resulting in bleaching and minute necrotic stiples in the intercostal areas (ref.23). Similar injury patterns are observed in many broad-leaved agricultural and horticultural plants (ref.26), and since affected groups of cells are often minute but distributed over the whole leaf area, colour of leaves get a bronzing appearance. 03
41 Each leaf passes through phases of different sensitivity. As a general role, leaves are most sensitive, when unfolded and just developed to normal size. Conifer needles are most sensitive during elongation and susceptibility decreases after maturation. Chronic effects result eventually in changes at the cellular level. The primary site of action for ozone is to oxidize organic compounds, like specific enzymes and lipid compounds of cell membranes, leading to changes in membrane permeability of the plasmalemma as well as the chloroplasts, as shown by changes in flux of organic and inorganic plant metabolites (refs.13,2730). The peroxidation of lipids is deduced from the increase of antioxidants
like glutathions, vitamin E and C (refs.31,32), most likly as protective measure. Phenomena of increased membrane permeability have been associated with increased leaching of essential nutrients (refs.30,33), accompanied or even enhanced by ozone induced weathering of the cuticle (ref.34). Photosynthesis is very frequently reduced (refs.35-41) either indirectly by closure of the stomata1 aperture resulting in reduced COZ uptake (refs.42,43), or directly by damage to the chloroplasts (refs.44,45).
Another
effect is ozone induced reduction in assimilate translocation to roots with a resulting decrease in root size and fewer stored reserves, with the potential for increased sensitivity to frost, heat, and water stress (refs.20,46-48). Other effects, such as reduction in chlorophyll content (refs.39-41,43,49) or chlorophyll bleaching in the presence of light due to oxidation processes (refs.39,42) have been observed. Biochemical perturbations are a further expression of subtle injury reactions, frequently indicating premature ‘senescence which occurs under chronic
03
pollution stress (refs.50-52).
These
include the oxidation of sulfhydryl groups (ref.53). and changes in the content of soluble sugars, starch, phenols, ascorbic acid, amino acids, and protein, as well as interferences with enzymes such as the nitrate- or nitritereductase involved in nitrogen metabolism (refs.33,46,54).
EFFECTS OF OZONE ON FOREST ECOSYSTEMS Our knowledge is rather limited in terms of the many plant species indigenous to forest ecosystems (ref.55). Ozone effects are much more difficult to evaluate than those of SOZ, because there are no point sources to allow observations along a concentration gradient. Furthermore, it is difficult to determine if tree responses are cumulative and the result of a number of influencing chronic stress factors, unless they can be traced back to specific biotic diseases or pollution exposure. In areas with chronic ozone exposure
(and I think many areas of Europe should be ranked in this category), decline in vigor of trees and forest ecosystems is a commonly observed response (refs.51,55-57). Symptoms of chronic decline differ markedly from acute visible injury and include, according to HcLaughlin (ref.56): (1) premature senescence with cast of older needles in autumn, (2) reduced assimilate storage in roots at the end of the growing season and reduced resupply capacity in spring, ( 3 ) increased reliance of new needles on self support during growth, ( 4 ) shorter new needles and thus reduced assimilate production, (5) reduced
availability of photosynthates for homeostasis, and ( 6 ) premature cast of older needles. The most complete study of ozone effects on forest ecosystems was done within the San Bernardino National Forest near Los Angeles, California where, due to specific climatic, orographic, and emission characteristics, elevated ozone levels of up to 580 ug . r 3 were present (ref.58). Tree species sensitive to ozone were listed as: Pinus ponderosa, Pinus jeffrevi, Abies conco-
lor,
Quercus velutina, Librocedrus decurrens and Pinus lambertiana. Foliar
injury and premature leaf fall coincided with decreased rates of photosynthesis, reduced radial growth, tree height and seed production, as well as retarded nutrient retention (ref.57,69). Injury to Pinus ponderosa occurred even at concentrations of 100 to 120 ug.r3 for 24 h. However, sensitive tree species were not eliminated by the photooxidant burden, but by their 03 induced predisposition to insect infestations such as bark beetles. The other predominant tree species affected under ambient exposure of ozone is eastern white pine (Pinus strobus), as has been seen in many parts of the United States, such as the southern Sierra Nevada in Central California, Indiana and Wisconsin (refs.59-61). or the northeastern United States, such as the Appalachian region (refs.62-64). In eastern Tennessee for example, annual average growth was reduced between 1962 and 1979 by as much as 70% in sensitive species as compared to tolerant ones. The cause of these growth effects was attributed to chronic ozone exposure, frequently in the phytotoxic range 0 1 6 0 ~ g . m - ~ ) . In addition to growth reductions, premature senescence, and lower photosynthetic rate, perturbations in the processes of carbon allocation were also observed. In another field study with filtered versus non-filtered air using open top chambers, Duchelle et al. (ref.65) showed that summer mean concentrations of 86 ug.m-3 produced visible injury at the end of the growing season on species such as Liriodendron tulipifera, Liauidambur stvraciflua, and Fraxinus pennsvlvanica, while those in filtered chambers showed no effect. Betula ~ e n ,&d
Fraxinus excelsior, and some species of Fraxinus americana were found
49
to have ozone specific injury after one growing season in rural southeastern England using the same type of exposure system, while svlvatica and Quercus robur were more tolerant (ref.66). According to Ashmore et al. (ref.671, 0 3 concentrations were markedly below summer means of 100 ~ g . m - ~ measured at the Schauinsland station in the Black Forest in FRG (ref.68). On the other hand, fumigation experiments with Picea abies and Abies alba revealed that these major, European native species were relatively tolerant because only 03 fumigation with ,200 ug.m-3 for )40 days, produced visible injury in form of mottling as well as lead to an inhibition of photosynthesis, respiration, and transpiration (ref.39).
POLLUTANT INTERACTIONS The atmosphere usually contains a complex and dynamic mixture of pollutants occurring simultaneously or sequentially with great regional variation (ref.79). Therefore, it is difficult to evaluate vegetation response in a given experimental design, since only limited pollution regimes out of many potential ones are reflected. Plant response to air pollutant mixtures can be additive, less than additive (antagonistic) or greater than additive (synergistic). The last response type has particularly led to great concern for forest ecosystems. The pollution situation in remote areas is mostly characterized by the presence of SOX, NO2, and 0 3 , as well aa acidic deposition. Combinations of these pollutants are discussed briefely under reference of an excellent, recent review published by Guderian and Tingey (ref .70). Considering combined effects of SO2 and 0 3 it seems generally that injury symptoms are related more to ozone than to SOr (refs.71-73); however, exceptions are also reported (refs.74-76). While most herbaceous plants show additive or synergistic effects when exposed to SOr and Oa (refs.77-79). woody species show slightly less than additive or even antagonistic responses in plant growth (ref . 6 ) . Combined effects of NO2 and 0 3 resulted in chlorotic mottling in Pinus taand were occasionally accompanied by tip-burn Hight growth was reduced by two or three pollutant combination of S O I / N O P / O ~ in close to ambient concentrations It was shown that effects of the three pollutant combination were similar to two pollutant combinations of 0 3 + SOr or 03+ Nor, respectively (ref. 80). Low levels of NO2 and SO2 increased early senescence in poplar trees, accompanied by premature leaf drop, irrespective of the addition of ozone (ref.81). Cuderian (ref.82) reported that the combined effect of NOX, SOP, and 0 3 was yellowing of needles of Picea abies, and when nutrient
.
&I
.
50
deficiency was present at the same time, the symptoms showed remarkable similarity with those of the new forest decline (ref.7). Experiments carried out with poplar species fumigated with S 0 2 , N O z , and 03 singly and in combination revealed a less sensitive reaction to combinations of S 0 2 1 N 0 2 than to N O z / 0 3 or N 0 2 / S O ~ / 0 3 . It seems that combinations of N O z / 0 3 are more important with respect to leaf injury than N O z I S 0 2 (ref.82). Fumigation of Platanus occidentalis with a combination of S O z / N O 2 / 0 3 showed, greater effects than with two-gas-mixtures without foliar injury (ref.83) .' Other experiments revealed that growth reductions in Pinus strobus were more influenced by 0 3 and/or SO2 than NO2 alone or combinations of NO2 + 0 3 or NO? t SO2 (ref.84). These findings contradict those of Moo1 (ref.81) where a greater decrease in growth occurred with the combination of either N O 2 1 0 3 or all three pollutants, than with SOz/NOo (ref.82). Interactions of gaseous pollutants and acidic deposition and their impact on forest ecosystems is another important pollutant combination having been discussed only recently and, as yet, not many studies are available. So far most research has focussed on interactions between ozone and acidic deposition in the form of either rain or fog. Foliar leaching of essential nutrients such as magnesium, calcium, zinc, or copper, as well as nitrate and ammonium occurred in Picea abies when plants were fumigated consecutively with 200 or 600 ug m-3 0 3 and treated with acidic mist (pH 3.5) once a week (refs.30,39,85). For most cations, leaching was dependent on 03-dose, H*-ion concentration of fog solution, and was further enhanced by low nutrient content of soils or a reduction in plant vitality prior to exposure (ref.34). Although similar results were obtained in combined 0 3 fumigation and fogging experiments, foliar leaching was further modified by additional frost treatments (ref.86). Skeffington and Roberts (ref.871, however, using a different methodological approach, found only increased nitrate leaching in Pinus svlvestris, while leaching of cations was not enhanced by Oafacidic rain. Combined fumigation experiments with S O Z , 03, and acidic rain over two years in open top chambers, using Picea abies, Abies w, and F m svlvatica, revealed a marked increase in cation leaching when all three pollutants were supplied in concentrations approaching ambient levels (ref.88). Combinations of ozone and acidic rain, however, had no particular pronounced effect on leaching. There were marked effects on the photosynthesis of red oak, sugar maple, and white pine at various low concentrations of ozone close to the ambient, but no such effects occurred for acidic deposition, nor for the combination of the two (ref.89). However, there is given indication that leaching of cations and nitrate is enhanced
51
after ozone episodes, as shown by Fabig (ref.90) for an older Norway spruce stand. Waldman and Hoffmann (ref.91) also assume that cation leaching from pine trees in San Gabriel mountains in California is stimulated by earlier ozone episodes. It is clear that pollutant mixtures should be given high priority in future research because the conflicting results from mixture studies are so difficult to interpret. Although combined effects of pollutants can be synergistic, especially at low concentrations, the results from experiments using artificial pollutant combinations should be addressed with care (ref.70). It is absolutely essential, therefore, to produce more reliable information on mixtures, using exposure regimes which simulate the temporal and spatial variation of representative mean and peak concentrations which occur under ambient conditions.
CRITICAL OZONE LEVELS FOR PLANT PROTECTION Most of the sensitivity ranking was derived from short term exposure studies mostly with seedlings. Particularly for long living organisms like forst trees these results are questionable, if exposed chronically.
Furthermore,
judgement on visible injury can be of rather limited value for sensitivity ranking, when other indirect induced factors such as for example nutrient leaching determines actual injury, as pointed out earlier (ref .92) Thus these data should be adressed with caution for dose-effect relationships. This applies principally also for other parameters like yield and growth data gained under short term conditions of exposure. A further problem for the evaluation of proper ozone threshold values for plant protection is the very complicated ozone concentration time pattern, which is difficult to simulate in appropriate experiments. This is due to the pronounced diurnal variation in ozone concentration which varies furthermore with increasing distance from precursor sources as well as elevation. Contrary. to the other primary gaseous air pollutants, ozone does not vary that much in peak then in average concentration between industrialized and remote areas (refs.93,94). The probably best approach so far was made with the National Crop Loss Assessment Network (NCLAN) in the USA (ref.95). According to this study a mean seasonal ozone concentration of 56-72 can lead to growth reduction in sensitive agricultural crops. For protection of vegetation against longer lasting ozone episodes a threshhold value of 60 p g r 3 for a seasonal mean over 100 days was established by experts in a recent WXO-study WHO (ref .96). Ac-
cording to the Air Resource Board of California (ref. S O ) ,
this standard would
52
also be sufficient for sensitive pine forests. Under consideration of the NCLAN-results with very sensitive species and possible combinatory effects with other pollutants present at the same time or sequentionally, Guderian (ref.97) suggested at the most recent ECE Critical Levels Workshop in Bad Harzburg, FRG a standard of 50 pgm-3 as seasonal mean, derived from 7 hour daily average concentrations (9.00
-
17.00 hours). However, this value is
very low and may reach into the natural fluctuation of background concentration in future, when ambient ozone levels will increase further (refs.97,98).
REFERENCES 1 2 3
4
5
6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
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C.L. Rezabek, J.A. Morton, E.C. Mosher, A.J. Prey and J.E. Cummings, Regional Effects of Sulfur Dioxide and Ozone on Eastern White Pine (Pinus strobus L.) in Eastern Wisconsin. Wisconsin Dept. of Nat. Resources, Rep. 78255, 2/1986, 20 p. C.R. Berry and L.A. Ripperton, Phytopath., 53, 1963, 552-557. C.R. Berry and C.H. Hepting, For.Sci., 10, 1964, 2-13. S.F. Duchelle, J.M. Skelly, J.L. Sharick, B.I. Chevonne, Y.S. Yang and J.E. Nelleson, J.Environ.Manag., 17, 1983, 299-308. S.F. Duchelle, J.M. Skelly and B.I. Chevonne,. WASP, 18, 1982, 363373. M.R. Ashmore, in P. Grennfeld, (Ed.), The Evaluation and Assessment of the Effects of Photochemical Oxidants on Human Health, Agricultural Crops, Forestry, Materials and Visibility. Swedish Environ.Res.Inst., Coteborg, 1984, pp.92-104. M.R. Ashmore, N. Bell and J. Rutter, Ambio, 14, 1985, 81-87. B. Prinz, C.H.M. Krause and K.-H. Jung, Waldschaden-Theorie und Praxis auf der Suche nach Antworten, Oldenbourg Verlag Miinchen, 1985, pp. 143-194. F.T. Last and D. Fowler, Forstw.Cbl., 103, 1984, 24-28. R. Cuderian and D.T. Tingey, Notwendigkeit und Ableitung von Grenzwerten far Stickoxide. UBA-Berichte 1/87, Umweltbundesamt Berlin, 1987. 96, D.T. Tingey, W.W. Heck and R.A. Reinert., J.Amer.Soc.Hort.Sci., 1971, 369-371. A.S.Heagle, D.E. Body and C.E. Neely, Phytopathology 64, 1974, 132136. T. Elkiey and D.P. Ormrod, Atmos.Environ., 13, 1979, 1165-1168. J.J. Crosso, H.A. Menser, G.H. Hodges and H.H. McKinney, Phytopathol., 61, 1971, 945-950. W.J. Render and F.H.F.C. Spierings, Neth.J.Plant Pathol., 81, 1975, 149-151. R.D. Shertz, W.J. Render and R.C. Musselman, J.Amer.Soc.Hort. Sci., 105, 1980, 594-598. D.T. Tingey, R.A. Reinert, C. Wickliff and W.W. Heck, Can.J.Plant Sci., 53, 1973, 815-879. A.S. Heagle, W.W. Heck, J.O. Rawlings and R.B. Philbeck, Crop.Sci., 23, 1983, 1184-1191. D.T. Tingey and R.A. Reinert, Environ. Pollut., 9, 1975, 117-125. L.W. Kress, J.M. Skelly and K.H. Kinkelman, Environ.Mon.Ass., 1, 1982, 229-239. J. Mooi, Forst- und Holzwirt, 39, 1984, 438-444. R. Guderian, K. Kiippers and R. Six, VDI-Berichte 560, 1985, 657-701. L.W. Kress and K.H. Hinkelman, Agric. Environ., 7, 1982, 265-274. Y.S. Yang, J.M. Skelly, B.I. Chevonne, Aquilo Ser. Bot., 19, 1983, 406-418. F. Jilttner, Spezielle Berichte der Kernforschungsanlage Jiilich, 369, 1985, 313-316. Chr. Bosch, E. Pfannkuch, K.E. Rehfuess, K.H. Runkel, P. Schramel and M. Senser, Forstw. Cbl., 105, 1986, 218-242. R.A. Skeffington and T.M. Roberts, Oecologia, 65, 1985, 201-206. G. Seufert and U. Arndt, Allg. Forst Z., 41, 1986, 545-549. P.B. Reich and R.C. Amundson, Science, 230, 1985, 560-570. W. Fabig, Chr. Boose, U. Fritsche, B. Crundmann, D. Hochrainer H. Kldppel, F.-J. Mdnig and H. Oldiges, In: Umneltforschungsplan des Bundesministers des Inneren, Forschungsvorhaben: 106070446 /01. Fraunhofer-Institut far Umweltchemie, Schmallenberg-Crafschaft, 1987, 241 p. J.M. Waldman and M.R. Hoffmann, WASP, in preparation. B. Prinz, in I.S.A. Isaksen (Ed.), Tropospheric Ozone, Reidel Publ. Comp., Dodrecht, 1988, pp. 161-184.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
57
GLOBAL ELEMENTAL CYCLES AND OZONE
J . VAN HAM TNO Study and I n f o r m a t i o n Centre f o r Environmental Research, P.O. Box 186, 2600 AD D e l f t , The Netherlands
SUMMARY I n t h i s paper t h e way o u r atmosphere responds t o emissions f r o m t h e s u r f a c e i s e x p l o r e d f o r components o f t h e elemental c y c l e s o f c h l o r i n e , carbon and n i t r o g e n . M o d i f i c a t i o n o f t h e c y c l e s by man i s d e s c r i b e d and responses i n ozone budgets o f t h e s t r a t o s p h e r e and t h e f r e e t r o p o s p h e r e a r e discussed. P o s s i b l e i m p l i c a t i o n s o f t h e s t r o n g r e g i o n a l m o d i f i c a t i o n o f ozone l e v e l s i n t h e f r e e troposphere f o r p o l i c y a r e i n d i c a t e d .
INTRODUCTION T h i s paper i s n o t j u s t d e a l i n g w i t h n o v e l t i e s , "Ozone" was a l r e a d y known t o t h e Greeks and stands f o r odorous. And Greek philosophy, which i n c l u d e d science i n those days, i s known t o have brought f o r w a r d a k i n d o f atom t h e o r y which a l s o i m p l i e d t h e l a w o f mass c o n s e r v a t i o n . L u c r e t i u s , a Roman who l i v e d i n t h e f i r s t c e n t u r y B.C.
and who w r o t e s e v e r a l books ( r e f . 1) i n which he
e x p l a i n s t h e Greek p h i l o s o p h y t o h i s f r i e n d Memnius, acknowledges t h e f l u x e s between t h e e a r t h s u r f a c e and t h e a i r i n t h e upward as w e l l as t h e downward d i r e c t i o n . T h i s elemental c y c l i n g , though w i t h d i f f e r e n t elements, i s e x a c t l y t h e s u b j e c t o f my t a l k . I w i l l update t h i s c l a s s i c a l theme w i t h 20th c e n t u r y science i n t h e n e x t 25 minutes, though I may want t o make a few p h i l o s o p h i c a l remarks i n t h e Greek t r a d i t i o n as w e l l . We w i l l have a l o o k a t OZONE f i r s t and we w i l l s t a r t w i t h t h e good news: ozone i s a n a t u r a l component o f o u r atmospheric system and i s f o u n d t h e r e a t a l t i t u d e s between D and 90 km. I t i s formed and s p l i t c o n t i n u o u s l y under v a r i o u s photochemical regimes. Ozone t h r o u g h o u t our atmosphere, by i t s unique s p e c t r a l p r o p e r t i e s , complements t h e f i l t e r f o r t h e UV-part o f t h e s u n l i g h t . More f u n c t i o n s a r e w o r t h w h i l e o f mentioning. Ozone d r i v e s t h e s e l f c l e a n i n g
-
process i n t h e f r e e troposphere as t h e m a j o r source o f OH-radicals, v i a hu
O3
58
Also, ozone has s t r o n g b a c t e r i c i d a l p r o p e r t i e s and may b e i n s t r u m e n t a l i n t h e c o n t r o l o f epidemic diseases. It i s even b e l i e v e d t o have t h e r a p e u t i c a l v a l u e as w i t n e s s e d by a B e r l i n H o t e l : we a r e i n v i t e d t o improve o u r h e a l t h by exposing o u r s e l v e s d e l i b e r a t e l y t o an atmosphere c o n t a i n i n g some ozone. The c o n c e n t r a t i o n l e v e l may w e l l be d e c i s i v e i n r e c o n c i l i n g t h i s v i e w w i t h t h e s c i e n t i f i c d a t a base on t h e t o x i c i t y o f ozone. We can o n l y r e s p e c t N a t u r e f o r t h e i n g e n i o u s i d e a t o s t o r e t h e m a j o r p a r t of t h i s a i r t o x i c between 10 and 50 k i l o m e t e r up i n t h e s t r a t o s p h e r e . The n o t i o n t h a t t h i s and o t h e r o b s e r v a t i o n s do f i t w i t h i n a m a s t e r p l a n prompts me t o mention a modern v e r s i o n o f t h e c o m b i n a t i o n o f s c i e n c e and p h i l o s o p h y : Lovelocks Gaia-hypothesis ( r e f . 2). I t h o l d s t h a t l i f e i t s e l f has been c r e a t i n g t h e c o n d i t i o n s f o r l i f e on e a r t h and p r o v i d e s t h e c o n d i t i o n s f o r c o n t i n u i t y o f l i f e : t h e p r i n c i p l e o f homeostasis. I t w i l l be v i r t u a l l y i m p o s s i b l e t o p r o v e t h a t t h e Gaia-hypothesis i s c o r r e c t ; i t ' s u s e f u l n e s s as a w o r k i n g h y p o t h e s i s f o r l o o k i n g a t g l o b a l i s s u e s has been proven indeed, s i n c e i t i n s p i r e s many s c i e n t i s t s t o have a c l o s e r l o o k a t t h e mechanisms t h a t a r e o p e r a t i v e i n Gaia. Such a s t i m u l u s i s o f u t t e r importance now t h a t we have bad news on ozone as w e l l : we a r e c o n f r o n t e d w i t h a decrease o f ozone i n t h e s t r a t o s p h e r e and an i n c r e a s e o f ozone l e v e l s i n t h e f r e e troposphere. B o t h e f f e c t s a r e r e l a t i v e l y r e c e n t . They p r o b a b l y d a t e back f r o m a few decades ago and have been c o n f i r m e d by measurements i n t h e e i g h t i e s o n l y . The q u e s t i o n t h a t a r i s e s i s whether man i s p r e s e n t l y m o d i f y i n g l i f e on e a r t h t o such an e x t e n t t h a t t h e c o n t i n u i t y i s a t risk. ATMOSPHERIC SYSTEM G a i a ' s l a w o f c o n s e r v a t i o n o f mass r e q u i r e s an e f f i c i e n t system t o p r e v e n t any m a t e r i a l t o escape i n t o space. The c h a r a c t e r i s t i c l a y e r e d s t r u c t u r e o f o u r atmosphere i s w e l l known. 50 km stratopause
8-15 km
tropopause
1-2 km
NBL-Nocturnal Boundary Layer
surface
F i g . 1. G a i a ' s Mass C o n s e r v a t i o n system.
59 Emissions from the surface w i l l be trapped i n t h e boundary l a y e r s f i r s t and so on. The system i s c o n t r o l l e d by the sun: i t helps t o form t h e l a y e r s as they are and i t i s the d r i v i n g force i n most, i f not a l l , atmospheric chemical transformations which b r i n g the emitted components i n a form t h a t i s f i t f o r deposition. The layered structure, though not permanently there, functions as a powerful m u l t i t r a p f i l t e r . Mechanisms o f removal are:
-
by d i s s o l v i n g i n t o cloudwater and subsequent r a i n - o u t and by wash-out (wet
-
deposition) by deposition from the atmosphere on land, sea, vegetation o r other surfaces (dry deposition)
-
by (photo)chemical conversion, t o be followed by e i t h e r d r y o r wet deposition o f the r e s u l t i n g product(s).
The r a t e s o f these processes (rwet,r together determine the and rchem) dry f l u x from the atmosphere f o r an i n d i v i d u a l component: concentration x
(rwet rdry +
+
'them)
as w e l l as i t s residence time i n the atmosphere: T
1
=
rwet
+
‘dry
+
‘chem
Within the closed system o f our planet several c y c l i c processes are operational. The most obvious example i s the hydrological cycle: t h e continuous downward stream o f l i q u i d water towards sealevel i s balanced by an atmospheric inland vapor and cloud transport. For most elements s i m i l a r cycles e x i s t , though the f l u x e s from and towards the oceans may be f a r from balanced. I n the atmospheric compartment components w i t h short residence times are transported w i t h i n t h e planetary boundary l a y e r , and where necessary converted and deposited again. Components w ith long residence times are dispersed i n the f r e e troposphere f o r the major p a r t , i n order t o be converted i n t o depositable products. For a number o f compounds there i s no apparent removal from the troposphere (N20,CFC’s) and these a l l
w i l l reach the stratosphere. They have t o be converted i n t h e stratosphere and are removed a f t e r r e t u r n o f t h e i r products i n t h e troposphere. When the f l u x e s i n t o and from the atmosphere are equal the averaged concentration o f a component remains constant; f l u c t u a t i o n s may occur, however.
GO CHANGES I N THE TROPOSPHERE I n Table 1 c h a r a c t e r i s t i c v a l u e s f o r a number o f components i n t h e f r e e troposphere have been c o l l e c t e d . Measurements d u r i n g r e c e n t y e a r s have r e v e a l e d an i n c r e a s e o f v i r t u a l l y a l l these components. For those w i t h s h o r t r e s i d e n c e times, such t r e n d s have n o t been e s t a b l i s h e d , b u t s h o u l d be expected on t h e b a s i s o f i n c r e a s e d emissions. By t h i s change i n t r o p o s p h e r i c c o m p o s i t i o n o u r atmospheric system i s
s i g n a l l i n g an apparent unbalance: we a r e l e a v i n g b e h i n d an e r a w h e r e i n o u r atmosphere t h r o u g h s e l f c l e a n i n g processes m a i n t a i n e d a c o n s t a n t c o m p o s i t i o n and we do t h i s a t a speed which, i n g e o l o g i c a l sense, i s i n c r e d i b l y f a s t . It i s s a i d by some t h a t t h e s e l f c l e a n i n g c a p a c i t y o f t h e t r o p o s p h e r e i s a f f e c t e d . I t [ABLE 1.
C o n c e n t r a t i o n s o f t r a c e gases i n t h e f r e e t r o p o s p h e r e and e s t a b l i s h e d changes i n t h e l a s t decades. I f n o t s t a t e d o t h e r w i s e t h e f i g u r e s i n column 2 a r e f r o m r e f . 3 and i n columns 3 and 4 f r o m r e f . 4.
Component
Concentr a t ions around 1965
Concentrations i n 1985
Present per year
conc. r i s e
61
i s unclear whether t h i s i s true. The increased production o f ozone, the precursor o r OH, which i s the cleaning agent f o r the troposphere i s t h e adequate response; our conclusion should be t h a t the self-cleaning capacity has i n creased. On the other hand, i t i s apparent t h a t the response i s n o t strong enough, since trace gas concentrations continue t o increase. Trace gases i n the troposphere i n p r i n c i p l e are i n competition f o r r e a c t i o n w i t h OH. When the concentration o f trace component A increases because o f increased emissions, the r a t e o f removal f o r trace component B may decrease. As a consequence the concentration o f B w i l l a l s o r i s e . D i f f e r e n t i a t i o n between these two causes f o r accumulation o f trace gases w i l l be d i f f i c u l t because o f the u n c e r t a i n t i e s i n the emission rates. We w i l l now have a look a t a selected number o f elemental cycles. I w i l l be short w i t h respect t o the implications f o r stratospheric ozone and r e f e r t o chlorine only here. I w i l l comment a b i t more on the s i t u a t i o n w i t h ozone i n the f r e e troposphere. STRATOSPHERIC MOD I F I C A T l ON
Chlorine c y c l e There i s no doubt any longer t h a t stratospheric ozone d e p l e t i o n i s caused by the emission o f a number o f ha,locarbon compounds, notably CFC-11 and 12, CC14 and CH3CC13, which accumulate i n t h e troposphere and leak from there i n t o the stratosphere ( r e f . 4).
"1
0natural man-made
p p t , ~in~ troposphere
1000
0
CHsCI
Fig. 2. Burden o f long l i f e c h l o r i n e i n the troposphere. I f we look a t f i g u r e 2 we see t h a t the burden o f c h l o r i n e i n t h e troposphere t h a t i s non-reactive and i s not depositable i s p r e s e n t l y f o r 80% manmade. I n other words man has i n t e n s i f i e d a global elemental c y c l e by a f a c t o r 4
and i s now confronted w i t h a massive and serious response. The o t h e r components t h a t i n t e r a c t w i t h stratospheric ozone, V o l a t i l e Organic Components (VOC), mainly methane) and N20 are responsible f o r an i n t e n s i f i c a t i o n o f the stratospheric hydrogen, resp. n i t r o g e n c y c l e by f a c t o r s
62 o f approximately 2.5 and 1.75. We may hope t h a t UNEP's Convention f o r the Ozone Layer w i l l be i n time and e f f e c t i v e i n order t o prevent ecological disasters.
TROPOSPHERIC OZONE I n urban as w e l l as i n r u r a l areas we are s t i l l confronted w i t h elevated ozone concentrations. Urban ozone receives serious a t t e n t i o n since the f i f t i e s .
A s a t i s f a c t o r y s o l u t i o n has not been achieved, despite enormous e f f o r t s t h a t have been undertaken i n the United States and i n Japan and which are now underway i n Western Europe and A u s t r a l i a . We have seen t h a t i n t h e seventies the scale o f the photochemical smog problem s h i f t e d from urban i n t o r u r a l : elevated ozone concentrations were observed i n areas w i t h minimal anthopogenic emissions ( r e f . 11). The r o l e o f transport was demonstrated i n numerous back-trajectory f i e l d studies; also, modellers showed t h a t , during representative episodes, ozoneconcentrations over areas as wide as 50Ox500km2 are hardly influenced by emission reductions w i t h i n t h i s area ( r e f . 12). During the e i g h t i e s the l a r g e scale o f t h e phenomenon became more apparent from t r e n d measurements o f ozone i n the middle and higher troposphere: H Ikml12-
10-
06-
4-
2-
Fig. 3. Trends i n f r e e tropospheric ozone a t the Hohenpeissenberg, Federal Republic o f Germany ( r e f . 9). Measurements by the "Umkehr technique" a t t h e Hohenpeissenberg Observatory ( r e f . 9) i n West-Germany revealed t h a t the concentration o f ozone i n the f r e e troposphere has been increasing during the l a s t decennia. A t m i d - l a t i t u d e s i n the Northern Hemi sphere ozone concentrations above the planetary boundary 1ayer
63 tend t o annual averages o f 40 ppb and can be observed i n remote unpolluted areas as w e l l . Van A a l s t ( r e f . 10) observed concentration l e v e l s o f t h a t order i n the absence o f l o c a l ozone production i n The Netherlands a t a coastal monitoring s i t e . He concluded t o a net production o f ozone i n the f r e e troposphere as had been suggested e a r l i e r by Crutzen ( r e f . 13) and Logan ( r e f .
14). Ozone measurements i n Paris during the 19th century, which were r e d i s covered recently, reveal a background value o f 10 ppb a t t h a t t i m e ( r e f . 15).
2
8 1
1
b
5
8
7
I
0 1 I 1 1 1 2
MONRT
Fig. 4. Ozone concentration as measured i n Paris i n t h e lgth century (ref. 15). Though comparisons are d i f f i c u l t t o make we may f i n d some arguments f o r the statement t h a t the m o d i f i c a t i o n o f t h e tropospheric ozone budget i s a problem o f s i m i l a r size as t h a t o f the ozone layer. While the dreaded e f f e c t s o f increased UV-B r a d i a t i o n have n o t y e t materialized, the continents o f Europe and North America already s u f f e r from f o r e s t dieback, which i s , a t l e a s t p a r t l y , caused by ozone, notably i n mountainous areas. I n f l a t areas we have reason f o r concern as well. S t a r t i n g from average background l e v e l s o f 40 ppb and higher values on s p e c i f i c days, a small margin f o r production o f ozone i n the PBL i s l e f t , before no-effect l e v e l s w i l l be exceeded. I n f a c t , i n combination w i t h other p o l l u t a n t s , ozone concentrations o f 30 ppb already produce s p e c i f i c e f f e c t s w i t h s e n s i t i v e vegetation ( r e f . 16).
Also, we may f i n d t h a t i t w i l l be even more d i f f i c u l t t o c o n t r o l the ozone budget o f the f r e e troposphere, than t o r e s t o r e the stratospheric ozone layer. Ozone formation i n t h e f r e e troposphere i s i n i t i a t e d by the p h o t o l y s i s o f ozone i t s e l f :
03
hv +
01D t H20
0 2 + O 1D
-
20H'
64
-
f o l l o w e d by:
O2
OH' + CH4
CH300' + H20
02
OH' + CO
HOO'
-+
+ C02
I f t h e peroxy r a d i c a l s r e a c t w i t h NO t h e y produce NO2, t h e d i r e c t p r e c u r -
s o r o f ozone i n d a y l i g h t : H02/CH300' + NO
+HO'/CH30'
+ NO2
(4)
f o l l o w e d by r e a c t i o n ( 3 ) o r t h e b r a n c h i n g r e a c t i o n ( 5 ) : CH30' + O2
d
CH20 + H02'
(5)
The a c t u a l ozone f o r m a t i o n t a k e s p l a c e t h r o u g h t h e sequence:
NO^
hv,
3
0P+O2
NO + O ~ P
(6)
O3
(7)
M
A t low l e v e l s o f n i t r o g e n o x i d e s a t e r m i n a t i o n between two peroxy r a d i c a l s i s more probable, f.i.: CH300'
+
HOO'
+ CH300H +
O2
(8)
-
o r a t t a c k on ozone i t s e l f :
HOO' t O3
OH t 202
(9)
T h i s s e t o f r e a c t i o n s , though f a r f r o m complete, i l l u s t r a t e s t h e v i t a l r o l e o f NOx i n t r o p o s p h e r i c ozone f o r m a t i o n ( r e f . 17). M o d e l l i n g s t u d i e s by Crutzen ( r e f . 13) showed t h a t a c o n c e n t r a t i o n o f 5-10 p p t NOx t h r o u g h o u t t h e troposphere i s s u f f i c i e n t f o r b a l a n c i n g ozone f o r m a t i o n and d e s t r u c t i o n a t a l e v e l o f 20-40 ppb, g i v e n t h e p r e v a i l i n g l e v e l s o f methane and CO i n t h e remote atmosphere. However, t h e NOx-concentration i n t h e c o n t i n e n t a l t r o p o s p h e r e i s o f t e n w e l l above 100 p p t a t m i d - l a t i t u d e s ( r e f . 18) and i s accompanied b y p e r o x y a c e t y l n i t r a t e (PAN) l e v e l s o f 30-50 p p t . ( r e f . 7 ) .
The s i g n i f i c a n c e o f
PAN i s t h a t i t a c t s as a r e s e r v o i r f o r NO2 upon d e s t r u c t i o n by OH o r s u n l i g h t i n t h e upper troposphere and so c o n t r i b u t e s t o ozone p r o d u c t i o n . As soon as t h e NO,-concentration
exceeds t h e "break even" c o n c e n t r a t i o n of
5-10 p p t , any i n c r e a s e i n CH4- o r CO-levels w i l l a c c e l e r a t e r e a c t i o n ( 4 ) and promote t h e f o r m a t i o n o f ozone as w e l l .
65 Nitrogen c y c l e The n i t r o g e n c y c l e i s represented i n f i g u r e 5.
0natural
a man-made
Fig. 5. The c y c l e o f n i t r o g e n i n t h e g l o b a l atmosphere. F i g u r e s f o r NO a r e from r e f s . 17-19; f o r N 0 f r o m r e f s . 20 and 21; f o r NH f r o m r g f s . 17, 18, 20, 22 and 23. The atmosphehc burden o f these components 9 s : NO : 0.4 TgN; N 0: 1300 TgN; NH3: 0.4 TgN. An atmospheric accumulation o f 5 TgN asXN20 has b6en estimated.
Both, ammonia and n i t r o u s o x i d e c o n t r i b u t e t o t h e NOx-burden t h r o u g h conversion processes. Ammonia i s a l s o i n s t r u m e n t a l i n promoting t h e s o l u t i o n o f NO;
i n cloudwater and t h e f o r m a t i o n o f a e r o s o l s . The shaded area r e p r e s e n t s t h e
anthropogenic c o n t r i b u t i o n . Source s t r e n g t h s a r e g i v e n i n f i g u r e 6. It f o l l o w s from t h i s consensus diagram t h a t g l o b a l anthropogenic emissions
a r e one and a h a l f t o two t i m e s as h i g h as t h e n a t u r a l emissions, though t h e inaccuracy o f t h e i n d i v i d u a l e s t i m a t e s s t i l l a l l o w s a w i d e r range. On a r e g i o n a l s c a l e t h e r a t i o between anthropogenic and n a t u r a l NO,-emission
can be
q u i t e d i f f e r e n t , however. The source s t r e n g t h f o r a n t h r o p o g e n i c NOx i s h i g h e s t a t m i d - l a t i t u d e s o f t h e n o r t h e r n hemisphere. W i t h r e s p e c t t o i t s r o l e i n t h e f r e e troposphere i t i s o f i n t e r e s t t o know t h e f r a c t i o n o f t h e NOx-emissions t h a t may escape f r o m t h e boundary l a y e r . T h i s appears t o be a m a t t e r of considerable uncertainty.
66
50
r
20
10
0natural man-made Tg Ny-l
from NH3 lightning soil
Rn
tratosphere oceans
F i g . 6. Breakdown o f NOx-emissions i n t o m a j o r g l o b a l sources. Carbon c y c l e I n t h e carbon c y c l e , emissions, a p a r t f r o m C02, a r e grouped b y mass and r e a c t i v i t y i n t h r e e m a j o r c l a s s e s : CH4, CO and non-methane hydrocarbons (NMHC) (see f i g u r e 7 ) .
F i g . 7. The c y c l e o f carbon i n t h e g l o b a l atmosphere. F i g u r e s f o r CO a r e d e r i v e d f r o m r e f s . 17, 18 and 24-26; f o r CH f r o m r e f s . 27-35; f o r NMHC f r o m r e f s . 36-40. The atmosphpric burden o f these c8mponents i s : CO: 200 TgC, p r e s e n t accumulation 10 TgCy- ; CH : 2680 TgC, p r e s e n t a c c u m u l a t i o n 45 TgC; NMHC: 8 TgC, p r e s e n t accumulation 8.1 TgC.
Of these, CH4 and CO escape f o r a m a j o r p a r t f r o m t h e PBL, due t o t h e i r low ‘ r e a c t i v i t y ; f o r NMHC, o r V o l a t i l e Organic Components (VOC) a more d e t a i l e d
67 s i t u a t i o n can be sketched. Natural emissions c o n s i s t f o r the major p a r t o f
0natural 2000 r
man-made
1500 1000 -
500 -
0-
Fig. 8. Breakdown o f emissions i n the g l o b a l carbon c y c l e which a r e r e l e v a n t f o r t h e ozone-budget. isoprene and terpenes. These compounds a r e very r e a c t i v e and w i l l be trapped w i t h i n the PEL f o r the major p a r t . A f r a c t i o n may be converted i n t o CO, however. Oceans a r e sources o f C2-C4-alkanes and alkenes. O f these a considerable p o r t i o n may escape from the PBL. Anthropogenic VOC-emissions may have a range o f r e a c t i v i t i e s ; on t h e average, r e a c t i v i t y i s lower than f o r t h e mix o f n a t u r a l emissions. Estimates o f t h e emission f l u x e s on t h e g l o b a l s c a l e ( f i g u r e 8 ) show a dominating anthropogenic c o n t r i b u t i o n i n CO-emission. F o r t h e VOC-emission nature dominates man, w h i l e CH4 shows approximately equal shares o f man and nature. On a r e g i o n a l scale t h e p r o p o r t i o n s a r e again q u i t e d i f f e r e n t as i s shown f o r VOC-emissions i n Table 2. The reason i s t h a t t h e major source o f n a t u r a l hydrocarbon emissions are t r o p i c a l f o r e s t s w h i l e anthropogenic a c t i v i t i e s a r e concentrated a t t h e m i d - l a t i t u d e s o f t h e n o r t h e r n hemisphere. The d i s t r i b u t i o n p a t t e r n resembles t h a t o f NOx-emissions. VOC/NO_ r a t i o s n
,
I n numerous s t u d i e s o f photochemical a i r p o l l u t i o n i n t h e f i e l d , t h e
l a b o r a t o r y and i n s i m u l a t i o n models much a t t e n t i o n has ever been p a i d t o t h e e f f e c t o f t h e VOC/NOx r a t i o on t h e ozone f o r m a t i o n i n c o n j u n c t i o n w i t h s t u d i e s on VOC-reactivity. The body o f c o l l e c t e d i n f o r m a t i o n was a p p l i e d i n t h e development o f c o n t r o l s t r a t e g i e s , which i n t h e United States l a i d t h e emphasis on r e d u c t i o n o f VOC as w e l l as s u b s t i t u t i o n o f r e a c t i v e VOC by l e s s r e a c t i v e ; t h i s s t r a t e g y has been adopted by o t h e r c o u n t r i e s as w e l l . T h i s strategy, super-
GO imposed on autonomic developments has r e s u l t e d i n e x t r e m e l y l o w VOC/NOx emission r a t i o s , when compared w i t h emissions i n t h e n a t u r a l environment. (Tabel 2 ) . So f a r , i t has n o t been s e r i o u s l y e v a l u a t e d on i t s consequences f o r t h e f r e e t r o p o s p h e r e and f o r background areas. TABLE 2 . VOC and NOx-emissions, g l o b a l and r e g i o n a l and t h e i r r a t i o . Total VOC-1 (TgCy ) World ( t o t a l ) World ( n a t u r a l emissions o n l y i The Nether nds PHOXA-area OECD-Europeb) a) b) c)
930 880 0.435 9.2 10
% Natural of t o t a l VOC
T o t a l NOx
94% 100%
60aJ 20a)
8% 18% 50%
0.15 3.8 3.95
( T g NY-')
vocc) -
Ref.
NOX
16 44
2.9 2.42 2.53
41,42 43 42,44
I n c l u d e s atmospheric p r o d u c t i o n f r o m NH3 Base-year 1980 i n TgC/TgN; these r a t i o s a r e averages and may d i f f e r a p p r e c i a b l y f o r d i f f e r e n t a reas.
We have i n d i c a t i o n s f r o m t h e sparse measurements o f NOx and NOx-compounds i n t h e c o n t i n e n t a l f r e e troposphere t h a t t h e l e v e l s a r e i n t h e o r d e r o f t e n t i m e s p r e - i n d u s t r i a l c o n c e n t r a t i o n s . Though t h e e m i s s i o n growth as w e l l as t h e i n c r e a s e i n in s i t u emissions ( a i r c r a f t , h i g h s t a c k s ) may e x p l a i n t h i s t o a m a j o r e x t e n t , we should c o n s i d e r an a d d i t i o n a l reason: i t m i g h t be t h a t t h e f i r s t t r a p o f o u r atmospheric mass conservancy system, t h e boundary l a y e r , i s n o t f u n c t i o n i n g as good as i t used t o do. L e t us compare t h e urban plume w i t h a n atmosphere above and downwind a f o r e s t canopy. I n t h e u n d i s t u r b e d f o r e s t s i t u a t i o n , n i t r i c o x i d e e m i s s i o n f r o m t h e s o i I and hydrocarbon emissions f r o m t r e e s show a s i m i l a r temperature dependence. Terpenes a r e v e r y r e a c t i v e and quench h y d r o x y l r a d i c a l s as w e l l as any ozone formed p r o d u c i n g a b l u e haze, which i s a b l e t o scavenge subseq u e n t l y r e s i d u a l atmospheric NO,
and HN03 b y heterogeneous processes. Tempera-
t u r e f a l l a t t h e end o f a day induces p a r t i c l e g r o w t h by c o n d e n s a t i o n and uptake o f watervapour and enhances d e p o s i t i o n . I n t h e urban plume on a t y p i c a l photochemical-smogday most o f t h e NO,
will
be c o n v e r t e d i n t o n i t r a t e s a t t h e end o f t h e day, d e s p i t e o f t h e l o w VOC/NO,r a t i o . A p a r t f r o m p e r o x y a c y l n i t r a t e s , t h e y w i l l d i s s o l v e i n c l o u d w a t e r and w i l l be d e p o s i t e d subsequently. Anthropogenic NOx- and VOC-emissions show a s l i g h t l y o p p o s i t e temperature dependence. On a w i n t e r d a y o r even an "average" day, NOx-conversion may be i n c o m p l e t e a t t h e end o f a day; t h i s r e s u l t s i n a h i g h e r p r o b a b i l i t y o f escape i n t o t h e f r e e troposphere.
I am a f r a i d we cannot escape f r o m a s k i n g o u r s e l v e s a p h i l o s o p h i c a l q u e s t i o n now: does i t make sense t o work o u t c o n t r o l s t r a t e g i e s which r e s u l t i n atmospheric m i x t u r e s so d i f f e r e n t f r o m t h e mix i n t h e u n d i s t u r b e d f o r e s t e d area? I n o t h e r words: c o u l d we b e a t Nature? Has i t been r i g h t t o l a y t h e p r i o r i t y w i t h t h e r e d u c t i o n o f VOC-emissions and t h e i r r e a c t i v i t y ?
I w i l l n o t p r o v i d e t h e answers t o t h e s e q u e s t i o n s . Our p r e s e n t knowledge o f t h e troposphere w i l l be p r o b a b l y i n s u f f i c i e n t t o p r o v e o r r e j e c t d e f i n i t e l y any theory. I o n l y hope t h a t we w i l l s c r u t i n i z e o u r p r e s e n t s t r a t e g i e s and t a k e o u r r e s p o n s i b i l i t i e s . We c e r t a i n l y s h o u l d n o t l o s e o u r time, s i n c e mankind w i l l c o n t i n u e t o b r i n g about i m p o r t a n t changes i n o u r atmosphere i n t h e n e a r f u t u r e . FUTURE TRENDS I t i s c o n c e i v a b l e t h a t t h e r a t i o o f VOC t o NOx emissions w i l l d r o p f u r t h e r
i n t h e f u t u r e . The f o l l o w i n g t r e n d s a r e t o be expected o r r e c o g n i z a b l e :
-
F o r e s t dieback F o r e s t v i t a l i t y has dropped t o 50% and even l o w e r values i n a m a j o r p a r t of Europe ( r e f . 45). T h i s w i l l undoubtedly r e s u l t i n a r e d u c t i o n o f i s o p r e n e and terpene emission.
-
Deforestation T r o p i c a l r a i n f o r e s t s , which i n 1980 f i l l e d an a r e a o f 2970x10
6 ha, a r e
d i s a p p e a r i n g a t a r a t e o f 0.6% p e r annum ( r e f , 46). The e f f e c t o f t h i s change f o r t h e ozone budget i n t h e N o r t h e r n Hemisphere has n o t been assessed i n d e t a i l . I t seems c l e a r , however, t h a t t h e area where e f f i c i e n t scavenging o f ozone and NOx by i s o p r e n e and terpenes t a k e s p l a c e w i l l be 'developed"
i n t o r e g i o n s w i t h a n e t c o n t r i b u t i o n t o atmospheric ozone
production.
-
Coastal system We have i n d i c a t i o n s t h a t e u t r o p h i c a t i o n i n c o a s t a l seas has r e p e r c u s s i o n s f o r t h e source s t r e n g t h o f marine emissions. Each y e a r i n May and June N o r t h Sea beaches f r o m t h e Channel up t o Scandinavia a r e covered w i t h a foamy mass, caused b y a bloom o f t h e a l g a Phaeocystis bouchetii ( r e f . 47), which i s known as a d i m e t h y l s u l f i d e e m i t t e r . T o t a l emissions f o r t h e N o r t h Sea r e g i o n have been e s t i m a t e d t o amount t o 60.000 t o n s / y (CH3)$ which i s e q u i v a l e n t t o 20% o f t h e t o t a l S02-emissions i n The Netherlands! Veldhuis ( r e f . 48) o b t a i n e d s t r o n g i n d i c a t i o n s t h a t t h i s bloom i s connected w i t h e u t r o p h i c a t i o n o f t h e N o r t h Sea b y phosphorus. I r e f e r t o t h i s o b s e r v a t i o n because i t m i g h t be t h a t t h e i n t e n s i f i c a t i o n o f t h e P-cycle t r i g g e r s responses i n o t h e r elemental c y c l e s as w e l l . Obvious areas f o r f u r t h e r r e s e a r c h i n r e l a t i o n t o t r o p o s p h e r i c ozone a r e
t h e marine e m i s s i o n o f t h e l o w e r hydrocarbons. With r e s p e c t t o s t r a t o s p h e r i c ozone marine p r o d u c t i o n o f halomethanes, such as CH3C1 and CH3Br, s h o u l d be
70
watched
.
Methane emission from r i c e p a d i ' s which i s supposed t o be t h e major anthropogenic cause f o r t h e r i s e i n CH4-concentrations i s c o n t r o l l e d by t h e n u t r i e n t s t a t u s i n the padi. An assessment o f f e r t i l i z i n g p r a c t i c e s i n r e l a t i o n t o methane emission could be u s e f u l . CONCLUSIONS 1.
Man i s i n t e n s i f y i n g elemental cycles o f c h l o r i n e , carbon and n i t r o g e n by
f a c t o r s between 2 and 5 on a g l o b a l s c a l e and up t o a f a c t o r 10 on a continent a l scale (see Table 3 ) . The response i s a change i n t h e ozone budgets o f t h e stratosphere and t h e f r e e troposphere, which, on a c o n t i n e n t a l scale, i s s t r o n g i n b o t h l a y e r s : t h e A n t a r c t i c Ozone Hole corresponds t o an ozone drop by a f a c t o r 2-3 d u r i n g t h e s p r i n g season; i n t h e f r e e troposphere an increase by a f a c t o r 2-3 i s observed a t m i d - l a t i t u d e s over Europe and N o r t h America. 2.
Large-scale e f f e c t s i n t h e biosphere, a n t i c i p a t e d as a consequence o f
s t r a t o s p h e r i c m o d i f i c a t i o n , have caused a worldwide p o l i t i c a l a c t i o n i n o r d e r t o s t o p the t h r e a t . Large-scale e f f e c t s o f t r o p o s p h e r i c ozone increase, a1 ready v i s i b l e i n o u r f o r e s t s , deserve a s i m i l a r a c t i o n . TABLE 3. Factors o f int e n s if ic a t ion o f e 1eme nt a 1 cyc 1es
G1 oba 1 Chlorine ( w i t h -spheric residence t i m e ) Carbon
co CH4
co,
Continental (Europe o r N o r t h America)
4
irrelevant
a
20+ 1 - 2
2 - 3 1.2 2 - 3 1.5-2
3.
.
5 -10 1.5-2
NOx-emissions a r e h e l d p r i m a r i l y r e s p o n s i b l e f o r increase o f t r o p o s p h e r i c
ozone. Increases i n anthropogenic source s t r e n g h t s as w e l l as a reduced t r a p p i n g e f f i c i e n c y o f t h e p l a n e t a r y boundary l a y e r b o t h c o n t r i b u t e t o a h i g h e r NOx-burden i n t h e f r e e troposphere. Increases i n CH4- and CO-emission enhance t h e f r e e t r o p o s p h e r i c ozone production. 4.
Knowledge on ozone budgets and d e t a i l e d i n s i g h t i n t h e i n t e r a c t i o n o f
g l o b a l elemental c y c l e s has a b e a r i n g on t h e f e a s i b i l i t y o f m a i n t a i n i n g an a i r q u a l i t y standard f o r ozone and should be i n c o r p o r a t e d i n ozone c o n t r o l strategies.
71 ACKNOWLEDGMENT The a u t h o r would l i k e t o thank t h e C o u n c i l f o r Environment and N a t u r e Research i n The Netherlands which enabled him t o make an e x p l o r a t o r y s t u d y o f g l o b a l atmospheric issues. S t i m u l a t i n g c o n t r i b u t i o n s o f B e t t y G e r r i t s e n , P e t e r Heederik and D i c k van d e r Gugten who e x p l o r e d g l o b a l elemental c y c l e s w i t h him a r e g r a t e f u l l y acknowledged. Drs. R. G u i c h e r i t and M. Roemer gave v a l u a b l e comments on t h e manuscript. References
1 2
3 4 5
L u c r e t i u s , The Nature o f t h e Universe. A new t r a n s l a t i o n by R.E. Latham. P i n g u i n Books, 1951. J.E. Lovelock, Gaia, A new l o o k a t l i f e on Earth. O x f o r d U n i v e r s i t y Press, Oxford 1979. B.D. Tebbens i n : A i r P o l l u t i o n (A.C. S t e r n , Ed.), Vol.1, 27, Academic Press, 2d E d i t i o n (1968). W.M.O., Atmospheric ozone 1985. Global ozone r e s e a r c h and m o n i t o r i n g p r o j e c t , r e p o r t no. 16. V. Ramanathan, R.J. Cicerone, H.B. Singh, J.T. K i e h l , J. Geophys. Res. 90,
D3, 5547-66 (1985). 6 7a b
8 9
10
11 12 13 14
R.F. Weiss, J. Geophys. Res. 86, 7185-95 (1981). H.B. Singh, L.J. Salas, W. V i E e e , N a t u r e 321, 588-91 (1986). H.B. Singh, Env. Sci.Techn. 21, 320 (1987). R. B o j kov. These ProceedingsR. Hartmannsgruber, W. Altsmannspacher, H. Claude, i n C.S. Zerefos, A. Ghazi ( E d i t o r s ) , Atmospheric Ozone, Reidel, Dordrecht, 1984, pp 770-774. R..M. van A a l s t , i n R. G u i c h e r i t , J. van Ham and A.C.Posthumus ( E d i t o r s ) , Ozon: f y s i s c h e en chemische veranderingen i n de atmosfeer en de gevolgen, Kluwer, Deventer, 1987, p p 84-91. W. Warmbt, Z e i t s c h r i f t fiur M e t e o r o l o g i e 29 (l), 24 (1979). P.J.H. B u i l t j e s , K.D. van den Hout, S.D. Reynolds, i n C. de Wispelaere ( E d i t o r ) , A i r P o l l u t i o n Modeling and i t s A p p l i c a t i o n 111, Plenum Press, New York, 1984, pp. 507-523. P.J. Crutzen, i n 8. B o l i n and R.B. Cook, ( E d i t o r s ) , The m a j o r biogeochemical c y c l e s and t h e i r i n t e r a c t i o n s , SCOPE 21, Wiley, C h i c h e s t e r (1983), pp 67-103. J.A. Logan, M.J. P r a t h e r , S.C. Wofsy, M.B. McElroy, J.Geophys.Res. @
(C 8), 7210-54, 1981. 15 A. Volz, H.G.J. S m i t . D. Kley. Ber. von d e r Tagung d e r Arbeitsgerneinschaft d e r Grossforschungsanlagen (AGF), Dec. 1985, Bonn, pp. 5-13. 16 A.E.G. T o n n e i j c k , i n R. G u i c h e r i t , J. van Ham, A.C. Posthumus ( E d i t o r s ) , 17 18
19 20
Ozon: f y s i s c h e en chemische veranderingen i n de atmosfeer en hun gevolgen, Proc. Symp. Ede 1986, Kluwer, Deventer, 1987, pp. 60-65. P.J. Crutzen. i n R.Guicherit, J. van Ham, A.C. Posthumus, ( E d i t o r s ) , Ozon: f y s i s c h e en chemische veranderingen i n de atmosfeer en hun gevolgen. Proc. Symp. Ede 1986, Kluwer, Deventer, 1987, pp. 11-17. J.A. Logan, J. Geophys.Res. 88 ( C 15), 10.785-10.807, 1983. P.J. Crutzen and L.T. G i d e 1 , J . Geophys.Res. (C ll), 6641-6661, 1983. I . E . G a l b a l l y , i n : The biogeochemical c y c l i n g o f s u l f u r and n i t r o g e n i n t h e remote atmosphere (Galloway e t a l , e d i t o r s ) , NATO AS1 S e r i e s 159,
a
1985. 21 M. K e l l e r , J. Geophys.Res. 91 (D ll), 11.791-11.802, 1986. 22 E. Buijsman, H.F.M. Maas, W2.H. Asman, Atm.Environ. 21(5), 1009. 1987. 23 R. Soderlund, B.H. Svensson, i n : B.H. Svensson and R.-%derlund ( E d i t o r s ) , N i t r o g e n , Phosphorus and S u l f u r B u l l . , 1976.
-
Global c y c l e s , SCOPE Report 7, Ecol.
72
24 A. Marenco, J.C. Delaunay, J. Geophys. Res. 85, 5599-5613, 1980. 25 R. Conrad, W. S e i l e r , Geophys.Res. L e t t . 2 (E),1353-6, 1982. 26 P.R. Zimnerman, R.B. Chatfield, J. Fishman, P.J. Crutzen, P.L. Hanst, Geophys-Res. L e t t . 5 (8), 679-82, 1978. 27 W. S e i l e r , i n : M.J. Klug, C.A. Reddy ( E d i t o r s ) , Current perspectives i n microbial ecology, Amer.Soc. f o r Microbiology, Washington D.C., 1984, pp. 468-77. 28 D.R. Blake, V.H. Woo, S.C. Tyler, F.S. Rowland, Geophys.Res. L e t t . 11, 1211-14, 1984. 29 A. Holzapfel-Pschorn, W. S e i l e r , I n t . J. Biometeorol. 28 (suppl. dated 1984), 53-61, 1985. 30 J.C. Sheppard, H. Westberg, J.F. Hopper, K. Ganesan, P. Zimerman, J. Geophysics.Res. 87, 1305-12, 1982. 31 D.H. Ehhalt, Naturwissensch. 66, 307-11, 1979. 32 P.R. Zimnerman, J.P. Greenberg, S.O. Wandiga, P.J. Crutzen, Science 218, 563-5, 1982. 33 R.A. Rasmussen, M.A.K. K h a l i l , Nature 301, 700-703, 1983. 34 P.J. Fraser, R.A. Rasmussen, J.W. C r e f s l d , J.R. French, M.A.K. K h a l i l , J.Atm.Chem. 4, 295-310, 1986. 35 M.A.C. KhaliT, R.A. Rasmussen, J. Geophys.Res. & (C 9), 5131-44, 1983. 36 R.A. Duce, V.A. Mohnen, P.R. Zimmerman, D. Grosjean, W. Cautreels, 37 38 39 40 41 42 43
R. Chatfield, R. Jaenicke, J.A. Ogren, E.D. P e l l i z z a r i , G.T. Wallace, Rev. o f Geophys. and Space Phys. 21, 921-52, 1983. D.R. Blake, F.S. Rowland, Nature 321, 231-3, 1986. S.A. Penkett, i n E.G. Goldberg ( E d i t o r ) , Atmospheric Chemistry, Dahlem Konferenzen 1982, Springer, B e r l i n . S. Sawada, T. Totsuka, Atm. Environ. 20, 821-32, 1986. P.R. Zimmerman, R.B. C h a t f i e l d , J. Fixman, P.J. Crutzen, P.L. Hanst, Geophys.Res. L e t t . 5, 679-82, 1978. P.J.H. B u i l t j e s , Basisdocumenten koolwaterstoffen I V , Rapport TNO-CMP 85/04, J u l y 1985. OECD Environmental Data: Compendium 1987. I S B N 92-64-02960-5. C. Veldt e t a l , Emission Data Base. PHOXA-report I, D r a f t r e p o r t
1979. 44 Concawe. Report no. 2/86. The Hague, May 1986. 45 V D I , S c h r i f t e n r e i h e der VDI-Komnission Reinhaltung der L u f t Bd 1, 1985. 46 United Nations Environment Programme, The disappearing forests. UNEP Environment B r i e f No. 3, 1987. 47 C. Lancelot, G. B i l l e n , A. Sournia, T. Weisse, F. C o l i j n , M.J.W. Veldhuis, A. Davies, P. Wassman, Ambio 16, 38-46, 1987. 48 M.J.W. Veldhuis, The ecophysiXogy o f t h e c o l o n i a l alga Phaeocystis bouchetii, Thesis Groningen U n i v e r s i t y , 1987.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
73
CHANGES I N ATMOSPHERIC COMPOSITION A N D CLIMATE
C. J. E . Schuurmans
Royal Netherlands Meteorological I n s t i t u t e , P.O.
Box 201, 3730 AE
De B i l t , The Netherlands
ABSTRACT
Concentrations of some atmospheric t r a c e gases increase and enhance s u r f a c e temperature. Tropospheric ozone causes t h e same greenhouse warming e f f e c t . Changes of s t r a t o s p h e r i c ozone w i l l have complicated e f f e c t s on c l i m a t e , but i t s d i r e c t e f f e c t s on s u r f a c e temperature a r e probably small. In t h e paper the s u b j e c t is reviewed and conclusions f o r policy i m p l i c a t i o n s a s well a s f u r t h e r research a r e formulated.
CLIMATE PROBLEM
The climate problem has been with u s f o r some time. Even i f we r e s t r i c t our view t o t h e r e c e n t p a s t , not looking a t i c e ages and o t h e r long term and severe d i s r u p t i o n of c l i m a t e , we have t o explain such remarkable v a r i a t i o n s on a decadal time s c a l e a s f o r instance t h e world wide warming around t h e 4 0 - t i e s
of t h i s century and t h e subsequent cooling i n t h e 6 0 - t i e s , e s p e c i a l l y i n t h e Northern Hemisphere. I n f i g u r e 1 yearly averaged temperatures f o r De B i l t , The Netherlands c l e a r l y show t h e s e v a r i a t i o n s . Although such v a r i a t i o n s i n i t s e l f a r e r e l a t i v e l y small
-
and l o c a l l y sometimes a r e h a r d l y s t a t i s t i c a l l y
s i g n i f i c a n t , due t o t h e l a r g e interannual d i f f e r e n c e s
-
their large areal t o
even global extent suggests some e x t e r n a l cause, which f o r t h e v a r i a t i o n s considered, u p t i l l now is not known, or a t l e a s t not u n i v e r s a l l y accepted. C02 AND OTHER TRACE GASES The climate problem, a s y e t not s o l v e d , g r a d u a l l y merged with t h e so-called C02-problem.
In t h e 6 0 - t i e s already t h e atmospheric concentration of C02
s t e a d i l y increased by more than 1 ppm per year and t h e p o t e n t i a l c l i m a t i c e f f e c t s of l a r g e i n c r e a s e s of C02-concentration were s u f f i c i e n t l y known t o l e t t h e 1970 Study of C r i t i c a l Environmental Problems (SCEP) conclude t h a t t h e implications of f u r t h e r C02-increases should be u r g e n t l y i n v e s t i g a t e d (Ref. 1 ) . Curiously enough i n t h e same s t u d y , t h e paragraph
on c l i m a t i c e f f e c t s of
74
10.5"C -r
0 00
10.0
--
0 0
0
0
0
0
0
0
0
00
0
00
0
0
0 0
0
0
9.5
--
-
0
0
00
0
0
0
0
0 00
0 0
0
0
0 0
0
0
0
a5 --
0
0
0
0
0
0
0
0
0
0 0
0
0
0
8.0 -0
7.7
I
: -
Fig. 1 . Yearly averaged temperatures a t De B i l t , The Netherlands, 1901-1987. The curve shows non-overlapping 10-year averages.
o t h e r t r a c e g a s e s ends with: "We do not consider t h e s e gases t o have a g l o b a l s i g n i f i c a n c e except i n s o f a r a s they form p a r t i c l e s " . O t h e r t r a c e gases were added t o t h e climate-C02-problem only i n t h e l a s t 5-10 years. The s i t u a t i o n a t present seems t o b e more or l e s s t h e following:
75 TABLE I
Trace gas
Present concentration
(name)
(ppbv)
Increase p e r year
IR-absorp t ion
( i n %)
( A i n pm)
co2
345000
0.4
15
CH4
1650
1 .o
5-7.5
N20
O3 ( t r o p ) O3 ( s t r a t )
304 5 t o 500 10000
0.25
8,16
0.25?
-
9.6 9.6
?
CFC 1 1
0.23
5.0
10-1 2
CFC 1 2
0.4
5.0
10-12
GREENHOUSE EFFECT Changes of atmospheric composition may a f f e c t c l i m a t e i n a number of ways ( t h i n k of t h e r o l e of water vapor i n weather and c l i m a t e ) , b u t t h e primary e f f e c t is through changes of t h e earth-atmosphere r a d i a t i o n balance. Strangely enough the minor c o n s t i t u e n t s o r t r a c e g a s e s play a dominant r o l e i n t h e r a d i a t i o n balance. Short wave s o l a r r a d i a t i o n a s well a s long wave r a d i a t i o n from the e a r t h and atmosphere a r e a f f e c t e d by changing t r a c e gas concentratons. The l a t t e r however is much more important than t h e former, which i n o t h e r words means t h a t we have mainly t o consider t h e so-called change of t h e greenhouse e f f e c t . I t may b e noted from Table I t h a t C02 and t h e so-called o t h e r t r a c e gases d i f f e r i n the wave l e n g t h s of IR-absorption (and emission). While C 0 2 c o n t r i b u t e s t o t h e greenhouse e f f e c t a t 15
pm.
quite far
from t h e so-called atmospheric window a t about 10 pm ( t h e place i n t h e spectrum where most of t h e e a r t h ' s r a d i a t i o n can disappear uninteruptedly i n t o s p a c e ) , some of t h e o t h e r t r a c e gases have t h e i r absorption bands e x a c t l y i n s i d e t h i s window. CFC 1 1 and 1 2 t h e r e f o r e a r e s a i d t o d i r t y the atmospheric window. In physical terms i t means t h a t t h e a d d i t i o n o f 1 molecule of CFC 11 or 1 2 has t h e same e f f e c t on the r a d i a t i o n balance a s the a d d i t i o n of 1 04 C02molecules. The greenhouse e f f e c t of t h e atmophere under p r e s e n t c o n d i t i o n s amounts t o a downward I R - f l u x from t h e atmosphere t o t h e e a r t h s u r f a c e of 96% of t h e incoming s o l a r f l u x a t t h e top of t h e atmosphere. See f i g u r e 2. The l a t t e r being 350 W/m2, means t h a t a 1 % p e r t u r b a t i o n of t h e normal greenhouse backradiation involves a change of t h i s f l u x of some 3.4 W/m2. For comparison, t h e estimated increase of IR-backradiation a t tropopause l e v e l
due t o a doubled C02-concentration of t h e atmosphere is 4.2 W/m2. We may conclude t h e r e f o r e t h a t the i n i t i a l (without feed backs) p e r t u r b a t i o n of t h e r a d i a t i o n balance caused by C02 and o t h e r t r a c e gas concentration
76
i n c r e a se s seems t o be extremely small. However, a s we w i l l s e e l a t e r on, t h i s is only apparently so.
space
atmosphere
surface
F i g . 2. Radiation budget of t h e earth-atmosphere system. Left is s o l a r
incoming r a d i a t i o n , s e t a t 100%. Reflected s o l a r r a d i a t i o n is 30%. About 51% is absorbed a t t h e e a r t h s u r f a c e ; t h e remainder is absorbed i n t h e atmosphere.
The r i g h t p a r t g i v e s the emission of i n f r a r e d r a d i a t i o n b y the e a r t h s u r f a c e I, a n d by t h e atmosphere I,. RADIATIVE-CONVECTIVE MODELS
Computing t h e c l i m a t i c consequences of changes i n t h e r a d i a t i o n balance is i n p r i n c i p l e p o s s i b l e b u t i n p r a c t i c e l i m i t e d by t h e complexity of the e a r t h -
ocean-atmosphere system. A s i m p l e and yet powerful model however is t h e ra dia tive -c onve c tive model (RCM),
i n which only one
-
vertical
-
dimension is considered and a thermal
equilibrium s t r u c t u r e is computed t ak i n g i n t o account a l l r e l e v a n t feedbacks a c t i n g upon an i n i t i a l p er t u r b at i o n of t h e r a d i a t i o n balance. The point is t h a t t h e r e i s not a balance of r a d i a t i o n a l f l u x e s , n e i t h e r a t t h e earth s u r f a c e , nor a t any l ay er i n t h e troposphere. In t h e s t r a t o s p h e r e however thermal equilibrium sometimes may b e eq u i v al ent t o r a d i a t i v e e quilibrium . Needless t o say t h a t i n R C M ' s o t h e r v e r t i c a l t r a n s p o r t s of energy than b y r a d i a t i v e t r a n s f e r have t o be incorporated. The most obvious of them is convective t r a n s p o r t i n t h e troposphere which keeps the troposphe ric l a p s e r a t e of temperature a t a quasi-fixed value. Horizontal t r a n s p o r t s of h e a t and substances a r e not included i n a RCM implying t h a t the a p p l i c a t i o n of such a
77 model is l i m i t e d t o some kind of g l o b a l average p o s i t i o n . With these r e s t r i c t i o n s one must say t h e t h e RCM h a s given u s a g r e a t deal
of i n s i g h t i n t h e r e l a t i v e importance of a number of atmospheric processes and furthermore some q u a n t i t a t i v e e s t i m a t e s of t h e temperature e f f e c t s t o be expected from changes i n t h e atmospheric composition. A t a meeting on ozone i n t h e l a t e 8 0 - t i e s i t is good t o remember t h a t t h e RCM’s of the e a r l y 6 0 - t i e s already provided u s w i t h answers t o such v i t a l questions a s : 1 . Is i t ozone t h a t keeps t h e s t r a t o s p h e r e
warm? The answer turned out t o
be: yes. 2. Does t h e ozone l a y e r have an important e f f e c t on s u r f a c e temperature?
The answer was: no. Figure 3 shows t h e equilibrium p r o f i l e s of temperature a s computed. The s t r a t o s p h e r e warming by ozone is e v i d e n t . Addition of ozone does n o t apparently change s u r f a c e temperature. Nevertheless looking i n some d e t a i l l e a d s t o the conclusion t h a t from t h e 33 K temperature i n c r e a s e due t o the greenhouse e f f e c t some 0.8 K is d u e t o ozone (9 K is by C02 and t h e l a r g e s t p a r t by H20).
2.3
10
(30)
1000
100
140
180 27.0 280 temmraturs VK)
300
Fig. 3. Thermal equilibrium f o r atmospheres w i t h a d i f f e r e n t atmospheric composition, a s simulated by an RCM ( r e f . 2 ) . MODIFICATION OF TEMPERATURE RCM’s provided t h e f i r s t evidence t h a t p e r t u r b a t i o n s of t h e r a d i a t i o n
balance, although apparently s m a l l , could g i v e r i s e t o r e l a t i v e l y l a r g e changes i n s u r f a c e temperature. Feedback e f f e c t s , e s p e c i a l l y w i t h water vapor c o n t e n t , a r e mostly p o s i t i v e , which means t h a t t h e i n i t i a l greenhouse e f f e c t is magnified and equilibrium is reached a t much h i g h e r s u r f a c e temperature
than is needed t o compensate t h e i n i t i a l d i s turba nc e of t h e ba c kra dia tion. I n t h i s way R C M ' s some 20 y ear s ago p r ed i ct ed a 2.4 K inc re a se of s u r f a c e
temperature f o r a doubling of t h e C02 co n t ent of t h e atmosphere. This value i s s t i l l a g e n e r a l l y accepted order of magnitude, though s i n c e then numerous models of varying s o p h i s t i c a t i o n and s p a t i a l dimensions have been a pplie d t o t h i s s e n s i t i v i t y problem.
RCM's a l s o prove t e b e t h e r i g h t t o o l t o s t u d y t h e r e l a t i v e importance of
the various t r a c e g as p er t u r b at i o n s . In Table I1 some of the se results a r e compared (according t o Ref. 3 ) . TABLE I1
Trace gase (name)
Introduced
Surface temperature
change
response (K)
co2
300-600 ppm
2.8
CH4
1.6-3.2 ppm
0.2
0.28-0.56
N20
0.6
ppm
CFC 1 1
0-2 ppb
0.5
CFC 1 2
0-2 ppb
0.5
O3
-25%
-0.5
Comments on Table I1 a r e t h e following: a. r e a l i s t i c changes o f o t h e r t r a c e gas co n c e ntra tions toge the r may cause a modification of s u r f ace temperature which i s of t h e same orde r of magnitude
a s the e f f e c t of a doubling of t h e C02-concentration. b. s u r f a c e temperature e f f e c t s of changes i n ozone c onc e ntra tion strongly
depend on the v e r t i c a l d i s t r i b u t i o n of t h e ozone changes. A s i t u a t i o n a 8 i n d i c a t e d i n Table I1
-
a 25% decrease a t a l l l e v e l s
-
i s very unlike ly t o
occur i n n a t ur e. Decreases i n t h e s t r a t o s p h e r e a t pre se nt go along with i n c r e a se s of tropospheric ozone co n cen t r ation. The l a t t e r of course w i l l enhance t h e greenhouse e f f e c t of the atmosphere and thus lead t o a warming a t t h e s u r f a ce. SCENARIO T I L L 2050 A
l o g i c a l extension of s e n s i t i v i t y s t u d i e s i s t h e work on s c e n a r i o ' s :
educated guesses about f u t u r e developments. In one such sc e na rio the inc re a se i n concentration of C 0 2 , CH4, N20 and CFC's i s such t h a t around t h e year 2020
the p o i n t may be reached t h a t t h e b ack r ad i ation i s equal t o t h e p e r t u r b a t i o n caused by a doubling of t h e C02-concentration. See f i g u r e 4 . Some people mention t h i s the year of t h e e f f e c t i v e doubling of t h e C02-concentration. The
79 value of t h e p a r t i c u l a r s cen ar i o may be d i f f i c u l t t o judge, b u t i t anyhow makes c l e a r t h a t t h e time a v a i l a b l e t o avoid such a p o s s i b l e s i t u a t i o n has become l e s s than one generation of mankind.
-2
wm
I
I
I
1
I
PP"
600
Fig. 4 . Possible increase of greenhouse r a d i a t i o n based on a sc e na rio of the increase of t h e atmospheric concentration of C02 and some o t h e r trace gases (ref. 4). MODIFICATION OF CLIMATE
Estimates of t h e response of s u r f ace temperature t o p e r t u r b a t i o n s of t h e r a d i a t i o n balance or more g en er al l y t o p er t urba tions of the atmospheric composition a s indicated above, a r e poor i n d i c a t o r s of t h e r e l a t e d changes of climate. This has t o do w i t h a t l e a s t t h r e e things: a . climate is f a r t o complex t o d es cr i b e i n a 1-dimensional fashion. Fortunately, 3-D models of t h e earth-atmosphere system, so-called General C i r c u l a t i o n Models (GCM's), e x i s t which more o r l e s s confirm t h e responses computed b y 1 - D R C M ' s . Unfortunately, GCM's a r e a s ye t not s o p h i s t i c a t e d enough t o use t h e i r 3-D-specified
output a s a r e l i a b l e i n d i c a t i o n of
( r e g i o n a l ) c l i mat e change. In g en er al , GCM's a r e a b l e t o sim ula te the broad f e a t u r e s of present day cl i mat e, b u t simulations of a number a re giona l c l i m a t i c f e a t u r e s or as p ect s of t h e seasonal c yc le a r e s t i l l g r o s s l y in error. b. some processes a t work i n t h e cl i mat e system a r e s t i l l not s u f f i c i e n t l y
well understood t o have them r e l i a b l y incorporated i n the models. This
80 causes u n c e r t a i n t i e s i n t h e model e s t i m a t e s . For t h i s reason t h e formerly mentioned 2.5 K i n c r e a s e of g l o b a l average s u r f a c e temperature should be presented with i t s u n c e r t a i n t y range of 1.5-4.5
K.
I t i s believed t h a t a
l a r g e part of t h e u n c e r t a i n t y is caused by t h e u n c e r t a i n r o l e o f c l o u d s . I t has been known f o r q u i t e some time t h a t a few p e r c e n t i n c r e a s e of cloud amount by i n c r e a s i n g t h e albedo may o f f s e t t h e expected greenhouse warming. On t h e o t h e r hand t h e o r e t i c a l p o s s i b i l i t i e s e x i s t t h a t changes i n cloud amount may enhance t h e greenhouse e f f e c t ( p o s i t i v e feedback). c . e s t i m a t e s of temperature or c l i m a t e response published t h u s f a r i n most c a s e s p e r t a i n t o the e q u i l i b r i u m s i t u a t i o n . The t r a n s i e n t c l i m a t i c response
is what we a c t u a l l y w i l l f e e l . Due t o t h e l a r g e heat s t o r a g e i n t h e oceans an equilibrium response t o a c e r t a i n p e r t u r b a t i o n w i l l only be reached some decades or maybe a century a f t e r t h e i n t r o d u c t i o n o f t h e p e r t u r b a t i o n . (By p e r t u r b a t i o n we e.g. mean t h e year of the e f f e c t i v e doubling of t h e C02concentration a s mentioned above). Numerical s i m u l a t i o n of t r a n s i e n t c l i m a t e response is i n its beginning s t a g e . I t is very (computer)time consuming, p a r t l y because a coupled atmosphere-ocean GCM must be employed. Though s i m u l a t i o n s of t r a n s i e n t c l i m a t e response make t h e impression of climate p r e d i c t i o n s , they of course do not and cannot i n c o r p o r a t e e f f e c t s of f u t u r e volcanic e r u p t i o n s o r v a r i a t i o n s i n s o l a r o u t p u t .
CONCLUSIONS One might t h i n k of conclusions f o r ( p o l i t i c a l ) a c t i o n and c o n c l u s i o n s from t h e p o i n t of view of r e s e a r c h . I w i l l t r y t o look a t t h e problem from both s i d e s . Without f u r t h e r research I t h i n k we may conclude t h a t : 1 . Reduction of t h e increase o f atmospheric c o n c e n t r a t i o n s of o t h e r t r a c e
gases than C02 w i l l have a s i g n i f i c a n t e f f e c t i n delaying t h e greenhouse warming. I e s p e c i a l l y think of those g a s e s f o r which t h e r e l e a s e might be e a s i e r stopped than t h a t of C02 or w h i c h r e l e a s e s m u s t be stopped anyway f o r o t h e r reasons (e.g. CFC 1 1 and 12). 2 . The response of s u r f a c e temperature t o s t r a t o s p h e r i c ozone changes is
probably small. In general however t h e r e l a t i o n between ozone c o n t e n t o f t h e atmosphere and c l i m a t e is s o complicated t h a t t h e use of c l i m a t e response arguments i n t h e ozone debate i s e a s i l y misleading. Research i n t h i s f i e l d must be strengthened f o r some important reasons mentioned i m p l i c i t l y before. Our a b i l i t y t o s i m u l a t e p r e s e n t atmospheric s t r u c t u r e , composition and c l i m a t e must b e improved, f o r i n s t a n c e . In view of t h e present conference, two a s p e c t s of a research e f f o r t m u s t be s p e c i f i c a l l y stressed :
81 1 . I n t e r a c t i o n processes between s t r a t o s p h e r e and troposphere l a r g e l y belong
t o the f i e l d of present unknowns or i n s u f f i c i e n t l y knowns. Cooling or warming of t h e s t r a t o s p h e r e , due t o changing ozone concentrations i n d i r e c t l y may a f f e c t t h e l a r g e s c a l e tropospheric c i r c u l a t i o n , being a major component in determining regional climate. Unless such dynamic coupling mechanisms a r e b e t t e r s t u d i e d and properly simulated, climate simulations continue t o contain a l a r g e margin of uncertainty. 2 . Ozone depletion o r increases l i k e in the troposphere involve f i r s t of a l l
atmospheric chemical processes. Such processes in t u r n a r e s t r o n g l y influenced by atmospheric conditions (some people think t h a t t h e C02produced cooling of t h e Antarctic s t r a t o s p h e r e has stimulated t h e chemical reactions leading t o the ozone h o l e ) . This c r e a t e s some i n t i m i t e l y linked climate-chemistry processes which in t h e present generation of climate simulation models a r e lacking o r only very poorly developed. REFERENCES
Man's Impact on the Global Environment, Report of t h e S t u d y of C r i t i c a l Environmental Problems ( S C E P ) , MIT 162, Cambridge, Massachusetts, 1970, p. 54. S.
Manabe and R.F. S t r i c k l e r , Thermal Equilibrium of t h e Atmosphere w i t h a
Convective Adjustment, J . A t m . Sci., 21 (1964). 361-385. A. Henderson-Sellers and P . J . Robinson, Contemporary Climatology, Longman, Harlow, 1986. Wigley, Relative contributions of d i f f e r e n t t r a c e gases t o t h e greenhouse e f f e c t , Climate Monitor, 16 (19871, 14-28. T.M.L.
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83
SESSION It
TROPOSPHERIC OZONE, OXIDANTS AND PRECURSORS: SOURCES AND LEVELS
Chairmen
L.J. Brasser A.P. Altshuller
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
85
MOTOR VEHICLES AS STRATOSPHERIC OZONE
AND
SOURCES
OF
COMPOUNDS
IMPORTANT
F.M. BLACK U.S. Environmental P r o t e c t i o n Agency (MD-46) C a r o l i n a 27711
,
TO
TROPOSPHERIC
Research T r i a n g l e Park, N o r t h
ABSTRACT One o f t h e most r a p i d l y growing human a c t i v i t i e s i n t h e U.S. of importance t o atmospheric ozone i s t h e use o f highway m o t o r v e h i c l e s . T r a n s p o r t a t i o n sources a r e e s t i m a t e d t o have been r e s p o n s i b l e f o r about 34% o f 1985 U.S. a n t h r o p o g e n i c hydrocarbon emissions , 70% o f carbon monoxide emissions, 45% o f nitrogen oxide emissions, 24% o f nonaerosol c h l o r o f l u o r o c a r b o n emissions, and 14% o f carbon d i o x i d e emissions. Data i s presented d e s c r i b i n g p o s s i b l e u n i n v e n t o r i e d t r a n s p o r t a t i o n hydrocarbon emissions t h a t c o u l d i n c r e a s e t h e i r e s t i m a t e d c o n t r i b u t i o n t o 45 50% o f t h e anthropogenic t o t a l . Data i s a l s o p r e s e n t e d s u g g e s t i n g m o t o r v e h i c l e s t o be r e l a t i v e l y i n s i g n i f i c a n t sources o f a n t h r o p o g e n i c n i t r o u s o x i d e , b u t n o t i n g t h a t these emissions a r e i n c r e a s e d by t h e c o n t r o l t e c h n o l o g i e s used t o reduce hydrocarbon, carbon monoxide, and n i t r o g e n o x i d e s emissions. The s e n s i t i v i t y of motor v e h i c l e e m i s s i o n r a t e s and c o m p o s i t i o n s t o such o p e r a t i n g v a r i a b l e s as ambient temperature, a l t i t u d e , and average speed i s discussed. Hydrocarbon and carbon monoxide e m i s s i o n r a t e s a r e g e n e r a l l y m i n i m i z e d a t ambient temperatures o f about 24°C (75"F), and e l e v a t e d a t h i g h e r and l o w e r temperatures. These emissions a r e a l s o e l e v a t e d by h i g h a l t i t u d e and reduced average speed o p e r a t i n g c o n d i t i o n s . N i t r o g e n o x i d e e m i s s i o n r a t e s a r e n o t as s e n s i t i v e t o v e h i c l e operating conditions. The r a t i o o f hydrocarbon t o n i t r o g e n o x i d e emissions, o f importance t o t r o p o s p h e r i c ozone c h e m i s t r y , v a r i e s w i t h o p e r a t i n g c o n d i t i o n s f r o m about 1 t o 5. The c o m p o s i t i o n o f hydrocarbon emissions v a r i e s w i t h v e h i c l e speed and ambient temperature; e l e v a t e d p a r a f f i n i c f r a c t i o n s a r e t y p i c a l o f h i g h speed and h i g h t e m p e r a t u r e o p e r a t i o n , and e l e v a t e d o l e f i n i c f r a c t i o n s a r e t y p i c a l o f l o w speed and l o w temperature o p e r a t i on.
-
INTRODUCTION Since enactment o f t h e 1970 Clean A i r Act, ozone has proven t o be t h e most p e r v a s i v e and d i f f i c u l t t o c o n t r o l o f a l l U.S. t h e o t h e r p o l l u t a n t s addressed by t h i s Act, from
sources;
rather,
it
results
from
a i r pollutants.
Unlike
ozone i s n o t d i r e c t l y e m i t t e d
complex
photochemical
reactions
i n v o l v i n g s u n l i g h t and v a r i o u s p r e c u r s o r e m i s s i o n s t h a t emanate f r o m b o t h man's a c t i v i t i e s and n a t u r a l processes.
Atmospheric t r a n s p o r t has c o m p l i c a t e d
e f f o r t s t o c o n t r o l ozone as a u t h o r i t i e s charged w i t h m a i n t a i n i n g l o c a l a i r q u a l i t y a r e o f t e n f r u s t r a t e d by ozone p r e c u r s o r s r e s u l t i n g f r o m a c t i v i t i e s hundreds o f m i l e s upwind o f t h e i r j u r i s d i c t i o n .
The phenomenon o f p o l l u t a n t t r a n s p o r t has a l s o awakened a growing i n t e r n a t i o n a l concern a b o u t changes i n stratospheric
a i r chemistry
wherein t h e
r a t e o f ozone
d e s t r u c t i o n i s being
86 accelerated
by
compounds
transported
from
the
earth's
surface.
Both
t r o p o s p h e r i c and s t r a t o s p h e r i c t e m p e r a t u r e change can a l s o be a s s o c i a t e d w i t h emissions a t t h e e a r t h ' s s u r f a c e .
The c h e m i s t r y o f t h e e a r t h ' s atmosphere i s
v e r y complex and t h e s u b j e c t o f much h y p o t h e s i z i n g and s t u d y .
It i s apparent
t h a t t h e t r o p o s p h e r i c and s t r a t o s p h e r i c systems a r e c o u p l e d and s h o u l d be c o l l e c t i v e l y c o n s i d e r e d when examining t h e impact o f man's a c t i v i t i e s on t h e atmosphere. One o f t h e most r a p i d l y growing a n t h r o p o g e n i c a c t i v i t i e s o f i m p o r t a n c e t o atmospheric ozone i s t h e use o f highway m o t o r v e h i c l e s . t r a t o r o f t h e U.S.
Lee Thomas, Adminis-
Environmental P r o t e c t i o n Agency (USEPA), r e c e n t l y n o t e d
t h a t s i n c e 1970 t h e U.S. economy grew a b o u t 44 p e r c e n t ,
t h e p o p u l a t i o n 18
p e r c e n t , and t h e k i l o m e t e r s d r i v e n by American m o t o r i s t 58 p e r c e n t ( r e f . 1) There a r e many compounds e m i t t e d f r o m m o t o r v e h i c l e s t h a t p a r t i c i p a t e i n atmospheric chemical and p h y s i c a l processes w h i c h i n f l u e n c e t h e c o n c e n t r a t i o n s o f t r o p o s p h e r i c and s t r a t o s p h e r i c ozone. n i t r o g e n o x i d e s (NOx o r ozone.
Methane
(CH4)
V o l a t i l e o r g a n i c compounds (VOC) and
NO + NO2) a r e t h e p r i m a r y p r e c u r s o r s o f t r o p o s p h e r i c and
carbon
monoxide
reactions
(CO)
control
the
atmospheric c o n c e n t r a t i o n s o f h y d r o x y l r a d i c a l (OH) w h i c h i n t u r n c o n t r o l s t h e atmospheric r e s i d e n c e t i m e o f compounds i m p o r t a n t t o r a d i a t i v e h e a t i n g o f t h e t r o p o s p h e r e (green house e f f e c t ) and compounds i m p o r t a n t t o ozone c h e m i s t r y i n c l u d i n g s t r a t o s p h e r i c ozone d e p l e t i o n .
CO,
although o f lower r e a c t i v i t y
t h a n most VOCs, i s a l s o c o n s i d e r e d a p r e c u r s o r o f t r o p o s p h e r i c ozone.
The
n i t r o u s o x i d e (N20), Freon-12 (CF2C12), and CH4 t r a n s p o r t e d f r o m t h e e a r t h ' s surface t o t h e stratosphere
p a r t i c i p a t e i n ozone d e p l e t i o n c h e m i s t r y .
A
p r o d u c t o f d e p l e t e d s t r a t o s p h e r i c ozone i s more i n t e n s e UV r a d i a t i o n i n t h e t r o p o s p h e r e where i t d r i v e s t h e f o r m a t i o n o f ozone.
Ozone, N20, CH4,
CF2C12,
and carbon d i o x i d e (C02) a l s o a l l i n f l u e n c e t h e r a d i a t i v e b a l a n c e o f t h e e a r t h ' s atmosphere.
I n c r e a s e d a t m o s p h e r i c c o n c e n t r a t i o n s o f t h e s e compounds
w i l l e l e v a t e t h e t e m p e r a t u r e o f t h e t r o p o s p h e r e and decrease t h e t e m p e r a t u r e o f t h e stratosphere. These t e m p e r a t u r e changes can i n f l u e n c e t h e r a t e s o f r e a c t i o n s f o r m i n g and d e s t r o y i n g ozone. MOTOR VEHICLE EMISSIONS The atmospheric c o n c e n t r a t i o n s o f CF2C12,
N20, CO,
C02,
and CH4 a r e
c u r r e n t l y i n c r e a s i n g a t annual r a t e s o f a p p r o x i m a t e l y 5%, 0.2%, 1-2%, 0.5%, and 1%, r e s p e c t i v e l y ( r e f .
2).
There a r e many a n t h r o p o g e n i c and b i o g e n i c
sources o f most o f t h e s e compounds.
The r e l a t i v e s t r e n g t h s o f t h e v a r i e d
sources a r e o f t e n debated and a r e i m p o r t a n t
t o the potential
impact o f
anthropogenic emissions c o n t r o l .
Only highway m o t o r v e h i c l e sources w i l l be
discussed i n
The U.S. government
t h i s presentation.
has t a k e n
measures t o
reduce ambient l e v e l s o f VOC,
NOx,
CO,
and i n d i r e c t l y C02, through motor
v e h i c l e emissions ( t a i l p i p e and evaporative) and f u e l economy regulations. Table 1 summarizes some o f these regulations. Countering the government mandated emission r a t e reductions have been t h e previously mentioned dramatic growth o f vehicle-kilometers-traveled
(VKT) and
a d i s t u r b i n g l y l a r g e amount o f v e h i c l e emission c o n t r o l system tampering. Fig. 1 i l l u s t r a t e s U.S.
light-duty
and heavy-duty v e h i c l e urban and r u r a l VKT
growth during the period 1975 t o 1985, w i t h p r o j e c t i o n s through 2000 ( r e f . 3). During the 1975 t o 1985 decade, l i g h t - d u t y urban and r u r a l VKT increased 26.8% and 29.2%, respectively, and heavy-duty urban and r u r a l VKT increased 53.0% and 61.1%, respectively. The r e s u l t s o f t h e 1986 USEPA Motor Vehicle Tampering Survey (15 c i t i e s ,
7541 vehicles)
suggested t h a t one o u t o f every f i v e
passenger cars and l i g h t - d u t y t r u c k s i n the U.S. the emission c o n t r o l
system tampered
(ref.
had a t l e a s t one component o f 4).
An a d d i t i o n a l 25% were
c l a s s i f i e d as "arguably tampered,''
meaning t h a t a determination could n o t be
made as t o whether t h e v e h i c l e ' s
c o n d i t i o n was due t o tampering o r poor
maintenance.
Tampering and m i s f u e l i n g can cause dramatic increases i n VOC,
CO, and NOx emissions.
For example, disconnected a i r pumps (found on 8% o f
the surveyed vehicles so equipped) can increase VOC emissions 200% and CO emissions 800%, and disconnected exhaust-gas-recirculation systems (found on
7% of
surveyed vehicles
so
equipped)
M i s f u e l i n g c a t a l y s t equipped vehicles vehicles
Fig. 1.
requiring
U.S.
unleaded f u e l )
can
can
increase
NOx
emissions
175%.
w i t h leaded gasoline (found on 9% o f increase
VOC emissions 500% and
motor v e h i c l e kilometers traveled, 1975 t o 2000.
CO
1972 1973 1974 1975 1977 1978 1979 1980 1981 1982 1983 1984 1985 1987
LDV; LDT" LDV, LDT HDGV, tDDV5 LDV, LDT' LDV LDV LDT LDV LDT HDGV, HDDV LDV LDV LDT LDV LDV LDV LDT LDV8 HDGV8 HDDV LDT HDGV HDDV
2.2 ;/mi 3.4 i / m i 3.4 g l m i
-
1.5 g/mi 2.0 g/mi 1.5 g/mi 1.5 g/mi 2.0 g/mi 1.5 g/mi 1.7 g/mi 1.5 glbhp-hr 0.41 g l m i 0.41 g/mi 1.7 g/mi 0.41 g/mi 0.41 glmi 0.41 glmi 0.8 glmi 0.41 glmi 2.5 glbhp-hr 1.3 glbhp-hr 0.8 g/mi 1.3 glbhp-hrg 2.5 glbhp-hr 1.3 glbhp-hr . .
23 ;/mi 39 glmi 39 glmi 40 glbhpyhr 15 glmi 20 glmi 15 gfmi 15 g/mi 20 glmi 15 glmi 18 glmi 25 glbhp-hr 7.0 glmi 3.4 glmi 18 g/mi 3.4 glmi 3.4 glmi 3.4 glmi 10 glmi 3.4 glmi 40 glbhp-hr 15.5 'glbhp-hr 10 g/mi 15.5 g/bhp-hr 40 glbhp-hr 15.5 g/bhp-hr
3.0 g/mi
-
3.1 3.1 2.0 2.0 3.1 2.0 2.3 2.0 1.0 2.3 1.0 1.0 1.0 2.3 1.0
g/mi g/mi glmi glmi g/mi g/mi glmi
-
glmi glmi g/mi glmi glmi g/mi glmi g/mi
16 g/bhp-hr -
10 g/bhp-hr
10.7 g/bhp-hr 10.7 g/bhp-hr
1.2 glmi 6.0 glbhp-hr 6.0 glbhp-hr 6.0 glbhp-hr
-
6 gltest 2 gltest 2 gltest
-
2 2 2 6 6 6 6
g/test gltest g/test7 g/test gltest g/test g/test
-
6 gltest 2 g/test 2 gltest 2 gltest 2 gltest 2 gltest 2 gltest 2 gltest 3 gltest, 4 gltest 2 gltest 3 gltest 4 gltest
--
18 mpg
-
19 mpg
-
20 mpg 22 mpg
-
24 mpg 26 mpg 27 mpg
--
27.5 mpg
-
.........................................................................................................................
1). LDV: l i g h t - d u t y passenger car; LDT: l i g h t - d u t y truck; HDGV: heavy-duty gasoline t r u c k l b u s ; HDDV: heavy-duty d i e s e l truck/bus, g/mi = grams per mile; g/bhp-hr = grams p e r brake horsepower hour, mpg = m i l e s p e r gallon. 2). 7-mode t e s t procedure f o r t a i l p i p e emissions 3). carbon t r a p procedure f o r evaporative emissions 4). CVS-72 t e s t procedure f o r t a i l p i p e emissions 5). 13-mode t e s t procedure f o r t a i l p i p e emissions 6). CVS-75 t e s t procedure f o r t a i l p i p e emissions 7). SHED procedure f o r evaporative emissions 8). t r a n s i e n t t e s t procedure f o r t a i l p i p e emissions 9). v e h i c l e s l a r g e r than 14,000 pounds gross-vehicle-weight
emissions 400%. The survey i n d i c a t e d t h a t l o c a l l y administered Inspection and Maintenance Programs and Antitampering Programs reduced tampering and m i s f u e l i n g by 35% and 50%, respectively. Highway motor vehicles are b u t one category o f anthropogenic source. combined impact o f motor v e h i c l e emissions regulations, VKT growth, tampering,
and
the
relative
importance
of
transportation
anthropogenic sources are i l l u s t r a t e d i n Figs. 2,3, NOx, respectively,
and
The and other
and 4 f o r VOC, CO, and 5). U.S. emissions
f o r t h e period 1940 t o 1985 ( r e f .
peaked during the e a r l y 1970's.
Since then,
NOx emissions have remained
r e l a t i v e l y constant, and VOC and CO emissions have decreased.
Transportation
as an anthropogenic source o f VOC has v a r i e d from 28.3% i n 1940, t o 45.6% i n 1970, t o 33.8% i n 1985.
S i m i l a r observations suggest t h a t t r a n s p o r t a t i o n
accounted f o r 35.9% o f CO i n 1940, 72.7% i n 1970, and 70.4% i n 1985, and accounted f o r 32.4% o f
NOx i n 1940, 42.0% i n 1970, and 44.2% i n 1985. I n 1985,
the estimated national t r a n s p o r t a t i o n VOC, CO, and NOx mass emission r a t e s were 7.2 m i l l i o n metric tons/yr, 47.5 m i l l i o n m e t r i c tons/yr, and 8.9 m i l l i o n m e t r i c tons/yr,
respectively.
This data was taken from t h e National A i r
Q u a l i t y and Emissions Trends Report,
1985, published February,
1987, which
used t h e EPA computer model MOBILE 3 t o estimate t r a n s p o r t a t i o n c o n t r i b u t i o n s . The current developmental version o f t h i s model ( t o be released as MOBILE 4 )
w i l l increase the estimated c o n t r i b u t i o n o f t r a n s p o r t a t i o n sources t o t h e nationwide VOC inventory. For example, using MOBILE 4, USEPA r e c e n t l y estimated t h a t motor vehicles c o n t r i b u t e d 48% o f t h e 1983 t o t a l U.S. non-
30
25 0 l0
H S o l i d Waste IS M i s c S t a t i o n a r y Combustion
27.2
rn
H I n d u s t r i a l Processes MTransportation
20
.r(
5 15 0)
x
u3 < 0
4
1985
e
10 5 0
33.8 % 1940197019801985 Year Source:EPA-450/4-86-018,
Fig. 2.
Jan. 1987
V o l a t i l e organic compound emissions trend, 1940 t o 1985.
The d i f f e r e n c e s between MOBILE 3 and
methane hydrocarbon i n v e n t o r y ( r e f . 6).
MOBILE 4 VOC e s t i m a t e s w i l l be discussed i n d e t a i l l a t e r . c a n t change i n v o l v e s
t h e use of
area-specific
The most s i g n i f i -
gasoline v o l a t i l i t i e s
and
ambient temperatures which s u b s t a n t i a l l y increases t h e magnitude o f evaporat i v e emission estimates d u r i n g
120
the
h i g h temperature
periods o f
7 H S o l i d Waste
the
summer
6 Misc
S t a t i o n a r y Combustion H I n d u s t r i a l Processes ,mTransportation
1985
6 % 70.4 %
Year Source: EPA-450/4-86-0 18, Jan. 1987 F i g . 3.
Carbon monoxide emissions trend, 1940 t o 1985.
2 m
5
1
1
m
S
o
u
i
d Waste 6 M i s c
S t a t i o n a r y Combustion
20
D I n d u s t r i a l Processes
c 0 I.fl
l
mTransportation
15
L
c,
2 10 (D
1985
< 0
e4 4 . 73
-+5
%
n u
1940 1970 1980 1985
Year Source:EPA-450/4-86-018.
Fig. 4.
N i t r o g e n o x i d e emissions t r e n d , 1940 t o 1985.
Jan. 1987
91 months.
CO and NOx emission estimates were n o t s i g n i f i c a n t l y changed.
Data i s n o t as r e a d i l y a v a i l a b l e f o r unregulated emissions such as N20,
C02, and CF2C12.
However, estimates can be made o f t h e r e l a t i v e strengths o f the anthropogenic sources o f these compounds. The t r a n s p o r t a t i o n sector accounted f o r l e s s than 10% o f 1985 anthropogenic N20 emissions ( r e f .
7), about 24% o f 1985 CFC emissions, i.e. nonaerosol CFC-11, CFC-12, and CFC-113 ( r e f . 8 ) , and about 14% o f 1985 anthropogenic COP emissions ( r e f . 9,lO). Fig. 5 depicts t h e r e l a t i v e strengths o f various sources o f C02 and CFC i n t h e U.S. during 1985. The 1985 t r a n s p o r t a t i o n mass emission r a t e s o f N20 and CFC can be estimated a t about 80 thousand m e t r i c tons/yr and 48 thousand m e t r i c tons/yr, respectively. Anthropogenic C02 emissions a r e associated p r i m a r i l y w i t h the combustion o f f o s s i l f u e l s and bio-mass. Globally, f o s s i l f u e l combustion has been estimated t o be responsible f o r about 50-70% o f C02 emissions ( r e f . 9). DeLuchi r e c e n t l y estimated t h a t i n 1985 highway motor v e h i c l e f u e l combustion was responsible f o r about 14% o f f o s s i l f u e l C02 emissions g l o b a l l y and 24% i n t h e U.S. ( r e f . 10). He estimated t h a t U.S.
Carbon Dioxide
Coal--21.6%
8 n 10A9 Metric Tons
Chlorofluorocarbons Solvents--26.
o b i l e A/C--23.5%
F l e x i b l e Foans--;3 g i d Foae--i8.9%
frigeration--6.9%
2 n 10A5 M e t r i c Tons Fig. 5. 1985 carbon d i o x i d e and nonaerosol chlorofluorocarbon emissions by source category.
92 highway motor vehicles emitted about 1.1
b i l l i o n m e t r i c tons o f C02 during
1985. VOC, CO, NOx emissions
Motor v e h i c l e emissions
are sensitive t o
maintenance, s i z e o f the vehicle, things,
the type o f engine,
type o f f u e l being used, and among o t h e r
t h e conditions under which t h e v e h i c l e i s operated,
a1 t i t u d e ,
age,
and ambient temperature.
e.g.
speed,
Depending on these considerations, the
composition and r a t e o f emissions w i l l vary.
The USEPA maintains a model
(MOBILE 3 c u r r e n t release, MOBILE 4 i n development) u s e f u l f o r p r e d i c t i n g f l e e t average VOC, CO, and NOx emission c h a r a c t e r i s t i c s as a f u n c t i o n o f many of these v a r i a b l e s (ref. 11).
Table 2 provides an example o f the i n f o r m a t i o n
t h a t can be obtained from t h i s model. Seven categories o f motor v e h i c l e s are incorporated. For each calendar year and v e h i c l e category, t h e VKT and emissions tailpipe
are d i s t r i b u t e d over emissions,
g/km
20 model years.
equivalents
of
The model
incorporates
evaporative emissions,
and g/km
equivalents o f r e f u e l i n g emissions ( i n t h e developmental v e r s i o n ) i n the THC emission rates.
The algorithms used t o c a l c u l a t e t h e g/km equivalents o f
evaporative and r e f u e l i n g emissions are based on the r e l a t i o n s h i p s : Evap., g/km = (Di t TPD x Hs) / KPD where
Di
d i u r n a l emissions, g/day;
(1) TPD = average t r i p s per day; Hs = hot
soak emissions, g / t r i p ; and KPD = average kilometers d r i v e n per day, and Refuel., g/km = RF / FE where RF = r e f u e l i n g emissions, g / l i t e r ; and
(2)
FE
= f u e l economy, k m / l i t e r .
Mobile 3 used 3.05 and 50.0 f o r f l e e t average TPD and KPD, r e s p e c t i v e l y .
The
developmental v e r s i o n o f t h i s model, MOBILE 4, v a r i e s TPD and KPD according t o the age o f the vehicle. The t a i l p i p e r a t e s can be reported as THC emissions (as regulated), o r as nonmethane hydrocarbon (NMHC) emissions. As i n d i c a t e d i n Table 2, emission c h a r a c t e r i s t i c s vary among v e h i c l e categories, and f l e e t average values, therefore, depend on t h e composition o f t h e f l e e t , VKT mix.
i.e.
the
The mix given i n Table 2 represents t h e model d e f a u l t values f o r
1985 and are used f o r most scenarios discussed i n t h i s paper.
This mix can be
v a r i e d t o correspond t o l o c a l f l e e t compositions. Fig. 6 i l l u s t r a t e s how MOBILE 4 characterizes f l e e t average THC, CO, and NOx emissions f o r the p e r i o d 1975 through 2000, a t 152 m (500 f t ) a l t i t u d e ,
24°C (75"F), 32 km/h (20 mi/h) average speed, w i t h Inspection and Maintenance
93
Veh. Spd, km/h 32.2 VKT Mix 0.652 Exhaust NMHC, g/km 1.06 Exhaust HC, g/km 1.14 Evap. HC, g/km 0.86 Refuel. HC, g/km 0.21 THC, g/km 2.21 11.95 COY g/km NOx, g/km 1.24
32.2 0.218 2.08 2.19 1.33 0.27 3.79 20.96 2.09
32.2 0.040 3.20 3.44 4.51 0.44 8.37 86.74 3.46
32.2 0.023 0.24 0.25
32.2 0.008 0.38 0.39
32.2 0.054 2.80 2.88
32.2 0.007 2.22 2.37 2.11
0.25 0.80 0.86
0.39 0.96 1.02
2.88 7.76 12.84
4.48 12.40 0.52
-
-
-
c
1.45 1.54 1.05 0.21 2.79 16.33 2.13
I------------------------------------------------------------------------------................................................................................ a l t i t u d e 152 m y ambient temperature 23.9OCY w i t h I n s p e c t i o n and Maintenance/Anti tampering Programs LDGV: l i g h t - d u t y g a s o l i n e v e h i c l e ; LDGT: l i g h t - d u t y g a s o l i n e t r u c k ; HDGV: heavy-duty g a s o l i n e v e h i c l e ; LDDV: 1 i g h t - d u t y d i e s e l v e h i c l e ; LDDT: 1 i g h t - d u t y d i e s e l t r u c k ; HDDV: heavy-duty d i e s e l v e h i c l e ; MC: m o t o r c y c l e
(I&M) and Anti-Tampering Programs (ATP).
From 1975 t o 1985 f l e e t average THC
emis s io n r a t e s were reduced 57%, CO e m i s sion r a t e s 62%, and NOx emissions r a t e s 35%.
The i n d i c a t e d e m i s s i o n r a t e s were det ermined u s i n g l a b o r a t o r y
simulations
of
E
urban d r i v i n g
conditions
as
used
in
Federal
Emissions
40
Y
\
m
E 0
10
0
0
75
80
Note: 24OC, 32 km/h, F ig . 6.
.
85 90 Year
95
00
152 m a l t i t u d e
F l e e t average NMHC, C O Y and NOx e m i ssion r a t e s , 1975 t o 2000.
U
C e r t i f i c a t i o n ( r e f . 12). Fig. 7 i l l u s t r a t e s how MOBILE 4 p r e d i c t s f l e e t average emission r a t e s as
NMHC and CO emission r a t e s continuously decrease as average speed i s increased. The 1985 f l e e t average NMHC and CO r a t e s a t 88 km/h (55 mi/h) were 32% and 12%, r e s p e c t i v e l y , o f t h e values a t 8 km/h (5 mi/h). The NOx f l e e t average emission r a t e passed through a minimum i n t h e 32 - 48 km/h (20 - 30 mi/h) range, and was elevated a t both lower and h i g h e r a f u n c t i o n o f v e h i c l e speed.
Fig. 7. speed.
1985 f l e e t average NMHC, CO, and NOx emission r a t e s as a f u n c t i o n o f
speeds. The NMHC/NOx r a t i o v a r i e d from 2.2 a t 8 km/h (5 mi/h) t o 0.7 a t 88 km/h (55 mi/h). Fig. 8 i l l u s t r a t e s how MOBILE 4 p r o j e c t s t h e s e n s i t i v i t y o f emission r a t e s t o ambient temperature.
The 1985 f l e e t average NMHC and CO emission
r a t e s were lowest a t 24OC (75OF), whereas NOx emission r a t e s continuously decreased as the temperature increased. The NMHC/NOx r a t i o i s minimum a t 24°C (75OF) and maximum a t 38°C (lOO°F), 1.3 and 4.6, respectively. The e l e v a t i o n o f t h e NMHC/NOx r a t i o a t 38OC (100°F) occurs p r i m a r i l y because o f increased evaporative HC emissions p r e d i c t e d by MOBILE 4. MOBILE 4 uses algorithms t o a d j u s t both t a i l p i p e and evaporative emission r a t e s f o r changes i n ambient temperature. Tailpipe emission rates are adjusted over t h e e n t i r e
35
Note: 32 km/h, 152 m altitude F i g . 8. 1985 f l e e t average NMHC, CO, and NOx e m i s s i o n r a t e s as a f u n c t i o n o f ambient temperature. s u m e r - w i n t e r temperature range, and e v a p o r a t i v e e m i s s i o n r a t e s o n l y i n t h e summer range.
A v a i l a b l e d a t a i s inadequate t o d e f i n e e v a p o r a t i v e emissions
s e n s i t i v i t y t o temperalures below 20°C (68°F).
Likewise, a v a i l a b l e data i s
c u r r e n t l y inadequate t o d e f i n e r e f u e l i n g emissions s e n s i t i v i t y t o ambient temperature. F i g . 9 i l l u s t r a t e s how MOBILE 4 p r o j e c t s t h e i n f l u e n c e o f a l t i t u d e on t h e c h a r a c t e r i s t i c s o f motor v e h i c l e emissions. increased
when
decreased.
vehicle
altitude
is
NMHC and CO e m i s s i o n r a t e s a r e
increased,
and
NOx
emission
rates
CO e m i s s i o n r a t e s a r e most s e n s i t i v e w i t h 1985 f l e e t average
v a l w s i n c r e a s i n g 55% as t h e v e h i c l e o p e r a t i n g a l t i t u d e i s i n c r e a s e d f r o m 152 m (500 f t ) t o 1676 rri (5500 f t ) .
The c h e m i s t r y o f t r o p o s p h e r i c NMHC/NOx r a t i o ( r e f . 13).
ozone f o r m a t i o n
depends c r i t i c a l l y on
When t h i s r a t i o i s l o w t h e ozone f o r m i n g p o t e n t i a l
i s dependent on HC r e a c t i o n r a t e s ,
v a r y i n g w i t h t h e s t r u c t u r e o f t h e HC
compound; b u t when t h i s r a t i o i s h i g h t h e r e l a t i v e l y l o w c o n c e n t r a t i o n s o f NOx a r e l i m i t i n g and t h e s t r u c t u r e o f t h e HC becomes l e s s i m p o r t a n t .
With motor
v e h i c l e emissions, t h i s r a t i o v a r i e s w i t h speed and t e m p e r a t u r e as i n d i c a t e d i n Fig.
10.
Over t h e s c e n a r i o s
p r e d i c t e d f o r 8 km/h (5 m i / h ) ,
examined,
the
highest
ratio,
38OC (100°F) o p e r a t i n g c o n d i t i o n s ,
5.31,
is
and t h e
96
Note: 24'C,
32 km/h
Fig. 9. 1985 f l e e t average NMHC, CO, and NOx emission rates as a function a1 titude.
-
37.8"C 23.9"C
.........
10.o"c 1111111111111111
-3.9"c -111
Fig. 10. 1985 f l e e t average NMHC/NOx temperature and average speed.
ratios as a function
of
ambient
lowest ratio, 0 . 6 7 , i s predicted for 88 km/h (55 mi/h), 24°C (75OF) operating conditions. There i s l i t t l e sensitivity of t h i s ratio t o ambient temperature from -3.9"C (25°F) t o 24°C ( 7 5 ° F ) a t 88 km/h (55 mi/h). The high values a t 38OC (100°F) result primarily from large increases in evaporative hydrocarbon emission rates predicted by MOBILE 4.
97 F ig . 11 compares t h e d i s t r i b u t i o n o f HC emission r a t e s between t a i l p i p e , ev a pora t iv e , and r e f u e l i n g sources p r o j e c t e d by MOBILE 4 a t 10°C (5OoF), 24°C (75"F), and 38°C (100°F).
A t 32 km/h (20 mi/h),
34% o f NMHC emissions were
from e v a p o r a t i v e sources a t 10°C (50°F), 39% a t 24°C (75"F),
--10.0"C
8
32 89
23.9"C
8
32 89
m R e f ue 1i n g
37.8'C
8
and 73% a t 38°C
BEvaporative Tailpipe
32 89
Speed, km/h Fig. 11. 1985 NMHC m o t o r eva pora t iv e , and r e f u e l i n g .
vehicle
emissions
distribution:
tailpipe,
(100°F). The s u b s t a n t i a l e v a p o r a t i v e e m i ssions i n c r e a s e p r o j e c t e d a t 38°C (100°F) r e s u l t s f r o m c o n t r o l system design. The e v a p o r a t i v e c a n i s t e r was developed t o p e r m i t compliance w i t h Federal Emissions C e r t i f i c a t i o n which i n c l u d e s measurement o f d i u r n a l e m i s s i o n s o v e r a 16"
-
29°C
(60"
-
84°F)
temperature ramp w i t h 60.0 t o 63.4 kPa (8.7 t o 9.2 p s i ) Reid Vapor Pressure (RVP) f u e l . The d a t a used i n MOBILE 4 were developed w i t h s u r v e i l l a n c e f l e e t v e h i c l e s u s i n g commercially marketed f u e l s w i t h an average RVP o f about 79.3 kPa (11.5 p s i ) . A d d i t i o n a l l y , t h e 38°C (100°F) t e s t s measured d i u r n a l emissions ov er a 29" 42°C (84"-108"F) t e m p erat ure ramp. There i s no dat a t o
-
su pport a djus t me n t o f e v a p o r a t i v e o r r e f u e l i n g emissions f o r v e h i c l e average speed. However, s i n c e t h e e v a p o r a t i v e c o n t r o l c a n i s t e r i s regenerat ed w h i l e t h e engine i s operated, and t y p i c a l l y t h e s e devices do n o t purge w h i l e t h e en g ine i s i d l i n g , e v a p o r a t i v e emissions c o u l d be e l e v a t e d when v e h i c l e s a r e op e ra t e d a t lo w average speed c h a r a c t e r i z e d by g r e a t e r engine i d l e o p e r a t i o n . W i t h MOBILE 3 a t 32 km/h ( 2 0 mi/h), 39% o f HC emissions were p r o j e c t e d f r o m e v a p o r a t i v e sources a t 24°C (75"F), and 34% a t 38°C (100°F). MOBILE 3 and MOBILE 4 NMHC e m i s s i o n r a t e s . Tailpipe,
evaporative,
and
refueling
HC
emissions
F ig. 12 compares are
emitted
at
98 different
times
considering
and
the
locations
during
impact o f motor
normal
vehicle
vehicle
emissions
operation.
When
on atmospheric
ozone,
however, t h e aggregate o f these sources must be considered. o f t h e VOC emissions from t a i l p i p e ,
evaporative,
The composition
and r e f u e l i n g sources a r e
d i f f e r e n t and t h e aggregate composition w i l l , t h e r e f o r e , depend on t h e r e l a -
88.5 km/h, 37.8OC
8.0 k d h , 37.8OC
< E
m
10
.$ 81 m U
12
0
I
6.35
10
d
cr8 m
6
u 6
4
.2 4
.II 2
.II 2
u
w o
C 0 .ri
C
v1
E
n
v1
E
Mob 4 Mob 3
Mob 4 Mob 3 Mode 1
Model
0T a i l p i p e
Evaporative
88.5 k d h , 23.9.C
Refueling 8 . 0 km/h.
23.9"C
< E
12 m 10
oi
cle m
c 0
.rl
ul
4
2 2 E w o
Mob 4 Mob 3 Model
F i g . 12.
Model
Mobile 3 versus M o b i l e 4 NMHC emission r a t e s .
t i v e amounts o f each.
Considering v e h i c l e c a t e g o r i c a l emission s t r e n g t h s and
VKT (see Table 2 ) , l i g h t - d u t y g a s o l i n e v e h i c l e s , r e s p o n s i b l e f o r about 802 o f t o t a l VOC, dominate t h e aggregate composition.
The compositions o f l i g h t - d u t y
g a s o l i n e v e h i c l e t a i l p i p e , e v a p o r a t i v e , and r e f u e l i n g VOC emissions have been examined and Table 3 provides data r e f l e c t i v e o f each source ( r e f . 1 4 ) . values
presented
gasolines.
are
considered
reasonable
for
currently
marketed
The U.S.
The Motor V e h i c l e Manufacturers A s s o c i a t i o n p e r i o d i c a l l y p u b l i s h e s
surveys o f n a t i o n a l g a s o l i n e c h a r a c t e r i s t i c s a s i n d i c a t e d i n Table 4 ( r e f .
15).
Emissions composition would be expected t o v a r y as t h e range o f g a s o l i n e
composition.
99 TABLE 3. T a i l p i p e , e v a p o r a t i v e , and r e f u e l i n g hydrocarbon e m i s s i o n s c o m p o s i t i o n
-------_-----___-_______________________------------------------------_--_--_________-_______________________-----------------------------Hydrocarbon C1a s s i f ica t i on
Ta i1p i p e
Evaporative
Refueling
55 5 4 18 25 2
72 23 15 10
85 32 19
paraffinic, % n-butane, % isopentane, % olefinic, % aromatic, % acetylenic, %
11 4
18
-_______________________________________------------------------...................................................................... Source:
Black (1988)
Both e v a p o r a t i v e volatile paraffinic Considering refueling
the
sources
and r e f u e l i n g emissions
components o f g a s o l i n e ,
fractional
contributions
indicated i n Fig.
a r e dominated b y t h e more
e.g. of
n-butane and isopentane.
tailpipe,
evaporative,
and
11, t h e c o m p o s i t i o n o f t h e aggregate
emissions w i l l v a r y w i t h speed and ambient t e m p e r a t u r e as i n d i c a t e d i n F i g . 13.
T h i s p r e s e n t a t i o n assumes, a t t h e r i s k o f o v e r s i m p l i f i c a t i o n , t h a t t a i l -
p i p e , e v a p o r a t i v e , and r e f u e l i n g e m i s s i o n s c o m p o s i t i o n s a r e n o t h i g h l y s e n s i t i v e t o speed and temperature, are, i.e.
b u t t h a t t h e r e l a t i v e c o n t r i b u t i o n s o f each
t h e compositions o f t a i l p i p e , e v a p o r a t i v e , and r e f u e l i n g e m i s s i o n s
i n d i c a t e d i n Table 3 a r e used i n a l l speed-temperature s c e n a r i o s . g a t e compositions ranged f r o m 70.8% p a r a f f i n i c (21.7% n-butane,
TABLE 4 Gasoline c o m p o s i t i o n
-
The aggre-
14.1%
isopen-
summer, 1986, w i n t e r 1986/1987
............................................................................. ............................................................................. Regular Leaded
Regular Unleaded
Premium Unleaded
SUMMER FUELS, JULY 1987 RVP, kPal R+M 2 Paraffinic, % Olefinic, % Aromatic, %
Octane,
71.0 (60.0
-
80.7) 89.8) 62.0 (55.6 - 68.3) 10.8 (6.6 - 15.0) 27.3 (23.9 - 31.3) 88.6 (86.2
71.7 86.9 59.8 10.6 29.5
(57.9 - 80.0) (85.1 88.4) 54.0 - 65.5) 7.3 - 16.1) (25.7 33.3)
-
t
-
73.8 91.8 58.3 7.1 34.6
(57.2 - 80.0) (89.6 - 92.5) 50.4 - 67.7) 3.7 - 13.5) (26.4 - 40.6)
I
W I m U E L S , JANUARY 1987 RVP, kPa
R+M
Octane, Paraffinic, % Olefinic, % Aromatic, %
93.1 (70.3 88.6 (85.1
-
-
110.3) 91.5)
93.1 87.3 62.1 5.9 32.0
-
(72.4 114.5) (84.0 - 90.8) (43.3 78.0) (2.2 - 16.6) (17.1 47.5)
92.4 91.8 59.9 5.1 35.0
(75.8 - 106.9) (85.9 - 94.7) (46.3 - 80.8) (1.0 - 14.0) (15.0 - 45.6)
............................................................................. NA NA NA
RVP - R e i d Vapor Pressure: Source: MVMA (1987)
average ( r a n g e )
100 tane), 10.8% o l e f i n i c , 18.2% aromatic, and 0.2% a c e t y l e n i c hydrocarbon a t 38°C (lOO°F),
88
km/h
(55
mi/h)
to
59.5%
paraffinic
(9.6% n-butane,
6.8%
isopentane), 16.2% o l e f i n i c , 22.9% aromatic, and 1.4% a c e t y l e n i c hydrocarbon a t 24°C (75"F), 8 km/h ( 5 mi/h).
The c o n t r i b u t i o n o f n-butane and isopentane
ranged from 35.8% a t 38°C (lOO°F), 88 km/h (55 mi/h) t o 16.4% a t 24°C (75"F), 8 km/h (5 mi/h). A t lower temperatures, the aggregate would be more dominated by t a i 1p i p e emi ss ions composition.
8 km/h,
88 km/h,
37.8.C
37.8OC
/ ther--35
other--39.8 isopentane--g.8 n-butane--14.5
Olef i n i c
isopentane--l4.1 -butane--21.7
18. 0.
@ Aromatic @ Acetylenic
8 km/h, 23.9OC
88.5 km/h, 23.9OC ther--38.2 18.
isopentane--6.8
Fig. 13. Aggregate hydrocarbon emissions ambient temperature and average speed.
Methane,
n o t being a component
eopentsne--l2.2
composition as
o f gasoline,
a function o f
i s emitted e x c l u s i v e l y
from the t a i l p i p e during engine operation. Over the temperature and speed array o f t h i s presentation, t h e CH4 f r a c t i o n o f t a i l p i p e emissions i s n o t h i g h l y v a r i a b l e f o r any selected calendar year. For example, d u r i n g 1985 c o n s t i t u t e d 5.69 f 0.23% o f t a i l p i p e THC emissions over the e n t i r e temperature-speed array. Because of t h e v a r i e d c o n t r i b u t i o n o f t a i l p i p e
CH4
emissions t o the t o t a l aggregate,
t h e CH4 f r a c t i o n o f the aggregate v a r i e d
from 0.58% a t 88 km/h (55 mi/h), 38°C (100°F) t o 4.92% a t 8 km/h (5 mi/h), -3.9"C (25°F). CH4 i s n o t reduced as e f f e c t i v e l y by c a t a l y s t c o n t r o l systems as other HC's, and therefore, t y p i c a l l y c o n s t i t u t e s a l a r g e r Thus, t h e CH4 f r a c t i o n o f f r a c t i o n o f exhaust from w e l l c o n t r o l l e d cars. t a i l p i p e and aggregate emissions increases w i t h calendar year. During
101 1975 CH4 c o n s t i t u t e d 5.00% o f t a i l p i p e and 2.95% o f aggregate HC emissions a t 32 km/h (20 mi/h), 24°C (75OF); and during the year 2000, i t i s p r o j e c t e d t o c o n s t i t u t e 8.99% o f t a i l p i p e and 4.57% o f aggregate HC emission a t 32 km/h (20 mi/h), 24°C (75°F).
The CH4 f r a c t i o n o f t a i l p i p e HC emissions from w e l l
c o n t r o l l e d cars has a l s o been reported t o be s e n s i t i v e t o speed and ambient temperature ( r e f s . 16, 17).
The CH4 f r a c t i o n decreases w i t h decreased average
speed, and w i t h decreased ambient temperature. With w e l l c o n t r o l l e d cars, operating conditions causing increased t a i l p i p e THC emissions w i l l r e s u l t i n decreased CH4 f r a c t i o n s . With
transportation
being
the
primary
source
of
anthropogenic
CO
emission (70% i n 19851, t h e r e has been i n t e r e s t i n using t h i s compound as a t r a c e r f o r motor v e h i c l e emissions.
Lead has been used f o r t h i s purpose
h i s t o r i c a l l y , b u t i s r a p i d l y being phased o u t o f gasoline, and fewer and fewer roadway vehicles are compatible w i t h leaded f u e l s .
Fig.
14 provides an
i n d i c a t i o n o f the v a r i a t i o n o f NMHC and NOx r a t i o s t o CO as a f u n c t i o n o f v e h i c l e speed and ambient temperature.
Over the scenarios examined NMHC/CO
r a t i o s v a r i e d from 0.098 a t 8 km/h (5 mi/h) and
-3.9"C
(25OF) t o 0.594
a t 88
-
37.8.C
......
23.9-C I
1O.O0C 11111111111
-3.9.c 111
"8:O
16.1
2i.l
3i .2
k.3 M . 4
Speed, km/h
ed.6
&.d
-
37.8.C
......
O 0.5 e6*
0 0
0.4
23.9.C
I
-
10.O'C 11111,11111
.
-3.9.c
0.30
z
111
,
0.2
-
Speed, km/h Fig. 14. 1985 f l e e t average NMHC/CO and NOx/CO r a t i o s as a f u n c t i o n o f ambient temperature and average speed.
102 km/h (55 m i / h ) and 38°C (100°F);
and NOx/CO r a t i o s v a r i e d f r o m 0.023 a t 8 km/h
( 5 m i / h ) and 38°C (100°F) t o 0.438 a t 88 km/h ( 5 5 m i / h ) and 24OC (75°F). C h l o r o f l u o r o c a r b o n emissions The f u l l y halogenated c h l o r o f l u o r o c a r b o n s (CFC) most w i d e l y used i n t h e U.S.
a r e CFC-11
(CC13F),
CFC-12
(CC12F2),
and CFC-113
(C2C13F3).
Motor
v e h i c l e s were t h e s i n g l e l a r g e s t nonaerosol s o u r c e o f CFC i n 1976, and a r e p r o j e c t e d t o be second t o s o l v e n t e m i s s i o n s i n 1990 ( r e f . 8 ) .
D u r i n g 1976
29% o f a combined 119 thousand m e t r i c t o n s e m i t t e d i n t h e U.S. m o t o r v e h i c l e a i r c o n d i t i o n i n g systems;
an a d d i t i o n a l
was f r o m
3.8% was f r o m t h e
p r o d u c t i o n o f f l e x i b l e foam f o r m o t o r v e h i c l e a p p l i c a t i o n s .
Emissions a r e
p r o j e c t e d t o i n c r e a s e t o 250 thousand m e t r i c t o n s d u r i n g 1990 w i t h 22% o f this
total
from
motor
vehicle
air
conditioning
e x c l u s i v e l y used i n m o t o r v e h i c l e a i r c o n d i t i o n i n g ;
systems.
CFC-12
is
CFC-11 i s used i n t h e
p r o d u c t i o n o f f l e x i b l e foam.
T a b l e 5 p r o v i d e s a summary o f m o t o r v e h i c l e
CFC-12 e m i s s i o n sources ( r e f .
18).
most s i g n i f i c a n t sources i n 1976.
R e p a i r s e r v i c i n g and l e a k a g e were t h e V e h i c l e d i s p o s a l i s p r o j e c t e d t o become
an a d d i t i o n a l s i g n i f i c a n t s o u r c e i n 1990 p r o j e c t i o n s .
NO, L
of
emissions It has been e s t i m a t e d t h a t t r a n s p o r t a t i o n c o n t r i b u t e d l e s s t h a n 10% 1985 g l o b a l
a n t h r o p o g e n i c N20 e m i s s i o n s f r o m f o s s i l
fuel
combustion
(ref. 7). S t u d i e s c h a r a c t e r i z i n g m o t o r v e h i c l e N20 e m i s s i o n s a r e sparse when compared t o t h o s e examining r e g u l a t e d THC, C O Y NOx emissions. Table 6 sumnarizes a v a i l a b l e e m i s s i o n s d a t a ( r e f s .
19-25).
Emissions were examined
f r o m v a r i e d v e h i c l e t y p e s under v a r i e d d r i v i n g c o n d i t i o n s . A l t h o u g h t h e d a t a i s l i m i t e d , i t can be concluded t h a t N20 e m i s s i o n s a r e e l e v a t e d a b o u t a n o r d e r of
magnitude
from
gasoline motor
vehicles
using catalysts
compared
to
103
noncatalyst configurations.
Other observations i n t h e a v a i l a b l e data i n c l u d e
an inc re as ed N20 e m i s s i o n r a t e as t h e v e h i c l e average speed i s decreased, i f EGR (exhaust gas r e c i r c u l a t i o n f o r NOx c o n t r o l ) i s d i s a b l e d , and as v e h i c l e i n e r t i a w e i g h t i s increased, passenger c a r emission r a t e s .
i.e. t r u c k emission r a t e s a r e g r e a t e r t han Using t h e v e h i c l e c a t e g o r i c a l average emission
f a c t o r s o f T abl e 6 and t h e 1985 f l e e t VKT d i s t r i b u t i o n , a f l e e t average N20 emis s io n f a c t o r o f about 30 mg/km can be estimated.
T h i s assumes t h a t l i g h t -
d u t y g a s o l i n e VKT i s d i s t r i b u t e d 80-20 c a t a l y s t - n o n c a t a l y s t .
Coupled w i t h
t o t a l f l e e t k i l o m e t e r s t r a v e l e d d u r i n g 1985, highway mot or v e h i c l e s e m i t t e d about 80 thousand m e t r i c t o n s o f N20.
L i ht-duty gasoline ?no c a t a l y s t ) L i ht-duty gasoline ?catalyst) light-duty diesel heavy-duty g a s o l i n e heavy-duty d i e s e l
3.7
1.9
37.9
1.9
NA 45.4 29.2
6.8 29.8 19.3
-
9.9
19,20
145.4
19,20,21,22,23
29.8 60.3 46.6
19 24 24, 25
The dat a base was examined f o r r e l a t i o n s h i p s between N20 emissions and
NOx
(n.38) diesel
emissions.
The
observed
N20/NOx
r a t i o s were
f o r c a t a l y s t equipped g a s o l i n e v e h i c l e s , trucks,
catalysts).
and
0.0055
f
0.0028
(n=2)
0.0018 for
*
0.0437
2
0.0002
(n=5) f o r
gasoline
0.0414
trucks
(no
The " c a t a l y s t equipped" d a t a base i n c l u d e d more t e s t v e h i c l e s
and a l a r g e r a r r a y o f d r i v i n g c o n d i t i o n s , i.e. speed, ambient temperature, m a l f u n c t i o n , and m i l e a g e accumulation, t han t h e t r u c k dat a base. The range o f observed N20/NOx r a t i o s was t h e r e f o r e g r e a t e r t h a n observed w i t h the trucks. There i s no c e r t a i n t y t h a t t h e t r u c k s w i l l e x h i b i t t h e same s e n s i t i v i t y t o these variables. As t h e w o r l d ' s v e h i c l e f l e e t s h i f t s t o c a t a l y s t t e c hnol o g y f o r abatement o f u r b a n ozone, CO and NOx, t h e c o n t r i b u t i o n o f t r a n s p o r t a t i o n sources t o g l o b a l N20 burden w i l l grow. Carbon d i o x i d e emissions As p r e v i o u s l y mentioned,
highway m o t o r v e h i c l e s
were e s t i m a t e d
t o be
r e s p o n s i b l e f o r about 24% o f C02 emissions f r o m 1985 f o s s i l f u e l combustion i n t h e U.S.
( r e f . 10).
The e m i s s i o n r a t e o f C02 f r o m motor v e h i c l e s i s a
104 function
of
fuel
economy and f u e l
consumed per kilometer driven, Significant
fuel
characteristics,
i.e.
and grams o f carbon
l i t e r s o f fuel
per l i t e r o f
fuel.
economy improvements have been r e a l i z e d i n the U.S.
in
recent years as a consequence o f the combined e f f e c t s o f market demand and federal regulations.
Fig.
15 i s i l l u s t r a t i v e o f f u e l economy improvements
i n both l i g h t - d u t y and heavy-duty v e h i c l e categories since 1975 w i t h p r o j e c t i o n s t o t h e year 2000 ( r e f . 3).
\
E
Y
10
>;8 E 0
= 6 0
"
75 80 85 90 95 00 Year
Light-Duty Vehicles Heavy-Duty V e h i c l e s All V e h i c l e s Source: Mobile 3 F u e l Consumption Model EPA-AA-TEP-EF-85-2, Feb. 1985 Fig. 15. Motor v e h i c l e f u e l economy, 1975 t o 2000. The two m a j o r t r a n s p o r t a t i o n typically
have 619 t o
respectively.
654 and
fuel
categories,
gasoline
and d i e s e l ,
706 t o 741 grams of carbon per l i t e r , respec-
Most o f t h i s carbon i s converted t o C02 w i t h l e s s e r amounts
t o CO and HC during combustion i n motor v e h i c l e engines.
C02 emission r a t e s
can be c a l c u l a t e d from f u e l economy data according t o the carbon balance relationship:
105
C02, glkm = ((KlxFD, where:
gla)
1 FE, kmla
- K1xHC,
g/km
- K2xC0,
K1 = carbon weight f r a c t i o n o f f u e l = .866;
f r a c t i o n o f CO = .429;
glkm) 1 K3
(3)
K2 = carbon weight
K3 = carbon weight f r a c t i o n o f C02 = .273;
FD = f u e l
density; and FE = f u e l economy. Combining MOBILE 4 THC and CO emissions data w i t h f u e l economy data,
C02
emission r a t e s can be c a l c u l a t e d as presented i n Table 7.
The trend, w i t h
improved f u e l economy, has been reduced C02 emission rates.
During t h e 1975
t o 1985 decade, the f l e e t average C02 emissions r a t e was reduced about 22%. During t h a t same period o f time VKT increased 30% (as i n d i c a t e d i n Fig. l), thus increasing the atmospheric C02 burden from motor v e h i c l e s on roadways i n the U.S.
Combining the estimated f l e e t average emission r a t e with estimated
nationwide miles traveled, metric tons o f COP i n 1985.
highway motor vehicles emitted about 0.9
billion
This value i s somewhat lower than t h e 1.1 b i l l i o n
metric tons estimated by DeLuchi, e t a l . ( r e f . 10).
1975 1985 1995
352.4 270.0 208.8
395.8 330.8 284.8
614.4 532.5 555.3
283.3 236.1 199.5
204.2 271.0 252.0
1293.7 1076.1 908.1
426.2 334.1 268.2
SUMMARY AND CONCLUSIONS
Stratospheric and tropospheric ozone concentrations are c o n t r o l l e d by complex chemical and physical processes which are influenced by both anthropogenic and biogenic emissions a t the earths surface. One o f t h e most r a p i d l y growing human a c t i v i t i e s important t o atmospheric ozone i s the use o f highway motor vehicles. Miles d r i v e n by American m o t o r i s t have increased 58% since 1970. There are many compounds emitted from highway motor vehicles t h a t p a r t i c i p a t e i n atmospheric processes important t o ozone formation and/or destruction i n c l u d i n g VOC, CO, NOx, C02, N20, and CFC-12. It has been estimated t h a t during 1985 7.2 m i l l i o n m e t r i c tons o f VOC were emitted from U.S. t r a n s p o r t a t i o n sources (about 34% o f the anthropogenic t o t a l ) , 47.5 m i l l i o n m e t r i c tons o f CO (about 70% o f the anthropogenic t o t a l ) ,
and 8.9
106 m i l l i o n m e t r i c t o n s o f NOx (about 45% o f t h e anthropogenic t o t a l ) .
Recent
improvements t o MOBILE 3, t h e model used t o c a l c u l a t e f l e e t average emission
will
factors,
increase the estimated transportation
contribution
to
VOC
emissions t o n e a r l y 50% o f t h e anthropogenic t o t a l .
Sumner month e v a p o r a t i v e
hydrocarbon emission
increased.
estimates
are
significantly
U.S.
motor
v e h i c l e s were a l s o estimated t o have been r e s p o n s i b l e f o r about 48 thousand m e t r i c t o n s of CFC d u r i n g 1985 (25% of U.S. anthropogenic t o t a l ) , and about 1 b i l l i o n m e t r i c tons o f COP (14% o f t h e anthropogenic t o t a l ) . Motor v e h i c l e s c o n t r i b u t e l e s s than 10% o f anthropogenic N20 emissions, b u t t h i s c o n t r i b u t i o n i s expected t o grow as t h e f r a c t i o n o f c a t a l y s t equipped v e h i c l e s increases. Through t h e c o o p e r a t i v e e f f o r t s o f government and i n d u s t r y , s u b s t a n t i a l reduction decade.
o f motor v e h i c l e
emissions
has been achieved d u r i n g
the past
From 1975 t o 1985, motor v e h i c l e VOC emission r a t e s were reduced
about 57%, CO r a t e s about 62%, NOx r a t e s about 35%, and C02 r a t e s about 22%. Much o f t h i s r e d u c t i o n was o f f s e t ,
however,
by a c o n c u r r e n t 30% growth o f
VKT. Motor v e h i c l e emission r a t e s a r e s e n s i t i v e t o d r i v i n g c o n d i t i o n s such as speed,
temperature, and a l t i t u d e .
G e n e r a l l y , VOC and CO emission r a t e s
a r e increased by reduced average speed. NOx emission r a t e s , n o t as s e n s i t i v e t o speed,
a r e g e n e r a l l y minimumized a t about 32 t o 48 km/h and i n c r e a s e
s l i g h t l y a t lower and h i g h e r average speeds.
VOC and CO emission r a t e s a r e
minimumized a t about 24°C (75°F) and i n c r e a s e a t l o w e r and h i g h e r temperatures.
NOx
emission
rates
increase
as
ambient
temperature
is
reduced.
T y p i c a l l y , VOC and CO emissions r a t e s i n c r e a s e as a l t i t u d e i s increased, and NOx emission r a t e s decrease. t h e emissions,
These v a r i a t i o n s i n f l u e n c e t h e NMHC/NOx r a t i o o f
an i m p o r t a n t c o n s i d e r a t i o n t o t r o p o s p h e r i c ozone chemistry.
T h i s r a t i o v a r i e s from about 0.7
t o 5.3 over t h e examined range o f d r i v i n g
conditions.
VOC emissions from motor v e h i c l e s o r i g i n a t e from t a i l p i p e , and r e f u e l i n g sources.
evaporative,
The composition o f each i s d i f f e r e n t , w i t h t h e more
v o l a t i l e C4 and C5 p a r a f f i n s dominating e v a p o r a t i v e emissions and, even more
s o , refueli,ng emissions. The aggregate emissions composition w i l l depend on t h e r e l a t i v e c o n t r i b u t i o n o f each, a f u n c t i o n o f v e h i c l e speed and ambient temperature.
A t 24°C (75"F), 8 km/h (5 mi/h),
1985 motor v e h i c l e VOC emis-
s i o n s were about 77% t a i l p i p e , 19% evaporative, and 4% r e f u e l i n g ; a t 38°C (lOO°F), 88 km/h (55 mi/h) t h e emissions were about 10% t a i l p i p e , 86% evapora t i v e , and 4% r e f u e l i n g .
The aggregate composition was 60% p a r a f f i n i c , 16%
o l e f i n i c , 23% aromatic, and 2% a c e t y l e n i c a t 24°C ( 7 5 " F ) , 8 km/h ( 5 m i / h ) ; and 71% p a r a f f i n i c , 11%o l e f i n i c , 18% aromatic, and 1%a c e t y l e n i c a t 38°C (lOO"F), 88 km/h (55 mi/h).
107 CFC-12,
t h e primary chlorofluorocarbon emitted from. motor vehicles,
r e s u l t s p r i m a r i l y f r o m a i r c o n d i t i o n i n g r e p a i r s e r v i c e and leakage. d i s p o s a l i s p r o j e c t e d t o become a s i g n i f i c a n t source b y t h e 1990's. U.S.
Vehicle motor
v e h i c l e CFC emissions a r e p r o j e c t e d t o be about 55 thousand m e t r i c t o n s p e r y e a r by
1990.
N20 emissions f r o m m o t o r v e h i c l e s have n o t been w i d e l y
s t u d i e d , b u t a v a i l a b l e d a t a suggests t h a t e m i s s i o n r a t e s v a r y o v e r a b o u t an order-of-magnitude
range
f r o m about
3.7
mg/km
from noncatalyst
gasoline
passenger c a r s t o about 37 mg/km f r o m c a t a l y s t s equipped g a s o l i n e passenger cars.
L i m i t e d d a t a suggests t h a t heavy-duty t r u c k e m i s s i o n r a t e s a r e g r e a t e r
t h a n passenger c a r e m i s s i o n r a t e s configurations).
( w i t h s i m i l a r engine emission c o n t r o l
F l e e t average C02 e m i s s i o n r a t e s were reduced f r o m about 426
g/km i n 1975 t o about 334 g/km i n 1985. F u r t h e r emission
rate
reduction
v e h i c l e tampering and m i s f u e l i n g , the
Congress
U.S.
evaporative,
is
i s possible
through c u r t a i l m e n t o f
and improved maintenance.
considering
expanded
Additionally,
regulation
and r e f u e l i n g emissions, and f u e l composition.
of
tailpipe,
U l t i m a t e l y , as
t h e p o t e n t i a l o f emission r a t e r e d u c t i o n becomes r e a l i z e d , o n l y c u r t a i l m e n t o f VKT growth w i l l be a v a i l a b l e t o l i m i t motor v e h i c l e emissions. ACKNOWLEDGEMENTS A l t h o u g h t h i s r e p o r t has been s u p p o r t e d b y t h e U n i t e d S t a t e s E n v i r o n mental P r o t e c t i o n Agency, therefore,
i t has n o t been s u b j e c t e d t o Agency r e v i e w and,
does n o t n e c e s s a r i l y r e f l e c t
t h e views o f t h e Agency and no
o f f i c i a l endorsement s h o u l d be i n f e r r e d .
The a u t h o r wishes t o acknowledge
and express g r a t i t u d e t o Susan Bass f o r a s s i s t a n c e i n m a n u s c r i p t p r e p a r a tion.
REFERENCES 1.
L.M. Thomas, Next Steps i n t h e B a t t l e A g a i n s t Smog, EPA J o u r n a l , 13(8) (1987) 2-4. - .R.T. Watson, M.A. G e l l e r , R.S. S t o l a r s k i , and R.H. Hamoson. Present S t a t e o f Knowledge o f t h e Upper Atmosphere: Processes t h a t C o n t r o l Ozone and O t h e r C1 i m a t i c a l l-y I m.p o r t a n t Trace Gases, NASA Assessment Report, January , 1986. M.A. Wolcott, D.F. Kahlbaum, MOBILE 3 Fuel Consumption Model, EPA-AA-TEB-EF-85-2, U.S. Environmental P r o t e c t i o n Agency, O f f i c e of M o b i l e Source, Ann Arbor, M I , February, 1985. M. Casey, 1986 M o t o r V e h i c l e Tampering Survey R e s u l t s Issued, U.S. EPA Press Release, October 6, 1987. N a t i o n a l A i r P o l l u t i o n Emission Estimates, 1940-1985, EPA-450/4-86-109, U.S. Environmental P r o t e c t i o n Agency, O f f i c e o f A i r Q u a l i t y P l a n n i n g and Standards, Research T r i a n g l e Park, N.C., January, 1987. \ - - - .
2.
3.
4. 5.
I
ino
-
V o l a t i l i t y Regulation f o r 1989 and L a t e r Notice o f Proposed Rulemaking Comnercial Gasoline. Review D r a f t , U.S. Environmental P r o t e c t i o n Agency, O f f i c e o f Mobile Source, Ann Arbor, M I , March, 1987. EPA Workshop on N 0 Emissions from Combustion, EPA-600/8-86-035, U.S. 7. Environmental Pro&ction Agency, A i r and Energy Engineering Research Laboratory, Research T r i a n g l e Park, N.C. September, 1986. Economic I m p l i c a t i o n s o f Regulating Chlorofluorocarbon Emissions from 8. Nonaerosol Applications , EPA-560/12-80-001 , U.S. Environmental P r o t e c t i o n Agency, O f f i c e o f P e s t i c i d e s and Toxic Substances, Washington, D.C. , October, 1980. H.A. Mooney, P.M. Vitousek, and P.A. Matson, Exchange o f M a t e r i a l s 9. Between T e r r e s t r i a l Ecosystems and t h e Atmosphere, Science, November 13, 1987, pp. 926-932. 10. M.A. DeLuchi, R.A. Johnston, and D. Sperling, Transportation Fuels and the Greenhouse E f f e c t , UER-182, Universitywide Energy Research Group, U n i v e r s i t y o f C a l i f o r n i a , Davis, CA, December, 1987. (Mobile Source Emissions Model), Guide to MOBILE 3 11. User's EPA-460/3-84-002 , U.S. Environmental P r o t e c t i o n Agency, Motor Vehicle Emissions Laboratory, Ann Arbor, M I , June, 1984. 12. U.S. Code o f Federal Regulations, T i t l e 40, Part 86 Control o f A i r P o l l u t i o n from New Motor Vehicles and New Motor Vehicle Engines' C e r t i f i c a t i o n and Test Procedures, July, 1983. 13. Dodge, M.C. , Combined E f f e c t s o f Organic R e a c t i v i t y and NMHC/NOx R a t i o on Photochemical Oxidant Formation A Modelling Study, Atmos. Env., 18 (1984) 1657-1665. Hydrocarbon Emissions from Late Model Gasoline Motor 14. F. M. Black, Vehicles, JAPCA, i n review, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, N.C. January, 1988. 1986/1987, Motor 15. MVMA National Gasoline Survey: Sumner -1986, Winter Vehicle Manufacturers Association, D e t r o i t , M I , 1987. 16. J.E. Sigsby, S. Tejada, and W. Ray, V o l a t i l e Organic Compound Emissions from 46 In-use Passenger Cars, Environ. Sci. Technol. 21(5) (1987) 466-475. 17. F. Stump, S. Tejada, W. Ray, D. Dropkin, F, Black, W. Crews, R. Snow, P. Suidak, C.O. Davis, L. Baker, and N. Perry, The I n f l u e n c e o f Ambient Temperature on T a i l p i p e Emissions from Late Model Light-Duty Gasoline Motor Vehicles, Atmos. Env. , i n review, U.S. Environmental P r o t e c t i o n Agency, Research T r i a n g l e Park, N.C. January, 1988. 18. R. E. Burt, Domestic Use and Emissions o f Chlorofluorocarbons i n Mobile A i r Conditioning , I n t e r n a t i o n a l Research and Technology Corporation, F i n a l Report #IRT-20000/1, A p r i l , 1979. 19. BMW AG, Annual Report t o USEPA on Emissions Characterization i n Compliance w i t h Section 202(1)(4) o f t h e Clean A i r Act, U.S. Environmental P r o t e c t i o n Agency, O f f i c e o f Mobile Sources, Ann Arbor, M I , December , 1986. 20. C.M. Urban, and R.J. Garbe, Regulated and Unregulated Exhaust Emissions from Malfunctioning Automobiles, SAE 790696, Society o f Automotive Engineers, Warrendale, PA, June, 1979. 21. J.N. Braddock, Impact o f Low Ambient Temperature on 3-way C a t a l y s t Car Emissions, SAE 810280, Society o f Automotive Engineers, Warrendale, PA, February , 1981. 22. L.R. Smith, and F.M. Black, Characterization o f Exhaust Emissions From Passenger Cars Equipped w i t h 3-way C a t a l y s t Control Systems, SAE 800822, Society o f Automotive Engineers, Warrendale, PA, June, 1980. 23. L.R. Smith and P.M. Carey, Characterization o f Exhaust Emissions from High Mileage Catalyst-equipped Automobiles, SAE 820783, Society o f Automotive Engineers, Warrendale, PA, June, 1982. 24. H.E. Dietzmann, M.A. Parness, and R.L. Bradow, Emissions from Gasoline and Diesel D e l i v e r y Trucks by Chassis Transient Cycles, American Society of Mechanical Engineers, New York, NY, October, 1981. 6.
-
-
-
25. H.E. Dietzmann, M.A. Parness, and R.L. Bradow, Emissions from Trucks by Chassis Version of 1983 Transient Procedure, SAE 801371, Society o f Automotive Engineers, Warrendale, PA, October, 1980.
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T.Schneideret al. (Editors),Atmospheric Ozone Research and its PolicyImplications 0 1989 Elsevier Science PublishersB.V.,Amsterdam - Printed in The Netherlands
111
EMISSION INVENTORIES FOR EUROPE
C. Veldt M.T.-TNO, P.O. Box 3 4 2 , 7300 AH
Apeldoorn (The Netherlands)
ABSTRACT An overview is given of the efforts made in Europe on air pollutant inventories of NOx and VOC, accomplished ones as well as those in progress. Differences and similarities both in data bases and results are indicated. Available data are confronted with what is needed by atmospheric scientists for modeling purposes. An attempt is made to summarize available knowledge about emission estimation techniques. From these two follow incompletions in emission data and gaps in the knowledge to estimate them. Priorities are suggested for the work that should be done for minimizing the difference between data supply and demand. Continuation of international cooperation is advocated.
1. INTRODUCTION
It is well known that nitrogen oxides and organic substances largely control photochemistry during episodes, the mayor substance of concern being ozone. In addition to these, carbon monoxide and methane have been recognised to be also of influence on long-term atmospheric phenomena such as the fate of ozone in the free troposhere. Further, several chemical species that for long were considererd as unimportant in atmospheric chemistry appeared to really cause adverse effects. Examples of these are chloro-fluoro-hydrocarbons and nitrous oxide. Of all these substances the emissions of nitrogen oxides have been estimated for some time, together with sulfur oxides. The latter, hardly important as precursors of ozone, have an even longer history of emission inventorying. Of the other species, having attracted attention only later, less emission data are available. The only exceptions to this are carbon monoxide that usually is inventoried simultaneously with NO,
and SO, and volatile organic substances
that only recently took the same place. The collection of emission data often started with the estimation of national annual totals for some base year and for some main source categories. Next, episodic model studies initiated the acccumulation of experience in making detailed inventories because they need spatially and temporally resolved input data, but this experience in general is restricted to the "classic" pollutants NO, and SOx and, to some lesser extent,
112 to organic compounds as a sum. The addition to data bases of technical and economical data made it possible to update inventories and study abatement scenarios. Since the study of long-term effects does not need such details, emission estimations of CO, CH4 etc. until now have only been made on a global scale. It has been learnt that natural sources of these species are larger contributors to initial concentrations in the air than antropogenic activities (with the exception of CLF-hydrocarbons). And since the understanding of the contribution of natural processes to atmospheric phenomena is very incomplete, the estimation of emissions of these substances still is developing. Therefore, for a discussion about what has been achieved and what is being done in Europe in the field of emission inventorying a restriction is made here to oxides of nitrogen and organic substances. 2. DEFINITIONS
Although consensus exists nowadays about what is meant by NO,,
there is not
yet a similar acceptance about organic compounds. In this paragraph therefore an attempt is made to define a term that is unambiguous with respect to atmospheric scientists' needs. The still used word "hydrocarbons" (HC), that at least linguistically excludes substances like alcohols and ketones, should not be used any more. Instead, all organic compounds should be involved. Users of emission data bases should decide what substances are of interest. Data base developers should present anything that their knowledge allows. In this way total organic emissions-notably from combustion sources consist
of
solid
and
liquid
particulate
as
well
as
-
will
gaseous material.
Particulate fractions could raise a problem in quantifying reactivity. For emission estimations in Europe this problem can be ignored because organic emissions form industrialized countries for a very large part consist of volatile substances. (However, for regions where the combustion of biomass considerably contributes to total organic emissions, attention should be given to this in clearly defining the emission factors involved). Thus, for emission inventorying a useful term for organic matter is "volatile organic compound(s)". The definition of VOC might be: any organic substance that, released into the atmosphere, is present there in the gaseous state. This definition is pragmatic in that volatility is not defined. Meanwhile the term gradually has found its way in the field of atmospheric science. VOC emissions should be reported without exclusions. Distinctions between substances on account of their reactivity should be bases only upon composition profiles. That is, wherever NMVOC is reported, the methane fractions should be given also.
113 3 . OVERVIEW OF EMISSION IVENTORIES
In Europe the first international programme on emission estimation was started by the OECD in the early seventies. A result of this activity was the Geneva ECE Convention on Air Pollution. Since 1983 the OECD has its Major Air Pollutants project (MAP), whereas about the same time the CEC started an inventory of emissions form large combustion sources in member countries and the Federal Republic of Germany and the Netherlands commenced a programme for Photochemical Oxidants and Acid Deposition Model Application (PHOXA). The acidification study of IIASA as well as the newest development, the CEC's programme on information about the state of the environment (CORINE) part of which is the CORINAIR project on information about air pollutants need also be mentioned. Mention could further be made of many national projects for the inventorying of national emissions or for air pollution studies for which transboundary inventories have been or are developed. It will be clear from this very brief survey that a considerable acceleration of emission inventorying activities has taken place in the last few years: obviously, as a result of an acceleration in atmospheric science. Maybe it is characteristic for a development like this that several inventories, serving different objectives, were developed more or less simultaneously although they have much in common. Meanwhile, fortunately, also a - still increasing cooperation has started and maybe it is no demonstration of over-optimism when a joint European air pollutants data base can be foreseen in the near future. Results of these activities are summarized in tables 1 and 2 . The amount of footnotes accompanying these tables might serve as an illustration of an European data base not yet about to be established. Similarities more often can be read from these tables than marked differences. Many of the latter can be explained, but within the scope of this survey this would go too far. Some remarks are appropriate, however: data bases a) A good agreement is to be expected between the OECD - and ECE
-
because both are filled with officially approved data. b) National methodologies for emission estimation, underlying OECD
-
and ECE
data, expectedly have less in common than they could have. c) The data used in the PHOXA-project and in IIASA's RAINS model are the result of work of research teams who basically operated independently of national experts, using chosen emission factors and published statistics. Consequently, emission data show inherent uniformities that can be considered to be too large. For a survey of similarities and differences between these projects reference is made to table 3 .
114 As a final comment it may be said, that in view of the growing awareness of the importance of reliable emission data and the increasing international cooperation in emission inventorying, emission data from European countries will be produced in the near future that are based on a common methodology but also
reflect
deviations
because
of
characteristic
differences
between
countries. In other words, in such a situation there always will be sound, technical reasons for the use of different emission factors. 4 . DEMAND AND SUPPLY
Cleaning the atmosphere obviously is the ultimate objective of air pollution studies. For this, concerted action of scientists, abatement engineers, economists and politicians is required and the emission inventory developer has to present his data in such a form and to such detail that the different diciplines are not at a loss about what to do with some quantification of the effects of human behaviour on the environment. In other words, by comparing the emission data users' needs - or demands
-
with the supplied inventory developers'
knowledge, gaps between the two will appear and attention should be focused on these. The study of atmospheric pollution needs, as far as modeling is concerned, spatially and temporally resolved emission data of selected substances and information about the extent of the penetration of emissions into the atmosphere. The degree of temporal resolution depends on the type of model used. Long-term models, especially when operated with statistical meteorological data, only require seasonal or yearly average emissions. Episodic models, on the other hand, need a temporal resolution down to one or some hours, because they are operated in a real time mode. Concentrations and depositions of pollutants can vary
considerably in time because
of
changing meteorological conditions
(temperature, relative humidity, UV-light intensity, rainfall etc.) and because of varations in emissions (some of which also are influenced by meteorological phenomena). Spatial resolution depends on the sophistication of the model. In practice values of grid cell sizes have a range of one order of magnitude. The organization of pollution abatement requires some technical background data about emissions. The type of activity - in economic terms - and its intensity - in capacity and production units
-,
installations connected to one spe-
cific stack, fuel data and abatement appliances in use are examples that serve this objective. They can also be used by economists to put in their scenarios. With the feedback of results, modelers continue to predict the outcome of proposed changes that, finally, enables policy makers to make a choice.
115 The inventory developers' knowledge can be listed by a description of the emission registration projects that take place in Europe nowadays. It should, however, be
emphasized
that, due
to
the
consequences of
international
cooperation and the independently developed histories of emission inventorying in countries, the present scope of these projects does not fully reflect todays' state-of-the-art. In table 3 ongoing work is presented in a simple scheme. It can e.g. be seen that only PHOXA has highly resolved emission data. But it obviously would be incorrect to conclude from this that the other projects do not have the means for this (insofar they need it). At first sight, then, table 3 presents a fairly complete set of instruments, apart from only PHOXA having information about VOC compositions. Of course this is not surprising since organizers of these projects can be expected to have done a complete as possible job. However, in the background is one European data base (which might be called EURAD). The increasing cooperation between projects already has been mentioned. Proposals for the organization of such a data base already have been submitted [1,21
So one could compare the demand with a supply that provides anything (or, at least, most) that is necessary for any modeling study, abatement strategy development and policy making. It will appear, then, that gaps in the knowledge of emission inventorying are found mainly among emission factors and temporal allocation procedures. 5. GAPS IN EMMISION INVENTORYING It is commency understood that the main contributors to air pollution by NOx and VOC are:
- large combustion sources - road traffic
-
solvent evaporation
- vegetation The first two emit between 80 an 90% of antropogenic NO,.
The second and third
emit about three quarters of antropogenic VOC. Although NO, emission factors for stationary combustion sources have been and still are
-
subject to intensive discussion, it is questionable whether
more measurements will add substantially to the quality of NOx estimation in terms of systematic error (quality in terms of uncertainty certainly can be improved by compiling and analyzing as much as possible reliable measurement data in the right way). To stimulate harmonization the CORINAIR project requested a group of experts on NO,
formation to discuss the present knowledge and propose a set of NO,
116 emission factors to be used in the project. The group recently finished its task. Of course, the proposed factors are not the final answer. Instead, they reflect the present state-of-the-art. Another remark that should be made is that in the CORINAIR project these factors are not meant to arrive at some artificial uniformity. Evidently there are differences between - and also in
-
countries that need be taken into account. Harmonization should be understood as a common basis with which differences in estimation techniques can be accounted for. More or l e s s the same can be said about mobile NOx sources. But contrary to stationary emitters, mobile ones - especially gasoline powered vehicles
-
still
are likely to have a systematic error because of incomplete understanding of the influence of cold starts and subsequent driving with a warming-up engine. (The influence on NOx of cold starting, as a matter-of-fact, is far less pronounced than is the case with VOC and CO. More serious is the still inadequate estimation of transiently driven vehicle kilometers). Another difference with stationary sources is that CORINAIR up to now has no expert group for mobile ones. Work is in progress, however, to establish one soon.
From the above it appears that, with respect to emission factors, the improvement of inventorying is necessary for VOC in the first place. About mobile sources as total exhaust VOC emitters the same remarks that have been made about NO, and valid, but the need of a reliable cold start correction is more evident. Another source of VOC from vehicles is the evaporation of gasoline. In contrast to the US, in Europe not much attention has been paid to this source that is estimated to emit about lo6 tons of gasoline vapour annually in OECD-Europe [ 3 ] . Recent investigations, however, raise the expectation that this gap can be filled [ 4 ] . It is very important to sufficiently investigate the independence on ambient temperature of these evaporative emissions. In modeling studies temporally and spatially resolved ambient temperature data are used to modify them. The second large contributor to anthropogenic VOC emissions is the use of solvents. No well-defined economic
OK
social activity - not even a group of
them - covers these emissions. The collective term demonstrates the lack of knowledge about emission estimation techniques and, simultaneously, the way it is attempted to overcome this lack, i.e. the application of national mass balances. An emission factor based on the products themselves hardly plays a role here. Values generally are unity: what is used, is lost. The reason for the purchase of solvents is their loss and if this is caused by their presence in
117 finished products, losses into the atmosphere occur when products are applied. Some products show a time-delay in this process. Where mass balancing fails, it is tried to relate emissions to products, e.g.
manufactured automobiles,
applied paint. In Europe, interest for solvent emission estimation seems to be only at the beginning. Only in a very few countries attempts have been made up to now to make detailed national mass balances. Among other things, work is hampered by an almost complete lack of relevant statistics which, as a matter-of-fact, shows that societies' very detailed statistical data serve economic and social, but not yet environmental purposes. A cooperative action is needed to fill this important gap and to better understand the effects of the use of solvents, of which annually several megatonnes are released in Europe. First attempts to quantify emissions with total yearly per capita
data [5] should now be considered
as
obsolete
OK,
at most,
sparingly used as a default value. Work to be done already has been indicated in this paragraph: development of emission factors per unit of activity and simultaneously - as a control measure - analyses of mass flows. Next to anthropogenic emissions, nature itself releases matter into the atmosphere that is chemically more or less comparable to what is produced by human activities. There are indications that natural NO, emissions (NO + N02) are much less in Europe than antropogenic emissions. But is has also be shown that natural VOC cannot be ignored and during episodes, even can become important. Little is known about natural VOC. With the exception of methane generating processes, the main source is chlorophyll bearing vegetation. It has been demonstrated that emission rates are influenced by many variables. Ambient temperature, light incidence, humidity and of course, the sort of vegetation are examples of these. Measurements therefore are complicated and comparison of results is difficult. The scarce measurements that have been done in Europe should be followed by a cooperative research programma. To date it is simply assumed that data from investigations done elsewhere
-
predominantly in the U.S.
-
also apply to
European species. 6 . COMPOSITION OF EMISSIONS
An important lack of knowledge will be dealt with separately in this paragraph. It is remarkable that the increasing attention that is given to the inventorying of emissions
so
poorly is parallelled by investigating their
composition. In Europe, speciated VOC has been inventoried by Dement and Hov [ 6 ] and in the PHOXA project [ 7 ] . A distinction between NO and NO2 and between SO2 and
SO4 only has been applied in the PHOXA project.
118 It is worthwile to use the state-of-the-art of the knowledge about composition in a coherent way. For most source groups this knowledge is too incomplete to describe relevant national differences and this situation is likely to remain s o in the near future. Therefore averaged composition data should be used to be modified only whenever deviations can be made acceptable. It should become standard practice to report NO,-
and SOx factors together
with their N02- and SO"4-fractions respectively. In the case of NO,,
N20-frac-
tions should also be considered. Only scarce data exist about antropogenic N20 emissions and their contribution should be studied. In describing VOC compositions, anything that is known about them should be included. Apart from the fact that mass comparisons are facilitated there are no good reasons to exclude compounds because of their slow conversion in the atmosphere. (The term NMVOC derives its meaning from the corresponding TVOC's methane content
so
if this is not known, NMVOC suggests more than it can ful-
fil). Compositions should be stated in mass fractions. Simple conversions can be applied for what other units are needed for specific purposes. An important conversion of this kind is one that provides a quantification of the reactivity of a VOC emission. Several condensed chemistries are in use today for the modelling of photochemical phenomena. VOC profiles, that always should be part of VOC emission factors, easily can be transformed into any required chemistry. An example is given in table 4 . Whereas it is easy to record data about NO,
and SOx because only a few
substances are involved, listing of organic species is more complicated because of their abundance. Although from a technical point of view there is no real problem in handling large numbers of organic species, one can doubt the use of filling e.g. all different alkane isomers from a source (supposing they are known). In practice some compromise will be found, but as knowledge of composition - and reactivity - is limited, it is sensible to record all available information.
7. TEMPORAL DISTRIBUTION OF EMISSIONS For the study of short term air pollution phenomena a disaggregation of emissions with respect to time is needed. Short range studies can allocate emission data by making use of existing statistical data and well known habits in the area involved; it is performable to fill gaps by surveys if the area is not too large (8.91. For long range studies, on the other hand, such an approach generally will be prohibitive. Relevant data are incomplete or non-existent in countries and some time pattterns out of necessity even have to be developed from guess work.
119
Cooperation in European emission inventorying ought to comprise also work on this subject. It can be expected that several time-patterns are not restricted to national habits. Just as there are climatic zones that cross national borders, one can think of zones of comparable social and economic behaviour, such as time patterns of transport and working hours. Of course there are differences between countries, due to e.g. legislation but anything that is expected to be comparable should be jointly investigated as a part of emission inventorying activities.
8. ACCURACY OF EMISSION INVENTORIES In terms of demand and supply users of emission data will take into account uncertainties in model structure, meteorological data etc. when they state desired levels of uncertainty of emission data. They will also take into account the fragmentary knowledge about the relation between uncertainty of emission data and uncertainty of model output. Finally they will consider the lack of any supply in this field up to now. In discussions between modelers and inventory developers tentative values of required uncertainties have been proposed: 90% confidence limits of 20% and 30% are desired for national annual NOx respectively VOC emissions. Additional uncertainties o f temporal and spatial distributions are not known but should be kept at a minimum of course. Analytical and synthetical work on the quantification of accuracy is scarce, which is not surprising in view of the problem involved. In the U.S. it has now a structured position within NAPAP [10,11]. In Europe recently a workshop has been held about the subject [12]. This initiative may be expected to be considered as a first step in a joint action in this field. Noteworthy contributions were an uncertainty analysis of the emission inventory in the U.K. [13] and a proposal for a system to quantify uncertainty in the CORINAIR emission inventory structure [ 1 4 ] . Attention was drawn to the large amounts of measured data, stored in many countries, that should be put to use for this purpose [15]. To optimally continue this relatively new work, cooperation between the U.S.
and Europe is
worthwile.
9. SUMMARY AND CONCLUSIONS Of the known precursors of ozone only NO, and - to
a
lesser extent - VOC
have been inventoried to an extent that makes it possible to take stock of what has been done and is going on in Europe. From a initial stage in which countries more shifted
OK
less independently prepared national inventories activities have
to an international scale in the last few years. Today, there still
120 are differences in inventories between countries that are not compatible with combined knowledge. It can, however, be expected that, stimulated by international organizations, in the near future only those differences will remain that reflect economic and social differences between countries. From a comparison of the needs of atmospheric research with the available supply of emission inventory developers gaps in existing knowledge are deduced. Priorities for further work are suggested. These are:
- Correction of automobile exhaust emissions for cold start and subsequent driving with the engine in thermal inbalance.
-
Emission factors for solvent evaporation per activity. Emission factors for natural VOC.
- Composition data for all NO,
and VOC emission factors (sub-priority: most
important VOC sources, i.e. road transport, solvent evaporation and vegetation).
- For episodic model studies: temporal resolution of emissions. It is important to continue this work on an international scale, exchanging experience to finally arrive at a coherent European data base that reflects similarities as well as differences between national emission estimates. In this paper emission inventorying in Europe has been discussed. Where cooperation is advocated it is not suggested that this should be restricted to this part of the world. Particularly since global effects of pollutants have entered
the scene a broader approach has
become necessary. Exchange of
knowledge between Europe and the USA mutually might stimulate emission inventory developers. REFERENCES B.Liibkert and K.-H.Zierock, A Proposal of International Worksharing in Maintaining a Permanent European Air Pollutant Emission Inventory, Proc. Int. Workshop on Methodologies for Air Pollutant Emission Inventories, Paris, June 29 - July 2, 1987, pp. 39 - 61. P. Grennfelt and T. Levander, Emission Inventories in Europe: the Possibility for a Joint Data Base, ibid, pp. 63-65. A.H. Edwards et al, Volatile Organic Compound Emission: An Inventory for Western Europe, CONCAWE Rep. No. 2 / 8 6 . Den Haag, May 1986. J.S. Mc Arragher, An Investigation into Evaporative Hydrocarbon Emissions from European Vehicles, CONCAWE Rep. No. 8 7 / 6 0 , Den Haag, September 1987. C. Veldt, VOC Composition of Automotive Exhaust and Solvent Use in Europe, Proc. Znd Annual Acid Deposition Inventory Symp., November 1985, EPA Report 6 0 0 / 9 - 8 6 / 0 1 0 (April 1986). R.G. Derwent and A.M. Hough, Ozone Precursor Relationships in the United Kingdom, AERE Report R 12408, December 1986. C. Veldt et al, PHOXA Emission Data Base, PHOXA Report No.1 (in preparation) and Th. Miiller et al, Temporal and Spatial Allocation of S O q - , NO,VOC-Emissions in Baden-Wurttemberg, Proc. Int. Workshop on Methodologies for Air Pollutant Emission Inventories, Paris, June 29 - July 2, 1987, pp. 249 261
121 9 B. Boysen et al, Methods for the Investigation of Emissions from Road Transport, in [ 121. 10 C.M. Benkovitz, Uncertainty Analysis of NAPAP Emission Inventory, Proc. Znd Annual Acid Deposition Emission Inventory Symposium, (November 1985), EPA Report 600/9-86/010 (April 1986). 11 C.M. Benkovitz and N.L. Oden, Uncertainty Analysis of NAPAP Emissions Inventory, Progress Report FY 1986, Brookhaven Nat.1. Lab. Report BNL 52132 (December 1987) (NTLS). 12 IIASAlNILU Task Force Meeting on Accuracy of Emission Inventories, Laxenburg, Austria, March, 8-10, 1988. 13 H.S. Eggleston, Accuracy of National Air Pollutant Emission Inventories, in [121. 14 R. Bouscaren, European Inventory of Emissions of Pollutants into the Atmosphere, in (121. 15 C. Veldt, Examples of data for Estimating the Accuracy of Emission Inventories, in [12]. 16 B. Liibkert and S. de Tilly, the OECD-MAP Emission Inventory for S02, NOx and VOC's in Western Europe, Proc. Int. Workshop on Methodologies for Air Pollutant Emission Inventories, Paris, June 29 - July 2 , 1987, pp. 263 276. 17 National Strategies and Policies for Air Pollutant Abatement, Convention on Long-Range Transboundary Air Pollution, Report ECE/EB.AIR/14, UN, New York 1987. 18 B. Lubkert, A model for Estimating Nitrogen Oxide Emissions in Europe, IIASA Working Paper WP-87-122, December 1987. 19 T. de Ryck and W. van Hove, Raming van de NO, - uitworp in Belgie (Estimation of NO, emissions in Belgium), Leefmilieu 1985/3, pp. 78-81. 20 W. Heck and G. Kayser, Les Bmissions de polluants atmosph6rique.s produits par la combustion en Belgique - Un bilan de dix annees, Trib. Cebedeau 38 (1985) 21-31. 21 A. Semb and E. Amble, Emissions of Nitrogen Oxides from Fossil Fuel Combustion in Europe, Norwegian Institute for Air Research Report TR 13/81 (November 1981).
122 TABLE 1 Estimated NO, emissions in European countries 1980; l o 6 kg
Power plants OECD Austria
20
Belgium
853) 1074)
CSSR Denmark Finland France
121 106
FRG GDR Greece Hungary
PHOXA
IECD
13l)
139
119 253 126
280
2511)
803
792 218
Ireland 287 Italy Luxemburg Netherlands 79 Norway 11) Poland 20 Portugal Spain Sweden 11) 5 Switzerland UK 85 1 Yugoslavia
Road transport
581)
2413) 1504)
PHOXA
OECD
841) (145)2 180
216
132 a3
74 1506) 1021
526 (1015)2 1472 238
1469 916) 816)7)
All sources
::31 3984) 243 284 1950 3094
441)
264 57
247 70 282
75 19 1105
Sources: OECD = [ 1 6 ] , PHO only).
IIASA
216
186
505
442
426
779 253
1204 25 1 280 1867
63 1 270 244 1976
3100 8005) 127 2707)
2.688 520 2 18 220
10721) 3182 1193
67 a4 1410-1550 452 35 23 40 466lO) 535 494 106 2159) 173 1704 8409) 1484 166 149 780 95 1 265 2897) 297 196 161 2642 1916 2454 19012) 339 98
1556
-
ECE
1301)
199l)
18
79
PHOXA
182 1386) 663
: [7],
517 119 166
179 971
ECE: [17
319 194 1924
IIASA: [ l a ] (combustion sources
1 ) Country partly in PHOXA area; 2 ) Calculated for whole country; 3 ) Ref. [ 1 9 ] ; 4 ) Ref. [ 2 0 ] ; 5 ) Ref. [ l a ] ; 6 ) ECE, all mobile sources; 7 ) 1984; 8) 1983; 9 ) 1985; 10) mob. sources: road transport only; 11) OECD and PHOXA 1982; 12) Ref. [ 2 1 ]
123
TABLE 2 Estimated VOC emissions in European countries 1980; lo6 kg
Road transport OECD PHOXA exhaust evap. Austria
98
130
99 209 48
6l) (10)2) 14 10 6
305l) 5802) 593 393
451) (8412) 1106) 12
677
491) (ao)2)
Belgium CSSR Denmark Finland France FRG GDR Greece Hungary
1233) 54 785) 1097 688
Solvents 3ECD PHOXA
96l) (173)2) 33
Ireland Italy 9 Luxemburg 172 Netherlands 217 41 44 Norway 8, Poland 498 Portugal Spain 111 206 Sweden Switzerland 925) UK 5 13 612 Yugoslavia
1664) 32
729
2.5l) (4.5)2 3
1 20 5
481) (75)2 127 76 67 3711) (698)2 40a7) a4
IECD 25 1
119l)
25011)
3514)
289 385 132
350
106 129 2192 1864
17
11
5 9 17) 48 178
1759 630
-2300 1800
158
301)
99 50
All sources PHOXA ECE
63 458 137
16 436 103 948
62 43412) 16013) 37 1
13
93
107
71
630
73 1
Sources: OECD = [16], PHOXA: [7], E only).
:
[17], IIASA
413 307 1541
254 1624
4279) 311 1961
[18] (combustion sources
1) Country partly in PHOXA area; 2 ) Calculated for whole country; 3) Ref. [ZO]; 4) nat.1. estimate for 1985 (CORINAIR); 5) ECE; all mobile sources; 6) calculated with PHOXA emission factor; 7) non-industrial; 8) OECD and PHOXA 1982; 9 ) 1980; 10) 1983; 11) 1984; 12) 1981; 13) 1985
124 TABLE 3
Current European Data Bases
~~
Ct PHOXA
OECD
EMEP
COR I NAI R
Large combustion source i n v e n t o r y
~~
IRIGINAL IBJECTIVE
itudy o f transIoundary f l u x e s i y 1ong-rangelong-term model
\bat ement j t r a tegy ievelopment
Study o f photochemistry and a c i d i f ic a t i on d i t h long-range e p i s o d i c and long-term models
)efinition of rroposed d i r e c t i v e ! )n l a r g e combustior nstallations with i a t ional backgrounc lata
Gathering and organizing o f consistent inf o r m a t i o n on a i r pollutants
WEA
iurooe
Yember c o u n t r i e
P a r t o f W.Europe P a r t o f E.Europe
lember c o u n t r i e s
Member c o u n t r i c
'OLLUTANT!
SO,,
SO,,
SO,, NO,, VOC (incl. detailed composi t i on) CO, NH3
;Ox, NO, CO 1art.matter
SO,
INFORMATI(
.(ember c o u n t r i f
Member c o u n t r ie
Contractants
lember c o u n t r i e s
Member c o u n t r i c
SOURCE RESOLUTIOl
None
Det a i 1 ed
Detailed
Zomb. sources > 300 MWth i n d i v . ; Dther comb. source i n ranges (nat.1. totals)
Detai 1 ed
SPATIAL RESOLUTIOI
150 x 150 km
50 x 50 km EMEP g r i d
30'long x 1 5 ' l a t Geogr . g r i d
None
EMEP g r i d
Smallest t e r r i . torial unit wi information fol gridded data
TEMPORAL RESOLUTIOI
None
None
Hourly
None
None
~~
NO,
NO,
VOC
NO,
VOC
125 TABLE 4 Transformation of VOC profiles in chemistries used for modeling. Example: exhaust emissions of LPG-powered vehicles.
Substance
%
CBM-IV reactive by wt. species mollkg
9
me thane
ethane propane ethylene acetylene propylene xylenes formaldehyde acetaldehyde organic acids l)
3 35 15 22 8
1,5 4 1 1.5 100
1) C
5
3 assumed
OLE PAR FORM ALD ETH UNR
2.4 24.0
1.35 0.10 5.4 25.8
TADAP reactive species wt.fraction ALKA ETHE ALKE AROM HCHO RCHO SLHC
0.015 l) 0.17 0.08 0.015 0.04
0.01
0.67
This Page Intentionally Left Blank
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
127
A.P.Altshuller Atmospheric Sciences Research Laboratory, U.S. Rwiromental Protection Agency, Research W i a q l e Park, North Carolina (USA)
A number of s i g n i f i c a n t Scurces of Ozone e x i s t i n t h e planetary boundary
layer, t h e f r e e troposphere and t h e 1-r stratosphere. "he c o n t r i t u t i o n s are estimated f o r each of these Scurces of ozone to g r a n d l e v e l ozone concent r a t i o n s . Both n a t u r a l and anthropogenic Scurces are considered. Horizontal and v e r t i c a l t r a n s p o r t of ozone and its precursors also are important i n determining the a m s p h e r i c d i s t r i t u t i o n of ozone. The measuretlents of the concentration and canposition of non-methane hydrocarbons and nitrogen o x i d e s have been evaluated a t both rural/ranote c o n t i n e n t a l sites and a t tropospheric backgramd locations. The e f f e c t s d i t ; cussed of t h e r e a c t i o n s of precursors with hydroxyl r a d i c a l s , ozone and nitrogen t r i o x i d e r a d i c a l s are discussed along with t h e l i f e t i m e s of o r g a n i c s and on t h e i r a m s p h e r i c canposition. Ratios of nonmethane hydrocarbons to nitrogen o x i d e s are important i n determining the e f f i c i e n c e s of ozone production. Experimental and modeling approaches to e s t h a t i n g t h e s e e f f i c i e n c i e s are reviewed. IrnrnICN
-
T h i s work w i l l f i r s t consider the sources of -one i n the v a r i c u s regions of the a m s p h e r e . Saxces both i n the f r e e troposphere and planetary bounddetail. The c o n t r i t u t i o n s of h o r i z o n t a l and a r y l a y e r are discussed i n vertical t r a n s p o r t of ozone and its precursors also are considered. The ranoval of organic species by r e a c t i o n s with -one,
nitrogen trioxide
The l i f e t i m e s of the
r a d i c a l s and e s p e c i a l l y hydroxyl r a d i c a l s is reviewed. individual species vary g r e a t l y influencing strongly the c a r p o s i t i o n of
organics a s they are transported f r a n sources through the planetary bamdary l a y e r and t h e f r e e trcposphere. The r e l a t i o n s h i p s between hydrocarbon to nitrogen oxide ratios and ozone production are inportant to understanding ozone d i s t r i t u t i o n s i n t h e atmosphere.
128
Organic c o n cen t r at i o n s and c a n p o s i t i o n a l measurements a t c o n t i n e n t a l r u r a l / r m t e sites are t a h l a t e d and discussed.
The corresponding measure-
ments of o r g a n i c species i n t h e background troposphere a t mid l a t i t u d e s i n t h e Northern Hemisphere are considered.
The l i m i t e d measuranents of nitroge n
o x i d e i n rural renote c o n t i n e n t a l and marine l o c a t i o n s a l s o are pre se nte d. The s i g n i f i c a n c e of p r ecu r s o r emissions and atmospheric c onc e ntra tion measurements to v ar i o u s r eg i o n al and t r w s p h e r i c models a l s o a r e emphasized. S(XIRCES OF OZONE I N THE FREE TROPOSPHERE
Se v e r a l types of ozone scurces c o n t r i b u t e to t h e ozone measured i n t h e trcposphere. 1-r
These Ozone scurces include (1) exchange of ozone f r a n t h e
s t r a t o s p h e r e a c r o s s t h e tropcpause i n t o t h e f r e e troposphere ( 2 ) i n s i t u
photochemical ozone production i n the f r e e trcposphere ( 3 ) ozone p r h c t i o n w i t h i n the p l a n e t a r y bcundary l a y e r .
Vertical t r a n s p o r t b e t m e n t h e pla ne ta ry
bcundary l a y e r , up to a h t 2 km, and t h e f r e e trcposphere can be important to t h e mvernent of ozone and its p r ecu r s o r s .
Stratospheric
to troposphere exchange
o f ozone
Se v e r a l processes can c o n t r i h t e to the f l u x of ozone from the 1-r s t r a t o s p h e r e i n t o t h e trcposphere ( r e f . 1 ) . H a e v e r a t m i d l a t i t u d e s i n t h e Northern Hemisphere l a r g e scale eddy t r a n s p o r t i n t h e region of the jet s t r e a n , o f t e n r e f e r r e d to as trcpopause f o l d ing ( r e f . 2 ) , is considered to be t h e daninant p r o ces s ( r e f . 3 ) . Analyses of the f r q u e n c y of such trapopause folding e v e n t s based on t h e Occurrence o f 5OO-mb low-pressure
t r o u g h s i n d i c a t e s t h e presence of a bout 4
t r c u g h s per day o v e r t h e Northern Hemisphere and about 1 t r q h per day sanewhere over North America ( r e f s . 3 , 4 )
?he frequency of such troughs vary
w i t h season, latitude and l o n g i t u d e ( r e f . 4 ) .
Aircraft masurements of t h e ozone p r o f i l e s d e f i n i n g dmnward m v 6 r e n t of ozone i n s t r a t o s p h e r i c air thrcugh t h e f r e e troposphere are available ( r e f . 5 ) . Ihe r e s u l t s i n d i c a t e that the s t r a t o s p h e r i c a i r t e n d s to bend ove r i n t o h o r i z o n t a l l a y e r s i n t h e f r e e troposphere o f t e n f a r above t h e t o p of the Secondary meteorological proc e sse s rm st be u t i l i z e d t o acccunt f o r s t r a t o s p h e r i c ozone mixing dcwn i n t o t h e pla ne ta ry boundary l a y e r . 'ho of t h e p o s s i b l e mechanism have sane theoretical and experimental
p l a n e t a r y bavldary layer.
support ( r e f . 5 ) .
These two m c h a n i s n s involve e i t h e r (1) coupling of the
s t r a t o s p h e r i c layer i n t h e f r e e troposphere to a f r o n t a l zone a s s o c i a t e d w ith
a c o l d f r o n t and t r a n s p o r t to the s u r f a c e by f r o n t a l d a m d r a f t s or ( 2 ) e n t r a i m n t i n organized f r o n t a l or p r e f r o n t a l convection w i t h t r a n s p o r t t o t h e su r f a c e i n d a m d r a f t s a s s o c i a t e d w i t h rainshcwers or thunderstorms ( r e f . 5).
129 These two mechanisns also would account f o r t r a n s p o r t of ozone produced by
s i t u photochemical
&
p r o ces s es i n t h e middle to upper f r e e trcposphere d m t o
t h e surface. Three-dimensional a i r p a r c e l trajectories have been used t o trace t r a n s p o r t of ozone f r a n the t r o p q x ws e down to the 7 0 0 4 level, 3 o b s e r v a t i o n s are a v a i l a b l e ( r e f s . 5 , 6 ) .
The -one
)an,
when meteorological
f l u x c a n be c a l c u l a t e d darn
through the area of the s u r f ace estimated to be involved a t the 7 0 0 4 level. The f r q u e n c y of ground l e v e l impacts of stratospheric ozone and t h e a s s o c i a t e d ozone co n cen t r at i o n s can be ev al u ate d f r a n episbdic reports i n t h e
literature.
A
c c n p i l a t i o n of 10 ep i s o d es h a s been made based on the criteria
used by the o r i g i n a l i n v e s t i g a t o r s f o r epis3des between 1964 and 1978 ( r e f . 6 ) . The o b s e r v a t i o n s were made a t l o c a t i o n s i n t h e United S t a t e s and Western Europe. u s u a l l y t h e e l e v a t ed ozone co n cen t r at i o n s o cc ur f o r periods of a f r a c t i o n of a n hcur t o s e v e r a l hcurs.
S ev er al o b s er v at i o n s of -one
c onc e ntra tion above 100
ppb a t ground l e v e l seem implausible conpared with ozone c onc e ntra tions b e b e e n The f r q u e n c y of 5 0 0 4 1 and 700-mb d u r i n g episodes observed a l o f t ( r e f s . 4-6). high ozone c o n c en t r at i o n s a t g r a d level a s s o c i a t e d w i t h s t r a t o s p h e r i c intrus i o n s reaching t h e s u r f ace were estimated t o occur less than 1%of t h e t h e (ref. 6 ) . A
number of estimates have been r ep o r t ed of seasonal c o n t r i b u t i o n of
s t r a t o s p h e r i c ozone to s u r f ace ozone concentration.
About 10 ppb of the s u r f a c e
ozone concentration h a s been a t t r i h t e d t o ozone of s t r a t o s p h e r i c o r i g i n ( r e f . 7).
me
in-situ photochemical production of ozone i n t h e troposphere A second SaJrce of Ozone is its photochenical prcduction f r a n reactions
involving m t h a n e , carbon mn o x i d e and o t h e r longer-lived volatile o r g a n i c s w i t h nitrogen o x i d es i n t h e f r e e troposphere ( r e f . R,9).
Because of several
shortcanings of earlier m d e l i n g s t u d i e s only t h e mre re c e nt s t u d i e s are p e r t i n e n t (ref. 9).
The results f r a n a number of these re c e nt s t u d i e s have been reviewed
elsehere ( r e f . 7 ) .
I f a n t h r o p g e n i c n i t r o g en oxide scurces a t the surface are
not included i n t h e model scenario, a h t 15 ppb of ozone is ge ne ra te d photochenic a l l y a t 1 km under sumnertime co n d i t i o n s a t mid l a t i t u d e s i n t h e Northern Hemisphere. I f t h e s u r f ace n i t r o g en oxide and non-methane hydrocarbon f l u x e s p r e s e n t i n remote areas a r e included t h e photochemically generated ozone c o n c e n t r a t i o n s in c r e a se to the 30 t o 50 ppb range ( r e f s . 7,lO). Several approaches have been used to es t im a te the h i s t o r i c background of ozone frcm n a t u r a l p r e c u r s o r s a t r u r a l l o c a t i o n s ( r e f . 10).
The approaches in-
c lu d e (1) r e s u l t s from scenarios ap p l i ed to v a rious trc posphe ric photochemical models ( 2 ) statistical an al y s es of t h e h i s t o r i c a l t r e n d s i n ozone c onc e ntra tions and ( 3 ) use of 7% and/or 90Sr tracers of the o r i g i n s of ozone i n t h e stra tosphe i
130 and/or upper trcposphere.
An
average late spring-smmr natural backgrmnd of
ozone i n the range of 10 to 20 p N can be obtained from the r e s u l t s a t midl a t i t u d e s i n the Northern Henisphere (ref. 10). Other sources of ozone The t h i r d major group of Scurces a r e those pmchcirq Ozone photochanically within the planetary boundary layer.
Active cumulus clouds often form under
the sane conditions favorable to ozone formation.
Updrafts in a c t i v e cumulus
can c a r r y ozone i n t o the lover f r e e traposphere ( r e f s . 11,12).
These updrafts
i n these venting clouds a l s o shculd transport o t h e r species including hydrocarbons, carbon mnoxide and nitrogen oxide a l o f t along w i t h the ozone.
SOURCES OF OZONE WITHIN THE PJANETARY BOUNWRY IAYER The r e s u l t s available up to 1984 on the characteristics of ozone formation within plumes a s w e l l as the episodic formation of ozone during passage of warm high pressure systems have been reviewed ( r e f . 7 ) .
Elevated ozone concentra-
t i o n s have been reported to occur within urban plumes, plumes f r m f o s s i l f u e l
m r plants and p l u m s f r m i n a s t r i a l m c e s ( r e f . 7 ) .
All of these w r c e s
can make a contribution to the regional backgroud of ozone. Ozone formation within urban plumes Because of cptimum hydrocarbon to nitrogen oxide ratios and t h e presence of highly reactive hydrocarbons t h e conditions i n urban plumes f r a n both large and -11 cities are favorable t o t h e rapid formation of ozone ( r e f . 7 , 13-17). Excess ozone concentrations 50 to 100 pfi above regional b a c k g r m d of ozone a r e observed during t h e f i r s t day of transport of urban plumes. Such plumes have been tracked by a i r c r a f t measuranent out to several hundred lan dwnwind of a number of large cities i n the united states ( r e f . 7 ) . plumes with less excess ozone have been observed from smller cities. In p r a c t i c e , i n heavily populated a r e a s plumes fran two or mre large and/or snaller c i t i e s can be canbined. Excess ozone over t h a t measured i n t h e a i r advected i n t o St. Louis was detectable i n the S t . mis plum on 189 days i n April through October 1975 and 1976 (ref. 13).
The 1-h maximum i n excess ozone over t h e regional background
during midday hours q u a l l e d or exceeded 40 ppb on abcut half of these 189 days.
The 1-h maximum i n excess Ozone qualled or exceeded 100 ppb on 4% of
These owne concentrations were measured a t nonurban m n i t o r i n g s t a t i o n s located up t o 40 lan outside of these days and exceeded 200 pfi on several days.
St. Lcuis. During those days on which the maxinnnn excess ozone 100 ppb t h e regional background of ozone based on ozone measuranents a t several upwind monitoring s t a t i o n s ranged f r a n 64 to 107
pN and averaged 81 ppb.
131 Aircraft measuranents tracking the St. Louis urban plume were available on four days i n 1975 and 1976 ( r e f . 13).
Excess ozone above regional background
on the edges of the plumes were tracked to 100 to 150 km d m i n d of St. Louis. urban plume widths viere estimated f r a n the a i r c r a f t measuremnts of the edges of plumes a s w e l l a s the ozone d i s t r i b u i t o n s a t monitoring s t a t i o n s ( r e f . 13). Based on plume transport distances and plume widths f r a n St. -is
and
other cities it has been estimated t h a t 5 to 10%of the land area west of the Appalachian Mountains and east of 105OW longitude is hpacted by excess ozone within urban plumes during t h e April t o October periods (ref. 13).
The @act
of urban plumes in this region is most frequent f o r the wind f l w s t h a t prevail f r a n t h e m t h e a s t to southwest sector onto land areas d m i n d . Fran measuremnts mde on four a i r c r a f t f l i g h t days i n A u g u s t 1978 when
t h e urban plume fran Boston traveled c u t over the Atlantic Ocean, t h e lifetime of nitrogen oxides ( l / k ) was calculated t o range frun 4 to 7 hcurs and averaged 5.5 hours under sunny sumrertine conditions ( r e f s . 14,15).
Fran measuremnts
made on two a i r c r a f t f l i g h t days in July and August 1979 the upper limit l i f e -
times ( l / k ) f o r nitrogen oxide i n the Philadelphia plume were estimated a s less than 5 and 8 hours respectively ( r e f . 1 6 ) . Therefore nitrogen oxides a r e r e l a t i v e l y rapidly depleted within urban plumes. The average rate of ranoval of ethylene was nearly the sane as f o r nitrogen oxides based on ethylene to acetylene ratios measured &ring traverses of the Boston plume ( r e f . 15). Several mdeling grcups have used Lagrangian t r a j e c t o r i e s to investigate 03 formation &ring t h e transport of urban plumes over non-urban a r e a s ( r e f . 7 ) . I n i t i a l conditions of the m d e l s have been based upon the urban concentrat i o n s of precursors f r a n s p e c i f i c u.S. cities. 'Ihe predicted ozone concentrations obtained a r e i n reasonable agreenent with observed ozone concentrations in plumes.
The e f f e c t of hydrocarbon to nitrogen oxide ratios on ozone production,
nitrogen oxide ranoval r a t e s and cycling of nitrogen oxide thrcugh proxyacyl n i t r a t e in multiday simulations have a l l been investigated. In scme of these modeling s t u d i e s the e f f e c t of added biogenic hydrocarbon on ozone formation has been simulated f o r emissions i n and around s p e c i f i c
cities and f o r generalized conditions ( r e f s . 7,18-20).
The results indicated
less than a 10%e n h a n c m n t of ozone formation i n urban plumes as a r e s u l t of biogenic hydrocarbons a n i t t e d i n t o the Tanpa-St. Petersburg, FL and Houston, TX plumes ( r e f . 18,19). The e f f e c t on ozone production i n the urban plume of a hypothetical c i t y was insignificant when biogenic hydrocarbons were a n i t t e d i n t o the urban plume during the afterncon hours ( r e f . 20).
However, when
132 biogenic hydrocarbons were e n i t t e d upwind of the hypothe tic a l urban area i n t h e morning t h e y e r e p r e d i c t e d to enhance ozone production i n t h e urban plume i n
late afternoon by 18%f o r a maximum i s cp r en e c onc e ntra tion of 63 ppbc and by 8% f o r a maximum i s cp r en e co n cen t r at i o n o f 11 ppbc ( r e f . 20). Ozone formation i n plumes f r a n f o s s i l f u e l power p l a n t s Excess ozone co n cen t r at i o n s over regional backgraind ranging f r a n 20 to 50 pP, h a s been m e a w e d &r i n g a i r c r a f t traverses of plumes fran f o s s i l f u e l
pwer p l a n t plumes i n the e a s t e r n United S t a t e s ( r e f . 7). Occurrences of total ozone c o n c e n t r a ti o n s above 100 ppb a t several g r a n d l e v e l monitoring s t a t i o n s i n t h e s c u t h e a st er n United S t a t e s have been a s s o c i a t e d w ith plumes f r a n f o s s i l f u e l p#er p l a n t s ( r e f . 21).
T h i s conclusion is based on c o r r e l a t i o n s of Ozone
and s u l f u r dioxide co n cen t r at i o n s and on t r a j e c t o r y a na lyse s.
The inpact on
t h e plumes a t the g r a n d l e v e l l o c a t i o n s occurred 3 to 8 h a r r s and f r a n t h e time of emission f r a n t h e power p l a n t s t a c k s ( r e f . 21). I n c o n t r a s t , e x c e s s ozone co n cen t r at i o n s have not been observed i n s e v e r a l f o s s i l f u e l power p l a n t plumes t r a v e l i n g o v er r u r a l areas of the western United S t a t e s or over areas of Ocean ( r e f . 7). The d i f f e r e n c e s i n Ozone prockction can be a s s o c i a t e d with t h e a v a i l a b i l i t y o f hydrocarbon emissions i n t h e areas t r a v e l e d over by the plumes. o x i d e s, bt lack hydrocarbons.
F o s s i l f u e l p e r p l a n t p l u m s are r i c h i n nitroge n Hydrocarbons are r q u i r e d to mix i n t o t h e
plumes to o b t a i n hydrocarbon to n i t r o g en o x i d e s ratios fa vora ble to ozone production.
S u f f i c i e n t hydrocarbon m i s s i o n s o f t e n are not a v a i l a b l e i n remote c o n t i n e n t a l areas nor are they a v a i l a b l e o v e r water, The hydrocarbon emissions need to g en era te ozone i n t h e f o s s i l f u e l puer p l a n t plumes may b e a n t h r q x q e n i c or bicgenic.
Highly r e a c t i v e hydrocarbon species w i l l g e ner at e ozone more r a p i d l y i n t h e s e p l u m s . -ling results for ozone p r h c t i o n w i t h i n t h e dimensions of p e r p l a n t plumes have not been published. Modelings have been r ep o r t ed of ozone formation a s s o c i a t e d w ith i s o l a t e d n i t r o g en oxide g r a n d l e v e l scurce 1 km on a s i d e assuning s e v e r a l d i f f e r e n t emission rates i n rural t e r r a i n ( r e f . 20).
Substantial increases i n
ozone c o n c e n t r a t i o n s a r e p r e d i c t e d f r a n i s cp re ne and d.-pinene m i s s i o n s associa t e d with q t i m u m hydrocarbon to n i t r o g en o x ide ratios. The incremental ozone a s s o c i a t e d w i t h t h e a d d i t i o n of the b i cg en i c hydrocarbon m i s s i o n s are very s e n s i t i v e to t h e emission rate of t h e n i t r o g e n oxides. Unfortunately it is d i f f i c u l t to kncw h a r u s e f u l such c a l c u l a t i o n s are
me p e r p l a n t plumes a l o f t are i s o l a t e d f r a n any grcund level SOurces of hydrocarbons f r a n late a fte rnoon
with respect t o pmer p l a n t plumes emitted a l o f t .
or e a r l y evening i n t o t h e morning h cu r s a f t e r s u n r i s e a s t h e n o c t u r a l s u r f a c e
133 in v e r si o n forms and disappears.
Mixing i n t o real plumes a l o f t may n o t be a s
hamgeneam a s a s s a d i n such s i mp l i f i ed lnodeling scenarios ( r e f . 2 2 ) . Ozone formation i n i n d u s t r i a l plumes Excess ozone h as been observed w i t h i n s eve ra l ind-lstria l plumes ( r e f . 7 ) . These p l u m s wre a s s o c i a t e d with several petroleum r e f i n e r i e s and w i t h a large autcmotive p a i n t p l an t . These Scurces are r i c h i n hydrocarbons as would
be o t h e r i n d u s t r i a l sources such a s petrochemical canplexes. These plumes tended to be n a r r m and d i f f i m l t to tra&. They also tend to involve less r e a c t i v e hydrocarbons mixed with l i mi t ed amcunts of nitroge n oxides. mperimental results on ozone formation d u r i n g the passage of warm high p r e s s u r e systems The a v a i l a b l e experimental s t u d i e s up to 1985 on ozone f o n r a t i o n a ssoc ia te d with warm high p r es s u r e systems i n t h e e a s t e r n United S t a t e s and M s t e r n Eurcpe have been reviewed elsewhere ( r e f . 7 ) . Aspects of v e r t i c a l s t r u c t u r e , d i u r n a l ozone p r o f i l e s , v a r i a t i o n of ozone with passage of a high pre ssure system, nocturnal j e t s and h o r i z o n t a l p r o f i l e s need to be considered ( r e f s . 7,23-27). The v e r t i c a l s t r u c t u r e of ozone is c o n s i s t e n t with a layer of e l e v a t e d ozone a l o f t d e v e l o p i q a t 1 to 2 km a l o f t during t h e cmrse of the episode ( r e f s . 2 3 , 2 4 ) . 'his layer is t h e r e s u l t of photochemical production of ozone i n t h e planetary boundary l a y e r &r i n g p r e v i m s d a y ( s ) and it is preserved i n t o the
following d a y ( s ) . A t t h e s u r f ace, ozone is d eple te d i n nonurban areas by d r y As the noc tura l inve rsion
d e p o si t i o n and chemical r e a c t i o n overnight ( r e f . 25).
breaks up t h e ozone a l o f t mixes down to i n cr ea se s u r f a c e ozone ( r e f .
26,27).
I n t h e f o l l m i n g hours f u r t h e r i n cr eas es i n m one occur a t t h e s u r f a c e because
of photochemical production ( r e f . 27). A s a r e s u l t by midday t h e r e is a damward g r a d i e n t i n t h e ozone co n cen t r at i o n f r m t h e surfa c e to several k i l a n e t e r s a l o f t ( r e f . 23,24).
ozone co n cen t r at i o n s near the surfa c e cutside of plumes
c a n h i l d up to 100 p@ and above ( r e f . 23,251. A t n i g h t h o r i zo n t al t r a n s p o r t can be increased by the noc tura l jet phenomena ( r e f s . 7,26).
Strong n o ct u r al jets are observed over c e r t a i n areas of t h e United
S t a t e s , e s p e c i a l l y over t h e Great P l ai n s , which can t r a n s p o r t species including ozone and its p r e cu r s o r s hundreds of kilaneters daunwind. A i r c r a f t traverses i n d i c a t e co n s i d er ab l e h o r i z o n t a l s t r u c t u r e i n the o m n e This s t r u c t u r e 1s the result
p r o f i l e s w i t h i n high p r es s u r e systans ( r e f . 23,25).
of t h e presence of i n d i v i d u al plumes co n t ai n i ng e xc e ss ozone a s disc usse d above.
134 mnger-range t r a n s p o r t o f ozone There is experimental evidence of t h e continued presence of e l e v a t e d conc e n t r a t i o n s of ozone during multiday t r a n s p o r t w ithin the p l a n e t a r y bcundary layer (ref. 7).
Tr an s p o r t times ranging f r a n 8 t o 48 h c u r s f o r ozone have been
observed over oceanic areas near c o n t i n e n t s ( r e f . 7 ) . Direct e va lua tion of longer-range ozone t r a n s p o r t over land ismore d i f f i c u l t s i n c e it depends upon p r q e r e s t i m a t i o n of a nunber of parmters r e l a t e d to production and ranoval of Ozone and its p r e c u r s o r s a s w e l l a s h o r i z o n t a l and v e r t i c a l t r a n s p o r t . k x k l i n g e f f o r t s t o simulated multiday t r a n s p o r t of omne began w ith the use of s i m p l i f i e d Lagrangian long-range t r a n s p o r t models ( r e f s . 28,29). i n i t i a l r e s u l t s from such e f f o r t s =re
approaches are u s ef u l i n r eg u l at o r y a p p l i c a t i o n s of modeling. l a r g e n&r
While the
i n t e r e s t i n g it is not clear t h a t such Aside f r u n t h e
of s i mp l i f y i n g as s u n p t i o n s made, t h e Lagrangian approach does n o t
appear p r a c t i c a l f o r g en er at i n g t h e l a r g e f i e l d of ozone c onc e ntra tions over a n e n t i r e region of a co n t i n en t needed i n p r a c t i c a l a p p l i c a t i o n s . More r e c e n t l y a three dimensional Eu l eria n re giona l oxida nt model (RCM) h a s been develcped.
This mDdel is capable of h a x l y p r e d i c t i o n s of t h e concen-
t r a t i o n s of Ozone and other species w i t h i n g r i d areas 18 km on a s i d e ( r e f s . 30-32). 'he second g en er at i o n v er s i o n of t h e mdel i n c l u d e s ( a ) day and n i g h t photcchenistry including subgrid c h e n i s t r y ( b ) anthropogenic and biogenic emissions of hydrocarbon and n i t r o g en o x i d e s d i s a g g r q a t e d by g r i d e l e m n t ( c ) h o r i z o n t a l t r a n s p o r t including t e r r a i n e f f e c t s ( d ) mesoscale v e r t i c a l n o t i o n and eddy e f f e c t s (e) cumulus cloud e f f e c t s ( f ) noc turna l jet p h e n m n a and (4) removal p r o c e ss es ( r e f . 31).
The 18 km g r i d s i z e r e s o l v e s abcut 80% of t h e
me of t h e major problems is t h a t f o r over 10% of t h e 200 h i g h e s t scllrce cells f o r hydrocarbon and nitroge n oxide emissions i n t h e United S t a t e s the tm anthrcpogenic i n v e n t o r i e s a v a i l a b l e , hydrocarbon and n i t r o g en o x i d e emissions ( r e f . 30).
d i f f e r by 300% and mre ( r e f . 3 0 ) . C l h t o l o g i c a l patterns o f ozone i n t h e United S t a t e s The climatological p a t t e r n s o f ozone co nc e ntra tions obta ine d f r a n m n i -
t o r i n g s t a t i o n s east of l O O o W l o n g i t u d e have been develcped.
The approach used
involved c a l c u l a t i n g monthly means of d a i l y maximum ozone c onc e ntra tons and d i sp l a y i n g t h e r e s u l t s a s monthly isopleth maps f o r July and August 1977 to 1981.
The maps i n d i c a t e that monthly means i n a geographical area can vary by
10 to 50 p@ during t h es e tem sumx m n t h s .
W n t h l y mean c o n c e n t r a t i o n s
d e c r e a s e by 20 t o 25 ppb across the midwestern United S t a t e s f r a n east to w e s t f r a n c e n t r a l Ohio and e a s t e r n Misscuri to northwestern Icwa.
I n northwestern
Icwa the ceone c o n cen t r at i o n s range f r a n belcw 40 ppb up to 60 ppb.
The ozone c o n c e n t r a t i o n s also are 1cw i n the extrew northe rn United S t a t e s . In c o n t r a s t i n mre heavily pcpulated areas such a s c e n t r a l Ohio, the Washington, DC area
135 and Connecticut almost identical ozone concentrations are obtained f o r values averaged over July-August 1977-1981.
The variations observed a t any given location
a r e a t t r i h t e d t o differing paths of the migratory high pressure systens ( r e f . 33).
However, differences in emission d e n s i t i e s of hydrocarbon and nitrogen
oxides across the midwestern United S t a t e s and less favorable meteorological conditions for ozone f o r m t i o n i n the northern United S t a t e s a l s o should c o n t r i t u t e t o the observed geographical variations in the m n t h l y mean values of ozone. 'Ihe incremntal omne concentrations observed climatologically i n the sumrer months a t grcund level over the mre pcpulated areas of the United S t a t e s a r e best explained by photochemical generation of ozone within the planetary bcundary
layer fran local or regional hydrocarhn and nitrogen oxide enissions ( r e f . 7 ) . Urban plumes a l s o are detectable ring the spring m n t h s ( r e f . 1 3 ) . Regional photochenical 03 production a l s o occurs during t h i s period of the year.
A
detailed analysis of ozone p r o f i l e s &ring both day and nighttime h m r s a t a r u r a l site a t G i l e s , TN is best explained by the substantial importance of daytime photochenistry during t h e spring m n t h s ( r e f . 21). A'IMDSF'HERIC LIFETIMES OF OFGRZiNIC SPECIES
The ranoval of most types of v o l a t i l e organic carpounds fran t h e atmosphere is predaninantly determined by t h e i r chemical reactions in the atmosphere r a t h e r than by wet or dry deposition. with the exception of alkenes, organic species react more rapidly w i t h hydroxyl r a d i c a l s than with omne or NO3 r a d i c a l s ( r e f s . 34-40).
Although alkenes react a t substantial r a t e s w i t h ozone ( r e f .
34), the daytime lifetimes of ethene, prcpene and other 1-alkenes also are primarily determined by t h e i r r a t e s of reaction with hydroxyl r a d i c a l s ( r e f s . 34,35). Alkenes with internal dcuble bonds react very rapidly with ozone ( r e f . 35). In addition acyclic alkenes such a s 2-methyl-2-tutene and related mlecules, most terpenes and cresols react rapidly w i t h nitrogen trioxide ( r e f s . 36-40). Solar photolysis c o n t r i t u t e s t o the rerPval of aldehydes and ketones f r a n t h e atmosphere.
The r a t e of f o r m t i o n of hydroxyl r a d i c a l s depends on t h e photolysis
of ozone to 0 ( b ) by u l t r a v i o l e t solar radiation and the reaction of O ( 1 D ) with
water vapor ( r e f . 34). Hydroxyl radical concentrations decrease rapidly a t low s o l a r radiation i n t e n s i t i e s ( r e f . 4 1 ) . Therefore hydroxyl radical reactions are only important in calculating daylight lifetimes of organics. Ozone is present in the atmosphere a t varying concentrations a t g r a n d level and a l o f t throughout the day and nighttime h m r s ( r e f . 7). Nitrogen trioxide radical concentrations increase during t h e nighttime hcurs t u t rapidly photolyzes to very l m concentrations a f t e r sunrise ( r e f . 36).
136 The l i f e t i m e s of alkenes w i t h i n t e r n a l double bonds are h c u r s or less both i n the day and n i g h t because ozone, hydroxyl r a d i c a l s or n i t r o g e n t r i o x i d e r a d i c a l s are a v a i l a b l e to r a p i d l y d e p l e t e t h e s e a l k e n e s ( r e f s . 34-36,39). l h e r e f o r e such a l k e n e s would not be expected to be d e t e c t a b l e a t nonurban l o c a t i o n s or r e g i o n s a l o f t u n l e s s r e c e n t l y impacted by source m i s s i o n s c o n t a i n i n g t h e s e canpounds. Based on t h e s e c o n s i d e r a t i o n s an a p p r c p r i a t e s i m p l i f i c a t i o n is to c o n s i d e r
only t h e rates of r e a c t i o n s of o r g a n i c species w i t h hydroxyl r a d i c a l s and the corresponding atmospheric l i f e t i m e s .
The rate c o n s t a n t s f o r the r e a c t i o n of
hydroxyl r a d i c a l s with a nunber or o r g a n i c species i n Table 1 are based e i t h e r on c a n p i l a t i o n of a v a i l a b l e experimental v a l u e s or on a n empirical c q u t a t i o n technique f o r e s t i m a t i n g t h e s e rates ( r e f s . 34,35,42). 'KI e s t i m a t e t h e l i f e t i m e s l i s t e d i n Table 1 a hydroxyl r a d i c a l c o n c e n t r a t i o n h a s to be s e l e c t e d .
A value
of 4 x 105 m l e c u l e s cm-3 as a n average d i u r n a l c o n c e n t r a t i o n v a l u e was used and
i s based on r e c e n t OH m e a s u r e m n t s near grcund l e v e l ( r e f . 41).
Based on
t r e n d s i n 7 y e a r s of m e a s u r a n t s of methyl chloroform a t f i v e backgrcund s t a t i o n s t h e average hydroxyl r a d i c a l c o n c e n t r a t i o n f o r 30" t o 90"N and 500 to 1000 mb is c a l c u l a t e d to be 4.95 0.9 x 105 molecule ( r e f . 43). i n Table 1 *re
The c a l c u l a t i o n s
m d e f o r a s m r t i m e atmosphere i n t h e p l a n e t a r y b a m d a r y
l a y e r assuning a n average t e n p e r a t u r e of 298°K.
For longer-lived species t h a t
s u r v i v e to be d i s t r i h t e d throughout t h e f r e e troposphere such as ethane or a c e t y l e n e this l i f e t i m e d o e s not q u a 1 their average t r o p o s p h e r i c l i f e t i m e .
For
a m l e c u l e such a s ethane its rate c o n s t a n t with hydroxyl r a d i c a l s i n t h e f r e e trcposphere is about 40% o f its rate i n t h e p l a n e t a r y boundary l a y e r . c o n s t a n t of a c e t y l e n e with hydroxyl r a d i c a l s w i l l be i n a f a l l - o f f t h e atmospheric p r e s s u r e s i n t h e upper troposphere.
The rate
region a t
For such molecules t h e
average t r o p o s p h e r i c l i f e t i m e s are somewhat l o n g e r than t h o s e g i v e n i n Table 1. The rate c o n s t a n t s and l i f e t i m e s w i t h i n a class of o r g a n i c species, a l k a n e s , a l k e n e s or a r m t i c s vary by f a c t o r s of 10 to 50.
Even w i t h i n a subclass such
a s t h e Cg t o Cg a l k a n e i m r s , rate c o n s t a n t s and l i f e t i m e s can vary by a f a c t o r of 10.
The c a n p o s i t i o n of o r g a n i c species a t r u r a l l o c a t i o n s o f t e n depends on the e x t e n t a l o c a t i o n is i s o l a t e d f r a n nearby m r c e emissions.
137 Table 1.
Rate C o n s t a n t s f o r s e l e c t e d Nonmethane Organic Canpcunds w i t h
Hydroxyl R a d i c a l s and Estimated L i f e t i m e s o f t h e s e species
e!?!EE!
Rate Constant
E s t i m a t e d L i f e t i m e s of
1012K, 298O~, m 3 m1-1s-1
Organic Species, day&
ethane
0. 274a
prcpane
1.18"
23
n-bu t a n e
2.53a
11
2-me thylprcpane
2.37a
12
100
n-pentane
4.06a
7
2-methyltu t a n e
3.9a
7
hexanes
1.8 t o 5.5b
heptanes
2.9 to 7.7b
3.6 t o 9
octanes
1.1 to 9.2b
3 t o 25
nonanes
2.2 to 11.0b
acetylene
0.7&la
benzene
1.28a
(760 torr)
5 to 15
2.5 t o 1 2 35 21
monoalkylbenzenes
5.7 t o 7.5a
3.6 to 4.8
o r t h o and para-
11 to 15a
1.8 to 2.5
m e t a l d i a l k y l benzenes
17, 24.5a
1.6, 1.1
trialkylbenzenesC
33 to 62.
0.4 to 0.8
e thene
8.54"
3.2
prcpene 1-htene
26.3
1.0
31.9"
0.8
2-
d i a lkylbenzenes
thylpropene
51.4"
.5
cis2-bu tene
56. la
.5
t rans-2-bu t e n e
63.7a
.4
2-methyl-2-bu t e n e
R6.ga
.3
cyc lohexene
fi7.4a
.4
1 3-bu t a d i e n e
66.aa
.3
2-methyl-l13-butadiene
101.a
.3
d -pinene
53.2a
.5
-p inene
78. 2a
.4
,
138 Table 1. (continued)
Rate Constant
Compound
1012K, 298'K,
Estimated L i f e t h e s of Qn3
Kd-151
Organic Species, day&
formaldehyde
9.0a
acetaldehyde
16. 2a
acetone
0.23a
120
methylethylketone
1.0a
27
methanol
0.9a
30
ethanol
2.9a
9
3 1.7
me thy1 c h l o r i d e
0.04a
>365
methylene d i c h l o r i d e
0. 14a
chlorofo m
0.10
>180 >180
trichloroethylene
2.3ha
9
perchloroethylene
0. 17a
->180
a R e c m n d e d value a t 298OK f r a n experimental measurements i n r e f e r e n c e 34 C a l c u l a t e d f r a n enpirical method given i n r e f e r e n c e 42
c Rased on a d i u r n a l l y averaged OH c o n c e n t r a t i o n o f 4 x 105 molecules cm-1
139
A
number of the organic species listed i n Table 1 such as ethane, prcpane,
a c e t y l e n e , acetone, methanol, methyl c h l o r i d e , methylene d i c h l o r i d e , perchloroe th y l e n e and benzene react very slcwly w i t h hydroxyl radicals as w e l l a s w ith Other halocarbons are even longer live d. Such species shculd be w e l l d i s t r i b u t e d th-h t h e f r e e trcposphere a t midlatitudes
ozone and n i t r o g en t r i o x i d e .
i n t h e Northern Hemisphere.
Therefore, t h e s e orga nic s should c e r t a i n l y c o n t r i b u t e
t o t h e carbon loading of t h e background on "clean" trcposphere. REIATIMSHIFS FIE'J3EEN OIGWIC CCf@OSITIM AND NON-I@Ell@NE OKANIC NITWX;EN
CcMpCuM,
TO
CXIDE RATIOS 'Rl OZONEiFORKCffi POTENTIAL
Extensive simulated s u n l i g h t e n v i r o m n t a l c h a r experimental s t u d i e s involving hydrocarbonnitrogen oxide mi x t u r es i n a i r c a r r i e d out during t h e 1950's to the 1970's danonstrated both the e f f e c t s of orga nic c a nposition a s well a s organic substance to n i t r o g en oxide ratios on v a r i o u s r e a c t i v i t y p a r a n e t e r s ( r e f s . 44-52). These r e a c t i v i t y paraneters involved nitroge n oxide conversion rates, ozone formation, peroxyawl n i t r a t e y i e l d s , aldehyde y i e l d s and b i o l o g i c a l e f f e c t s , p l a n t damage and eye i r r i t a t i o n ( r e f s . 45,46). orga nic c a n p o s i t i o n was s h a m t o have a strong e f f e c t on these r e a c t i v i t y paraneters ( r e f s . 44-49,51,52). Ambient a i r measurenents made &r i n g t h e 1960's indic a te d t h a t a lka ne s were the most a h d a n t class of organic ccanpounds i n p o l l u t e d atmospheres ( r e f . 48). Therefore it was recognized t h a t t h e e f f e c t s on ozone formation of a lka ne s and t h e s u b s t i t u t i o n of other classes of o r g a n i c s f o r a lka ne s r q u i r e d addit i o n a l i n v e st i g a t i o n ( r e f s . 47,49,52). Alkanes and other lcwer r e a c t i v i t y o r g a n i c s were shown to becare r e l a t i v e l y more e f f i c i e n t i n producing ozone a t h ig h e r ratios to nitrogen oxide carpared to alke ne s and other highe r r e a c t i v i t y o r g a n i c s ( r e f . 47,49). I n a s u b q u e n t study involving mixtures of several alkanes, a l k e n e s and aranatics with n i t r o g en oxide s s u b s t i t u t i o n of a lka ne s or a r m t i c s f o r al k en es a t lawer hydrocarbon to nitroge n oxide ratios reduced ozone f o n m t i o n ( r e f . 52). These r e s u l t s were c o n s i s t e n t w ith t h e earlier s t u d i e s t h a t used less c m p l e x systems ( r e f s . 47,49). These experimental studies a t t r a c t e d the a t t e n t i o n of p h o t c c h m i c a l mdelers i n t h e 1980's ( r e f s . 53-55). Photochemical models were used to i n v e s t i g a t e the e f f e c t s of o r g a n ic ccmposition a s well as o r g anic canpcunds to nitroge n oxide ratios with p a r t i c u l a r i n t e r e s t i n ozone-forming p o t e n t i a l . The azone-forming p o t e n t i a l of mi x t u r es of r+kutane, prcpene and carbon m n o x i d e (with snall i n i t i a l co n cen t r at i o n s of aldehydes, hydrogen pe rioxide , ozone, peroxylacetyl n i t r i t e and n i t r c u s a c i d ) were inve stiga te d w i t h nitrogen oxide c o n c e n t r a t i o n s s e l e c t e d t o g i v e ratios of 4.3/1, 53).
me
13.9/1 and 43/1 ( r e f .
r e l a t i v e ozone-forming p o t e n t i a l s of n-tutane t o prcgene inc re a se d
140 w i t h increasing hydrocarbon to nitrogen oxide ratio f r a n 0.14 a t a 4.3/1 ratio t o 0.34 a t a 43/1 ratio.
Another approach to estimating ozone-forming p o t e n t i a l
involved a d d i t i o n of prcpane or trans-2-htene
to two d i f f e r e n t n-txltane-pre
pene-~4( c a r p o s i t i o n mixtures a t carbon c o n t e n t s q u a 1 to 10% o f the i n i t i a l carbon content of the mixture ( r e f . 52). The oxidant-forming p o t e n t i a l was
evaluated by determining the m n t of the i n i t i a l mixture which had to be subtracted to restore the ozone concentration to its o r i g i n a l level.
For both
mixtures it was f m d that the ozone-forming p o t e n t i a l of trans-2-txltene t o prcpane decreased d r a s t i c a l l y with increasing ratio. For exanple t h e r e l a t i v e omne-forming p o t e n t i a l of trans-2-htene to prcpane was 20.9 and 12.7 a t a ratio of 4/1 f o r the two base mixtures carpared t o 5.1 and 2.4 a t a ratio of 40/1. Higher hydrocarbon to nitrogen oxide ratios were considered to occur as a i r masses are transported downwind of urban sarces. Therefore, the ozoneforming p o t e n t i a l of t h e lcwer molecular weight alkanes was concluded to beccme much mre important relative to a l k e n e s a s a i r masses are transported d m i n d
(ref. 53). I n a s u b s q u e n t modeling study a n i n i t i a l mixture was developed based on snbient a i r hydrocarbon measurments i n Atlanta GA ( r e f . 54). S i x hydrocarbons were t r e a t e d e x p l i c t l y i n the mechanisn. Sunmer daytime c o n d i t i o n s were used. Isopleths of maximcan ozone concentrations were develcped modeling the i n i t i a l mixture a t ratios f r a n 3/1 t o 30/1. l M l v e individual o r g a n i c s were added one a t a time to this mixture a t a concentration q u i v a l e n t t o 10% of the carbon c o n t e n t of the mixture. The d i f f e r e n c e i n maximum ozone c o n c e n t r a t i o n s a t t a i n e d was used a s the m a s u r e of ozone-forming p o t e n t i a l f o r these organics. Ethane was the least e f f e c t i v e organic i n ozone f o r m t i o n w h i l e a t laver ratios the a d d i t i o n of ethene, prcpene, trans-2-butene, E x y l e n e , formaldehyde and acetaldehyde a l l caused large i n c r a e n t s i n ozone concentrations. prcpane, ?butane, toluene, methanol and ethanol a d d i t i o n caused rnoderate incremental i n c r e a s e s i n ozone. H m v e r , t h e ozone concentration i n c r a n e n t s f o r those o r g a n i c s which were l a r g e a t low ratios decreased r a p i d l y w i t h i n c r e a s e i n ratio. For example, a d d i t i o n of trans-2-butene caused a n increment of 106% i n t h e 03 concentration a t a 3/1 ratio, a n 03 increment of 11%a t a 10/1 ratio and a 03 incranent of 2% a t a 30/1 ratio. Similar behavior was c a l c u l a t e d f o r ethene, propene, E x y l e n e , fonmldehyde and acetaldehyde. The increments i n 03 r e s u l t i n g f r a n a d d i t i o n s of prcpane and n-txltane were mall a t low ratios but decreased more slowly with increasing ratio. A t ratios above 10/1 and 20/1 toluene and m x y l e n e a d d i t i o n s r e s u l t e d i n decreases i n maximum ozone concentrations. overall t h e increments i n maximum ozone concentrations r e s u l t i n g f m n t h e i n c r e a s e s of 10% i n the carbon c o n t e n t s of the mixtures a t ratio above 10/1 f e l l w i t h i n +lo% f o r a l l twelve organics. I t was concluded t h a t the ozone forming p o t e n t i a l of ozone
141 c a n be r e l a t e d t o t h e rates of r e a c t i o n of hydroxyl radicals w i t h o r g a n i c s a t The negative e f f e c t s of t o l u e n e and m x y l e n e on
lw,but not a t high r a t i o s .
ozone formation a t higher ratios was a t t r i i x t e d to sane of their products, t h e
cresols and t h e aromatic aldehydes, serving as s i n k s f o r n i t r o g e n o x i d e s ( r e f . 53). It was concluded t h a t a t t h e higher alkene to n i t r o g e n oxide ratios trans-2-butene becaws less e f f e c t i v e a t forming o m n e than ethene because of t h e r a p i d consunption of t h e ozone a s it is p r a c e d by i n t e r n a l l y d o u b l e b a s e d alkenes ( r e f . 54). Because of t h e importance of removal of n i t r q e n oxides, a r e a c t i v i t y para-
meter based on both ozone formation and n i t r i c oxide consumption h a s been proposed ( r e f . 5 5 ) . A l i m i t i n g i n c r e n e n t a l r e a c t i v i t y a s the incremental o r g a n i c concentration approaches zero also was suggested.
These concepts were a p p l i e d
t o a d d i g or s u b s t r a c t i n g s i x o r g a n i c s to a four-hydrocarbon-NOk
mixture.
The
i n c r e m n t a l r e a c t i v i t i e s decreased w i t h i n c r e a s i n g r e a c t i o n time w i t h those o f toluene beccrnirq negative. always negative.
me
The i n c r e n e n t a l r e a c t i v i t y of benzaldehyde was
increnrental r e a c t i v i t y of trans-2-butene
also becam nega-
T h i s effect was a t t r i t x t e d more to t h e high
t i v e a t lorqer r e a c t i o n tines.
p e r x q a c e t y l n i t r a t e formation serving a s a n NO, sink than to the d i r e c t r a p i d r e a c t i o n of trans-2-butene
with ozone ( r e f . 5 5 ) .
No higher molecular weight alkanes were i n v e s t i g a t e d i n the s t u d i e s discussed above ( r e f s . 53-55).
Higher molecular weight a l k a n e s can form s u b s t a n t i a l
alkyl n i t r a t e yields ( r e f . 41).
Both r a d i c a l sources, t h e a l k y l p r o x y r a d i c a l s ,
and nitrogen dioxide are r e m v e d by the formation of a l k y l n i t r a t e s ( r e f . 42). However, t h e a l k y l n i t r a t e y i e l d s are dependent on the s t r u c t u r e of the alkane
imr.
Larger a l k y l n i t r a t e y i e l d s are a s s o c i a t e d with alkane isaners forming
secondary proxy r a d i c a l s ( r e f . 42).
As
a r e s u l t of high a l k y l n i t r a t e y i e l d s ,
i n t h e r e a c t i o n s of some of t h e h i g h molecular weight a l k a n e s o m n e y i e l d s shcllld decrease rapidly and becaw negative a s alkane t o n i t r o g e n oxide ratios
increase, H Y C R X Y W D N AND NITRCGEN OXIDE MEFSUREMENTS AT GKXJND
LEVEL RJRAL/RlXlTE SITES
Measuranents of hydrocarbons obtained on s a n p l e s c o l l e c t e d a t rural/ranote l o c a t i o n s i n t h e u n i t e d S t a t e s between 1975 and 1982 are t a b u l a t e d i n Table 2 ( r e f s . 4,27,56-63).
The molecular weight range f o r carpcunds r e p o r t e d covered
d i f f e r s among t h e s e s t u d i e s .
For sane s t u d i e s only i d e n t i f i e d canpounds are
r e p o r t e d ( r e f s . 4,55, 57,61). I n o t h e r s t u d i e s i d e n t i f i e d and u n i d e n t i f i e d ccanpounds are included ( r e f . 37, 59-61,63).
I n one study o n l y biogenic hydro-
carbons a r e i d e n t i f i e d , b u t total normethane hydrocarbon c o n c e n t r a t i o n s are given ( r e f . 2 7 ) . I n scme s t u d i e s m e a s u r m n t s of o n l y a few a l k a n e s above the pentanes are included ( r e f s . 56-58).
I n s e v e r a l s t u d i e s only t h e c6 to c8
aromatic hydrocarbons are included ( r e f s . 56-58,62)
but i n tw of t h e s e s t u d i e s
142 Table 2.
Non-mthane Hydrocarbon Concentrations Measured a t G m n d level Rural/Ranote Locations i n the United S t a t e s
m i a n or ( m a n Concentration), pgbc Total Month
Alkanes
Alkenes Armtics Ident. m t a l
m a t ion
Year
(C7-Cg)
(Bigenic) (c6-C~)
Glaqcw, I L
7-8/75
NAa(16)
1.0
0.7
NMHC NMHC Ref. -56
95 51
NA 82 NA 112 0.17
5% have a design value NI.20 ppm.
ppm.
For
The w o r s t
The h i g h e s t design v a l u e s i t e s a r e
l o c a t e d i n MSAs near o r adjacent t o t h e New York, Los Angeles, and Chicago major m e t r o p o l i t a n areas. The 6th-highest 1-hour d a i l y maximum design value i s a s u r r o g a t e i n d e x f o r t h e 5 ExEx i n d i c a t o r .
The p e r c e n t i l e values a r e 80-8546 l o w e r
t h a n t h e corresponding 1-hour design v a l u e f o r t h e same p e r c e n t i l e rank. As can be seen, o n l y 25% o f MSAs exceed a 5 ExEx 0.12 ppm ozone concentration. T u r n i n g t o t h e l a s t i n d i c a t o r , t h e r e a r e many expected exceedances
o f an 8-hour d a i l y maximum 20.08 ppm.
There a l s o i s wide v a r i a b i l i t y i n
t h e i r number, from 0 f o r 18 MSAs t o 160 f o r t h e worst MSA.
The mean i s
208
about 18, and t h e standard d e v i a t i o n o f t h e sample I s l a r g e r t h a n t h e mean. Longer-term Exposure I n d i c a t o r s The two longer-term I n d i c a t o r s o f i n t e r e s t a r e t h e max monthly and 3month mean indices.
The d a i l y maximum averaging t i m e used f o r t h e s e
i n d i c a t o r s i s 1-hour and 8-hour,
respectively.
Cumulative frequency
d e s c r i p t i v e i n f o r m a t i o n f o r t h e s e two i n d i c a t o r s i s shown i n T a b l e 2.
TABLE 2 Cumulative frequency d e s c r i p t i v e s t a t i s t i c s a s s o c i a t e d w i t h l o n g e r - t e r m ozone a i r q u a l i t y i n d i c a t o r s i n urban areas Maximum Monthly Mean f o r 1-Hour D a i l y Maximums (ppm)
S t a t i s t ic
Maximum 3-Month Mean f o r 8-Hour D a i l y Maximums (ppm)
Mean Standard D e v i a t i o n
.074 .020
.057 .014
Minimum Median 75th Percentile
.025 .072 .084
.016 ,056 .063
90th Percentile 95th Percentile Maximum
.094 .lo2 .219
.072 .078 .140
Sample S i z e
2 1 3*
216
Y h i s i n d i c a t o r cannot be computed f o r t h r e e MSAs due t o l a c k o f a v a l i d 3-month mean f o r t h e MSA design value monitor. There i s moderate sample v a r i a b i l i t y i n t h e two i n d i c a t o r s , as evidenced by t h e small d i f f e r e n c e between t h e mean and median values and t h e small standard d e v i a t i o n s r e l a t i v e t o t h e i r means.
The l a r g e 3-month
means o f t h e t o p 50% MSAs i n t h e sample should be noted. value i s 0.056 ppm.
The median
The worst area has a maximum 3-month mean o f 8-hour
d a i l y maximum averages o f 0.140 ppm--higher t h a n t h e c u r r e n t 1-hour d a i l y maximum NAAQS!
(The area i s Los Angeles.)
RELATIONSHIPS AMONG EXPOSURE INDICATORS I N URBAN AREAS As an i n t r o d u c t i o n t o r e l a t i o n s h i p analyses among exposure i n d i c a t o r s , we consider F i g u r e 1.
Depicted a r e Pearson product-moment l i n e a r c o r r e l a t i o n
c o e f f i c i e n t s among t h e a i r q u a l i t y i n d i c a t o r s o f i n t e r e s t . depict a correlation c o e f f i c i e n t
>I
.751.
Solid lines
Only t h e r e l a t i o n between t h e
209
Exposure Patterns o f I n t e r e s t Mu 1t i p l ePeak, ShortTerm
Peak, ShortTerm
6th-high 1-hour Daily Maximum
4
LongTerm Average
Expected Number o f .90
++
8-hour Days '.08 D a i l y Max.
J. Maximum 3Month Mean o f 8-hour D a i l y Maximums
D a i l y Max.
.70 Expected Number o f Days >.08( Maximum
T Fig. 1.
D a i l y Max. .82
*go$
i
.ir .85
Maximum 3Month Mean o f 8-hour D a i l y Maximums
Maximum Monthly Mean JSg2 o f 1-hour D a i l y Max.
Correlations among short- and long-term a i r q u a l i t y i n d i c a t o r s .
2nd-high d a i l y max and 3-month mean i n d i c a t o r s i s
< I .75).
Note t h a t t h e
max monthly mean index i s h i g h l y c o r r e l a t e d w i t h b o t h s h o r t - t e r m and longterm a i r q u a l i t y indicators. Numerous analyses o f r e l a t i o n s h i p s among t h e s i x exposure i n d i c a t o r s o f i n t e r e s t a r e reported i n Refs. 4 and 5.
The focus o f these analyses was
t o s i m u l a t e attainment o f one exposure i n d i c a t o r i n a l l areas and i n v e s t i g a t e how t h i s a f f e c t e d t h e subsequent frequency d i s t r i b u t i o n o f o t h e r a i r q u a l i t y exposure i n d i c a t o r s .
The s i m u l a t i o n was accomplished by f i t t i n g
a l o g i s t i c o r exponential equation t o t h e frequency d i s t r i b u t i o n o f s t r a t i f i e d data sets.
The r a t i o n a l e and procedure used f o r t h e s t r a t i f i c a t i o n
i s described i n Ref. 4.
As i s t o be expected whenever r e l a t i o n s h i p s a r e f i t t o data, t h e r e i s some " s c a t t e r " around t h e f i t t e d curves.
I n t h i s case, t h e s c a t t e r occurs
f o r t h e s t r a i g h t - l i n e f i t s t o yarameters o f t h e l o g i s t i c o r exponential r e l a t i o n s h i p s t h a t were subsequently used, w i t h o u t u n c e r t a i n t y , t o s i m u l a t e attainment o f an i n d i c a t o r .
Obviously t h e r e i s u n c e r t a i n t y i n h e r e n t i n t h e
use of these curves due t o t h e c u r v e - f i t t i n g procedure.
There i s a d d i t i o n a l
u n c e r t a i n t y associated w i t h t h e concept i t s e l f o f u s i n g s t a t i s t i c a l l y d e r i v e d r e l a t i o n s h i p s f o r c u r r e n t a i r q u a l i t y d a t a s e t s and a p p l y i n g them t o a f u t u r e s i t u a t i o n t h a t may be i n h e r e n t l y d i f f e r e n t than t h e present condition.
I n p a r t i c u l a r , t h e frequency d i s t r i b u t i o n o f f u t u r e a i r q u a l i t y
under a p o s t - c o n t r o l s i t u a t i o n may be d i f f e r e n t than t h e p r e - c o n t r o l d i s t r i b d t i o n c u r r e n t l y observed.
While t h i s i s l i t e r a l l y t r u e , I do n o t
t h i n k t h a t the r e l a t i o n s h i p s among i n d i c a t o r s would be g r e a t l y a f f e c t e d under a p o s t - c o n t r o l scenario f o r t h e reasons e l a b o r a t e d upon i n g r e a t d e t a i l i n Ref. 4. U n c e r t a i n t y o f t h e f i r s t t y p e can be addressed s t a t i s t i c a l l y .
However,
as o f t h e present, a " g o o d n e s s - o f - f i t "
s t a t i s t i c c o u l d n o t be found f o r t h e
l o g i s t i c o r exponential r e l a t i o n s h i p s .
Undoubtedly such a s t a t i s t i c e x i s t s ,
b u t i t i s not i n t h e general s t a t i s t i c a l l i t e r a t u r e . c u r r e n t l y underway t o uncover s a i d s t a t i s t i c ) .
(An e f f o r t i s
The second t y p e o f un-
c e r t a i n t y probably i s best addressed u s i n g a " s e n s i t i v i t y a n a l y s i s " approach, where a l t e r n a t i v e hypotheses regarding p o s t - c o n t r o l a i r q u a l i t y d i s t r i b u t i o n s c o u l d be tested. however.
Resources t o do t h i s a r e n o t a v a i l a b l e a t t h i s time,
The reader must r e a l i z e t h a t t h e i n a b i l i t y t o e x p l i c i t l y address
u n c e r t a i n t y i n t h e r e l a t i o n s h i p s d e p i c t e d below i s an a n a l y t i c shortcoming o f t h i s paper. The r e l a t i o n s h i p s among c e r t a i n . exposure i n d i c a t o r s a r e g r a p h i c a l l y depicted i n Figures 2 through 5.
F i g u r e 2 r e l a t e s t h e number o f 8-hour
d a i l y maximum averages >.08 ppm ( x a x i s ) t o t h r e e a l t e r n a t i v e 1-hour
211
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Expected Number o f 8-Hour Averages >.08 ppm
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Daily Maximum
F i g . 2. P r o p o r t i o n ( i n p e r c e n t ) o f urban s i t e s exceeding s p e c i f i e d expected number o f 8-hour d a i l y maximum averages 0.08 pprn f o r t h r e e 1-hour d a i l y maximum standards ( a t t a i n e d i n a l l areas i n t h e d a t a s e t ) .
2 12
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.06
.07
.08
.09
.I0
Maximum Monthly Mean o f I-Hour D a i l y Maximum Values (ppml
F i g . 3. Proportion ( i n p e r c e n t ) o f urban s i t e s exceeding s p e c i f i e d maximum monthly 1-hour d a i l y maximum values f o r t h r e e 1-hour d a i l y maximum standards ( a t t a i n e d i n a l l areas i n t h e d a t a s e t ) .
213 standards:
0.08,
0.10,
and 0.12 ppm.
Since t h e x-axis v a r i a b l e i s
an i n t e r v a l - s c a l e expected exceedance v a r i a b l e i n t h i s case, t h e c u r v e s f o l l o w a n e g a t i v e e x p o n e n t i a l shape. An example o r t w o may a i d t h e reader i n r e a d i n g F i g u r e 2 and subsequent f i g u r e s .
F i g u r e 2 i n d i c a t e s t h a t i f a 0.12 ppm 1-hour d a i l y
maximum s t a n d a r d i s met by a l l s i t e s i n t h e d a t a set, 10% o f a l l MSAs m i g h t have 1 7 o r more days w i t h an &hour
d a i l y maximum >.08 ppm.
l e a s t one area m i g h t have as many as 30 days.
At
F i f t y p e r c e n t o f t h e MSAs
m i g h t have 4 o r more days w i t h an 8-hour ExEx i n d i c a t o r >.08 ppm.
If the
1-hour d a i l y maximum a i r s t a n d a r d was lowered t o 0.10 ppm and a t t a i n e d by a l l areas i n t h e d a t a s e t , 10% o f t h e MSAs may have 8 o r more days o v e r a
If a 0.08 ppm d a i l y max 1-hour were
0.08 ppm d a i l y max 8-hour average.
a t t a i n e d , no area would have any day w i t h an 8-hour ExEx v a l u e >.08 ppm. F i g u r e 3 shows t h e l o g i s t i c t y p e of c u r v e common f o r t h e c o n t i n u o u s concentration variables.
The x - a x i s r e p r e s e n t s t h e maximum m o n t h l y mean
a i r q u a l i t y i n d i c a t o r ( f o r 1-hour d a i l y maximum values).
The c u r v e s a r e
I f a 0.12 ppm 1-hour s t a n d a r d
f o r t h e t h r e e 1-hour d a i l y rnax i n d i c a t o r s .
was a t t a i n e d i n a l l areas, 10% o f a l l MSAs m i g h t have a max m o n t h l y mean o f 0.075 ppm o r h i g h e r .
T h i s drops t o 0.063 ppm f o r 50% of t h e areas.
A t i g h t e r s t a n d a r d o f course reduces t h e percentage of s i t e s a t o r
above any s p e c i f i c c u t p o i n t on t h e x-axis.
For example, 30% o f MSAs
would see a max m o n t h l y mean o f 0.062 ppm o r h i g h e r i f a 0.08 ppm 1-hour d a i l y max s t a n d a r d i s a t t a i n e d by a l l areas.
T h i s p r o p o r t i o n drops t o
a p p r o x i m a t e l y 5% f o r a 0.10 1-hour standard. The n e x t r e l a t i o n s h i p t h a t w i l l be d e s c r i b e d i s t h e one between t h e 2nd-high d a i l y max and 3-month mean i n d i c a t o r s . o f t h i s r e l a t i o n s h i p appears as F i y u r e 4.
A yraphic d e p i c t i o n
The F i g u r e shows t h a t t h e 3-
month means i n MSAs a r e n o t a l t e r e d g r e a t l y by a t t a i n i n g a 0.10 ppm 2ndh i g h d a i l y max s t a n d a r d r a t h e r t h a n a 0.12 ppm standard. d r a m a t i c a l l y f o r a 0.08 ppm standard,
however.
The means d r o p
O f course, i t i s q u i t e
d i f f i c u l t t o a t t a i n such a r e l a t i v e l y l o w peak ozone value.
I f a 3-month
mean i n d i c a t o r i s o f i n t e r e s t i n MSAs, such an i n d i c a t o r s h o u l d be addressed d i r e c t l y by e s t a b l i s h i n g a NAAQS w i t h a maximum 3-month 8-hour d a i l y maximum a v e r a g i n g time.
T r y i n g t o l o w e r a l o n g - t e r m mean w i t h a
peak a i r q u a l i t y s t a n d a r d i s d i f f i c u l t t o accomplish. F i g u r e 5 d e p i c t s t h e impact o f a t t a i n i n g a l t e r n a t i v e 5 expected exceedance standards on t h e 2nd-high 1-hour d e s i g n value.
As can be seen,
a 0.12 ppm 5 ExEx s t a n d a r d may a l l o w a 2nd-high d e s i g n v a l u e o f almost 0.14 ppm i n t h e w o r s t 10% o f MSAs.
The 2nd-high d e s i g n v a l u e m i g h t be
o v e r 0.12 ppm i n t h e w o r s t 10% o f MSAs w i t h a 5 ExEx s t a n d a r d o f 0.10 ppm. To j u s t a t t a i n a 2nd-high 1-hour d e s i g n v a l u e o f 0.12
ppm i n t h e w o r s t
214
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F i g . 4. Proportion ( i n p e r c e n t ) o f urban s i t e s exceeding s p e c i f i e d threemonth 8-hour d a i l y maximum averages f o r t h r e e 1-hour d a i l y maximum standards ( a t t a i n e d i n a l l areas i n t h e d a t a s e t ) .
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F i g . 5. P r o p o r t i o n ( i n p e r c e n t ) of urban s i t e s exceeding s p e c i f i e d secondh i g h 1-hour d a i l y maximum c o n c e n t r a t i o n values f o r t h r e e 5-expected exceedances standards ( a t t a i n e d i n a l l areas i n t h e d a t a s e t ) .
216 10% o f MSAs r e q u i r e s a 5 ExEx standard o f 0.097 ppm; t h i s then, i s a reasonable "equivalency r e l a t i o n " between t h e two expected exceedances standards. SUMMARY
T h i s paper presented d e s c r i p t i v e ozone data f o r s i x exposure i n d i c a t o r s associated w i t h peak, multiple-peak, times.
and longer-term averaging
Analyses were performed on r e l a t i o n s h i p s between s e l e c t e d p a i r s
o f t h e s i x exposure i n d i c a t o r s . I t was suggested t h a t a maximum monthly mean o f one-hour d a i l y maximum
ozone concentrations c o u l d f u n c t i o n as a s u r r o g a t e exposure i n d i c a t o r o f both s h o r t - and long-term exposure averaging times.
Using t h i s , o r
any o t h e r surrogate i s a t b e s t a compromise, however, f o r t h e more d i r e c t and r i g o r o u s approach o f u s i n g a s e t o f d i f f e r e n t averaging t i m e standards t o p r o t e c t a g a i n s t adverse e f f e c t s s p e c i f i c t o those averaging times. REFERENCES E.H. Lee, D.T. Tingey, and W.E. Hogsett. S e l e c t i o n o f t h e Best ExposureResponse Model Using Various 7-Hour Ozone Exposure S t a t i s t i c s , C o r v a l l i s , OR: U.S. Environmental P r o t e c t i o n Agency, 1987. P.J. Lioy, T.A. Vollmuth, and M. Lippmann. "Persistence o f Peak Flow Decrement i n C h i l d r e n f o l l o w i n g Ozone Exposures Exceeding t h e n a t i o n a l J. A i r Pol. Cont. Assoc. 35: 1068ambient a i r q u a l i t y standard," 1071, 1985. W.W. Heck and D.T. Tingey. "Ozone Time-Concentration Model t o P r e d i c t Acute f o l i a r I n j u r y , " pp. 249-255 i n : H.M. Englund and W.T. Berry (eds), Proc. o f t h e Second I n t e r . Clean A i r Cong., New York: Academic Press, 1971. T. McCurdy. " D e s c r i p t i v e S t a t i s t i c a l Analyses o f Ozone A i r Q u a l i t y I n d i c a t o r s i n Rural/Remote and M e t r o p o l i t a n Areas," Durham, N.C.: S t r a t e g i e s and A i r Standards D i v i s i o n , U.S. EPA, May 1987. T. McCurdy. " A d d i t i o n a l Ozone A i r U u a l i t y I n d i c a t o r s i n M e t r o p o l i t a n Areas," Durham, N.C.: S t r a t e g i e s and A i r Standards D i v i s i o n , U.S. EPA, J u l y 1987.
217
SESSION 111
EFFECTS ON VEGETATION AND ECOSYSTEMS
Chairmen
K. Verhoeff W. Heck
This Page Intentionally Left Blank
T. Schneider et al. (Editors),Atmosphenk Ozone Reaearch and its Policy Implications 0 1989 Elsevier Science Publishers B.V.,Amsterdam -Printed in The Netherlands
219
ANALYSIS OF CKOP LOSS FOR ALTERNATIVE OZONE EXPOSURE INDICES
DAVID T. T I N G E Y l , WILLIAM E. HOGSETTl and E. HENRY LEE2 l U . S . Environmental P r o t e c t i o n Agency, 200 SW 3 5 t h S t r e e t , C o r v a l l i s , OR, 97333 (U.S.A.)
2Northrop S e r v i c e s , Inc.,
200 SW 3 5 t h S t r e e t , C o r v a l l i s , OR, 97333
(U.S.A.)
ABSTKACT Determining t h e a p p r o p r i a t e exposure i n d e x that b e s t relates p l a n t response t o 0 3 exposure is r e l i a n t on a c o n s i d e r a t i o n of t h e u n d e r l y i n g b i o l o g i c a l basis f o r t h e response and a method of c h a r a c t e r i z i n g t h e temporal concentrat i o n v a r i a t i o n s in p o l l u t a n t occurrence. Numerous e m p i r i c a l and m e c h a n i s t i c models have been developed t o assess t h e impact of 0 3 on crop l o s s . I n t h i s paper, a series of exposure i n d i c e s (having d i v e r s e characteristics) are e v a l u a t e d using p l a n t growth d a t a from s e v e r a l c r o p s t o determine which i n d i c e s perform t h e "best." Although r e s u l t s i n d i c a t e that no s i n g l e exposure i n d e x is " b e s t " f o r a l l s p e c i e s , t h e d a t a c l e a r l y i n d i c a t e several g e n e r a l t r e n d s and c o n c l u s i o n s : 1) peak c o n c e n t r a t i o n s are more i m p o r t a n t t h a n low c o n c e n t r a t i o n s in determining p l a n t r e s p o n s e , 2) p l a n t s respond t o t h e cumulative impacts of exposure and 3 ) p l a n t s e n s i t i v i t y v a r i e s w i t h t h e p h e n o l o g i c a l s t a g e of p l a n t development.
INTKOUUCTION
The g o a l of a i r p o l l u t a n t r e s e a r c h is to determine t h e r e l a t i o n s h i p between p o l l u t a n t exposure and p l a n t response.
The q u a n t i f y i n g f u n c t i o n f o r t h i s
p r o c e s s is f r e q u e n t l y termed "dose-response;"
however, i n t h i s d i s c u s s i o n of
exposure dynamics i t w i l l be termed "exposure-response," concept.
a more g e n e r i c
An understanding o f exposure r e s p o n s e r e q u i r e s t h r e e t y p e s of
i n t o r m a t i o n : 1 ) a measure of p l a n t response; 2) a n a p p r o p r i a t e i n d e x t o d e s c r i b e t h e p o l l u t a n t exposure; and 3) a mathematical f u n c t i o n that relates p l a n t response t o p o l l u t a n t exposure.
Defining t h e a p p r o p r i a t e exposure i n d e x
t h a t " b e s t " relates p l a n t r e s p o n s e t o exposure n e c e s s i t a t e s a c o n s i d e r a t i o n of t h e underlying b i o l o g i c a l b a s i s f o r t h e response and a method f o r characteri z i n g t h e temporal v a r i a t i o n s in p o l l u t a n t occurrence. P l a n t s react d i f f e r e n t i a l l y t o temporal v a r i a t i o n s i n p o l l u t a n t concentrat i o n s [ r e f s . 1-41; c o n s e q u e n t l y , i t is n e c e s s a r y t o elect exposure i n d i c e s that s p e c i t i c a l l y account f o r t h e temporal v a r i a t i o n in exposure. I f p l a n t
response were not moditied by t h e e p i s o d i c n a t u r e ( t e m p o r a l v a r i a t i o n ) of t h e e x p o s u r e s , t h e n i t would be s u f f i c i e n t t o c h a r a c t e r i z e t h e exposure w i t h a n
index such as a mean t h a t does n o t r e f l e c t t h e c o n c e n t r a t i o n v a r i a t i o n over time. I n e v a l u a t i n g exposure i n d i c e s that c h a r a c t e r i z e p l a n t response, t h e u l t i m a t e g o a l is t o develop exposure i n d i c e s t h a t i n c o r p o r a t e a l l c o n t r i b u t i n g f e a t u r e s and account f o r a l l ( o r most) of t h e v a r i a t i o n i n t h e exposure response.
A second, more p r a c t i c a l l y o r i e n t e d g o a l i s t h e development o f
exposure i n d i c e s u s e f u l i n t h e s t a n d a r d s e t t i n g process.
An i n d e x f o r a
s t a n d a r d should be easy t o develop and a p p l i c a b l e t o a wide range of s p e c i e s and environmental/exposure c o n d i t i o n s . T h i s o b j e c t i v e may r e p r e s e n t a compromise i n t h e f e a t u r e s i n c l u d e d i n t h e f o r m u l a t i o n of t h e " b e s t " exposure index. The magnitude of p l a n t response t o 03 i s a l t e r e d by s e v e r a l components i n c l u d i n g 1) c l i m a t i c and edaphic f a c t o r s ; 2) b i o l o g i c a l f a c t o r s such as phenological s t a g e of development and g e n e t i c p o t e n t i a l ; and 3) t h e temporal Because t h e s e components and t h e i r i n f l u e n c e on
v a r i a t i o n i n 03 exposure.
p l a n t response have been r e c e n t l y reviewed [ r e f s . 3-41,
t h i s presentation w i l l
focus on t h e e v a l u a t i o n and development of exposure i n d i c e s t h a t i n c l u d e t h e temporal components of t h e exposure.
EVALUATION OF EXPOSURE INDICES There i s no consensus about t h e most a p p r o p r i a t e exposure index ( m e t r i c ) f o r d e p i c t i n g p l a n t response t o 03 exposure [ r e f s .
4-51.
Different indices
have been used, but t h e i r adequacy f o r c h a r a c t e r i z i n g long-term exposures (over a season) i s d o u b t f u l , s i n c e t h e y do n o t account f o r exposure dynamics (i.e.,
temporal v a r i a t i o n ) . A d d i t i o n a l l y , t h e i n d i c e s d o n o t account f o r o t h e r
known i n f l u e n c e s , such as e f f e c t s of exposures a t s p e c i f i c and perhaps c r i t i c a l periods i n p l a n t development.
Most i n d i c e s , such as a s e a s o n a l mean,
do n o t cumulate t h e impact of t h e exposure over t h e growing period. An
a p p r o p r i a t e exposure index should u l t i m a t e l y be d e r i v e d from a
c o n s i d e r a t i o n of t h e underlying b i o l o g i c a l basis f o r t h e response and a procedure f o r q u a n t i f y i n g t h e temporal v a r i a t i o n s i n 03 occurrence. An e v a l u a t i o n of v a r i o u s exposure i n d i c e s i s e s s e n t i a l l y a comparison of t h e i n f l u e n c e of d i f f e r e n t s c a l i n g s of t h e exposure v a r i a b l e on t h e exposure response f u n c t i o n (Fig.
1). The comparison i s based on a s i n g l e set of
b i o l o g i c a l responses (e.g.,
p l a n t y i e l d ) but they are r e l a t e d t o d i f f e r e n t
mathematical c h a r a c t e r i z a t i o n s of 0 3 exposure ( s c a l e s ) such as a mean or a cumulation of hourly c o n c e n t r a t i o n s . The d i f f e r e n t i n d i c e s o r s c a l i n g s do not change t h e magnitude of t h e measured p l a n t response, but t h e y do govern how t h e s e responses are p o s i t i o n e d along t h e exposure a x i s (Fig. 1).
221
I
Exposure Index Fig. 1. An example of a h y p o t h e t i c a l exposure-response f u n c t i o n i l l u s t r a t i n g t h e t h r e e key elements i n understanding exposure dynamics. The exposure index connotates a d e s c r i p t i o n of 03 exposure and i s used a s a scaling factor. A pair of examples i l l u s t r a t e s t h e e f f e c t of using d i f f e r e n t i n d i c e s f o r
c h a r a c t e r i z i n g t h e temporal v a r i a t i o n s i n 03 exposure ( F i g . 2).
In the f i r s t
example (Fig. 2A, B), a l f a l f a p l a n t s were exposed t o e p i s o d i c 03 exposures [ r e t . 21 and harvested (when t h e p l a n t s reached one-tenth bloom) t h r e e times during t h e season. A comparison was made between two exposure i n d i c e s : 1) t h e 7-h (0900 t o 1559) s e a s o n a l mean c o n c e n t r a t i o n [ r e f . 61 and 2) t h e g e n e r a l i z e d phenologically weighted cumulative impact (GPWCI) t h a t cumulated t h e exposure and emphasized t h e peak c o n c e n t r a t i o n s [ref.7].
The f i t of t h e same exposure-
response f u n c t i o n t o t h e i d e n t i c a l response d a t a was c l e a r l y b e t t e r when t h e GPWCI (Fig. 2B) was used t o a r r a y t h e observed p l a n t responses a l o n g t h e exposure a x i s than when t h e 7-h s e a s o n a l mean was used (Fig. 2A).
With t h e
GPWCI, t h e t r e n d f o r reduced p l a n t growth w i t h i n c r e a s i n g exposure i s p l a i n l y seen; however, t h i s p a t t e r n is not e v i d e n t when t h e mean is used. A second example (Fig. 2C. D) is provided by a comparison of t h e maximum y i e l d l o s s observed i n a range of crop s p e c i e s . The e v a l u a t i o n of exposure i n d i c e s compared t h e 7-h s e a s o n a l mean and t h e t o t a l exposure (sum of c o n c e n t r a t i o n s throughout t h e study). I n t h i s example, as i n t h e p r e v i o u s one (Pig. 2A, B), t h e r e i s a c l e a r t r e n d showing a n i n c r e a s e i n maximum y i e l d l o s s w i t h i n c r e a s i n g i n c r e a s i n g exposure (Fig. ZD); however, when t h e 7-h s e a s o n a l mean was used t h i s t r e n d was n o t e v i d e n t (Fig. 2C). The p r i n c i p a l d i f f e r e n c e between t h e two
I n d i c e s was t h e i n c l u s i o n of exposure d u r a t i o n (number of days) i n t h e t o t a l exposure index. Several of t h e s t u d i e s had e s s e n t i a l l y t h e same 7-h s e a s o n a l
222 mean, but t h e s t u d y d u r a t i o n s d i f f e r e d by a p p r o x i m a t e l y two-fold,
which caused
t h e l a c k of a clear t r e n d i n t h e d a t a . In both examples, t h e mean was n o t a n a p p r o p r i a t e index ( s c a l i n g f a c t o r ) f o r d e s c r i b i n g t h e r e s p o n s e of p l a n t s t o
long-term (e.g.,
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GPWCI Pig. 2. Two comparisons o f d i f f e r e n t exposure i n d i c e s u s i n g t h e same b i o l o g i c a l r e s p o n s e d a t a . The d a t a i n F i g u r e 2A and B were d e r i v e d from Hogsett e t a l . [ r e f . 21 and t h e d a t a i n F i g u r e ZC and D a r e from Lee e t a l . [ r e f . 141. I n F i g u r e 2C and D, t h e symbols i n d i c a t e t h e y e a r of t h e s t u d y and t h e s p e c i e s used; A = a l f a l f a , C = c o t t o n , S = soybean, W = wheat. The mathematical mean of t h e h o u r l y 03 c o n c e n t r a t i o n s , o v e r v a r i o u s t i m e p e r i o d s , i s f r e q u e n t l y used t o c h a r a c t e r i z e p o l l u t a n t e x p o s u r e s . The 7-h (M7) and 12-h (M12) s e a s o n a l means have g a i n e d c r e d e n c e f o r r e l a t i n g p l a n t y i e l d t o 03 exposure because of t h e i r u s e i n t h e N a t i o n a l Crop Loss Assessment (NCLAN)
program [ r e f s . 6 , 8 , 9 ] . The s p e c i f i c 7-h p e r i o d (0900-1559)
s e l e c t e d was
thought t o correspond t o t h e p e r i o d o f g r e a t e s t p l a n t s e n s i t i v i t y and t h e h i g h e s t 03 l e v e l s [ r e f . 61. The s e a s o n a l mean c o n c e n t r a t i o n is a summation of a l l hourly c o n c e n t r a t i o n s ( f o r t h e s e l e c t e d t i m e p e r i o d ) d i v i d e d by t h e number
of o b s e r v a t i o n s .
Cure e t a l . [ r e f . 81 r e p o r t e d t h a t s e a s o n a l mean
c h a r a c t e r i z a t i o n s of 03 e x p o s u r e were much l e s s s e n s i t i v e t h a n t h e 1-h maximum to yearly variations i n
03 p a t t e r n s . An i n f i n i t e number of h o u r l y
d i s t r i b u t i o n s (from t h o s e c o n t a i n i n g many peaks t o t h o s e c o n t a i n i n g none) can y i e l d t h e same 7-h s e a s o n a l mean. If a mean is s e l e c t e d a s a n exposure i n d e x i o r c h a r a c t e r i z i n g e x p o s u r e s , c e r t a i n assumptions are implied and must be considered in a s t u d y ' s i n t e r p r e t a t i o n : o A mean t e n d s t o minimize t h e c o n t r i b u t i o n s of peak c o n c e n t r a t i o n s t o t h e response, implying t h a t peak e v e n t s do n o t need t o be g i v e n s p e c i a l cons i d e r a t i o n .
o All c o n c e n t r a t i o n s w i t h i n t h e s e l e c t e d a v e r a g i n g t i m e are e q u a l l y e t t e c t i v e in e l i c i t i n g a response. o Reduced crop y i e l d r e s u l t s from t h e accumulation of d a i l y 03 i m p a c t s o v e r t h e growing season. o Exposure d u r a t i o n is n o t s p e c i f i c a l l y included: i.e.,
t h e mean can not
d i s t i n g u i s h between exposures t o t h e same c o n c e n t r a t i o n but of d i f f e r e n t durations (i.e.,
10 o r 100 days).
o The d i s t r i b u t i o n of hourly 03 c o n c e n t r a t i o n s ( o v e r t h e a v e r a g i n g t i m e ) a r e unimodal and not h i g h l y skewed. However, ambient 03 c o n c e n t r a t i o n d i s t r i b u t i n s a r e f r e q u e n t l y skewed toward t h e h i g h e r c o n c e n t r a t i o n s . I d e a l l y , t h e s e l e c t i o n o f t h e most a p p r o p r i a t e exposure i n d e x would be derived irom s c i e n t i i i c p r i n c i p l e s and be v a l i d a t e d by e x p e r i m e n t a l s t u d i e s
s p e c i t i c a l l y designed f o r that purpose.
However, t h i s approach would d e l a y
r e s o l v i n g t h e s e l e c t i o n of exposure i n d i c e s f o r y e a r s u n t i l t h e n e c e s s a r y experiments were designed and conducted. An a l t e r n a t i v e approach i s t o conduct a r e t r o s p e c t i v e a n a l y s i s ot e x i s t i n g p l a n t - r e s p o n s e d a t a . T h i s approach p e r m i t s t h e r e a n a l y s i s of e x i s t i n g d a t a f o r e v a l u a t i n g o r developing a range o t exposure i n d i c e s and d e r i v i n g p r i n c i p l e s of exposure response.
Nevertheless,
t h e i n d i c e s developed by t h i s method w i l l u l t i m a t e l y need t o be v a l i d a t e d e x p e r i m e n t a l l y . A major l i m i t a t i o n w i t h r e t r o s p e c t i v e a n a l y s i s is that t h e s p e c i t i c s t u d i e s were not designed t o r developing exposure i n d i c e s o r t e s t i n g exposure hypotheses; consequently t h e u s a b i l i t y of t h e d a t a is l i m i t e d . An e v a l u a t i o n of e x i s t i n g and proposed exposure I n d i c e s was conducted [ r e f .
7 1 on c r o p y i e l d d a t a o b t a i n e d from t h e U.S.
Environmental P r o t e c t i o n Agency's
NCLAN Program [ r e t . 91. P l a n t p r o d u c t i o n and hourly 03 m o n i t o r i n g d a t a were
o b t a i n e d from t h e NCLAN Data L i b r a r y in R a l e i g h , North Carolina.
Data from
f i e l d experiments on soybean, wheat, c o r n , sorghum, and c o t t o n were used i n t h e a n a l y s e s . Crops were grown a c c o r d i n g t o s t a n d a r d a g r i c u l t u r a l p r a c t i c e s and exposed t o a range of 03 c o n c e n t r a t i o n s (ambient l e v e l s and above) i n open-top chambers [ r e f . 9 ] . Exposure i n d i c e s were c a l c u l a t e d from c r o p y i e l d data f o r t h e f i v e s p e c i e s ( w i t h m u l t i p l e y e a r s and c u l t i v a r s f o r a t o t a l o f 17 i n d i v i d u a l cases). The d e t a i l s of t h e data s o u r c e s and a n a l y t i c a l procedures used i n t h e r e t r o s p e c t i v e
224 a n a l y s i s are d e s c r i b e d by Lee e t a l . [ r e f . 71. The a u t h o r s e v a l u a t e d s i x d i f f e r e n t t y p e s of exposure i n d i c e s f o r t h e 17 i n d i v i d u a l cases; t h e d i f f e r e n t t y p es of i n d i c e s had d i s p a r a t e c h a r a c t e r i s t i c s . The v a r i o u s t y p e s of exposure i n d i c e s used i n t h e a n a l y s e s are compared i n Tab l e 1 and t h e a b b r e v i a t i o n s used i n Table 1 are d e s c r i b e d : 1. One Event: i n c l u d e s t h e maximum 7-h (P7) and maximum 1-h ( P l ) d a i l y a v e r a g e s [ r e f . 61 and t h e 9 0 t h (PERSO), 9 5 t h (PER95), and 9 9 t h (PER99) p e r c e n t i l e s of hourly d i s t r i b u t i o n . 2. Mean: i n c l u d e s t h e s e a s o n a l means [ r e f . 61 o f 7-h d a i l y means (M7), 1-h d a i l y means ( M l ) and t h e e f f e c t i v e mean [ r e f . 107](EFFMEAN). 3. Cumulative: r e p r e s e n t s t h e s e a s o n a l sum of a l l h o u r l y c o n c e n t r a t i o n s , i.e., t o t a l exposure (TOTDOSE).
4. C o n cen t r at i o n Weighting: Two s e p a r a t e t y p e s of w ei g h t i n g i n d i c e s were used; a. Sum C o n c e n tr a ti o n (Sum Conc) i n d i c e s cumulated t h e exposure and used e i t h e r d i s c o n t i n u o u s or c o n t in u o u s weighting of c o n c e n t r a t i o n [ r e f . 41. The d i s c o n t i n u o u s i n d i c e s i n c lu d e d s e a s o n a l sum of h o u r l y c o n c e n t r a t i o n s a t o r above 0.06 ppm (SUMO6), 0.07 ppm (SUMO7), 0.08 ppm (SVMOS), or 0.10 ppm (SUM10); s e a s o n a l censored sum of h o u r l y c o n c e n t r a t i o n s a t o r above a t h r e s h o l d , i.e., c u m u l a t iv e sum o f t h e area o v er t h r e s h o l d of 0.08 ppm ( A O M B ) or 0.10 ppm (AOT10). The co n t i n u o u s i n d i c e s i n cl u d ed t o t a l impact [ r e f . 111 (TIMPACT); ALLOMETRIC i n which t h e h o u r l y c o n c e n t r a t i o n was r a i s e d t o a power and summed; and SIGMOID i n which t h e h o u r l y c o n c e n t r a t i o n was m u l t i p l i e d by a sigmoid w ei g h t i n g f u n c t i o n (inflection 0.062 ppm) and summed [ r e f . 71.
-
b. Number of Episodes (Num Episodes) i n d i c e s counted t h e e p i s o d e s o v e r a growing season. This t y p e of i n d e x i n c lu d ed t o t a l h o u r s w i t h co n cen t r at i o n s a t or above t h r e s h o l d s of 0.08 ppm (HRSOB) o r 0.10 ppm (HRS10); t h e number of e p i s o d e s above a t h r e s h o l d of 0.08 ppm (NuMEPO8) or 0.10 ppm (NUMEP10); and a v e r a g e e p is o d e l e n g t h u s i n g t h r e s h o l d s of 0.08 ppm (AVGEP08) o r 0.10 ppm (AVGEP10).
5. Multicomponent: t h e s e i n d i c e s i n c o r p o r a t e s e v e r a l c h a r a c t e r i s t i c s o f exposure [ r e f . 41. Lee e t a l . [ r e f . 71 e v a l u a t e d a number o f multicomponent i n d i c e s 0 5 0 0 ) that in c l u d e d d i f f e r e n t w ei g h t i n g 8 f o r concent r a t i o n and p h e n o lo g i c a l stages of development. T h i s e v a l u a t i o n u s e s t h e i r [ r e f . 71 " b e s t" multicomponent i n d ex (GPWCI) which has t h e f o l l o w i n g f e a t u r e s : 1) a sigmoid c o n c e n t r a t i o n w e i g h t i n g f u n c t i o n ( i n f l e c t i o n p o i n t 0.062 pprn), 2 ) e x p o s u r e s o c c u r r i n g 20 t o 40 d ay s b ef o r e harvest were g i v en maximum weight, and 3) t h e weighted h o u r l y c o n c e n t r a t i o n s were cumulated f o r t h e exposure p e r io d .
-
6. R es p i t e Time: t h e a v e r a g e number o f days between e p i s o d e s ( a n e p i s o d e was d e f i n e d as a n e v e n t w i t h h o u r l y 03 c o n c e n t r a t i o n s above a t h r e s h o l d v a l u e ) u s i n g t h r e s h o l d v a l u e s o f 0.08 ppm (DAYBETO8) o r 0.10 ppm (DAYBET10). The exposure i n d i c e s were computed from a c t u a l h o u r l y 03 m o n i t o r i n g d a t a and r e g r e s s e d a g a i n s t i n d i v i d u a l chamber h a r v e s t y i e l d s u si n g t h e Box-Tidwell model [ r e f . 71. The " b e s t" exposure i n d e x f o r each set of r esp o n se data ( c a s e )
was t h e one d i s p l a y i n g t h e minimum r e s i d u a l sum of s q u a r e s (RSS). For a n i n d i v i d u a l case, t h e r e l a t i v e performsnce of a n i n d ex was measured as t h e r a t i o of i t s RSS t o t h e i n d e x w i t h t h e minimum RSS and ranked i n ascen d i n g o r d e r , i.e.,
t h e " b e s t" i n d e x f o r a case has a r e l a t i v e RSS o f 1. For o v e r a l l
comparison, t h e exposure i n d i c e s were e v a l u a t e d a c c o r d i n g t o t h r e e c r i t e r i a :
225 (1) t h e average s c o r e c a l c u l a t e d as t h e mean r e l a t i v e RSS's averaged a c r o s s t h e 17 c a s e s ; (2) t h e range of r e l a t i v e RSS's; and (3) p e r c e n t v a r i a t i o n ,
(i.e.,
[range/mean s c o r e ] x 100). The nonparametric Wilcoxin signed ranks test
was used t o perform p a i w i s e comparisons of r e l a t i v e RSS's among i n d i c e s a c r o s s cases i r e f . 1 2 ) . TABLE 1. Comparison of v a r i o u s exposure I n d i c e s . Exposure Index GPWCI SUMO7
SUM06 SIGMOID SUM08 AOTO8 PER99 TIMPACT
EFFMEAN M7 TOTDOSE ALLOMETKIC
PER90 PER95 AOTlO MI SUM10
P7 P1 NUMEP08 HKSlO AVGEPOB HKSOU
AVGEP 10 NUMEPlO DAYbET 10 DAYBETO8
Mean Score
1.12 1.14 1.15 1.17 1.17 1.18 1.19 1.20 1.20 1.20 1.21 1.22 1.22 1.23 1.24 1.26 1.27 1.31 1.40 1.40 1.43 1.46 1.49 1.74 1.78 4.49 5.35
Minimum Maximum Range Score Score
1.02 1.01 1.04 1.04 1 a05 1.01 1 .oo 1.01 1.02 1.02 1.02 1.01 1.01 1.00 1.02 1.02 1.00 1.00 1.07 1 .oo 1 .00 1.01 1.05 1.00 1.03 1.37 1.49
1.36 1.32 1.38 1.35 1.54 1.80 2.06 1.70 1.65 1.63 1.63 1.74 1.86 1.99 2.84 2.11 2.96 2.32 2.34 2.04 4.67 4.93 5.07 4.08 5.46 15.20 17 .OO
0.34 0.31 0.34 0.31 0.49 0.79 1.06 0.69 0.63 0.61 0.61 0.73 0.85 0.99 1.82 1.09 1.96 1.32 1.27 1.04 3.67 3.92 4.02 3.08 4.43 13.83 15.51
x Variation
Index 5Pe
30 Multicomponent 27 Sum Conc Sum Conc 30 26 Sum Conc 42 Sum Conc Sum Conc 67 One Event 89 58 Sum Conc 52 Mean 51 Mean Cumulative 50 Sum Conc 60 One Event 70 80 One Event Sum Conc 147 Mean 87 Sum Conc 154 One Event 101 91 One Event 74 Num Episode 257 Num Episode 268 Num Episode 270 Num Episode 177 Num Episode 249 N u m Episode 308 R e s p i t e Time 290 R e s p i t e Time
No s i n g l e exposure index performed "best" (based on minimum RSS) f o r a l l p l a n t s p e c i e s / c u l t i v a r s , but t h e r e was p o s i t i v e agreement among t h e top-ranked i n d i c e s f o r t h e 17 c a s e s [ r e f . 71.
A comparison of t h e 27 i n d i c e s used found
that 20 had average s c o r e s of 1.20 o r h i g h e r (Table 1).
The p a i r e d sample
Wilcoxin signed ranks test showed no s i g n i f i c a n t d i f f e r e n c e s ( a t t h e 0.05 l e v e l ) between t h e top-ranked
Index (GPWCI) and o t h e r i n d i c e s which a l s o gave
g r e a t e r weight t o e l e v a t e d c o n c e n t r a t i o n s and cumulated t h e exposures (SUM07, SUM06, SIGMOID, SUMO8, AOTO8, ALLOMETRIC, AOT10, SUM10).
The weighted
cumulative i n d i c e s SUM07, SUMO6, and SIGMOID had s i m i l a r average s c o r e s (1.14,
1.15, and 1.17 r e s p e c t i v e l y ) and d i s p l a y e d s i m i l a r p e r c e n t v a r i a t i o n s t o t h e
226 top-ranked GPWCI i n d e x a c r o s s a l l s p e c i e s / c u l t i v a r s .
Although t h e SUMOB,
AOTOB, and PER99 i n d i c e s were n o t s i g n i f i c a n t l y d i f f e r e n t from t h e top-
performing i n d e x , t h e y d i s p l a y e d g r e a t e r p e r c e n t v a r i a t i o n t h a n t h e toppertorming GPWCI index.
I n p a r t i c u l a r , t h e noncumulative i n d e x , PER99, had
r e l a t i v e f i t s ranging from 1.00 t o 2.06 a c r o s s t h e c a s e s , which r e p r e s e n t s a t h r e e - t o l d i n c r e a s e o v e r t h e top-performing
GPWCI's range of r e l a t i v e RSS's.
Three i n d i c e s , ALLOMETKIC, SUMl0, and AOT10, had a v e r a g e s c o r e s g r e a t e r t h a n 1.20,
but were n o t s i g n i f i c a n t l y d i f f e r e n t from t h e top-ranked GPWCI i n d e x due
t o a n e x t r e m e l y poor f i t i n a s i n g l e c a s e ( t h e 1981 c o t t o n s t u d y w i t h droughtstressed plants).
Based on o u r c r i t e r i a , SUM07, SUM06, and SIGMOID were
n e a r l y e q u a l i n performance t o t h e top-ranked
GPWCI index. Based on a v e r a g e
s c o r e and v a r i a t i o n , t h e M7 performed b e t t e r t h a n PER99 (non-cumulative i n d i c e s ) , but i t s performance was s i g n i f i c a n t l y i n f e r i o r t o t h e f o u r top-ranked i n d i c e s (GPWCI, SUMO7, SUMOC, and SIGMOID). For t h e s e a n a l y s e s , t h e exposure i n d i c e s t h a t emphasize peak c o n c e n t r a t i o n s and cumulate c o n c e n t r a t i o n s o v e r t i m e performed b e t t e r t h a n t h o s e t h a t only a v e r a g e c o n c e n t r a t i o n s .
S i m i l a r c o n c l u s i o n s were reached by Lefohn e t a l . [ r e f . 131 and Lee e t a l . ( r e f . 141 who used NCLAN d a t a and c u m u l a t i v e i n d i c e s w i t h sigmoid [ r e f . 131 and a l l o m e t r i c [ r e f . 141 c o n c e n t r a t i o n weighting f u n c t i o n s .
of Lee e t a l .
[ r e f . 7 1 found t h a t t h e sigmoid-weighting
The r e c e n t work
f u n c t i o n s were
p r e f e r r e d t o a l l o m e t r i c ones. The GPWCI i n d i c e s w i t h sigmoid w e i g h t s (which emphasized c o n c e n t r a t i o n s >0.06 ppm) performed b e t t e r t h a n d i d d i s c o n t i n u o u s l y weighted cumulative exposure i n d i c e s that i g n o r e h o u r l y c o n c e n t r a t i o n s below t h r e s h o l d s of 0.08 ppm and higher.
However, t h e d i s c o n t i n u o u s l y weighted
cumulative i n d i c e s (SUMO7 and SUMO6) t h a t used t h r e s h o l d c o n c e n t r a t i o n s (0.06 o r 0.07 ppm) t o emphasize c o n c e n t r a t i o n and accumulated e x p o s u r e performed s i m i l a r l y t o t h e top-ranked
GPWCI index.
CONCLUSION
Our a n a l y s e s s u p p o r t t h e c o n c l u s i o n s from p r e v i o u s s t u d i e s t h a t demonstrated t h e importance of peak c o n c e n t r a t i o n s i n d e t e r m i n i n g p l a n t r e s p o n s e .
Although
no s i n g l e i n d e x was deemed " b e s t " ( i n a l l cases) f o r r e l a t i n g 03 exposure t o p l a n t r e s p o n s e , t h e top-performing
exposure i n d i c e s were t h o s e that ( 1 )
cumulate t h e h o u r l y 03 c o n c e n t r a t i o n s o v e r t i m e , ( 2 ) emphasize c o n c e n t r a t i o n s o f 0.06 ppm and h i g h e r e i t h e r by c o n t i n u o u s sigmoid w e i g h t s o r by d i s c r e t e (0 o r 1) w e i g h t s of t h e t h r e s h o l d i n d i c e s , and ( 3 ) gave g r e a t e r weight t o exposures o c c u r r i n g 20 t o 40 d a y s b e f o r e h a r v e s t .
When a s s e s s i n g t h e impact of
03 on p l a n t growth, t h e s e f i n d i n g s i l l u s t r a t e t h e importance of exposure
d u r a t i o n , t h e importance o f r e p e a t e d peaks, and t h e t i m e of i n c r e a s e d p l a n t sensitivity.
227 REFERENCES R.C. Musselman, R.J. Oshima and R.E. G a l l a v a n , " S i g n i f i c a n c e of p o l l u t a n t c o n c e n t r a t i o n d i s t r i b u t i o n i n t h e r e s p o n s e of ' r e d kidney' beans t o ozone,'' J. Am. SOC. Hortic. Sci. 108 (1983) 645-648. W.E. H o g s e t t , D.T. Tingey and S.R. Holman, "A programmable exposure c o n t r o l system f o r d e t e r m i n a t i o n of t h e e f f e c t s o f p o l l u t a n t exposure regimes on p l a n t growth," Atmos. Environ. 19 (1985) 1135-1145. U.S. Environmental P r o t e c t i o n Agency, A i r Q u a l i t y Criteria f o r Ozone and o t h e r Photochemical O x i d a n t s , 1986 I , Research T r i a n g l e Park, NC, EPA-LOOI 8-84-020aF. W.E. H o g s e t t , D.T. Tingey and E.H. Lee, Exposure i n d i c e s : Concepts f o r development and e v a l u a t i o n of t h e i r u s e . In: Assessment o f Crop Loss from Air P o l l u t a n t s : Proceedings of t h e i n t e r n a t i o n a l c o n f e r e n c e , R a l e i g h , N.C., USA, (ed.) W.W. Heck, O.C. Taylor and D.T. Tingey, London, Elsevier Applied Science, 1988 (In p r e s s ) . A.S. Heagle, and W.W. Heck, F i e l d methods t o assess crop l o s s e s due t o o x i d a n t a i r p o l l u t a n t s . In Crop Loss Assessment: Proceedings o f E.C. Stakman Commemorative Symposium, ed. by P.S. Teng and S.V. Krupa, Misc. P u b l i c a t i o n # 7 , U n i v e r s i t y of Minnesota, St. P a u l , 1980, pp. 296-305. W.W. Heck, W.W. Cure, J.O. Rawlings, L.J. Zaragoza, A.S. Heagle, H.E. Heggestad, K.J. Kohut, L.W. Kress and P.J. Temple, "Assessing i m p a c t s of ozone on a g r i c u l t u r a l c r o p s : I. Overview," J. A i r P o l l u t . C o n t r o l Assoc.
34: (1984) 729-735. E.H. Lee, D.T. Tingey and W.E.
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H o g s e t t , " E v a l u a t i o n of ozone exposure i n d i c e s i n exposure-response modeling. In Assessment of c r o p l o s s from a i r pollutants," Environ. P o l l u t . (1988) (In p r e s s ) . W.W. Cure, J . S . Sanders and A.S. Heagle, "Crop y i e l d r e s p o n s e p r e d i c t e d w i t h d i f f e r e n t c h a r a c t e r i z a t i o n s of t h e same ozone t r e a t m e n t s , " J. Environ. Qual. 15: (1986) 251-254. W.W. Heck, O.C. T a y l o r , R.M. Adams, G. Bingham, J. Miller, E. P r e s t o n and L. Weinstein, "Assessment of c r o p l o s s from ozone,'' J. A i r P o l l u t . C o n t r o l Assoc. 32: (1982) 353-361. K.I. Larsen and W.W. Heck, "An a i r q u a l i t y d a t a a n a l y s i s system f o r i n t e r r e l a t i n g e f f e c t s , s t a n d a r d s , and needed s o u r c e r e d u c t i o n s : P a r t 8 . An e f f e c t i v e mean 03 c r o p r e d u c t i o n mathematical model," J. A i r P o l l u t . C o n t r o l Assoc. 34: (1984) 1023-1034. R . I . Larsen, A.S. Heagle and W.W. Heck, "An a i r q u a l i t y d a t a a n a l y s i s s y s t e m f o r i n t e r r e l a t i n g e f f e c t s , s t a n d a r d s , and needed s o u r c e r e d u c t i o n s : P a r t 7. An 03-502 l e a f i n j u r y mathematical model," J. A i r P o l l u t . C o n t r o l A S ~ O C . 33: (1983) 198-207. W.J. Conover, P r a c t i c a l Nonparametric S t a t i s t i c s . John Wiley & Sons, New York, 1971, 461 pp. A.S. Lefohn, J.A. Laurence and R.J. Kohut, "A comparison of i n d i c e s that d e s c r i b e t h e r e l a t i o n s h i p between exposure t o ozone and r e d u c t i o n i n t h e y i e l d of a g r i c u l t u r a l c r o p s , " Atmos. Environ. (1988) (In p r e s s ) . E.H. Lee, U.T. Tingey and W.E. H o g s e t t , S e l e c t i o n of t h e b e s t exposureresponse model using v a r i o u s 7-hour ozone exposure statistics, U.S. EPA, Oi-tice of A i r Q u a l i t y Planning and S t a n d a r d s , Research T r i a n g l e P a r k , NC,
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T. Schneider et aL (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlanda
223
EFFECTS OF OZONE ON AGRICULTURAL CROPS
S.V. KRUPAL and M. NOSAL' 1 Department o f Plant Pathology, U n i v e r s i t y o f Minnesota, S t . Paul, Minnesota 55108 (USA) a Department o f Mathematics and S t a t i s t i c s , U n i v e r s i t y o f Calgary, Calgary, A l b e r t a T2N 1N4 (Canada). ABSTRACT Time s e r i e s , s p e c t r a l coherence a n a l y s i s showed t h a t a t low 0s f l u x dens i t y , median h o u r l y Oa concentration provided t h e h i g h e s t coherence w i t h a l f a l f a h e i g h t growth, w h i l e a t h i g h Oa f l u x density, i t was t h e cumulative i n t e g r a l o f exposure. These and a d d i t i o n a l r e s u l t s f o r Oa and o t h e r approp r i a t e exposure terms f o r SO' were j o i n t l y u t i l i z e d i n a non-linear regression t o r e l a t e ambient p o l l u t a n t exposure dynamics t o a l f a l f a harvest biomass. INTRODUCTION
Much o f t h e e a r l y research on t h e e f f e c t s o f ozone ( O a ) on crops was d i r e c t e d t o acute exposures and p r o d u c t i o n o f v i s i b l e i n j u r y under c o n t r o l l e d environment and greenhouse c o n d i t i o n s .
Such e f f o r t s , among o t h e r d i s c o v e r i e s ,
l e d t o t h e i d e n t i f i c a t i o n o f s e n s i t i v e crop genera, species. and c u l t i v a r s . However, over t h e p a s t two decades, t h e emphasis has s h i f t e d toward examining chronic 0s exposures and changes i n crop growth, p r o d u c t i v i t y , and q u a l i t y ( r e f . 1). According t o Krupa and Manning ( r e f . 2), answering t h e key q u e s t i o n o f whether o r n o t 0s s i g n i f i c a n t l y a f f e c t s c r o p growth and y i e l d has proven t o be e x t r a o r d i n a r i l y d i f f i c u l t .
This i s due t o t h e n a t u r e o f t h e p o l l u t a n t and
i t s d i s t r i b u t i o n i n t h e ambient a i r .
During t h e crop growth season, Oa i s
an a l l - p e r v a s i v e p o l l u t a n t , making i t d i f f i c u l t t o exclude i t and s t i l l have c o n d i t i o n s t h a t are r e l e v a n t t o those t h a t occur I n nature.
Side-by-side
com-
parisons o f t h e e f f e c t s o f ambient Or on crops a r e impossible, unless some way can be devised t o exclude 01 from t h e c o n t r o l treatment t o background levels.
Development o f a u n i v e r s a l l y accepted method, under normal c o n d i t i o n s
has n o t been s u c c e s s f u l l y accomplished a t t h i s time.
This means t h a t a l l
experimental determinations o f t h e e f f e c t s o f ambient Oa on crop growth and y i e l d must be q u a l i f i e d by t h e i n h e r e n t l i m i t a t i o n o f whatever method was used t o achieve them (Table 1).
230 Table 1. Comparative advantages and disadvantages o f some f i e l d assessment methods o f O3 exposure and c r o p response.
1)
Oprn-top chambers (up-draft)
2)
Open-top Chambers (downdraft)
a) Most u l d r l y used system l n the w: a) A r t l f l c l a l chambrr e f f e c t on p l a n t growth and p r o d u c t l v l t y present. s c m 15 years o f h l s t o r l c a l records. b) Wlqh c o s t f o r (ncludlng s u f f t c l e n t b) Many crops can be groun t o w t u r l t y undrr condltlons s a w h a t a~ulogws number of t n a t m n t s and labor lntenslr e, t o the amblmt. c) L f f r c t s o l rlr p o l l u t a n t s can be c) Conplea colputer c o n t r o l l e d systrm requlred t o mlnlck amblent p o l l u t a n t evaluated s l n g l y o r as mlxtuns. exposure dynamlcs u l t h l n the chambar. d) CDlnparlsons can be made b e t w e n 4 ) P o l l u t a n t flat u l t h l n the chambrr f l l t e r e d (OMp o l l u t a n t removal) a r t l f l c l a l and not s l m l l a r to the and u n l l l t e r r d a d l m t a l r , ablent. a) I l o d l f l c a t l o n s I n t h r n l c r o c l l n r t e a) Reasonable c o n t r o l on e n v l n n u l t h l n the chimbrr can b a d t o a l t e r e d mrntal variables u l t h l n the chabrr lncldencr of pathogens and pests 1) Raln shadows prasent g l Is subject t o weather hazards, lncludlng lncurslon of a d l e n t a l r i n t o the chambrr.
a t tlnrs. a ) Sam as (a). (b). l c ) . and 1.1
of f ( 1 )
b) 0. r a c l u s l o n (ran the m b l e n t a t r enterlng the c h a d a r varles from 255 t o
1M c ) Anblent r a l n I s excluded. d ) As u l t h ( I ) . I s subject t o w a t h e r hazards, 3)
Oprn-alr. chanberlrss. a r t l f l c l a l f i e l d exposure
a ) Wo chamber a f f e c t
b) Largr n d r r of plants can b r raposrd t o varylng 01 exposure re9 l n r s ,
c ) Oeslrablr approach if(b). I d ) . and (e) under the dlradrantages am rec tl f led.
a) -11 chanqrs l n u l n d t u r b u l r n c r can cause l a r q r chanqrs l n 0. concrntratlons. b) Hlgh p r r c l s l o n i n a frrd-back c o n t r o l of 01 r r l r a s c and l n t r n s l v r and r x t c n s l v r monitorlng o f 01 w l t h l n the study p l o t rrqulrrd.
c) Control, study p l o t d l f f l c u l t t o d r r l w i t h due t o the m l - p r e s r n c a of 01. d ) I n t r n s l v r and r x t c n s l v r monltortnp of other a t r p o l l u t o n t s and a n v l r o m n t a l varlablas r r q u l rrd, e) Powerful. m u l t l v a r l a t r . tlmr s r r l r s modrls r r q u l r r d t o f u l l y #valuate t h r r c s u l t s .
4)
Natural pradlents of ambient 0.
a) Lvaluatlon of the n a l world sltuitlon. b ) lllqh degree of nilkith posslble
5)
Chrmlcal protectants (ant!-oxldmts)
a) Close t o the r e a l world b) Wlgh degree of n p l l c a t l o n poltlblr
6[
C u l t l v a r scnanlng
Modlflad from Krupa ( r e f . 23)
a) S u f f l c l r n t number of treatments (varylng 01 rxposure r e g l w s ) u l t h l n a s n s l l gropraphlc arra requlrrd. b) 0 s and o t h r r p o l l u t a n t s . and envlronmental varlablcs must be i n t r n s l v r l y monltorrd a t each sltc. c ) V a r l a b i l l t y due to t h e i n f l u r n c a of l o l l must be accounted, unlrss standardlied sol1 i s usrd a t a11 study sites. d) saw as ( C ) Of f(3) e ) Year t o y r a r v a r l a b l l l t y I n 0, raposurr and crop responsr must be accountrd I) L f f r c t o f t h r p r o t r c t a n t l t s r l f on p l a n t
grobth and y l c l d posslble: thus p r l o r testlng rrqulrrd b) The amount of p r a t e c t l o n provtdrd by d l f f e r r n t chrnlcal dose on d l f f r r e n t p l a n t speclei not f u l l y undrrstood. c ) Snr as a l l o t h r r s l l s t r d under (4).
a) Closest t o the m a 1 world
a) D l f f r r r n c e s I n t h r t h r o n l c rrrponses
b) No chambers. no chmlcal protectants
of c u l t l v a r c t o 01 exposurrs must be knaun . b) S a i i s (b). (d). and ( e l l l s t e d I n f(4).
231 ESTABLISHING NUMERICAL D E F I N I T I O N S
OF CAUSE (CHRONIC 0 0 EXPOSURE) - EFFECTS
(CROP RESPONSE) RELATIONSHIPS
A necessary step i n a l l exposure s t u d i e s i s t h e q u a n t i t a t i v e d e s c r i p t i o n o f t h e cause-effect r e l a t i o n s h i p s .
While a number o f i n v e s t i g a t o r s have devel-
oped models t o e x p l a i n such r e l a t i o n s h i p s ( r e f . 3), t h e mathematical d e f i n i t i o n o f 03 exposure parameters u t i l i z e d i n such models has been t h e s u b j e c t o f much debate ( r e f s . 3-7).
According t o Krupa and K i c k e r t ( r e f . 3 ) . any
d e f i n i t i o n of t h e 00 exposure q u a n t i f i c a t i o n term(s) must be b i o l o g i c a l l y meaningful and must be b r o a d l y a p p l i c a b l e .
While achieving t h a t goal could
prove t o be mathematically complex, a i r q u a l i t y r e g u l a t o r s and p o l i c y makers wish simple, a d m i n i s t r a t i v e l y a p p l i c a b l e s o l u t i o n s .
I n addressing t h i s objec-
t i v e , t h e use o f o v e r - s i m p l i f i e d 00 exposure terms, such as t h e a p p l i c a t i o n o f crop growth season average 00 concentrations ( r e f . 8) has been subjected t o much c r i t i c i s m ( r e f s . 3 . 5 ) .
Such c r i t i c i s m s a r e based on t h e l a c k o f b i o -
l o g i c a l meaning and u n i v e r s a l a p p l i c a b i l i t y o f such models ( r e f s . 6.7.9). I n t h e i r a n a l y s i s o f t h e numerical models o f a i r p o l l u t a n t exposure and Krupa and K i c k e r t ( r e f s . 3.10) concluded t h a t a
vegetation response (Table 2 ) ,
s a t i s f a c t o r y expression o f t h e p o l l u t a n t exposure term(s) should consider: a)
The a r t i f a c t s of p o l l u t a n t averaging techniques, since t h e frequency d i s t r i b u t i o n s o f ambient 00 concentrations, i n general, a r e n o t normally d i s t r i b u t e d .
They a r e b e s t described by t h e f a m i l y o f Weibull
f u n c t i o n s ( r e f s . 11.12); b)
t h e e p i s o d i c i t y o f t h e occurrence o f ambient Oa o r t h e peak exposures (refs
c)
.
7.1 3.14.1 5.1 6) ;
t h e t i m e i n t e r v a l s between such episodes, t h e r e s p i t e t i m e f o r t h e crop t o e s t a b l i s h some degree o f r e p a i r o r e x h i b i t p r e - d i s p o s i t i o n ( r e f s . 17,18,19);
d)
and
t h e r e l a t i o n s h i p between t h e occurrences o f Oa episodes and t h e d i f f e r i n g p h y s i o l o g i c a l s e n s i t i v i t y o f t h e crop growth stages ( r e f s . 7.20).
I n attempting t o r e c o n c i l e w i t h these and o t h e r requirements. a number o f i n v e s t i g a t o r s i n t h e U.S.
have developed and evaluated t h e a p p l i c a b i l i t y o f
0 s exposure i n d i c e s ( r e f s . 6.7).
The conclusion drawn from a l l these
studies i s t h a t no s i n g l e numerical d e f i n i t i o n o f 00 exposure has y e t been found which i s u n i v e r s a l l y a p p l i c a b l e .
This i s n o t s u r p r i s i n g s i n c e t h e
ambient 0 s exposure-crop response r e l a t i o n s h i p s must be considered t o be inherently stochastic i n nature ( r e f . 21).
Further, such r e l a t i o n s h i p s a r e
obviously i n f l u e n c e d by a number o f v a r i a b l e s ( c r o p species and c u l t i v a r i n question, occurrence o f o t h e r p o l l u t a n t s , pathogens and pests. a g r i c u l t u r a l P r a c t i c e s , o t h e r non-pollutant atmospheric and edaphic v a r i a b l e s , e t c . ) . Given t h i s complexity, one wonders about t h e v a l i d i t y o f r e g i o n a l s c a l e
232
Table 2. Sumnary comments on some numerical models used to relate O3 exposures to crop responses. Reference
Type of Model
0. Ixposure Parameters
1.
Benson e t a l . (24)
Non-linear. polynomial o r multivariate. linear
Sum of h o u r l y average On Concentration p e r day o r sums o f h o u r l y average 01 concentrations. weekly over t h e growth season.
2.
Heagle e t a l . (8)
Various forms o f non-linear Weibull and polynomials
1-hrlday. seasonal mean
3.
Heck e t 11. (25)
Linear, p l a t e a u l i n e a r
1-hrlday. seasonal mean
4.
Kinsman e t a l . ( 2 6 )
Linear. l o g - l i n e a r . exponential second degree p o l ynoni a 1, quadratic , square r o o t and Y e i b u l l
12-hr m a n . 1-hr mean. 12-hr t o t a l , 1-hr t o t a l . 1 5 t h p e r c e n t i l e of 12-hr values. 9 0 t h p e r c e n t l l e of 12-hr values, a l l d u r i n g f l w e r i n g t o m a t u r i t y of soybean.
5.
Lefohn e t a l . ( 6 )
Linear. Weibull
Number of occurrences equal t o o r above s p e c i f i c h o u r l y mean concentration: sun of a l l h o u r l y m a n concentrations equal t o o r above a selected concentratlon; weighted sum o f a l l h o u r l y mean concentrations.
b.
Loehman and Y i l k l n s o n (21)
L i n e a r o r n o n - l i n e a r quadratic
1-hr d a i l y continuous concentration
1.
Nosal (12)
M u l t i v a r i a t e . polynomial. Fourier
Peak concentratlon, frequency of exposure. cumulative i n t e g r a l of exposure
8.
Oshima e t 11. (20)
linear
Sum o f h o u r l y average 0 s concentration >0.10 pprn d u r i n g d a y l i g h t hours over e n t i r e growth season.
9.
Roue and Chestnut (29)
Llnear
Average h o u r l y 0 s concentrations per m n t h surmed over growth season o r number o f d a y l l g h t hours of 0 . >0.10 ppn.
Tingey e t a l . ( 1 )
Box-Tidwcll
Maximum 7-hr and maaimum 1-hr d a l l y averages and the 90th. 95th. and 9 9 t h p e r c e n t i l e s o f h o u r l y d i s t r i b u t i o n ; seasonal means o f 1 - h r d a i l y means; 1-hr d a i l y m a n s and e f f e c t i v e mean; seasonal sum of a l l h o u r l y concentrations: two separate types of concentration welghting. seasonal sum o f h o u r l y concentrations a t o r above 0.06 ppn. 0.01 ppm. 0.00 ppm. o r 0.10 ppn; seasonal censored sum of h o u r l y concentrations a t o r above a threshold, i . e . . cumulatlve sum o f t h e area over t h r e s h o l d of 0.00 ppn o r 0.10 ppm, t o t a l impact i n which t h e h o u r l y concentratlon was r a i s e d t o a power and s u m d ; o r t h e h o u r l y c o n c e n t r a t i o n was m u l t i p l i e d by a s i g m i d weighting f u n c t l o n ( i n f l e c t i o n 0.062 ppm) and sunmed. t o t a l hours w i t h concentrat l o n s a t o r above thresholds o f 0.08 ppn o r 0.10 ppm; average episode l e n g t h using thresholds o f 0.00 ppm o r 0.10 ppm: multi-component which included d i f f e r e n t weightlngs on c o n c e n t r a t i o n and phenologlcal staqes o f development; t h e average n u e e r o f days between c p l sodel using t h r e s h o l d values o f 0.00 ppm o r 0.10 ppm.
10.
-
Modified from Krupa and K i c k e r t ( r e f . 3 )
233 0s-induced crop l o s s assessment ( r e f . 22).
Such assessments, however,
obviously have a c r i t i c a l impact on t h e promulgation and implementation o f a i r q u a l i t y regulatory p o l i c i e s . I n an attempt t o determine t h e Importance o f various Oa exposure parameters i n crop response, Nosal ( r e f . 12) found t h a t t h e frequency o f exposure, peak 01 concentration, and t h e cumulative i n t e g r a l o f Oa exposure over t h e crop growth season were a l l important i n examining soybean y i e l d responses. These conclusions were r e c e n t l y s u b s t a n t i a t e d ( r e f . 7). R e g r e t f u l l y , many o f t h e e f f o r t s t o develop Oa exposure i n d i c e s a r e based upon studies, t h e r e s u l t s o f which a r e d e r i v e d from i n a p p r o p r i a t e experimental design ( r e f s . 3.10).
While Oa may be t h e s i n g l e dominant a i r p o l l u t a n t
v a r i a b l e i n a p a r t i c u l a r p l a c e and time, one should n o t f o r g e t t h a t ambient a i r i s n o t f r e e o f o t h e r p o l l u t a n t s , pathogens and pests.
Any Oa exposure
i n d i c e s developed must consider these f a c t o r s and must be based on r e a l i s t i c ambient parameters. APPLICATION OF TIME SERIES, SPECTRAL COHERENCE ANALYSIS, AND BEST NON-LINEAR REGRESSION TO RELATE AMBIENT Oa AND SO2 EXPOSURES TO ALFALFA RESPONSES
I n a study conducted i n Minnesota, a l f a l f a (De Kalb 120) was grown i n open a i r i n a comnon s o i l type a t 9 s i t e s over two sunmers. were obtained a t each s i t e . scale O a and
SO2
A t o t a l o f 7 harvests
During t h e study t h e p l a n t s were exposed t o area
from a p o i n t source.
During each harvest period, t h e h e i g h t growth o f a l f a l f a was measured once a week a t each s i t e and i n d i v i d u a l growth curves f o r t h e h a r v e s t p e r i o d were developed using an exponential model.
Based on these growth curves, a l f a l f a
growth a t each s i t e d u r i n g each harvest was d i v i d e d i n t o t h r e e phases (1-15 days; 16-30 days and 31-45 days, h a r v e s t ) .
The impacts o f O a and
SO2 on each growth phase were evaluated using t h e f o l l o w i n g exposure para-
meters:
mean; median; p e r c e n t i l e s ; peaks; frequency o f exposure and cumula-
t i v e i n t e g r a l o f exposure. F o u r i e r transformations and time s e r i e s , s p e c t r a l coherence a n a l y s i s were used i n examining t h e r e l a t i o n s h i p s between t h e p o l l u t a n t exposure dynamics and a l f a l f a h e l g h t growth.
The u n d e r l y i n g concept o f these numerical methods
i s t h a t each t i m e s e r i e s or f u n c t i o n o f t i m e can be m e a n i n g f u l l y represented as a l i n e a r combination o f pure s i n e waves sunmed over d i f f e r e n t frequencies, w i t h d i f f e r e n t amplitude and phase a t each frequency ( r e f . 30).
Spectral
a n a l y s i s proceeds by F o u r i e r t r a n s f o r m a t i o n o f t h e t i m e s e r i e s t o o b t a i n t h e c o e f f i c i e n t s o f sinusoids a t a d i s c r e t e s e t o f frequencies. grouping nelghbouring frequencies i n t o frequency bands and e s t i m a t i n g various q u a n t i t i e s i n one frequency band a t a time.
234 The s p e c t r a l d e n s i t y o f a v a r i a b l e i s estimated by computing t h e average squared amplitude o f t h e sinusoids w i t h i n a frequency band.
T h i s estimated
s p e c t r a l d e n s i t y i s p l o t t e d as a f u n c t i o n o f frequency (more p r e c i s e l y as a f u n c t i o n of band frequency c e n t e r and frequency bandwidth).
The s p e c t r a l
d e n s i t y i n d i c a t e s how t h e v a r i a t i o n e x h i b l t e d by t h e data i s d i s t r i b u t e d over t h e d i f f e r e n t frequency bands. Spectal a n a l y s i s o f i n d i v i d u a l v a r i a b l e s can be u s e f u l l y extended t o p a i r s o f t i m e s e r i e s and i n v e s t i g a t i o n s o f t h e i r i n t e r r e l a t i o n s h i p .
One o f t h e most
important frequency domain concepts i s t h e coherence f u n c t i o n ( r e f . 31). Coherence resembles t h e usual a n a l y s i s o f two random v a r i a b l e s .
Only here
adjacent frequencies w i t h i n a frequency band t a k e t h e p l a c e o f t h e independent observations.
Coherence i s a measure o f a s s o c i a t i o n between t h e two t i m e
s e r i e s (expressed i n terms o f t h e i r frequencies) s i m i l a r t o squared c o e f f i cient of correlation.
The phase, o r phase d i f f e r e n c e between t h e two t i m e
s e r i e s i n d i c a t e s t h e d i r e c t i o n o f t h e a s s o c i a t i o n and i s analogous t o t h e s i g n of the correlation coefficient.
Broadly speaking, t h e coherence i s intended
t o measure t h e degree t o which t h e two t i m e s e r i e s vary t o g e t h e r and t h e phase captures t h e e x t e n t t o which they a r e i n step. A sumnary o f t h e r e s u l t s o f t h e t i m e s e r i e s , s p e c t r a l coherence a n a l y s i s
between Oa exposure dynamics and a l f a l f a h e i g h t growth dynamics i s provided i n Table 3 .
O f a l l t h e exposure parameters examined, "median" h o u r l y 00 con-
c e n t r a t i o n provided t h e h i g h e s t coherence value w i t h t h e a l f a l f a h e i g h t growth, when t h e degree o f OS f l u x d e n s i t y (expressed as frequency) was low.
However,
when t h e O a f l u x d e n s i t y was high, t h e "cumulative i n t e g r a l " o f OS exposure provided t h e h i g h e s t coherence value w i t h t h e a l f a l f a h e i g h t growth.
These
f i n d i n g s a r e extremely important i n t h e c o n t e x t o f previous s t u d i e s conducted by others ( r e f e r t o Table 2 ) .
I n those e f f o r t s a s i n g l e o r m u l t i p l e exposure
q u a n t i f i c a t i o n term(s) computed over t h e whole growth season were used i n examining t h e cause-effects r e l a t i o n s h i p s and no s i n g l e d e s c r i p t o r o f t h e exposure parameter was deemed t o be t h e best.
The r e s u l t s o f t h e t i m e s e r i e s ,
coherence a n a l y s i s p r o v i d e an e x p l a n a t i o n f o r t h e conclusion reached.
The
exposure parameter p r o v i d i n g t h e h i g h e s t coherence value w i t h t h e crop growth dynamics, changes w i t h t h e degree o f O a f l u x d e n s i t y .
Ambient 01 exposure
regimes a r e governed by t h e s t o c h a s t i c i t y and t h e v a r i a b i l i t y o f t h e c l i m a t o l o g i c a l processes. time.
Thus, Oa f l u x d e n s i t y i s h i g h l y v a r i a b l e i n space and
The c h a r a c t e r i s t i c s o f t h i s f l u x d e n s i t y appear t o determine t h e t y p e
o f exposure parameter t h a t can b e s t d e s c r i b e t h e crop response a t any given time.
Since t h e crop growth stage o r phenology a l s o changes w i t h time,
a p p r o p r i a t e d e s c r i p t o r s o f exposure must be i d e n t i f i e d f o r each growth stage and u t i l i z e d i n t h e f i n a l equation(s) e x p l a i n i n g t h e c r o p y i e l d responses.
235 Table 3 .
Study S i t e 1
1
2 2 3 3 4 4 5 5 6 6 1
1 9 9 10 10
Time s e r i e s , s p e c t r a l a n a l y s i s o f coherence between 0s exposure parameters and a l f a l f a h e i g h t growth.
01 Exposure Parametera Median Concentration (MC) Cumulative I n t e g r a l ( C I ) MC C I MC CI MC C I MC CI MC CI MC CI MC CI MC C I
Highest Coherence
Frequencyb
0.64b 0.98b 0.44 0.92 0.56 0.96 0.60 0.95 0.58 1 .oo 0.36 0.88 0.40 0.96 0.46 0.96 0.56 0.98
0.004 0.480 0.004 0.480 0.055 0.480 0.380 0.480 0.055 0.480 0.385 0.480 0.155 0.480 0.380 0.480 0.060 0.480
a OS exposure parameters were computed from h o u r l y data, 24 hrs/day. Frequency = l / p e r i o d i c i t y ; a t lower frequencies, median 0s concentrations provided t h e highest coherence; w h i l e a t h i g h e r frequencies, cumulative exposure i n t e g r a l provided t h e h i g h e s t coherence w i t h a l f a l f a h e i g h t growth.
236 Table 4.
R e l a t i o n s h i p s between ambient ozone ( 0 s ) and s u l f u r d i o x i d e exposures and a l f a l f a l e a f d r y weight p e r 100 stems.
(Sol)
A l f a l f a l e a f d r y weight p e r 100 stems = 0.92 x Oa Med. 1 + 0.001 x Oa I n t . 1 + -4.2 x Oa Med. 2 + -0.28 x Oa Peak. 2 + 0.002 x Oa I n t . 2 + 3.6 x Oa Med. 3 + -0.001 x Oa I n t . 3 + 0.19 x Oa Peak. 1 + 0.47 x SO2 Ep'is. 2 t -0.002 x SO2 Peak. 1 P2 + -0.02 x SO2 Epis. 2 P2 + 0.0001 x SO2 I n t . 2 P2 + -0.013 x SOa Epis. 3. P2. Best non-linear regressiona, Ra = 0.90
V a r i a b l eb 1) 2) 3) 4) 5) 6)
Hed. 1 Int. 1 Hed. 2 0 s Peak. 2 0s Int. 2 0 s Med. 3 Oa Oa Oa
Contribution t o RaC 0.02 0.01 0.13 0.09 0.12 0.15
M u l t i p l e c o r r e l a t i o n = 0.95; a Mallows Cp = 9.34;
Variableb 7) 6) 9) 10) 11)
C o n t r ib u t t o n t o R2C
Oa I n t . 3 Oa Peak. 1
S o t Epis. 2 SO2 Peak. 1 P2 SOa Epis. 2 P2 1 2 ) soz I n t . 2 P2 13) SOa Epis. 3 P2
0.01 0.04 0.01 0.03 0.01 0.01 0.01
S i g n i f i c a n c e ( T a i l Prob.) = 0.0000
A t o t a l o f 63 treatments were i n c l u d e d i n t h e regression.
Med. = Median concentration; I n t . = Cumulative i n t e g r a l o f exposure; Peak = peak concentration; Epis = number o f episodes o r frequency o f exposure. Exposure parameter f o l l o w e d by 1, 2 o r 3 i n d i c a t e s f i r s t (1-15 days), second (16-30 days) o r t h i r d (31-45 days) growth phase o f a l f a l f a . Exposure parameter ending as P2 i n d i c a t e s power 2 o f t h e term. F o r Oa. a l l parameters were computed from h o u r l y data; f o r SO,, a l l parameters were computed from continuous data. The value o f t h e f i n a l R 2 i s s e q u e n t i a l l y reduced by t h e f r a c t i o n i n d i c a t e d i n each case.
237 Krupa and Nosal ( r e f . 32) p r e v i o u s l y developed a d u a l t i m e s e r i e s model t o r e l a t e SOz exposures t o a l f a l f a responses.
This model consisted o f a com-
b i n a t i o n o f t i m e s e r i e s a n a l y s i s and response surface methodology.
The
r e s u l t s o f t h e a p p l i c a t i o n o f t h e same model w i t h t h e a d d i t i o n o f t h e approp r i a t e Om exposure parameters i d e n t i f i e d from t h e t i m e s e r i e s coherence a n a l y s i s a r e presented i n Table 4.
The "median" h o u r l y Om c o n c e n t r a t i o n and
t h e "cumulative i n t e g r a l " o f exposure d u r i n g 1-15 days o f growth were t h e best p r e d i c t o r s o f t h e f i n a l harvested a l f a l f a biomass.
The Om peaks were Impor-
t a n t b u t were i d e n t i f i e d by t h e regression as t h e f o u r t h and t h e e i g h t h best p r e d i c t o r s among a l l independent v a r i a b l e s i n c l u d e d i n t h e equation.
The
SOz exposure parameters i n t h i s p a r t i c u l a r study were l e s s i m p o r t a n t than
t h e 01 exposure parameters.
The reader should n o t conclude, however. t h a t
t h i s i s a u n i v e r s a l statement a p p l i c a b l e t o o t h e r cases i n v o l v i n g S O Z . SUMMARY We have discussed i n t h i s paper some considerations r e l e v a n t t o t h e numeric a l a n a l y s i s o f a i r p o l l u t a n t exposure and crop response.
Based on t h i s , we
have described an approach c o n s i s t i n g o f F o u r i e r t r a n s f o r m a t i o n and t i m e s e r i e s , s p e c t r a l coherence a n a l y s i s i n i d e n t i f y i n g numerical d e s c r i p t o r s o f
Om exposure parameters t h a t best describe a l f a l f a growth dynamics.
The
exposure parameter p r o v i d i n g t h e best d e s c r i p t i o n o f t h e crop growth response varied w i t h the 0 s f l u x density.
Since t h e f l u x d e n s i t y o f 01 v a r i e s i n
t i m e and space, one can conclude t h a t a p p r o p r i a t e exposure term(s) should be i d e n t i f i e d f o r each s p e c i f i c crop growth stage and such terms a p p l i e d i n t h e f i n a l equation d e s c r i b i n g t h e crop y i e l d response.
Thls paper provides an
explanation as t o why previous e f f o r t s by others t o i d e n t i f y a s i n g l e , u n i v e r s a l l y a p p l i c a b l e exposure term were unsuccessful. ACKNOWLEDGEMENTS The s e n i o r author i s h i g h l y g r a t e f u l t o t h e United States Department o f A g r i c u l t u r e , Cooperative S t a t e Research Service f o r p r o v i d i n g t h e f i n a n c i a l support f o r t h i s research.
The s e n i o r a u t h o r would a l s o l i k e t o convey h i s
a p p r e c i a t i o n t o D e l l a Patton f o r her very a b l e assistance i n t h e p r e p a r a t i o n o f t h i s manuscript. REFERENCES
1 2
3
United States Environmental P r o t e c t i o n Agency. A i r Q u a l i t y C r i t e r i a f o r Ozone and Other Photochemical Oxidants, Vol. 111, U.S. EPA, Research T r i a n g l e Park, 1986. S.V. Krupa and W.J. Manning, Environ. P o l l u t . , 50 (1988) 101-137. S. Krupa and R.N. K i c k e r t , Environ. P o l l u t . , 44 (1987) 127-158.
238 4 5 6 1
8 9 10 11 12 13 14 15 16 11 18 19 20 21
22 23 24 25 26 27 28 29 30 31 32
W.E. Hogsett, D.T. Tingey and E.H. Lee, i n W.W. Heck, D.T. Tingey and O.C. T a y l o r ( E d i t o r s ) , Proc. I n t . Conf. Assessment o f Crop Loss from A i r P o l l u t a n t s , E l s e v i e r Applied Science, Barking. 1988, i n press. A.S. Lefohn and V.C. Runeckles. Atmos. Environ., 21 (1987) 561-568. A.S. Lefohn, J.A. Laurence and R.J. Kohut, Atmos. Environ., (1988) I n press. D.T. Tingey, W.E. Hogsett and E.H. Lee, Proc. 8 5 t h A i r P o l l u t . C o n t r o l Assoc. Ann. Meetings, Dallas, i n press. A.S. Heagle, V.M. Lesser, J.O. Rawlings, W.W. Heck and R.B. Philbeck, Phytopathology, 76 (1986) 51-56. E. Brennan, I . Leone, B. Greenhalgh and 6. Smith, J. A i r P o l l u t . C o n t r o l ASSOC., 37 (1987) 1429-1433. S.V. Krupa and R.N. K i c k e r t , An Analysis o f Ambient A i r P o l l u t i o n Exposure Regimes i n Vegetation Response Research, A l b e r t a Government-Industry A c i d i c Deposition Research Program, Calgary, 1988, i n press. A.S. Lefohn and H.M. Benedict, Atmos. Environ., 16 (1982) 2529-2532. M. Nosal, Proc. 1 7 t h A i r P o l l u t . C o n t r o l Assoc. Ann. Meetings, San Francisco. 84-104.5 (1984) 1-16. W.E. Hogsett, D.T. Tingey and S.R. Holman, Atmos. Environ., 19 (1985) 1135-1 145. A.S. Lefohn and C.K. Jones, J. A i r P o l l u t . C o n t r o l Assoc., 36 (1986) 1123-1 129. R.C. Musselman. A.J. Huerta, P.M. McCool and R.J. Oshima, J. Am. SOC. H a r t . Sci., 111 (1986) 410-413. G.C. P r a t t , R.C. Hendrickson, 8.1. Chevone, D.A. Christopherson, M.V. O'Brien and S.V. Krupa, Atmos. Envlron., 1 7 (1983) 2013-2023. J.W. Johnston, J r . and A.S. Heagle, Phytopathology. 72 (1982) 381-389. V.C. Runeckles and P.M. Rosen, Can. J. bot., 52 (1974) 2607-2610. E.H. Steinberger and Z. Naveh, A g r i c . Environ., 7 (1982) 255-263. U.T. alum and W.W. Heck, Environ. Expt. Bot., 20 (1980) 13-85. S.V. Krupa and P.S. Teng, Proc. 7 5 t h A i r P o l l u t . C o n t r o l Assoc. Ann. Meetings, New Orleans, 82-6.1 (1982) 1-10. R.M. Adams, S.A. Hamilton and 8.A. McCarl, J. A i r P o l l u t . Control Assoc.. 35 (1985) 938-943. S.V. Krupa, Proc. 1 1 t h A i r P o l l u t . C o n t r o l Assoc. Ann. Meetings, San Francisco, 84-104.2 (1984) 1-13. F.J. Benson, S.V. Krupa, P.S. Teng and D.E. Welsch, F i n a l Rept., Minnesota P o l l u t . Control Agency, R o s e v i l l e , pp.270. W.W. Heck, O.C. Taylor, R. Adams, 6. Bingham, J. M i l l e r , E. Preston and L. Weinstein, J. A i r P o l l u t . Control ASSOC., 32 (1982) 353-361. J.D. Kinsman, W.P. Saunders and R.E. Wyzga, Environ. P o l l u t . (1988) i n press. E. Loehman and T. Wilkinson, Purdue Univ. Agr. Expt. Sta. B u l l . , 426 (1983) pp.38. R.J. Oshima, M.P. Poe, P.K. Braegelmann. D.W. B a l d i n g and V. van Way, J. A i r P o l l u t . Control Assoc., 26 (1916) 861-865. R.D. Roue and L.G. Chestnut, J. A i r P o l l u t . C o n t r o l Assoc. 35 (1985) 128-134. P. Bloomfield, F o u r i e r Analysis o f Time Series, John Wiley & Sons, New York. 1976. W.A. F u l l e r , I n t r o d u c t i o n t o S t a t i s t i c a l Time Series. John Wiley b Sons, New York, 1976. S.V. Krupa and H. Nosal. Environ. P o l l u t . (1988) submitted.
T.Schneideret al. (Editors),Atmospheric Ozone Research and its P o l e Implicatwna 0 1989Elsevier Science PublishersB.V.,Amsterdam -Printed in The Netherlands
239
EFFECTS OF OZONE AND OZONE-ACIDIC PRECIPITATION INTERACTION ON FOREST TREES IN NORTH AMERICA
William J. Manning Department of Plant Pathology, University of Massachusetts, Amherst, MA., 01003, USA
ABSTRACT Ozone is the principal cause of declines of ponderosa and Jeffrey pine in California, 1. hartwegii, p. montezumae and p. patula around Mexico City, and sensitive eastern white pines in the northeast USA and Canada. There is no evidence that ozone, or ozone-acidic precipitation interaction, is involved in sugar maple decline, red spruce decline, or radical growth reductions of yellow pines. Ozone and acidic precipitation can affect ectomycorrhizal associations in roots of tree seedlings. INTRODUCTION Ozone (0,) is the most prevalent and phytotoxic gaseous air pollutant in North America [ l ] . For many years, researchers have focused primarily on the effects of O3 on the productivity of crop plants.
During the last few years,
however, increased attention has been given to the possible direct or interactive role that O3 may play in what appears to be unusual or accelerated declines in several forest trees.
These declines are usually characterized by
visible symptoms and reduced terminal and radial growth which results in tree decline and eventual death.
The several tree decline syndromes have been ex-
tensively described by others [ 2 , 3 , 4. 5, 61 and are summarized in Tables 1 and 2 . My purpose is to review the possible effects of Og, alone and in combination with acidic precipitation, on the growth, productivity and longevity of several North American forest trees.
240
TABLE 1 Examples where ozone or ozone/acidic precipitation may cause tree injury and decline in forests in North America Trees
Locations
References
Caused by ozone Pinus hartwegii Pinus montezumae
Mountains around Mexico City
Pinus jeffreyi Pinus ponderosa
San Bernadino and other mountains in Southern California
[9-181
Pinus strobus -
Northeast USA and Southeast Canada
[ 19-28]
Ozone or ozonelacidic precipitation may be involved Abies religiosa Acer saccharum
Mountains around Mexico City Northeast USA and Southeast Canada
Picea rubens --
Northeast and southern Appalachian mountains
Pinus echinata Pinus rigida
New Jersey Pine Barrens
Pinus echinata Pinus elliottii Pinus taeda --
Southeast USA
[ 7 , 81 [29-351
[36-461 [ 4 , 47-48]
DIRECT EFFECTS There are only a few examples where the direct effects of 0, on trees have been extensively investigated and well-documented.
Long-term exposure to
ambient O3 has resulted in injury, decline, and disappearance of sensitive genotypes within natural populations of several species of pine in southern California, Mexico, and the eastern USA and Canada [ 2 , 4 , 7 , 81 (Table 1 ) . Pines in California and Mexico By the early 1 9 6 0 ' ~the ~ continued effects of O3 transport from Los Angeles to the San Bernadino Mountains began to be noticed on stands of trees [ 9 ] . Ponderosa pine ponderosa) and Jeffrey pine (p. ieffreyi) were the most
(m
seriously affected, white fir
(wconcolor) and California black oak
(Quercus k e l l a ) were moderately affected, while sugar pine (p. lambertiana) and incense cedar (Libocedrus decurrens) were least affected.
Since then,
similar symptoms have been noticed on ponderosa and Jeffrey pine elsewhere in southern California mountains [ l o , 111 and on the western slopes of the Sierra Nevada Range [ 1 2 ] . O3 from the San Joaquin Valley and San Francisco has recently been shown to reduce radial growth for large Jeffrey pines in Sequoia
241 and Kings Canyon National Parks (131. Symptoms of O3 injury on sensitive ponderosa and Jeffrey pine include chlorotic needle mottle and tip necrosis, with reduced needle length, number and retention. 191.
Carbohydrate production in older needles is reduced [14],
leading to reduced terminal and radial growth. Branches die from the base of the crown upward.
Roots decline and may be more readily invaded by the root
pathogen Heterobasidion annosum [l, 15, 161.
03-injured ponderosa pines are
readily invaded by bark beetles, which hasten their decline and death [17, 181. Many 0,-sensitive ponderosa pines have died and disappeared. The effects of O3 on ponderosa pine seedlings, under controlled experimental conditions, have been investigated extensively. Needle symptoms observed in the field have been confirmed as symptoms of 0, injury [9. 11, 181.
As a
result, it is generally accepted that O3 causes needle injury. tree decline and death of sensitive genotypes of ponderosa pine in southern California. Mexico City is located in a basin, surrounded by high mountains.
As in
southern California, winds carry O3 to the forests in the mountains at Ajusco where several species of pine (p. hartwegii, p. montezumae, p. montezumae var. Lindleyi, and p. patula) exhibit needle symptoms identical to those of ponderosa pine in southern California. 1. hartwegii is the most severely affected. Sensitive individuals decline, are invaded by bark beetles, and then die. Infestations of dwarf mistletoe are also more extensive on weakened trees [7.
(w
religiosa) are declining in radial 81. At Desierto de 10s Leones, firs growth. Older needles develop white stipples and turn brown and die. O3 is the suspected cause of this fir decline. Eastern white pine White pine (Pinus strobus) is widely-distributed in eastern USA and Canada. In the 1960'6, there were many reports of foliar injury to individual trees that resembled possible O3 injury [19]. Needles on affected trees had chlorotic mottling or banding, with tip necrosis. Needle length and retention were reduced as were terminal and radial growth [20. 211.
Needle symptoms
have been duplicated under controlled conditions with known
03
concentrations
[22, 231. In the Blue Ridge Mountains of Virginia, Os-weakened trees were more readily invaded by the root pathogen Verticicicladiella procera and by bark beetles [24]. This is similar to ponderosa pine decline in southern California.
Sensitive and tolerant trees in a 25-year-old plantation in Tennessee were evaluated for growth and development. Tolerant trees were 3 times taller and had nearly double the radial growth of sensitive trees with symptoms. Sensitive trees had fewer and shorter needles, which was considered to be responsible for growth reductions [25]. In a labelled carbon study with needles from
242 these trees, 0, was shown to accelerate senescence of older needles, which are the primary source of photosynthate for new developing needles [ 2 6 ] . Annual increments of diameter growth for 50-year-old white pine in the Blue Ridge Mountains were determined for trees with different degrees of foliar symptoms. Average annual increment of diameter growth correlated with predicted degree of sensitivity of different genotypes to O3 [ 2 7 ] . Also in the Blue Ridge Mountains, white pine seedlings were grown in opentop field chambers for three years. Those grown in carbon-filtered ambient air were 45% taller than those in ambient air chambers where O3 was present [281.
SUSPECTED EFFECTS OF OZONE/ACIDIC DEPOSITION Sugar Maple Sugar maple (& saccharum) is a major hardwood tree in eastern North America. Since 1900, tree declines of several kinds have been attributed to various abiotic and biotic causes [ 4 , 291.
In several cases, exact causal
relationships have not been determined. The most recent incidence of sugar maple decline began in Canada in the late 1970's [ 4 ] . Symptoms include small chlorotic leaves, gradual leaf drop, branchlet death from the top of the crown downward, peeling bark on main branches and tree death. Trees tapped for maple syrup are more affected than forest trees. Syrup yields are reduced and tap holes heal very slowly [ 4 ] . Decline seems most severe in southern Quebec in highly humid areas and in thin soils at high elevations. Decline and dieback have also been noted on American
(w
beech (Fagus grandifolia) , balsam fir balsamea) , white ash (Fraxinus americana), white spruce (Picea glauca) and yellow birch (Betula alleghaniensis) 1301.
In Vermont and Ontario, feeding by insects such as the maple webworm and saddled prominent caterpillar, is known to reduce carbohydrate translocation to roots. Weakened trees are more susceptible to drought [ 3 1 ] or invasion by the root rot fungus Armillaria mellea. mortality [321.
This leads to dieback and shoot
Insect infestations have not been a problem in Quebec and
tree recovery is not improving [ 4 ] . Ozone is another stress factor that is known to affect photosynthate translocation in trees [ 3 3 ] .
Incidence of maple decline in North America also
coincides with an area known to be impacted by ambient 0,.
While reductions in
growth and photosynthesis have been reported for sugar maple seedlings [ 3 4 , 351, there is no evidence to relate O3 to sugar maple decline in North America. Red Spruce Red spruce (Picea rubens) is a major component of the spruce-fir forests
243
of the eastern USA and Canada.
It grows on a wide variety of soil types and
at a pH range of 3.6 to 5 . 0 [ 4 ] . In the 1 9 5 0 ' s and 1 9 6 0 ' 6 , tree growth ring studies indicated a decline in red spruce growth rates. This was first noted at high elevations and later at lower elevations in a less drastic form [ 3 . 361. At high elevations in New York and New England, declining red spruce die from the top down and from older branch regions to newer ones.
The newest
needles on the outer tips of branches at the tops of tree crowns become chlorotic and then die and drop [37, 381. In the southern Appalachian mountains, decline proceeds in reverse order. Chlorosis and needle drop progress from oldest to youngest needles and inside outward on branches and from the lower crown upward [ 3 9 ] . This resembles 03caused pine decline in southern California, Norway spruce decline in central Europe [ 4 ] , and 0,-induced
injury to white pine in eastern North America [ 2 ] ,
(Table 2 ) . Red spruce decline has received much attention and has been ascribed to one or more of the following causes: winter damage due to excessive nitrogen from acidic precipitation, dessication from cold injury. drought, frost plus air pollution, long range transport of pollutants, ozone/acidic precipitation, natural stand ageing and decline processes, or acceleration of these due to long-term climatic changes [ 4 ] . Historical records have been examined and trends have been constructed for the last 180-200 years.
One explanation for red spruce decline is that climate
change, particularly a warming trend, since 1800 is the major reason for declines in radial growth [ 4 0 , 411.
Recent increases in tree declines can also
be viewed as due to unique combinations of climatic stresses or interactions with air pollutants [ 4 2 ] .
If, however, changes that occur over a very long
time period are viewed with a short-term perspective, misleading conclusions can be drawn regarding causal relationships [ 4 0 ] . Red spruce growth decline can also be viewed as a normal phenomenon when allowance is made for different growth rates at different tree ages [ 4 3 ] . All growth reductions are not necessarily evidence of tree declines, but may be explained as expected reduced growth for natural stands as they mature [ 4 4 ] . Experiments designed to determine the effects of 03 and other pollutants on red spruce seedlings have not produced results comparable to those achieved for ponderosa and Jeffrey pine and white pine [ 2 ] . 0 3 injury on red spruce seedlings has not been reported. When red spruce seedlings were exposed to acidic mist, acidic precipitation, O3 and two types of collected soils, no interactive effects were observed [ 4 5 ] . Evidence is lacking that 0 3 or other air pollutants adversely affect red spruce growth and physiology [ 2 ] .
244 TABLE 2 Summary of symptoms expressed by trees involved in forest declines in North America. Trees
Symptoms Caused by ozone
Pinus hartwegii Pinus montezumae Pinus jeffreyi Pinus ponderosa
Chlorotic mottle, banding, and tip necrosis of older needles Reduced needle retention Reduced terminal and radial growth Branches die from the base of the crown upward
Pinus strobus --
Chlorotic mottling, flecking or banding of needles Needle tip necrosis Reduced needle retention Thin crowns Reduced terminal and radial growth
Ozone Abies religiosa Acer saccharum
or ozone/acidic precipitation may be involved White stipples, turning brown, on upper needle surfaces Small chlorotic leaves Gradual leaf drop Crown dieback from the top downward Peeling of bark on main branches
Picea rubens --
New York and New England Chlorosis and needle drop, beginning with newest needles and outer tips of branches Branches die from top of crown downward Southern Appalachians Chlorosis and needle drop, beginning with oldest needles, progressing from older to young branch sections Branches die from base of crown upward
Pinus echinata Pinus rigida
Abnormally narrow growth rings, beginning in 1955
Pinus echinata Pinus elliottii Pinus taeda --
Widespread decreases in annual growth rates, without other symptoms
-
Yellow pines Loblolly (Pinus taeda), shortleaf
(p.
echinata), and slash
pines are common lumber trees in the southeastern USA.
(11.
elliottii)
Widespread decreases
in radial growth have been noted, without any other symptoms [ 4 ] . It is not known whether these declines are due to natural processes or are in response to stress. Possible causes include: the combined effects of increased density and ageing of natural stands, which results in tree growth rate decreases,
245 more intense competition from hardwood species, and chronic O3 stress [ 4 6 ] . There is no evidence that O3 reduces radial growth of yellow pines. Abnormally narrow growth rings in shortleaf and pitch pines (P. rigida) in the Pine Barrens area of southeastern New Jersey were reported to begin around 1955 [ 4 7 ] . Soils in this area are sandy, with low pH values and low cationexchange capacity. Acidic precipitation has been suggested as a cause of radial growth declines [ 4 7 1 . The area is also impacted by ambient Os [ 4 ] .
When pitch pine seedlings were grown in soil cores from the Pine Barrens, and treated with synthetic acid rain, at pH 5.6, 4.0 or 3.0, through two cycles of growth, no negative effects were observed [ 4 8 ] . There is no evidence that O3 affects the growth of shortleaf and pitch pines in the New Jersey Pine Barrens. USE OF FIELD CHAMBERS TO DETERMINE EFFECTS OF O3 ON TREES Several types of field chambers have been used to determine the effects of Growth in ambient air or ambient air plus 0, can be compared to that in charcoal-filtered air. Most 0, on crop plants and to a lesser extent trees [ l ] .
studies to date have been short-term in nature, but many long-term studies with open-top chambers and O3 and Os/acidic precipitation interactions are now in progress, especially with yellow-pines. Portable fumigation chambers were placed over representative plants in major plant communities and Os fumigations were conducted at 0.15, 0.25, 0.30 or 0.40 ppm 0, for two hours. Trembling aspen (Populus tremuloides) had the lowest injury threshold at 0.15 ppm 0, [ 4 9 ] . Height growth for native seedlings of tulip poplar (Liriodendron tulipifera), sweetgum (Liquidambar styraciflua), black locust (Robinia pseudoacacia), eastern hemlock (Tsuga canadensis), table mountain pine (Pinus pungens), eastern white pine (Pinus strobus), and Virginia pine
(wvirginiana).
after
two years growth in carbon-filtered air in open-top chambers in Shenandoah National Park, was increased, when compared to trees in ambient air chambers
DO]. Reductions in total above-ground biomass for clonal hybrid poplars (P. masimowiczii x trichocarpa), grown in open-top chambers for 17 days, and exposed to 0.06 or 0.10 ppm 03, were 14 and 30%, respectively [ 5 1 ] . Ambient air reduced productivity and height growth for hybrid poplars, black locust and eastern cottonwoods (Populus deltoides), grown in carbon-filtered or ambient air open-top chambers in Millbrook, N.Y.
A growth reduction of
19% for hybrid poplar was statistically significant and occurred without visi-
ble O3 injury symptoms [ 5 2 ] . Ambient O3 in New Jersey had no effects on symptom expression, growth, or chlorophyll content of potted seedlings of green ash (Fraxinus pennsylvanica)
246 or white ash (Fraxinus americana), in open-top chambers, over a three-year period [53]. OZONE ACIDIC PRECIPITATION INTERACTIONS There has been a great deal of interest in possible interactions between 0, and acidic precipitation. Until recently, most investigations focused on crop plants, rather than trees. Interaction studies with trees have been done for short durations and with seedlings, rather than older trees. Results usually indicate no direct effects of the synthetic acid rain (SAR) solutions used on leaves, unless pH values are lowered to below pH 3.0.
In most cases, signif-
icant, reproducible interactions between SAR and O3 do not occur. O3 reduced photosynthesis in sugar maple and red oak (Quercus rubra) seed-
lings, but SAR at pH 3.0, 4.0, and 5.0 had no effects nor did interactions occur between O3 and SAR [35]. Treatment of paper birch (Betula papyrifera) seedlings with SAR at pH 3.5 for 1 2 weeks caused increased seedling growth, especially in seedlings exposed to 0.06 to 0.08 ppm 0, for the same period [55]. SAR, at pH 3.0 or 5.6. applied just before or after O3 fumigations had no significant effects on yellow poplar or white ash seedlings [56, 571. SAR at pH 2.5, however, decreased all growth parameters for yellow poplar seedlings that were exposed to O3 for eight weeks 1541. Dry matter production for yellow poplar seedlings, wetted with SAR prior to O3 fumigations, was significantly reduced when compared results where SAR was applied after O3 fumigations [56]. Based on limited work with tree seedlings, there is no evidence to support 03/SAR interactions that result in direct foliar effects.
O3 injury may be en-
hanced, however, by increasing leaf wetness or relative humidity [4]. SECONDARY EFFECTS OF OZONE Primary effects of 0, on trees are reflected in changes in growth and physiology. As a result of these changes, other changes, known as secondary effects, can occur. These affect important relationships that trees have with potential plant-pathogenic fungi, insects and ectomycorrhizal fungi [58]. Secondary effects of 0, include previously considered increases in susceptibility of 03injured pines to bark beetle infestations and incidence of root disease fungi [14, 16, 17, 241.
The association of ectomycorrhizal fungi with the fine roots of most trees is essential for their growth and development. The formation of ectomycor-
rhizae, as a result of invasion of fine roots by ectomycorrhizal fungi, affects uptake of water and nutrients and serves as a barrier to invasion by root disease fungi. The effects of O3 and SAR on ectomycorrhizal formation by roots of tree seedlings has recently been reviewed [ 5 9 ] .
247 In open-top and greenhouse chamber studies with red oak, white pine and sugar maple seedlings, SAR was found to decrease naturally-occurring ectomycorrhizae on red oak and white pine, white O3 increased ectomycorrhizae on red oak and white pine.
There were no interactions between SAR and O3 [60]. Treatment of white birch seedlings, grown in soil infested with the mycor-
rhizal fungus Pisolithus tinctorius, caused increases in seedling growth which was more apparent in seedlings also exposed to 03. No interactions between O3 and SAR were found [55]. Cenococcum graniforme also increased growth of yellow birch seedlings exposed to 0, [61]. P. tinctorius infected feeder roots of loblolly pine seedlings were protected from the effects of 0,. p. tinctorius apparently increased the demand for photosynthate translocation to roots and negated the expected negative effects
of O3 on root development [62]. CONCLUSIONS During the last few years, there has been a great increase in funding for research on the effects of O , , SAR and other air pollutants on tree growth and physiology. Many large experiments are currently in progress and a considerable amount of data will be obtained in the next two to three years.
In the
meantime, however, some conclusions, based on current reports in the literature, can be made regarding the effects of 0, and 0, acidic precipitation in interaction on trees in North America: 0, directly affects growth of ponderosa and Jeffrey pines in California,
several Pinus spp. near Mexico City, and sensitive genotypes of eastern white pine in the northeast USA and eastern Canada. There is no evidence that 0, is a factor in sugar maple, red spruce and yellow pine declines and decline of
Abies
religiosa in Mexico.
Direct effects of SAR on tree leaves has not been demonstrated, nor have significant interactions between 0, and SAR been demonstrated in studies with tree seedlings. The secondary effects of O3 or SAR on incidence of diseases, insects and mycorrhizal fungi may be of considerable importance and warrant further investigation. REFERENCES
S. V. Krupa and W. J . Manning, Environ. Pollut., 52 (1988) 101-137. B. I. Chevone and S. N. Linzon, Environ. Pollut., 50 (1988) 87-99. R. M. Klein and T. D. Perkins, Bot. Rev., 54 (1988) 2-24. J. L. Kulp, Chapter Seven, in NAPAP Interim Assessment Document, Vol IV (1987) U. S. Govt.. Washington, D.C. 5 S. B. McLaughlin, J. Air Poll. Contr. Assoc., 35 (1985) 512-534. 6 R. Stottlemyer, Environ. Management, 11 (1987) 91-97.
1 2 3 4
248 7 M. L. deBauer. T. H. Tejeda and W. J. Manning, J. Air Poll. Contr. Assoc. 35 (1985) 838. 8 M. L. de Bauer, T. Hernandez and D. Alvarado, Proc. Int. Bot. Congress, Berlin (1987) p. 404. 9 P. R. Miller, J . R. Parmeter, 0. C. Taylor and E. A. Cardiff, Phytopathology, 53 (1963) 1072-1076. 10 P. R. Miller and A. A. Millecan, Plant D i s . Rep., 55 (1971) 555-559. 11 B. L. Richards, 0. C. Taylor, and G. F. Edmunds, J. Air Poll. Contr. ASSOC., 18 (1968) 73-77. 12 W. T. Williams, M. Brady and S. C. Willeson, J. Air Poll. Contr. Assoc., 27 (1977) 230-234. 13 D. L. Peterson, M. J . Arbough, V. A. Wakefield and P. R. Miller, J . Air Poll. Contr. ASSOC., 37 (1987) 906-912. 14 J. R. Parmeter and P. R. Miller, Plant Dis. Rep., 52 (1968) 707-711. 15 R. L. James, F. W. Cobb, P. R. Miller and J. R. Parmeter, Phytopathology, 70 (1980) 560-563. 16 P. R. Miller, in D. D. Davis. A. A. Miller and L. Dochinger (Eds.) Proc. Air Pollution and the Productivity of Forests, Izaak Walton League, Washington, D. C., (1983) p . 161-197. 17 F. W. Cobb, Jr., D. L. Wood, R. W. Stark and J. R. Parmeter. Jr., Hilgardia, 34 (1968) 141-152. 18 P. R. Miller, J. R. Parmeter, B. H. Flick and C. W. Martinez, J. Air Poll. Contr. Assoc.. 9 (1969) 435-438. 19 C. R. Berry and L . A. Ripperton, Phytopathology, 53 (1963) 552-557. 20 E. M. Hayes and J. M. Skelly, Plant Dis. Rep., 61 (1977) 778-782. 21 R. W. Usher and W. T. Williams, Plant Disease, 66 (1982) 199-204. 22 Y. S . Yang, J. M. Skelly and B. I. Chevone, Can. J. For. Res., 12 (1982) 803-808. 23 D. B. Houston, Can. J. For. Res., 4, (1974) 65-68. 24 J. M. Skelly, Y. S. Yang, B. I. Chevone, S. J. Long, J. E. Nellesen, and W. E. Winner, in D. D. Davis, A. A. Miller, and L. D. Dochinger (Eds.) Proc. Izaak Walton League, Washington, D. C., (1983) p. 143-159. 25 L. K. Mann, S. B. McLaughlin and D. S. Shriner, Environ. Exp. Bot.. 20 (1980) 99-105. 26 S. B. McLaughlin, R. K. Conathy, D. Durick and L. K. Mann, For. Sci., 28 (1982) 60-70. 27 L. F. Benoit, J. M. Skelly, L. D. Moore, and L. S . Dochinger, Can. J . For. Res., 12 (1982) 673-678. 28 S. F. Duchelle, J. M. Skelly, and B. I. Chevone, Water, Air, Soil Pollut., 18 (1982) 363-373. 29 W. D. McIlveen, S. T. Rutherford and S. N . Linzon, Ontario Ministry of the Environment, Report No. ARB-141-86-Phyto and A. P . I. 0. 5.-010/86 (1986). 30 L. Robitaille, in Maple Decline, Maple Producers Information Session, Quebec City, Canada, 1986, AGDEX 300/637. 31 W. M. Banfield, Phytopathology, 57 (1967) 338. 32 R. A. Gregory, M. W. Williams Jr., B. L. Wong and G. J. Hawley, IAWA Bulletin, 7, (1986) 357-369. 33 D. R. Cooley and W. J. Manning, Environ. Pollut., 47 (1987) 95-113. 34 P. B. Reich and R. G. Amundson, Science, 230 (1985) 566-570. 35 P. B. Reich, A. W. Schoettle and R. G . Amundson, Environ. Pollut., 40 (1986) 1-15. 36 S. B. McLaughlin, J. Air Poll. Contr. Assoc.. 35 (1985) 512-534. 37 A. H. Johnson and T. G. Siccama, Environ. Sci. Tech., 17 (1983) 294-306. 38 J. T. Scott, T. J. Siccama, A. H. Johnson and A. Briesch, Bull. Torrey Bot. Club, 111, (1984) 438-444. 39 R. I. Bruck, in H. S . Stubbs (Ed.), Proc. Air Pollutants Effects on Forest Ecosystems, The Acid Rain Foundation, St. Paul, MN., (1985), p . 137-155. 40 S . P. Hamburg and C. V. Cogbill, Nature, 331 (1988) 428-431. 41 A. H. Johnson and S . B. McLaughlin. in Acid Deposition Long-term Trends, National Academy Press, Washington, D. C., (19861, p. 200-230. 42 S. B. McLaughlin, D. J. Downing, T. J. Blasing, E. R. Cook and H. S. Adam.
249 Occologia, 72 (1987) 487-501. 43 D. M. Hyink and S. M. Zedaker, Tree Phys., 3, (1987) 17-26. 44 J. W. Hornbeck, R. B. Smith and C. A. Federer, Water, Air, Soil Poll., 31 (1986) 425-430. 45 G. E. Taylor, Jr., R. J. Norby, S. B. McLaughlin, A. H. Johnson and R. S. Turner, Occologia, 70 (1986) 163-171. 46 R. M. Sheffield and D. N. Cost, J. For., 85 (1987) 29-33. 47 A. H. Johnson, T. G. Siccama, D. Wang, R. S . Turner and T. H. Barringer, J. Environ. Qual., 10 (1981) 427-430. 48 G. A. Schier, Can. J. For. Res., 16 (1986) 136-142. 49 M. Treshow and D. Stewart, Biol. Conservation, 5 (1973) 209-214. 50 S. F. Duchelle, J. M. Skelly and B. I. Chevone, Water, Air, Soil Poll., 18 (1982) 363-373. 51 P. B. Reich, J. P. Lassoie and R. G. Amundson, Can. J. Bot., 62 (1984) 2835-2841. 52 D. Wang, F. H. Bormann and D. G. Carnosky, Env. Sci. Tech., 20 (1986) 11221125. 53 C. L. Elliott, J. C. Eberhardt and Eberhardt and E. G. Brennan, Environ. Pollut., 44 (1987) 61-70. 54 L. S. Dochinger and K. F. Jensen, USDA For. Serv. NE Forest Exp. Sta. Res. Paper, NE-572, 1985. 55 K. D. Keane and W. J. Manning, Environ. Pollut., 52 (1988) (In Press). 56 A. H. Chappelka, B. I. Chevone and T. E. Burke, Environ. Exp. Bot., 25 (1985) 232-244. 57 A. H. Chappelka and B. I. Chevone, Can. J. For. Res., 16 (1986) 786-790. 58 W. J. Manning and K. D. Keane, in W. W. Heck, 0. C. Taylor and D. T. Tingey (Eds.), Proc. Crop Loss Assessment Cong., Raleigh, 1987, Elsevier, London (In Press). 59 K. D. Keane and W. J. Manning, Proc. APCA Meeting, New York, 1987, Program no. 87-36.4. 60 P. B. Reich, A. W. Schoettle, H. F. Stroo, and R. G. AMundson. J. Air Poll. Contr. Assoc., 36 (1986) 724-726. 61 D. L. Krupczak and W. J. Manning, Phytopathology, 77 (1987) 1616. 62 M. J. Mahoney, B. I. Chevone, J . M. Skelly and L. D. Moore, Phytopathology, 75 (1985) 679-682.
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T. Schneider et al. (Editore),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
251
EVALUATION OF OZONE EFFECTS ON VEtiETATION I N THE NETHERLANDS
A.E.G.
Tonneijck
Research I n s t i t u t e f o r Plant Protect on, P.O. (The Nether1 ands)
Box
9060,
6700
GW
Wageningen
ABSTRACT The current knowledge concerning ozone-induced e f f e c t s on vegetation i n t h e Netherlands i s discussed. Results w i t h i n d i c a t o r p l a n t s show t h a t ozone occurs i n phytotoxic concentrations throughout t h e country each year. F o l i a r i n j u r y i s generally most severe i n t h e western p a r t o f t h e country. The region w i t h t h e highest average e f f e c t i n t e n s i t i e s does not necessarily c o i n c i d e w i t h t h e region w i t h t h e highest average ozone concentrations. Ozone i s considered as t h e most important a i r p o l l u t a n t i n terms o f crop loss. It i s estimated f o r 1983 t h a t ambient a i r p o l l u t i o n reduced crop production w i t h 5%, o f which 70% i s caused by ozone. Especially h o r t i c u l t u r a l crops are affected. From 1i t e r a t u r e data maximum acceptable ojone concentrations3for p r o t e c t i o n o f v g e t a t i o n have been proposed: 150 .yg.m’ f o r 1 h, 65 1.1g.mf o r 8 h and 50 pg.m” f o r the growing season. Ambient ozone concentrations i n t h e Netherlands, measured i n t h e period 1980-1985, s u b s t a n t i a l l y exceeded these values. The frequency o f exceedances appears t o increase w i t h an increase i n t h e d u r a t i o n o f exposure.
I NTRODUCT I ON V i s i b l e i n j u r y o f p l a n t s i s o f t e n t h e e a r l i e s t and most obvious i n d i c a t i o n o f the presence o f a i r p o l l u t a n t s . I n t h e Netherlands t h e f i r s t observations o f ozone-induced
plant
symptoms
were made i n 1965 ( r e f . 1). For t h e purpose t o
monitor t h e e f f e c t s o f a i r p o l l u t i o n i n t h e
Netherlands
the
Dutch
National
Monitoring Network was established i n t h e e a r l y 1970’s. Subsequently, f o l i a r i n j u r y on i n d i c a t o r p l a n t s f o r ozone such as spinach, bean, c l o v e r species and tobacco
has
been
frequently
observed.
Besides, ozone i n j u r y on f i e l d grown
crops has been recorded (ref. 2). This paper evaluates t h e vegetation
in
current
knowledge o f
ozone-induced
effects
on
the Netherlands, Information on exposure-response re1 ationships
i s incorporated t o assess t h e p o t e n t i a l f o r ozone i n j u r y t o t h e vegetation. The foliar
injury
response o f
tobacco
ambient ozone. The impact o f ozone on provide
Be1 crop
W3
i s r e l a t e d t o concentrations o f productivity
ozone concentrations were derived from an evaluation o f t h e values
is
quantified.
To
f u r t h e r information f o r pol i c y abatement s t r a t e g i e s maximum acceptable literature.
These
are subsequently compared w i t h ambient ozone concentrations as measured
i n t h e Netherlands.
252 AMBIENT OZONE AND FOLIAR INJURY ON INDICATOR PLANTS
Since t h e e a r l y 1970's an extended network f o r monitoring t h e e f f e c t s o f a i r pollution
on
i n d i c a t o r p l a n t s has e x i s t e d i n t h e Netherlands. This network i s
managed by t h e Research I n s t i t u t e f o r Plant Protection, Wageningen, and forms a part
t h e National Monitoring Network f o r A i r P o l l u t i o n t h a t i s d i r e c t e d by
of
t h e National I n s t i t u t e o f Public Health and Environmental Cultivars
Hygiene,
Bilthoven.
o f ozone s e n s i t i v e p l a n t species such as bean, spinach, subterranean
c l o v e r and tobacco have been used t o levels.
indicate the
presence
of
toxic
ozone
I n many countries, t h e f i r s t i n d i c a t i o n o f ozone r e s u l t e d from t h e use
o f the s e n s i t i v e tobacco c u l t i v a r Be1 W3 ( r e f . 3). Therefore, t h e response o f t h i s p l a n t species w i l l be described i n more d e t a i l . During t h e growing season tobacco p l a n t s were exposed t o ambient a i r f o r one week and t h e n other
groups.
replaced
by
E f f e c t s were immediately determined a f t e r exposure by assessing
percentage i n j u r y on a l l leaves o f f o u r p l a n t s per l o c a t i o n . High e f f e c t i n t e n s i t i e s on tobacco g e n e r a l l y elevated
occurred
after
periods
with
concentrations o f ozone ( r e f . 4). P l a n t s were s l i g h t l y more s e n s i t i v e
t o ozone i n autumn than i n spring. I n each week a t l e a s t several p l a n t s a t some locations
showed f o l i a r i n j u r i e s . This i n d i c a t e s t h e continuous r i s k f o r ozone
i n j u r y t o t h e vegetation. Analyses o f t h e
results
for
the
period
1976-1983
showed t h a t t h e average i n j u r y l e v e l on tobacco p l a n t s was reasonably constant over years ( r e f . 5). The geographic d i s t r i b u t i o n s o f
ambient
ozone
concentrations
and
effect
i n t e n s i t i e s on tobacco f o r t h e summers of 1984 and 1985 are presented i n Fig. 1. F o l i a r i n j u r y was g e n e r a l l y more severe i n t h e western p a r t o f t h e
whereas
the
highest
injury
intensities
southwest depending on t h e year. always
occurred
in
the
The
norhtwestern
highest part
located f a r from t h e p o l l u t i o n sources and i s practices.
average
ozone
largely
used
for
agricultural
These r e s u l t s show t h a t , a t l e a s t i n geographical terms, a c l e a r - c u t not
exist.
Varying
c o n d i t i o n s and t h e presence o f o t h e r a i r p o l l u t a n t s a r e l i k e l y t o p l a y
an a d d i t i o n a l r o l e i n b r i n g i n g about t h e p a t t e r n o f exposure
concentrations
of t h e Netherlands. This area i s
r e l a t i o n s h i p between ambient ozone and f o l i a r i n j u r y does weather
country,
occurred i n t h e northwest o r i n t h e
regime a l s o may
be
important:
the
plant
frequency
injury. of
The peak
ozone ozone
concentrations i s greater i n t h e southern regions than i n t h e n o r t h ( r e f . 7). Fumigation experiments
have shown t h a t t h e i n j u r y l e v e l o f tobacco changed
more i n response t o a s e r i e s o f ozone concentrations t h a n t o a s e r i e s o f exposure times between 1-7 days ( r e f . 8). However, tobacco p l a n t s already showed some i n j u r y due t o average ozone concentrations o f ca 3 0 ~ g . m - ~a f t e r a 7 days exposure p e r i o d both under l a b o r a t o r y c o n d i t i o n s and i n t h e f i e l d (Fig. 2).
253
Fig. 1. (ieographic d i s t r i u t i o n o f mean values of 24 h average ozone concentrations ( r i g h t , dg.m-’) and o f i n j u r y i n t e n s i t i e s t o tobacco Be1 W3 ( l e f t ) f o r t h e summers o f 1984 and 1985 ( r e f . 9).
Fol i a r ambient
injury ozone
observations
on
tobacco
exceeded recorded
plants
further
increased
60-70 ~ ~ 9 . m ’ ~(Fig.
10-20%
injury
2).
i n weeks
when c o n c e n t r a t i o n s o f
Over
t h e years
with
concentrations below 80 ~19.m’~. These r e s u l t s suggest t h a t
all the
several
hourly
ozone
importance
of
peak concentrations i n terms o f f o l i a r i n j u r y should n o t be over-estimated. Other
indicator
plants
for
ozone
such
as
spinach,
bean,
poplar
subterranean c l o v e r g e n e r a l l y showed l e s s symptoms a t t h e f i e l d l o c a t i o n s
and than
tobacco Be1 W3. This i n d i c a t e s t h e r e l a t i v e l y h i g h s e n s i t i v i t y o f t h e tobacco cultivar. However, i n f u m i g a t i o n experiments bean ( r e f . 8) and p o p l a r (unpublished d a t a ) appeared t o be more s e n s i t i v e than tobacco
and
p l a n t species showed s i m i l a r i n j u r y responses t o ozone ( r e f . 5).
some
other
254
Follar Injury, X
241
'I 6
0 0
120
SO
24h average
180
O3 conc..
Fig. 2. F o l i a r i n j u r y t o tobacco Be1 W3 i n r e l a t i o n t o t h e 24 h average ozone c o n c e n t r a t i o n (1983 f i e l d data).
OZONE
DAMAGE TO CROPS
Negative e f f e c t s o f ozone on frequently
described
for
the
North
growth
America
w i t h o u t signs o f v i s i b l e i n j u r y ( r e f .
and y i e l d (ref.
9).
of
crops
have
been
These e f f e c t s can occur
10). I n r e c e n t years
it
became e v i d e n t
t h a t ambient ozone a l s o reduced crop p r o d u c t i v i t y i n European c o u n t r i e s l i k e UK and Denmark ( r e f s . 11-12).
Since ozone c o n c e n t r a t i o n s i n t h e
Netherlands
are
s i m i l a r t o t h e l e v e l s i n these c o u n t r i e s ( r e f . 13) n e g a t i v e e f f e c t s o f ozone on Dutch crops are v e r y l i k e l y t o occur. A study was undertaken i n order t o determine t h e impact o f a i r p o l l u t i o n
Dutch
crop
production
(ref.
14).
Ozone e f f e c t s
were
on
evaluated u s i n g t h e
exposure-yield r e l a t i o n s h i p s o f Linzon e t a l . ( r e f . 15). The ozone exposure was expressed (10.00-17.00
as
the
seasonal
mean
of
the
7-h
daily
mean
crop l o s s was c a l c u l a t e d f o r each of 14 crops (Table 1) and (Table
2).
concentrations
h r s ) from May through September. Based on 1983 d a t a ozone-induced The
1983 ozone
level
with
for
each
region
a mean o f 8 9 ~ g . m -was ~ considered
r e p r e s e n t a t i v e f o r t h e whole p e r i o d 1980-1985.
255 TABLE 1 Estimated crop l o s s (X) f o r 14 crops caused by ambient ozone i n 1983. Crop l o s s ( X )
Crop Fruit Floriculture Arbor ic u l t ure F1ower bulbs Grass seeds Pasture Cereals
Crop l o s s ( X )
Crop Glassh. vegetables Vegetables Glassh. potted p l a n t s Fodder crops Potatoes Glassh. c u t flowers Legumes
0.0 0.0 0.0 0.0 1.6 1.6 1.7
Estimated crop losses caused by ambient legumes,
potatoes,
cut
flowers
and
ozone were
3.1 4.4 4.6 6.2 6.3 6.3 6.6
relatively
lower f o r vegetables and potted plants. The highest percentage calculated
for
large
for
fodder crops. Crop losses were s l i g h t l y
the province o f Zuid-Holland.
crop
loss
was
The l a r g e amount o f crop l o s s i n
t h i s province mainly r e s u l t e d from t h e extensive c u l t i v a t i o n o f vegetables glasshouse
crops.
The importance o f a i r p o l l u t i o n i n c l u d i n g ozone i n r e l a t i o n
t o t h e extensive glasshouse crop production occurring i n t h e Netherlands principal
matter
of
concern.
Research
has
i n s i d e glasshouses can increase up t o 70% o f when
ventilators
combination
are
with
and
open
sulfur
(ref.
16)
d i o x i d e and
is
a
shown t h a t ozone concentrations ambient
and t h a t
concentrations these
outdoors
concentrations
in
n i t r o g e n d i o x i d e can cause s i g n i f i c a n t
losses t o tomatoes ( r e f . 17). TABLE 2 Estimated crop l o s s ( X ) i n t h e 12 Dutch provinces caused by ambient
ozone
i n 1983. Crop l o s s (X)
Province Fries1 and Noord-Hol 1and Limburg Overi j s s e l Utrecht Noord-Brabant ~~
1.7 1.8 2.2 2.7 2.7 2.9
Gel d e r l and Gronlngen Drenthe Zeel and IJsselmeerpol ders Zuid-Holland
~~
~
I n general,
Crop l o s s (X)
Province
~
3.5 3.5 3.8 3.9 4.2 4.7
~ _ _ _
a i r p o l l u t i o n causes r e l a t i v e l y l i t t l e damage t o t h e producers
due t o p r i c e supports ( r e f . 14). Consumers, thus, are t h e primary b e n e f i c i a r i e s from
a decrease
in
the
levels
Netherlands would be reduced t o
of
air
pollution.
I n case ozone i n t h e
background concentrations,
consumers. would
experience a n e t galn o f D f l 460 m i l l i o n ( r e f . 18). I n the
Dutch
study
(ref.
14) i t i s estimated t h a t i n 1983 a i r p o l l u t i o n
i n c l u d i n g ozone, s u l f u r d i o x i d e and hydrogen f l u o r i d e reduced crop production
256
Exposure time
1OQdays
.
.
.-• :.
10
i 0
\=
12 hours. 1
BOmIn.
1
i
.. . .. .. . ' . : . . .. . . . .. a
':*
0
.
0 . . 0 .
1
**
8 .
1
10
' *'
102
103 2'.103
0, conc. In porn*
Fig. 3. Concentration-time model used t o i nj u r y t o vegetation.
derive
limiting
values
for
ozone
5% and t h a t 70% o f t h e t o t a l r e d u c t i o n i s caused by ozone. Observations i n t h e USA have i n d i c a t e d t h a t o f t h e crop loss due t o a i r p o l l u t i o n , ozone i s by
responsible
9016, which
for
amounts
t o 2 t o 4% o f t h e t o t a l crop production
( r e f . 19). I n view o f these r e s u l t s ozone i s l i k e l y t o be
the
most
important
p o l l u t a n t i n terms o f crop loss. MAXIMUM OZONE CONCENTRATIONS FOR THE PROTECTION
OF THE VEGETATION
The concept o f determining l i m i t i n g values as presented e a r l i e r by Jacobson ( r e f . 20) was used t o provide i n f o r m a t i o n on doses
on t h e vegetation.
the
and y i e l d reduction as reported by Guderian e t a1 concentration-time
effects
of
specific
ozone
Data on ozone-induced f o l i a r i n j u r y as well as growth
. (ref.
3) are presented i n
a
model (Fig. 3 ) . The o b j e c t i v e o f t h i s model i s t o determine
t h e boundary conditions between combinations o f concentration and t i m e t h a t a r e probably
i n j u r i o u s and
those
conditions
t h a t are not. Each p o i n t i n Fig. 3
represents t h e lowest concentration and exposure d u r a t i o n used i n a study resulted
i n a negative e f f e c t . The curve has been drawn under t h e points. For
c x t combinations below and t o t h e l e f t vegetation
that
is
not
to
be
side
of
this
curve,
injury
to
the
expected. Above and t o t h e r i g h t s i d e o f t h e curve
ozone exposures may cause negative e f f e c t s on p l a n t s .
257 From Fig. 3 l i m i t i n g values f o r t h r e e d i f f e r e n t exposure durations have been selected
(Table
3).
The
1 h and
8 h values were chosen a t l e v e l s without
v i s i b l e i n j u r y t o t h e vegetation caused by acute ozone exposures. The 8 h value i s considered t o be extremely relevant since, i n t h e Netherlands, t h e maximal 8 h concentrations o f ambient ozone are concentrations
slightly
less
than
May through
maximal
1 h
4). The average concentration during t h e growth season,
(Table
expressed as t h e average of 7-h d a i l y mean concentrations from
the
(10.00-17.00
hrs)
September, was chosen as an i n d i c a t o r f o r chronic exposures
since: (a) reductions i n growth and y i e l d by chronic ozone exposures can occur without v i s i b l e symptoms ( r e f . 10) (b) no clear-cut r e l a t i o n s h i p e x i s t s between t h e frequency o f h i g h ozone peaks and the average concentrations during t h e summer ( r e f . 7).
I t should be emphasized t h a t
the
datasets
used,
and
hence
the
derived
l i m i t i n g values, r e f l e c t i n a d d i t i o n t h e l i m i t a t i o n s i n experimental techniques and measurements. Furthermore, i t should be pointed out
that
data
are
only
r e l a t e d t o experiments i n which t h e e f f e c t s o f ozone as a s i n g l e component were studied, although t h e r e i s ozone,
sulfur
dioxide
and
increasing
evidence
for
synergistic
effects
of
nitrogen d i o x i d e ( r e f . 21). On t h e o t h e r hand t h e
presented data i n t e g r a t e t h e ozone responses o f a wide v a r i e t y o f p l a n t species under a varying set o f external conditions. TABLE 3 L i m i t i n g values
and
proposed maximum acceptable
ozone
concentrations f o r
p r o t e c t i o n o f vegetation. Duration o f exposure
L i m i t i n g values ( ~ ~ g . m - ~ ) ’ Max. concentrations ( ~ ~ g . m - ~ )
1 hour 8 hours growing seasonb
150 65 50
200 75 60 ~~
L i m i t i n g values derived from Fig. 3 Expressed as t h e seasonal mean o f t h e 7-h d a i l y mean concentrations (10.00-17.00 hrs) from May September.
-
However, recent i n f o r m a t i o n suggests t h a t t h e l i m i t i n g values in
Table
as
presented
3 do not e n t i r e l y prevent t h e vegetation from ozone i n j u r y under a l l
conditions. I n experiments w i t h poplar, c o n t r o l c u t t i n g s l o s t more leaves EDU-treated
cuttings
concentration o f 5 9 ~ g . m - ~f o r 6-7 weeks ( r e f . 22). Wolting (ref. 17) that
60 ~ ~ g . m -ozone ~
of
tomatoes
reported
i n t h e presence o f s l i g h t l y elevated concentrations o f
s u l f u r d i o x i d e and n i t r o g e n d i o x i d e caused leaves
than
when exposed t o ambient a i r w i t h a daytime average ozone
premature
ageing
of
the
oldest
and y i e l d losses o f 12-19 X . Therefore, i t i s considered
258 necessary
to
propose
an
additional
set
of
maximum acceptable
ozone
concentrations t h a t are lower than t h e derived l i m i t i n g values (Table 3). CURRENT STATUS OF AMBIENT OZONE I N RELATION TO VEGETATION INJURY
Some data regarding ambient ozone measured i n t h e
monitoring
concentrations
in
network from 1980-1985,
the
Netherlands,
as
a r e presented i n Table 4
( r e f . 23). During t h e growing season, t h e maximum values o f t h e 1 h and 8 h ozone concentrations are 230-430 and 190-350 jg.m' 3 , respectively. The
maximal
average concentration during t h e growing season v a r i e s but
increased
up
between
70-90
j g .n~-~,
t o almost l 2 O ~ l g . m ' ~ i n a y e a r w i t h increased production o f
photochemical oxidants. TABLE 4 Sumnary o f data o f concentrations o f ambient ozone ( ~ g . m - ~ )i n t h e during t h e growing seasons o f 1980
- 1985.
50 Perc.
95 Perc.
Netherlands
98 Perc.
Maximum
183-263 157-223
227-431 191-350 77-117
~~
Max. 1 h Max. 8 h Growing season
78-104a 64- 90b 70- 91
159-223 134-122
--
--
Ranges i n d i c a t e d i f f e r e n c e s between l o c a t i o n s Data are mean concentrations i n stead o f 50 p e r c e n t i l e values Not determined From Tables
3 and
f r e q u e n t l y exceed
the
4 i t i s concluded t h a t concentrations o f ambient ozone proposed maximum acceptable
concentrations
and t h e
l i m i t i n g values. Calculations showed ( r e f . 18) t h a t t h e 1 h value o f 1 5 0 ~ g . m - ~ and t h e 8 h value of 65$g.me3 respectively,
of
the
days
a r e exceeded on 10-15% and d u r i n g an
average
on
more than
50%
growing season. The proposed
maximum acceptable ozone concentration f o r t h e growing season (50 y9.m' 3)
was always exceeded a t a l l l o c a t i o n s i n every year. These r e s u l t s i n d i c a t e t h a t t h e frequency w i t h which ambient ozone concentrations exceed t h e proposed maximum acceptable
concentrations
for
protection
of
vegetation,
increases w i t h an
increase i n t h e d u r a t i o n o f exposure. CONCLUSIONS Ambient ozone concentrations adversely a f f e c t t h e vegetation throughout
the Netherlands. F o l i a r i n j u r y t o p l a n t s such as t h e ozone s e n s i t i v e tobacco Be1 W 3 has been f r e q u e n t l y observed a f t e r ozone.
periods
with
elevated
concentrations
of
This i n j u r y response i s n o t c l e a r l y r e l a t e d t o average ozone concentra-
t i o n s . The value o f simple exposure-response functions r e l a t i n g a s i n g l e
para-
253 meter
o f p l a n t response t o a s i n g l e exposure parameter, i s s t i l l questionable.
Interactions o f
ozone w i t h environmental
c o n d i t i o n s and w i t h
other
air
p o l l u t a n t s may be important. Because production o f photochemical oxidants, and hence concentrations o f ozone, depend on
s u i t a b l e weather
conditions,
these
i n t e r a c t i o n s are very complex and u r g e n t l y need f u r t h e r i n v e s t i g a t i o n s . Although
ozone
concentrations
d u r i n g t h e growing season are s u f f i c i e n t t o
reduce growth and y i e l d of Dutch crops, s p e c i f i c information i s mostly lacking. Ambient
ozone
concentrations i n the Netherlands s u b s t a n t i a l l y exceed proposed
maximum acceptable frequency
of
concentrations
for
protection o f
the
vegetation.
The
exceedances appears t o increase w i t h an increase i n t h e duration
o f exposure. Therefore, studies need t o be conducted t o determine t h e i n f l u e n c e o f chronic ozone exposures on t h e vegetation. REFERENCES 1 J.G. Ten Houten, Landbouwk. T., 78 (1966) 2-13. 2 A.E.G. Tonneijck, Neth. J. P1. Path., 89 (1983) 99-104. 3 R. Guderian, D.T. Tingey and R. Rabe, i n R. Guderian ( E d i t o r ) , A i r p o l l u t i o n by photochemical oxidants. Formation, transport, c o n t r o l , and effects on plants. Springer-Verlag, B e r l i n , 1985, pp. 129-333. 4 A.E.G. Tonneijck and A.C. Posthumus, VDI-Ber., 609 (1987) 205-216. Tonneijck and H. Floor, Bedrijfsontwikkeling, 15 (1984) 440-443. 5 A.E.G. 6 Anonymous, L u c h t k w a l i t e i t . Jaarverslag 1984 en 1985, R i j k s i n s t i t u u t voor Vol ksgezondheid en Milieuhygiene, Bilthoven, 1986. 7 F.A.A.M. de Leeuw, i n R. Guicherit, J. van Ham and A.C. Posthumus (Editors), Ozon: fysische en chemische veranderingen i n de atmosfeer en de gevolgen, Kluwer, Deventer, 1987, pp. 40-44. 8 A.E.G. Tonneijck, i n P. Grennfelt ( E d i t o r ) , Proc. I n t . Workshop on t h e evaluation and assessment o f t h e e f f e c t s o f photochemical oxidants on human health, a g r i c u l t u r a l crops, f o r e s t r y , m a t e r i a l s and v i s i b i l i t y , Goteborg, Sweden, Febr. 29- March 2, 1984, Swedish Environmental Research I n s t i t u t e , Goteborg, 1984, pp. 118-127. 9 D.T. Tingey, i n P. Grennfelt ( E d i t o r ) , Proc. I n t . Workshop on t h e evaluation and assessment o f t h e e f f e c t s o f photochemical oxidants on human health, a g r i c u l t u r a l crops, f o r e s t r y , m a t e r i a l s and v i s i b i l i t y , Goteborg, Sweden, Febr. 29 March 2, 1984, Swedish Environmental Research I n s t i t u t e , Goteborg, 1984, pp. 60-75. 10 J.S. Jacobson, i n M.H. Unsworth and D.P. Ormrod (Editors), E f f e c t s o f gaseous a i r p o l l u t i o n i n a g r i c u l t u r e and h o r t i c u l t u r e , Butterworths, London, 1982, pp. 293-304. 11 M.R. Ashmore, i n P. Grennfelt ( E d i t o r ) , Proc. I n t . Workshop on t h e evaluation and assessment o f t h e e f f e c t s o f photochemical oxidants on human health, a g r i c u l t u r a l crops, f o r e s t r y , m a t e r i a l s and v i s i b i l i t y , Goteborg, Sweden, Febr. 29 March 2, 1984, Swedish Environmental Research I n s t i t u t e , Goteborg, 1984, pp. 92-104. 12 H. Ro-Poulsen, L. Mortensen and I. Johnsen, i n P. Grennfelt ( E d i t o r ) , Proc. I n t . Workshop on t h e evaluation and assessment o f the e f f e c t s of photochemical oxidants on human health, a g r i c u l t u r a l crops, f o r e s t r y , materials and v i s i b i l i t y , Goteborg, Sweden, Febr. 29 March 2, 1984, Swedish Environmental Research I n s t i t u t e , Goteborg, 1984, pp. 105-112. 13 P. Grennfelt, J. Saltbones and J. Schjoldager, Oxidant data c o l l e c t i o n i n OECD-Europe 1985-87 (Oxidate). A p r i l September 1985, Norwegian I n s t i t u t e f o r A i r Research, L i l l e s t r a m , 1987. Tonneijck and J.H.M. Wijnands, Environ. P o l l u t . 14 L.M. van der Eerden, A.E.G.
-
-
-
-
260
15 16
17 18 19 20 21 22 23
(1988), i n press. S.M. Linzon, R.G. Pearson, J.A. Donnan and F.M. Durham, Ozone e f f e c t s on crops i n Ontario and r e l a t e d monetary values, Ontario M i n i s t r y o f t h e Environment , 1984. H.G. Wolting, E.A.M. van Remortel and N. van Berkel, Acta H o r t i c u l t u r a e , 174 (1985) 351-357. H.G. Wolting, Annual Report 1986, Research I n s t i t u t e f o r Plant Protection, Wageningen, 1986, p.43. W. S l o o f f , R.M. van Aalst, E. Heijna-Merkus and R. Thomas ( E d i t o r s ) , Ontwerp basisdocument ozon, R i j k s i n s t i t u u t voor Volksgezondheid en Milieuhygiene, Bilthoven, 1987. W.W. Heck, O.C. Taylor, R. Adams, G. Bingham, J. M i l l e r , E. Preston and L. Weinstein, J. A i r P o l l u t . Control ASSOC., 26 (1982) 325-333. J.S. Jacobson, VDI-Ber., 270 (1977) 163-173. A.S. Lefohn and D.P. Ormrod, A review and assessment o f t h e e f f e c t s o f p o l l u t a n t mixtures on vegetations. Research recomnendations, EPA, Corvall i s , 1984. H.G. M o l t i n g and J. Mooi , B e d r i j f s o n t w i k k e l i n g , 15 (1984) 449-454. uurgemiddelde ozonJ. Erisman, Enkele aspecten van 1 uur- en 8 concentraties i n Nederland, R i j k s i n s t i t u u t voor Volksgezondheid en Milieuhygiene, Bilthoven, 1987.
T. Schneider et al. (Editore),Atmospheric Ozone Research and it8 Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
261
CONSEQUENCES OF DECREASED ATMOSPHERIC OZONE: EFFECTS OF UTRAVIOLET RADIATION ON PLANTS
L.O.
BJURN
Department of P l a n t P h y s i o l o g y , U n i v e r s i t y o f Lund, Box 7007, 5-220 07 Lund, Sweden
ABSTRACT A r e v i e w i s g i v e n o f t h e work on e f f e c t s o f u l t r a v i o l e t r a d i a t i o p on p l a n t s (and r e l a t e d work) t h a t has been c a r r i e d o u t by o u r group o v e r t h e p a s t few years.
INTRODUCTION The t o t a l amount o f ozone i n t h e e a r t h ' s atmosphere shows a d e c r e a s i n g t r e n d (1.0% p e r y e a r ) s i n c e many y e a r s ( r e f . 1 ) .
A t t h e same t i m e , t h e b i o l o g i c a l l y ef-
f e c t i v e u l t r a v i o l e t r a d i a t i o n , somewhat s u r p r i s i n g l y , a l s o shows a d e c r e a s i n g t r e n d ( 0 . 5 t o 1% p e r y e a r i n t h e U n i t e d S t a t e s , r e f . 2 ) . S i n c e we do n o t unders t a n d t h e causes o f e i t h e r change, no r e l i a b l e f o r c a s t can be made. I t i s i m p o r t a n t i n t h i s s i t u a t i o n t o a q u i r e some knowledge a b o u t t h e r e a c t i o n s o f o r ganisms, i n c l u d i n g p l a n t s and t h e ecosystems i n which t h e y p a r t i c i p a t e , on poss i b l e f u t u r e increases i n d a y l i g h t u l t r a v i o l e t r a d i a t i o n . Most r e s e a r c h on t h i s s u b j e c t has been c a r r i e d o u t i n t h e U n i t e d S t a t e s , and some i n West Germany. A g r i c u l t u r a l experiments i n d i c a t e t h a t f o r each p e r c e n t decrease i n ozone, one m i g h t expect about one p e r c e n t h a r v e s t r e d u c t i o n i n some c r o p s ( r e f . 3,4), w h i l e t h e e f f e c t s on h a r v e s t s from t h e sea m i g h t b e g r e a t e r ( r e f . 5) A g r i c u l t u r a l experiments o f t h e t y p e performed by Teramura a r e v e r y expens i v e and time-consuming.
D i f f e r e n t p l a n t s r e a c t v e r y d i f f e r e n t l y t o enhanced UV
r a d i a t i o n ( t h i s i s t r u e even for. d i f f e r e n t c u l t i v a r s o r ecotypes w i t h i n t h e same s p e c i e s ) . I t i s t h e r e f o r e n o t f e a s i b l e t o c a r r y o u t such e x p e r i r i c n t s w i t h e v e r y p l a n t v a r i e t y o f i n t e r e s t . We must understand t h e reasons f o r t h e d i f f e r ences i n UV s e n s i t i v i t y , and we must understand j u s t what UV does t o t h e p l a n t . UV work i n o u r group has proceeded a l o n g f i v e d i f f e r e n t l i n e s , w h i c h w i l l be
d e s c r i b e d be1ow:
( 1 ) E f f e c t s o f u l t r a v i o l e t r a d i a t i o n on p h o t o s y n t h e t i c e l e c t r o n t r a n s p o r t . ( 2 ) E f f e c t s o f u l t r a v i o l e t r a d i a t i o n on stomata.
262 ( 3 ) Penetration o f u l t r a v i o l e t r a d i a t i o n i n t o p l a n t s measured by a f i b e r o p -
t i c probe, and e v a l u a t i o n o f f a c t o r s a f f e c t i n g penetration. ( 4 ) Development o f a computer program far e s t i m a t i n g d a y l i g h t UV and i t s b i o l o g i c a l a c t i o n under d i f f e r e n t circumstances. (5) Probing u l t r a v i o l e t r a d i a t i o n e f f e c t s on p l a n t s by measuring p l a n t l u m i nescence. EFFECTS OF UV RADIATION ON PHOTOSYNTHETIC ELECTRON TRANSPORT Bornman e t a l . ( r e f . 6) determined an a c t i o n spectrum f o r i n h i b i t i o n o f phot o s y n t h e t i c e l e c t r o n t r a n s p o r t i n i s o l a t e d spinach choroplasts. Action spectra were determined a l s o by i r r a d i a t i n g i n t a c t leaves o f EZodea and Oxalis ( r e f . 7 ) . I n ha2i.s i r r a d i a t i o n was from e i t h e r t h e upper o r the lower side, and i t was
found t h a t the p l a n t s were much more s e n s i t i v e f a r i r r a d i a t i o n from t h e lower side. The explanation was found i n a d i f f e r e n t amount o f screening compounds i n the epidermis. The a c t i o n spectra determined i n t h i s way a r e i n good agreement w i t h a c t i o n spectra f o r i n h i b i t i o n o f e l e c t r o n t r a n s p o r t measured by o t h e r groups. However, they are much f l a t t e r than a c t i o n spectra f o r complete photosynthesis (carbon dioxide uptake) measured by several groups w i t h simultaneous i r r a d i a t i o n by UV and p h o t o s y n t h e t i c a l l y a c t i v e 1 i g h t . T h i s discrepance,
important f o r computing
r a d i a t i o n a m p l i f i c a t i o n f a c t o r s and e f f e c t s o f ozone depletion, has n o t y e t been explained. For f u r t h e r discussion o f r a d i a t i o n a m p l i f i c a t i o n f a c t o r s , see r e f . 8. The reader i s r e f e r r e d t o Bornman ( r e f . 9) f o r more i n f o r m a t i o n on t h i s aspect o f UV work a t our department. EFFECTS OF UV RADIATION ON STOMATA U l t r a v i o l e t i r r a d i a t i o n o f p l a n t s causes stomata t o close. Action spectra w i t h d i f f e r e n t background 1 i g h t s f o r t h e c l o s i n g a c t i o n have been determined by Negash & B j o r n ( r e f . 10) and Negash ( r e f . 11). Radiation o f 305 nm o r longer wavelength has l i t t l e e f f e c t . I t i s thought t h a t the UV e f f e c t on stomata takes place v i a an e f f e c t on t h e potassium i o n content of t h e guard c e l l s ( r e f . 12, 13). Since the c l o s i n g i s prevented by strong v i s i b l e l i g h t , i t i s doubtful whether stomata1 c l o s i n g by UV r a d i a t i o n i s e c o l o g i c a l l y important. For f u r t h e r discussion o f UV e f f e c t s on stomata, see ref. 14. PENETRATION OF UV RADIATION INTO PLANTS The basic procedure f o r measuring t h e p e n e t r a t i o n o f l i g h t i n t o p l a n t s using f i b e r o p t i c s was described by Vogelmann & Bjorn ( r e f . 15). I t was f u r t h e r d i s cussed by Chwirot & S l e v i n ( r e f . 161, B j o r n (ref.17)
and Vogelmann & B j o r n
263 ( r e f . 181, and has been used w i t h d i f f e r e n t p l a n t o b j e c t s by Vogelmann & Haupt ( r e f . 1 9 ) , Vogelmann e t a l . ( r e f . 20) and Widell E Vogelmann ( r e f . 21). I n short t h e procedure involves heating a glass f i b e r and p u l l i n g i t t o a f i n e t i p (a few POI diameter), properly t r e a t i n g the t i p and the surface o f t h e f i b e r , i n s e r t i n g the f i b e r t o the place o f measurement i n the p l a n t t i s s u e using a micromanipulator, and c o l l e c t i n g t h e l i g h t a t t h e o t h e r end o f the f i ber i n t o a spectroradiometer. Great a t t e n t i o n must be p a i d t o c a l i b r a t i o n , c o l l e c t i n g l i g h t i n proper d i r e c t i o n s , and adding the measurements i n a c o r r e c t way. The procedure has been adapted f o r measurements o f u l t r a v i o l e t r a d i a t i o n by Bornman & Vogelmann ( r e f . 2 2 ) i n Vogelmann's laboratory. The main change necessary f o r measurements o f UV i s the use o f a quartz f i b e r instead o f a glass fiber; t h i s i n t u r n necessitates heating t h e f i b e r ( f o r p u l l i n g i t t o a f i n e t i p ) w i t h an acetylene-oxygen flame instead o f an e l e c t r i c c o i l . Other improvements include covering the f i b e r surface w i t h l a y e r s o f metal t o exclude entrance o f l i g h t except a t the t i p . Borman & Vogelmann ( r e f . 22) found t h a t (a) UV-A r a d i a t i o n (360 nm) i s more r a p i d l y attenuated i n spruce and f i r needles than i s b l u e l i g h t (460 nm); ( b ) l i t t l e blue l i g h t o r UV-A was attenuated by the e p i c u t i c u l a r wax l a y e r ; ( c ) most o f the UV-A was attenuated by the epidermal c e l l s I n spruce (Picea engel-
m n n i i ) about 7% o f the i n c i d e n t 360 nm r a d i a t i o n remained a t 100 Um depth, w h i l e i n fir (Abies lasiocarpa) only 1.5% remained a t t h e same depth. I n spruce t h i s attenuation i s almost completely due t o soluble UV-absorbing substances (presumably flavonoids) i n t h e epidermal l a y e r , w h i l e i n f i r o t h e r substances may contribute. D i f f e r e n t s t r u c t u r e s o f t h e mesophyll f u r t h e r accentuate d i f ferences i n penetration f u r t h e r i n t o needles. DEVELOPMENT AND TESTING OF COMPUTER PROGRAMS FOR ESTIMATING DAYLIGHT UV AND I T S BIOLOGICAL EFFECTS The computer program described by Bjorn & Murphy ( r e f . 23) has undergone
some modifications and extensive comparisons w i t h o t h e r programs. D e t a i l s o f t h i s are discussed by Bjorn ( r e f . 241, and I s h a l l l i m i t myself here t o some aspects. The program c a l c u l a t e s the d i r e c t and scattered spectral components of dayl i g h t seperately, which, i n t h e recent version, allows t h e i r combinations as e i t h e r spectral i r r a d i a n c e on
a h o r i z o n t a l o r t i l t e d surface o r spectral f l u -
ence rate. As fluence r a t e i s the more appropriate magnitude i n most photobiol o g i c a l applications, w h i l e o t h e r programs u s u a l l y g i v e irradiance, t h i s i s a great advantage. The program a l s o has a b u i l t - i n choice o f various a c t i o n spect r a (weighting functions) , so an expression f o r effectiveness f o r various phot o b i o l o g i c a l DroceSses can he obtained e a s i l y . This f l e x i b i l i t y has allowed a
264 comparison w i t h spectroradiometric measurements as we1 1 as various more special i z e d procedures and measurements w i t h s p e c i a l i z e d detectors, such as t h e Robertson-Berger meter. Bjorn ( r e f , 24) shows comparisons between r e s u l t s obtained by t h i s program and several others ( r e f . 25-27) as w e l l as comparison w i t h measured values. EFFECTS OF ULTRAVIOLET RADIATION ON PLANT LUMINESCENCE Two d i f f e r e n t kinds o f luminescence from p l a n t s should be distinguished, exc l u d i n g fluorescence. One i s "photosynthetic luminescence", "afterglow" o r "delayed l i g h t emission", discovered by S t r e h l e r & Arnold ( r e f . 28) and extensivel y used i n many l a b o r a t o r i e s f o r e x p l o r i n g the mechanism o f photosynthesis. T h i s l i g h t i s generated by the recombination o f charges separated by the primary phot o s y n t h e t i c process i n photosystem 2 ; thus, somewhat s i m p l i f i e d , i t can be described as reversal o f photosynthesis. We have constructed a "phytoluminograph" ( r e f . 29,30) w i t h which t h e p l a n t can be imaged i n i t s own luminescence l i g h t . Such an image shows the s p a t i a l d i s t r i b u t i o n o f t h e c a p a c i t y f o r photosynthesis. I t can be used a l s o f o r studying the s p a t i a l d i s t r i b u t i o n o f u l t r a v i o l e t damage
t o the photosynthetic system (Fig. 1).
Fig. 1. Phytoluminogram of an u l t r a v i o l e t i r r a d i a t e d l e a f of oxutis deppei. Dur i n g i r r a d i a t i o n p a r t o f t h e l e a f was shaded by a metal r i n g , t o provide a cont r o l area. The 1 i g h t e m i t t i n g c a p a c i t y (an i n d i c a t o r o f photosynthetic c a p a c i t y )
265 was decreased by u l t r a v i o l e t i r r a d i a t i o n . From r e f . 29. Recently we have modernized the phytoluminograph (Fig.2) and connected i t t o a computerized image processing system, and intend t o resume use o f i t f o r UV e f f e c t studies
.
Fig. 2. View o f the present phytoluminograph. I t c o n s i s t s of a l i g h t - t i g h t samp l e box ( t o the l e f t ) , l i g h t source, f i b e r o p t i c l i g h t guide and s h u t t e r assemb l y , image i n t e n s i f i e r and video system. The other k i n d o f 1uminescence i s " u l traweak luminescence" a r i s i n g through various biochemical reactions unrelated t o photosynthesis. Most p l a n t c e l l s exh i b i t t h i s k i n d o f luminescence, b u t the i n t e n s i t y v a r i e s considerably. P a r t of i t i s due t o peroxidation o f unsaturated l i p i d s . The phenomenon has been reviewed by Abeles ( r e f . 31) and, i n a more popularized way, by Popp r e f . 32).
Ultraweak luminescence, as the name implies, i s exceedingly f a i n t , and a t present cannot be used f o r generating images. To record i t , we have t o use a cooled p h o t o m u l t i p l i e r i n the photon counting mode. I n t e r e s t i n g i n t h i s context i s t h a t ultraweak luminescence i s
g r e a t l y stimu-
l a t e d by exposure o f p l a n t t i s s u e t o u l t r a v i o l e t r a d i a t i o n (Fig. 3)
266
3000
I
0
200
400
600
800
1000
1200
seconds Fig. 3. Ultraweak luminescence from non-photosynthetic p l a n t t i s s u e ( c e l e r y r o o t ) . Sections 1, 3 and 5 o f t h e curve show background photon count ( i n the absence of sample). Section 2 shows the luminescence from the sample before irr a d i a t i o n , section 4 a f t e r a p e r i o d o f u l t r a v i o l e t i r r a d i a t i o n . Possibly the luminescence and i t s decay can g i v e i n f o r m a t i o n on t h e nature and f a t e o f the primary products o f the damaging photochemical reactions. REFERENCES 1. K.P. Bowman, Science 239 (1988) 48-50. 2. J. Scotto, Science 239 (1988) 262-264. 3. R.C. Worrest, t h i s volume. 4. A.H. 5. A.H.
Teramura, Physiol. Plantarum 58 (1983) 414-427. Teramura, J.G. T i t u s ( E d i t o r ) , Effects o f Changes i n Stratospheric
Ozone and Global Climate, Vol. 2, US Environmental P r o t e c t i o n Agency, Washing1986, 255-262. ton, D.C., 6. J.F.
Bornman, L.O.
( 1984) 305-31 3. 7. L.O. Bjorn, J.F.
B j o r n and H.-E.
Akerlund, Photobiochem. Photobiophys. 8
Bornman and E. O l s o n , i n R.C.
Worrest ( E d i t o r ) , Proc. NATO
Adv. Res. Workshop on The Impact o f S o l a r U l t r a v i o l e t (UV-B Radiation) upon Ter-
restrid Ecosystems. I. A g r i c u l t u r a l Systems, Springer, B e r l i n , 1986, pp. 185197. 8. L.O.
Bjorn,
J.F.
Bornman and L. Negash, J.G.
Titus (Editor), Effects o f
267 Changes i n Stratospheric Ozone and Global Climate, Vol 2, US Environmental Prot e c t i o n Agency, Washington, D.C.
, pp.
263-276.
9 J.F. Bornman, E f f e c t s o f U t r a v i o l e t Radiation on Plants, Doctoral Dissertat i o n , Lund 1985. 10. L. Negash and L.O.
Bjorn, Physiol. Plantarum 66 (1986) 360-364.
11 L. Negash, P l a n t Physiol. Biochem. 25 (1987) 753-760. 12 L. Negash, P. Jensen and L.O. Bjorn, Physiol. Plantarum 69 (1987) 200-204. 13 L. Negash and L.O. Bjorn, P l a n t Physiol. Biochem. 26 (1988) 14 L. Negash, Response o f Stomata t o U l t r a v i o l e t Radiation, Doctoral Dissertat i o n , Lund 1988.
15 T.C.
Vogelmann and L.O. Bjorn, Physiol. Platarum 60 (1984) 361-368.
16 S. Chwirot and J. Slevin, Physiol. Plantarum 67 (1986) 493-494 17 L.O.
Bjorn, Physiol. Plantarum 67 (1986) 493-499.
18 T.C.
Vogelmann and L.O. Bjorn, Physiol. Plantarum 68 (1986) 704-708.
19 T.C. 20 T.C.
Vogelmann and W. Haupt, Photochem. Photobiol. 41 (1985) 569-576. Vogelmann, A.K. Knapp, T.M. McClean and W.K. Smith, Physiol. Plantarum
72 (1988) 623-630. 21 K.-0. Widell and T.C Vogelmann, Physiol. Plantarum 72 (1988) 706-712. 22 J.F. Bornman and T.C. Vogelmann, Physiol. Plantarum 72 (1988) 699-705. 23 L.O. Bjorn and T.M Murphy, Physiol. Veg. 23 (1985)555-561 24 L.O.
Bjorn, i n B.L.
D i f f e y ( E d i t o r ) , Radiation Measurement i Photobiology,
Academic Press, London 1986, pp.
25 R.E.
B i r d and C. Riordan, J. o f Climate and Appl. Meteorology, 25 (1986)
87-97. 26 S.A.W.
Gerstl, A Zardecki and H.L. Wiser, UV-B Handbook, vol. I , Los Alamos
National Laboratory, Los AlamOs, N.M.
1983.
27 W. Josefsson, Solar U l t r a v i o l e t Radiation i n Sweden, Swedish Meteorological and Hydrological I n s t i t u t e , Norrkoping 1986.
28 B.L.
S t r e h l e r and W. Arnold, J. Gen. Physiol.
34 (1951) 609-820.
29 E. Sundbom and L.O. Bjorn, Physiol. Plantarum 40 (1978) 39-41. 30 L.O. Bjorn and A.-S. Forsberg, Physiol. Plantarum 47 (1979) 215-222. 31 F.B. Abeles, Annu. Rev. P l a n t Physiology 37 (1986) 49-72. 32 F.-A. Popp, B i o l o g i e des L i c h t s : Grundlagen der ultraswachen Zellstrahlung, Paul Parey, Berlin/Hamburg 1984.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
269
WHAT ARE THE EFFECTS OF UV-B RADIATION ON MARINE ORGANISMS?
R. C. Worrest
U. S.Environmental Protection Agency, Environmental Research Laboratory, Corvallis, Oregon 97333 (U.S.A.)
INTRODUCTION Marine systems, covering a vast area, contribute significantly to global productivity (ref. 1). The coastal kelp forests have productivities said to rival those of tropical rain forests, generally considered the world's most productive plant ecosystems (refs. 2-3). Of the five major marine habitats, the microscopic plants of the open sea are the most productive, contributing 75% of the total marine production through photosynthetic processes, or 24% of the global total. As early as 1925, scientists were aware of damaging effects on aquatic organisms from the ultraviolet component of sunlight (refs. 4-12). It was shown at these early dates that there exists a differential sensitivity among species to UV radiation, and that this differential sensitivity might relate to the depths at which the species were normally found. Several more recent studies on the effects of UV-B radiation (290-320 nm) have examined a variety of marine organisms (ref. 13). Regardless of the species investigated, each study has potential importance through the role of the particular organism in its environmental or food-web context. Some studies, in addition, have considered economically important zooplankton species, such as larval stages of certain shrimp, crab, and fish. Literature reviews (refs. 14-18) have summarized the results of most of these studies. PHYSICAL EFFECTS ON ORGANISMS UV-B radiation is readily absorbed by proteins and nucleic acids, and induces photochemical reactions in plants and animals (refs. 19-21). Even though proteins and nucleic acids are commonly involved in biological responses to UV-B radiation, the action spectra for tissue damage in many organisms may differ because of wavelength-dependent refraction, reflection, or absorption, and hence protection, by outer tissues (ref. 22).
270
Based on a model of total incident solar radiation, a 10% ozone reduction at 45ON latitude would result in only a 1% increase in total solar ultraviolet (290-360 nm) daily exposure at the surface of the earth. This would be of minimal consequence if radiation throughout the solar spectrum were of equal biological effectiveness. However, when biological weighting functions based on the action spectra are employed, a very different picture emerges (ref. 23). Based on DNA damage (ref. 24), a 10% ozone reduction would result in a 28% increase in biologically effective radiation (Table 1). The generalized terrestrial plant response (damage) (ref. 25) would increase by 21%. TABLE 1 Relationship between ozone depletion and biological effectiveness of . . UV-R .-r Ozone e 10% 20%
30% 40%
790-370nm 2 8YO 17% 27% 38%
9 1.l% 2.4% 3.7% 5.2%
0 28% 67% 125% 21 3%
-
0 21 Yo 49% 85% 132%
aAction spectra are referencedto 300 nm = 1.OO. Levels of UV-B irradiance vary latitudinally, with the highest exposures in the tropics. The current difference between the extremes of exposures is about 3- to 6fold, but biota probably are adapted to levels that are normally experienced at their current locations. The increased exposure to biologically effective (DNA, Plant) ultraviolet radiation resulting from a 10% decrease in stratospheric ozone would be equivalent to migrating over 30° latitude toward the equator-a substantial ecological change. PHYTOPLANKTON The amount of UV-B radiation reaching the ocean's surface has long been suspected to be a factor influencing primary production. Research convincingly shows that ultraviolet radiation, at levels currently incident at the surface of natural bodies of water, is either at or near levels that inhibit phytoplankton productivity (refs. 26-28). It has been calculated that, near the surface of the ocean at temperate latitudes, enhanced UV-B radiation simulating a 25% reduction in ozone concentration would cause a decrease in primary productivity by about 35% (ref. 29). The estimated reduction in production for the whole euphotic zone would be about 10%. These calculations are based on attenuation lengths, i.e., the product of depth in the water
271
column and the diffuse attenuation coefficient of the water. On this basis, waters of various turbidities and absorption characteristics can be compared. Effects induced by solar UV-B radiation have been measured to depths of more than 20 m in clear waters and more than 5 m in waters with significant productivity (ref. 18). The euphotic zone (i.e., those depths with levels of light sufficient for positive net photosynthesis) is frequently taken as the water column down to the depth at which the surface level of photosyntheticallyactive radiation is reduced 99%. In marine ecosystems, UV-B radiation penetrates about the upper 10% of the euphotic zone before it is reduced 99% from its surface level of irradiance. Penetration of UV-B radiation into natural waters is a key variable in assessing the potential impact of this radiation on any aquatic ecosystem. If one assumes that present phytoplankton populations sense and control their average vertical position in such a way as to limit UV-B exposure to a tolerable level, then a 10% increase in solar UV-B radiation would necessitate a downward movement of the average position, thereby reducing the average UV-B exposure by 10%. There would be a corresponding reduction of light for photosynthesis. The loss of photosynthetically active radiation in many locations might not be significant. However, in some very productive areas, especially high latitude ocean areas, photosynthetically active radiation is the primary limiting factor for marine productivity (ref. 30). The loss of photosyntheticallyactive radiation from optical measurements has been estimated to be in the range of 3 to 5% for a 10% increase in UV-B radiation (ref. 31). If the photosynthetic base of aquatic ecosystems were perturbed, one would expect ramificationsto extend throughout the food web as a result of predator-prey relationships. Experiments with marine diatoms have shown significant reductions in biomass, protein and chlorophyll at UV-B irradiances equivalent to ozone reductions ranging from 5 to 15 percent. In addition, studies on chain-forming diatoms and other phytoplankton in the laboratory show that increased growth occurs when the UV-B radiation is filtered out of the incident solar radiation, indicating that existing levels of UV-8 radiation depress productivity (refs. 15, 32). Furthermore, indirect effects of ambient levels of UV-B radiation have been shown to endanger the survival of some freshwater microorganisms (Euglena, some blue-green algae) by decreasing their motility and by inhibiting phototactic and photophobic responses (refs. 33-34). This reduces the ability of a population to move into favorable environments, which could impair growth and development. Direct measurements of photosynthesisthat span only a single day could underestimate the overall action of solar UV exposure by failing to account for the next day's reduced population level. Due to growth delay or direct mortality, the subsequent population could fall below the numbers that an unexposed population would attain. Prolonged delays (about two days) in growth of the suwivors have been
272
observed when two strains of the diatom Thalassiosira were irradiated with simulated solar UV-B radiation at doses below lethal levels (ref. 35). If unicellular organisms are in a rapid growth phase, a growth delay equalling the time of one growth cycle produces the same effect on the subsequent population as would be produced by 50% mortality (without growth delay). In Hawaii (USA) long-term photoinhibition of growth of six algal species under natural sunlight has been measured (ref. 36). Two strains could not grow at all at the levels of irradiance for full natural surface sunlight. Of the species tested, those collected from tropical surface water showed the greatest adaptive power, but it is reasonable to conclude that resistance to solar UV radiation is achieved through expenditure of resources that can be better applied to other needs in less exposed species. In marine microcosms enhanced UV-B radiation levels, simulating decreases in ozone of 15 percent, resulted in shifts of the species diversity and community composition of phytoplankton communities (ref. 37). Thus, in natural communities, a change in species composition rather than a decrease in net production might be a more likely result of an enhanced UV-B exposure. The decreased species diversity observed in simulated field studies is usually not accompanied by deleterious effects on biomass and chlorophyll accumulation, or by deleterious effects on total community primary productivity. However, a change in community composition might result in a more unstable ecosystem and might influence higher trophic levels (ref. 38). One effect of enhanced levels of UV-B radiation would be to alter the size distribution of the component producers in a marine ecosystem. Increasing or decreasing the size of the representative primary producers upon which consumers graze can significantly increase the energy allotment required from consumption, thereby reducing the feeding efficiency of the consumer. In addition, the food quality of the producers is altered by exposure to UV-B radiation. It has been demonstrated that the protein content, dry weight, and pigment concentration are all depressed by enhanced levels of UV-B radiation (refs. 39-42). ZOOPLANKTON Zooplankton are critical components in typical aquatic food webs (nutrient pathways) that lead to larger animals, including those comprising commercial fisheries (finfish and shellfish) and therefore man himself. With respect to potential impacts of enhanced solar UV-B radiation, only the zooplankton living in daylight in the upper several meters would be directly affected. Most zooplankton species are vertical migrators and normally spend a significant portion of their life very close to the surface. The near-surface layer is a very important zone in the interactions of the physical/chemical/biological components of aquatic systems. Zonplankton have apparently evolved mechanisms and behavior by which they have adjusted to current
273
levels of UV radiation (ref. 43), but they may not be able to adjust to relatively rapid increases in solar UV radiation. Ifthere were changes in abundance of zooplankton species, those changes would have an impact far beyond any direct effects because of the critical role of zooplankton in energy transfer within the ecosystem. Karanas et at. (refs. 44-45) presented evidence that acute exposure of a marine invertebrate zooplankton resulted in reduced survival of the organisms. They also showed that exposure of this species to sublethal exposures of UV-B radiation could also reduce the fecundity of the parents. It has been demonstrated that current levels of UV-B radiation significantly reduce the development of several species of shellfish (ref. 46). For some species a 10% decrease in total atmospheric ozone could lead to as much as an 18% increase in the number of abnormal larvae produced. Before feeding by zooplankton can begin, variations in exposure to UV-B radiation may cause stresses at various stages of egg and very early larval development, causing in the absence of behavioral avoidance responses significant numbers of mortalities or an alteration in time of occurrence at the surface. The matching in time of the onset of larval feeding and the spring phytoplankton bloomwhich, in turn, depends on climatic events for its timely occurrence-will, in fact, determine the sizes of year classes of grazers (ref. 47). FISHERIES Fish stocks suffer most from the vagaries of climate through the effects that changes in ambient conditions have on the larvae or their food source. The biological dynamics at the larval stages in the life cycles of fishes and aquatic invertebrates have a short-time horizon and are highly variable. Instant mortality coefficients during the larval stages range between 300 and 400, while they are 0.2 to 1.5 in the juvenile and adult stages (ref. 48). The most catastrophic and not all that rare event that can befall larvae is a mismatch in time between their food needs and the prevalence of their food (ref. 47). Larval stages last on the order of days. Small as the biomass of fishes is during very early life, their future numbers are largely determined then and not later in life, when the biomass is large and when the commercial fishery takes its toll. Hunter el al. (ref. 49) exposed anchovy eggs and larvae and mackerel larvae to high doses of UV-B radiation in small closed containers. Their data indicated that anchovy larvae off southern California are typically centered in moderately productive ocean water having about 0.5 rng Chl a m-3. Baker et al. (ref. 50) calculated surface DNA-effective UV-B irradiance levels expected for this area, and Smith and Baker (ref. 51) calculated the penetration of UV-B radiation into the moderately productive ocean water. Regardless of the cellular-level responses to UV irradiation, it is usually noted that up to some level of UV exposm there is no apparent effect on the target organism (refs. 52-53). At greater doses either the repair systems themselves may have become
274
inactivated by the radiation, or the damage to the general tissues is beyond the capacity of the repair systems (ref. 54). To be effective, these threshold levels probably must be exceeded during several consecutive days. The apparent UV thresholds are near current incident UV levels. The thresholds for all groups in one test appeared to be above the present median solar incident UV levels at the test location, at least until late in the time span of natural occurrence near the surface. This season could be significantly shortened by a 20% ozone reduction. Whether or not the populations could endure with a drastically reduced time of near-surface occurrence is not known. Success of any year-class depends on the timing of a great number of other events in addition to levels of exposure to UV-B radiation (ref. 49). Apparently at all months about 36% of the larval anchovy population is above 10 m (ref. 55). The greatest numbers of anchovy larvae are found in April (20% of annual population), so that, based on one experiment, 7.2% of the annual larval population would be eliminated with a 9% ozone decrease. Based on this experiment, the total predicted loss, due to a 9% decrease in total atmospheric ozone, would be about 8% of the larval anchovy population. Because of complex interactions between mixing-depths, vertical distribution of larval anchovy, seasonal changes in solar irradiance and the penetration of UV radiation into seawater, and seasonal changes in anchovy abundance, there is not a linear relationship between mixing-depth and predicted annual loss of anchovy larvae. In addition to the direct effects upon the fisheries, it is possible that with less primary production of organic biomass there would also be an increased mortality in larval fish due to food limitation. There may also be a synergistic effect on mortality such that some animals die from direct exposure, some die from lack of food, and some die from the combination of a reduction in food and the weakening from exposure (or are weakened and become outcompeted by other fauna for limited food reserves). The impact on marine fisheries as a food supply to humans would be significant if the species of phyto- and zooplankton to enhanced levels of UV-B radiation were of different nutritional value (if UV-B irradiation altered the growth and fecundity of the consumers). If the indirect impact of suppression upon consumers were linear, a 5% reduction of primary production would result in a 5% reduction in fish production. A question still under investigation is whether the trophodynamic relationships might be nonlinear. For example, there may be an amplification factor that results in a relatively greater impact at higher trophic levels than at the primary-producer level. As illustrated would give an annual yield of in Table 2, a 5% reduction in primary production (PI) 115 x 109 kg of fish flesh (a 5% reduction); whereas a 5% reduction in the ecological efficiency of energy transfer (e) would yield 103 x 109 kg of fish flesh (a 14% reduction).
275
TABLE 2 Annual fish production in coastal waters. Baseline data for coastal waters d from R W 56). Baseline Primary production, kJ m-2 y r l , (PI)
4200
-5% P i 4000
-5% e 4200
Ecological efficiency per trophic level, (e)
0.15
0.15
0.14
Number of trophic levels from plant production to fish production, (n)
3
3
3
Fish production, kJ m-2 y r l , (Pien)
14
13
12
Total fish production, lo9 kg y r 1 (using Winberg's transformation, 4.2 kJ = 1 g fish flesh)
121
115
103
(95%)
(86Yo)
Percentage of baseline fish production
(100%)
The recovery of a depleted fishery population may require many years, even if catches are prohibited in the meanwhile. Economic survival of the existing resource industry may, however, depend upon continuing catches, even though these will delay rebuilding of the stock and perhaps increase the probability of the population's collapse. In the language of the mathematical theory of games, common-property resource exploitation has the characteristics of the so-called 'prisoner's dilemma'. SUMMARY AND CONCLUSIONS Various experiments have demonstrated that UV-B radiation causes damage to fish larvae and juveniles, shrimp larvae, crab larvae, copepods, and plants essential to the aquatic food web. These damaging effects include decreases in fecundity, growth, survival and other functions of these organisms. In natural marine plant communities a change in species composition rather than a decrease in net production is the probable result of enhanced UV-B exposure. A change in community composition may result in a more unstable ecosystem and would likely have an influence on higher trophic levels. A decrease in total atmospheric ozone would shorten the season of greatest abundance for near-surface zooplankton. Whether the population could endure a significant shortening of this season is unknown. The direct effect of UV-B radiation on food-fish larvae closely parallels the effect on invertebrate zooplankton. Information is required on seasonal abundances and vertical distributions of fish larvae, vertical mixing, and penetration of UV-B radiation
276
into appropriate water columns before effects of incident or increased levels of exposure to UV-8 radiation can be predicted. However, in one study involving anchovy larvae, a 20% increase in incident biologically damaging UV-8 radiation (a result of about a 9% decrease in the total atmospheric ozone) would result in all of the larvae within a 10-meter mixed layer in April and August being killed after 15 days. It was calculated that about 8% of the annual larval population throughout the entire water column would be directly killed by a 9% decrease in total atmospheric ozone. The usual effects of many environmental stresses are changes in overall productivity and reductions in species diversity. Diversity is often associated with stability in ecosystems, allowing alternate routes and choices within food webs. In field situations under slight stress, one often cannot measure changes in productivity or size of specific populations, but sometimes changes in species diversity can indicate that adverse effects are occurring. With loss of species an ecosystem may lose some of its natural resiliency and flexibility. In aquatic ecosystems we must consider a great number of species, with different life stages and different trophic levels. With increased knowledge of ecosystems and the physicakhemical environment, the effects of enhanced solar UV radiation on single species could be placed in perspective. Many of the changes that occur in marine ecosystems as a result of natural or man-made events occur on time scales of tens of years. The changes may be associated, in some general context, with gradual climatic trends, but ecological changes seem to occur quite rapidly, with relatively persistent communities existing in the intervening periods. In any region rather than having one 'ecosystem', there are two, or possibly several, alternatives-each resilient to some range of variability but capable of being replaced if some factors in the environment pass a threshold. To this natural episodic response, we must now add the effects of anthropogenic perturbations such as enhanced UV-B stress. The evidence suggests that we shall continue to have such changes but shall have added questions of attributing cause to natural stresses or to stresses resulting from human activities. Although we may not be able to predict when, or possibly why, such changes occur, they can be regarded as alternative ecological solutions. Once again, whether we consider these changes deleterious or beneficial is a matter of human values, but we must keep in mind that these problems are occurring on a global scale. This manuscript has been reviewed in accordance with the U.S. Environmental Protection Agency's peer and administrative review policies and approved for presentation and publication.
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33 D.-P. Hader, in R. C. Worrest and M. M. Caldwell (Eds.), Stratospheric Ozone Reduction, Solar Ultraviolet Radiation and Plant Life, Springer-Verlag, New York, Heidelberg, Berlin, 1986, pp 223-233. 34 D.-P. Hader, in J.G. Titus (Ed.), Effects of Changes in stratospheric Ozone and Global Climate, Vol. 2: Stratospheric Ozone, United States Environmental Protection Agency and United Nations Environment Programme, 1986, pp. 197201. 35 J. Calkins, in J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Plenum, New York, 1982, pp. 651-661. 36 P.L. Jokiel and R.H. York, Jr., Limnol. Oceanogr., 29 (1984) 192-199. 37 R.C. Worrest, B.E. Thomson and H. Van Dyke, Photochem. Photobiol., 33 (1981) 861-867. 38 J.R. Kelly, in J.G. Titus (Ed.), Effects of Changes in Stratospheric Ozone and Global Climate, Vol. 2: Stratospheric Ozone, United States Environmental Protection Agency and United Nations Environment Programme, 1986, pp. 237251. 39 G. Dohler, Z. Naturf., 39 (1984) 634-638. 40 G. Dohler, J. Plant Physiol., 118 (1985) 391-400. 41 G. Dohler and I. Biermann, J. Plankton Res., 9 (1987) 881-890. 42 G. Dohler, R.C. Worrest, I. Biermann and J. Zink, Physiol. Plantarum., 70 (1987) 51 1-515. 43 D.M. Damkaer, in J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Plenum, New York, 1982, pp. 701-706. 44 J.J. Karanas, H. Van Dyke and R.C. Worrest, Limnol. Oceanogr., 24 (1979) 11041116. 45 J.J. Karanas, R.C. Worrest and H. Van Dyke, Mar. Biol., 65 (1981) 125-133. 46 B.E. Thomson, in J.G. Titus (Ed.), Effects of Changes in Stratospheric Ozone and Global Climate, Vol. 2: Stratospheric Ozone, United States Environmental Protection Agency and United Nations Environment Programme, 1986, pp. 203209. 47 D.H. Cushing, Symp. Zool. SOC.London, 29 (1972) 213-232. 48 B.J. Rothschild, BioScience, 31 (1981) 216-222. 49 J.R. Hunter, S.E. Kaupp and J.H. Taylor, in J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Plenum, New York, 1982, pp. 459497. 50 K.S. Baker, R.C. Smith and A.E.S. Green, Photochem. Photobiol., 32 (1981) 367374. 51 R.C. Smith and K.S. Baker, Photochem. Photobiol., 29 (1979) 311-323. 52 D.M. Damkaer, D.B. Dey, G.A. Heron and E.F. Prentice, Oecologia, 44 (1980) 149158. 53 D.M. Damkaer and D.B. Dey, in J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Plenum, New York, 1982, pp. 417-427. 54 D.M. Damkaer and D.B. Dey, Oecologia, 48 (1983) 178-182. 55 J.R. Hunter, S.E. Kaupp and J.H. Taylor, Photochem. Photobiol., 34 (1981) 477486. 56 J.H. Rylher, Science, 166 (1969) 72-76.
279
SESSION IV
EMERGING HEALTH STUDY METHODOLOGIES AND ISSUES
Chairmen
R. Kroes F.G. Hueter
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T. Schneider et ol. (Editors ), Atmospheric Ozone Research and i t s Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
28 1
CRITICAL ISSUES I N INTRA- AND INTERSPECIES DOSIMETRY OF OZONE
FREDERICK J. MILLER and JOHN H. OVERTON H e a l t h E f f e c t s Research Laboratory, U.S. Environmental P r o t e c t i o n Agency, MD 66, Research T r i a n g l e Park, N o r t h C a r o l i n a 27711 ( U S A )
ABSTRACT Knowledge o f dose a t t h e t a r g e t s i t e i s a fundamental s t a r t i n g p o i n t i n making i n t e r s p e c i e s d o s i m e t r i c comparisons. To t h e e x t e n t t h a t i n f o r m a t i o n i s a v a i l a b l e on t h e e f f e c t i v e dose o f a compound, o u r c o n f i d e n c e i n r i s k assessments i s increased. To f a c i l i t a t e judgments about e f f e c t s determined i n animals r e l a t i v e t o l i k e l i h o o d o f r i s k a s s o c i a t e d w i t h human exposure t o ozone ( O 3 ) , a mathematical d o s i m e t r y model has been developed f o r i n t e r s p e c i e s comparlsons. The model i n c o r p o r a t e s t h e major f a c t o r s a f f e c t i n g t h e a b s o r p t i o n of 0 3 i n t h e r e s p i r a t o r y t r a c t : t h e morphology o f t h e r e s p i r a t o r y t r a c t , t h e r o u t e , depth and r a t e o f b r e a t h i n g , physicochemical p r o p e r t i e s o f 03, t h e p h y s i c a l and chemical processes which govern gas t r a n s p o r t , and t h e physlcochemical p r o p e r t i e s o f t h e l i n i n g f l u i d s and t i s s u e m a t e r i a l o f t h e airways and gas exchange u n i t s . T h i s model i s used t o i d e n t i f y i s s u e s c r i t i c a l l y i m p o r t a n t t o t h e modeling process i t s e l f , such as model v a l i d a t i o n and modeling uptake o f 03 i n t h e head. A l s o discussed a r e t h e a p p l i c a t i o n o f t h e dosimetry model f o r examining age-dependent s u s c e p t i b i l i t y t o 03 and t h e p o t e n t i a l u s e f u l n e s s o f such models f o r r e l a t i n g m i c r o d o s i m e t r y t o m l c r o t o x l cology. INTRODUCTION
Ozone i s a u b i q u i t o u s a i r p o l l u t a n t .
In t h e United States, m i l l i o n s o f
people a r e exposed t o 03 l e v e l s t h a t exceed t h e c u r r e n t N a t i o n a l Ambient A i r Q u a l i t y Standard (NAAQS) of 0.12 t h a n once per year.
ppm for one hour, n o t t o be exceeded more
Recently, t h e need f o r an e i g h t - h o u r 0 3 s t a n d a r d has
been advocated s i n c e l a r g e segments o f t h e p o p u l a t i o n may b e r o u t i n e l y exposed f o r extended p e r i o d s t o 03 l e v e l s j u s t below t h o s e o f t h e c u r r e n t 1-hour standard ( r e f .
1).
The r a t i o n a l e f o r such a recommendation i s based m a i n l y
upon: 1 ) well-documented biochemical and f u n c t i o n a l e f f e c t s i n l a b o r a t o r y animals and man a s s o c i a t e d w i t h b r i e f exposures t o 03 ( r e f . 2), and 2 ) a concern t h a t long-term exposure t o e l e v a t e d 03 l e v e l s may p o s s i b l y l e a d t o t h e development of c h r o n i c l u n g diseases.
W h i l e v a r i o u s m o r p h o l o g l c and
Disclaimer: T h i s paper has been reviewed by t h e H e a l t h E f f e c t s Research Laboratory, U.S. Environmental P r o t e c t i o n Agency, and approved f o r p u b l i c a tion. Mention o f t r a d e names o r commercial p r o d u c t s does n o t c o n s t i t u t e endorsement or recommendatlon f o r use.
282 h i s t o p a t h o l o g i c changes have been observed i n a n i m a l s exposed s u b c h r o n i c a l l y and c h r o n i c a l l y t o 03 ( r e f .
2,
3, 41, whether such changes l e a d t o i r r e v e r s i -
b l e disease has n o t y e t been e s t a b l ished. logy, human c l i n i c a l s t u d i e s ,
Among t h e f i e l d s o f epidemio-
and animal t o x i c o l o g y ,
animal s t u d i e s can
p r o v i d e t h e most complete d a t a on t h e a r r a y o f e f f e c t s a s s o c i a t e d w i t h c h r o n i c exposure. Mathematical models have been developed ( r e f .
5,
6 ) f o r use i n i n t e r -
s p e c i e s comparisons o f dose when a s s e s s i n g t h e r e l e v a n c e and I m p l i c a t i o n o f r e s u l t s from animal s t u d i e s f o r t h e l i k e l i h o o d o f s i m i l a r e f f e c t s o c c u r r i n g a t 03 l e v e l s t o which humans a r e exposed.
While advances have been made i n
our u n d e r s t a n d i n g o f t h e r e s p i r a t o r y t r a c t d o s i m e t r y o f 03, v a r i o u s t o p i c s r e l a t i v e t o t h e models per se, t o t h e i n p u t d a t a r e q u i r e d by t h e models, and t o model a p p l i c a t i o n must b e addressed i n l i g h t o f t h e i n c r e a s e d u t i l i z a t i o n o f t h e s e models t o make i n t r a - and i n t e r s p e c i e s d o s i m e t r l c comparisons.
A
d i s c u s s i o n of some o f t h e s e t o p i c s i s t h e i n t e n t o f t h i s paper.
DOSIMETRY MODEL:
FORMULATION AND COMPUTER SIMULATION
D e t a i l e d d e s c r i p t i o n s a r e a v a i l a b l e elsewhere ( r e f . d o s i m e t r y model used i n t h i s paper.
Here,
5,
6, 7 ) o f t h e 03
a b r i e f d e s c r i p t i o n o f t h e model
f o r m u l a t i o n s and t h e computer s i m u l a t i o n program i s p r o v i d e d t o i n f o r m t h e r e a d e r o f t h e n a t u r e o f t h e d o s i m e t r y model and a p p l i c a t i o n s o f it. Major f a c t o r s a f f e c t i n g t h e u p t a k e o f 03 a r e t h e morphology o f t h e r e s p i r a t o r y t r a c t , t h e route,
depth,
and r a t e o f b r e a t h i n g ,
physicochemical proper-
t i e s o f 03, t h e p h y s i c a l processes g o v e r n i n g gas t r a n s p o r t , and t h e p h y s i c o chemical p r o p e r t i e s o f t h e r e s p i r a t o r y t r a c t l i n i n g f l u i d s and t i s s u e o f t h e a i r w a y s and gas exchange u n i t s .
The complex i n t e r a c t l o n o f t h e s e f a c t o r s
determines t h e dose d e l i v e r e d t o t a r g e t s i t e s w i t h i n t h e r e s p i r a t o r y t r a c t . Although i t i s d e s i r a b l e t o c o n s i d e r as many as p o s s i b l e o f t h e above f a c t o r s i n d e v e l o p i n g a s i m u l a t i o n model, simp1 i f y l n g assumptions and s t r u c t u r e s a r e o f t e n r e q u i r e d t o make t h e modeling problem t r a c t a b l e . Species lung dimensions a r e t a k e n i n t o a c c o u n t u s i n g anatomical or a i r w a y models such as t h o s e a v a l l a b l e f o r t h e r a t ( r e f . (ref.
9).
In t h e s e models,
8) and for man
lower r e s p i r a t o r y t r a c t (LRT) a i r w a y s a r e charac-
t e r i z e d b y a sequence o f s e t s of r i g h t c i r c u l a r c y l i n d e r s . r e s p i r a t o r y t r a c t (URT) r e g i o n i s i n c l u d e d , r a t i o n s " o r s e q u e n t i a l segments.
I f t h e upper
I t c o n s l s t s o f p r e t r a c h e a l "gene-
Data on t h e number o f a i r w a y s or segments
and t h e i r d i a m e t e r s and l e n g t h s a r e needed f o r each g e n e r a t i o n o r segment i n t h e model r e s p i r a t o r y t r a c t .
Also,
e s t i m a t e s o f a l v e o l a r volumes and
s u r f a c e a r e a s must b e a v a i l a b l e for t h e pulmonary r e g i o n , w h i l e s u r f a c e a r e a and volume e s t i m a t e s a r e needed for URT segments.
283 Given t h e 03 concentration a t t h e f i r s t model segment (e.g.,
nose,
mouth, o r trachea), t h e model simulates t h e t r a n s p o r t and absorption o f 03 i n each airway,and a l v e o l a r space o f t h e a n a t m l c a l model d u r l n g one o r more breaths.
During t h e simulated b r e a t h l n g cycle, changes I n lung volume a r e
accounted f o r by l s o t r o p l c a l l y v a r y l n g t h e l i n e a r dlmenslons o f t h e LRT a l r way generations.
Volume f l o w r a t e s can be simulated d u r l n g b r e a t h l n g based
e i t h e r upon experimental data o r upon an assumed time-dependent f u n c t l o n . Gas t r a n s p o r t I n t h e lumen and a i r spaces, as w e l l as chemical r e a c t l o n s and t r a n s p o r t I n t h e l i q u i d I l n l n g , t i s s u e , and blood compartments,
Is taken
i n t o account i n t h e s l m u l a t l o n model v l a p a r t i a l d l f f e r e n t l a l equations.
The
complex s e r i e s o f r e a c t i o n s o f 03 w l t h v a r i o u s b i o l o g i c a l c o n s t l t u e n t s I s s i m p l l f i e d t o one r e a c t i o n i n v o i v l n g an e f f e c t l v e second-order
r a t e constant
and t h e o v e r a l l constant c o n c e n t r a t i o n o f chemical components ( r e s u l t i n g I n a pseudo f i r s t order r e a c t i o n ) t h a t r e a c t w l t h 03. conditions,
Given l n l t i a l and boundary
I n a d d i t i o n t o values f o r t h e physical, chemical, and b l o l o g l c a l
parameters o f t h e model, t h e s o l u t i o n s o f t h e equatlons p r o v i d e p r e d i c t e d 03 doses f o r each model compartment I n any given a n a t m l c a l generatlon.
Conse-
quently, r e s p i r a t o r y t r a c t p a t t e r n s can be compared among various animal species and man f o r s p e c i f i e d 03 concentrations. CRITICAL ISSUES
Model V a l i d a t i o n The usefulness o f doslmetry models t o r i s k assessment and e x t r a p o l a t l o n modeling depends t o a l a r g e e x t e n t on t h e degree t o whlch model p r e d i c t l o n s agree w i t h t h e r e s u l t s o f experlments.
U n t l l r e c e n t l y t h e r e was v e r y I l t t l e
experlmental data a v a i l a b l e f o r 03; however, technlques have been and a r e being developed t o measure t h e uptake and d l s t r l b u t l o n of 03 I n t h e r e s p l r a t o r y t r a c t o f humans and animals ( r e f . 10, 1 1 ) . ( r e f . 10) f o r r a t s and o f G e r r i t y e t at.
The d a t a of Wlester e t a1
( r e f . 1 1 ) f o r humans c h a r a c t e r l z e
t h e t o t a l uptake and t h e URT and LRT uptakes o f 03, r e s p e c t i v e l y .
However,
these data a r e i n s u f f i c i e n t t o I n f e r t h e d l s t r l b u t l o n of absorbed 03 w l t h l n t h e tracheobronclal (TB) and pulmonary r e g l o n s o f t h e LRT.
P o s l t l o n emlsslon
tomography and isotope r a t l o mass spectroscopy a r e experlmental methodologies t h a t may a l l o w t h e determination o f t h e d i s t r l b u t l o n o f absorbed 0 3 I n speclf l e d regions o f anlmals and humans.
The r e s u l t s of a l l these experlmental
approaches w i l l a l l o w f o r t h e refinement o f t h e values o f t h e p h y s l o l o g l c a l parameters used i n doslmetry models, r e s u l t l n g I n more accurate p r e d i c t i o n s and an Increased confidence I n doslmetry model r e s u l t s .
284 Accounting f o r 03 Loss I n t h e URT Because t h e URT can remove as much as f o r t y percent ( r e f . 1 1 ) and p o s s i b l y more o f 0 3 from i n s p i r e d a l r , t h i s r e g i o n p l a y s a major r o l e I n t h e dose o f 03 d e l l v e r e d t o d i f f e r e n t l o c a t l o n s I n t h e LRT.
The major e f f e c t o f
t h e URT i s t o reduce t h e q u a n t i t y o f 03 t h a t penetrates t o t h e LRT; however, t h e e f f e c t on t h e r e l a t i v e d i s t r i b u t i o n o f absorbed 0 3 I s probably minor (ref.
12).
Modeling uptake I n t h e LRT by o n l y s p e c i f y i n g an e m p i r i c a l l y
derived concentratlon a t t h e t r a c h e a l entrance can lead t o l a r g e e r r o r s I n p r e d l c t e d LRT dose, depending on specles and magnltude o f URT removal ( r e f . 12).
Thus, a complete r e s p l r a t o r y t r a c t model t h a t a c c u r a t e l y p r e d l c t s URT
uptake f o r a wide range o f v e n t i l a t o r y parameters and specles i s necessary. One way t o account f o r URT removal i s t o use a simple chamber t h a t removes t h e a p p r o p r i a t e q u a n t l t y o f 0 3 (determined by experiments) I n t h e animal species belng modeled.
A t t h e o t h e r extreme, v a l l d a t e d mathematical models
t h a t take I n t o account t h e complex URT anatomy and p h y s l o l o g l c a l processes o f 03 removal could be used.
In e l t h e r case, experiments conducted s p e c i f i c a l l y
t o c h a r a c t e r l z e uptake by t h e URT o f l a b o r a t o r y animals and humans a r e c r i t i c a l l y needed.
Age S u s c e p t l b l l l t y t o Ozone I n 1974, B a r t l e t t and coworkers ( r e f . 13) suggested t h a t young anlmals have an increased s e n s i t l v l t y t o 03, although t h e experlrnental design o f t h e l r s t u d i e s d i d n o t r e a l l y p r o v i d e t h e a p p r o p r l a t e framework f o r such an Inference. Biochemical changes I n t h e lung have been more r e a d i l y observed i n neonatal and young animals than i n o l d e r animals ( r e f . 14,151.
On t h e o t h e r hand,
postnatal r a t s a r e r e s i s t a n t t o 0 3 exposure u n t l l weaning ( r e f . 16).
In
s t u d i e s comparlng t h e e f f e c t s o f 0.12 ppm and 0.25 ppm 03 on t h e proximal a l v e o l a r r e g i o n o f j u v e n l l e and a d u l t r a t s , B a r r y e t a l .
( r e f . 3) found no
s t a t i s t l c a l l y s l g n l f i c a n t age-dependent e f f e c t s on a m u l t l t u d e of morphom e t r l c measures o f volume, s u r f a c e area, and d e n s l t l e s o f c e l l s and o t h e r t i s s u e components.
However, e f f e c t s l n d l c a t i v e o f e p i t h e l i a l i n j u r y were
a t t r i b u t a b l e t o 0 3 even a t t h e 0.12 ppm exposure l e v e l I n b o t h j u v e n i l e and adult rats. In humans, t h e r e I s evidence from epidemiological and f i e l d s t u d i e s t h a t e x e r c i s i n g c h i l d r e n and adolescents may experience decrements i n pulmonary f u n c t l o n when exposed t o amblent l e v e l s o f 03 below t h e p r e s e n t NAAQS o f 0.12 ppm d u r i n g normal a c t l v l t l e s ( r e f . 17,18).
However, expo-
sures o f a d u l t s f o r two hours w i t h I n t e r m i t t e n t heavy e x e r c i s e t o 0.1 does n o t a l t e r pulmonary f u n c t i o n ( r e f . 19).
ppm 03
285 While t h e above s t u d i e s would appear t o support an a s s e r t i o n t h a t c h i l d r e n are more s e n s l t l v e t o 03 than adults, t h e s t u d l e s do n o t p r o v l d e a d e f l n i t l v e answer s l n c e b o t h groups were n o t examlned under comparable condltlons.
To date, o n l y McDonnell and coworkers ( r e f . 20) have compared t h e
e f f e c t s o f 03 exposure on t h e pulmonary f u n c t l o n o f c h l l d r e n and non-smoklng adults, normallzlng t h e e x e r c l s e f o r body s i z e t o y l e l d a mlnute v e n t l l a t l o n
( V E ) o f approxlmately 35 l i t e r s per min per square meter o f body s u r f a c e area
.
Demographlc, d e s c r l p t l v e s t a t l s t l c a l , and r e s p l r a t o r y f u n c t l o n data from t h e M c b n n e l l e t a l . ( r e f . 20) study a r e given I n Table 1.
Wlth r e s p e c t
t o t h e t y p i c a l l y r e p o r t e d measurements o f forced v i t a l capacity (FVC) and forced e x p i r a t o r y volume I n one second (FEVI), t h e r e appears t o be a simll a r l t y i n response t o 0.12 ppm 03 between c h l l d r e n and a d u l t s f o r l e v e l s o f exerclse y l e l d l n g comparable VE normalized f o r body s u r f a c e area (BSA). However, w l t h respect t o t h e r e p o r t l n g o f cough as a symptom associated w l t h t h e 0 3 exposure, a d u l t s experlenced a s l g n l f l c a n t Increase (p 0.05 by repeated-masures analysis of variance). Reactors s h d s i g n i f i c a n t (P < 0.01) variation, with considerably s n a l l e r man respcnses in auturm and winter than in the i n i t i a l spring exposure.
In the f i n a l spring followup, m a n
response was similar to t h a t in the i n i t i a l expasure one year earlier.
In the
17 subjects who completed the spring followup, individual FEY respcnses 1 were r e l a t i v e l y consistent between spring 1986 and spring 1987 ( c o r r e l a t i o n c o e f f i c i e n t = 0.79, P < 0.001).
A
similar degree of correlation was found by
McDonnell e t a l . i n duplicate exposures to 0 concentrations between 0.18 3 and 0.40 ppm, spearated by periods of a few weeks to mre than me year, in subjects n o t extensively exposed to ambient 0 ( r e f . 2 ) . 3
315
Tests for acute respiratory i l l n e s s were not helpful in explaining
Nearly a l l subjects showed positive v i r a l individual r e a c t i v i t y to 0 3' titers in one or mre instances. The overall incidence was greater in reactors than in nonreactms, ht the difference was explained by two reactors in than nearly a l l r e s u l t s wre positive. One of these was highly reactive in a l l exposures in tern of FEV loss, bt the other showed seasonal variation 1 similar to t h a t of the reactor group as a whole. Abnormal h w n q l o b u l i n E assays, sedimntation rates, or white ell counts were rare in reactors as tell as mreactors. Table 2 shows the proporticns of reactive and nonreactive subjects with allergy history, "nonspecific" airmay hyperreactivity as determined by a mthacholine challenge, and positive answers to questions concerning s e l f perceived s e n s i t i v i t y to a i r pollution. Both allergy history and airway r e a c t i v i t y to mthacholine were strongly associated with r e a c t i v i t y to 0 3'
A w l +200 ML
-
.............
A W W
SPRING
1988
w m
SPRING 1987-
Figure 1. Seasonal variaticn in response (change in forced expired v o l m in one second a f t e r 2 b u r s of ozone exposure). Points = mans; f l a g s = standard deviations. Solid circles = subjects studied through winter: open circles = subjects studied in spring 1987.
316 TABLE 2 ASSOCIATIONS RFIWEEN INDIVICUAL SCREENING MAMINATION FINDINGS AND REACTIVITY TO OZONE, I N 25 SURJECTS WHO C@lPLEl'ED W'IUMN-WINTER F O W P D<poSURES "REACMRS
FINDING
P*
REF\CTORS
yes no
0 13
8 4
.0005
History of nonrespiratory a l l e r g i e s yes no
2 11
6 6
.Oll
Methacholine PD20 < 1000 breath u n i t s ( "reactive airways" )
Yes no
0 13
8
.0005
Increased upper respiratory swtoms an = m m Y days
Yes no
2 11
9 3
,004
Increased lower resp. symptoms with exercise on smggy days
Yes no
1 12
5 7
.063
Increased lower resp. symptoms a t rest cn srnggy days
Yes
0 13
2
.220
no
10
More s e n s i t i v e to smg than mst
yes no
6 6
.005
13
Yes no
3 10
10 2
.004
History of respiratory allergies'
people of similar age "Positive" €or any of above 4 characteristics
0
4
.
*Probability that associatian is due to chance, determined bq one-tailed Fisher exact test l'Association of ozone r e a c t i v i t y with allergy was confirmed bq skin tests: see text.
F m past experience in t h i s laboratory, the l o w e r l i m i t of normal airway
r e a c t i v i t y , expressed as the provocative dose of mthacholine necessary to
(PD ), was estimted to be 1,000 1 ,20 breath units. (One breath u n i t is defined as one vital-capacity breath of aerosolized solution containing one microgram of mthacholine chloride per milliliter.) Nonreactors' PD values ranged from 1,250 to mre than 6,000 20 breath units. Only 4 reactors had PD above 1,000: the other 8 reactors' 20 values ranged from 4 to 470 breath units. In their answers to intervew questions, reactors were s i g n i f i c a n t l y mre l i k e l y than nonreactors to report excess respiratory symptoms on smggy days, and to r a t e themselves as "mre induce a 20 percent decline in FEV
s e n s i t i v e to s m q " than nost people t h e i r m age.
317
h n g nonreactors, 8 subjects had no c l e a r l y positive skin test r e s u l t s (no wheal-and-flare responses of 2+ or greater i n t e n s i t y ) , 2 subjects had sinqle positive tests, 2 subjects had 2 p i t i v e tests each, and one subject was rot tested. ?rmng reactors, m l y 4 subjects had rn c l e a r l y p s i t i v e tests, and the other 8 subjects had 5 or mre positive tests each. "?E difference in positive respcnses between reactors and nonreactors was s i g n i f i c a n t (P < 0.05, Wilcoxon-Mann-Whitnev rank-sum test). DISCUSSION
These r e s u l t s suggest, mre strocqly than previous information, t h a t some
ms Angeles area residents show seasonal variation in t h e i r r e a c t i v i t y to 0 3
, consistent
with "adaptation" to repeated ambient exposures during the
sumner pollution season.
However, t h i s apparent "adaptation" vas not
consistent with predictions from laboratory wrk: it seemed im p e r s i s t for m n t h s in the absence of frequent ambient exposures, whereas laboratory "adaptation" is lost a f t e r a few days.
These r e s u l t s also suggest, mre
strongly than previous information, that upper-respiratory a l l e r g i e s or as-
mv be r i s k factors for excess r e a c t i v i t y
to 0 3
.
A t the
same time, both
these and previous findings show that high r e a c t i v i t y is by no means a consistent finding in a l l e r g i c or asthmatic persons.
The present questionnaire
answers indicate that self-perceptions of " s q s e n s i t i v i t y " m y be f a i r l y accurate in residents of an 0 -polluted area. 3
Thus amnunity-wide
questionnaire surveys m y be useful in research to identify and characterize reactive subgroups of the wpulation. b t h major findinqs from t h i s experimnt-the a w a r e n t seasonal variation i n response and the apparent association of asm or allergy with reactivitym y have important i w l i c a t i o n s for p l b l i c health, and thus for regulatory policy. H m v e r , the findings cannot be considered d e f i n i t i v e , qiven the limitations of the experimental design and the ccnparatively few subjects. They should be reinvestigated in a laver popllatim followed for a longer period of time. I t m y turn out that individuals who are inherently highly reactive to 0 or cannot "adapt" are nost a t r i s k f r a n ambient exposure, in 3 t h a t t h e i r repeated short-term responses eventually lead to i r r e v e r s i b l e lung damage and d i s a b i l i t y . Conversely, it m y turn out t h a t individuals who are consistently nonreactive or "adapt" readily are mt a t r i s k , i f curmlative pathological responses to 0 occur independent of the observable short3 term response. These possibilities need to be investigated, through basic
318
science to elucidate the mechanisms of response to 0 and through 3 empirical, longitudinal epidemiologic surveys of 0 - e x w e d pnxllatims. 3 REFERENCES
A i r Quality C r i t e r i a f o r Ozone and Other Photochemical Oxidants, 1J.S. Environmental Protection Agency, Fssearch Triangle Park, North Carolina, 1986. W.F. McDonnell, D.H. Horstmn, S.A. Salaam, and D.E. House, Am. Rev. Ilespir. D i s . 131 (1985) 36-40. J.D. Hackney, W.S. Linn, R.D. Buckley, and H.J. Hislop, Environ. Heal. Perspectives 18 (1976) 141-145. S.R. Hayes, A.S. Fasenbarn, T.S. Wallsten, R.G. Whitfield, and R.L. Winkler, Assessment of Lung Function and Synptorn Health R i s k s Associated with Attainnent of Alternative Ozone NAAQS ( f i n a l report, Environmental Protection Pgency c o n t r a c t 68-02-4313) , Systems Applications Inc., San Rafael, California, 1987. W.F. McDwvlell, D.H. Horstman, S.A. Salaam, L.J. Faqgio, and J.A. Green, Toxicol. Indust. Heal. 3 (1987) 507-517.
T.Schneideret al. (Editors),Atmospheric Ozone Researchand its Policy Implications
313
0 1989 Elsevier SciencePublishersB.V., Amsterdam - Printed in The Netherlands
WSIMETRIC MODEL OF ACUTE HEALTH EFFECTS OF OZONE AND ACID AEROSOLS IN CHILDREN
M.E. Raizennel and J.D. SpenglerZ 'Health and Welfare, Canada, Environmental Health Directorate, Room 203, Tunney's Pasture, Ottawa, Ontario, Canada, K1A OL2 2Harvard School of public Health, 655 Huntingdon Avenue, Boston, Massachusetts, 02115
USA,
FblmxFicr
During the summer of 1986, 112 young females, 7 to 14 years of age attended one of three, 2 week sessions, at a residential s m e r camp located on the north shore of Lake Erie, Ontario, Canada. Children performed standardized spirometry each afternoon and on at least one occassion completed a standardized exercise test. Over the course of the 41-day study, 0,, SO,, NO,, and acid aerosols (H2S04) were continuously monitored. Hourly ozone varied between 40 and 143 ppb. The 12 hour acidic particle concentrations expressed as H2S0, equivalent was 28 pgg/m3 during one episode and fine particle sulphate was 100 kg/m3 for the peak hour. During the exercise test minute volume (V,) and heart rate (HR) were measured. Each day different children wore portable heart rate recording devices which recorded heart rates for each minute for up to twelve hours. Using a dosimetric model, a child's estimated dose of ozone and [H+] was calculated for various time periods prior to the time of lung function testing. This paper reports the development of individual exposure estimates, based on time-activity data, and relates these exposures to changes in lung function observed in children.
1mcr10N
In the past decade significant improvements have been made in the design of air pollution studies through the incorporation of improved measurements of both
biologic and aerometric indices of exposure.
However, important
limitations remain in relating ambient concentrations of air pollutants to actual population exposures (ref. 1).
This is a critical issue in the
functional transition of data between clinical and epidemiologic studies. Epidemiologic studies assessing the acute health effects of ozone exposures have provided supporting evidence of relationships reported in human chamber studies (ref. 2).
Human studies have repeatedly demonstrated that ozone at
concentrations currently observed in ambient air, elicit significant transient physiological changes in lung function and increased respiratory symptomatology (refs. 3-11).
However the intercomparison of laboratory and atmospheric
studies for acidic aerosol exposures is less clear.
320
In order to improve our understanding of the relationship between exposures and adverse health responses, the estimate of personal exposure and/or dose delivered to the respiratory system requires greater resolution.
Complex
models have been developed which estimate the delivered dose of gases to the lower respiratory tract (ref. 12,13).
These have provided vaLuable information
in predicting delivered dosages to specific areas of the respiratory tract. The models however are limited by their irrelevance to "free living" exposures where the dynamics of multiple factors (i.e. breathing mode, exercise, anatomical and behavioral variability) increase or reduce the effective dose delivery of pollutants. Mage et al. (ref. 14) demonstrated that an increase in activity, as reflected by heart rate measurements, could modify the estimated airway/lung dose of ozone by 70%. The delivered dose or cumulative dose may be the important determinant of altered lung function responses.
Thus more
accurate estimates of dose would reduce error inherent in the reliance on measurements of concentrations or even exposures in the population. environmental chambers, concentrations during
In
exposure and dose are assumed
correlated since many variables can be controlled and monitored. However, the limitations inherent to chamber studies in general (ref. 15) also limit the development of dose over extended periods of time. In this paper subject specific and day specific dose estimate models for ozone and for acidic aerosols are developed. These estimates will then be used to assess the relationship between dose estimates and observed changes in lung
function in children. IIE!l!EOJlS
An acute respiratory health study was conducted in southern Ontario during the s m e r of 1986. One hundred and twelve (112) healthy young females, 7 to 14 years of age, attended one of three, 2 week residential s m e r camp sessions
in July and August. The camp was located on the north shore of Lake Erie, near Dunnville, Ontario.
Prior to attending the camp, parents completed a self-
administered respiratory questionnaire and signed an informed consent for their child to perform the health tests. 15:OO
and
17:OO
hours,
spirometric maneuvers.
In the afternoon of each camp day, between
children performed
standard
forced
expiratory
On at least one occassion a 12 minute, graded cycle
ergometer exercise test, to a target heart rate of 170 beats/min, was completed by all children.
Heart rate (HR) and minute volume (V,)
throughout the exercise test.
were recorded
In addition, on each of 24 days, 5 randomly
chosen children wore portable heart rate monitors that recorded mean heart rate each minute for up to 12 consecutive hours throughout their daily activities (Sport-tester, PE 5000, Finland). acid aerosols (i.e. H,SO,)
Air pollution monitoring for 0, and strong
was performed at the camp site. Ozone was measured
321 continuously by a Monitor Labs 8410E chemiluminescent monitor and sulphur measurements were derived from the modified Meloy speciation flame photometry analyzer (ref. 16).
particle
285 thermal
With a thermal volatilization
technique this instrument can measure the presence of strong acid particle sulphur.
Details of health and aerometric methodologies have been reported
elsewhere (refs. 9,17). ExposuRE/DosE D O -N
To examine the relationship between exposure-dose and changes in lung function, day specific and child specific dose estimates to 0, and equivalent were calculated.
H,SO,
To demonstrate the development and application of the
dose estimate we will use the aerometric data collected during the second camp period when a significant episode of high ozone and high acid particle levels was observed.
The hourly mean, minimum and maximum values for air pollutants
on a low pollution day (July 16th) and on the episode day (July 25th) are presented in table 1.
The analyses of data for all children and all days will
be reported elsewhere. The following general formula was applied to calculate dose for any time period : Dose (pg) = r * V, * t [pollutant] (eq. 1) The symbol 'r' is the retention factor to the respiratory tract. For ozone, data from Young have suggested that ozone retention/penetration beyond the oropharyngeal region is a complex function of V, and 0, concentration (ref. 18).
A step function for r over a range of V, at .1 ppm was used to calculate
appropriate retention factors since the ambient measurements were distributed around .1 ppm.
For acidic particles the penetration factor was fixed at 0.6
because most of the acidic component is contained in particle sizes between 0.2 and 0.6
pm
(ref. 19) and the depositional characteristics of hygroscopic
acidic aerosols in this size range have deposition characteristics described by Tu et al. (ref. 20).
Adult airway characteristics have commonly been used in
gas and particle penetration studies. factors in estimating ozone and H,SO,
Thus the application of retention
dose in children is recognized to be of
limited accuracy. V,
child.
(minute volume) estimates were derived from empirical data for each Individual functions for minute ventilation were generated by
regressing the logarithm of the exercise minute ventilation against the heart rate obtained for each child separately. These were expressed in the form: V,
= exp (a + 8 HR) where a is the logarithm of V,
relationship between HR and V,.
(eq. 2) at zero heart rate and 13 defines the
322 TABLE 1.
Aerometric Profile (Hourly Data) on Control Day (July 16th) and Episode Day (July 25th) 8:OO to 19:oo Control (July 16th)
Episode (July 25th)
Mean
Min
Max
Mean
Hin
Max
03 (PPb)
44
39
50
121
93
143
SO, (PPb)
0.6
bdl
2
bdl
15
SO, (w/m’)
4.0
1.7
7.2
84
71.5
101.6
HzSG (pg/m’)
0.2
bdl
0.5
23.7
bdl
47.7
1.1
bdl
2
5.1
2.0
10.0
1.2
1.0
2.0
4.5
2.0
7.0
21.7
18.6
24.9
24.5
21.7
25.7
48
17
81
77
91
NO,
(PP~)
NO2 (PPb)
Temp.(“C) Relative Humidity ( % )
59
9.4
bdl : below detection limit Individual mean hourly heart rates were then substituted in the equation 2 to determine the mean minute ventilation for each hour. rates (8:OO
-
Mean hourly heart
18:59 hours, 11 hours total) were calculated for each subject on
the day they wore the heart rate monitor. The symbol ‘t‘ is the duration of exposure and represents an interval of time.
‘[pallutant]’ is
defined as
the mean
concentration over
the
corresponding period of time for the pollutant of interest. The estimate of cumulati-ge dose for the ith child, Di, is given by: OZONE W S E (pg) = 0, Di
J 0, D, =
E t, * 03 r,, j=1
V=I,
[03I3
where, t, = one hour for all j; j = index for time interval; J
=
number of time
intervals; 0, r,, = ozone retention factor in airways for the ith child, in the jth time interval; H,SO,
ri, = 0.6 retention factor; V,
=
ventilation rate
323 for ith child, in the jth time interval (L/hr); [O,], = ozone concentration for jth time interval (pg/L); [H,SO,], = H,SO, concentration for jth time interval (W/L). RESULTS
Since heart rate data for each child were only available on one day it was necessary to extrapolate the heart rate values to all days of lung function testing in order to develop a unique exposure measure per child.
However a
major interest in this paper was to investigate the exposure profile on the day of a large episode in which no heart rate measurements were taken. A mixed effects model was used to investigate the source of variation for heart rate. The response, heart rate, involved up to 11 hourly average measurements on 104 children, with approximately 5 children sampled each day for 24 days. The mean hourly heart rate over the daytime interval is presented in figure 1.
Heart
rate was modelled by the child's age, height and weight, with variance components, day, child within day and time (hour).
Time explained the largest
percentage of variation, 60%. while child explained 36% and day
Since the
4%.
variation in heart rate between days is the smallest we replicated each child's hourly heart rate pattern across days. Thus for the 27 children at the camp on the day of the episode we applied individual heart rate profile from their sample day and from this we derived estimates of minute ventilation (eq. 2). Figure 1
Mean Heart Rates vs Time of Day (Mean
5
1 standard deviation)
130 125
120 115 110 105
100 95
90 85
-- 1
Rll
7
I
I
I
I
I
I
I
I
I
I
I
8
9
10
11
12
13
14
15
16
17
18
Time of Day ( h o u r )
19
324 In order to relate heart rate to minute volume ventilation, each child performed an exercise test in which the logarithm of minute ventilation was regressed on heart rate for each child separately.
This linear function
explained approximately 99% of the variation in each child's response. Colucci (ref. 21) developed a series of equations relating V, equation for children (V,
=
and heart rate.
His
1.635 exp (0.0185 HR)) closely approximates our
results (V, = 2.200 exp (0.016 HR)) when the calibration slopes are averaged across all children.
The coefficient of determination was .72 when a common
slope for all children was derived from the logarithm of V,
to heart rate.
Since we had child specific slope estimates we chose to use individual slopes rather than an average slope for all children. The dose estimate model is derived in part from ventilation rates and it has been necessary to assume that heart rates are correlated with physical activity. Ventilation rate in turn is derived from heart rate therefore it was necessary to assess the independent effect of heart rate on lung function. This was examined by regressing lung function on the average heart rate in the hour previous to the test and adjusting for the child's age, height and weight This analysis indicated little evidence that heart rate was related
(N=107).
to lung function changes. Figures 2 and 3 are plots of the percent change in PEFR versus the cumulative dose estimates to 0, and H,SO,,
respectively, for the 6 hour period
prior to the lung tests. Figure 4 is a plot of the episode day, hourly polluFigure 2
Individual 6 Hour Estimated Cumulative Dose f o r Ozone vs P e r c e n t Change PEFR, Episode Day (July 25, 1986) 8
6 4
2 0 -2 -4 -6 U
-8 -10
-12 -14 -16
L
--
-
0
0 0
0 1
.
1
.
I
I
I
I
*
I
,
325 Figure 3
Individual 6 Hour Estimated Cumulative Dose for H2S04 vs Percent Change PEFR, Episode Day (July 25,1986) 9 7
E W a
0
5 3
0. -- ----_0----_ 0 0 ---__ a0 ----- ---_----_
: A
; d
0
0
0
0
.-
c" 2 0
0
0
-1
-3
m
-5 -7
0
----,
0
0
-9
0
0
-1 1
-13 0 -
-15
-17
'
20
I
I
I
I
I
I
40
60
00
100
120
140
Estimated H,SO,
mean = -1.45
160
Dose (Micrograms)
_--------
slope = -.033
Figure 4
Mean Hourly Pollutant Concentrations Episode Day (July 25, 1986) 300
"
50
h
E
280
\
I
40
v
v
"v, -0
2 60
240 220
h
c
a
200
\
10
3 , v
180
0
326 tant concentrations.
From this figure it can be seen that both 0, and H,SO,
followed a similar pattern.
However the increase in acid was markedly
different in that the concentration increased threefold between 1O:OO and 14:OO for H,SO,.
For the same interval, ozone levels increased by 70 pg/m3 and are
noted to be relatively stable for the
hour period prior to the lung tests.
4
The percent change in lung function is calculated using the mean of the child's lung function value measured daily at camp and subtracting this value from the observed value on the episode day and divided this difference by the mean value.
The mean percent decrement is given by the broken line (N=27) and
the least squares regression liie for percent change on dose is also given in these figures.
Although the slopes of these lines did not differ from zero
(p>.lO) there exists a negative trend in lung function as cumulative dose
increases for both 0, and H,SO,. DISCUSSION
We
have
used
biometric
and
aerometric data
collected during
environmental health study to provide exposure and dose estimates.
an The
dosimetric model examined reflects the observed relationships between exposure and decreases in lung function, specifically PEEX.
Decreases in lung function
have been observed for ozone and acidic aerosols in chamber studies and, for ozone, in acute epidemiologic studies.
Without individualized dose estimates
all children would have been assumed to experience the same exposure as measured by the fixed site monitors. The data presented here indicate that the range of personal exposures to air pollutants varies markedly
between
individuals. All essential variables required in the development of an exposure/dose estimate have been quantitatively addressed.
The retention factors used in
equations 2 and 3 were derived from limited data and estimated for ozone (ref. 18)
and for aerosols (ref. 20).
Retention factors for ozone have not been
included in dose estimates in original studies and in dose assessment reviews (refs. 10,21).
As proposed by Young, 'rl is a complex function of mode of
breathing, minute ventilation and exposure concentration (ref. 1 8 ) .
Evidence
from human clinical studies have indicated that -50% of inspired ozone is removed by the upper airways (Gerrity, this symposium).
It has also been shown
that the lung function response is dependent on ventilation rate and on 0, concentration (refs. 22-24). then the estimates of ,V estimates.
Since r is a function of V,
and concentration
take on greater significance in dose modelling and
Recently, Folinsbee et al. reported calculations of effective dose
for 6.6 hour exposures to ozone at .120 ppm (ref. 10).
The cumulative dose
estimates for adult subjects were approximately 1500 pg of ozone however these calculations did not include a penetration/retention factor. The same authors
32 7
also calculated cumulative exposures for other chamber studies with exercise and varying duration.
The mean exposure ranged from 490 to 1164 pg.
For
children at our camp, on a high pollution day, we estimate the mean ozone dose in children to be approximately 300 pg when a retention/penetration factor is included.
In contrast, without a retention/penetration function applied, a
mean ozone dose of 1100 pg would be estimated.
This latter dose estimate is
remarkably similar to data reported for adults in chamber studies where lung function changes have been associated with ozone exposures (refs. 10.21.22). The
data
described
in
this paper
does
not
indicate
significant
relationships between decreases in lung function and modelled dose.
However,
the direction and magnitude of the lung function changes are consistent with results of acute epidemiologic studies where small changes in lung function have been associated with ozone (refs. 3-11) and other air pollutants (refs. 26,27).
Note that the purpose here is to demonstrate the application of a
child specific dose model to determine if it should be used for the entire data set. Using integrated particulate acid data Spengler et al. (ref. 16) have estimated that children would experience acidic aerosol doses having a mean H+ concentration of 2350 nmoles (230 pg equivalent H,SO,
) over a 12 hour period.
It was also noted that this dose estimate was to reported values in chamber exposures ( - 110 pg equivalent H,SO,
)
to acid aerosols.
We examined the
cumulative dose for the 6 hours preceding the lung tests using the continuous particle sulphur data.
For this paper we make a simplifying assumption that
all the particle sulphur volatilized at 120°C is equivalent to sulphuric acid. This will be
an underestimate if there are additional acidic particle
volatilizated at 300°C.
The mean H,SO,
retention fraction of 60% was
-
91 pg.
equivalent
F,
hour dose estimate with a
The relationship of the 6 hour dose
estimate to lung function was similar to that observed for ozone in that the model predicts that small changes in lung function can be expected to be related to acid exposures (figure 2). The day to day variation in heart rate and the variation in heart rate across children were observed to be less than the hour to hour variations. These results indicate that, at least for this specific camp, the daily program elicited a similar heart rate profile each day.
As
noted previously, the
differences in heart rate between children and across hours of the day are strong sources of variation in heart rate and V,.
Nonetheless, the dose
estimates derived for each child on the episode day indicate that small changes in lung function, could be observed to be related to cumulative dose estimates for both ozone and H,SO,.
328 SUlllvLRY
The application of a child specific dose calculation is an advantage over the alternative methods for exposure estimates. The conventional approach used in previous acute health studies has equated dose to ambient concentrations. Typically, the maximum one hour ozone concentration occurring in the previous 12 or 24 hours is used as the exposure measure. Similarly, particle exposures were time averaged concentrations. Using these conventional approaches, assumes that all children have the same ventilation volume, retention and are exposed to time and spatially averaged pollution. The errors associated with these assumptions are never explicitly stated nor incorporated in the analysis. Hourly pollution data and child specific ventilation volume were used to estimate an ozone and acidic particle dose for children participating in an acute respiratory health study. A single 6-hour episodic event was selected to demonstrate this approach. Calculated dose varied substantially among children. Ozone dose ranged from 150 pg to 750 pg. The equivalent sulfuric acid dose ranged from 50 pg to 150 pg. The conventional approach would implicitly assume a single value for all children. This study is important because it illustrates the
"between subject
variation in dose" not accounted for in previous studies.
We recognize that
this has been a demonstration exercise.
Nevertheless, it suggests that
refining exposure measures may enhance the ability of acute health studies in ascertaining effects. -
A
The authors which to acknowledge the collaboration of Mr. Douglas Haines and Dr. Richard Burnett in the preparation of this manuscript. We also wish to thank Dr. M. Lippmann for his review and comments on the manuscript.
1. M. Lippmann, P.J. Lioy, Environ. Health Perspect., 62 (1985) 243-258. 2. D.W. Dockery and D. Kriebel, in E.J. Calabrese and D. Gilbert (Editors), Proceedings of the Northeast Regional Public Health Environment Center: Ozone Risk Communication Conference, 1987, Lewis Publishers (in press). 3. M. Lippmann, P.J. Lioy, G. Leikauf, K.B. Green, D. Baxter, M. Morandi, B.S. Pasternack, D. Fife and F.E. Speizer, in S.D. Lee, M.G. Mustafa and M.A. Mehlman (Editors), Advances in Modern Environmental Toxicology, Vol. 5, Princeton Scientific, Princeton, 1983, pp. 423-446. 4. N. Bock. M. Lippmann, P. Lioy, A. Munoz, F.E. Speizer, in S.D. Lee (Editor) Scientific Basis for Ozone/Oxidant Standards, APCA International Specialty Conference TR-4; Houston, Texas, 1984, pp. 297-308. 5. P.J. Lioy, T.A. Vollmuth, M. Lippmann, JAF'CA, 35 (1985) 1068-1071. 6. D.M. Spektor, M. Lippmann, P.J. Lioy, G.D. Thurston, K. Citak, D.J. James, N. Bock, F.E. Speizer and C. Hayes, Am. Rev. Respir. Dis., 137 (1988) 313320. 7. M.E. Raizenne, R.T. Burnett, J.D. Spengler, Arch. Environ. HealthSubmitted April, 1988.
329
8. M.E.
Raizenne, R.T. Burnett. B. Stern, C.A. Franklin, J . Spengler, Proceedings from the International Symposium on the Health Effects of Acid Aerosols, Submitted to Environ. Health Perspect., Presented October 19-21,
1987. 9. L.J. Folinsbee, W.F. McDonnell and D.H. Horstman, JAFCA, 38 (1988) 28-35. 10. E.L. Avol, W.S. Linn, D.A. Shamoo, L.M. Valencia, U.T. Anzer, T.G. Venet, J.D. Hackney, Am. Rev. Respir. Dis., 132 (1985) 619-622. 11. W.F. McDonnell 111, R.S. Chapman, M.W. Leigh, G.L. Strope, A.M. Collier, Am. Rev. Respir. Dis. 132 (1985) 875-879. 12. F.J. Miller, J.H. Overton Jr., R.H. Jaskot, D.B. Menzel, Toxicol. Appl. Pharmacol., 79 (1985) 11-27. 13. J.H. Overton Jr., in F.J. Miller and D.B. Menzel (Editors), Fundamentals of
Extrapolation Modeling of Inhaled Toxicants: Ozone and Nitrogen Dioxide, Hemisphere, U.S.A., pp. 273-294. 14. D.T. Mage, M.E. Raizenne, J.D. Spengler, in S.D. Lee (Editor) Scientific Basis for Ozone/Oxidant Standards, APCA International Specialty Conference TR-4; Houston, Texas, 1984, pp. 238-249. 15. M.J. Utell, in R. Frank, J.J. O'Neil, M.J. Utell, J . D . Hackney, J. Van Ryzin and P.E. Brubaker,(Editors) Inhalation Toxicology of Air Pollution: Clinical Research for Regulatory Policy. American Society for Testing and Materials, Philadelphia, 1985, pp. 43-52. 16. G.A. Allen, W.A. Turner, J.M. Wolfson, J.D. Spengler, Description of a Continuous Sulphuric Acid/Sulphate Monitor. Presented at the 4th National Symposium on Recent Advances in Pollutant Monitoring of Ambient Air and Stationary Sources., Raleigh, NC.. 1984. 17. J.D. Spengler, G.J. Keeler, P. Koutrakis, M.E. Raizenne, C.A. Franklin, Proceedings from the International Symposium on the Health Effects of Acid Aerosols, Submitted to Environ. Health Perspect., Presented October 19-21, 1987. 18. J. Young, Johns Hopkins University School of Hygiene and public Health,
Baltimore, (Master's Essay), 1977. 19. P.E. Koutrakis, J.M. Wolfson, J.D. 20. 21. 22. 23.
24.
Spengler, B. Stern, C. Franklin, submitted for publication, Harvard School of Public Health, Boston, Mass. K.W. Tu, and E. 0. Knutson, Aerosol Sci. Technol. 3 (1984) 453-465 A.V. Colucci, in T. Schneider and L.Grant (Editors), Air Pollution by Nitrogen Oxides, Elsevier, Amsterdam, 1982, pp. 427-440. M.J. Hazucha, J. Appl. Physiol., 62 (1987) 1671-1680. M. Hazucha, F. Silverman, C. Parent., S. Field, D. Bates, Arch. Environ. Health, 27 (1973) 183-188. F. Silverman, L. Folinsbee, J. Bernard, R. Shephard, J. Appl. Physiol., 41
(1976) 859-864. 25. W. McDonnell, D. Horstmann, M. Hazucha, E. Seal Jr., E.D. Jaak, S.A. Salaam, D.E. House, J. Appl. Physiol. 54 (1983) 1345-1352. 26. D.W. Dockery, J.H. Ware, B.G. Ferris,Jr., F.E. Speizer, N.R. Cook, JAPCA 32 (1982) 937-942. 27. W. Dassen, B. Brunekreef, G. Hoek, P. Hofschreuder, B. Staatsen, H. de Groot, E. Schouten, K. Biersteker, JAPCA 36 (1986) 1223-1227.
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T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implicatwns 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
331
Is There a Threshold for Human Health Risk from Ozone? Daniel B. Menzel', Robert L. Wolpert2 Department of Pharmacology'2, Departme9 of Medicine', and Institute of Statistics and Decision Sciences Duke University, Durham, NC 27710 (U.S.A.)
ABSTRACT The existence of a "threshold," or concentration below which no adverse health effects are observed, is the basis for current air quality standards in the U.S. After using a regional dosimetry model (Miller-Overton) to adjust for variations in animal species, exposure scenario, breathing patterns, etc., measurements of several different toxicity end-points reported by different laboratories were found to lie on a straight line passing through the origin, suggesting the absence of a threshold or no-effect level in animals. On the other hand, the biochemistry of ozone and its detoxification mechanisms suggests that a threshold should exist. Two mathematical population models are examined to illustrate how repair mechanisms affect such thresholds and how a population-wide threshold might not exist. The probability of injury can, however, be calculated so that an acceptable level of risk can be chosen. The models also illustrate how specific populations at risk can be identified, in this case for vitamin E deficiency as in cystic fibrosis patients. INTRODUCTION Toxic chemicals are currently classified as either "threshold chemicals, having some concentration of exposure below which no observable toxic effect occurs, or as "nonthreshold" chemicals, exhibiting some toxic effect even at vanishingly small exposure concentrations. Carcinogens, mutagens and other genotoxic chemicals are thought to be "nonthreshold" chemicals, while the majority of non-genotoxic or systemic toxic chemicals are thought to be "threshold" toxicants. Two different regulatory approaches have evolved as a consequence. "Non-threshold chemicals are regulated at levels which will produce a socially acceptable level of risk, such as 1 adverse reaction in lo6 members of the exposed population. "Threshold" chemicals are regulated by establishing an "acceptable daily exposure (or intake)" level, judged to provide an "adequate margin of safety." Exposure to the accepted daily exposure level should not result in any adverse reactions, because of the margin of safety incorporated into the selection. Ozone and other air pollutants that are not established carcinogens are regulated in the U.S. under the assumption that an acceptable time-averaged exposure level can be tolerated by most individuals without injury, and that an adequate margin of safety can be provided to prevent adverse reactions even in highly susceptible subpopulations. The advent of mathematical dosimetry models (ref. 1) allows nne to combine evidence from several different human and animal experiments from different laboratories to examine the relation between the delivered dose, called molecular dose here, and toxic response. Observing the same
332
molecular dose-toxic end-point relationship in several animal species enhances our confidence that the same events and molecular dose-response will occur in humans. The Miller-Overton dosimetry model can be used to predict the molecular dose sustained by an animal at any lung site during a specxed period of exposure to a given concentration of an air pollutant; of course the animal species, strain, sex, size, and breathing pattern must be specifled in detail. Since the model’s molecular dose predictions are proportional to the exposure concentration and duration, they may be summarid in the form of a constant p (which we call the Miller modulus). the predicted molecular dose for an exposure to 1.0 ppm for 1.0 day. Upon comparing observed health effects with model predictions of molecular dose from a number of r e p o d ozone exposure experiments, no threshold or no-observable-effect level has been found for ozone in any animal species. From the biochemistry of owne injury, an individual threshold, 8, is hypothesized and two population-based models are presented to examine how biological repair of owne-induced injury affects risk and how a subpopulation’s deficiency in repair may leave that subpopulation at high risk to the effects of ozone toxicity. The models are used to present a way in which an acceptable level of risk from ozone exposure might be calculated, even in the absence of a population-wide threshold. favorine a thmhold for ozone The toxicity of ozone has been reviewed recently by Menzel and Shoaf (refs. 2,3). The theory proposes that ozone’s toxicity stems from its oxidation of essential protein groups, thiols, and polyunsaturated fatty acids (PUFAs). The toxic symptoms are thought to arise from the cytotoxic effects of oxidation of the PUFAs in the cellular membrane. This hypothesis is supported by the evidence that vitamin E, the principal intracellular antioxidant, has a profound effect on ozone toxicity. The reaction of owne with PUFAs is one of the few reactions with high enough reaction rates to account for the removal of inhaled ozone from the airways (nf. 1). Ozone exposure causes major increases in the metabolic pathways leading to detoxification of lipid peroxides (ref. 2). Pulmonary edema, a common symptom of ozone toxicity in several animal species (including humans), arises from cell membrane destruction caused by lipid peroxidation. Lipid peroxidation is initiated by the combination of owne with ethylene groups of membrane PUFAs leading to the production of ownides (ref. 4). Ozonides can decompose directly to peroxides capable of further free-radical reactions in the presence of oxygen. As reported elsewhere in this symposium by Rietjens and Alink (ref. S), glutathione can react with and detoxify ownides by inhibiting the further promotion of lipid peroxidation. Similarly, vitamin E reacts with both ozone and lipid peroxides to terminate lipid peroxidation (ref. 4). The induction of glutathione peroxidase by owne could also facilitate the elimination of lipid peroxides. These molecular defenses all suggest that major lipid peroxidation is unlikely to occur until the cell defenses (primarily vitamin E) are overwhelmed, and hence that there should exist a threshold below which no cytotoxicity will occur. If cytotoxic effects are primarily responsible for the observed toxic effects of ozone, this suggests the existence of a threshold
333
for omne toxicity.
..
m b i m l e-al The animal exposure experiments reviewed in (refs. 2.3) study different effects of ozone in differing species at varying concentrations, exposure regimens, and breathing patterns. We have sought to render the experiments more nearly comparable by correlating reported exposure-related injury, not to ambienr concentration, but to the estimated time-integrated regional dose at the site of tissue injury in each study of ozone toxicity. We have used the Miller-Overton ozone dosimetry model (ref. 1) to estimate regional doses for each animal species, ambient concentration, exposure regimen, body size, and breathing pattern employed in experiments reported in the literature. Under the assumptions inherent in the Miller-Overton model the ozone burden at each site in the lung of each species, under each exposure regimen and breathing pattern, is proportional to the product of the exposure concentration and the exposure duration; the proportionality constant is the Miller modulus, p. It is convenient to use units of (pgozone)/(g wet tissue weight).ppm .d for p. so that an exposure to c ppm ozone for t days will lead to a tissue burden at the site of injury of p c .t pg 03/gtissue.ppm .d. We assume that molecular ozone is the toxicant. With tabulated values of the Miller modulus p for various sites, animal species, body weights, breathing patterns, etc. it is possible to measure exposure doses on the same scale for all experiments (pg 0 3 / gtissue.ppm .d at the site of injury) to assist in comparing or combining the results of different studies and in making health effect predictions for one species on the basis of evidence gathered about another. Examples of p calculated for mice and adult humans are ~ ~ 7 0and . 4~ ~ ~ 1 pg 7 03/g . 8 tissue.ppm d ,respectively. 1000
0
900
.
0
.
I
.
.
I
~
~
~
~
"
~
"
"
~
"
.
'
"
'
I
10 20 30 40 50 60 70 Total Lung Dose of Ozone (pg)
Figure 1. Increase in lung lavage fluid protein in rats following omne exposure. Each point represents a separate study reported in the literature. Total lung molecular dose was estimated using the Miller-Overton dosimetry model.
334
We have reported such inter-species extrapolations and comparisons of ozone toxicity evidence elsewhere (ref. 6). Figure 1 illustrates the results of such a research synthesis studying pulmonary edema in rats. This evidence does not support the existence of a threshold for ozone toxicity in rats. A variety of other end-points follow the same type of relationship as shown in Figure 1.
A FAMILY OF MATHEMATICAL MODELS FOR OZONE TOXICITY If each individual in the population has a threshold tissue burden 0>0 (measured in pg03/gtissue.ppm.d) below which that individual will sustain no injury, and if for each OQ 0, it is simpler (and conservative) to consider only the asymptotic or steady-state risk at a given concentration c . For the probit model, this has already been calculated in equation (5):
M, = ~ ( p . c . p - ' )= @(og8'ln(p.c/p.Dgl)), leading to the calculated value c = p F-'(M,)
I p = ~LL@ e
oI O-'(R )
Ice.
(7a)
for the concentration leading to a life-time risk of l00R %. The asymptotic calculation (7a) is the (constant) concentration which would lead to a risk of R for an infinitely-long exposure; exposed only for its lifetime, an animal would experience a somewhat smaller risk. In that sense the use of asymptotic value is "conservative." The calculation under the log-logit model is similar, and is also conservative:
339 c = p F-'(MJ I p = pm#
(-)"I
R
1-R
For (assumed) repair rates of 0.1%. 1%. and are given in Table 3.
I p.
(7b)
lo%, the concentration limits for the two models
Table 3. Daily Repair Rate: Lifetime Risk
0.1%
0.50
0.030 0.007 0.003 0.002 0.002
10-2 10-4 10-5 10-6
1.0%
10% log-probit c @pm) 0.300 0.071 0.030 0.022 0.016
3.000 0.714 0.302 0.216 0.160
0.1%
1.0%
10%
log-logit c (ppm)
0.0300 0.0054 0.0010 O.OOO4 0.0002
0.300 0.054 0.010 0.004 0.002
3.000 0.538 0.096 0.040 0.017
If a linear repair mechanism proceeds at a daily rate of at least 1%. then under either model a constant concentration of 0.005 ppm would be expected to lead to a risk of no more than lK5or so, while the risk at 0.2 ppm would only be under if the repair rate is at least p=50% for the log-logit model or ~ ~ 1 1for% the log-pmbit model. Note that the flatter tails of the logistic distribution lead to predictions of wider variability among individuals' thresholds for the log-logit model than for the log-probit model, and consequently lead to higher risk estimates at a given (low) concentration or, conversely, to lower concentration bounds for guaranteeing a specified bound on the risk.
..
W m a t ing the rate of repair of ozone inilary In the absence of an assumed repair mechanism the dose and consequent molecular burden were both exactly proportional to c'r for exposure at a fixed concentration, or more generally to jc(r)dr, so an arbitrary exposure regimen would be expected to have the same health effect as a constant exposure with the same average concentration. Under linear repair the exposure regimen i s no longer unrelated to the expected health effects: a short exposure to a very high concentration, followed by a long period Without exposure, leads to higher molecular burdens and consequently to more harmful health effects than does a long exposure to the same average concentration. An exposure with peaks and valleys will be more harmful than a constant exposure to the same average concentration. Instead of interpreting the log-probit model without repair (3a) as a regression equation relating the survival log-probit to time, we can interpret it as a regression equation relating survival for a fixed time to concentration or, more generally, to a multiple log-probit regression equation:
340
The striking feature of this equation is that the coefficients expressing the dependence of the survival probit upon log-time and upon log-concentration are both equal to the same quantity, namely as-'. Under the competing hypothesis of linear repair a log-probit regression of mortality on concentration will still yield an estimate of ag-', but when plotted against log-time the mortality probit will eventually level off at the bound
This suggests that we first estimate the asymptotic mortality M , and then estimate the repair rate by:
Under the log-logit model the estimate is even simpler:
It is more problematic to estimate p if an estimate of the asymptotic mortality rate M, is not available, but any leveling of the log-logit or log-probit plots of mortality against time is evidence in favor of a repair mechanism; routine statistical methods permit one to test the hypothesis of no-repair or to estimate the rate by numerical optimization. Under the ( l o g - n o d ) probit model with estimated parameters LD#=30.0 and at an og=0.617, the daily repair rate would have to be ~25.6%to attain a risk as low as average environmental concentration of 0.12 ppm ozone, and would have to be ~ 2 7 . 5 %for a risk as low as la-6 (see Equation 7a). The log-logistic (or logit) model's broader tails suggest that a higher repair rate would be necessary to attain such low risks. With our previously estimates of LD#=30.0 and ag=0.374 for this model, the repair rates would have to be at and would have to be ~270.2%to attain a lo4 risk (see least ~229.7%for a risk of Equation 7b). for ozone .
.
Each of the possible mechanisms for ozone toxicity suggested above is amenable to biological repair. For example, regions of lipid peroxidation might be removed from cell membranes, or damaged mature cells might be replaced by immature progenitor cells. Vitamin E oxidized by ozone could easily be replaced, leading to a membrane free of ozone damage. Reacylation of phospholipids with polyunsaturated or saturated fatty acids to replace oxidized PUFAs could also lead to such repair. The remodeling observed in rodent and primate lungs exposed to ozone for prolonged periods suggests that some ozone damage may be repaired by replacing Type 1 cells with Type 2 cells. Several of these mechanisms might proceed at rates as high as those suggested in the paragraph above.
34 1
HIGH-RISK HUMAN SUBPOPULATIONS It is possible that some segments of the population can tolerate significantly less ozone than would be expected by l o g - n o d or log-logistic models. Cystic fibrosis patients seem to represent just such a subpopulation. In (ref. 7) we observed that mi= fed diets low in (or enrhly lacking) vitamin E suffered far greater ozone damage than did mice fed diets containing higher mounts of vitamin E. The low-vitamin E diets comspond to about the same value as the current Recommended Daily Allowance of vitamin E (ref. 8). In our studies of vitamin E in cystic fibrosis patients at the Duke University Medical Center we have found 41.2% of the patients to have unusually low levels (c 5.0 pgImL) of serum vitamin E. If the mouse data of (ref. 7) is representative of the relative risk of humans consuming low vitamin E diets, then cystic fibrosis patients have a higher relative risk than the n o d population. The risk calculations based on lognormal or logistic models do not account for such high-risk subpopulations.
CONCLUSIONS The division of hazardous compounds into "non-threshold and "threshold" chemicals is arbitrary and misleading. An individual might have the ability to withstand a certain dose of chemical, as in our population models above, but neither epidemiological evidence nor laboratory experiments will enable the detection or identification of a population-wide threshold. Even for non-carcinogenic compounds, there may be no dose at which the entire human population is safe. The presence of subpopulations of individuals unusually susceptible to the toxic effects of a chemical (due to an inherited defect or to a preexisting disease) casts doubt on extrapolated low-dose risk estimates which do not account for those subpopulations, and complicates the use of extrapolated data from animal exposure experiments for the prediction of human health effects. Estimates of lifetime human cancer risk from various compounds have played an important role in the deliberations of regulatory agencies. These estimates are usually made by extrapolating data from lifetime bioassays of healthy animals exposed to high concentrations, in an effort to predict the health effects for humans exposed to much lower environmental concentrations. Multistage mathematical models are often used in the extrapolation. Concenare often trations leading to conservatively predicted human mortality risks of lo4 or regarded as acceptable to society, providing the "adequate margin of safety" required by the U.S.Clean Air Act. It is now apparent that these methods must be supplemented by a study of the molecular mechanisms of toxicity and by estimates of the rates of repair of tissue damage, both in the general population and in unusually susceptible subpopulations, in order to reach defensible standards. The mice experiments with varying levels of dietary vitamin E suggest that individuals with unusually low serum levels of vitamin E may be at high risk for cell damage from exposure to environmental ozone. Cystic fibrosis patients appear to represent a subpopulation of such individuals. The high rate of incidence of this disease (about 1 in 1600 live births) and
342
of its genetic marker (about 1 in 20 individuals carries the gene for cystic fibrosis) suggest that this group should be examined for health risk from ozone exposure. The existence of a biological repair mechanism would invalidate the common assumption that toxic effects depend linearly on the time-integrated dose, or on the product c.2 for an exposure of duration t to a concentration c . This assumption, which underlies many commonly used dose-effect and low-dose extrapolation models, leads to a systematic overestimation of the long-term effects of low-dose exposure as exnapolated from short-term high-dose experiments. The effect is magnified if the repair mechanism is saturable. Ozone exposures in urban areas show a marked diurnal pattern, with peaks during and just following the morning and evening rush-hours and generally higher levels during the summer than during the winter. Meteorological events and seasonal patterns contribute to the unevenness of urban ozone exposure. Under linear repair (and even more so under saturable repair) this exposure pattern will pose a somewhat higher risk than would a constant exposure to the same average concentration. The magnitude of this effect would depend on the rate of repair. The identification of the molecular processes involved in both causing and repairing ozone damage, and the measurement of the rates of the relevant chemical and biological processes, would improve greatly our ability to estimate the human health risks associated with the observed patterns of environmental exposure to ozone. The study of those processes in high-risk subpopulations is especially important in enabling reliable low-dose extrapolations.
ACKNOWLEDGEMENTS Drs. F.J. Miller and J.H. Overton, Jr. generously supplied the ozone dosimetry model used in this work. Dr. C.R. Shod supplied the data on vitamin E, and Mr. J.R. Boger III assisted with computer programming. Although the research described in this article has been funded in part by the U. S. EPA through the Center for Extrapolation Modeling agreement number CR813113 to Duke University, it has not been subjected to the agency’s peer and policy review and, therefore, does not necessarily reflect the views of the agency and no official endorsement should be inferred.
REFERENCES 1
FJ. Miller, J.H. Overton, Jr.. R.H. M o t , and D.B. Menzel. Toxicol.Appl. Phurtnacol. 79 (1985) 11-27.
2
D.B. Menzel, J. Toxicol. Environ. Health 13 (1984) 183-204. C.R. Shoaf and D.B. Menzel, in C.K. Chow (Mmr). Cellular Anti-Oxidant Defense Mechanisms, C.R.C. Ress (1988). J.N. Roehm, J.G. Hadley, and D.B. Menzel. Arch. Environ. Health 23 (1971) 142-148. I.M.C. Rietjens and G.M. Mink. These proceedings, 1988. E.D. Smolko, DJ. McKee, and D.B. Menzel, J. Amer. Col. Toxicol. 5 (1986) 589-598. D.H. Donovan, SJ. Williams, J.M. Charles. and D.B. Menzel, Toxicol.Left. 1 (1977) 125-139. U.g National Academy of Sciences, Food and Nutrition Board Recommended Daily Allowunces (9 edn.), National Academy of Sciences. Washington D.C., 1979.
3 4 5 6 7 8
343
T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
OZONE-INDUCED CBANGBS IN TEE PULUONARY CLBARANCB OF 99?'c-DTPA E.R. KEERL',
L.n. VINCENT',
D.E. EORSTMN',
R . J . KOVALSKY~,
IN HAN J.J. ~"EIL1,
V.E. HcCARTNd, and P.A. BROMBERG3
'Clinical Research Branch, USEPA:Eealth Effects Research Laboratory, Research Triangle Park, 27711 2Department of Radiology, School of Hedicine, University of North Carolina, Chapel Bill 27514 3Center for Environmental Hedicine and Lung Biology, School of Hedicine, University of North Carolina, Chapel Bill 27514
ABSTRACT
Ozone is a respiratory irritant that has been shown in aniMlS to increase the permeability of the respiratory epithelium. We have recently reported that respiratory epithelial permeability was similarly affected in eight healthy non-smoking young men exposed to ozone (ARRD, 135 (1987) 1124-8). Permeability was evaluated by determining the pulmonary clearance of inhaled aerosolized 99mTc-DTPA with sequential posterior lung imaging by a computer-assisted gaua camera. Ve now report our findings for an additional 16 subjects. In a randomized crossover design, the 16 young men were exposed for 2 h to purified air and 0.4 ppm ozone while performing intermittent high intensity treadmill exercise; forced vital capacity (WC) was measured before and at the end of exposures. The pulmonary clearance of 99mTc-DTPA vaa measured 75 minutes after the exposures. Ozone exposure was associated vith a man endexposure W C decrement of 0.50 liters (10% of baseline; p 0.007). The mean (* SIN) 99mTc-DTPA pulmonary clearance rate of 1.16 + 0.08 W m i n observed after ozone exposure was over 60% greater than the rate of 0.71 0.08 %/.in following air exposure (p < 0.001). The results demonstrate that ozone exposure increased respiratory epithelial permeability. Such an increase may be a manifestation of direct ozone-induced epithelial cell injury, lung inflammation or both.
-
*
DISCLAIMER:
This paper has been reviewed by the Eealth Effects Research Laboratory, U.S. Environmental Protection Agency and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency nor does mention of trade names or commercial products does not constitute endorsement or recommendation for use.
344
INTRODUCTION Hembrame permeability coefficients membranes can be derived when the membrane area is known and the transmembrane driving forces with the resultant fluxes of tracer molecules are measured. Recently, nuclear medicine techniques for evaluating respiratory epithelial permeability have been developed that are both non-invasive and suitable for human study. This approach involves inhalation of an aerosol of a radiolabelled probe molecule and then monitoring its clearance from the lung with sequential gamma camera imaging. Although this methodology does not provide the information required for the computation of permeability coefficients, the measurement obtained is considered to reflect the permeability of the respiratory epithelium. It is a method that has been sucessfully utilized by numerous laboratories in a variety of investigative settings (refs. l-S)! most laboratories have used as the probe molecule, the chelating agent diethylenetriamine pentaacetate labelled with technetium ( 99?c-DTPA). Increased 99%-DTPA clearance has been observed in persons with interstitial lung disease (refs. 1,2), cigarette smokers (ref. 3) and patients with diffuse pulmonary injury who manifest lung edema (ref. 4). We have used the pulmonary clearance of inhaled aerosolized "%-DTPA to evaluate changes in respiratory epithelial permeability due to ozone exposure in human subjects. An ozone-induced increase in permeability seemed likely since the respiratory epithelial membrane is the first cellular barrier encountered by inhaled pollutant gases and ozone is very reactive gas with the potential for disrupting cellular membranes, tight junctions and enzyme systems necessary for maintaining epithelial integrity and function. Furthermore, studies in animals have shown that exposure to ozone causes both measureable increases in permeability (refs. 6,7) and histologic changes (refs. 8, 9) consistent with a damaged, more permeable membrane. Such changes could have potential health consequences as the permeability properties of the respiratory epithelium play an important role in regulating the composition of membrane surface liquid and maintaining normal lung homeostasis. In a previous report, we described our findings of increased 99?c-DTPA pulmonary clearance in eight subjects following exposure to sufficient ozone to cause respiratory symptoms and an obvious decrement in the spirometric performance in most of the subjects (ref. 10). We have now repeated the study with an additional 16 subjects. These results form the basis for this report.
34 5 METH0D S The subjects were 16, healthy, nonsmoking, 20 to 30 year old, white men. The subjects were informed of the purpose, risks, and procedures of the experiment and signed informed consent forms. This study was approved by both the Committee on the Protection of the Rights of Human Subjects and the Radiation Safety Committee of the University of North Carolina School of Medicine. Prior to the exposures, the subjects were trained in the performance of spirometry, body plethysmography, and treadmill walking; for each subject, the treadmill speed and elevation required to elicit a target ventilation (3,) of 35 l/min per m2 body surface area was determined. The subjects were then exposed in a randomized, cross-over double-blinded fashion for 2.25 hours to both 0.4 ppm ozone and clean air with an initial five minute 0.1 ppm ozone sham. The exposures were separated by a minimum of two weeks. During their exposures in the chamber the subjects alternately rested for 15 minutes and performed 15 minutes of treadmill exercise at the predetermined speed and elevation; measurements of iE were obtained during each exercise interval. Pulmonary function was measured prior to exposure in clean air and at endexposure while still in the chamber atmosphere. Endexposure measurements were obtained within 10 minutes of the last exercise interval. Before and after the exposures, the subjects also answered a symptom questionnaire. The exposures were conducted in a 4 X 6 X 3.2 meter stainless steel chamber maintained at 22O C and 40% relative humidity. The control systems, ozone generating system, monitoring systems, and operating characteristics of this chamber have been previously described (refs. 11). Specific airways resistance (SRaw), the product of airways resistance and its concomitant thoracic gas volume, was measured at a panting frequency of 1.5 Hz in a body plethysmograph (CPI Model 2000). The middle value of three SRaw measurements obtained during the testing sessions was selected for data analysis. At least three preexposure and endexposure measurements of forced vital capacity (FVC) were obtained on a 12 liter dryseal spirometer (Ohio Instruments Model 220) with volumes corrected to BTPS. The single largest FVC maneuver of each testing session was selected for data analysis. Due to either technical reasons or subject performance, complete plethysmography and spirometry data sets were obtained for only 12 and 14 subjects respectively. 8,, obtained during the 11th and 12 minutes of each exercise, was determined from the integration of the digitized flow signal of a heated pneumotachometer (Pleisch no. 3) and corrected to BTPS. Seventy-five minutes following the exposure (90 minutes after the last exercise), respiratory epithelial permeability was evaluated by determining the clearance rate of inhaled aerosolized 99?c-DTPA. The radiopharmaceutical was prepared with Nag9%04 and an AN-DTPA kit (Syncor International Corp.); binding of the 99%2 to the DTPA was routinely greater than 98%. The aerosol
346
was generated with the Syntevent aerosol delivery system (Synaco, Inc.), a system which has been characterized as producing a particle with a dry mass median aerodynamic diameter of 0.50 to 0.65 um and a geometric standard deviation of 2.0. The subjects inhaled the aerosol through a mouthpiece for two minutes of tidal breathing8 the amount of radioactivity calculated to be delivered to the mouthpiece was 0.50 - 1.0 mCi. During aerosol inhalation and for the subsequent 20 minutes, sequential 15 second frame scintillation images of the posterior upright chest were acquired with a computer assisted gamma camera (Elscint Apex 415) equipped with a low-energy collimator (Elscint APC-1). A "region of interest" (ROI) was selected to include the entire right lung and the natural logarithm of lung radioactivity (corrected for radioactive decay) within the ROI was plotted as a function of time. The negative slope (clearance constant, K value) of this relationship for the first seven minutes after peak lung radioactivity was determined by the least squares method and expressed as per cent decrease in radioactivity per minute. This approach does not correct for background activity but minimizes the effects of increasing blood and tissue radioactivity upon both total lung counts and back diffusion by fitting the line to the initial portion of the curve. The methods used were similar to those first described by Chopra et al. (ref. 12) and subsequently expanded upon by Rinderknecht and co-workers (ref. 1). The hypothesis of no difference in the postair and postozone K values was tested with multivariate analysis of variance. We also tested the hypotheses of no differences in FVC and SRaw between the changes observed from preexposure to endexposure during the air and ozone exposures with multivariate analysis of variance.
RESULTS After air exposures, the individual "9c-DTPA clearance rates ( K values) showed considerable variability with a range from 0.25 to 1.33 %/min and a mean (f SEH) value of 0.71 f 0.08 X/min. However, compared with the air K value, 15 of the 16 subjects showed an increase in "9c-DTPA clearance after ozone exposure; the mean of 1.16 f 0.10 %/inin was more than 60% larger than the clearance rate observed after air exposure. An ozone-induced increase of 1.08 W m i n in "9c-DTPA clearance, the largest change observed, was incurred by two subjects (No. 3 and 13). The K values observed 75 minutes after air and ozone exposures and the preexposure and endexposure measurements of FVC on the two exposure days are presented in Table 1.
347
TABLE I Postexposure permeability constants and pre and postexposure FVC measurements.
K valuesa AIR SUBJECT NUUBBR
FVC (liters)
OZONE
75 min postexp
01
0.46
0.68
02
0.73
AIR preexp
OZONE postexp
5.12
5.15
03
0.35
1.56 1.43
04
1.10
1.05
05 06
0.61
0.89
5.50 4.90 4.95
0.67 0.25
0.83
5.11
preexp
postexp
5.24
5.26
5.45
5.64
5.22
4.96
4.91
4.41
4.79
4.96
4.83
5.26 5.19
4.99 5.02
07 08
5.08
0.52
0.85 1.11
5.19 5.12
5.29
5.35
5.17
5.25
09
1.33
1.58
5.46
10
0.43
1.28
5.46 4.72
4.68
5.09 4.72
3.35 3.50
11 12
1.01 0.69
1.11
6.17
6.17
6.25
4.86
0.82
13
1.23
2.31
5.70
5.78
0.74
1.06
3.84
6.00 3.84
5.91
14 15
3.84
3.68
0.69 0.62
1.06 0.99
4.92 4.98
4.76
4.73
4.77
4.82
4.59 4.19
0.71
1.16
5.13
5.13
4.64
0.08
0.10
0.14
5.12 0.16
0.15
0.19
16
Hean f SEH
a~ values expressed as per cent decrease in activity per minute
The baseline pulmonary function of the 16 subjects was very similar with all but one subject (No. 9 ; 7%) showing less than 4X individual variance in preexposure FVC performance between the two exposure days. The ventilatory responses to exercise were also nearly identical with a mean (f SEH) tE over the final three exercise intervals of 58.6 f 2.5 and 60.3 f 2.1 l h i n on the air and ozone exposure days respectively. Following ozone exposure, most subjects reported respiratory symptoms of cough and chest tightness. There was a significantly greater increase in SRaw from the baseline of 3.8 f 0.3 to
348 5.1 f 0.4 cmH20*sec following ozone exposure than the change from 3.9 f 0.4 to 4.1 f 0.3 cmH20.sec observed during air exposure (p = 0 . 0 0 2 ) . In comparing the air and ozone responses, most subjects (8 of 14) shoved more than a 0.3 1 decrement in PVC attributable to ozone exposure and three subjects incurred decrements in excess of 1.3 liters. The mean decrement observed during ozone exposure vas 0.49 1 (10% of baseline value; p 0.007).
-
DISCUSSION The most important aspect of our study is the convincing demonstration that healthy volunteer6 acutely develop accelerated pulmonary clearance of 99?c-DTPA when exposed to ozone under these conditions These results confirm the findings of our previous study (ref. 10). The observation that 15 of 16 subjects showed increased 99%-DTPA clearance after ozone exposure suggests that this measurement is a sensitive indicator of ozone's effects. Indeed, when comparing the air and ozone exposure performances, only 10 of 14 subjects experienced a decline in FVC of greater than 100 ml attributable to ozone exposure. Thus it appears that the determination of ''%-DTPA pulmonary clearance may rival the sensitivity of forced expiratory spirometry in detecting the effects of ozone exposure. The mean ozone-induced decrement in NC of 10% observed in this study was less than the 14% demonstrated in our previous report (ref. 10) or than was expected from past work in our laboratory (ref. 13). Also, given the exposure conditions, there were a relatively large number of non-responders. This is likely due to the inherent unpredictable variability of the ozone response (ref. 14) as other conditions including exercise intensity, ozone concentration, duration of exposure and subject selection criteria were similar to those described in the previous reports. We attribute the accelerated 99%-DTPA clearance observed in our study, at least in part, to an ozone-induced increase in the permeability of the respiratory epithelium. This contention is supported by animal studies that used more direct measures of respiratory epithelial permeability and found that increases occur in both guinea pigs (ref. 6) and rats (ref. 7) exposed to ozone. There are, hovever, several other mechanisms that could possibly account for an increase in 99@Tc-DTPA clearance after ozone exposure. Ozone exposure might simply enlarge the effective lung surface area available for "%c-DTPA transfer by altering the aerosol deposition pattern' or increasing lung volume. The latter is unlikely, for even in the setting of large ozone-induced decrements in spirometric volumes, functional residual capacity remains unchanged (ref. 13). As for a change in deposition, the radioaerosol
was inhaled during resting tidal breathing and ozone exposure should not appreciably affect inspiratory flow rates or volumes. Additionally, examination of the gamma camera images showed no discernible differences between the air and ozone exposure days. Of note, Euchon and co-workers clearance observed in smokers (ref. 5) have shown that the increased "?c-DTPA with overt obstructive lung disease is mainly attributable to their smoking status and not the presence of airways disease. Consequently, small unrecognized differences in aerosol deposition due to changes in respiratory timing or small airways dysfunction, would likely not affect the clearance rate. Thus, the accelerated pulmonary clearance of "%c-DTPA observed in our subjects is probably not due to an ozone-induced augmentation of effective lung epithelial surface area. Another means of accounting for increased 99?c-DTPA clearance is the has a dissociation of the gamma-emitting technetium from the DTPA. "%04much faster clearance than the ''?c-DTPA complex and dissociation of even small of amounts "%c (rapidly oxidizes to 99%04-) would greatly influence is well the overall clearance rate (ref. 15). Radiolabel instability recognized as a problem with ultrasonic aerosol generation (ref. 16), but not with the compressed gas jet nebulization system used in our studies. Additionally, multiple tests of our 99yc-DTPA solution always showed greater to the DTPA both before and after than 98% binding of the 99%04nebulization. Along similar lines, Nolop and co-workers (ref. 15) have demonstrated that in vitro oxidative stress of "Yc-DTPA solutions causes rapid dissociation of "%04from the DTPA. These same investigators have shown that in vivo oxidative stripping of the 99%04- from the DTPA may be partially responsible for the rapid clearance observed in smokers (ref. 15). Since inflammation entails leukocyte infiltration with the creation of an oxidative milieu as well as increased permeability, lung inflammation could potentially lead to accelerated clearance of the isotope by both mechanisms. It is certainly possible that the accelerated 99%-DTPA clearance after ozone exposure manifested by our subjects was partly due to the increased permeability and oxidative environment brought on by lung inflammation. Indeed, inflammation is an integral component of the response of the lung to ozone exposure. In dogs, inflammation has been implicated in the enhanced bronchoconstriction to inhaled histamine observed after ozone exposure (ref. 17). Similarly, Seltzer and co-workers (ref. 18) found an increased number of neutrophils in the bronchoalveolar lavage fluid of human volunieers obtained three hours after exposure to 0.4 or 0.6 ppm ozone; the presence of neutrophilia was associated with an ozone-induced increase in bronchial reactivity to inhaled methacholine. More recently, Devlin and co-investigators (ref. 19) demonstrated both an increase in neutrophils as well as the total
350 protein and albumin in lavage fluid of volunteers obtained 18 hours after exposure to 0.4 ppm ozone in a protocol identical to the conditions employed in our study. It is not known, however, whether neutrophil infiltation of the respiratory surfaces is present as early as 75 minutes after a two hour exposure to ozone. Thus, inflammation of the lung in response to ozone exposure and the mediators of inflammation may contribute to the accelerated pulmonary clearance of "Yc-DTPA observed in our study both by increasing respiratory epithelial permeability and promoting an oxidant environment favoring dissociation of the It also is likely that direct ozone chelated "Yc in the form of 99%04-. toxicity upon the epithelium with the resultant cellular injury and disruption of integrity is partially responsible for the increase in lung 99?c-DTPA clearance. Histologic studies in animals have shown that injury occurs to the ciliated airways epithelium and type I alveolar cells in both rats (ref. 8) and monkeys (ref. 9) after short-term exposures to less than 1.0 ppm ozone. Such an injury pattern would provide a likely morphologic correlate for an increase in permeability, especially since the submicronic size of the radioaerosol inhaled by our subjects favors deposition in the gas exchange regions and small airways of the lung. Although the exact mechanisms for the flux of "Yc-DTPA across the respiratory epithelium and into the blood remain unclear, it appears that the is a useful and sensitive technique for pulmonary clearance of "?'c-DTPA evaluating the effects of ozone and other inhaled pollutants upon human respiratory function. Other than bronchoalveolar lavage, the measurement of "%c-DTPA pulmonary clearance is the only available method that has successfully detected the effects of ozone in the gas exchange regions of human subjects. It is a relatively easily performed technique that can be applied to the unsettled concerns regarding the response of human subjects to ozone exposure as well as provide a means of correlating human and animal ozone toxicology.
REFERENCES 1 J. Rinderknecht, L. Shapiro, H. Krauthammer, G. Taplin, K. Yasserman, J.H. Uszler, and R.H. Effros, Am Rev Respir Dis, 121 (1980) 105-17. 2 H.P. Jacobs, R.P. Baughman, J. Eughes, and M . Pernandez-Ulloa, Am Rev Respir Dis, 131 (1985) 687-9. 3 J.G. Jones, P. Lawler, J.C. Crawley, B.D. Minty, G. Eulands, and N. Veall, Lancet, 1 (1980) 66-8. 4 G.R. Mason, R.H. Effros, J.H. Uszler, and I. Hena, Chest, 88 (1985) 327-34.
351
5 G.J. Huchon, J.A. Russell, L.G. Barritault, A. Lipavsky, and J.F. Murray, Am Rev Respir Dis, 130 (1984) 457-60. 6 P.C. Hu, F.J. Miller, M.J. Daniels, G.E. Hatch, J.A. Graham, D.E. Gardner, and M.K. Selgrade, Environ Res, 29 (1982) 377-88. 7 D.L. Costa, S.N. Schafrank, R.W. Wehner, and E. Jellett, J Appl Toxicol, 5 (1985) 182-6. 8 R.J. Stephen, M.F. Sloan, M.J. Evans, and G. Freeman, Am J Pathol, 74 (1974) 31-58. 9 W.L. Castleman, D.L. Dungworth, L.W. Schwartz,and W.S. Tyler, Am J Pathol, 98 (1980) 811-40. 10 H.R.. Kehrl, L.M. Vincent, R.J. Kowalsky, D.H. Horstman, J.J. O’Neil, W.H. McCartney, and P.A. Bromberg, Am Rev Respir Dis, 135 (1987) 1124-8. 11 D.E. Glover, J.H. Bernsten, W.L. Crider, and A.A. Strong, J Environ Sci Health, 16 (1981) 501-22. 12 S.K. Chopra, G.V. Taplin, D.P. Tashkin, and D. Elam, Thorax, 34 (1979) 63-7. 13 W.F. McDonnell, D.H. Horstman, M.J. Aazucha, E. Seal Jr., E.D. Aaak, S.A. Salaam, and D.E. House, J Appl Physiol, 54 (1983) 1345-52. 14 W.F. McDonnell, D.H. Horstman, S.A. Salaam, and D.E. House, Am Rev Respir DiS, 131 (1985) 36-40. 15 K.B. Nolop, D.L. Maxwell, J.S. Fleming, S. Braude, J.M.B. Hughes, and D. Royston, Am Rev Respir Dis, 136 (1987) 1112-6. 16 D.L. Waldman, D.A. Weber, G. Oberdsrster, S.R. Drago, M.J. Utell, R.W. Hyde, and P.E. Horrow, J Nucl Mcd, 28 (1987) 378-82. 17 M.J. Holtzman, L.M. Fabbri, P.M. O’Byrne, B. Gold, 8. Aizawa, E. Walters, S.E. Alpert, and J.A. Nadel, Am Rev Respir Dis, 127 (1983) 686-90. 18 J. Seltzer, B.G. Bigby, M. Stulbarg, M.J. Holtzman, J.A. Nadel, I. Ueki, G. Leikauf, E. Goetz1,and H.A. Boushey, J Appl Physiol, 60 (1986) 1321-6. 19 R. Devlin, D. Graham, W. Kozumbo, R. Mann, and H.S. Koran, J Leuk Biol, 42 (1987) 394.
ACKNOWLEDGEMENT: The writers thank Susan McCallister of UNC and the staff of Environmental Monitoring and Services for technical assistance. Statistical analyses were performed by Dennis House of the Biostatistics Branch of tha Biometry Division, USEPA:Health Effects Research Laboratory.
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353
SESSION V
GLOBAL ATMOSPHERIC CIRCULATION AND MODELING
Chairmen
C.J.E. Schuurmans W. Johnson
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T. Scbneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
CHEMISTRY OF STRATOSPHERIC OZONE DEPLETION UNDERLYING THE ANTARCTIC OZONE HOLE
355
INCLUDING P O S S I B L E MECHANISMS
G .D. H a y m a n E n v i r o n m e n t a l and M e d i c a l S c i e n c e D i v i s i o n , H a r w e l l Laboratory, D i d c o t , O x o n O X 1 1 ORA, UK
Our understanding of the distribution of ozone in the stratosphere has
improved substantially since Chapman (ref. 1) first proposed that the ozone concentration was controlled by a series of reactions in which 'odd-oxygen' is produced, lost or interconverted.
0 +02+M
= 03tM
interconversion
....(1) ....( 2 )
+ hv
= 0 t o 2
interconversion
....( 3 )
= 202
loss
....( 4 )
loss
....( 5 )
02
03
+ hv
= 0
0 t O3 0 t o
t o
( X A I I b u t c o n t r o l s f o r BII>BI, t h e strategy demonstrating attainment requires c o n t r o l s on c a t e g o r y A 2 t h o s e needed i n Scenario I w h i l e t h o s e on Category must be 2 t h o s e necessary i n S c e n a r i o 11.
B
The r a t i o n a l e f o r t h i s i s t h a t a
l i m i t e d number o f s c e n a r i o s a r e considered, and t h e p a r t i c u l a r i n c i d e n t r e p r e s e n t i n g a m e t e o r o l o g i c a l s c e n a r i o may n o t be t h e w o r s t such i n c i d e n t . MOST EFFECTIVE WAY TO REDUCE OZONE Models have been used t o assess e f f e c t i v e n e s s o f s t r a t e g i e s i n (1) r e d u c i n g peak 03 and ( 2 ) r e d u c i n g p o p u l a t i o n exposure t o h i g h 03.
To i l l u s t r a t e such
a p p l i c a t i o n s , t h e remainder o f t h i s paper o u t l i n e s how EKMA and UAM can be u s e d t o assess whether s t r a t e g i e s , f e a t u r i n g b o t h RHC and N 4 , c o n t r o l s a r e more e f f e c t i v e t h a n t h o s e i n which o n l y RHC i s reduced. EKMA The CALC r o u t i n e i n OZIPM4 p l o t s p r e d i c t e d 03 vs. t i m e ( r e f . 2 ) .
CALC can
be used t o see whether r e d u c t i o n i n peak 03 accompanying a g i v e n r e d u c t i o n i n RHC i s d i m i n i s h e d f u r t h e r by an accompanying NOx r e d u c t i o n .
The f o l l o w i n g
procedure has been suggested ( r e f . 7).
( 1 ) E s t i m a t e ~ 0 3accompanying a s p e c i f i e d r e d u c t i o n i n RHC o v e r a f i n i t e t i m e (e.g.,
5 years).
U t i l i z e t h e most l i k e l y NO,
projection
f o r t h i s time. (2)
Repeat ( l ) , b u t a l s o e s t i m a t e ANO,
f r o m a d d i t i o n a l NOx c o n t r o l s .
(3)
Compare ~ 0 3 o b t a i n e d i n (1) and ( 2 ) t o see w h i c h r e d u c t i o n i n 03 i s larger.
EKMA i s n o t w e l l s u i t e d f o r e s t i m a t i n g e f f e c t s o f a l t e r n a t i v e s t r a t e g i e s on p o p u l a t i o n exposure t o h i g h 03. i n d i c a t o r ( r e f . 7).
However, t h e f o l l o w i n g can be used as a r o u g h
F i g u r e 2 was o b t a i n e d u s i n g CALC, and i l l u s t r a t e s how t h e
e f f e c t o f r e d u c i n g NOx a l o n e by 50% m i g h t be assessed f o r a p a r t i c u l a r set' o f conditions.
By choosing a r e s u l t a n t w i n d v e l o c i t y (e.g.,
can c o n v e r t t h e x - a x i s t o d i s t a n c e . i n F i g u r e 2.
f r o m 10 AM-4 PM), one
T h i s i s shown f o r a 5 mph r e s u l t a n t wind
Assuming t h e t r a j e c t o r y b e g i n s a t C e n t e r City, F i g u r e 2 suggests
a p o t e n t i a l f o r p o p u l a t i o n exposure t o 03 t o i n c r e a s e w i t h i n about 20 m i l e s o f
568
-28. ,
#
0
.08
w IV, --BASECASE - - W %Nox
H c m x
-
10: 1
1 T I E
Fig. 2.
400
MINUTES
1
800
E f f e c t o f a c o n t r o l s t r a t e g y on p o p u l a t i o n exposure estimated w i t h EKMA.
UAM Use o f UAM t o e v a l u a t e e f f e c t s o f a l t e r n a t e s t r a t e g i e s on peak 03 i s s i m i l a r t o t h e procedure w i t h EKMA. can be considered.
With UAM however, a wider v a r i e t y o f s t r a t e g i e s
UAM a l l o w s e x p l i c i t c o n s i d e r a t i o n o f such f a c t o r s as source
l o c a t i o n and r e a c t i v i t y o f a source c a t e g o r y ' s RHC emissions.
A f o u r step p r o -
cedure f o r u s i n g UAM t o decide whether NOx c o n t r o l i s advisable i s enumerated below. (1)
Simulate base case d a i l y maximum 03 f o r each m e t e o r o l o g i c a l scenario.
(2) Repeat (1) w i t h ARHC a n t i c i p a t e d over a f i n i t e t i m e (e.g.,
5 years).
Do n o t consider changes i n NOx beyond those l i k e l y t o r e s u l t from growth o r programs already i n place.
(3)
Repeat ( 2 ) , b u t a l s o s i m u l a t e NO,
r e d u c t i o n due t o a d d i t i o n a l c o n t r o l s .
(4) Compare p r e d i c t e d changes i n peak d a i l y maximum 03 obtained i n s t e p s ( 2 ) and ( 3 ) t o determine which s t r a t e g y i s most e f f e c t i v e .
569
U n l i k e EKMA, UAM i s w e l l s u i t e d f o r a s s e s s i n g e f f e c t s o f a l t e r n a t e c o n t r o l s t r a t e g i e s on p o p u l a t i o n exposure t o h i g h 03.
This f o l l o w s from t h e model's
c a p a b i l i t y t o display s p a t i a l d i s t r i b u t i o n o f predicted concentrations. E f f o r t s o f c o n t r o l s on p o p u l a t i o n expsure t o ozone may be d e t e r m i n e d as follows. (1)
S i m u l a t e base case c o n d i t i o n s f o r each m e t e o r o l o g i c a l s c e n a r i o .
(2)
Determine ARHC f o r a c o n t r o l s t r a t e g y w i t h i n f i n i t e t i m e (e.g., 5 y e a r s ) and most l i k e l y ANO,
only. (3)
based on growth and p r e s e n t c o n t r o l s
Apply model t o e s t i m a t e r e s u l t i n g 03 c o n c e n t r a t i o n f i e l d .
Repeat (2) i n c l u d i n g a d d i t i o n a l r e d u c t i o n s i n NOx c o r r e s p o n d i n g t o a d d i t i o n a l contemplated c o n t r o l s .
Steps ( 1 ) - ( 3 ) y i e l d g r i d d e d o u t p u t r e f l e c t i n g s p a t i a l / t e m p o r a l d i s t r i b u t i o n o f 03 f o r t h e base case and two c o n t r o l s t r a t e g i e s .
The c a p a b i l i t y now e x i s t s
t o compare p o p u l a t i o n exposed t o 03 between each s t r a t e g y and t h e base case and between t h e two s t r a t e g i e s . (a)
P l o t hO3 i s o p l e t h s (i.e..
T h i s can be done i n s e v e r a l ways. l o c a t i o n s o f constant d i f f e r e n c e i n
p r e d i c t e d 03 f o r t h e model domain f o r hours o f i n t e r e s t (e.g., t o l a t e afternoon).
F i g u r e 3 i l l u s t r a t e s such o u t p u t ( r e t . 8).
midday
By knowing s p a t i a l d i s t r i b u t i o n o f p o p u l a t i o n , n e t g a i n o r r e d u c t i o n i n
p o p u l a t i o n exposed t o 03 can be estimated.
Fig. 3.
Oelta 03 i s o p l e t h p l n t for 50% RHC r e d u c t i o n , SY wind.
570
(b)
U t i l i z e " d e f i c i t diagrams" l i k e those i n F i g u r e 4 ( r e f .
9, r e f . 10).
I n t h e example shown i n F i g u r e 4. a s t r a t e g y f e a t u r i n g g r e a t e r NOx c o n t r o l increases p o p u l a t i o n exposed t o moderate 03 l e v e l s
( < 0.15 ppm), b u t p o p u l a t i o n exposed t o c o n c e n t r a t i o n s >0.15 i s decreased.
-.-10
II
iz
ia
14
is
16
I?
ozowc concctmnr;on
F i g . 4.
is
19
10
ti
za
za
IPPMMI
Changes i n ozone exposure from implementing strategy 2 (RHC =-4S%, NO, vs. strategy 1 (RHC =-36%, NO,=-23%).
=-37%)
SUMMARY
Two ways f o r u s i n g EKMA and UAM t o e v a l u a t e c o n t r o l s t r a t e g i e s have been illustrated:
(1)
i s a s t r a t e g y adequate t o a t t a i n an a i r q u a l i t y standard?
( 2 ) what i s t h e r e l a t i v e e f f e c t i v e n e s s o f s t r a t e g i e s t o reduce 031 The l a t t e r q u e s t i o n can be evaluated b o t h i n terms o f p r e d i c t e d changes i n peak
03 and r e d u c t i o n i n p o p u l a t i o n exposed t o h i g h 03.
RE[:ERENCES 1 U.S. EPA, OAR, OAQPS, G u i d e l i n e f o r Use o f C i t y - s p e c i f i c EKMA i n P r e p a r i n g Post-1987 Ozone SIPS, ( D r a f t ) , (Sept. 1987). Manual f o r OZIPM4 Ozone I s o p l e t h P l o t t i n g w i t h 2s O p t i o n a l Mechanisms/Version 4, ( D r a f t ) , (Sept. 1987). 3 J . Ames, T. C. Meyers, L. E. Reid, 0. Whitney, S. H. Golding, S. R. Hayes and S. 0. Reynolds, S A I Airshed Model Operation Manuals, NTIS Nos. PB85191567 and PB85-191568, (1984). 4 U.S. EPA, OAR, OAQPS, G u i d e l i n e on Air Q u a l i t y Models (Revised), EPA450/2-78-027R, ( J u l y 1986).
571
5
6
7 8 9
S. T. Rao, A p p l i c a t i o n o f t h e Urban Airshed Model t o t h e New York M e t r o p o l i t a n Area, EPA-450/4-87-011, (May 1987). E. L. Meyer, "Urban Scale Modeling Requirements," Paper presented a t t h e Air P o l l u t i o n Control Association S o e c i a l t v Conference on S c i e n t i f i c and Technical Issues Facing Post-1987 Okone Control Strategies," H a r t f o r d , CT, USA, (Nov. 1987) E. L. Meyer, "Consideration o f NOx Control i n S I P S f o r Ozone," ( D r a f t ) , Paper i n c l u d e d i n docket f o r US EPA proposed post-1987 Ozone P o l i c y , (Oct. 1987). J. L. Haney and T. Braverman, E v a l u a t i o n and A p p l i c a t i o n o f t h e Urban Airshed Model i n t h e P h i l a d e l p h i a A i r Q u a l i t y Control Region, EPA 450/4-85-003. (June 1985). Systems A p p l i c a t i o n s , In;. , Analysis o f Population Exposure and Dosaqe
Association. (Nov. 1982). 10 E. L. Meyer; Review o f Control S t r a t e g i e s f o r Ozone and T h e i r E f f e c t s on Other Environmental Issues, N T I S No. PB87-171195/AS, (Nov. 1986).
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T.Schneider et al. (Editore),Atmospheric Ozone Research and its Policy I ~ l i t ~ t i ~ n ~ 0 1989 Elaevier Science Publishera B.V.,Amsterdam -Printed in The Netherlands
573
OZONE AND OXIDANTS IN THE PLANETARY BOUNDARY LAYER
R.M.van Aalst National Institute of Public Health and Environmental Protection, P.O.Box 1, 3720 BA Bilthoven (The Netherlands)
ABSTRACT Some measuring and modelling results for ozone and oxidants (0 + N02)in the boundary layer in the Netherlands are discussed. Backgrouid average ozone levels are estimated, and their relation with tropospheric ozone levels is indicated. A short overview is presented of the chemical and physical processes contributing to buildup and degradation of ozone and oxidant in the boundary layer. An analysis of oxidant measuring data from a meteorological mast provides information about dry deposition of oxidant on grassland. INTRODUCTION: Some results from the basis document In 1987, a basis document for ozone has been finalised (ref. 1). Basis documents are produced in the Netherlands for so-called priority pollutants. They cover aspects of emission, use and origin of the pollutant, its occurrence in air, water and soil compartments, the exposure of humans, vegetation, ecosystems and materials to the pollutant, and an evaluation of the risks with respect to health and damage, as well as technical and economical consequences of reduction of these risks. Information in the basis document on concentrations of ozone in air were mainly obtained from the Netherlands Air Quality Monitoring Network. This network, which is in operation since the mid-seventies, has.30 stations for continuous, hourly meausurement of ozone, and 40 stations for hourly NO and NO2 concentrations. In the Netherlands, the spatial variations of ozone levels is determined to a large extent by the reaction of ozone with
30. As a consequence, ozone and NO2, which is produced in
this reaction, show complementary spatial patterns, while the concentration levels of oxidant (03 + NO2, in ppbv), show little variation (see fig. 1). The Netherlands interim limit value for ozone of 240 ug/m3, hourly aversgo, is exceeded on several thys in an average year, while in years with meteorological conditions favburable for ozone formation, like 1982, exceedance on more than five days has breii rroted on About half of the stations. The 8-hours maximum values, considered to be relevant to expoeure of humans and of vegetation, are not much lower, as is shown in table 1.
574
...................... ..........
0x Fig.
CEnIOoELOE
1. Average concentration of oxidant in the Netherlands in 1987.
TABLE 1 Daily maximum concentrations (ug/m3) of ozone in the Netherlands. The ranges indicate variation over the stations. maximum 98-percentile SO-percentile
1-hour average 227-431 164-227 62- 79
8-hours average 191-350 138-194 48- 71
Modelling studies ( r e f . 2 ) indicate that emissions of volatile organic compounds (VOC) and nitrogen oxides (NOx) in the Netherlands contribute only ca. 10% to these ozone peak levels. The calculations suggest that if exceedance of the interim limit value is to be avoided, European emissions of VOC should be reduced by 20% for an average year, or even by 60% for a year with high ozone peak levels. Emission reduction of NOx in Europe was found to result in relatively small changes in peak levels, with both increases and decreases (ref. 3) Growing season averaged concentration of ozone are of interest to vegetation damage (ref. 4). The averages over the growing season (May to 3 September) at daylight hours (10-17 h) varied from 80 to 95 ug/m over the Netherlands, as an average over the period 1980-1985. In years with
575 enhanced photochemical activity, values of average
levels
are
close
to what
85-115 ug/m3
is believed
are
found, The
to be the tropospheric
background of ozone, for which the growing season daylight hours was estimated at 78 ug/m3 for this five year period (see below).
average
Model calculations of growing season averaged ozone concentrations in the Netherlands have also been carried out: results are reported in ref. 5. Reduction of
is
European emissions of NOx
increased average ozone
expected
to
cause
concentrations in the Netherlands. Reductions of
European VOC emissions will decrease ozone levels but the effects are relatively small. Concurrent reduction of NOx and VOC emissions in Europe can still result in increased ozone levels in the Netherlands. The of
these model
results
concentrations. On Netherlands
is evidenced by
Sundays, the
networks
the weekend
average ozone
reality
effect on ozone
concentration on
the
rural stations are increased by 7% with respect to
weekdays. At Delft, a semi urban location, average ozone concentrations are increased by 11% on Sundays, while VOC and NO
concentrations are 25% lower
than on weekdays (ref. 6). In the industrialised Rijnmond urban area, the average
ozone
levels
on
Sunday are
20-40% increased, while VOC
concentrations are 20% lower, and NOx concentrations 25-35% lower. BACKGROUND CONCENTRATIONS OF OZONE IN THE NETHERLANDS Background concentrations of ozone were derived from data of the National Air Quality Monitoring Network in the period 1980-1986. Hourly were used for the calculation of ozone and 2 NO2) monthly averages for daylight hours (10-17 h). Oxidant
concentrations of ozone and NO oxidant
(03
+
concentrations were considered rather than ozone concentrations in order to avoid effects of local NO-emisisons. The results for Den Helder, a station in the relatively clean North-Western part of the country, and semi-rural location
Cabauw, a
in the centr8, are given in fig. 2 for different wind
directions. The oxidant concentration at Den Helder shows a spring maximum, and
a
secondary maximum
in July/August, which
is more pronounced at
Easterly winds. The spring maximum is also discernible for Cabauw, but summer
maximum
is
more
pronounced
here.
The
spring maximum
the is
characteristic for ozone concentrations at remote locations at Northern midlatitudes (ref. 7) and reflects the seasonal variation of ozone in the lower free troposphere. The summer maximum is likely to orginate from precursor
emissions in Western Europe. This hypothesis is supported by the
dependence of the concentrations of ozone and oxidant on wind speed (see fig. 3). In the first three months of the year, ozone concentrations increase with wind speed, indicating influence of enhanced vertical mixing. During
the
tropospheric ozone by
summer months, oxidant and ozone
concentrations decrease with increasing wind speed, suggesting dilution of oxidant formed in the mixing layer. The behaviour of ozone can be explained
576 from oxidant behaviour and decreasing influence of NOX upon dilution.
Fig. 2. Monthly average concentration of oxidant (ppb) during daylight hours (10-17h) at the stations Den Helder (left) and Cabauw (right) for different wind directions, period 1980-1986. Fiyre 4 shows the concentration of ozone and oxidant at Den Helder at North-Westerly wind with speed in excess of 5 Js. These concentrations are believed to be close to free tropospheric background ozone levels. At four Northerly rural stations, we found quite similar levels, with daylight hours growing season averages for oxidant of 42-44 ppb, and for ozone 38.5-
577 3 39.3 ppb (77-79 ug/m ) . The concentration of ozone during daylight hours on a more landinward station (Cabauw) is compared to these background levels in figure 5.
At
Cabauw,
the ozone
concentration is depleted by
NO-
emissions, especially during the winter months. In summer, the ozone than the background because of concentration is slightly higer photochemical production. Growing season daylight averages for ozone at 3 Cabauw are 85 ug/m ( 4 2 . 5 ppb), and for oxidant 53 ppb.
"I
'1 Fig. 3. Three monthly averaged concentrations (ppb) of oxidant (thick line) and ozone (thin line) as a function of wind speed, for months January to March (left) and July to September (right) at the station Cabauw.
Fig. 4. Monthly average concentration (ppb) of oxidant (thick line) and ozone (thin line) during daylight hours (10-17h) at station Den Helder, for NorthWesterly wind with speed more than 5 m/s. Period 1980-1986.
Both historical evidence (ref. 8) and model calculations (ref. 9 ) indicate that the lower tropospheric background concentration of ozone at our latitudes is to an important extent of antropogenic origin. There is evidence that ozone concentrations have increased by a factor two or more, and the model calculation indicate that emissions of NOx. VOC, methane and CQ have contributed to this increase.
Fig. 5. Monthly average concentration (ppb) of ozone during daylight hours (thick line) and background concentration from fig. 4 (thin line).
BUILDUP AND DEGRADATION OF OZONE IN THE BOUNDARY LAYER Drocessez The main processes contributing to the formation and removal of ozone in the boundary layer are: - vertical transport: stratospheric intrusions and exchange with the troposphere - (photo-)chemical formation - (photo-)chemical degradation - wet and dry deposition Direct emissions of ozone are of minor importance. Vertical transuort Stratospheric intrusions, although relatively frequently occurring, seldom lead to marked increases of boundary layer ozone concentrations (ref. 10). The vertical flux corrected with this transport is estimated for 2 the Northern Hermisphere to 0.02-0.07 ug/m /s (ref. 11). The contribution of this flux to average ground concentration is not well known; the flux could be balanced by dry deposition of an average concentration of 10-35 ug/m 2 , assuming a deposition velocity of 0 . 2 cm/s on a global scale.
573 However, it is estimated that chemical formation and degradation also play an important role in the tropospheric ozone budget (ref. 12). Exchange of boundary layer air with tropospheric air can be brought about by several processes, among which: - mixing layer depth variation vertical transport in high/low pressure systems - vertical transport in clouds These processes are discussed by Builtjes (ref. 13). Mixing layer depth variation is a major cause of diurnal variation of boundary layer ozone and oxidant concentrations. The diurnal variation of oxidant (see fig. 6 ) can be largely explained by dry deposition of ozone during the night, downward transport of ozone aloft due to mixing layer rise in the morning, and photochemical production during the day (ref. 14).
-
"
i
!
I
il*
I
I
Fig. 6 . Diurnal variation of hourly average concentrations (ppb) of oxidant.
photochemical formation Photochemical formation of ozone is a complex process. Rather than reviewing the vast literature on the subject, we would like to touch on a few aspects only. An important aspect of ozone chemistry is its production by photolysis of NO2 and its reaction with NO 1. NO2 + hv --> NO + 0 2. 0 + O2 + M --> O3 + M 3. 03 + NO --> NO2 + O3 leading to the well-known photostationary state relationship.
500 Here, K and kl are proportional to the W-light intensity. The quantities oxidant (Ox O3 + NO2) and NOx (- NO + NO2), expressed in molar units, e.g. ppbv, are consenred in these rapid reactions.
-
In
the Netherlands, where
NOx concentration levels are high, these
reactions are an important factor determining the variations time
and
space. The concentration of
oxidant
of
ozone
in
shows much less spatial
variation than the ozone concentrations. Equations of the form of (1) have been used successfully to calculated hourly average or even monthly averaged N02-concentrations from concentrations of NOx, a species that can be
more easily (ref. 15). However, close to sources of NOx, like
modelled
in urban surroundings or close to roadways, K may deviate from kl/k3. Photochemical formation of oxidant and ozone is mainly the result of oxidation of organic species by hydroxyl radicals (OH).
In this process,
organic peroxy radicals and hydrogen peroxyradicals (H02) are formed, which oxidise NO
to NO2.
regenerates
NO.
Photolysis of
During
the
the oxidation
NO2
formed produces
step, hydroxyl
03, and
radicals are
regenerated: in this way the oxidation process continues as long as sufficient NO and organic compounds are available. Similar reactions occur during the oxidation of unsaturated organic compounds by the
photolysis of
ozone,
and upon
carbonyl species. Many other reactions complicate this
simplified picture (ref. 16). For a quantitative description of oxidant formation. chemical kinetic mechanisms, as a part of photochemical dispersion models, are 17).
The main
function of
oxidant production from the concentrations of various organic NOx
used
(ref.
these mechanisms is to provide the ozone or species
and
in air, resulting from emissions. The enormeous variety of organic
compounds and the many reactions involved precludes complete treatment of
the
relevant
reactions, Either
and
explicit
"surrogate" or
"lumped"
mechanisms are used. In a "surrogate" mechanism, the chemistry of a limited number of species is described, for which ozone formation is assumed to be similar to that from the ambient air organic mix. In groups
of
compounds with
"lumped" mechanisms,
similar properties are represented by a single
species, for which representative chemical reactions are formulated. In the so-called "lumped structure" mechanisms such as the Carbon Bond Mechanisms (ref. 18) functional groups of organic molecules, e.g. methyl groups, double bonded carbon pairs or carbonyl groups are considered rather than complete molecules. Table 1 shows as an example the chemistry of
oxidant
formation from paraffinic carbon units (PAR) in the CBM-I1 chemical kinetic mechanism. The scheme illustrates several characteristic features, such as peroxide radical formation (Me02, HO ) , peroxide radical oxidation of NO t o 2 NO2, and OH radical regeneration, and termination by hydrogen peroxy radical recombination. Note the negative coefficient of PAR in the second reaction. This is necessary in order to maintain carbon balance; the single
58 1 carbon species Me02 cannot produce both the carbonyl unit CARB and another peroxy radical Me02 without consumption of another methyl unit PAR. The reaction is formulated to simulate the reactions of multi-carbon organic peroxy-radicals.
TABLE 2 Chemical reactions describing the photochemical oxidation of PAR by the Carbon Bond Mechanism I1 (ref. 20).
OH
in
k (ppm-' rn1n-l) 1. PAR + OH --> Me0 2. Me02 + NO --> NO; + CARB 3. Me02 + NO --> NO + CARB 4. Me02 + NO --> nierate 5. H02 6. H02
PAR
+
+ +
+ Me02 + H02
-PAR
NO --> NO2 + OH H02 --> H202 + O2
OH --> (1.41 + 0.94 p) OX + 1.41 CARB + 0.94 p OH - 0.47 PAR - 0.04 NOx
1500 4000 8000 500 12000 15000
1500
Although the CBM-I1 mechanism gives a reasonable description of oxidant formation in polluted atmospheres, it is difficult to understand from the mechanism the characteristics of oxidant formation, such as the stoechiometry: the number of oxidant molecules produced per unit of
-
organic species consumed the reaction rate
-
the effect of conditions and of other pollutants, such as NOx, on stoechiometry and rate of oxidant formation
More insight can be gained from an equivalent formulation, which summarizes the
chemistry
in table 1 in one single reaction, also shown in the table.
Here, it has been assumed that the reaction of OH with PAR is the ratelimiting step, and that the concentrations of radical species are in a quasi-steady state. The coefficients in the reaction are derived from the reaction
rate constants. The factor p represents the fraction of hydrogen peroxy radicals reacting with NO to NO2 and OH, and is calculated from the steady state condition. It is a function of the total hydrogen peroxy
radical production rate divided by the square of the NO concentration. From the equivalent reaction it is seen that oxidation of PAR by OH.in the CBM-I1 mechanism produces at most 2.35 molecules of oxidant per "molecule" PAR consumed (less under conditions of low NO concentrations) and is seen to constitute a small sink for OH (more so if NO is low). By this technique, the mechanism CBM-11, consisting of 65 reactions, can be reduced to 12 reactions of 12 species, including the CBM organic species, OH, PAN, HN03, and NOx. This reduces computing time considerably,
582 without affecting model performance, as model calculations for realistic ambient air conditions indicate (ref. 19). Model calculations for the Netherlands (ref. 2 , 3) indicate that the rate of oxidant production in the polluted boundary layer is probably of the order of 10-20 ppb/h during a sunny day in summer. Assuming a mixing height of 1000 m, this is equivalent to 5-10 ug/m 2 /s. From the annual average emission density of VOC in the Netherlands and surroundings (ref. 21), expressed in CBM organic units, and assuming a stoechiometry factor of 2 oxidant molecules per organic unit, an average production density of ca. 2 2 ug/m /s is found. From an analysis of measured oxidant concentrations in the Netherlands (ref. 22), net oxidant production rates of several ppb/h were found on sunny summer days at rural stations. In winter, net production was found to be close to zero during the day. Photochemical deeradatioq The main chemical sinks for oxidant and ozone in the polluted boundary layer are reaction with NO and subsequent nitric acid formation, and reaction with olefines. Reaction with NO produces NO2: O3 + NO --> NO2 NO2 can be converted to nitric acid by OH radicals: OH + NO2 --> HN03 which constitutes loss of one oxidant molecule per molecule nitric acid formed. NO2 can also be converted by O3 to NO3, and directly or via N205 to HN03, in which case three molecules of oxidant are removed to produce two molecules of nitric acid: NO2 + O3 - - > NO3 + O2 NO3 + NO2 - - > N205 N 0 + H 2 0 - - > 2HN03 2 5 Also, photolysis of NO3 into NO and O2 constitutes a loss of two oxidant molecules: NO3 + hv - - > NO + O2 The average loss rate of oxidant by nitrate formation in the Netherlands is estimated of the order of 2 % per hour (ref. 1). Reaction of ozone with olefines does not always contribute to oxidant loss, as ozone may be regenerated in the reaction sequence. In the shortened version of the CMB-I1 mechanism discussed above, reaction of the double bonded carbon pair unit OLE produces net (0.76 p - 0.46) q.Ox, where p and q are factors less than 1, dependent on the NOX -concentration. Under conditions of low NOX concentration, the olefines are a sink for ozone. The ethylenic double bonded species ETH produces, upon reaction with ozone, (0.2 p-1) q Ox, thus constituting a net sink under all circumstances.
583 Wet and drv deDosition Wet deposition is not an efficient removal process for ozone. The time constant for non-reactive scavenging by rain and cloud water may be estimated by H.I./h, where I is the precipitation rate, h the depth of the layer in which precipitation takes place, and H the Henry constant for ozone, equal to about 3 (ref. 23). Assuming h 1000 m and I 800 mm/y, we
-
-
find a removal time constant of the order of negligible with respect to dry deposition removal.
10-'Os-l,
Reaction of ozone with other pollutants in cloud possibly
more
and
completely
rain water
is
efficient. An upper estimate of aqueous phase oxidation of
SO2 by ozone of l%/h (annual average) and concentrations of SO2 and O3 of 10 and 80 ug/m3 gives an estimated effective removal time constant of 2. Dry deposition of ozone is a more efficient removal process. In table 3, the deposition velocity for various surfaces is given. The deposition velocity over water and snow is very low. Over land, an average deposition leads, with a mixing layer height of 1000 m, velocity vd of ca. 0.5 to removal with an effective time constant vd/h of ca. 5.10m6s-l.
ems-'
TABLE 3 Dry deposition velocities (in cm.s-l) for ozone (from ref. 24) summer day niiht
short grass grassland crop (mayze, soybean)
day night day night
forest summer
soil soil (wet) snow sea (water)
0.6 0.3 0.0-1 0.4-1.3 0.1-0.3 0.2-1 0.05-0.1 0.25-0.6 0.1 0.06 0.01-0.05
Recently, new information about dry deposition of oxidant has been obtained from continuous measurements of NO2 and O3 at 4, 100 and 200 m height at the meteorological mast at Cabauw, The Netherlands, 1986.
The
surroundings of
in
the period
1980-
this mast are mainly grassland with some tree
rows and few orchards. From the measurements of oxidant, wind and global 4m and z2 radiation the deposition velocity vd related to the heights z1 100 m was calculated according to
-
-
here, F is the flux, c the oxidant concentration, and resistance:
ra
the
aerodynamic
584
fa (zl,z2)
- i:
l/Kz(z)
&
The coefficient of turbulent diffusion KZ was calculated from the friction velocity u* and Monin Obuhkow lenght L, which, in turn, were calculated from the measured wind speed and global radiation (ref. 2 5 ) . Situations with an estimated mixing layer height below 110 m were excluded from the analysis; this included an important fraction of the nocturnal hours. In order to check for flux divergence, the deposition velocity was also calculated for z1 4m and z2 200m. Only if flux divergence is neglibile, the flux can be equated to the deposition flux.
-
-
. . I
6 1111 u n s s t m
I2
II
__ I I J O_ i u,u m i
1
14
Fig. 7. Deposition velocity (cms
-1
) at Cabauw, as a function of time of the day
average for the period 1980-1986. 0 : as derived from concentration measurement at 4 m and 100 m. +: idem, for 4 m and 100 m.
Fig. 8. Deposition velocity (cms-1 ) at Cabauw, for summer (left) and winter (right) half year periods. Symbols as in fig. 6 .
585 The
average
diurnal
profile
of the deposition velocity is shown in
fig. 7. The deposition velocity, and also the f l w , is higher day
during
the
night, During the morning hours, there is considerable f l w
than at
divergence, as a result of mixing height increase. Fig. 8 shows results for the
summer- and winter
half year periods. During winter, the deposition
velocity is rather low, both because of shorter day value
during
the
day.
lenght,
and
a
lower
In the summer, flux divergence during the morning
hours is large, especially in instable conditions (Pasquill classes A, and C) and for neutral stability (D) in conditions of low mixing height. The flux divergence can be
estimated
from
the
mass
balance
B
equation.
Neglecting smaller terms we have dF/dZ
*
-dc/dt
-
u dc/&
+Q
where u is the horizontal wind, and Q represents chemical reaction. In case of concentration changes due to mixing height increase, we have dc/dt
- l/h
.
.
dh/dt
(c~-c)
and the error in vd can be approximated by
.
I/h. dh/dt
AVd
(C,-C)/C
.A Z
where h is the mixing height, c the concentration and ct the
concentration
above the mixing layer. With l/h.dh/dt of the order of 5O%/h. (ct-c)/@l and A z 100 m, we have vd 1.4 cm/s, which is of the order of the
-
divergence
-
effect
found. The influence of advection (second term) on the
deposition velocity was estimated to be less than 0.05
cm.s-l. A l s o ,
for
oxidant, chemical reaction is not causing important flux divergence. However, the flux of ozone may be strongly affected by chemical reaction
-
with NO. Writing Q k.c. where k is some effective first order rate constant, the estimated effect of chemical reaction on vd is: Avd
F/c
-
kAz
-
-
For reaction of O3 with 5 ppb NO at night, k z and even forb z 4 m. vd 0.8 cm.s-'. Therefore, a deposition velocity for ozone cannot be derived from these measurements. The estimated yearly average deposition flux for oxidant is ca. ug/m 2/s, corresponding to a yearly averaged deposition velocity of ca. -1 cm.s . In summer during daylight hours the flux is ca. 0.9 pg/m 2/s, the deposition velocity 0.8 cm.s-l. In part, this flux is caused by deposition
of
NOp,
which
0.4 0.5 and dry
gives an important contribution to the oxidant
concentration at ground level in Cabauw. It is interesting to compare this flux to the flux from the 2 stratosphere to the troposphere (0.01-0.07 pg/m /s). Even taking into account that dry deposition over sea is an order of magnitude lower than that over land, it still follows that oxidant dry deposition may be larger than this stratospheric flux. In view of tropospheric degradation processes, this points to a considerable chemical production of ozone in the troposphere (ref. 12). Part of this production is taking place in the mixing layer, and in the Netherlands there is an upward flux of oxidant from the mixing layer.to the troposphere. This is indicated by the fact that the average concentration of oxidant, measured at Cabauw at 200 m height, is larger than the background tropospheric concentration, estimated from fig. 4. Averaged for the summer half year, the difference is about 13 ppb. This indicates that the photochemical production in the mixing layer 'is larger than the removal by dry deposition. Acknowledeement The analysis of the CBM-I1 mechanism was carried out in cooperation with J.H.Duyzer (TNO, Delft). The analysis of oxidant data at the Cabauw mast was carried out in cooperation with J.A.van Jaarsveld (RIVM, Bilthoven). REFERENCES 1. W.Slooff, R.M.van Aalst, E.Heijna-Merkus and R.Thomas (eds.), Basis document ozone (in Dutch), National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands (1987). 2 . K.D.van den Hout and F.A.A.M.de Leeuw, Modelberekeningen met het MPA trajectoritinmodel van episoden met fotochemische luchtverontreiniging, in: Ozon: fysische en chemische veranderingen in de atmosfeer en de gevolgen, Kluwer, Deventer 1987, pp 92-96. 3 . P.J.H.Builtjes and S.D.Reijnolds, Evaluatie en toepassing van een grootschalig verspreidingsmodel voor fotochemie - hat RTM-111-PHOXA model, in: Ozon: fysische en chemische veranderingen in de atmosfeer'en de gevolgen, Kluwer, Deventer 1987, pp 97-105. 4. A.E.G.Tonneijk, Effects on agricultural crops, this symposium. 5. F.A.A.M.de Leeuw, Long-term averaged ozone calculations, this symposium 6. R.Guicherit, TNO, Delft, personal communication, 1987. 7. J.A.Logan, Tropospheric ozone; seasonal behaviour, trends and (1985), p. 10463. anthropogenic influence, J.Geophys. Res. 8. R.D.Bojkov, Monitoring ozone layer and background ozone in the troposphere, this symposium. 9. O.Hov, K.H.Becker, P.Builtjes, R.A.Cox and D.Kley, Evaluation of the photo-oxidants-precursorrelationship in Europe, CEC Air Pollution Research Report-1, 1986. 10. United Kingdom Photochemical Oxidants Review Group, Ozone in the United Kingdom, UK Department of the Environment, 1987. 11. W.Johnson, Global modelling of ozone and trace gases, this symposium. 12. D.Kley, A.Volz and H.G.J.Smit, Tropospheric ozone-natural budget and anthropogenic perturbation, Chemistry related to tropospheric ozone,
.
a
587 proc. workshop COST 611 WP2, Cologne 1985, CEC, 1985. 13. P.J.H.Builtjes, Interaction of planetary boundary layer and free troposphere, this symposium. 14. 1.Colbeck and R.M.Harrison, Dry deposition of ozone: some measurements of deposition velocity and of vertical profiles to 100 meters, Atmos. Environ. (1985), p. 1807. 15. N.D.van Egmond and H.Kesseboom, A numerical mesoscale model for (1985), longterm average NOi and N02-concentrations, Atmos. Environ. p. 587. 16. R.Atkinson and A.C.Llovd. Evaluation of kinetic and mechanistic data for modelling of photkhemical smog. J.Phys. Chem. Ref. Data U (1984) D. 315. 17. R.G.Derwent, Comparison of chemical mechanisms in models, this symposium. 18. G.Z.Whitten, J.P.Killus and R.G.Johnson, Modelling of auto exhaust smog chamber data for EKMA develoriment.. reuort under contract number 68-02. 3735, EPA, 1983. 19. R.M.van Aalst and J.H.Duvzer. unDublished results. TNO, Delft, 1984. 20. G.Z.Whitten et al., M h e l i i n g of Simulated Photochemical smog with kinetic mechanisms Vol 1; interim report EPA-600/3-79-0010, 1979. Huidige emissies van koolwaterstoffen, Basisdocumenten 21. C.Veldt, koolwaterstoffen I (in Dutch), report CMF' 85/01, TNO, Delft, 1985. 22. N.D.van Egmond, H.Kesseboom and R.M.van Aalst, Relaties tussen NO2- NO en 0 -niveaus in de buitenlucht; afleiding van een NO -grenswaarde, RIVM3 report 227905050, National Institute of Publi'd Health and Environmental Protection, Bilthoven, 1982. 23. T.V.Larson, N.R.Horike and H.Harrison, Oxidation of sulfur dioxide by oxygen and ozone in aqueous solution; a kinetic study with significance to atmospheric rate processes, Atmos. Environ. 12 (1978), p. 1597. 24. J.A.Garland, Principles of dry depositon: application to acidic specles and ozone, VDI-berichte 500 (1983) p. 83. 25. D.Onderdelinden, J.A.van Jaarsveld and N.D.van Egmond, Bepaling van de depositie van zwavelverbindingen in Nederland, RIVM report 842017001, National Institute of Public Health and Environmental Protection, 1984.
re
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T. Schneider et al (Editors), Atnwupheric Ozone Research and its Policy Implications 1989 Elaevier Science Publishers B.V., Amsterdam -Printed in The Netherlanda
589
COMPARISON OF CHEMICAL MECHANISMS IN PHOTOCHEMICAL.MODELS
R.G. DERWENT and A.M. HOUGH Modelling and Assessments Group, Environmental and Medical Sciences Division, Harwell Laboratory, Oxfordshire, England
ABSTRACT The production of photochemical ozone in the atmospheric boundary layer is now a well established occurrence during most summers in Europe. Ozone concentrations during these episodes may approach and exceed air quality criteria values set to protect human health and prevent crop damage. Photochemical models are an accepted tool in the development and assessment of control policies designed to reduce exposure levels to ozone and other secondary pollutants. These models clearly show that abatement of hydrocarbon and nitrogen oxide emissions should bring some improvement in secondary pollutant air quality. To describe the complexity of the atmospheric photochemistry, many hundreds of chemical reactions are required in photochemical models.
In most models, computer limitations require that
drastic simplifications are made to the chemical schemes, in others the realism with which the chemistry is represented is limited only by present understanding and the completeness of emission inventories. The chemical schemes used in 20 photochemical models from the literature have been analysed carefully and implemented in the Harwell trajectory model using common input assumptions and evaluated chemical kinetic data. The implications of the 20 different chemical schemes on model calculated ozone, PAN, nitric acid, hydrogen peroxide and sulphate aerosol concentrations are described. Attention is then directed to the evaluation of two particular ozone control strategies
using the 20 different chemical schemes. INTRODUCTION Photochemical ozone formation over Europe is now a widely recognised regional scale pollution problem of some significance. During summertime anticyclonic conditions, sunlight-driven chemical reactions involving hydrocarbon and nitrogen oxide emissions may lead to t h e build-up of elevated ozone concentrations close to the surface in the atmospheric boundary layer. The hydrocarbons and nitrogen oxides act as photochemically-generated secondary pollutant precursors and are emitted largely from man's activities. The ozone
590 concentrations during these pollution episodes may approach or exceed environmental criteria levels which have been promulgated to protect human health and crops.
Most countries in Europe have the potential to cause some
photochemical secondary pollutant formation; furthermore, long range transboundary transport has been an important feature of this regional scale pollution phenomenon in North West Europe and Scandinavia. The discussion of control policies to combat photochemical air pollution formation is currently underway in several international fora. A coherent policy will require a full understanding of the chemical and physical mechanisms of the formation, transport and removal of photochemical ozone, together with the costs and performance of the available abatement technologies and an understanding of the damage mechanisms in the environment and their dose-response relationships.
This understanding is not complete in detail for
Europe, though much progress can be made if uncertainties and gaps in present understanding are taken adequately into account.
This paper addresses the
chemical mechanisms currently thought to account for photochemical ozone formation and the importance to be attached to the remaining uncertainties in their representation in the large photochemical models used for control policy assessment. MECHANISMS OF PHOTOCHEMICAL OZONE FORMATION AND THEIR REPRESENTATION IN MODELS Over the last three decades, a significant amount of research effort has been devoted to the understanding of photochemical smog chemistry.
This has
involved extensive programmes of ambient air quality monitoring, field studies of ozone transport and deposition and laboratory chemical kinetic studies involving smog chambers. This large body of understanding has been extensively reviewed by a number of sources and the following elements are considered to account for all the essential features of photochemical ozone formation in the atmospheric boundary layer:
-
nitrogen dioxide photolysis, the actual ozone source,
+
NO2
radiation (280 nm CXC 400 nm)
NO
+
0
the photochemical reaction system coupling together nitric oxide (NO), nitrogen dioxide (N02) and ozone ( O 3 ) ,
+
NO2
radiation
+
NO
+
NO
+
0
- o ~ + H
O + 0 2 + M
03
+
NO2
+
02
peroxy radicals (H02 and organic R02) which oxidise NO to NO2, R02
+
NO * RO
+ NO2
hydroxyl radicals which react with hydrocarbons to form peroxy radicals,
+ RH + 02 + M
OH R
-
+
R
+ H20
R02
+M
591 photochemical sources of hydroxyl radicals, O3
+
O(lD) HCHO
H
+
HCO
HOq
-
radiation (280 nm lo isomers)
heptenes
(>lo isomers)
octenes
(>lo isomers)
aromatic hydrocarbons. benzene toluene o-xylene m-xylene p-xylene ethyl benzene alicyclic hydrocarbons. cyclobutanes cyclopentanes cyclohexanes oxygenated hydrocarbons. alcohols aldehydes ketones
596 carboxylic acids esters ethers o
chlorinated hydrocarbons. chloroalkanes chloroethers
.
3 chemical schemes and this is an imnortant model simplification At this level of detail, three principal model approaches can now be discerned and these are: o
complete schemes.
o
direct approaches.
o
parameterised approaches. In the, -
the identity of all the hydrocarbons within
any of the above classes is retained and an explicit degradation scheme would be provided for each.
In the absence of emissions data for a particular
hydrocarbon then that hydrocarbon would be omitted from the model.
Clearly,
the explicit scheme approach generates the largest chemical scheme and this level of detail can only be handled with a box or trajectory model. In the direct amroach then the separate identities of all the hydrocarbons within each class are lost and that complete class is replaced by one or two members, which may be real species or ideal members of the class.
These
members act as surrogates for the class and their emission rates are adjusted to reflect the emission rates for the class.
Much of the detailed description
of organic degradation products particularly aldehydes, ketones and peroxyacylnitrates are lost but often these have little significance and there are unlikely to be any observational data against which to compare them against.
Care is required in the selection of surrogates to preserve the
overall reactivity of the class, to maintain the correct balance in degradation product formation and to ensure the same non-methane hydrocarbon concentration in ppbC. These three constraints are not satisfied uniquely for any of the classes given above and errors are introduced in this approach. However the chemistry scheme adopted is the explicit scheme of the hydrocarbons chosen to act as surrogates so these can be evaluated against the chemical kinetic literature. In the parameterised scheme amroach then the separate identities of all the hydrocarbons within each class (or part of a class) are lost and that complete class is replaced by one member. This member acts not only as a surrogate for the class but its degradation scheme is also set up to act for the class. The one parameterised scheme for a particular class would then represent that classes contribution to OH reaction rates, degradation product formation and
597 non-methane hydrocarbon concentrations in ppbC.
These three criteria cannot be
satisfied by a unique lumped scheme. Furthermore, considerable experimentation is required to draw up the imaginary scheme which which often requires non-stoichiometric reaction products to represent a range of degradation pathways from a range of real species. These schemes are often problem specific, of unknown accuracy and cannot be realistically evaluated against the chemical kinetic literature. They can only be evaluated by comparison with the results from a more complete chemical scheme using either test or real emissions data. There is no unique way of lumping the hydrocarbons in one class together to reproduce accurately the contribution to OH reaction rates, degradation product formation and non-methane hydrocarbons concentration in ppbC and two general approaches have been adopted: o o
parameterisation by mass. parameterisation by chemical structure. The Carbon-Bond approach provides important examples of the techniques of
parameterisation by chemical structure.
In this approach hydrocarbons are
split up into structural units such as C-C double bonds, aromatic rings and C-C frameworks as a means of representing the different members of each hydrocarbon class. Several versions of the carbon bond approach have been formulated to generate chemical schemes of varying complexity for incorporation into large Eulerian grid models. CLASSIFICATION OF CHEMICAL SCHEMES USED TO MODEL PHOTOCHEMICAL AIR POLLUTION FORMATION In Table 1, 20 chemical schemes employed in models of photochemical air pollution formation and used to evaluate ozone control strategies have been listed and some of their principal features drawn out for comparison. No attempt has been made to be exhaustive but many of the schemes from the major research models have been included. Each of the mechanisms is different and any classification scheme can only give a general indication of the simplifications which have been used.
Moreover, the definitions of the terms
used to describe such simplifications vary widely. In implementing these schemes for the United Kingdom, a simple trajectory model approach has been formulated to provide an account of the potential for ozone and other secondary pollutant formation downwind of London. The different chemical mechanisms have been applied using the United Kingdom hydrocarbon emission inventory, making use of as much detail as possible in terms of the range of hydrocarbons. The table shows how many emitted hydrocarbons could be used, the number of chemical reactions involved and a comparative measure of the CPU time required for a two day's calculation. The range in computer time requirements covers an order of magnitude showing the gain in speed that can be
achieved using the simplification techniques described above.
The CPU time
required for a two day's calculation. The range in computer time requirements covers an order of magnitude showing the gain in speed that can be achieved using the simplification techniques described above. COMPARISON OF A LARGE NUMBER OF CHEMICAL SCHEMES IN A SIMPLE TRAJECTORY MODEL The model used in this evaluation employed a two-layer trajectory model approach and has been reported in detail elsewhere (ref. 1).
Differences in
model results can arise from a range of factors and the methodology adopted here has the main aim of focussing on the differences introduced by the representation of the hydrocarbon chemistry, and its contribution to ozone formation. This hydrocarbon chemistry is a subset of the entire chemistry used in the model.
The remainder describes the chemistry of the small molecules
containing 0 , H, N ,
S
and C, but excluding any hydrocarbon degradation
reactions. The first steps were therefore to: o
take the published sources for each chemical scheme and remove the small molecule chemistry and replace it by the 54 reaction scheme from ref. 1, using rate coefficients reviewed in refs. 2 and 3.
o
set up life cycles for all secondary pollutants including dry deposition and aerosol scavenging.
o
add the methane chemistry to each scheme if not already included and adjust rate coefficients where necessary.
o
take the hydrocarbon chemical scheme used in the original reference and update all recognisable rate coefficients to the standard set.
o
set up the emissions for each scheme and relate them to the UK hydrocarbons emissions inventory.
o
take out all photochemical processes from the schemes and replace them by a standard set of time-dependent photochemical rate coefficients. In general, the above protocol worked well and for many of the more modern
chemical schemes the changes introduced were minimal and of little consequence. However, for some of the Carbon-Bond schemes with highly parameterised reactions, the chemical rate Coefficients could not be updated and this may present difficulties in interpreting our results. Table 2 presents the peak model concentrations calculated downwind of London for a number of species of interest in the twenty mechanisms and in the nine most recent mechanisms.
There is good agreement in the peak ozone
concentrations found with the different schemes, though with considerably poorer agreement concerning the timing of that peak in each model.
The more
recent schemes show excellent agreement between themselves with a peak ozone concentration of (95.5 t 3.1) ppb. In the case of the peroxyacylnitrates (PANS), the pattern is markedly
599 different with the time of the maxinun defined more accurately than the peak concentration. In fact, the calculated peak concentrations cover a wide range of (4.2
f
1.6) ppb which is not reduced much if attention is restricted only to
the nine more recent mechanisms. This behaviour for PANS is also repeated for hydrogen peroxide with the models showing better agreement on the timing of the maximum rather than on its magnitude. For both hydrogen peroxide and PANs this range of results is large enough to make calculations almost worthless. They show that the formulation of chemical mechanisms is far from perfect and that the good performance found for ozone reflects the careful adjustment and design inherent in the original mechanisms rather than the adequacy of present understanding of the basic atmospheric chemistry. It is nevertheless important to consider how relevant these chemical mechanisms are for ozone control strategy evaluation. EVALUATION OF OZONE CONTROL STRATEGIES It is often stated that although a given model has a limited ability to reproduce a particular behaviour exhibited in the real world, it has the ability to register reliably the consequences of changes in its input data.
In
photochemical air pollution modelling this would mean that a model which had difficulties in reproducing all facets of some observational ozone database for an episode would still have some value in evaluating ozone control strategies. In this paper this topic is investigated using the twenty chemical schemes from Table 1 and a simple scenario formulation which entails a 1984 base case and year 2000 scenarios in which all motor vehicles meet two different sets of emission controls, the Luxembourg Agreement and stringent emission standards (see ref. 4). Table 3 shows the peak concentrations of ozone, PAN and hydrogen peroxide calculated downwind of London in the 1984 base case and in the year 2000 cases in which motor vehicle emissions have been controlled. Despite the scatter in the absolute results, the relative results are encouraging. For ozone, every mechanism predicts a decrease in peak concentration between the 1984 base case and the year 2000 scenario with the Luxembourg Agreement and a further decrease following the implementation of the stringent vehicle emissions scenario. For ozone, the percentage reductions calculated using the nine recent mechanisms are all similar, as indeed are the results from some of the older mechanisms. The percentage decreases in the peak ozone concentration which occur between the 1984 base case and the two year 2000 scenarios appear to be robust with respect to changes in the chemical mechanism employed. For the PANs the pattern is similar to that for ozone although it should be noted that the results for three mechanisms have been excluded since they produced either zero PAN since the mechanism did not include the species or produced unacceptably low concentrations, less than 0.5 ppb.
One important
difference is however apparent looking at the results from the more recent mechanisms. Whereas for ozone the results from the more recent mechanisms were all grouped in the centre of the distribution of results, in the case of the PANs they are spread evenly throughout the entire range of values.
Again the
decrease in going to the year 2000 Luxembourg Agreement from the 1984 base case was smaller than the decrease in going on to the implementation of stringent emission controls. Hydrogen peroxide exhibits model decreases on implementation of the Luxembourg Agreement and further generally small decreases on moving to stringent emission controls.
The recent mechanisms give results which are in
rather better agreement than those obtained for the whole set of chemical mechanisms.
However, although the results of the earlier mechanisms when taken
together as a set are not inconsistent with the results from the more recent schemes, they exhibit little agreement between themselves. CONCLUSIONS In this study we have discussed some of the principle model simplifcations used in the formulation of photochemical air pollution models.
A
classification has been adopted and twenty chemical schemes covering the elements of the classification have been selected for more detailed evaluation from the literature. A simple trajectory model has been assembled and each of the twenty chemical schemes used to evaluate photochemical air pollution formation downwind of London. The results for 1984 base case emissions show that significant ozone, PAN and hydrogen peroxide concentrations develop downwind of London and that model
,
estimates of the peak concentrations depend on the chemical scheme chosen. For ozone. the scatter in the peak concentrations between the twenty chemical schemes amounted to 8.8 ppb or 9.3%. The scatter for PANs and hydrogen peroxide were somewhat higher at 38% and 54%, respectively. In evaluating control scenarios, these differences in absolute concentration seemed less relevant and despite the distinctions between the chemical mechanisms employed, all indicated that substantial decreases in peak ozone concentrations below the base case would result from the implementation of motor vehicle exhaust emission controls. Few mechanisms indicated changes in peak concentration that were demonstrably different from the mean of the results, including some of the earliest mechanisms.
The uncertainties in
photochemical air pollution models have therefore decreased with time for ozone but not necessarily for PAN and hydrogen peroxide. ACKNOWLEDGEMENTS This work was funded by the United Kingdom Department of the Environment as part of an air pollution research programme. The assistance with the
601 calculations of Miss C Reeves of the School of Environmental Sciences, University of East Anglia, Nowich, Norfolk is gratefully acknowledged. REFERENCES 1 A.M. Hough, The significance of physical and chemical processes in a photochemical oxidant model, AERE Report-R12294, H.M. Stationery Office, London, (1987), 79pp. 2 D.L. Baulch, R.A. Cox, R.F. Hampson, J.A. Kerr, J. Troe and R.J. Watson, Evaluated kinetic and photochemical data for atmospheric chemistry, J. Phys. Chem. Ref. Data, 1259-1375, (1984).
u,
3 R. Atkinson and A.C. Lloyd,. Evaluation of kinetic and mechanistic data for modelling of photochemical smog, J. Phys. Chem. Ref. Data,
u, 315-444,
(1984). 4 A.M. Hough and R.G. Dement, Environmental Pollution, &, 109-118, (1987). 5 R.G. Dement and 0. Hov. Computer modelling studies of photochemical air pollution in north-west Europe, AERE Report-R9434, H.M. Stationery Office, London, (1979), 147pp.
a,
1073-1095, (1987). 6 A.M. Hough, Atmospheric Environment 7 W.R. Stockwell, Atmospheric Environment 20, 1615-1632, (1986)
u,437-464, (1985). Geophysical Research a,
8 J.A. Leone and J.H. Sainfeld, Atmospheric Environment 9 F.W. Lurmann, A.C. Lloyd and R. Atkinson, J. 10905-10936, (1986).
10 G.E. Whitten, J.P. Killus and R.G. Johnson, Modelling of auto exhaust smog chamber data for EKHA development, SAX, 101 Lucas Valley Road, Sen Rafael, California, USA, (1985). 11 G. E. Whitten and M.W. Gery, Development of CBM-X mechanisms for urban and regional AQSMs, SAI, 101 Lucas Valley Road, San Rafael, California, USA, (1985), 160pp. 12 A.T. Cocks and I.S. Fletcher, personal communication. 13 A.Eliassen, 0. Hov, I.S.A. Isaksen, J. Saltbones and F. Stordal, A Lagrangian long-range transport model with atmospheric boundary layer chemistry, J. Applied Meteorology 2,1645-1661, (1982). 14 R. Atkinson, A.C. Lloyd and L. Winges, Atmospheric Environment
u,
1341-1355, (1982). 15 W.R. Stockwell and J.G. Calvert, J. Geophysical Research
a,6673-6682,
(1983). 16 A.H. Falls and J.H. Seinfeld, Environmental Science and Technology 1398-1406, (1978).
u,
17 K. Selby, Computer calculation of ozone formation during anticyclonic weather episodes in Europe. Report TNER-85-044. Thornton Research Centre, Shell Research Ltd, PO Box 1, Chester, United Kingdom, (1985).
602 18 J.P. Killus and G.E. Whitten, A new carbon bond mechanism for air quality simulation modelling.
Report EPA 600/3-82-041, U . S . Environmental
Protection Agency, Research Triangle Park, North Carolina, USA, (1982). 19 J.W. Bottenheim and O.P. Strausz, Atmospheric Environment
u,85-97, (1982).
20 H. Rodhe, P. Crutzen and A. Vanderpol, Tellus 33, 132-141, (1981). 21 A.Q. Eschenroeder and J.R. Martinez, Advances in Chemistry
u, 101-167,
(1972). TABLE 1 Twenty chemical mechanisms from the literature used in modelling photochemical air pollution formation.
No
Mechanisms
1 Harwell 2 H-SIMPLE 3 NCAR
Ref.
4,5 6 7 4Ls 8 9 5 UA-Full 6 LLA-Condensed 9 7 CBM-X 10 8 CBM-IV 11 9 CEGB 12 10 EMEP 13 11 ALW 14 12 sc 15 13 FS 16 14 SHELL 17 15 CBM-I 18 16 CBM-I1 18 17 CBM-111 18 18 BS 19 19 RCV 20 20 EM 21
Number of Number of emitted organic hydrocarbons reactions* 36 8 9 15 20 9 10 7 5 8 14 15 6 8 4 5 5 5 2 2
272 38 48 188 246 82 108 34 50 43 60 88 32 71 19 51 58 24 4 9
CF'U time required 345 67 73 300 367 112 121 69 71 78 96 89 57 88 46 69 81 52 36 41
Simplifications used Complete Direct Direct Complete Parameterised Parameterised Parameterised Parameterised Direct Direct Direct Direct Direct Direct Parameterised Parameterised Parameterised Parameterised Direct Direct
Notes Complete: Direct :
all hydrocarbons included with detailed degradation chemistry. each hydrocarbon class represented by one or two members with degradation chemistry represented explicitly. Lumped : each hydrocarbon class represented by one or two members with degradation chemistry approximated by non-stoichiometric coefficients. *: the tabulated number does not include 54 reactions involving small molecules containing 0, H, N, S and C atoms.
603 TABLE 2
The peak concentrations of a number of photochemically-generated secondary pollutants calculated downwind of London in the base case 1984 scenario. Peak Concentrations, ppb Twenty Mechanisms Nine Mechanismsa
Species Ozone
94.95
f
8.79
95.52
f
3.07
PAN8
4.21
f
1.62
4.60
f
1.19
10.18 f 1.03
9.98
f
0.49
HNo3 HCHO~
6.30 f 1.95
5.98 f 0.90
H202
2.25
f
1.21
2.43 f 0.57
Sulphate aerosol
5.17
f
0.55
5.08 f 0.32
OHd
9.77
f
2.68
9.72
f
1.41
Notes: 1 standard deviation or 67% confidence limits quoted. these are the nine most recent mechanisms studied and all have been published since 1984. b: only 19 mechanisms were included. c: only 16 mechanis s were included. d: lo6 molecule cm' f
a:
J.
TABLE 3
The peak concentrations of a number of photochemically-generated secondary pollutants calculated downwind of London in two different scenarios for the year 2000.
(Concentrations in parts per billion by volume).
Species Ozone
Year 2000 Luxembourg Agreement 20 Mechanisms 9 Mechanismsa
Year 2000 Stringent Emission Limits 20 Mechanisms 9 Mechanisms'
83.65
3.05
67.87 f 4.92
f
10.47 86.07
f
69.28 f 2.27
PAN&
3.55 f
1.45
3.98 f 1.01
2.12 f 0.82
2.30
f
0.60
HNo3
9.88 f
1.00
9.88
0.49
7.86 f 0.47
7.79
f
0.25
HCHO~
4.16
f
2.47
4.94 f 0.73
2.75 I 1.55
3.28 i 0.44
H202
1.58 f
0.93
1.68 i 0.52
1.31 i 0.62
1.40
f
0.35
Sulphate aerosol
5.27 f
0.67
5.33 f 0.37
5.60 t 0.46
5.58
f
0.38
10.19 f
3.34
11.88 f 2.48
11.76
f
1.50
0Hd
10.42
f
f
1.71
Notes 1 standard deviation or 67% confidence limits quoted. these are the nine most recent mechanisms studied and all have been published since 1984. b: only 19 mechanisms were included. c: only 16 mechanis s were included. d: lo6 molecule cmf
a:
J.
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T.Schneideret aL (Editors),Atmospheric Ozone Research and its Policylmplications 0 1989 Elsevier SciencePublishersB.V., Amsterdam
-Printed in The Netherlande
605
INTERACTION OF PLANETARY BOUNDARY LAYER AND FREE TROPOSPHERE
P.J.H. Builtjes, MT-TNO, .Department of Fluid Dynamics, P.O. Box 342, 7300 AH Apeldoorn, the Netherlands
ABSTRACT Results from photochemical episodic dispersion model calculations and historical trends observed in the Los Angelos Air Basin, show that the relation between the precursor VOC- and NOx-emissions leading to hourly 03-concentrations in the atmospheric boundary layer is strongly non-proportional and that substantial emission reductions only lead to relatively small decreases in peak 03- concentrations. However, 03-concentrations during episodes are added upon a background 03-level of about 40-50 ppb which is, at least partly, also from antropogenic origin. Models capable of calculating this 03-background level, and the influence of precursor emissions on these levels, do need a description of the exchange between the free troposphere and the boundary layer, of which only some limited information is available uptill now.
1. INTRODUCTION
Much attention has been devoted in Europe as well as in the United States to the study of photochemical oxidant formation during episodes. These studies are motivated by the adverse effects that high hourly ozone concentrations have on human health. Levels of hourly ozone concentrations of 120 ppb (240 pg/m3), which serve often as an air quality guideline are regularly exceeded in the United States as well as in Europe. Uptill now only limited attention has been paid to more long term average ozone levels. However, there are at least two good reasons to adress long term average ozone levels: long term average ozone levels in the atmospheric boundary layer. for
-
-
example growing season daylight averages, have shown to have adverse effects on vegetation, including forests; episodic photochemical ozone levels are build upon an existing background level, which is closely linked to the long term average ozone level.
Considering the last point, several remarks can be made. Model studies carried out concerning photochemical oxidant formation during episodes clearly
show the non-proportional relationship between VOC- and NO,-precursor
emis-
sions and hourly maximum 03-levels. Recent applications of trajectory models and Eulerian grid models, both for one-day urban type situations as well as for multi-day long range transport situations all reveal similar trends: VOC-emission reduction brings down maximum 03-levels, but less than proportional (quite often calculations indicate for a XX VOC-emission reduction about an 0.5
x 9: reduction of 03-peak levels). NO,-emission
reductions also brings down
maximum 03-levels at locations where NO,-concentrations are low, which means in rural areas relatively far from large NO,-emission sources. However, in situations where NOx-concentrations are high, in and around industrial areas, NO,emission reductions result in an increase of maximum 03-levels (see for recent European calculations for example references 1, 2 , 3, 4 ) . Apart from this rather specific description of calculated effects of NO,and VOC-emission reductions a more general result is that calculations show a remarkable stiff behaviour of episodic 03-concentrations to considerable changes in NO,-and
VOC-emissions. In view of all the discussions devoted to an
evaluation of the historical trends in 03-concentrations in relation to emission trends for VOC and NO, as observed in the Los Angelos Air Basin (ref. 5 ) it can be stated that also reality shows a quite stiff behaviour, which is not in contradiction with model results. Next to this, it should be kept in mind that all these model studies assume a background ozone concentration of about 40-50
ppb which is kept unchanged
when NOx- and VOC-emissions are reduced in the calculations. A recent evaluation by Altshuller (ref. 6 ) pointed out that natural background 03-levels will be in the order of 10-20 ppb. This in in line with the observed increase in 03-concentrations in the (background) free troposphere of about 1% per year (ref. 7) over the last 15 years. Consequently, it is very likely that a substantial part of the background 03-leve1, either at groundlevel at remote places or in the free troposphere is of antropogenic origin. Two-dimensional global model calculations performed by Isaksen (ref. 8 ) do indicate the role of NO,-,
VOC- and CH4- and CO-emissions on the ozone forma-
tion in the free troposphere. Consequently, emission reductions of NO, and VOC will also have an effect on the background ozone level upon which the episodic ozone levels are 'added'. In this way, abatement of background ozone levels will also assist in bringing peak ozone levels down, and will obviously serve in decreasing long term average ozone levels. It is clear that the background ozone levels will be influenced by precursor-emissions over a very large area. However, apart from a first attempt by De Leeuw e.a. (ref. 9 ) , no models have been developed and applied to calculate more long term average background ozone levels in the boundary layer and the influence of precursor emissions.
607 To be able to do this global 2-dimensional models as developed by Isaksen (ref. 8) have to be coupled with boundary layer models. Critical in this is the description of the exchange between the boundary layer and the free troposphere. Some remarks on these exchange processes will be made. First in chapter 2 some observations will be presented. Chapter 3 contains a overview of exchange processes and some descriptions. The paper ends with chapter 4, conclusions and recommandations. 2. OBSERVATIONS OF BACKGROUND 03-LEVELS The atmosphere can be devided in the atmospheric, planetary boundary layer or mixed layer with a height of upto about 2 km, the free troposphere with a height from above the mixed layer upto the tropopause at about 10-15 km and above that the stratosphere. In all three layers ozone is present and photochemical activity occurs. On a yearly averaged basis the 03-concentration increases from groundlevel to reach a maximum at about 1-2 km; further upward a steady decrease is found to about 10 km, after which an 03 increase into the stratosphere is found to levels
reaching 10 ppm
(see
for example ref. 7).
Our interest here are the ozone levels in the background free troposphere and at remote sites far from antropogenic emission sources. The ozone budget in the troposphere (free troposphere + atmospheric boundary layer) consists of four components: transport from the stratosphere, photochemical production, deposition at the ground and photochemical destruction. It is now generally accepted that the photochemical production term is significant and often even dominant (ref. 10, 11).
Some of the background ozone observations will be
described here. At moderate latitudes the seasonal pattern of observed 03-concentrations at remote sites shows a maximum in spring (aprillmay). This maximum has a value of about 40 ppb; the winter minimum is 20 ppb (ref. 11).
As has been stated
earlier, the observations show an increase in this value of about 1-2% per year at the moment. In areas with more industry and traffic the ozone pattern shows a maximum in the summer, a direct consequence of emissions of NOx and VOC from antropogenic origin. Analysis of Dutch ozone-stations for situations where the mean wind velocity was high also showed a seasonal pattern with a maximum in spring of 40-50 ppb (ref. 13, 14). In the situation with high windspeed the mixing is vigorous and the groundlevel 03 values can be considered to be the level of the free troposphere.
608 The question about the origin of the ozone in the free troposphere, where it
has a life time of several weeks is still open. Stratopheric intrusions can play a role, the observed spring 03-maximum is an indication. Tropopause folding at the occurance of a surface cold front associated with a so-called jet-streak can produce strong stratospheric intrusions, see for example Reiter, ref. 15. However, in general these intrusions do not reach ground level but spread out in horizontal direction at a height of 1-2 km. High ozone concentrations observed at ground level are an order of magnitude more often due to photochemical production in the atmospheric boundary layer than to stratospheric intrusions, ref. 16. Obviously the long term average 03 concentration at ground-level will have a stratospheric contribution. It is tempting to compare the rather uncertain estimate of this contribution of 12-15 ppb made by Reiter, ref. 15, with the estimate of the natural ozone level of 10-20 ppb made by Altshuller, ref. 6. However, the contribution of stratospheric intrusions to the ozone in the free troposphere could be larger than this 12-15 ppb and in this way could be of comparable magnitude to the contribution by transport of antropogenic ozone and precursors from the atmospheric boundary layer into the free troposphere. The exact antropogenic part of the ozone levels in the free troposphere is still unknown. 3 . EXCHANGE PROCESSES BETWEEN THE FREE TROPOSPHERE AND THE BOUNDARY LAYER
Most models, Eulerian grid as well as trajectory models which are used to calculate ground level 03-concentrations during episodic conditions have a maximum vertical extent to upto about 2 km, which means that at the upper boundzry the free troposphere starts. Only the 'super'-models which are Eulerian grid models used for the calculation of acidifying pollutants and photochemistry during episodes reach upto about 10 km, see for example ref. 17. These models need this vertical extent to incorporate the convective clouds which play an important role in the formation and transport of acidifying pollutants. Photochemical models in principle do not need this vertical extent explicitly. However, to calculate long term average ozone levels boundary layer models need to be 'coupled' with a model for the free troposphere. Before discussing the exchange processes which have to be described between the boundary layer and free troposphere model some remarks should be made concerning the 'free tropospheric' 2-dimensional model developed by
Isaksen, ref. 8 .
This
zonal
averaged global model has several vertical layers from the ground level upto a height of 17 km. The fluxes at the upper boundary layer were determined by the stratospheric transport into the troposphere as a function of season and latitude. This exchange process as well as the vertical distribution in the model domain itself are determined by using a modification of the mean velocity
609 and diffussion field derived by Plumb and Mahlman (ref. 18) which are a function of the season and month. So in this approach the exchange processes between the boundary layer and the free troposphere are given by the vertical mean velocity and the vertical turbulent diffusivity as prescribed in an averaged way by Plumb and Mahlman, ref. 18. However, to calculate the ground level ozone concentrations for longer time periods using a specific boundary layer model coupled with the for example by the Isaksen-model calculated values at a height of 2 km (the free tropospheric values) the calculations should be performed for the actual meteorological conditions in a brute-force approach (see ref. 9 ) . This requires an explicit description of the exchange processes. The following exchange processes occur between the free troposphere and the atmospheric boundary layer:
-
cumulus convective clouds stratus clouds high and low pressure systems diurnal growth of the mixed layer rain scavenging and wet chemistry frontal systems landlsea breeze and heat island phenomena topographic effects. First, some general remarks should be made. These eight exchange processes
-
can - in a parametrized way most convenient be described by a mean vertical velocity which is either upwind or downwind. Although also real turbulent transport takes place which can be described by gradient type transport the use of a mean vertical velocity is more convenient to avoid 'counter-gradient'-
transport and arbitrary splits between the two descriptions, which are to a large extent splits based on averaging time. In principle, complex weather forecast models as used for example at the European Centre in Reading, United Kingdom. have implicitly incorporated all these exchange processes. However, a calculation with such a forecast model with build-in complex non-lineair chemistry can not be foreseen for the near future, and in addition the grid resolution of those models is quite large which will average out local effects. In recent literature concerning exchange processes most attention is given to cumulus convective clouds, see ref. 19, 20. 21, 22. A cumulus nimbus cloud can reach upto 10 km, with a cloud base at about 0.5-2 km. Vertical upward velocities inside and close to the cloud reach from 1-10 m/s, or even upto 40
m l s . Downward velocities occur in the cloud itself, and also further away,
610 covering a total area around the cloud of about 20 x 20 km. So the cloud causes mixing over a box of about 20 x 20 km upto a height of 10 km, although the effectivity of the mixing process is only about 70% (ref. 2 2 ) . How large the exchange process over an area is depends on the cloud cover. On a long term average basis the exchange depends on the occurence of cumulus clouds. In Europe on a yearly basis this is only 4-8%. In addition cumulus clouds will hardly play a role during photochemical episodes. Stratus clouds are associated with much smaller upward velocities of about 0.05-0.10 m/s. Although these mean vertical velocities are small, stratus
clouds occur frequently in Europe and
so
will play a role in the long term
average exchange process. High and low pressure systems which have a scale of about 1000 x 1000 km are
-
apart from a frontal zone
-
always present. Although the associated vertical
velocity is only about 0.01 m/s, it occurs very frequently. These vertical velocities can easily follow from the divergence and convergence of the horizontal windfield, or simply from the anomaly of the yearly average pressure (which is 1013 Mbar at sea level). The diurnal growth of the mixed layer is of course an important entrainment/ detrainment process which has to be taken into account, but is often already incorporated in the boundary layer models. Rain scavenging and wet chemistry are of less importance for ozone but are essential for a number of other pollutants. Frontal systemslstructures and conveor belts occur in line shaped compact areas and are also associated with vertical upward and downward velocities. Finally, land-sea breeze, heat island phenomena and orography are local effects which can produce vertical velocities. An assessment which of the processes is of more importance can not be given.
This depends heavily on whether episodes or only long term averages are considered, and on the finest horizontal grid resolution desired. It should also be noted that often more than one process will be in operation, for example frontal structures with clouds. Simple parametrizations
of
the
different exchange
processes
are
not
available, but are required in any calculation of ozone in the atmospheric boundary layer where the influence of the free troposphere has to be taken into account. 4 . CONCLUSIONS AND RECOHMANDATIONS
-
Long term average ozone levels should be evaluated because of their adverse
effects on vegetation and their role as background ozone level upon which high episodic ozone levels are 'added'. In view of model results and historic NOxand VOC-emission and ozone trends the effect of emission reductions on peak
611 ozone levels is less than proportional. Abating long term average ozone levels would be an additional way to bring peak ozone levels down.
-
The observed increase of 1-2'6 per year in the background ozone levels in the free troposphere and at remote sites show the influence of antropogenic emissions on these levels. At the moment an accurate quantative value for this contribution to the background ozone levels and the contribution due to stratospheric intrusions can not yet be given.
-
To determine long term average ozone levels in the atmospheric boundary
layer the common type boundary layer models should be coupled with free tropospheric models, for example 2-dimensional global models. A description of the exchange processes between the free troposphere and the boundary layer is required for an adequate coupling, but parametrized descriptions are to a large extent still lacking.
REFERENCES Hov, 0. e.a., Evaluation of the photo-oxidants precursor relationship in Europe, CEC Air Poll. Res. Rep. 1, 1986. Dement, R.G. and Hough, A.M., The impact of emission reduction scenarios on photochemical ozone and other pollutants formed downwind of London, Bamberg Workshop, FRG, October 1987. Builtjes, P.J.H. e.a., PHOXA, the use of a photochemical dispersion model for several episodes in north-western Europe, 16th Int. Tech. Meeting on Air Poll. Modell. and its Appl., Lindau, FRG, April 1987. Selby, K., A modelling study of atmospheric transport and photochemistry in the mixed layer during anticyclonic episodes in Europe, Part 11: Calculations of photo-oxidant levels along air trajectories, J. of Climate and Appl. Met. 26, 1317-1338, October 1987. Kuntasal, G. and Chung, T.Y., Trends and relationships of 03, NOx and HC in the south coast air basin of California, JAPCA 37, 1158-1163, 1987. Altshuller, A.P., Estimation of the natural background of ozone present at surface rural locations, JAPCA 37, 1409-1417, December 1987. Hartmannsgruber, R. e.a., Opposite behaviour of ozone measurements at Hohenpeissenberg 1967-1983. In: Atmospheric Ozone Symp. Halkidiki 1984. Isaksen, I. and Hov, O., Calculation of trends in the tropospheric concentration of 03, OH, CO, CH4 and NO,, Tellus, 1986. Leeuw, F.A.A.M. de, e.a., Long term averaged ozone calculations, Symp. Atm. Ozone Research and its policy implications, Nijmegen, the Netherlands, May 1988. 10 Verkovich, F.M. e.a., The reservoir of ozone in the boundary layer of the
Eastern United States and its potential impact on the global tropospheric ozone budget, J. of Geoph. Res. 90, no. D 3 , pg. 5687-5698, June 1985. 1 1 Logan, J.A., Tropospheric ozone: seasonal behaviour, trends and antropogenic influence, J. of Geoph. Res. 90, pg. 10463, 1985. 12 Bojkov, R.D., Surface ozone during the second half of the nineteenth century, J. of Climate, Appl. Met. 25, 343, 1986. 13 Aalst, R.M. van, Emissions, chemical processes and deposition. In: Dutch Ozone-Symposium, Ede, November 1986 (in Dutch).
612 14 Guicherit, R., Ozone on an urban and regional scale with special reference to the situation in the Netherlands, MT-TNO Rep. no. P 871030, May 1987. 15 Reiter, E.R., Stratospheric-Tropospheric Exchange Processes, Rev. Geoph. and Space Physics 13, 4, 459-474, 1975. 16 Derwent. R.G. editor, Ozone in the United Kingdom, Dep. of Environment Rep., February 1987. 17 Stern, R.M. e.a., Application of a regional model for the transport and
18 19 20
21 22
deposition of acidifying pollutants to Central Europe, 16th Int. Tech. Meeting on Air. Poll. Modell. and its Appl. Lindau, FRG, April 1987. Plumb, R.A. and I.D. Mahlman, The zonally-averaged transport characteristics of the GFDL general circulationltransport model, J. Atm. Scien.. 1986. Ching, J.K.S., Evidence for cloud venting of mixed layer ozone and aerosols, Atm. Env. 22, 2, 225-242, 1988. Isaac, G.A. e.a., The role of cloud dynamics in redistributing pollutants and the implications for scavenging studies, p. 1-13, In: Precipitation Scavenging, Dry Deposition and Resuspension, Pruppacher e.a. editors, Elsevier Science Publish, Co. Inc. 1985. Dickerson, R.R., Thunderstorms: An important mechanism in the transport of air pollutants, Science, vol. 235, 460-464, January 1987. Ching, J.K.S., Modelling non-precipitating cumulus clouds as flow-throughreactor transformer and venting transporter of mixed layer pollutants, Int. Conf. on Energy Transf. and Interactions with small and meso-scale atm. processes, Lausanne, Switzerland, March 1987.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implieations 0 1989 Elaevier Science Publishers B.V., Ameterdam - Printed in The Netherlanth
613
DEVELOPMENT AND EVALUATION OF THE REGIONAL OXIDANT MODEL FOR THE NOHTHEASTERN UNITED STATES
K.L.
Scherel and R.A.
Wayland2
1National Oceanic and Atmospheric Administration, on assignment t o t h e U.S. Environmental Protection Agency, Research T r i a n g l e Park, NC 2Computer Sciences Corporation, Research Triangle Park, NC
27711 (U.S.A.) 27709 (U.S.A.)
ABSTRACT The second generation U.S. EPA Regional Oxidant Model (ROM2) has been developed over t h e l a s t 10 years and i s now operational. The 3-0 g r i d model has been applied t o t h e Northeast U.S. f o r a 50-day p e r i o d i n 19110. Model evaluation r e s u l t s show t h e ROM2 i s performing w e l l w i t h respect t o p r e d i c t i n g t h e frequency d i s t r i b u t i o n s and s p a t i a l p a t t e r n o f observed D3 concentrations.
INTRODUCTION
The need f o r a comprehensive simulation model o f photochemical smog on regional (1000 km) scales became apparent w i t h t h e r e a l i z a t i o n t h a t t h e 03 and oxidant p o l l u t i o n problem, f i r s t studied i n t h e context of s i n g l e urban areas, o f t e n extended over l a r g e geographical regions o f t h e U.S.,
encompassing many
urban areas. I n response t o t h i s need EPA began a development e f f o r t toward a Regional Oxidant Model (ROM) nearly t e n years ago.
Today we have a second
generation operational model (ROM2) t h a t continues t o be developed, tested, and r e f i n e d ( r e f s . 1-3). The model i s p r i m a r i l y designed f o r use i n e v a l u a t i n g t h e effectiveness o f various emission c o n t r o l s t r a t e g i e s on t h e regional scale. The purpose o f t h i s paper i s t o provide a b r i e f overview o f t h e ROM2 and t o describe the f i r s t phase o f a model evaluation study using data from t h e
.
Northeast U S. MODEL OVERVIEW The ROM has been designed t o simulate most o f t h e important chemical and physical processes responsible f o r t h e production o f photochemically produced 03 on scales o f 1000 km, o r several days o f t r a n s p o r t time. These processes include horizontal transport, atmospheric chemistry (using t h e Carbon Bond I V chemical mechanism, r e f . 4), nighttime wind shear and turbulence episodes associated w i t h t h e nocturnal j e t , cumulus cloud e f f e c t s on v e r t i c a l mass t r a n s p o r t and photochemical r e a c t i o n rates, mesoscale v e r t i c a l motions induced by t e r r a i n and t h e l a r g e scale flow, t e r r a i n e f f e c t s on advection, d i f f u s i o n
614
and deposition, sub-grid s c a l e chemistry processes, emissions o f n a t u r a l and anthropogenic precursors, and d r y d e p o s i t i o n . They a r e mathematically simulated i n t h e 3-D g r i d model w i t h v e r t i c a l r e s o l u t i o n o f 3 1/2 v e r t i c a l l a y e r s i n c l u d i n g t h e boundary l a y e r and t h e capping i n v e r s i o n o r c l o u d l a y e r . H o r i z o n t a l r e s o l u t i o n i s approximately 18.5 km; however, t h e exact g r i d c e l l s i z e v a r i e s somewhat over t h e model domain because t h e c o o r d i n a t e system used i s based on l a t i t u d e - l o n g i t u d e . D e t a i l e d d e s c r i p t i o n s o f t h e t h e o r e t i c a l b a s i s and design o f t h e ROM modeling system a r e a v a i l a b l e elsewhere ( r e f s . 1-3). The t o p t h r e e ROM l a y e r s are p r o g n o s t i c ( p r e d i c t i v e ) and a r e f r e e t o l o c a l l y expand and c o n t r a c t i n response t o changes i n t h e p h y s i c a l processes o c c u r r i n g t h e r e i n . The bottom l a y e r i s a shallow d i a g n o s t i c surface l a y e r designed t o approximate t h e sub-grid s c a l e e f f e c t s on chemical r e a c t i o n r a t e s from a s p a t i a l l y heterogeneous emissions d i s t r i b u t i o n . Layers 1 and 2 model t h e depth o f t h e well-mixed l a y e r d u r i n g t h e day. I n l o c a l areas where s t r o n g winds e x i s t o r t h e surface heat f l u x i s weak, s u b s t a n t i a l wind shear can e x i s t i n t h e f i r s t few hundred meters above ground. This phenomenon can be t r e a t e d s e p a r a t e l y i n l a y e r 1. Layer 3 represents t h e s y n o p t i c s c a l e subsidence i n v e r s i o n , t h e base o f which i s t y p i c a l l y 1-2 km above ground. Clouds, where they e x i s t , are a l s o t r e a t e d i n l a y e r 3. A t n i g h t , t h e r e i s some readjustment i n l a y e r depths as t h e upper l a y e r s become decoupled from t h e lower s u r f a c e i n v e r s i o n l a y e r . MODEL APPLICATION I n t h e c u r r e n t study t h e model has been a p p l i e d t o t h e Northeastern U n i t e d States f o r t h e p e r i o d J u l y 12-August 31, 1980. Several r e g i o n a l photochemical smog episodes occurred d u r i n g t h i s p e r i o d w i t h measured 03 c o n c e n t r a t i o n s as h i g h as 300 ppb i n t h e Northeast U.S.
Emissions, a i r q u a l i t y , and
meteorologlcal data bases were prepared f o r use by t h e ROM modeling system, which includes n e a r l y 30 separate d a t a preprocessing programs. I n a d d i t i o n t o t h e r e g u l a r network o f m e t e o r o l o g i c a l and a i r q u a l i t y m o n i t o r i n g s t a t i o n s already i n place d u r i n g t h e p e r i o d o f i n t e r e s t , s p e c i a l a i r c r a f t and s u r f a c e measurements were taken as p a r t o f an EPA-sponsored f i e l d study, t h e Northeast Regional Oxidant Study ( r e f . 5). A comprehensive anthropogenic source emissions i n v e n t o r y f o r hydrocarbons, NO,
and CO was developed w i t h a s p a t i a l and
temporal r e s o l u t i o n on t h e same s c a l e as t h e ROM ( r e f . 6).
I n a d d i t i o n , an
i n v e n t o r y o f b i o g e n i c a l ly-produced hydrocarbon species was a1 so developed ( r e f . 7 ) and i n c l u d e d as p a r t o f t h e t o t a l emissions i n v e n t o r y .
The model s i m u l a t i o n was s t a r t e d on a day w i t h r e l a t i v e l y c l e a n t r o p o s p h e r i c conditions.
I n i t i a l model concentrations were s e t t o values r e p r e s e n t a t i v e o f
these c o n d i t i o n s , i n c l u d i n g N 4 = 2 ppb, NMHC.15
ppbC, and 03=35 ppb, w i t h no
s p a t i a l v a r i a t i o n considered. Model s i m u l a t i o n proceeded c o n t i n u o u s l y through
615 t h e 50 day p e r i o d , and t h e assumed i n i t i a l c o n c e n t r a t i o n f i e l d was e f f e c t i v e l y swept out o f t h e model domain by t h e f o u r t h s i m u l a t i o n day. I n f l o w boundary concentrations were updated d u r i n g t h e s i m u l a t i o n every 12 hours. Several remotely-located 03 monitors were used t o determine t h e temporal v a r i a t i o n s o f i n f l o w concentrations. MODEL EVALUATION D e t e r m i n i s t i c vs. n o n - d e t e r m i n i s t i c modes The 03 surface m o n i t o r i n g networks o f t h e p o r t i o n s o f t h e U.S.
and Canada
i n c l u d e d i n t h e ROM s i m u l a t i o n domain used here i n c l u d e d 214 s i t e s d i s t r i b u t e d throughout t h e model domain. The vast m a j o r i t y o f t h e m o n i t o r i n g s i t e s a r e l o c a t e d w i t h i n o r near urban and m e t r o p o l i t a n areas. As a r e s u l t t h e r e i s good m o n i t o r i n g coverage i n s e l e c t e d p o r t i o n s of t h e domain and poor s p a t i a l coverage i n much of t h e remainder o f t h e domain. Also, some of t h e urbano r i e n t e d monitors o f t e n show t h e e f f e c t s o f l o c a l N3,
scavenging o f 03.
Nevertheless t h e l a r g e number o f monitors and t h e extended s i m u l a t i o n p e r i o d p r o v i d e u s e f u l data f o r performing an e v a l u a t i o n of t h e a b i l i t y o f t h e ROM t o s i m u l a t e 03 c o n c e n t r a t i o n s over r e g i o n a l scales. We l i m i t our d i s c u s s i o n here t o t h e performance o f t h e model f o r p r e d i c t i n g 03 o n l y near ground l e v e l . H i s t o r i c a l l y , model e v a l u a t i o n e x e r c i s e s have used t h e p r e d i c t i o n s o f s i m u l a t i o n models i n a " d e t e r m i n i s t i c " sense. That i s , t h e model p r e d i c t i o n f o r a given time and a given p l a c e i s determined e x a c t l y by t h e data a s s i m i l a t e d by t h e model and t h e model's component algorithms. T h i s mode o f o p e r a t i o n does n o t e x p l i c i t l y consider model o r data u n c e r t a i n t i e s . For t h e t i m e and space scales used i n urban-scale modeling, t h e d e t e r m i n i s t i c mode may be a p p r o p r i a t e . For t h e 1000 km r e g i o n a l scale, however, where m u l t i - d a y t r a n s p o r t i s simulated, t h e d e t e r m i n i s t i c mode becomes i n a p p r o p r i a t e . This i s b a s i c a l l y because t h e s p a t i a l scales o f many key d a t a elements a r e c o n s i d e r a b l y coarser t h a n t h e scales o f t h e model. For instance, t h e u p p e r - a i r m e t e o r o l o g l c a l network i n North America t h a t provides e s s e n t i a l i n f o r m a t i o n f o r d e t e r m i n i n g t h e t r a n s p o r t component o f t h e ROM has s i t e l o c a t i o n s separated by s e v e r a l hundred k i l o m e t e r s and soundings taken o n l y every 12 hours. I n t h e process o f i n t e r p o l a t i n g t o t h e r e q u i r e d s p a t i a l and temporal scales o f t h e ROM, some of t h e determinism o f t h e d a t a s e t i s l o s t t o t h e v a r i o u s assumptions i n h e r e n t i n t h e i n t e r p o l a t i o n method chosen; numerous i n t e r p o l a t i o n methods e x i s t each w i t h i t s own s e t o f assumptions. Lamb ( r e f s . 8-9) maintains t h a t more a p p r o p r i a t e ways o f i n t e r p r e t i n g t h e r e s u l t s o f r e g i o n a l s c a l e s i m u l a t i o n models a r e i n a " p r o b a b i l i s t i c " o r "quasi - d e t e r m i n i s t i c " sense. I n t h i s study we use t h e " q u a s i - d e t e r m i n i s t i c "
mode, where model p r e d i c t i o n s
and observations a r e n o t compared f o r a s p e c i f i c l o c a t i o n and time, b u t r a t h e r
616 t h e comparisons are made f o r aggregate groups o f r e c e p t o r l o c a t i o n s such t h a t t h e r e e x i s t s a comnon c h a r a c t e r i s t i c u n i t i n g t h e members o f each r e c e p t o r group.
For our a n a l y s i s t h e groups were formed by a n a l y z i n g t h e frequency
d i s t r i b u t i o n s o f d a y l i g h t h o u r l y 03 c o n c e n t r a t i o n s d u r i n g t h e sumner o f 1980 a t t h e m o n i t o r i n g s i t e s i n our s u r f a c e d a t a base. Normalized frequencies o f occurrence o f 03 concentrations between 5 and 20 ppb, 20 and 40 ppb, 40 and 80 ppb, and g r e a t e r than 80 ppb were c a l c u l a t e d f o r each m o n i t o r i n g s i t e . A c l u s t e r a n a l y s i s was performed u s i n g t h i s d a t a and 6 groups o f r e c e p t o r m o n i t o r i n g s i t e s were selected based on t h e i r c h a r a c t e r i s t i c frequencies o f observed 03 concentrations.
The groups i n c l u d e those with r e l a t i v e l y h i g h
frequencies o f >80 ppb 03 (groups 1 and 2), those w i t h more moderate l e v e l s (groups 3 and 4), one w i t h unusually h i g h frequencies o f 03 values 80 ppb appears q u i t e good from t h e data i n Table 1, w i t h t h e possible exceptions o f groups 5 and 6. The members o f group 5 were chosen based on an unusually high frequency o f 03 concentrations l e s s than 20 ppb. This i n d i c a t e s t h a t these monitors were most l i k e l y influenced by near-source NOx scavenging o r other l o c a l processes t h a t would cause ambient l e v e l s t o drop considerably below background. Hence t h i s i s a pre-selected group o f s i t e s t h a t are biased low i n comparison t o t h e m d e l ' s expected p r e d i c t i o n s ; t h e data i n Table 1 appear t o confirm t h e expectation. Group 6 contains o n l y 2 s i t e s , those whose observed concentration d i s t r i b u t i o n conforms t o a p a t t e r n c h a r a c t e r i s t i c o f remotely-located s i t e s
(i.e., r e l a t i v e l y few values below tropospheric background l e v e l s ) . I n f a c t , these s i t e s are considerably d i s t a n t from l o c a l source influences. One i s located a t Whiteface Mountain i n northern New York and t h e other i s a t Long
610 Point Park i n southern Ontario. The r e s u l t s f o r t h i s group o f monitors show t h e
ROM t o underpredict t h e occurrence o f >80 ppb 03. Small e r r o r s i n t h e f l o w f i e l d can cause s i g n i f i c a n t e r r o r s i n t h e p r e d i c t e d t r a j e c t o r i e s o f a i r p a r c e l s from p a r t i c u l a r source areas. These e r r o r s tend t o worsen w i t h i n c r e a s i n g distance from t h e source. Since t h e remote s i t e s are located a t l a r g e r distances from source areas, one p o s s i b l e reason f o r t h e R O M l s underprediction o f higher concentrations a t these s i t e s i s e r r o r s i n t h e t r a j e c t o r i e s o f a i r parcels a f f e c t i n g t h e s i t e s from major source areas (see discussion o f determinism i n regional a i r qua1 it y model s above)
.
The data i n Table 1 also show t h a t t h e ROM p r e d i c t s t h e occurrence o f moderate 03 l e v e l s (40-80 ppb) considerably more f r e q u e n t l y (66-93% o f t h e t i m e ) than do t h e observations (19-63% o f t h e time). This r e s u l t f o l l o w s from t h e model's underestimation o f t h e frequency o f low 03 l e v e l s and i s probably r e l a t e d t o t h e l o c a l source i n f l u e n c e a t many o f t h e urban-oriented m o n i t o r i n g sites. Fig. 1 ( a - f ) presents p l o t s o f t h e observed cumulative frequency d i s t r i b u t i o n o f daytime 03 concentrations versus t h e p r e d i c t e d d i s t r i b u t i o n f o r each o f t h e 6 receptor groups. The s o l i d l i n e i n each f i g u r e represents t h e l i n e o f p e r f e c t agreement between t h e d i s t r i b u t i o n s and t h e d o t t e d l i n e s show t h e 210% e r r o r bound about t h e s o l i d l i n e . Each
' + I
symbol represents a
p e r c e n t i l e l e v e l i n t h e frequency d i s t r i b u t i o n , and t h e d e c i l e l e v e l s from 10% t o 100% are marked by t h e i n t e g e r s 1,2,. ..,9,0.
For example, i n receptor group
1. approximately 80% o f t h e observed 03 concentrations and 90% o f t h e p r e d i c t e d
concentrations are l e s s than 100 ppb. The p l o t s c o n f i r m t h e model Is tendency t o overpredict a t lower concentration values over a l l receptor groups. Group 1 contains t h e s i t e s w i t h t h e highest observed concentration values and t h e ROM shows a tendency o f increasing underprediction w i t h concentration l e v e l . The agreement between p r e d i c t i o n s and observations i s best f o r groups 2-4 f o r moderate t o h i g h 03 values, up through t h e 99.5% l e v e l o f t h e frequency d i s t r i b u t i o n s . The maximum value o f t h e d i s t r i b u t i o n i s c o n s i s t e n t l y underpredicted by t h e model. Group 5, as discussed above, i s an anomalous group. Fig. l ( e ) confirms t h i s anomaly by showing systematic overpredictions. Most groups show a more h o r i z o n t a l tendency i n t h e d i s t r i b u t i o n below about t h e 70-80% l e v e l , i n d i c a t i n g t h a t t h e range o f t h e model p r e d i c t i o n s a t lower concentrations i s narrower than t h a t o f t h e observations. Another key aspect o f e v a l u a t i n g t h e ROM i s i t s a b i l i t y t o r e p l i c a t e s p a t i a l patterns o f observed p o l l u t a n t concentrations. Fig. 2(a) shows t h e modeling domain used i n t h i s study. The maximum observed 03 concentrations a t t h e monitoring s i t e s i n t h e eastern p o r t i o n o f t h e domain f o r t h e episode t h a t occurred d u r i n g 20 July 22 July are shown i n Fig. 2(b), and t h e corresponding model p r e d i c t i o n s are contoured i n Fig. 2(c). For t h i s episode t h e model r e p l i -
-
613
zw , , , , (I)
, ,, ,,,, , ,,
, , ,
,,,
I
,
I
,
, , ,
,’
, , , , , ,0
2w -
-
MAX
,
,
(b)
I
I I
I’ 0 8 1 6 PERCENTILE .((PERCENTILE
1w-
160
1w
GROUP 1 14,lW OM. D N A 18.41 PRED. UATA
GROUP 2
33.112 PRED. UATA
24.W Dm DATA 20.612 PRED. UATA
io,mo PRED. DATA
EM U r n DATA iws PREU. UATA
OBSERVED OZONE CUNCENTPaTIDN. onb
F i g . 1. Observed versus ROM-predicted cumulative frequency d i s t r i b u t i o n s o f daytime (08-19 h, LST) h o u r l y ozone concentrations a t each o f s i x groups o f receptor l o c a t i o n s over t h e period 14 J u l y 31 August 1980. Each p e r c e n t i l e l e v e l i n t h e d i s t r i b u t i o n i s shown and every t e n t h l e v e l i s i n d i c a t e d by an integer.
-
F l g . 2 ( a ) . Northeast U.S. ROM domain (dotted lines show F i g s . 2(b) and 2 ( c ) ).
area analyzed i n
621
Fig. 2(b,c). Maximum observed hourly ozone concentrations (ppb) f o r the period 20-22 July 1980 ( b ) , and contours of maximum predicted hourly ozone concentrations (ppb) for each ROM g r i d during t h e same period ( c ) .
622 cated t h e s p a t i a l p a t t e r n o f maximum 03 q u i t e w e l l i n t h e New England area. Portions o f c e n t r a l Connecticut show >200 ppb 03 b o t h i n t h e observations and t h e p r e d i c t i o n s . The ROM p r e d i c t e d another area o f >ZOO ppb 03 over e a s t e r n Long Island, although no m o n i t o r i n g s i t e s e x i s t e d t h e r e . Washington, D.C.
I n t h e c o r r i d o r from
t o Philadelphia, t h e model underestimated maximum 03 concen-
trations.
I n summary, t h e ROM has been a p p l i e d t o t h e n o r t h e a s t e r n U.S.
f o r a 50-day
p e r i o d d u r i n g t h e summer o f 1980. P r e l i m i n a r y model e v a l u a t i o n r e s u l t s show t h a t t h e model reproduces t h e observed frequency d i s t r i b u t i o n s o f 03 concentrat i o n s best f o r moderate t o h i g h values. There appears t o he a systematic tendency t o o v e r p r e d i c t t h e lowest observed values and t o u n d e r p r e d i c t t h e h i g h e s t values. The model r e p l i c a t e d t h e s p a t i a l p a t t e r n o f maximum 03 c o n c e n t r a t i o n s i n t h e New England area q u i t e w e l l f o r t h e 3-day episode c o n t a i n i n g some o f t h e h i g h e s t observed concentrations of t h e summer o f 1980. REFERENCES R.G. Lamb, A Regional Scale (1000 kin) Model o f Photochemical Air P o l l u t i o n . P a r t 1. Th eoret ica 1 Fo rmu1a t ion, E PA-600/ 3 -83-035, U S E PA, Research T r i a n g l e Park, NC 27711, 1983, 239 pp. R.G. Lamb, A Regional Scale (1000 km) Model of Photochemical A i r P o l l u t i o n . P a r t 2. I n p u t Processor Network Design, EPA-600/3-84-085, U.S. EPA, Research T r i a n g l e Park, NC 27711, 1984, 298 pp. R.G. Lamb and G.F. Laniak, A Regional Scale (1000 km) Model o f Photochemical A i r P o l l u t i o n . P a r t 3. Tests o f t h e Numerical Algorithms, EPA/600/3-85/037, 1J.S. EPA, Research T r i a n g l e Park, NC 27711, 1985, 265 pp. G.Z. Whitten and M.W. Gery, Development o f CBM-X Mechanisms f o r Urban and Regional AQSMs, EPA/600/3-86/012, U.S. EPA, Research T r i a n g l e Park, NC 27711, 1986, 160 pp. W.M. Vaughan, Transport o f P o l l u t a n t s i n Plumes and PEPES, EPA/600/3-85/033, U.S. EPA, Research T r i a n g l e Park, NC 27711, 1985, 60 pp. D.A. Taothman, J.C. Yates and E.J. Sabo, Status Report on t h e Development o f t h e NAPAP Emission Inventory f o r t h e 1980 Base Year and Summary o f P r e l i m i n a r y Data, EPA-600/7-84-091, U.S. EPA, Research T r i a n g l e Park, NC 27711, 1984, 91 pp. J.H. Novak and J.A. Reagan, A Comparison o f N a t u r a l and Man-Made Hydrocarbon Emission I n v e n t o r i e s Necessary f o r Regional Acid Deposition and Oxidant Modeling, 79th Annual Meeting o f t h e APCA, A i r P o l l u t i o n Control Association, Pittsburgh, PA, 1986. R.G. Lamb, Atmos. Environ., 18 (1984) 591-606. R.G. Lamb and S.J. H a t i , J. C l i . Appl. Met., 26 (1987) 837-846.
..
T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implicatwna 0 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
EVALUATION OF OZONE CONTROL STRATEtiIES I N THE NORTHEASTERN REGION
623
OF THE
UNITED STATES N. C. P o s s i e l , *
J. A. T i k v a r t , l J. H. Novak,2 K. L. Schere,2and E. L. M e y e r l
l E n v i ronmental P r o t e c t i o n Agency, Research T r i a n g l e Park, NC
27711 (USA)
ZNational Oceanic and Atmospheric A d m i n i s t r a t i o n on Assignment t o EPA, Research T r i a n g l e Park, NC
27711 (USA)
ABSTRACT
The t r a n s p o r t o f ozone and p r e c u r s o r p o l l u t a n t s o v e r hundreds o f k i l o meters has an i m p o r t a n t impact on a i r q u a l i t y i n t h e N o r t h e a s t e r n U. s. O f p a r t i c u l a r concern i s t h e r e l a t i v e l y c l o s e p r o x i m i t y o f s e v e r a l m a j o r urban areas, j o i n e d w i t h t h e i n f l u e n c e o f l a r g e r u r a l f u e l combustion sources. T h i s paper reviews i n i t i a l a p p l i c a t i o n s o f a r e g i o n a l s c a l e model t o assess t h e e f f e c t o f s e l e c t e d c o n t r o l s t r a t e g i e s f o r r e d u c i n g ozone c o n c e n t r a t i o n s i n t h e N o r t h e a s t r e g i o n , and e s p e c i a l l y i n t h e urban c o r r i d o r . G e n e r a l l y i t i s found t h a t r e d u c i n g emissions o f v o l a t i l e o r g a n i c compounds i s an e f f e c t i v e c o n t r o l measure. The need f o r f u r t h e r j o i n t c o n t r o l s o f v o l a t i l e o r g a n i c compounds and n i t r o g e n o x i d e s i s addressed. INTRODUCTION Ozone and ozone p r e c u r s o r s a r e known t o be t r a n s p o r t e d beyond s o u r c e a r e a s and t o subsequently impact a i r q u a l i t y hundreds o f k i l o m e t e r s downwind.
Such
t r a n s p o r t i s o f p a r t i c u l a r i m p o r t a n c e i n t h e N o r t h e a s t r e g i o n o f t h e U. S. due t o several factors.
The r e g i o n c o n t a i n s f i v e major u r b a n areas i n c l o s e p r o x -
imity: Washington, DC; B a l t i m o r e , MD; P h i l a d e l p h i a , PA; New York, NY and Bost o n , MA.
I n a d d i t i o n , s e v e r a l medium-size c i t i e s and t h e suburban a r e a s s u r -
r o u n d i n g t h e m e t r o p o l i t a n c e n t e r s n e a r l y o v e r l a p t o p r o v i d e an a l m o s t c o n t i n -
uous C o r r i d o r o f sources e m i t t i n g ozone p r e c u r s o r s .
Included a r e s t a t i o n a r y
and m o b i l e sources o f v o l a t i l e o r g a n i c compounds (VOC) and n i t r o g e n o x i d e s (NO,).
Thus, i n t e r u r b a n t r a n s p o r t , t o g e t h e r w i t h c o n t r i b u t i o n s f r o m m a j o r
r u r a l f u e l combustion sources, i s o f concern.
A compounding f a c t o r i s t h e
m e t e o r o l o g i c a l c o n d i t i o n s t h a t e x i s t f r e q u e n t l y i n t h e N o r t h e a s t e r n U. S. d u r i n g t h e summer.
I n p a r t i c u l a r . t h e wind f l o w o f t e n f a v o r s ozone and p r e c u r s o r
t r a n s p o r t between urban areas i n t h e C o r r i d o r and an exchange o f p o l l u t a n t s w i t h other p a r t s o f t h e Northeast.
The r e s u l t may be m u l t i - d a y episodes o f
h i g h ozone c o n c e n t r a t i o n s a l o n g t h e C o r r i d o r and a c r o s s b r o a d areas o f t h e Northeast region ( r e f .
1).
Because o f t h e s p a t i a l s c a l e s i n v o l v e d , c a n d i d a t e p o l l u t i o n c o n t r o l s t r a t e g i e s must be evaluated on a r e g i o n a l s c a l e i n o r d e r t o assess t h e i r o v e r a l l effectiveness.
T h i s r e q u i r e s t h e use o f a complex r e g i o n a l s c a l e photochem-
i c a l model such as t h e EPA Regional Oxidant Model (ROM) which i s now a v a i l a b l e f o r o p e r a t i o n a l use ( r e f s . 2-3).
The purpose o f t h i s paper t h e n i s t o review
some i n i t i a l a p p l i c a t i o n s o f ROM t o assess t h e e f f e c t i v e n e s s o f s e l e c t e d cont r o l s t r a t e g i e s f o r reducing ozone i n t h e C o r r i d o r and i n o t h e r p a r t s o f t h e Northeast.
Thus f a r , a base case w i t h 1980 emissions and t h r e e c o n t r o l s t r a -
t e g i e s have been examined.
NO,
The c o n t r o l s t r a t e g i e s i n c l u d e :
(1) reduction o f
emissions from major f u e l combustion sources i n t h e Northeast r e g i o n ; ( 2 )
r e d u c t i o n o f NOx emissions i n t h e C o r r i d o r from Washington, OC t o Boston, and ( 3 ) r e d u c t i o n of VOC emissions across t h e region.
MA
The need f o r a d d i t i o n a l
j o i n t VOC/NOx c o n t r o l s t r a t e g y assessments i s a l s o discussed.
MODELING APPROACH The Model The ROM i s an episodic, m u l t i l a y e r , E u l e r i a n g r i d model which t r e a t s t h e photochemical f o r m a t i o n o f ozone from VOC and NOx species through t h e Carbon Bond chemical mechanism ( r e f . 4 ) .
It p r o v i d e s a b a s i s t o s i m u l a t e a i r p o l -
l u t a n t c o n c e n t r a t i o n s over a several day/1000 km s c a l e domain and a l s o t o p r o vide county-level spatial resolution.
As shown i n F i g u r e 1, t h i s domain i n -
cludes t h e n o r t h e a s t e r n auadrant o f t h e U.
s.
e x t e n d i n g from Ohio e a s t t o t h e
A t l a n t i c Ocean and from V i r g i n i a n o r t h t o Canada.
The ROM thereby p r o v i d e s
a means f o r understanding t h e r e g i o n a l t r a n s p o r t phenomenon and a i d s i n plann i n g f o r e f f e c t i v e c o n t r o l s t r a t e g i e s t o m i t i g a t e t h e ozone p o l l u t a n t burden. The model i n c l u d e s a 3-D E u l e r i a n framework w i t h 3 1/2 v e r t i c a l l a y e r s ext e n d i n g through t h e boundary l a y e r and t h e capping i n v e r s i o n o r c l o u d l a y e r . Among t h e processes t r e a t e d a r e a d v e c t i v e t r a n s p o r t , photochemistry,
nighttime
wind shear and t u r b u l e n c e episodes, cumulus c l o u d e f f e c t s on v e r t i c a l mass t r a n s p o r t and photochemical r e a c t i o n r a t e s , t e r r a i n i n f l u e n c e s , b i o g e n i c and anthropogenic emissions, and removal by d e p o s i t i o n .
A shallow diagnostic sur-
face l a y e r i s designed t o account f o r t h e s u b - g r i d s c a l e chemical e f f e c t s o f a heterogeneous emissions d i s t r i b u t i o n .
H o r i z o n t a l r e s o l u t i o n o f emissions, met-
e o r o l o g i c a l phenomena and p r e d i c t e d p o l l u t a n t species i s a g r i d t h a t i s 1/6" l a t i t u d e x 1/4" l o n g i t u d e (
,.. 18.5
x 18.5 km g r i d s i z e ) .
Data Bases The emissions i n v e n t o r y used i n t h e present a p p l i c a t i o n s i s based on 1980 emissions f o r VOC, NO,,
and carbon monoxide ( C O ) as compiled under t h e N a t i o n a l
625
F i g . 1. Northeast domain o f the Regional Oxidant Model.
Acid P r e c i p i t a t i o n Assessment Program ( r e f . 5).
Emissions are based on county-
wide estimates which are then a l l o c a t e d t o t h e g r i d s used i n ROM. emissions f o r hydrocarbons are a l s o included ( r e f . 6).
Biogenic
The i n v e n t o r y encom-
passes t h e e n t i r e Northeastern U. S. ROM domain, i n c l u d i n g p o r t i o n s o f Canada. The most e f f i c i e n t use o f ROM i s t o operate i t w i t h multi-day meteorologi c a l scenarios representative o f those events t h a t l e a d t o high p o l l u t a n t concentrations.
Based on previous studies o f meteorological conditions f o r t h e
Corridor, two scenarios are considered from 1980: and a 10-day period i n August.
a 14-day p e r i o d i n J u l y
During t h e J u l y scenario t h e predominant met-
eorological regimes favor t r a n s p o r t from t h e southwest and west t o t h e n o r t h east and east.
On many o f t h e days southwest f l o w occurs along t h e C o r r i d o r
w i t h i n the lower p a r t o f t h e daytime mixed l a y e r and i n t h e nocturnal boundary layer.
A l o f t , a more westerly component p r e v a i l s capable o f t r a n s p o r t i n g p o l -
l u t a n t s from source areas i n t h e western p a r t o f t h e domain i n t o t h e Corridor. I n contrast t h e August scenario i s characterized by more stagnant conditions w i t h a northeast t o e a s t e r l y wind f l o w on several days.
Both scenarios c o n t a i n
multi-day episodes favorable f o r ozone formation w i t h measured maximum daytime 1-hour concentrations exceeding C.15 ppm i n areas along t h e Corridor, as w e l l as near major c i t i e s i n other p a r t s o f t h e region.
626 Limitations I n t e r p r e t a t i o n o f model r e s u l t s should be l i m i t e d t o a q u a l i t a t i v e assessment d e s p i t e t h e appearance o f q u a n t i t a t i v e r e s u l t s . u s i n g t h i s model q u a n t i t a t i v e l y are:
Among t h e l i m i t a t i o n s i n
t h e u n c e r t a i n t i e s and known d e f i c i e n c i e s
i n t h e 1980 i n v e n t o r y used i n t h e model; t h e l a c k o f a complete v a l i d a t i o n o f t h e model; t h e unknown biases i n t r o d u c e d i n assessing p o i n t source dominated s t r a t e g i e s w i t h a r e g i o n a l s c a l e model; t h e adequacy o f a l a r g e g r i d s i z e t o c h a r a c t e r i z e g r a d i e n t s i n p o l l u t a n t concentrations t y p i c a l o f ozone plumes; t h e representativeness o f meteorological scenarios o f t y p i c a l worst-case cond i t i o n s ; and t h e i n h e r e n t u n c e r t a i n t y i n i n i t i a l a p p l i c a t i o n s o f a model. These l i m i t a t i o n s must be k e p t i n mind i n d e s c r i b i n g and u s i n g t h e ROM r e s u l t s .
DESCRIPTION OF STRATEGIES F o r t h i s a n a l y s i s t h e e f f e c t o f several c o n t r o l s t r a t e g i e s have been tested.
The s t r a t e g i e s i n c l u d e independent c o n t r o l s f o r VOC and NO,
within
t h e Northeast region, as w e l l as t h e c o n t r o l o f major i s o l a t e d sources versus c o n t r o l i n t h e urban C o r r i d o r .
The s t r a t e g i e s , which a r e discussed below,
a r e evaluated t o assess (1) t h e r e l a t i v e decrease/increase o f ozone concent r a t i o n s when compared t o t h e 1980 base case and ( 2 ) t h e magnitude and s p a t i a l d i s t r i b u t i o n o f concentrations as they r e l a t e t o t h e N a t i o n a l Ambient Air Q u a l i t y Standard (NAAQS) f o r ozone ( t h e l e v e l o f t h e NAAQS i s a 0.12 ppm, 1-hour value). NOy S t r a t e g y 1
--
Power P l a n t Control A major c o n t r i b u t i o n t o NO, emissions i n t h e Northeast region i s from
c o a l - f i r e d power p l a n t s .
These emission sources a r e d i s t r i b u t e d across t h e
region, b u t about 80 percent o f t h e power p l a n t NO, western p o r t i o n .
emissions emanate from t h e
A s t r a t e g y which c o n t r o l s these sources may p r o v i d e u s e f u l
i n f o r m a t i o n on t h e e x t e n t t o which u t i l i t y NO,
c o n t r o l can be expected t o i n -
fluence areas above t h e ozone NAAQS.
Thus a s t r a t e g y i s considered t h a t i m -
poses s t r i n g e n t , b u t reasonable, NO,
c o n t r o l s on a1 1 power p l a n t s throughout
t h e region. 0.4
T h i s s t r a t e g y v a r i e s c o n t r o l by b o i l e r t y p e and s i z e as f o l l o w s :
lb/MM BTU NO,
emissions l i m i t on t a n g e n t i a l b o i l e r s , 0.5 lb/MM BTU l i m i t
on w a l l - f i r e d b o i l e r s , and 1.0 lb/MM BTU l i m i t on cyclone b o i l e r s . t h i s r e s u l t s i n a 39 percent r e d u c t i o n i n NO, region.
Overall
emissions f r o m u t i l i t i e s i n t h e
This amounts t o an 11 percent r e d u c t i o n i n region-wide t o t a l NOx emis-
sions considering a l l source categories. NOy S t r a t e g y 2
--
Northeast C o r r i d o r / D e t r o i t Control
Since i t i s expected t h a t a major cause o f h i g h ozone concentrations
i s due t o emissions from t h e C o r r i d o r , a second NO,
c o n t r o l s t r a t e g y i s con-
627 s i d e r e d t o examine a more i n t e n s i v e r e d u c t i o n i n NOx emissions c o n f i n e d t o t h e C o r r i d o r i t s e l f ; a g a i n t h e r e d u c t i o n i s t o be s t r i n g e n t , b u t reasonable. I n addition,
s i m i l a r c o n t r o l s are applied t o t h e D e t r o i t area t o determine
t h e e f f e c t s o f such c o n t r o l s i n a more i s o l a t e d u r b a n area, i n c o n t r a s t t o t h e Corridor.
The s t r a t e g y c o n s i s t s o f c o n t r o l on j u s t t h o s e u t i l i t i e s i n
t h e C o r r i d o r and i n D e t r o i t .
Also included are reductions i n mobile source
emissions and reasonable c o n t r o l s on i n d u s t r i a l b o i l e r s i n t h e s e t w o areas. The u t i l i t y emissions a r e c o n t r o l l e d b y l i m i t s i d e n t i c a l t o t h o s e i n S t r a t e g y 1.
F o r m o b i l e sources, a NOx emissions r e d u c t i o n o f 32 p e r c e n t i s e s t i -
mated u s i n g t h e MOBILE3 model t o r e f l e c t t h e n a t i o n - w i d e change i n m o b i l e source emissions between 1980 and 1995 r e s u l t i n g f r o m t h e c u r r e n t F e d e r a l Motor V e h i c l e C o n t r o l Program (FMVCP) standards.
Industrial boilers of at
l e a s t 100 t o n s p e r y e a r were c o n t r o l l e d by b o i l e r t y p e depending on a v a i l a b l e technologies.
Most b o i l e r s were c o n t r o l l e d by 50 p e r c e n t .
The t o t a l e f f e c t
o f c o n t r o l l i n g t h e s e t h r e e source c a t e g o r i e s i s a 22 p e r c e n t r e d u c t i o n o f NOx emissions i n t h e C o r r i d o r and a p p r o x i m a t e l y a 10 p e r c e n t r e d u c t i o n o f t o t a l NOx emissions i n t h e region.
VOC S t r a t e g y
--
Region-wide C o n t r o l
I t i s w i d e l y e s t a b l i s h e d t h a t VOC e m i s s i o n s have a m a j o r impact on ozone
concentrations ( r e f . 7).
Thus t o assess t h e impact o f e x i s t i n g VOC c o n t r o l
r e g u l a t i o n s on ozone c o n c e n t r a t i o n s i n areas above t h e NAAQS, p a r t i c u l a r l y those i n t h e Northeast Corridor, a s t r a t e g y f o r s p e c i f i c c o n t r o l s w i t h i n t h e C o r r i d o r and more general c o n t r o l s t h r o u g h o u t t h e N o r t h e a s t r e g i o n i s considered.
The VOC c o n t r o l s t r a t e g y reduces base case VOC emissions t o r e -
f l e c t a p p r o x i m a t e l y t h e e f f e c t s o f b o t h emissions growth t o 1987 and cont r o l s mandated p r i o r t o t h e r e q u i r e m e n t s o f t h e c u r r e n t c o n t r o l programs. I n a d d i t i o n , t h i s s t r a t e g y i n c l u d e s VOC e m i s s i o n r e d u c t i o n s due t o FMVCP f r o m 1980 t o 1995.
F o r areas c u r r e n t l y exceeding t h e ozone NAAQS, c o u n t y -
wide c o n t r o l s range f r o m 27 t o 7U percent.
F o r a r e a s c u r r e n t l y below t h e
NAAQS a 30 p e r c e n t VOC emissions r e d u c t i o n i s a p p l i e d .
This strategy
t r a n s l a t e s t o a 5 0 p e r c e n t r e d u c t i o n o f VOC e m i s s i o n s i n t h e C o r r i d o r and a
4 2 p e r c e n t r e d u c t i o n i n r e g i o n - w i d e VOC emissions.
No change i n NOx emis-
s i o n s i s considered. RESULTS Using t h e model and d a t a bases d i s c u s s e d above, r e g i o n - w i d e ozone concent r a t i o n s a s s o c i a t e d w i t h t h e base case 1980 emissions and t h e t h r e e c o n t r o l s t r a t e g i e s have been s i m u l a t e d by ROM.
The r e s u l t s a r e d i s c u s s e d below.
628 Base Case ROM p r e d i c t i o n s o f ozone c o n c e n t r a t i o n s f o r base case emissions i n d i c a t e
l a r g e areas above t h e ozone NAAQS, p r i m a r i l y near and downwind o f major urban areas f o r b o t h scenarios.
F o r example, as shown i n F i g u r e 2 a s i g n i f i c a n t area
o f h i g h ozone c o n c e n t r a t i o n s i s p r e d i c t e d a l o n g t h e C o r r i d o r i n t h e J u l y scenario, e s p e c i a l l y from New York t o Boston.
Fig. 2. i4aximurn 1-hour ozone c o n c e n t r a t i o n s (ppm) p r e d i c t e d d u r i n g t h e J u l y 1980 episode.
NOr C o n t r o l o f Power P l a n t s F o r t h e f i r s t NOx s t r a t e g y , c o n t r o l o f power p l a n t s , t h e r e a r e b o t h small r e d u c t i o n s o f ozone peaks i n i s o l a t e d r u r a l areas and moderate increases i n peaks i n o t h e r areas.
The changes i n 1-hour maximum ozone c o n c e n t r a t i o n s
range from approximately a 20 percent i n c r e a s e t o a 10 percent decrease. For example, F i g u r e 3 shows t h e percent change i n maximum 1-hour concentrat i o n s d u r i n g t h e J u l y scenario.
The f i g u r e i n d i c a t e s t h a t t h i s s t r a t e g y
had l i t t l e e f f e c t on peak c o n c e n t r a t i o n s i n most p a r t s o f t h e region, i n cluding the Corridor.
However, ozone i s reduced i n several r u r a l areas i n
Ohio and West V i r g i n i a where l e v e l s i n t h e base case a r e low.
I n contrast,
r a t h e r l a r g e increases a r e p r e d i c t e d i n p o r t i o n s o f c e n t r a l Pennsylvania and i n t h e v i c i n i t y o f P i t t s b u r g h .
I n t h e l a t t e r area, base case p r e d i c -
t i o n s a r e a l r e a d y above 0.12 ppm.
S i m i l a r mixed r e s u l t s a r e found f o r t h e
August scenari 0.
629
Fig. 3. The percent change i n maximum 1-hour ozone c o n c e n t r a t i o n s between t h e base case and NOx power p l a n t s t r a t e g y f o r t h e J u l y 1980 episode.
NO, Control i n t h e Northeast C o r r i d o r / D e t r o i t For t h e second NOx s t r a t e g y , c o n t r o l i n t h e C o r r i d o r and D e t r o i t , t h e r e a r e (1) small reductions o f ozone peaks downwind o f urban areas and ( 2 ) modera t e increases i n peaks near several urban areas.
Large p o r t i o n s o f t h e region, p a r t i c u l a r l y i n t h e C o r r i d o r , remain above t h e NAAQS. The e f f e c t s range from
approximately a 35 percent increase i n I - h o u r maximum ozone c o n c e n t r a t i o n s t o about a 15 percent decrease.
I n t h e J u l y scenario, as shown i n F i g u r e 4, maxi-
mum 1-hour concentrations decrease i n suburban/rural areas between t h e major C o r r i d o r c i t i e s and t o t h e n o r t h e a s t (downwind) o f D e t r o i t as w e l l as over t h e A t l a n t i c Ocean.
Ozone increases, however, i n h i g h l y populated areas, c l o s e - i n
t o New York City, P h i l a d e l p h i a , and D e t r o i t .
S i m i l a r mixed r e s u l t s a r e found
f o r t h e August scenario, although t h e changes a r e i n o t h e r l o c a t i o n s due t o d i f f e r e n c e s i n f l o w p a t t e r n s between t h e two scenarios. VOC Control Regi on-wi de
F o r t h e region-wide VOC s t r a t e g y t h e r e i s widespread r e d u c t i o n i n ozone concentrations w i t h (1) l a r g e d e c l i n e s i n peak values near and downwind of c i t i e s and ( 2 ) no estimated increase i n peak ozone anywhere i n t h e region. Although t h e s i z e o f t h e areas above t h e NAAQS has decreased, t h e r e a r e s t i l l l a r g e areas w i t h I - h o u r maximum c o n c e n t r a t i o n s g r e a t e r t h a n 0.12 ppm.
The
630
Fig. 4. The percent change i n maximum 1-hour ozone concentrations between the base case and NOx C o r r i d o r / D e t r o i t s t r a t e g y f o r the J u l y 1980 episode. e f f e c t s range from a n e g l i g i b l e change t o about a 40 percent decrease i n 1-hour maximum ozone concentrations. As shown i n Figure 5, t h e area o f subs t a n t i v e decrease (greater than 10 percent) i s spread throughout and covers much o f the Corridor, e s p e c i a l l y downwind o f l a r g e urban areas. This i n cludes much o f t h e ocean area considered i n t h e regional g r i d .
Rural areas
f a r beyond major urban/point sources and those p o r t i o n s o f t h e C o r r i d o r immediately adjacent t o upwind r u r a l areas tend t o show n e g l i g i b l e impact. Also, i t i s apparent t h a t f o r many areas p r e v i o u s l y above t h e NAAQS, ozone l e v e l s have improved t o become lower than t h e standard, p r i m a r i l y i n areas on t h e periphery o f t h e Corridor. A s i m i l a r r e s u l t i s obtained f o r t h e August scenario. VOC/NOx STRATEGIES
The above a n a l y s i s i n d i c a t e s t h a t c o n t r o l o f VOC alone may be r e l a t i v e l y e f f e c t i v e i n reducing ozone concentrations across t h e Northeast region. However, t h e r e s u l t s suggest t h a t NOx c o n t r o l alone could produce mixed e f f e c t s , w i t h increases i n ozone concentrations apparently g r e a t e r i n magnitude t h a n any decreases. I n f a c t , t h e r e i s some evidence t h a t i s o l a t e d exceedances could be created w i t h t h e NOx s t r a t e g i e s where none p r e v i o u s l y existed. However, one should n o t i n f e r from t h i s t h e r e l a t i v e m e r i t s o f j o i n t l y c o n t r o l l i n g these two precursor p o l l u t a n t s . There i s evidence t h a t j o i n t c o n t r o l o f both
63 1
Fig. 5. The percent change i n maximum I - h o u r ozone c o n c e n t r a t i o n s between the base case and VOC s t r a t e g y f o r t h e J u l y 1980 episode. p o l l u t a n t s c o u l d o p t i m i z e t h e r e d u c t i o n o f ozone concentrations w h i l e m i n i m i z i n g t h e r e q u i r e d c o n t r o l o f e i t h e r VOC o r NO.,
The need f o r a v a r i e t y o f
c o n t r o l l e v e l s f o r b o t h p o l l u t a n t s and t h e s p a t i a l d i s t r i b u t i o n o f such cont r o l s i s evident.
It i s expected t h a t a range o f j o i n t VOC/NOx c o n t r o l s t r a -
t e g i e s w i l l be considered as p a r t o f f u t u r e EPA model a p p l i c a t i o n s . SUMMARY
This study used a r e g i o n a l s c a l e model t o e v a l u a t e t h e s e n s i t i v i t y o f p r e d i c t e d ozone concentrations t o components o f p o t e n t i a l c o n t r o l a l t e r n a t i v e s i n t h e Northeast U.
S.
The area o f ozone NAAQS exceedance was s i m u l a t e d w i t h
a 1980 emissions base case and then t h e e f f e c t i v e n e s s o f s e l e c t e d c o n t r o l s t r a t e g i e s f o r p r e c u r s o r p o l l u t a n t s was evaluated.
I n general, i t was found t h a t
region-wide c o n t r o l o f VOC was e f f e c t i v e i n reducing ozone c o n c e n t r a t i o n s by up t o 40 percent, w h i l e a l s o reducing t h e area o f c o n c e n t r a t i o n s g r e a t e r t h a n t h e
NAAQS.
However, c o n t r o l o f NOx from major r u r a l p o i n t sources o r from m u l t i p l e
sources i n t h e C o r r i d o r produced a range o f r e s u l t s i n c l u d i n g increases up t o 35 percent and decreases t o 15 percent i n 1-hour ozone concentrations.
I n some
cases exceedances were p r e d i c t e d f o l l o w i n g NOx c o n t r o l where none were p r e d i c t e d i n t h e base case.
The need f o r j o i n t VOC/NOx c o n t r o l s t r a t e g y assessments
t o more r e a l i s t i c a l l y examine t h e l e v e l o f c o n t r o l f o r a i r q u a l i t y improvement was made c l e a r .
632 REFERENCES
N. C. Possiel, et. al., Northeast C o r r i d o r Regional Modeling P r o j e c t : Ozone and Precursor Transport i n New York City and Boston During t h e 1980 F i e l d Program, EPA-450/4-84-011, Research T r i a n g l e Park, NC, 1984. R. 6. Lamb, A Regional Scale (1000 KM) Model o f Photochemcial A i r PolResearch l u t i o n : P a r t l. T h e o r e t i c a l Formulation, EPA-600/3-83-025, T r i a n g l e Park, NC, 1983. R. 6. Lamb, A Regional Scale (1000 KM) Model o f Photochemical A i r Poll u t i o n : P a r t 2. I n p u t Processor Network Design, EPA-600/3-84-085, Research T r i a n g l e Park, NC, 1984. M. W. Gery. et. al., Development and T e s t i n g o f t h e CBM-IV For Urban and Regional Modeling, EPA P r o j e c t Report, Research T r i a n g l e Park, NC 1988. J. K. Wagner, et. al., Development o f t h e 1980 NAPAP Emissions Invent o r y , EPA-600/7-86-057a. Research T r i a n g l e Park, NC, 1986. J. H. Novak and J. A. Reagan, A Comparison o f Natural and Man-made Hydrocarbon Emission I n v e n t o r i e s Necessary f o r Regional A c i d Deposit i o n and Oxidant Modeling, Paper Presented a t t h e 79th APCA Annual Meeting, Minneapolis, MN, 1986. Envi ronmental P r o t e c t i o n Agency, A i r Q u a l i t y C r i t e r i a , EPA-600/8-84020aF, Research T r i a n g l e Park, NC, 1986.
T. Schneider et aL (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishera B.V., Amsterdam - Printed in The Netherlands
633
PHOTOCHEMICAL O X I D A N T MODEL APPLICATION WITHIN THE FRAMEWORK OF CONTROL S T R A T E G Y DEVELOPMENT I N THE DUTCH/GERMAN PROGRAMME PHOXA
J. P a n k r a t h Umweltbundesamt,
B i s m a r c k p l a t z 1, D-1000 B e r l i n 3 3
ABSTRACT The D u t c h - G e r m a n Programme PHOXA ( P h o t o c h e m i c a l O x i d a n t a n d A c i d D e p o s i t i o n Model A p p l i c a t i o n i n t h e Framework o f C o n t r o l S t r a t e g y Development) i s concerned w i t h p h o t o c h e m i c a l o x i d a n t s and t h e d e p o s i t i o n o f a c i d i f y i n g species. E f f e c t i v e measures t o reduce e l e v a t e d ozone c o n c e n t r a t i o n s i n Europe need t r a n s b o u n dary s t r a t e g i e s ; i t s impact can o n l y be e v a l u a t e d by a p p l y i n g r e g i o n a l d i s p e r s i o n models which p r o v i d e s u b s t a n t i a l s u p p o r t t o the transboundary c o n t r o l strategies. The o b j e c t i v e o f PHOXA c o n s i s t s i n t h e p r e p a r a t i o n o f a n i n s t r u m e n t a t i o n i n o r d e r t o e v a l u a t e abatement s t r a t e g i e s f o r photoc h e m i c a l o x i d a n t s and a c i d i f y i n g p o l l u t a n t s w i t h r e g a r d t o t h e i r European-wide e f f e c t on a i r q u a l i t y and d e p o s i t i o n . F o r t h e t r e a t ment o f p h o t o c h e m i c a l o x i d a n t s t h e R T M - I 1 1 m o d e l was u s e d t o i n v e s t i g a t e e p i s o d e s o f h i g h ozone c o n c e n t r a t i o n s . The e v a l u a t i o n o f t h e f i n d i n g s shows t h a t t h e l o n g r a n g e d i s p e r s i o n model R I M - I 1 1 p r e d i c t s t e m p o r a l and s p a t i a l p a t t e r n s o f ozone r e a s o n a b l y w e l l i n r u r a l a r e a s b u t u n d e r p r e d i c t s t h e h i g h e s t o b s e r v e d h o u r l y o z o n e v a l u e s i n m o r e i n d u s t r i a l i z e d a r e a s . The e v a l u a t i o n o f some b r o a d e m i s s i o n s c e n a r i o s f o r s e l e c t e d p h o t o chemical episodes supports t h e f a c t t h a t t h e RTM-I11 model responds i n a n e x p l a i n a b l e way t o c h a n g e s i n t h e e m i s s i o n i n p u t .
INTRODUCTION The D u t c h - G e r m a n Programme PHOXA ( P h o t o c h e m i c a l O x i d a n t a n d A c i d D e p o s i t i o n Model A p p l i c a t i o n w i t h i n t h e Framework o f C o n t r o l S t r a t e g y D e v e l o p m e n t ) w h i c h s t a r t e d i n 1984,
i s designed t o apply
s i m p l e a n d c o m p l e x d i s p e r s i o n m o d e l s o n t h e l a r g e s c a l e ( r e f 1). The s t a r t i n g - p o i n t
f o r c a r r y i n g o u t t h e p r o g r a m m e P H D X A was
t h e nowadays g e n e r a l l y acknowledged f a c t t h a t a i r p o l l u t a n t s c o u l d be t r a n s p o r t e d over l a r g e distances;
therefore the region o f im-
pact can be hundreds o f k i l o m e t e r s remote from t h e r e g i o n o f corresponding emissions. A l s o g e n e r a l l y acknowledged i s t h e f a c t t h a t d u r i n g atmospheric t r a n s p o r t p h y s i c a l and c h e s i c a l r e a c t i o n s o c c u r p r o d u c i n g s p e c i e s
634
and a c i d s w h i c h a r e d i s c u s s e d i n c o n t r i b u t i n g t o t h e l a r g e s c a l e d e t e r i o r a t i o n e f f e c t s i n e c o s y s t e m s o f E u r o p e and N o r t h A m e r i c a . I n s o f a r as b o t h groups o f s p e c i e s a r e p a r t i c i p a t i n g i n t h e l o n g r a n g e t r a n s p o r t and a r e p r o d u c e d f r o m t h e i r p r e c u r s o r s t h e r e i s t h e n e c e s s a r y consequence:
A reduction o f t h e i r concentration
and d e p o s i t i o n c a n be a c h i e v e d o n l y b y a E u r o p e a n w i d e r e d u c t i o n o f t h e i r precursors. W i t h r e g a r d t o t h e p h o t o o x i d a n t problem t h e l a r g e s c a l e emiss i o n r e d u c t i o n o f t h e main p r e c u r s o r s , v o l a t i l e o r g a n i c compounds ( V O C ) ,
n i t r o g e n o x i d e s (NOx) and
i s needed.
The o n l y p o s s i b i l i t y
t o p u t s u c h a b a t e m e n t d e c i s i o n s on a q u a n t i t a t i v e and c o n t r o l l e d b a s i s i s t h e a p p l i c a t i o n o f d i s p e r s i o n models ( r e f 2 ) . I n t h i s context short-term necessary.
as w e l l as l o n g - t e r m models a r e
I n t h e f o l l o w i n g t h e f o c u s i s on e p i s o d i c s i t u a t i o n s
i n t h e atmospheric boundary l a y e r ;
corresponding long-range d i s -
p e r s i o n m o d e l s f o r t h e a p p l i c a t i o n i n P H O X A a r e summarised i n fig.
1.
1
[EPISODIC MODELS
LpiGGG-1
j
EULERIAN
II
i n co-oDeration w i t h
receptor-oriented simple meteorology complex chemistry
i
/ THD Model
RTM-I11 Model
3 dim., m u l t i l a y e r simple meteorology l i n e a r chemistry SOx’ NOx
3 dim.,
3 1/2 l a y e r simple meteorology complex gas-phase chemistry
I
ADOM/TADAP Model
3 dim.,
multilayer complex meteorology complex gas- and aqueous-phase
F i g . 1 E p i s o d i c 1o n g - r a n g e t r a n s p o r t m o d e l s f o r a p p l i c a t i o n i n PHOXA. The R T M - I 1 I m o d e l i s e s p e c i a l l y d e s i g n e d f o r t h e s i m u l a t i o n o f p h o t o o x i d a n t s episodes i n t h e atmospheric boundary l a y e r . One o b j e c t i v e o f t h e PHOXA programme i s t o p r o v i d e a t o o l s u i t a b l e f o r e v a l u a t i n g abatement s t r a t e g i e s f o r p h o t o c h e m i c a l o x i d a n t s . T ak i n g i n t o a ccount t h e European-wide
aspect o f t h e formation
o f photooxidants a close co-operating
w i t h t h e ECE programme EMEP
has b e e n e s t a b l i s h e d .
A c l o s e c o - o p e r a t i o n w i t h EEC and OECD h a s
been i n i t i a t e d a l r e a d y i n 1985,
635
P H O T O O X I O A N T E P I S O D E S I N THE BOUNDARY LAYER M o d e l c a l c u l a t i o n s i n t h e PHOXA f r a m e w o r k were a c c o m p l i s h e d f o r s e l e c t e d episodes.
The s e l e c t i o n f o r t h e a d e q u a t e m o d e l t o
b e a p p l i e d i n E u r o p e was made f o r t h e R e g i o n a l T r a n s p o r t M o d e l
I11 (RTM-111) corporation.
w h i c h h a d been d e v e l o p e d by System A p p l i c a t i o n I n -
PHOXA came t o t h i s d e c i s i o n b y c o n s i d e r i n g t h e f i n d i n g s
o f t h e US-EPA/OECD
I n t e r n a t i o n a l C o n f e r e n c e on Long Range T r a n s -
p o r t M o d e l s f o r P h o t o c h e m i c a l O x i d a n t s and t h e i r P r e c u r s o r s ( r e f 3 ) . According t o c e r t a i n c r i t e r i a d e f i n e d a t t h a t conference t h e
R T M - I 1 1 m o d e l was a t t h a t t i m e t h e o n l y E u l e r i a n - t y p e m o d e l b o t h f u l l y o p e r a t i o n a l and a p t f o r c o n t r o l s t r a t e g y d e v e l o p m e n t . The R T M - I 1 1
model was t h e n i n s t a l l e d i n P H O X A a s a s u b s t i t u t e
o f r e g i o n a l t r a n s p o r t models s p e c i f i c a l l y d e v e l o p e d as a t o o l f o r i n v e s t i g a t i n g t h e p e r f o r m a n c e o f d i s p e r s i o n models i n c a r r y i n g o u t s c e n a r i o c a l c u l a t i o n s t o be u s e d i n e m i s s i o n a b a t e m e n t s t r a tegies. To-day able,
f u r t h e r d e v e l o p e d and y e t o p e r a t i o n a l m o d e l s a r e a v a i l -
f o r i n s t a n c e t h e ADOM/TADAP
m o d e l o f t h e German-Canadian
c o - o p e r a t i o n and t h e R A D M model o f t h e U S .
PHOXA t h e ADOM/TADAP
I n t h e framework o f
model i s a t p r e s e n t i n s t a l l e d f o r t h e eva-
luation o f acid deposition;
i n t h e long term i t i s planned t o
u s e i t f o r t h e p h o t o o x i d a n t p r o b l e m as w e l l . I n t h e framework o f PHOXA, p e r s i o n model R T M - I 1 1
t h e long-range
photochemical d i s -
was used t o s i m u l a t e t h e f o l l o w i n g p h o t o -
chemical o x i d a n t episodes: episode
I:J u l y 22
episode
11: May 29
episode
111: June 3
-
-
26,
1980
June 2, 6,
1982
1982
The most i m p o r t a n t c r i t e r i a f o r t h e e p i s o d e s e l e c t i o n h a v e been : ( i ) t h e h o u r l y ozone c o n c e n t r a t i o n s must b e s u f f i c i e n t l y h i g h (more t h a n 80 ppb 03) on l a r g e g e o g r a p h i c a l a r e a s ,
at least i n
t h e r e c e p t o r a r e a s ( t h e F e d e r a l R e p u b l i c o f Germany and t h e N e t h e r lands), ( i i ) t h e h o u r l y ozone c o n c e n t r a t i o n s s h o u l d s t a y h i g h f o r some c o n s e c u t i v e days.
636 The t h r e e e p i s o d e s h a v e b e e n s e l e c t e d o u t o f a l a r g e n u m b e r o f p o s s i b l e c a n d i d a t e s i n s u c h a manner a s t o c o v e r r e a s o n a b l y w e l l s i t u a t i o n s r e p r e s e n t a t i v e f o r photoxidant episodes. I was d e f i n e d b y P H O X A ,
Episode
e p i s o d e I 1 a n d I11 were s e l e c t e d b y PHOXA
i n c o o p e r a t i o n w i t h t h e EEC a n d t h e OECD,
D E S C R I P T I O N OF THE R T M - I 1 1
respectively'.
MODEL
W i t h i n t h e PHOXA programme a model a r e a w i t h t h e f o l l o w i n g
l o o w e s t t o 24O e s t a n d The e n c l o s e d a r e a h a s a n e x t e n s i o n o f 3.13.10 6
b o r d e r l i n e s has been t a k e n a s a b a s i s : 47,5O
t o 60° n o r t h .
km2 a n d c o v e r s m o s t o f t h e i n d u s t r i a l i z e d r e g i o n s i n E u r o p e . The g r i d u s e d i n t h e m o d e l l i n g s t u d i e s h a s s i z e s o f 6 0 ' t u d e and 3 0 '
latitude,
longi-
corresponding t o g r i d c e l l s o f approxima-
t e l y 5 0 km x 5 0 km. The R T M - I 1 1 m o d e l ,
adapted f o r t h e a p p l i c a t i o n i n PHOXA ( r e f
4 ) i s a E u l e r i a n g r i d model based o n t h e n u m e r i c a l s o l u t i o n o f a 3 1/2
l a y e r multispecies d i f f u s i o n equation.
The v e r t i c a l l a y e r s
are :
-
a s u r f a c e l a y e r i m m e d i a t e l y above t h e ground;
-
a mixed l a y e r up t o t h e base o f t h e t e m p e r a t u r e i n v e r s i o n , varies temporally
-
which
and s p a t i a l l y ;
a l o w e r i n v e r s i o n l a y e r i m m e d i a t e l y above t h e b a s e o f t h e temperature inversion;
-
an u p p e r i n v e r s i o n l a y e r above up t o t h e t o p o f t h e m o d e l l i n g region, The m o d e l c o n t a i n s a m o s t r e c e n t v e r s i o n o f t h e C a r b o n - B o n d
Mechanism
-
t h e CMB-IV
-, w h i c h
c o n s i s t s o f 70 r e a c t i o n s d e s c r i -
b i n g t h e chemical k i n e t i c s o f 17 t r a n s p o r t e d species, 7 d i f f e r e n t c l a s s e s o f VOC. CBM-IV
hereby u s i n g
The p h o t o l y s i s r a t e c o n s t a n t s o f t h e
v a r y d i u r n a l l y and s p a t i a l l y a s a f u n c t i o n o f s o l a r z e n i t h
a n g l e and c l o u d c o v e r .
I N P U T DATA BASE P r e r e q u i s i t e t o t h e a p p l i c a t i o n o f d i s p e r s i o n models i s t h e a v a i l a b i l i t y o f s u i t a b l e d a t a bases.
For t h e RTM-I11
model t h e
f o l l o w i n g i n p u t data p r e p a r a t i o n i s necessary: (i) E m i s s i o n i n p u t d a t a a r e p o i n t and a r e a s o u r c e s i n 3 h o u r l y
t i m e r e s o l u t i o n f o r t h e s p e c i e s NO, classes (ethene,
olefins,
paraffins,
NO2,
SO2, SO4, C O a n d 7 V O C -
aldehydes,
formaldehyde,
xy-
637 lenes, toluenes),
which a r e adapted t o t h e CBM-IV
mechanism,
in
each h o r i z o n t a l g r i d ; ( i i ) meteorological i n p u t data are layer-averaged data i n 3 h o u r l y time r e s o l u t i o n f o r h o r i z o n t a l wind v e l o c i t y , mixing height,
temperature
r a i n f a l l and c l o u d c o v e r i n each h o r i z o n t a l g r i d ;
(iii) l a n d use d a t a a r e c a t e g o r i s e d i n 1 0 c l a s s e s ( w a t e r ,
land,
grassland,
permanent c r o p ,
coniferous forests,
b u i l t - u p areas,
mixed f o r e s t s ,
bare s o i l ,
crop-
deciduous f o r e s t s ,
wetland) f o r t h e
c a l c u l a t i o n o f d r y d e p o s i t i o n r a t e s i n each h o r i z o n t a l g r i d ; ( i v ) a i r q u a l i t y d a t a a r e n e c e s s a r y t o d e r i v e i n i t i a l and boundary c o n d i t i o n s . Tab,
1 shows t h e t o t a l y e a r l y e m i s s i o n s o f SO
X,
NOx,
VOC a n d
C O i n 1980 and t h e c o n t r i b u t i o n o f d i f f e r e n t s o u r c e c a t e g o r i e s
t o t h e s e t o t a l e m i s s i o n s i n t h e PHOXA r e g i o n . TABLE 1 P H O X A e m i s s i o n d a t a b a s e 1980. C o n t r i b u t i o n o f d i f f e r e n t s o u r c e c a t e g o r i e s t o t o t a l e m i s s i o n s i n t h e PHOXA r e g i o n .
Source ~
AnthroDoaenic
30.0
12.5
7.6
47.4
T h e p r e p a r a t i o n o f t h e s p e c i f i e d d a t a b a s e s was a m a i n t a s k
f o r t h e PHOXA programme. d a t a base,
The s e t t i n g - u p o f t h e PHOXA e m i s s i o n
i n c l u d i n g programmes t o d e r i v e e p i s o d i c e m i s s i o n f i l e s ,
a l l o w e d f o r t h e f i r s t t i m e t h e u s e o f complex d i s p e r s i o n m o d e l s f o r p l a n n i n g p u r p o s e s i n Europe.
The P H O X A e m i s s i o n d a t a b a s e
i s t h e o n l y d a t a base i n E u r o p e w h i c h h a s a r e l a t i v e l y f i n e r e s o l u t i o n o f s o u r c e s and s o u r c e c a t e g o r i e s f o r a v a r i e t y o f s p e c i e s
630
b e i n g p r e r e q u i s i t e t o t h e development o f e m i s s i o n abatement scenarios.
T h i s p o i n t i s o f u t m o s t i m p o r t a n c e i n so f a r a s no model
is a b l e t o p r o d u c e r e l i a b l e r e s u l t s when t h e n e c e s s a r y i n p u t d a t a a r e n o t a v a i l a b l e or a r e a v a i l a b l e o n l y w i t h i n s u f f i c i e n t q u a l i t y . The m o d e l l i n g o f p h o t o o x i d a n t s i s i n t h i s r e s p e c t p a r t i c u l a r l y s u s c e p t i b l e t o t h e q u a l i t y o f t h e used p r e c u r s o r emissions and t h e s p l i t t i n g o f VOC i n r e a c t i v i t y c l a s s e s . MODEL VALIDATION The t h r e e s e l e c t e d PHOXA e p i s o d e s h a v e b e e n s i m u l a t e d w i t h the RTM-111
5).
model f o c u s s i n g m a i n l y o n ozone c o n c e n t r a t i o n s ( r e f
As a n e x a m p l e f o r a n h o u r l y a v e r a g e d p r e d i c t e d m i x e d l a y e r
ozone f i e l d o v e r Europe t h e c a l c u l a t e d ozone c o n c e n t r a t i o n s a t 03:DO
pm UTC f o r
J u l y 26,
1980 a r e g i v e n i n f i g .
i n boxes a r e measured h o u r l y ozone c o n c e n t r a t i o n s .
2.
The n u m b e r s From a r e v i e w
F i g . 2 C a l c u l a t e d h o u r l y a v e r a g e d ozone c o n c e n t r a t i o n s i n t h e m i x e d - l a y e r o f t h e R T M - I 1 1 m o d e l f o r J u l y 26, 1 9 8 0 , 03:OO p.m. U T C . Numbers i n b o x e s p r e s e n t o b s e r v a t i o n s .
639
o f the results,
i t becomes a p p a r e n t t h a t t h e m o d e l e x h i b i t s some
s k i l l i n p r e d i c t i n g ozone c o n c e n t r a t i o n s ; observed s p a t i a l p a t t e r n are reproduced.
many f e a t u r e s o f t h e Fig.
3 shows e x a m p l e s
f o r p r e d i c t e d and measured ozone c o n c e n t r a t i o n s i n t w o a r e a s o f t h e m o d e l i n g r e g i o n d u r i n g t h e PHOXA e p i s o d e
7/23/80
7/24/80
(bl 4
I
12
16
20
The Netherlands 24
1
0
I2
I6
7/24/80
(d)
I. The m e a s u r e d o z o n e
7/25/80
-
7/26/00
Rhinemond A r e a 20
24
I
8
12
16
20
24
I
7/2weo
I
12
I6
20
24
7/26/80
Langenbrigge, West Germany
F i g . 3 C a l c u l a t e d and measured ozone c o n c e n t r a t i o n s i n two a r e a s o f t h e PHOXA-modelling r e g i o n : ( a ) t h e Rhinemond-area o f t h e N e t h e r l a n d s ( b ) L a n g e n b r u g g e o f West-Germany. c a l c u l a t e d lower i n v e r s i o n l a y e r c a l c u l a t e d mixed l a y e r c a l c u l a t e d ground l e v e l
----
....
p e a k s were i n m o s t c a s e s u n d e r e s i m a t e d b y t h e m o d e l c a l c u l a t o n s . Some s t a t i s t i c a l i n f o r m a t i o n c a n b e i n f e r e d f r o m t a b .
2 which
c o n t a i n s t h e r e s u l t o f t h e t h r e e PHOXA e p i s o d e s ( r e f 6 ) .
640 TABLE 2 Some s t a t i s t i c a l i n f o r m a t i o n f o r t h e t h r e e PHOXA-episodes b y comp a r i n g measured g r o u n d l e v e l ozone c o n c e n t r a t i o n s f r o m 30 t o 40 s i t e s w i t h c a l c u l a t e d m i x e d - l a y e r ozone c o n c e n t r a t i o n s .
episode I
ozone average p r e d i c t e d (ppb) a v e r a g e measured ( p p b ) average c o r r e l a t i o n coefficient percentage o f p r e d i c t i o n s within a factor o f 2
episode I 1
42.4 45.9
47.8 55.4
0.62
56.6 60.7
0.54
76
e p i s o d e I11
0.51
80
78 ~
F a i l i n g i n t h e m o d e l i n g o f t h e o b s e r v e d maximum h o u r l y o z o n e c o n c e n t r a t i o n s may be p a r t l y due t o t h e r e l a t i v e l y l a r g e g r i d r e s o l u t i o n o f a p p r o x i m a t e l y 50 km x 50 km.
A l s o an u n d e r e s t i m a -
t i o n o f t h e a n t h r o p o g e n i c VOC-emissions a n d / o r o f t h e V O C e m i s s i o n s seem p o s s i b l e . with the RTM-I11
the r e a c t i v i t y
Nevertheless,
tests applied
model have d e m o n s t r a t e d ( r e f 7 ) t h e l e v e l o f
performance t o be ( i ) good f o r t h e r e p r o d u c t i o n o f t h e t e m p o r a l and s p a t i a l ozone p a t t e r n i n r u r a l areas, ( i i ) l e s s good f o r t h e r e p r o d u c t i o n o f NOx and o z o n e f i e l d s i n h i g h l y i n d u s t r i a l i z e d areas. S E N S I T I V I T Y ANALYSES S e n s i t i v i t y analyses are very important i n order t o determine t h e response o f t h e model t o e r r o r s i n i n p u t d a t a ;
t h i s procedure
i s u s u a l l y done by a s y s t e m a t i c v a r i a t i o n o f t h e i n p u t . v i t y r u n s have been i n v e s t i g a t e d w i t h t h e R T M - I 1 1
Sensiti-
model i n o r d e r
t o a s c e r t a i n t h e i n f l u e n c e o f c e r t a i n p a r a m e t e r s on t h e m o d e l results. The g e n e r a l c o n c l u s i o n w h i c h c o u l d be drawn f r o m t h e s e s e n s i t i v i t y c a l c u l a t i o n s c a n be s u m m a r i z e d a s f o l l o w s : ( i ) C l o u d a v e r a g e and m i x i n g h e i g h t h a v e a s t r o n g l o c a l e f f e c t on t h e m o d e l r e s u l t s . ( i i ) The i n f l u e n c e o f t h e u p p e r and l a t e r a l b o u n d a r i e s on t h e model r e s u l t s i s s m a l l . ( i i i ) The q u a l i t y o f t h e m o d e l r e s u l t s depends f i r s t o f a l l on t h e q u a l i t y o f t h e d a t a b a s e f o r N O x and n a t u r a l ) - e m i s s i o n s .
and V O C ( a n t h r o p o g e n i c
641
S E N S I T I V I T Y OF THE R T M - I 1 1
AND VOC-EMISSIONS
MODEL T O OVERALL REDUCTIONS OF NOx-
I N THE PHOXA-AREA
To g e t some i n d i c a t i o n o f t h e c h a n g e o f d i r e c t i o n o f o x i d a n t c o n c e n t r a t i o n s when e m i s s i o n s o f NO
X
o r / a n d VOC a r e a l t e r e d ,
the
f o l l o w i n g o v e r a l l e m i s s i o n r e d u c t i o n s have been i n v e s t i g a t e d : ( a ) N O x e m i s s i o n s r e d u c e d b y 50 # , V O C e m i s e i o n s u n c h a n g e d ( b ) NOx e m i s s i o n s u n c h a n g e d , ( c ) NOx- a n d V O C - e m i s s i o n s
VOC-emissions
r e d u c e d b y 50 %
r e d u c e d b y 50 %,
A l l r e d u c t i o n s have been c a r r i e d o u t u n i f o r m l y o v e r t h e w h o l e modeling region,
i n c l u d i n g anthropogenic and n a t u r a l emissions;
a l l o t h e r i n p u t data remained u i s l t e r e d . As an e x a m p l e o f t h e e f f e c t o f t h e s e o v e r a l l h y p o t h e t i c a l e m i s s i o n r e d u c t i o n s t h e c h a n g e i n t h e maximum h o u r l y o z o n e c o n c e n t r a t i o n s compared t o t h e base c s s e o f t h e 1980 e p i s o d e i s d e p i c t e d in fig. episodes
4
.
-
6.
S i m i l a r f i n d i n g s have been o b t a i n e d f o r t h e 1982
F i g . 4 C o n t o u r l i n e s o f c a l c u l a t e d b a s e c a s e maximum h o u r l y o z o n e c o n c e n t r a t i o n s p p b Oj on J u l y 26, 1980. The p e r c e n t a g e c h a n g e o f t h e p r e d i c t e d maximum h o u r l y o z o n e c o n c e n t r a t i o n s d u e t o a 50 X NO - e m i s s i o n r e d u c t i o n i s m a r k e d .
642
F i g . 5 Same a s f i g .
4 b u t f o r a 50 % V O C - e m i s s i o n
F i g . 6 Same a s f i g .
4 b u t f o r a 5 0 X NOx-
reduction
and VOC-emission
reduction
643
The p r e l i m i n a r y c o n c l u s i o n s w h i c h c a n b e d r a w n f r o m t h i s b r o a d s e n s i t i v i t y a n a l y s i s on a p e r c e n t a g e e m i s s i o n r e d u c t i o n f o r t h e t h r e e e p i s o d e s u n d e r c o n s i d e r a t i o n i n t h e PHOXA m o d e l i n g a r e a , a r e summarized q u a l i t a t i v e l y i n t a b .
3
TABLE 3
,
Q u a l i t a t i v e b e h a v i o u r o f a n o v e r a l l 5 0 L r e d u c t i o n f o r NO VOC a n d c o m b i n e d N O x , V O C i n c o m p a r i s o n w i t h t h e b a s e c a s e mo'6el run.
-
-
5 0 X NO.,
03 i n c r e a s e i n l o c a l r e g i o n s w i t h h i g h NOx emi s s i o n s ( u r b a n / i n d u s t r ia 1 i z e d areas)
50
-
x voc
0 decrease i n t h e wffole r e g i o n
0 decrease i n regions 3 w i t h low NOx emissions ( r u r a l areas)
50
X
NO..,
VOC
Diminished O3 increase i n l o c a l regions with high NOx e m i s s i o n s ( u r b a n / i n dus t r i a l i z e d areas) E n h a n c e d O 3 decrease i n regions w i t h l o w NOx e m i s sions ( r u r a l areas)
A d e c r e a s e i n NOx e m i s s i o n s l e a d s t o a n i n c r e a s e i n 0 t r a t i o n s c l o s e t o l a r g e NO
X
3 concensources i n u r b a n / i n d u s t r i a l i z e d areas
a n d a d e c r e a s e i n O 3 c o n c e n t r a t i o n s i n r u r a l a r e a s w i t h l o w NOx emissions there.
T h i s c a n b e u n d e r s t o o d i n q u a l i t a t i v e way b y
k e e p i n g i n m i n d t h a t ozone i s produced p r i m a r i l y as a r e s u l t o f t h e p h o t o l y s i s o f NO2 m o d i f i e d b y p r o d u c t s o f V O C - p h o t o l y s i s , and t h a t ozone i s removed p r i m a r i l y by d r y d e p o s i t i o n a n d r e a c t i o n
w i t h V O C a n d N O x . I n a r e a s w i t h h i g h NOx e m i s s i o n s a NO results i n less O3 o f O3
compared t o t h e b a s e c a s e run.
s i o n s a NO
X
X
reduction
d e s t r u c t i o n which appears as a r e l a t i v e increase I n a r e a s w i t h l o w NOx e m i s -
reduction r e s u l t s i n lesser O3
t o t h e base case run.
p r o d u c t i o n compared
V O C r e d u c t i o n s d i m i n i s h t h e amount o f p e r o x y
r a d i c a l s produced by t h e photochemical degradation o f hydrocarbons w h i c h u s u a l l y c o n v e r t s NO t o N O 2 i n f a v o u r o f O 3 p r o d u c t i o n . Tab.
4 c o n t a i n s c a l c u l a t e d mean o z o n e v a l u e s ( 9 6 h o u r a v e r a g e
f o r t h e w h o l e PHOXA r e g i o n a s w e l l a s f o r t h e r e c e p t o r r e g i o n s (West-Germany
a n d The N e t h e r l a n d s ) w h i c h r e s u l t e d f r o m t h e o v e r a 1
percentage emission r e d u c t i o n scenarios f o r t h e t h r e e s e l e c t e d episodes.
644
TABLE 4 C a l c u l a t e d mean o z o n e c o n c e n t r a t i o n ( 9 6 h o u r a v e r a g e ) f o r d i f f e r e n t p a r t s o f t h e P H O X A r e g i o n a n d i t s mean maximum v a l u e . The p e r c e n t a g e n u m b e r s g i v e t h e c h a n g e s i n t h e s e mean o z o n e c o n c e n t r a t i o n s f o r t h e three hypothetical o v e r a l l emission reduction scenarios. Episode mean ozone concent r a t i o n (ppb) o f t h e base case run Episode I: PHOXA r e g i o n West-Germany The Netherlands Mean peak value i n PHOXA
Percentage o f mean 0) c o n c e n t r a t i o n change by t h e o v e r a l l emission r e d u c t i o n scenarios 50 % NOx 50 X UOC 50 E NOx, VOC
-
-
+ 1.1
36.4 53.0 44.5
+ +
3.8 28.9
56.0
-
1.3
-
-
-
4.2 10.0 15.7 8.0 ~~
Episode 11: PHOXA r e g i o n West-Germany The Netherlands Mean Peak value i n PHOXA
+ 0.3
42.9 49.0 52.9 65.0 ~
Episode I11 PHOXA r e g i o n West-Germany The Netherlands Mean Peak value i n PHOXA
+
8.2 10.6
-
7.7
-k
~
-
50.8 57.4 78.1 97.0
-
4.6 12.2 9.1
-
5.0
-
-
8.0
-
4.4 ~~
-
~
-
+
1.4 1.4 15.9
~
~~
3.5 5.2 3.9
-
__
+
3.2 1.1 1.6
-
8.0
-
6.5 12.0 18.7 10.0
7.3 12.0 12.0 14.0
The d i f f e r e n t b e h a v i o u r o f t h e t h r e e e p i s o d e s d e p e n d s o n t h e l o c a t i o n o f t h e a r e a o f c a l c u l a t e d maximum o z o n e c o n c e n t r a t i o n s . I n e p i s o d e I a n d I 1 o z o n e maxima w e r e c a l c u l a t e d p a r t l y o v e r u r -
b a n / i n d u s t r i a l i z e d areas,
i n e p i s o d e I 1 1 t h e o z o n e maxima o c c u r e d
g e n e r a l l y over r u r a l areas. SUMMARY AND CONCLUSIONS I t i s f o r t h e f i r s t t i m e t h a t i n t h e framework o f t h e PHOXA programme a E u r o p e a n d a t a base, complex l o n g - r a n g e
suitable for the application of
d i s p e r s i o n models,
has been set-up.
means i t became p o s s i b l e t o u s e a n E u l e r i a n m o d e l , model,
t o s i m u l a t e p h o t o c h e m i c a l smog e p i s o d e s .
By t h i s
the RTM-I11
The m o d e l r e s u l t s
f o r t h r e e s e l e c t e d photochemical episodes and t h e comparison of model r e s u l t s w i t h measurements d e m o n s t r a t e d t h a t t h e R T M - I 1 1 model s i m u l a t e d q u i t e w e l l t h e observed long-range
increase o f
ozone c o n c e n t r a t i o n s d u r i n g e p i s o d e s as w e l l a s i t s a v e r a g e t r e n d
645 and l e v e l .
Peak ozone c o n c e n t r a t i o n s ,
The a p p l i c a t i o n o f t h e R T M - I 1 1
however,
were u n d e r e s t i m a t e d .
m o d e l on h y p o t h e t i c a l e m i s s i o n
s c e n a r i o s p r o v e d t h e r e a s o n a b l e r e s p o n s e o f t h e model t o a l t e r a t i o n s i n emission data.
I n a l l e m i s s i o n r e d u c t i o n s c e n a r i o s ozone
maximum c o n c e n t r a t i o n s e x p e r i e n c e d a s t r o n g e r d e c r e a s e t h a n averaged concentrations. The i n v e s t i g a t i o n o f t h e r e d u c t i o n o f h o u r l y ozone maxima w i t h the RIM-I11
model i s s u f f i c i e n t f o r p h o t o c h e m i c a l e p i s o d e s .
i n v e s t i g a t i o n o f l o n g - t e r m a v e r a g e d ozone c o n c e n t r a t i o n s ,
The
however,
demands t h e i n c o r p o r a t i o n o f t h e p h o t o c h e m i c a l r e a c t i o n s o f t h e f r e e atmosphere.
The R T M - I 1 1 model i s n o t y e t d e s i g n e d f o r l o n g
term c a l c u a l t i o n s . W i t h r e g a r d t o t h e e v a l u a t i o n o f t h e e f f e c t o f e m i s s i o n red u c t i o n measures on t h e s h o r t - t e r m
formation o f oxidants,
i t can
be confirmed:
-
q u a l i t a t i v e s t a t e m e n t s can be met w i t h r e a s o n a b l e c o n f i d e n c e , q u a n t i t a t i v e statements a r e merely p o s s i b l e w i t h r e s e r v a t i o n s m a i n l y due t o t h e u n c e r t a i n t i e s i n t h e i n p u t d a t a bases.
I t s h o u l d be emphasized t h a t t h e P H O X A m o d e l l i n g a p p r o a c h i s w e l l e l a b o r a t e d f o r t h e t r e a t m e n t o f r e g u l a t i v e measures.
I f the
e v a l u a t i o n scheme f o r p h o t o o x i d a n t s was f o r m u l a t e d i n t h e E C E c r i t i c a l l e v e l c o n c e p t i t s h o u l d be p o s s i b l e t o i d e n t i f y a n d o p t i m i z e e f f e c t i v e a b a t e m e n t measures. The a p p l i c a t i o n o f t h e PHOXA m o d e l i n g i n s t r u m e n t s i m u l t a n e o u s l y p o i n t s t o f u r t h e r necessary improvements i n o r d e r t o s e c u r e t h e r e l i a b i l i t y o f the findings.
Objectives o f t h i s k i n d are f i r s t
of all: ( i ) t o e x a m i n a t e t h e e m i s s i o n d a t a bases,
VOC and t h e i r s p l i t t i n g i n t o CBM-IV
e s p e c i a l l y of
the
r e a c t i v i t y classes;
( i i ) t o a c c o m p l i s h more s e n s i t i v i t y s t u d i e s u s i n g t h e R T M - I 1 1 model w i t h i m p r o v e d d a t a b a s e s and f i n e r s p a t i a l r e s o l u t i o n a n d t o i n v e s t i g a t e t h e r e a s o n f o r e p i s o d i c peak u n d e r e s t i m a t i o n s ; ( i i i ) t o d e v e l o p and r e a l i z e i n t e r r e g i o n a l measurement camp a i n g n s f o r p r e c u r s o r s and o x i d a n t s i n o r d e r t o v e r i f y t h e complex model c a l c u l a t i o n s . ( i v ) t o f u r t h e r develop d i s p e r s i o n models i n o r d e r t o s i m u l a t e l o n g t e r m o x i d a n t c o n c e n t r a t i o n s i n t h e b o u n d a r y l a y e r and i n t h e f r e e atmosphere.
646
On t o p o f t h i s i t h a s t o b e k e p t i n m i n d t h a t a c o m p r e h e n s i v e abatement s t r a t e g y f o r a i r p o l l u t i o n c o n t r o l s h o u l d t a k e i n t o a c c o u n t p h o t o o x i d a n t s as w e l l as a c i d i c s p e c i e s i n s h o r t - t e r m and l o n g - t e r m s i t u a t i o n s .
Appropriate state-of-the-art
modeling
t o o l s f o r t h e a p p l i c a t i o n i n t h e framework o f c o n t r o l s t r a t e g i e s a r e a l r e a d y u n d e r p r e p a r a t i o n a n d t e s t i n g i n t h e PHOXA programme. REFERENCES
1 C. L u d w i g , H . M e i n l , i n P r e p r i n t s o f t h e 1 6 t h I T M on A i r P o l l u t i o n M o d e l i n g a n d i t s A p p l i c a t i o n , L i n d a u , FRG, A p r i l 6 - 1 0 , 1987. P.J.H. B u i l t j e s , i n P r o c . EPA-OECD I n t . C o n f . o n 2 S . Zwerver April Long-Range T r a n s p o r t R e s e a r c h , EPA T r i a n g l e P a r k , U.S.A., 1985. 3 US-EPA ( E d i t o r ) , P r o c . EPA-OECD I n t . C o n f . o n Long-Range T r a n s p o r t Models f o r P h o t o c h e m i c a l O x i d a n t s and T h e i r P r e c u r s o r s , EPA-600/9-84-006, R e s e a r c h T r i a n g l e P a r k , U.S.A., 1984. 4 D.A. S t e w a r t , R.E. M o r r i s , S.D. R e y n o l d s , F i n a l R e p o r t SYSAPP-87/ 030, S y s t e m s A p p l i c a t i o n I n c . , San R a f a e l , U S A , 1 6 0 p., F e b r u a r y 24, 1 9 8 7 . 5 J. P a n k r a t h , R . S t e r n , P. B u i l t j e s , i n G r e f e n , L o b e 1 ( E d i t o r s ) , E n v i r o n m e n t a l M e t e o r o l o g y , R e i d e l P u b l . Comp., D o r d r e c h t , 1 9 8 7 . 6 R . M . S t e r n , P.J.H. B u i l t j e s , i n ECE/WMO-EMEP W o r k s h o p on Mod e l l i n g T r a n s f o r m a t i o n Processes and T r a n s p o r t o f A i r P o l l u t i o n w i t h S p e c i a l R e f e r e n c e t o N i t r o g e n O x i d e s , Potsdam, GDR, M a r c h 21-24, 1988. 7 P. B u i l t j e s , R . S t e r n , 5. R e y n o l d s , i n P r e p r i n t s o f t h e 1 6 t h I T M on A i r P o l l u t i o n M o d e l l i n g and i t s A p p l i c a t i o n , Lindau, FAG, A p r i l 6-10, 1 9 8 7 .
647
T.Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishera B.V.,Amsterdam -Printed in The Netherlands
CALCULATION OF LONG TERM AVERAGED OZONE CONCENTRATIONS
1 Frank A.A.M. DE LEEUWl, H.Jetske VAN RHEINECK LEYSSIUS and Peter J.H. BUILTJES2 'National Institute for Public Health and Environmental Protection, P.0.Box 1, 3720 BA, Bilthoven (The Netherlands) 'MT-TNO, Department of Netherlands)
Fluid Dynamics, P.0.Box 342, 7300 AH Apeldoorn
(The
ABSTRACT Seasonal averaged ground level concentrations for ozone have been calculated for the Netherlands by means of a lagrangian long-range transport model. The calculations indicate that the influence of European anthropogenic emissions of nitrogen oxides (NO ) and volatile organic compounds (VOC) on the growing season, day-time averzged (may to September, 10-17h) ozone concentrations in the Netherlands is small. A European VOC emission reduction will lead to a reduction in growing season averaged ozone and oxidant (sum of O3 and NO ) concentrations. A reduction of European NO emissions leads to a reduction 8f oxidant concentrations, but in areas xwith a high NOx concentration such as the Netherlands, an increase in ground level ozone concentrations is predicted due to a shift in the photostationary equilibrium. When VOC emission reductions are combined with NO emission reductions a slightly decreased groundlevel ozone concentration is eftpected.
INTRODUCTION Much attention is given to the calculation of peak-concentrations of ozone during episodes with photochemical air pollution, see for example the number of papers presented at this symposium. Although it is known that short-term exposures to high ozone levels causes adverse effect both on human health as on vegetation, there is a growing evidence that damage is also
caused by
a
long-term exposure to moderate levels. Growth and yield reduction agricultural crops is induced by ambient ozone concentrations above 60 pg during
the
growing season
(ref. 1).
for -3 m For natural vegetation strong visual
effects can be avoided when growing season averaged levels do not exceed 100 pg m-3; the no-effect level is estimated to be ca. 50 pg m-3 (ref. 2). In contrast to the peak values of ozone, which are predominantly determined by processes within the planetary boundary layer, the long-term averaged concentrations at groundlevel strongly depend on the concentrations in the free troposphere (ref. 3). Hodel studies to the influence of anthropogenic emissions of volatile organic compounds (VOC) and nitrogen oxides (NOx) on the ozone production and loss processes therefore requires the application of
648 global tropospheric models (see e.g. ref. 4). From modelcalculations the influence of precursor emissions
this type of on the trend of
tropospheric ozone is deduced. For increased release rates of 3% year-' for C O , NOxl and VOC and 0.5% year-' for CH4 an increase in tropospheric ozone of 1% year- has been estimated (ref. 4). The spatial resolution in the global 2-D models is generally too low to provide information on a continental scale. As zonally averaged concentrations are calculated the influence of European emissions on the concentrations in Europe, and more particularly in the Netherlands, can not be estimated. In order to improve the information on an European scale in this paper a model for the calculation of long-term averaged concentrations in the planetary boundary layer is presented. By means of this model the influence of European anthropogenic emissions on the growing season, day-time averaged (may to September, 10-17h) concentrations in the Netherlands is examined. MODELDESCRIPTION Groundlevel concentrations are calculated by means of a lagrangian longrange transport model. In this receptor oriented trajectory model two air parcels - one representative for the mixed layer, the other representative for the polluted layer above the mixed layer (aged smog layer) - are followed along 96h back trajectories. Long-term averaged concentrations are estimated in a brute-force method, i.e. by averaging the concentrations
calculated
for
four arrivaltimes per day for all days in the considered period. Essentially the long-term model (called MPA-LT model) presented in this paper is a repeated
application of the earlier developed episodic model (HPA-model, ref.
5). The model includes emissions, non-linear atmospheric chemistry, deposition, exchange between boundary layer and free troposphere and fumigation between mixed layer and aged-smog layer. The boundary conditions (initial concentrations at the start of the trajectory and the concentrations in the free troposphere) are obtained from a two-dimensional tropospheric model (ref. 4).
The pressure
long-range transport level which
were
is
described by
obtained
from
trajectories on the 850 mbar the
Western
Meteorological
Synthesizing Centre of ECE/WEP in Oslo. For 1980 information is available for four arrivaltimes per day (00, 06, 12 and 18 GMT) for four the the
receptorpoints
in
Netherlands (see figure 1). Additional meteorological information along trajectory was partly obtained from routine measurements in the
Netherlands
assuming persistence along the trajectory. Other parameters, such
as global radiation, mixing height and stability, were calculated by procedures.
standard
649
Fig. 1. Location of receptorpoints. The emissions of NOx, VOC and SOp are based on the inventories of ECE/EMEP (ref. 6-7); for countries within the PHOXA-area total numbers were adjusted in accordance to the PHOXA-inventory (ref. 6). For the Netherlands and direct surroundings emissions are based on the more detailed TNO-inventory (ref. 9 10).
Dry deposition in the mixed layer is modelled by a deposition velocity v g according to: l/vg The
-
ra + rb + rc (1) aerodynamic resistance ra and the quasi-laminar boundary resistance rb
depend on atmospheric stability (ref. 11). The surface resistance rc is different for every component and depends on the nature and conditions of the surface. There is no deposition of O3 and NO2 on water surfaces. In the present modelversion, where emphasis is laid on the calculation of ozone- and oxidant-concentrations, wet deposition is neglected. In earlier calculations by means of the episodic version of the model. it was found that the influence of wet deposition and concentration is small.
in-cloud oxidation on the oxidant
A vertical exchange of pollutant mass between mixed layer and aged-smog layer is induced by variations in the mixing height (fumigation). Processes
which account for the exchange between the plnnetary boundary layer and the free troposphere are summarized by Builtjes (ref. 12). Among these processes cloud venting (especially cumulus-nimbus) and vertical transport in high and low pressure
areas are
the most
important ones.
For long-term averaged
exchange not only the effectiviness of the process but also the frequency of occurance must be considered. As in the Netherlands cumulus-nimbus is observed
650 only ca. 4% of the time
-
for Europe as a whole this is ca. 8%
-
cloud venting
is initially neglected. However, further research is needed to prove the (in)correctness of this assumption. The downward flux in a high-pressure area is
modelled by a vertical windvelocity which is assumed to be proportional to
the pressure and range from 0 cm s-'
for pressures below 1015 mbar up to 1
cm
9-l for pressures of 1045 mbar or more. The chemical
reactions which
take
place
in both
air
parcels
during
transport are described by a slightly modified version of the CBM-IV mechanism (ref. 13). As mentioned above in-cloud oxidation is in the present version not yet included.
RESULTS A summary of the observed and calculated groundlevel growing season daytime averaged (may to September, 10-17h) concentrations for 1980 is given in table 1 for the reference situation. As NO is to a large extend emitted at groundlevel (emissions from traffic, space heating) the NOx concentration decrease with increasing height. The modelled mixed layer averaged concentration systematically underpredictes the groundlevel concentration. Although a correction, depending on the emission density in the receptor area modelled groundlevel and atmospheric stability, is applied, the NoX concentrations strongly underpredict thp measurements. The effects of a too low NO concentration on the production of ozone on an European scale is X probably small, the local influence is much larger. This is shown by the overestimation of the O3 concentration depicted in table 1. Due to a shift in the photostationary equilibrium an underestimation in NOx concentrations will The result in an overestimation of ozone concentrations. concentrations (Ox, sum of 0 and NO2) are slightly overpredicted. 3
oxidant
TABLE 1 Observed
and
calculated groundlevel growing season day-time averaged (may to
September, 10-17h) concentrations for 1980 (in ppb) for four receptorpoints in the Netherlands.
1 obs
NO NO NO: ox O3
2.0 7.5 9.6 38.8 45.6
2 calc 0.3 1.8 2.2 51.8 53.7
obs 4.9 9.1 14.3 39.8 47.3
receptorpoint 3 calc obs calc 1.0 3.9 4.9 52.2 56.1
3.4 1.2 11.4 4.7 14.9 6.0 40.6 49.6 51.6 54.3
4
obs 5.0 12.2 17.3 41.6 53.6
calc 1.4 5.2 6.6 52.5 57.7
651 The temporal behaviour of calculated NO, and Ox concentrations is in fair agreement with the measurements, see figure 2. Episodes with enhanced Oxconcentrations
are
well
concentrations. For NO
predicted by
the
model,
both
in
concentrations a reasonable correlation
time in
as
in
time
is
found but the underprediction by the model is clearly seen. A least-squares analysis of observed and measured
concentrations
arrival ttmes (about 600 datapoints) showed for ozone correlation coefficient of 0.6-0.7; for oxidant 90-97% of concentrations
are
and the
for
all
oxidant a calculated
within a factor of two of the measurements, for ozone 60-
73% is calculated within this range. Validation
of
other
components involved in the chemical scheme is hardly
possible due to the paucity of measured data, It can only be stated obtained
results
are
not
in disagreemenc with
that
the
measured or modelled data
presented in the literature. In several sensitivity runs the influence of European anthropogenic VOC and NOx emissions on the growing season averaged concentrations in the Netherlands is investigated. An overview of the emission scenarios is presented in table
2. The relative changes in Ox, NOx and O3 concentrations compared to the reference run are given in figure 3. In all calculations a constant CH 4 background concentration is assumed. The natural emissions and the CO emissions, both natural as anthropogenic, are kept constant. TABLE 2 Reductions ( % ) on calculations
European anthropogenic emissions
run number
NoX
7
30 50 70 0 0 30 50
8
50
on
scenario
voc 0 0 0 40 70 40 40 70
As on a local scale the underestimation of NO effect
in
emission reduction
1 2 3 4 5 6
pronounced
applied
the
O3
concentrations
may
have
a
concentrations due to the NO/03 titration, a
correction is applied on the modelled ozone concentrations. In this procedure the relative changes in Ox and NOx concentrations as predicted by the model are applied on the measured concentrations. The O3 concentration is now
652
mcetnet-data:
5
3 1 1
1980
iuli
t-model :
10
juli ippbi
550
I(=
15
i
~
=4 4 5 0
20
25 30 t.ijd (dagen)
1980
; tr a380
grondconcanti-stir;
15
5
10
refel entierun
50
1s
20
30 t i j d rdagen)
25
Thu flar 24 1 0 : 4 9 : 8 5
(ppb)
; tra300
19
gr ondconc e n t r a t I e s
t i j d fdagcn) r e f e r e n t 1erun
Thu M a r 2 4 1 0 : 4 9 : 0 5
Fig. 2. Observed (top) and calculated (bottom) groundlevel Ox and NOx(ppb); july 1980, receptorpoint 3.
15
concentrations
of
653
change in Ox concentration
0
-5 - 10
I
d
1
2
3
4
5
6
7
8
change in NOx concentration
40
I
0
-40
I -80
'
1
2
3
4
5
6
7
8
change in ozone concentratlon
0
- 10
-20
'
1
2
3
4
5
6
7
8
run number Fig. 3. Calculated changes in Ox, NO
X
run: run numbers correspond shaded bar receptorpoint 3. reference
and O3 concentrations to
relative
to
the
table 2; closed bar receptorpoint 1,
654 recalculated
using
an
effective
value for the photostationairy equilibrium
constant which was obtained from the measurements. From figure 3 it is seen that the relative changes in Ox and NO concentrations differ only slightly for the two receptor areas. Larger differences are found in the changes in O3 concentrations due to differences in local NOx emission density.
A
reduction
in NO
Ox concentrations, increase. The
emissions in Europe (scenario 1-3) leads to decreasing
but
reduction
in
the
Netherlands
the
ozone
concentration
will
in Ox concentrations is too small to compensate the
ozone increase resulting from a shift in the photostationary equilibrium. However, in more remote areas with a low NO, emission density i t is expected that the decrease in Ox concentrations will lead to decreasing ozone levels. In global tropospheric models a reduction in yearly averaged, zonally averaged ozone concentrations is calculated in case a NOx emission reduction is assumed (ref. 4). For a 70% reduction in NOx emissions an ozone reduction is found in the less polluted part of the Netherlands but in the more polluted Rijnmond area (receptorpoint 3) the ozone concentrations still increase. Reduction in European VOC emissions (scenario 4-5) results in a lowering of both
Ox
and
O3
concentrations
in
the Netherlands. The NO
concentrations
increase in this situation. For reductions in the order of ten of VOC
emission
reduction
is more
effective than a NO,
percents
lowering the Ox concentrations. For strong -reductions (about 70%) VOC and emission reductions are equally effective. For a concurrent reduction in NOx and VOC
emissions
a
emission reduction in
(scenario
NOx
6-8) the
ozone increase due to NOx emission reduction is compensated by the VOC emission reduction. The net result is a reduction in ozone levels of a few percent. In all scenario calculations the emissions outside Europe were not changed. In a
last
scenario run it was assumed that anthropogenic emission in Europe
were reduced by 40% for VOC and 30% for NOx (comparable with scenario 6 ) but this reduction is counterbalanced by increasing emissions outside Europe in such a way that the total global emissions remain the same. For this scenario the Ox concentrations in the Netherlands decrease by ca. 5% but the ozone concentrations are nearly invariant ( -0.5% for receptorpoint 1. +1.7% for receptorpoint 3 ) . Global emissions have to be stabilize to avoid a further increase in ozone concentrations. CONCLUSIONS The influence of European anthropogenic emissions of VOC growing
season day-time averaged
and
NO,
on
the
ozone concentration in the Netherlands is
small. In all calculations a reduction on an European scale in VOC and/or NOx emissions results in a decrease of Ox levels (sum of O3 and NO2). However, in
655 the NOx-scenarios increasing groundlevel ozone concentrations are found in the Netherlands but in more remote areas with low NOx concentrations a reduction in ozone concentrations is expected. For moderate reductions (about 50% or less) a VOC emission reduction is more effective than a NOx emission reduction in lowering the Ox concentrations. For strong reductions (about 70%) VOC NO emission reductions are equally effective.
and
X
Strong visual effects on vegetation is expected for growing season averaged ozone concentrations of 100 pg The measured values in the Netherlands are ca. 85 pg
Global emissions have to be
stabilized
to
avoid
a
further
increase in groundlevel ozone concentrations. REFERENCES 1 A.E.G. Tonneijck, Evaluation of ozone effects on vegetation in the Netherlands. Third US-Dutch International Symposium, Atmospheric Ozone Research and its Policy Implications, Nijmegen. the Netherlands, May 9-13, 1988. 2 T. Schneider and A.H.M. Bresser (Editors) Dutch priority programme on acidification; interim evaluation. Report 00-04, RIVM, Bilthoven, the Netherlands, 1987. 3 R.M. van Aalst, Emissions, chemical processes and deposition. In: R.Guicherit, J. van Ham and A.C. Posthumus (Editors) Ozone, physical and chemical changes in the atmosphere and its effects. Kluwer, Deventer, pp8491, 1987. 4 I.S.A. Isaksen and 0. Hov, Calculation of trends in the tropospheric concentrations of 0 CO, CH4 and NOx. Tellus, 39B, 271-285, 1987. 5 F.A.A.M. de Leeuw, &e Dutch Aerosol Study: modeling aspects. In: S.D. Lee, T. Schneider, L.D. Grant and P.J. Verkerk (Editors) Aerosols, research, risk assessment and control strategies, Lewis Publishers, Chelsea, pp301315, 1986. 6 A. Eliassen, 0. Hov, I.S.A. Isaksen, J. Saltbones and F. Stordal. A lagrangian long-range transport model with atmospheric boundary layer chemistry. J. Appl. Meteorology, 21, 1645-1661, 1982. 7 A. Eliassen and J. Saltbones, Modelling of long-range transport of sulphur over Europe: a two-year run and some model experiments. Atmospheric Environment 17, 1457-1473, 1983. 8 J. Pankrath, Photochemical oxidant model application within the framework of control strategy development in the Dutch/German joint project PHOXA. Third US-Dutch International Symposium, Atmospheric Ozone Research and its Policy Implications, Nijmegen, the Netherlands, May 9-13, 1988. 9 H.J. Huldy and C. Veldt, Air Quality Management System VI: emissions. CMPreport 80/8, TNO, Delft, 1981. 10 C. Veldt, Air Quality Management System XLVI: current emissions of volatile organic compounds, CMP-report 85/01, TNO, Delft, 1985. 11 M.L. Wesely and D.D. Hicks, Some factors that affect the deposition rate of sulphur dioxide and similar gasses on vegetation. J. Air Pollut. Control ASSOC. 27, 1110-1116, 1977. 12 P.J.H. Builtjes, Interaction of planetary boundary layer and free troposphere. Third US-Dutch International Symposium, Atmospheric Ozone Research and its Policy Implications, Nijmegen, the Netherlands, May 9-13, 1988. 13 G.E Whitten and M.W. Gery, Development of CBM-X mechanisms for urban and regional AQSMs. System Application Inc., 101 Lucas Velly Road, San Rafael, CA94903, USA, 1986.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Znrplicatio~ 0 1989 Elsevier Science Publishers B.V.,Amsterdam -Printed in The Netherlande
MODEL CAL(XILATI0NS
657
OF OZONE IN THE ATUXPHWIC BWNDARY LAYER OVER EUROPE
0. HOV Norwegian Institute for Air Research, P.0.Box 64, N-2001 LillestrQm (Nomay1 ABSTRACT Ozone episodes in the atmospheric baundary layer over Europe in the sunner are superimposed on a background level which has an early aumner maximum and which increases 1-3% annually. The Norwegian long-range transport model based on trajectory calculations with chemistry, is used to calculate the concentrations of ozone at 14 rural sites in Europe during the ozone episode 28 May-3 June 1982. The effects of changing physical parameters and emissions of nitrogen oxides and volatile organic canpounds, are discussed.
INTRODUCTION There are canprehensive networks of rural ozone measuring instnnnents in many European Countries and in North America. It is well established that the ozone concentrations can be elevated in episodes during the sumner half year in anticyclonic weather situations. On a different time scale, ozone near the ground Over Europe has an annual cycle with a late spring to early sumner maximum and a mid winter minimum. The monthly mean concentration in the spring maximum was about 45 ppb at R6rvi.k south of Gothenburg in Sweden for the 1980-1983 period and about 25 ppb in the winter minimum (ref. l), while the maximum hourly ozone concentration at t h i s site in 1985 was 107 ppb (ref. 2). The annual variation of ozone at Relxvik for clean air oompared to polluted air situations, judged fran the particle counts, showed that in polluted air the spring maxirmrm is higher and is delayed by more than one month, while in clean air the spring maximum canes earlier and is laver than the average for all measurements (ref. 1). This indicates that there is an anthropogenic influence on the ozone concentrations measured at t h i s rural site throughout the year. Historical records of ozone measurements in Europe and North America indicate that in the last part of the nineteenth century the values were anly about half of the mean of surface ozone measurements taken in the same geographical regions during the last 10-15 years (refs. 3, 4 ) , while measurements Over the last decsdes in Europe support a linear increase in ozone by 1-3%/a (refs. 5-7). Ozone episodes in the atmospheric boundary layer are therefore superimposed on a background level which is slowly
658 increasing. Tne change i n the backgraud concentration is probably con( r e f . 8). t r o l l e d by changes i n the emissions of nitrogen oxides (-) Both changes i n the emissions of volatile organic canpounds (Voc) and Nox are important for changes i n episodic ozone, as w i l l be further discussed i n t h i s paper. MODEL DESCRIPTION Model calculations using the Norwegian lagrangian long-range transport model with CM6-X chemistry (ref. 9) for the time period 28 May 1982, 1200 W , to 3 June 1982, 1200 W, were carried out to 14 receptor points within the grid area, see Figure 1. Calculations were carried o u t every 6 h M, i . e . at arrival times oo00, 0600, 1200 and 1800 @TF a t each site.
Fig. 1. Map of PlIEP grid and 96 h back trajectories for 28 May, 1 and 3 June 1982, 1200 W,t0 (1) Illmitz, A u s t r i a , (2) Langenbrlgge, (3) Schauinsland and (4)Deuselbach, a l l FRG, ( 5 ) Ri&, Denmark, ( 6 ) Rl)rvik, Sweden, (7) Langesund and (8) Jelm, Norway, (9) Sappe-r and (10) Waarde, The N e t h e r l a n d s , (11)Colders, France, (12) Bottesford, (13) Sibton and (14) Stoddey, UK.
659 The model has been described in sane detail previously (refs. 10, 11). The pollutants are assumed to be cunpletely vertically mixed throughout the boundary layer which has a variable depth along the 96 h long 850 mb trajectories. No mass transport takes place through the top of the wellmixed layer. Lateral diffusion is not treated explicitly, but the emission data are given in a 150 km grid where finer details than 150 km in the concentration fields are smoothed out. During transport, pollutants are emitted into the air parcel according to the emission maps for NOx and VOC. Instantaneous concentrations are predicted upon arrival of a trajectory. The horizontal resolution of the concentration fields is determined by the choice of emission grid and density of trajectory arrival points. The canbined effects of vertical wind shear and diffusion due to heat exchange is difficult to handle in lagrangian models. Radiosonde observations are used to estimate the mixing height field over Europe at 1200 C X F every day. Objective analysis of temperature, relative humidity and absolute humidity are carried out at OOOO and 1200 in the 150 )an grid, as vertical averages between the surface and the 850 mb level. The temperature is used to evaluate temperature-dependent reaction rate coefficients. The relative humidity is used as a rough indication of cloud cover, which influences the photodissociation rates. Dry deposition velocites for 1 m above the ground were taken for ozone as 0.5 m / s for daytime over land, 0.05 m / s for nighttime over land and 0 over sea, for NO2 0.5 m / s over land, 0 over sea, for HN03 1.0 cm/s, PAN 0 . 2 m/s. To arrive at a model where average boundary layer concentrations are calculated rather than the concentration at 1 m, the deposition velocities at 1 m for 03,NOz and PAN were simply reduced by 50%. Detailed calculations for June 1985 using meteorological data fran the Numerical Weather Prediction Model at The Norwegian Meteorological Institute for surface pressure, surface stress, sensible heat flux density and temperature at 2 m height together with data for the surface roughness length
and Businger’s equations which relate the deposition velocity at the top of the surface layer (50 m height) to the deposition velocity at 1 m above the ground, show that the deposition velocity for SO2 at 50 m typically was 50-75% of the value at 1 m (ref. 12). The initial concentrations assigned at the starting point of the 96 h long trajectories can be important for the developnent along the trajectory. The integration was started with a set of wncentrations corresponding to a slightly polluted atmosphere, with the removal processes in equilibrium with Nihc and VOC emissions at 10% of the average emissions for Western Europe.
660 The
emissions of
Nox
estimated by the PHOXA-project f o r the ozone
episode in late May 1982 for the part of the g r i d RTM-I11
model
area
covered by
the
13) were found to be about the double of the emis-
(ref.
sions estimated in PlIEP f o r the PHOxA-arsa and for that time of t h e year ( r e f . 12), while the VUC-emissions estimated by PHOXA w e r e canparable with the emissions estimated in connection with model work i n (ref. 10). The doubling of Nox emissions estimated by the PHOXA-project f o r t h e l a t e May 1982 episode wmpared to the emissions estimate f o r t h a t time of the year, w a s applied throughout the PZEp grid, whlle t h e voc emissions were kept approximately as in r e f . 10. RESULTS AND DISCUSSION I n the t i m e period
28 May-3
June 1982, there w a s a high pressure
system located Over north Europe w i t h its center Over Denmark on 30 May 1982, moving eastward and w i t h its center Over E a s t Europe on 2 June. The wind speeds were law, and the maximum hourly ozone concentration recorded w a s about 160 ppb, i n the N e t h e r l a n d s on 1 June. I n Figure 1 is shown 4 day back t r a j e c t o r i e s to the 14 receptor sites for 1200 GWT on 28 May, 1 and 3 June 1982, while i n Figure 2 is shown the 1200 GWT mixing height f i e l d f o r 31 May 1982.
MIXING HEIGHT
24 6 8101214161~0eTzli2~~~~~~8 height f i e l d i n metres f o r 1200 m, 31 May (Contours f r a n 204 to 2492 m i n i n t e r v a l s of 458 m. )
Fig. 2.
Mixing
1982.
661
The measurements of ozone are made near the ground surface, usually only one or a few metres above the pund. This means that the measured concentrations usually are significantly reduced at night through ground removal below the noctural inversion and by local emissions of NOx becoming trapped in the shallow ncctural mixed layer. On the other hand, in the model a concentration representative of a layer with height canparable to the M o n mixing height the day before, is calculated at night. This concentration is only weakly influenced by ground removal at
night, and therefore the calculated diurnal variation of O3 is usually smaller than the measured. It should be kept in m i n d that for measured and calculated ozone concentrations, only the day time values when the atmospheric boundary layer is well mixed, are really canparable. In Figure 3 is shown the caparison of calculation and measurement for 4 sites where the agreement was satisfactory. Sane sites (in particular Colaniers and Illmitz) showed a poor agreemant between measured and calculated ozone concentrations. The calculations with the choice of physical and chemical parameters giving the results shcun in F i g . 3, were canpared with the results of calculations where sane of the most important parameters were altered. In Table 1 is given an indication about the changes calculated in the ozone concentrations when the temperature, mixing height, cloud cover, ground deposition velocities or initial conditions were changed. It can be seen that the parameter changes all influenced the ozone ooncentrations significantly. The degree of change canpared to the reference case can be evaluated fran the b o t h 3 lines of Table 1; increasing T by 2% increases the 03-levels in general less than 10 ppb, 50% reduction in mixing height reduces O3 by typically 10 ppb, a clear sky assumption causes O3 to go up nearly 10 ppb, deposition reduced a factor of 2 increases O3 le8S than 10 ppb, reducing the initial concentfations significantly reduces O3 between 10 and 20 ppb (canpared to an initial concentration of 32 ppb in the reference case). Calculations were carried out to see haw the concentrations of O3 at the 14 receptor sites changed during the 28 May-3 Jue 1982 perid with changes in the emissions of NOx and Mc. Uniform emission changes were carried out throughout the grid.
662
LANGESUNO m
I
1
J
I
SAPPERMEER
1
I
I
y
g I30
50 ppb ference, 0 >70 ppb Aference, O3 >80 ppb
A
8 11 8 14 14 4 17 1 2 4
-0
TABLE 2 Percentage of trajectories with more than 60 ppb 0 at the arrival point for the sites in each of 4 geographical areas and fbr the sum of those sites. Time period 28 May 1200 M - 3 June 1982 1200 m (25 trajectories per site). See Fig. 1 for explanation of site nurnbers. Description A N O x ( % ) A=(%)
0 -25 -50 -62.5 -75 0 -50
-25
0 0 0 0 0 -25 -25 -25
FRG
sites vian sites sites ( 2+3+4) ( 5+6+7+8) 29.3 46.7 49.3 41.3 24.0 9.3 33.3 21.3
22.0 24.0 17.0
34.0 22.0
9.3 16.0 28.0 25.3 17.3 4.0 13.3 8.0
19.0 31.7 36.7 33.0 23.0 4.3 25.3 16.7
reduction in NOx emissions by 25% was calculated to increase O3 in all 4 geographical areas where receptor points were located. Reduction in NOx by 50% led to a further increase in O3 over the -25% case, but the increase w a s slight everywhere except in the UK. A further reduction in NOx emissions to -62.5% and then to -75% is 88en to decrease O3 mwhere. The CaSe w i t h ANDX = 50% end A W C = 0 o c Using the PlEP estimate of NDx and VOC emissions for May/June 1982, and starting A
664 f m m t h i s level of Nox emissions a further reduction in NOx
emissions
reduces O3 everywhere. The Nox emissions used in the reference case are so high that the O3 formation is suppressed (ref. 14). A reduction in VOC emissions by 25% is calculated to reduce O3 efficiently both relative to the reference case and to the case where A N O x = -50%. The decrease is dramatic in the A N o x = 0, A V O C = -25% case, which underlines the effect that very high NOx emissions has on episodic boundary layer ozone by prolonging its formation time. This leads to an increase in the probability that the boundary layer air is mixed into the free troposphere before the precursors are depleted. In the free troposphere the precursors are further diluted and take part in an efficient production of free tropospheric ozone. ACKNOWL-
This work is sponsored by the Cannission of the European Carmunities through two subcontracts with TNO, the Netherlands and by the Royal Norwegian Research Council for Science and Technology ("I?). The work has been carried out in co-operation with EMEP MSC-W at the Norwegian Meteorological Institute. REFERENCES
7 8 9 10 11 12 13 14
P. Grennfelt and J . Schjoldager, Ambio, 13 (1984) 61-67. P. Grennfelt and J . Schjoldager. Oxidant data collection in O E O Europe 1985-87 (OXIDATE). LillestrQm (NILU OR 22/87), 1987. R.D. Bojkw, J . Climate Appl. Meteor., 25 (1986) 343-352. A. Volz and D. Kley. Nature, 332 (1988) 240-242. U. Feister and W. Wannbt, J . A b s . chem, 5 (1987) 1-21. W. AttmaMspacher, R. Hartrnannsgruber and P. Lang, Meteomlo. Rdsch., 37 ( 1984) 193-199. 0. Hov, K.H. Becker, P. Builtjes, R.A. Cox and D. Kley, Air Pollution Research Report 1, CEC, Brussels, 1986. I.S.A. I~aksenand 0. H W , Tell-, 39B (1987) 271-285. G.Z. Whitten, J.P. Killus and R.G. Johnson, Modeling of auto exhaust snmg chamber data for EKMA developnent. SAI, California, 1984. A. Eliassen, 0. Hov, I.S.A. Isaksen, J . Saltbones and F. Stordal. J . Appl. Meteor., 21 (1982) 1645-1661. 0. Hov, F. Stordal and A. Eliassen. Photochemical oxidant control strategies in Europe: A 19 days case study using a Lagrangian model with chemistry. Lilles(NILU TR 5/85), 1985. 0 . Hov, A. Eliassen and D. Simpson, in I.S.A. Isaksen (Editor), -eric Ozone, Reidel, Dordrecht, 1988. P.J.H. Builtjes and E. Luken, Developnent of a strategy against photochemical oxidants, Phase VI Long-range transport. mE0, The Netherlands, 1987. S.C. Liu. M. Trainer. F.C. Fehsenfeld. D.D. Parrish. E.J. Williams. D.W. F&y, G. Htlbler and P.C. Murphy; J . Geophys R e s . , 92D (1987). 4191-4207.
SESSION X
STATIONARY SOURCE CONTROL TECHNOLOGIES
Chairmen
J.H. Blorn G.B. Martin
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam Printed in The Netherlands
-
667
HYDROCARBONS 2000 N. Stenstra Task Force VOC 2000
Much has been said in the last few days about the effects of ozone in the troposphere on animals and plants. Although in many ways, effects cannot be separated from those resulting from mineral acid concentration, effects are nevertheless considered unacceptable. Therefore it is important that ways and means are found to reduce that ozone concentration. As far as Europe is concerned this is a continental problem. As you know the ozone forming in principle can be opposed in two different ways, one by reducing NO, emissions and two by reducing the emissions of volatile organic substances. Dutch Environmental Policy attacks the latter. Scientists among you have told us many times which VOS reductions will be necessary to achieve a negligible effect of ozone on the environment. They say 80 percent would be necessary. Apart from the fact that at this moment it is impossible to produce a quantitative justification for such a reduction it is also a fact that in practice such a very large reduction is unattainable for the time being. For practical purposes, for an intermediate period, up to the year 2000, the Ministry of the Environment in the Netherlands considers that the reduction of 50 percent compared with the base year 1981 would be necessary. In order to see whether such a reduction is possible and to Indicate how it could be achieved in 1986 a project was started named Hydrocarbon 2000. For the record it must be stated that in the context of this presentation volatile organic substances and hydrocarbons must be considered identical. Sources of volatile organic substances in the Netherlands and probably everywhere can be distinguished in a number of categories as specified in the table below together with the accompanying emissions in 1981 and 1985.
668
emissions in millions kg.
traffic industry small business domestic agriculture combustion installations TOTAL
I 1981
I 1985
200 130 83 31 24 10
190 118 80 32 24 10
478
454
I
For traffic emissions in the EEC a policy is being developed that should lead to reduction of the hydrocarbon emissions in that sector of 50 percent. Also with regard to agriculture such a procedure is being followed. Further it must be considered that in combustion installations only a very limited possibility exists to reduce the VOS emissions. As a result, the categories industry, small business and domestic emissions will have to achieve a halving of the emissions in order to achieve the overall desirable reduction of 50 percent. Project Hydrocarbon 2000 is aimed at the last three sectors. Most of the emissions result from some twenty different categories. To name a few: chemical industry, painters, metal industry, households and the oil industry. About 65 percent of those emissions were caused by the use of solvents and about 30 percent by applying paints. Consequently a large part of the reduction must be found by reducing the use of solvents generally and in the application of paints in particular. The approach of Hydrocarbon 2000 is the desire to achieve approximately a 50 percent reduction. The purpose of Hydrocarbon 2000 was to indicate the road which would achieve that reduction; developing a reduction strategy. In that respect the starting points for the Ministry of the Environment were the following: - Hydrocarbon 2000 would have to adress itself to all source categories within society. The problem of hydrocarbons is indeed one of many small contributors which together cause a large emission and that meant that many sectors of enterprises had to be considered. - Hydrocarbon 2000 would have to adress all volatile organic substances. It is true that some substances are more reactive
669 than others but in view of the international character of the ozone problem is wasn't useful to distinguish between them. - Fluorinated hydrocarbons which cause problems because of their non-reactivity in other areas and methane which is very much less reactive than heavier substances have not been considered. A combatment strategy which has as its objective that all sources are reduced by 50 percent did not appear very opportune. The possibility to reduce emissions differ from sector to sector and consequently that had to be taken into account. Another aspect of the approach of the project Hydrocarbon 2000 was the desire that the combatment strategy would have to be developed in very close co-operation with all parties concerned. In other words the purpose was to develop a strategy with the greatest percentage of consensus and which therefore could count on general support. This has been proven possible. The cooperation and concurrence has been obtained from provinces and municipalities (within the framework of the law they are responsible for applying environmental policy), the inspectorate, the Ministry of Economic Affairs and -last but not leastindustry. It will be seen that the method chosen was one, where all concerned, contributed to finding the solutions to problems within their sphere of interest from the beginning rather than reacting to solutions invented behind a desk in the Ministry. The open and interactive structure of the discussion ensured that all areas of concern could be fully ventilated and given its due weight. In this context it must be pointed out that the effectiveness of the Hydrocarbon 2000 strategy is related to the assumption that the ozone problem will be attacked at the European level. Other countries will have to achieve comparable reductions and other categories of emitters such as traffic will have to achieve comparable hydrocarbon emission reductions. Of course in formulating the measures and the goals it had to be assumed that the present knowledge of the mechanisms of photochemical reactions both concerning the part of volatile organic substances as well as the role of nitrogen oxides was essentially correct. The objective to obtain a workable strategy meant that a number of parts would have to be developed: - a Reduction plan which describes how each source of emission will have to be reduced and by what time,
670
- an Implementation plan, which indicates how various reductions will be introduced, and who will be responsible for what,
- a plan for international co-ordination which indicates how the Netherlands in an international environment will try to stimulate the reduction of the emission of volatile organic substances. During the project a need became apparent to create a so-called after care organization which, in the coming years would control and direct the introduction of the strategy and manage necessary or desirable changes. The methodology The first problem the project group KWS 2000 had to tackle was the preparation of an inventory of hydrocarbon emitting sources and the size thereof, hardly a simple task. With the help of several individual companies and trade associations nevertheless, reliable emission data could be accumulated. The next step was preparing an inventory of possible reduction measures where the aspect of cost activity was emphasized. An important aspect was that the policy should be directed as much as possible to realize preventive measures, like replacing solvents by alternative products and replacing and adapting certain processes. On top of that application of additional combatment measures like adsorption, condensation and biofiltration were seen in some cases as a solution to specific problems. From these data per association a choice was made for the measures to be taken and an assessment was made of the reduction in hydrocarbon emission that could be achieved as a result. The primary considerations in this choice were the environmental benefits to be achieved, the cost effectivity and the economic viability. These considerations were based on a number of criteria which had been formulated as an assessment basis for possible measures. The criteria included the absolute percentage-wise emission reduction, the possible infringement on the competitive position of trade associations, societal acceptability (for instance, when the composition of products was changed) sideeffects and micro economic costs. Completing the draft reduction marked the beginning of a very important phase in the project namely that of consultations. With
671
various trade associations extensive discussions were held concerning the viability of the measures and possible alternatives. Constructive discussions were held which led to adjustments in the Reduction plan. This revised plan was again submitted for comments and after including these later comments and suggestions the Reduction plan could be formulated in its definite form. It will be clear that the procedure was carefully followed and as many desires as possible were taken into account. The original plan envisaged that during this procedure at some time a choice would be made on the basis of criteria which measures should be persued and which ones should be dropped. A n objective method to guide the choice was difficult to find and therefore in consultation within the group a choice based on insight and experience was made. As it happened the result in reduction was slightly above 50 percent which removed a significant difficulty. In the meantime, discussions were held with regional government and environmental inspections about an Implementation plan and an after care organization. It will be noted that where the measures had to be paid for by industry the primary lead function in this respect was with industry. In the implementation, the significance of co-ordination with regional authorities was envisaged and thus the lead was laid with the regional governments. After substantial discussions the Reduction plan was also found acceptable to the regional government and the implemention plan and after care organization are still under discussion with the trade associations but expectations are that they can be finalized shortly. After that, in principle the strategy for Hydrocarbon 2000 will be finished. Reduction plan Although the combatment strategy consists of all plans the basis is formed by the Reduction plan in which the measures and the reductions to be achieved per trade association are indicated. The measures and reductions to be achieved are subdivided in four categories, ie; Autonomous reductions: reductions which will occur without formulating separate requirements: Examples are reduction of emissions by replacement of outdated apparatus and/ or inotallationo or reduotiono by
672 changes in the raw material composition. Certain measures : measures which can be applied without any restrictions and therefore are considered mandatory. Conditional measures : measures that can only be applied if certain conditions are met. These conditions can be that a certain combatment method is sufficiently developed or that a product formulation has to be developed.It could be the necessity of international co-ordination with regard to the measures or presence of a sufficiantly large societal acceptability. Uncertain measures : these are measures which in principle are considered achievable but some uncertainties remain, such as the economic position of the trade association at time of introduction measure (which could be some years away) or the uncertainty whether an alternative process or product can be developed at all. Clarity must exist about solving these uncertainties before the viability of the measure can be decided upon definitely. These various kinds of measures - particularly the conditional and uncertain ones for which preliminary actions have to be taken, necessitate a phasing of the introduction. Therefore the measures have been allocated over three periods of four years. For each trade association it has been indicated when the desired measures will have to be achieved. Another reason for this phase approach is that as we look further into the future, uncertainties accumulate. In 1988 it is difficult to predict what the possibilities will be in say eight years, and that implies that the Hydrocarbon 2000 strategy may have to be reviewed and adjusted with some regularity. That review will be made once every four years starting in 1992. These variations will lead to smaller or larger changes in Reduction plan. For the coming four years, the plan is just about fixed however.
673 For the coming 12 years that will result, if all conditions and uncertainties are resolved, in the following reductions for the various categories.
emissions in kton/annum 1981
2000 (KWS 2000)
chemical industry painting metal industry private households oil industry printing industry storage companies gasoline stations carspray paint installations wood conservation foodstuff rubber- synthetic materials dry cleaning metal conservation furniture- wood construction textile industry leather industry automobile trade other industry In total the reduction will follow the cause as outlined below as far as industry, small enterprises and domestic consumption is concerned. KWS
2000
-
Eniissies tot he: jaa: 2000 0res:
Oza mz
voaw
mwoor
Fig. 1. Reduction of VOS (1981-2000)
674
Implementation The various reduction objectives which have been laid down in the reduction plan will have to be realized by the various enterprises and other emitters. Many sources exist and consequently much will be required of the executive bodies for the environmental policy. It has been indicated how each measure will be implemented, that is to say: who will initiate that, what instrument will be used and when can that implementation be expected. In that way it is clear for everybody when certain actions may be expected. For the implementation preferably the choice has been for "soft" instruments: information, guidelines and adapting permits to include certain requirements. Secondly, if necessary, legislation will be introduced. Such an implemention which will have to be realized during the coming 12 years requires a good organization. For that reason a so-called after care organisation will be created, in which again close co-operation will be realized between the Ministry, industry and lower government. If that implementation goes as expected very substantial emission reduction of volatile organic substances will be realized by the year 2000 in the Netherlands. If the countries surrounding us will achieve similar reductions a considerable step will have been set in the direction of an acceptable ozone level.
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989Elsevier Science Publishers B.V., Amsterdam Printed in The Netherlands
675
-
VOC CONI'ROL IN STORAGE AND PROCFSS INWSTRY
J.J. Verhoog Environmental Coordinator - ESSO Netherlands, Rotterdam Refinery
ABSTRACI-
VOC emissions from refineries, petrochemical industry and storage companies in the Netherlands were about 52.000 tons in the year 1985, Administrative loss control is not the adequate tool for an emission reduction program. A special environmental loss control is needed on the basis of the following three steps 1) Identification of all potential emission source. 2) A proper design of equipment with respect to emission control. 3) A preventive maintenance program.
INlRODUCTION The contribution to the VOC emissions in the Netherlands from storage and process industry is about 50.000 tons/year or roughly 20% of the total VOC emission level (excluding autanotive exhaust emission). A substantial part of these emissions takes place in the Rotterdam harbour area where the handling, storage and processing of hydrocarbon products (oil products and petrochemicals) is concentrated. You will find there 5 referencies, sane of them with integrated petrochemicals production, several large oil and petrochemical storage and shipping companies and a nunber of petrochemical plants. The VOC emission picture for the Netherlands as a whole has been summarized in the table below.
year 1985 (Ktons/year) Ex refineries Ex petrochem. plant Ex storage companies
14.5* 28.0 19.5 52.0
*
Process 20-40 30-50 5-15
Storage 20-40 10-30 50-70 1
Shipment 20-40 20-40 20-40 1
1985 refinery thruput 60.000 Kton/year (VOC loss = 0.026%)
1
676
ADMINISTRATIVE LOSS CONTROL VOC emission means product loss. The question arises if it is possible to control these losses as part of a general administrative loss control system. The famous gospel song learns us to count our blessings every day. In the oil and petrochemical business it certainly pays to account for your product losses, if not on a daily basis at least on a monthly basis. Occasionally this leads to a surprise. Instead of calculating a loss figure, you will sanetimes calculate a product gain. Sanetimes this f'gainll will compensate partly for a high loss in the previous month and if not you know in advance that you will have to face a high loss figure the next month. It is obvious that reducing of the measurement inaccuracy is the main challenge in the field of administrative loss control. The administrative loss figure will vary from 0.2 up to about 1 weight percent of total thruput. The estimated losses into the air were less than 0.03% for the refinery branch in 1985. In addition to air losses there are losses via effluent water or via waste disposal. Together these environmental losses are called the 'accounted for' losses, The other part, called the 'non-accounted for' losses results from measurement inaccuracies and even at a very low administrative loss figures of 0.2% of total thruput the 'non-accounted for' part of the losses is in general higher than the 'accounted for' part of the environmental product losses. The overall conclusion is: Over and above the administrative loss control there is a need for extra registration and measurement to arrive at a reliable and accurate (at least not too inaccurate) emission figure in other words a separate environmental loss control system.
ENVIROMWTAL. LOSS COMROL As mentioned before there are three VOC emission categories a) Loss from storage tanks. b) Loss fran product loading and unloading. c) Loss from process equipment and activities.
As far as the categories a and b is concerned the VOC emissions are primarily determined by the design of the equipment.
677 It is obvious that product losses €ran a cone roof tank with an open vent into the atmosphere are much higher than a well designed (and properly maintained) tank with a floating roof or an innerfloater. This also implies that emissions in the category a and b can be calculated rather accurately if all relevant parameters like product vapor pressure, storage temperature, meteo conditions, type of seal, loading velocity etc. etc. are taken into account. By several test programs these calculations have been verified by measurements so that accurate registration is possible without frequent measurements in the field. And above mentioned product losses are normally a part of the administrative loss control system as well. When we consider the category c emissions, those are the emissions related to the process activities, it becomes much more difficult. How can this category of emissions be reduced in an effective way and in what way can we follow up whether or not we are really improving the situation. This requires a systematic approach in which the following three steps can be distinguished: Step 1: Identification of all (potential) emission sources. In the first place a systematic inventory has to be made of all the losses which will or can take place. In the following list I have summarized the most important ones: 1. Vent systems into atmosphere. 2. Safety valves leaking in the atmosphere. 3 . Seals of rotating systems (pumps, compressors). 4. Valves, packing glands etc. 5. Draining of product or water with product contamination 6 . Evaporation from sewer systems. 7 . Waste water treatment. 8. Cleaning, turnaround and maintenance activities. 9. Flare systems (incomplete combustion). The above mentioned emissions are also mentioned fugitive emissions and control of something called fugitive is not easy. So one have to set priorities. For each specified situation it has to be established firstly what the main contributors are. The TNO emission registration system in the Netherlands provides general emission factors for all above mentioned types of losses.
678
Step 2 : A proper design of equipment with respect to emission control. We have done certain things in the past which we will not do anymore, In new plant designs we will not have open vent systems, most of the safety valves will be connected to a closed system (safety valve discharge header) and vessel or drum content will be drained via a closed drain header into a low point drain system. In those situations where improvements of older systems will have to be made it will be done preferably in combination with modernisation and replacement investments. A modern and well designed plant will have a low emission figure on paper (represented by a fixed amount in the administrative loss system). However a next step is needed to guarantee that the paper figures (emission factors) are and remain representative for the actual emissions. So
we now have to consider the next step.
Step 3: A preventive maintenance program. New technology will only yield good results when it goes together with a preventive maintenance program to ensure that the equipment is properly maintained and will meet its design conditions. Preventive maintenance will have a direct and an indirect impact. The direct impact is obtained by for instance replacing a packing or seal before it is worn out or at least to replace it as soon as the first leakage will occur. The indirect impact is via an increased reliability of the operations. For instance frequent repairs of pumps requires cleaning and draining activities causing extra emissions, Unit upsets will result in extra flaring and a variation in flaring load means lower combustion efficiency. The final question arises: What can we gain with all these measures? Pollution prevention pays. That is certainly true but as explained earlier, this profit is not measurable due to the inaccuracy of the administrative loss system. But although it is difficult to quantify the money figure what we gain is more than profit. Environmental awareness together with safety and industrial hygiene awareness helps to make business more healthy, more pleasant and more challenging. Or to say it in other words: It is the human factor that counts.
679
Let me finish with a final remark. I have already mentioned the word Industrial Hygiene. Especially in the chemical industry exposure monitoring programs have been developed to protect the workers from exposure by toxic vapors. High exposure will alert the organization and will start an investigation to find the source of the emission. For instance: Is there a leak into the sewer system resulting in high air concentrations in the waste water treatment unit. And when we are able to stop high exposures, we automatically stop VOC emissions. In this respect a well balanced hydrocarbon monitoring and leaking detections system can be of great help to increase awareness to stimulate preventive maintenance and to decrease fugitive emissions.
This Page Intentionally Left Blank
T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Zmplicatwna 0 1989 Elsevier Science Publishers B.V., Ameterdam - Printed in The Netherlands
NO,
681
CONTROL TECHNOLOGY FOR LARGE COMBUSTION INSTALLATIONS
J. VAN DER KOOIJ Environmental Research Department, N.V. KEMA. P.O. Box 9035, 6800 E T Arnhem (The Netherlands)
ABSTRACT Advances to the state of the art of low NO, combustion technology f o r gas and coal fired boilers offer the possibility for considerable NO, emission reduction. In the Netherlands the utilities have developed on a voluntary basis a concerted NO, Abatement Programme in order to reduce the NOx emissions of both existing and new installations. The programme also comprises a number of demonstration projects in order to assess the applicability of new techniques and to prepare for decisions on cost-effective NO, controls. INTRODUCTION Most of the anthropogenic nitrogen oxides are produced during combustion processes. These processes may occur in stationary or mobile sources. An inventory of the NO, emissions in the Netherlands is presented in Table 1 for the years 1980 and 1985.
TABLE 1 NO, emissions in The Netherlands in 10’ t/a (ref. 1). I980
1985
80 20 44 26 45
83 17 43 20 46
road tcaff ic
264
261
other t canspor tat ion
57 536
57 527
power stations re€ineries industry, combustion industty, processes Other stationary S O U C C B S
Powerstations, refineries and part of the industrial combustion belong to the category of the large combustion installations. Under the idea that 5 0 % of the industrial combustion
602
processes occur in installations w i t h a capacity larger than 50 MWth, approximately 110 ton/a NO, is produced in large combustion installations, equalling 20% of the national emissions. As t h e power stations produce 75% of these emissons, there is a good reason to confine t h e discussion to power station emissions. Another reason is that the emission standards for combustion installations are thus far not applicable to process furnaces whereas government and industry a r e cooperatively investigating the N O x emissions of these installations and the technology to reduce it (ref. 2). Reduction of t h e N O x emissions of the power stations in t h e Netherlands w i l l have a small effect o n ground level concentrations, acid deposition and ozone formation. If however these measures a r e taken in collaboration with neighbouring countries the environmental relevance increases considerably. T h i s can be seen from Table 2 in w h i c h the power plant NO, emissions in a number of countries are given. T h e N O x emissions vary between 12 and 44% of the national emi6sions. w i t h 25% as a n average value. If w e furthermore consider a NO, emission reduction by 408 in agreement vith t h e Proposal for a Council Directive on the limitation of emission of pollutants into the air from large combustion plants w e c a n expect a reduction in t h e average ambient concentrations of NOx typically i n the order of 10% (ref. 3).
TABLE 2 N O X emissions in neighbouring countries. nat iona 1
power: stations
103 t/a
103 t/a
%
Belgium
415
85
20
Denmark
265
115
43
France
2567
297
12
Germany
3 100
850
27
Italy
1595
530
44
00
15
Netherlands
536
683 NOX A B A T E m N T STRATEGY In the United States the New Source Performance Standards came into effect in 1971. This led to the construction of larger furnaces in new power stations and the incorporation of combustion modification. In this respect it is important to note that NOx formation depends strongly on furnace conditions. Even small modifications in the combustion process can greatly influence emission levels. Combustion modifications to reduce NOx are generally based on promoting a more gradual mixing of fuel and air to reduce flame temperature and the use of a richer fuel-air mixture to reduce oxidation of nitrogen in the fuel. In Japan the regulation of NO, emission started in 1973 and was tightened in a number of stages. In early the eighties the standards became so stringent that flue gas treatment was needed in addition to combustion modification. In the Federal Republic of Germany in 1984 a council of environmental ministers promulgated targets for NOx emission standards for both new and existing installations, that were so stringent that flue gas treatment was needed. Moreover the time schedule for the incorporation of the controls was so short that most efforts were directed towards flue gas treatment. In the Netherlands the first applications of combustion modifications occurred in the early seventies. For many power stations the NOx emissions were limited by the provincial authorities in licenses according to the Air Pollution Act. Only in 1987 a General Administrative Order on the emissions of large COmbUStiOn installations came into force (ref. 2). The standards are strict especially for new installations (coal 400 mg/m 3 , oil 300 mg/m3 and gas 200 mg/m 3 ) . However it is expected that the development of low NO, combustion technology has developed so far that with advanced combustion modifications these standards can be met. The differences between these national approaches are so large that it is considered useful to evaluate the state of the art of NOx control technology for large combustion installation in some detail and to describe the efforts of the 1
electric power companies in the Netherlands in their concerted NOx Abatement Programme (ref. 4). This programme is implemented on a volumentary basis. It consists primarily of the application of low N O technology in new and existing inX
684
stallations. In the second part of the programme new technologies are demonstrated to assess their applicability and to prepare for decisions on cost-effective NO, controls.
COMBUSTION MODIFICATIONS FOR GAS/OIL FIRED INSTALLATIONS Since 1980 the amount of fuel oil fired in Dutch power stations has decreased considerably and in the present situation fuel oil is mainly used as a substitute for natural gas. on days when the gas supply is interrupted. Therefore w e have no recent experience with oil fired installations in the Netherlands. However, it is our view that the extremely low N O concentrations that have been reported in the literature, X especially from Japan do not hold for the Dutch situation, because of the differences in fuel oil composition (e.9. sulfur content, residual oil v s . crude oil). Natural gas is a very important fuel for the Dutch power stations. An ambitious programme consists of the repowering of a steam turbine in existing installations with a gas turbine. In these installations the new gas turbine replaces the existing air blowers and the regenerative air heater. The exhaust gases of the gas turbine with an oxygen content of approximately 15% are used instead of fresh air for the combustion of gas or oil in the existing boiler. Increasing the thermal efficiency from a typical value of 40% to 45% and reducing the NOx emission are the main goals of the programme that is applied t o 10 power stations with an equivalent capacity of 3650 MWe (Table 3.1). T h e NO, emission is reduced primarily because of the low combustion temperature in the boiler; as a matter of fact the adiabatic flame temperature is lowered by the inert material in the gas turbine exhaust and the boiler load is reduced to approximately 70% as the other part of the combustion takes place in the gas turbine. A very important point is the selection of the proper gas turbine as there is a close relation between rating of the existing steam turbine and the gas turbine. Therefore there is not a free choice for a gas turbine with a high efficiency an a low NOx emission. The NOx emission of the gas turbine and control measures in the boiler are also important for the NOx emission of the combined cycle. It was expected that the N O X
emission of the power stations could be reduced by 30% and would amount to 100 g/GJ as an average, although some of the installations had high NO, emissions because of the.high thermal load in the furnace. At present it is already known that reductions higher than 5 0 % have been achieved at full load in a number of installations. The usual combustion modifications are applied in a demonstration project of low NO, combustion technology for gas and oil firing in Flevo Station 1. Flevo station 1 has been retrofitted with advanced low NO, burners, after air ports and gas recirculation into the combustion air. The expected emission 3 values are 200 mg/m3 for gas firing and 300 mg/m for oil firing. However the main objective of the project is the application of reburning technology, also known as In Furnace NO, Reduction (Table 3.2). Reburning is a distributed combustionsystem in which part of the fuel is injected into the furnace through burners placed above the top row of main burners. By correct adjustment of the fuel and air distribution. the reburn zone is operated fuel rich, thereby converting NO from primary zone combustion into N2. The aim of the project is to demonstrate the technology for gas and oil firing with rapid load fluctuations and to investigate the optimum NO, emission level, the quality of the combustion process (CO, and unburned carbon) and the mixing processes of upper fuel and over fire air the combustion gases. The NOx goal is 100 mg/m3 for natural gas and 200 mq/m3 for fuel oil.
686
TABLE 3 Concerted NO,
Abatement Programme.
Gas/oil firing Conversion of existing steam boilers to combined cycles power station
capacity (MWe)
commissioning
336 336 328 273 159 645 622
1986 1987 1987 1987 1988 1988 1988 1988 1989 1989
~~
Bergum station 1 Bergum station 2 Harculo station 5 r,age Weide station 5 Merwedehaven station 6 Eems station 2 Hemweg station 7 Waalhaven station 5 Flevo station 3 Waalhavsn station 4
313
451 3 13
Demonstration project o € €or gas and oil firing Flevo station 1
low NO,
combustion technology
capacity 185 MW
commissioninq 1988
- advanced low NO, bucnecs - gas mixing into the combustion air - two stage combustion - infurnace NO, reduction COMBUSTION MODIFICATIONS FOR COAL FIRED INSTALLATIONS I t is known that in a number of coal fired power stations in Japan NOx concentrations have been obtained in the range between 500 and 600 mg/m3 have been obtained. In order to obtain N O concentrations below the desired value of 400 ~ n g / m ~ ~is i tnecessary to equip the boiler with advanced low-NO, burners and two stage combustion. The results obtained in Japan with the PM burner developed by Mitsubishi Heavy Industries for tangentially fired boilers and HT-NR burner developed by Babcock Hitachi for frontwall and horizontally opposed fired boilers prove that the technology has advanced and conforms to the requirements (ref. 5). In the Netherlands the Power Stations Maasvlakte and Borssele have been converted from gas/oil to coal firing. These boilers have tangential firing systems. As the decision about conversion was taken at a time that the P M burner was not yet available for
687 coal firing, the SGR burner was used. Because of enlarged furnace volume, increased over fire air and the application of the Low NOx concentric firing system the boiler manufacturer "de Schelde" considered that NOx Concentrations below 600 mg/m3 can be reached. In the framework of the concerted NOx Abatement Programme a measurement programme is executed (Table 4.1). The preliminary results of Borssele and Maasvlakte are encouraging. For horizontally opposed and frontwall fired installation the experience in the Netherlands with modern combustion modifications is considered to be insufficient. Therefore the decision has been taken to perform a demonstration project in the Maas Station 5 (Table 4.3). The unit will be retrofitted with HTNR burners and after air ports by the boiler manufacturer "Stork Boilers" with a license of Babcock Hitachi. The aim of the project is to show that a NO, concentration of 400 m g / m 3 in new power stations can be obtained by the combination of advanced low NOX burners and two stage combustion in frontwall and horizontally opposed fired boilers. In addition to the primary measures mentioned before, the National Government of the Netherlands is of the opinion that flue gas denitrification has to be applied in future when the results with low NO, combustion technology are insufficient. A demonstration project, fully paid by the government, is in progress in Power Station Gelderland 12. This project is based on MHI high dust SCR technology. Originally the discussion of flue gas treatment technology was dominated by Japanese suppliers and users of SCR systems. However in recent years in Western Europe, with emphasis on Germany, a stormy development has taken place resulting in a large number of installations (ref. 6): 70 pilot SNCR/SCR plants with a total flue gas volume of about 250.000 m3/h 50 demonstration and commercial plants of 12.000 MWel.
688 TABLE 4 Concerted NO,
Abatement Programme.
Coal firing 1 Conversion of gas/oil fired power station to coal firing
Maas station 6 Maasvlakte station 2 Borssele station 12 Maasvlakte station 1
capacity 223 MW 517 MW
commi ss i o n i np 1986 1987
405 MW 517 MW
1987 1988
2 Study in existing power stations Gelderland station 13 AmeK station 8 3 Demonstration project combustion technology Maas station 5
603 MW 645 MW
of
low
180 MW
NO,
pulverized
coal
1988
- advanced low NO, burners - two stage combustion 4 Flue gas denitcification
Gelderland station 12
- SCR is
123 MW
1987
50% of flue gas stream
CONCLUDING REMARKS NO, abatement for stationary sources can be realized primarily by combustion modifications. The low-NOx technology that is applied depends on a number of aspects e.g. retrofit or new installations, fuel and boiler type. On the basis of information obtained thus far estimated NO, emission levels for new installations are presented in Table 5. The use of combustion modifications can be limited by side-effects such as - increased fouling - corrosion by reducing atmospheres - increased CO emission - incomplete burn out. In the Netherlands the quality of the fly ash is considered to be of great importance. There are Bome indications that the physical properties of the ash may change because of the lower
688
furnace temperatures, and that this may have consequences for the applicability of fly ash in construction materials. The potential of combustion modifications is even greater if reburning technology is taken into account, with potential emission reduction in the order of 5 0 % . The technology has been proven for natural gas and fuel oil. There are indications that a highly volatile and low nitrogen containing fuel should be used as a reburn fuel. There is a difference of opinion about the feasibility of the technique with coal as upper fuel. If however combustion modifications are insufficient or are considered to form a great risk. the NO, emissions can be reduced by flue gas denitrification. Selective catalytic reduction is the most promising technology. But other techniques like SNCR or the injection of urea can be cost-effective alternatives especially when the necessary emission reduction is limited. From the first results in Western Germany it seems that SCR can be applied without problems. However it is necessary to point out that there is no long term experience. This is especially important in determining catalyst life, when these materials are subjected to frequent temperature excursions, due to changes in boiler load. Major other problems are the use of different coals and different types of coal fired boilers whose ash may contain constituents that prematurely erode or deactivate the catalyst. Also ammonia slip is considered t o be a potential problem, because of the deposition of ammonium bisulphate in the air preheater and possible contamination of fly ash by these ammonium components.
630 TABLE 5 Estimated NOx emission on levels for new installations in mg/mi (ref. 5 ) .
coa 1
oil
gas
(6% 02)
(3%0 2 )
( 3 % 02)
1000-1400
500-700
300- 600
combustion modifications
600-900
200-300
150-270
advanced low NO, burners) combustion modifications)
300- 600
130-250
5 0 - 110
advanced low NO, burners) combustion modifications) SCR 1
65-130
without control
advanced low NO, burners) combustion modifications) r e bu r ni ng 1
(120-300)
50
65-130
25
25-50
REFERENCES Milieuprogramma 1 9 8 8 - 1 9 9 1 , Tweede Kamer, vergaderjaar 1 9 8 7 - 1 9 8 8 , 2 0 2 0 2 nrs. 1 - 2 . General Administrative Order "Emission standards for combustion installationsaa,Staatsblad 1987. nr. 1 6 4 , 2 8 april 1987.
E C COM ( 8 3 ) 7 0 4 final. Proposal for a Council Directive on the limitation of emissions of pollutants into the air from large combustion plants. W E N . Voorstel Totaal Programma NOx-uitworpbeperkende Maatregelen (maart 1 9 8 6 ) . J.G. Witkamp, J . van der Kooij, M.E.A. Hermans. status of low NO, combustion technology in Japan; a report of a technical visit in KEMA report 02562-MOL 8 6 - 3 0 4 0 . UNIPEDE Sorrento Congress. Actual status of nitrogen oxide reduction technologies in the THERNOX member countries (1988).
T.Schneideret aL (Editors),Atmoepheric Ozone Research and its Policy ZrnpricOtiona 0 1989Elsevier SciencePublishere B.V.,Ameterdam -Printed in The Netherlands
691
PERSPECTIVES FOR LOW-SOLVENT PAINTS
J.C. den Hartog, Sigma Coatings B.V., P.O. Box 42, 1420 AA Uithoorn, The Netherlands.
ABSTRACT Paint is a product with very complicated properties. Before drying it is a fluid which easily can be applied by spraying or with a brush. After drying it forms a durable coating. The functions of the coating are colour and protection. The protective function means conservation of our raw materials. In this respect all paint is ecologically sound. Paint technology was for a great part based on the use of solvents. The solvent was used as the carrier medium for application. It is now generally understood that the use of solvents in paint forms an environmental problem. Per definition, all solvents used in paint are emitted into the atmosphere where they contribute to the production of ozone. The total solvent vapour emission from pain application is in The Netherlands 95 K.Tons a year. This is around 35 % of the total industrial and not industrial emissions. This situation will not significant differ from other industrialized countries. The objective of the project Hydrocarbons 2000 is a 50 % reduction of those VOC emissions in the year 2000. The best way to achieve is to reformulate paint products away from solvents. The new paints developped by the paint industry are: waterborne paints - powder coatings - high solid paints W curing paints The composition of these products and the fields of application will be discussed.
-
PAINT Paint is the name commonly used for surface coatings. It is applied on a variety of materials like metal, wood, concrete, stone and synthetic materials. The main two functions of paint are colour and protection. Because
of these two functiones, we cannot give up the use of paint. Colour makes our world more attractive. Without colour, the world would be much more sad; no paintings, no colour on the furniture in our homes, on our cars, on buildings, etc. But, it is not only the aesthetically function of colour that is important. In some cases the safety function is even more important. Just think of road-marking and road-signs as an example. Without colour road-safety woiild he a much bigger problem than it even is now.
692 The protective function of paint is also obvious. The surface coating forms a protective layer between the substrate and the environment. It prevents metal substrates from corrosion and it prevents wood from attack by moulding or degradation by W radiation. This protective function of paints gives an important cohtribution to the conservation of our raw materials. Paint is indispensable to save our raw materials, and this is why all paint is ecologically sound. COMPOSITION Paint has a number of typical properties (table 1).
It is amazing that all
these properties are combined in a thin layer of maybe 100 um thickness, and that this thin layer retains those properties for many years.
TABLE 1: TYPICAL PAINT PROPERTIES Easy to apply Strong adhesion to substrate Mechanical strong Resistant to weathering Elastic Chemical resistant Colour Gloss Strippable Special properties (anti-corrosive, anti fouling, etc
The technology developed by paint industry in the past decades was based on the use of solvents. Based on this technology, very specialized products were developed and there is a lot of experience in the application and use of these products. TABLE 2: PAINT COMPONENTS
1) Binders 2) Solvents 3) Extenders 4) Pigments 5) Additives
(alkyds, epoxies, polyurethanes, acrylics, etc. ) (hydrocarbon, water) (clay, silica, talc, bariumsulfate, etc.) (organic and inorganic) (defoamers, flow 8gBntS, driers, thickeners, etc.)
Conventional paint consists of 5 different types of raw materials (table 2). First there is the binder. After drying the binder forms a strong layer with
693 the other paint components. Adhesive properties are also determined by the binder. The function of the solvents is to dissolve the binder and it plays a role in the film forming proces on drying
.
The extenders are mostly inorganic materials used as a filler. The pigments can be of organic or inorganic nature. They are used to give the paint colour and special properties like anti-corrosion. The additives are used in small amounts to improve the performance of the paint.
SOLVENTS Of the components used in the formulation of paint, it are the solvents which are highlighted from an environmental point of view. Although all paint is environmentally friendly, the solvents from paint have a negative impact on the environment. Because solvent is used as carrier medium in the paint application, all solvent evaporates into the atmosphere. In the atmosphere the organic solvents are ozone precursors.
TABLE 3: Emission of hydrocarbons in The Netherlands (k tons)
Total process
+ not
industrial
1981
1985
264
248
Paint : Metal products Professional painters Car refinish Wood industry Do-it-yourself
33 38 8 2 15
33 32 11 1,5 16
Total paint
96 (36%)
93,5 (38%)
--
----
The total amount of organic solvents from paint is in The Netherlands approximately 36% (1981) of the total amount of hydrocarbons emitted from process and not industrial sources (table 3). In 1985 it was even 2% more. From these figures it is clear that paint must give a substantial contribution to the reduction of ozone levels, by lower solvent emissions. In co-operation with the authorities, paint industry and paint users a strategy was developed to achieve a considerable reduction in the year 2000 (table 4). For paint there will be an overall reduction of solvent emissions by 45% i n comparison to the emissions in the year 1981.
694
TABLE 4: Percentage of reduction of solvent emissions from paint K tons 1981 Metal products Professional painters Car refinish Wood industry Do-it-yourself
K tons 2000
33
38 8
2 15
----____--_
TOTAL
96
% reduction
15 22 8
54
42 0 60
0,s 7
53
__-______--
_ _ _ _ _ _ _ _ r _ -
45
52,8
EMISSION REDUCTION There are two ways to achieve solvent emission reduction: gas cleaning installations to prevent solvent vapours from escaping the operations and to reformulate paint away from solvents. Gas cleaning equipment like incinerators, carbon absorbers or biofilters are only applicable in stationary sources, and can only give a solution for a part of the problem. Moreover, this equipment is very expensive. Also in some cases another environmental problem is created instead of the air problem. Because of environmental and economical reasons in The Netherlands we choose to formulate away from solvents. It is apparent that this is an enormous challenge for the paint industry.
LOW SOLVENT PAINT PRODUCTS At the moment there are four alternatives to conventional solvent borne paint; the high solids, the waterborne paints, the radiation curing paints and the powder coatings (table 5 ) . TABLE 5 : Solvent content of coating systems % organic solvent
High solids/solvent free Waterborne Radiation curing Powder coating Solvent borne (conventional)
0 5 0
-
25 10 10
0
40
-
60
Powder coatings are a very attractive alternative because they are really solvent free. It is a powdery mixture of resin, pigments and extenders.
695 It is applied by electrostatical spraying onto the substrate, followed by stoving. Because of the electrostatical application there are very little losses from overspray. The radiation cured paints are solvent free or are containing only a few percentages of organic solvent. Those paints are cured by an electron beam or W-radiation. W is mostly used. The technology is based on the use of acrylic prepolymers mixed with low molecular weight acrylates. Those low molecular weight acrylates are used as a reactive diluent. Under influence of W-radiation a polymerisation reaction is started. The reactive diluent is incorporated into the polymer, so there is hardly any emission of organic compounds. To give the paint special properties, sometimes a few percent of organic solvent is added. The waterborne paints are very often dispersions of acrylates in water. The normal water content is 40% by weight. It is a general misunderstanding that waterborne products are completely solvent free. They contain in general 5
-
10 % of a low boiling solvent, as a film forming agent and as co-solvent. Very
often propylglycols are used for this purpose. High solid paints are based on the use of low molecular weight binders with a low viscosity. Because of this low viscosity of the binder less solvent is needed to get the right viscosity of the paint. The normal solvent content of a two-component High Solid paint i s about 20% (w). By still using lower molecular weight binders and reactive diluents, it is even possible to produce so-called solvent free products, for example solvent free epoxies. CURRENT USE AND SUITABILITY
TABLE 6 : Suitability of low solvent coatings Powder W-curing water-borne high solids On site application Temperature sensitive substrates Small series substrates Industrial roller application Dipping Curtain coating Spraying High gloss Metal substrates Wooden substrates
+=
suitable
- = not suitable
+ +
+ + + -I+ + -I+ +
+ + + + + t + +I+ +
+ + + +
+It
+ + +
-
+I
696 The low solvent products are not a panacea to all solvent problems. They all have their specific application and use (table 6). But although there are limitations there are many coating operations where low solvent products can be used. Often the results are even better then with the conventional coatings: Some typical applications are given in table 7.
TABLE 7: Some applications of low solvent paints Powder
W-curing
Do-it-yourself Metal: furniture construction cans cars machines
water-borne
high solids
t
+ + +
Wood : furniture architectural Paper Plastics House painting
+
+ +
+ + + +I+ + + + +
+ = suitable CURRENT USE AND PERSPECTIVES There are no exact figures available on the used amounts of the different coating sytems. An estimation of the current use in Western Europe is given in table 8. TABLe 8: Use of coating systems in Western Europe Usage Conventional solvent borne High solids Waterborne Powder coating Radiation curing
(%I
75 10 10
4 1
Total paint usage : 4,800 I( ton (1986) The conventional solvent borne paints still form the majority; The low solvent paints together form only roughly estimated 25% of the total usage.
697 The reason is that technic81 and economical limitations are still preventing really large scale introduction. Not for every application are low solvent products available with equal performance and quality with respect to conventional systems. Also industry must invest to install new production and application equipment: Because the paint market is an international market, it is also absolutely necessary to take similar measures in the different
countries. However, one of the most important conditions to reduce the amount of solvents emitted from paints, is
8
public understanding that because of
environmental reasons it is absolutely necessary to use low solvent paints whenever it is technical and economical possible. In some cases we also must accept a somewhat different appearance or a higher price of the paint in exchange for a better environment. We need paint for colour and protection, we also need protection of our
environment. This even goes better with low-solvent paints. The perspectives for low-solvent paints can only be good.
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699
SESSION XI
RECENT STUDIES ASSESSING THE NEED FOR AN ADDITIONAL LONG-TERM OZONE STANDARD
Chairmen
P.J.A. Rombout B. Goldstein
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T.Schneider et al. (Editors), Atmospheric Ozone Research and it8 Policy Implications 0 1989 Elsevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
701
THE NEED FOR AN EIGHT HOUR OZONE STANDARD
P.J.A. ROMBOUT', L. VAN BREEl, S.H. HEISTERKAMP* AND M. HARRA' lhboratory for Toxicology and =Centre for Mathematical Methods, National Institute of Public Health and Environmental Protection, P.O. Box 1, NL.-3720 BA Bilthoven (The Netherlands)
ABSTRACT Analysis of ozone aerometrics demonstrates that exposure of the population may extend over 8 to 12 h per day to levels slightly below the 1 h maximum concentration. Current ozone standards may not be protective for extended exposures since they incorporate averaging times of 1 h and are mainly based on clinical exposure of humans for 1 to 2 h. Information on the impact of exposure time on ozone induced effects is scarce. For that reason animal studies were performed to establish a data base for ozone exposure-response relationships. Concentrations (C) ranged from 0.25 to 4.0 m u m s and exposure times (T) were varied from 1 to 12 h. The time course of protein and albumin concentration in bronchoalveolar lavage fluid was used as the endpoint. A response model described by a quadratic polynomial function indicates a strong influence of T to the response which increases with increasing C. The impact of T is still significant at the 0.25 mg/ms level. The study contributes to the growing data base that supports the introduction of an ozone standard with an 8 h averaging time and a substantially lower concentration than current 1 h mean standards. Furthermore, the health risk of exposure to ambient ozone appears to be more serious than was expected previously. INTRODUCTION In former days photochemical air pollution caused a typical diurnal ozone profile with a rather sharp peak in the early afternoon (ref. 1). Nowadays the emission of ozone precursors is spread out over large areas. This causes the mesoscale character of this type of air pollution and results in rather broad ozone peaks during the late afternoon (ref. 2). Analysis of data gathered by the Dutch National Air Quality Monitoring Network revealed that maximum 4 , 8, and 12 h mean ozone concentrations amount to 95, 85, and 75% of the maximum 1 h mean concentration respectively (ref. 3). The 1 h maximum concentrations reach values of 0.40 mg/ms (0.20 ppm) and higher. Episodes with increased photochemical activity may last from several days to 2 weeks and occur several times during the summer season (ref. 4). Similar diurnal profiles and episodes are encountered in the U.S.A. (ref. 1). Air quality guidelines and standards for ozone are primarily based on controlled human studies in which young healthy exercising volunteers are acutely exposed to ozone for short exposures of 1 to 2 hours and with physiological changes as endpoints (ref. 1). However the actual exposure of
702 the population, including more sensitive subgroups, to submaximal ozone concentrations may last up to 12 hours for several consecutive days. This exposure may exert apart from physiological alterations more serious biochemical, irmaunological or even structural effects (refs. 5
-
7). Therefore concern has risen regarding the health risk involved with these exposure conditions as well as the protection offered by current ozone standards since they restrict the averaging time to 1 h for a single exposure. The classic concept of Haber's rule referring effects to inhaled dose, taken as the product of concentration and exposure tine, is generally accepted in inhalation toxicological studies with systemic acting gases. However the application of this rule to the toxicity of the deep lung irritant ozone has mainly been restricted to acute short term exposures of humans (ref. 8). The recently recognized extended exposure of the population to ozone and the virtual lack of toxicological data on the contribution of exposure duration to acute ozone induced effects prompted us to perform 8 comprehensive, systematic study on concentration (C) and exposure time (T) relationships. A broad range of concentrations (0.25 to 4.0 mg/na) and exposure times (1 to 12 h) were investigated in sedentary and active animals, with influx of protein and 81bUin in bronchoalveolar lavage fluid (BALF) as indicators of lung injury. Results on the contribution of the number of exposure days to the effect are reported by Van Bree et al. (ref. 9). The experiments reported here are part of an ongoing research program on the relationship of ozone exposure patterns and effects. Part of this program is carried out in collaboration with the Toxicology Branch of the Health Effects Research Laboratory of the US Environmental Protection Agency and the Department of Inhalation Toxicology of the Laboratory for Toxicology of the Dutch National Institute of Public Health and Environmental Protection.
KdTHODS Animals Seven week old male, specific pathogen free Wistar rats were obtained from our Institutes breeding colony. They were maintained under barrier conditions during a one week acclimatization period and during exposure. The animals were kept on a normal 12 h light cycle. Food and water were provided ad libituql.
l%zuK== Animals exposures were performed in a facility, consisting of twelve 0.2 m' stainless steel and glass ~nhalationchambers. Haximally 15 rats were housed in one chamber. Air was purified by an activated charcoal, a permanganate and a highly efficient particle filter, and was conditioned at a temperature of 22 5 1'C and 55 f 5% relative humidity. Through each chamber an air flow of 6 ma/h was maintained. An ozone-oxygen mixture, generated by irradiation of oxygen with W-light. was metered into the inlet air stream with a stainless
703 steel mass flow controller. The exposures were performed automatically using an exposure control program running on an Altos 1086 microcomputer interfaced to the exposure equipment. Concentrations in the chambers were measured at
two
minute intervals with Monitor Labs 8810 ozone analyzers, and adjustments of the flow controllers were made to maintain the desired concentrations. The analyzers were checked several times per day against a reference ozone-air mixture and zero-air generated by a Monitor Labs 8550 calibrator, which was calibrated weekly by means of gasphase titration with an NBS-traceable nitric oxide-nitrogen gas mixture. h v a e e f u d urenaration and Bronchoalveolar lavage (BAL) was performed by the method of Hatch et a1
-
(ref. 10) using 40 instead of 35 ml/kg bodyweight of warmed (37'C)
saline.
Cell free lavage fluid supernatant (400 g; 10 min.) was analysed for protein (ref. 11) and albumin (ref. 12).
Protein and albumin concentrations in BALF were transformed to their
natural logarithms. Quadratic polynomial functions were tested with ozone concentration (C), exposure time (T) and autopsy moment (A) as variables. ntal d e s i a Two experiments were performed in which CxT relationships were investigated
in sedentary (experiment 1) or active rats (experiment 2). (i) ExDeriment 1. CXT studv. dav-. To study the time course of protein influx in BALF as a function of C and T, 4 sub-experiments were carried out in which rats were exposed to either 0.75, 1.5, 2.5, or 4.0 mg/d ozone. For each sub-experiment 102 rats were divided at random into 5 groups, and were exposed during day-time for either 0, 1, 2, 4, or 8 h. Exposures started at 08:00, light was on from 08:OO until 20:OO h. BAL was performed in
3 rats at autopsy moments as indicated (x) in the following scheme:
Exposure time (h) 0 1 2 4 8
Autopsy moment (h from start of exposure) 4 8 14 22 34 54 1 2 x x
x x x
x x x x
x x x x X
(ii) ExDeriment 2. CXT study.
X X X X X
X X X X X
X X X X X
ninht-time exuosure .
X X X X X
Number of rats 24 24 21 18 15
To study the time course
of albumin influx in BALF as a function of C and T, 3 sub-experiments were carried out, in which rats were exposed to either 0.25, 0.50, or 0.75 mg/ms ozone. For each sub-experiment 75 rats were divided at random into 4 groups, and were exposed during night-time for either 0, 4, 8 , or 12 h. Exposures
704 started at 18:00, light was on from 06:OO until 18:OO h. BfG was performed in 3 rats at autopsy moments as indicated (x) in the following scheme:
Exposure time (h)
Autopsy moment (h from start of exposure) 4 8 12 24 36 48 72 x x
0 4
a
x x x
12
X X
X X
x x
x x
X X X X
X X X X
X X X
X
Number of rats 21 21 18 15
RESULTS nt 1. C x T . dav-This experiment consisted of 4 sub-experiments that were separated in time by one week. Statistically they were treated as being performed at the same time since the variance in the concentration of protein in BALF of all control
-
animals (n 9 6 ) did not differ from the variance of the protein concentration within any subexperiment. The same considerations were valid for experiment 2. The time course of the protein influx in BALF after acute exposure of sedentary rats displayed a fast increase followed by a gradual decrease of the protein concentration with a maximum response at 22 h from the start of the exposure. Figure 1 shows the data for 1.5 mg/m3 ozone. The protein concentrations were still significantly elevated at 54 h from the start of the exposure for exposure times of 4 and 8 hours. Exposure time exerted a profound, more than proportional concentration dependent influence on the
hars frcm start
Fig. 1. Time course of the protein concentration (mg/l) in bronchoalveolar lavage fluid after day-time exposure of rats to 1.5 mg/m3 ozone for
0 (+), 1 (A), 2
(O),
4 (+), or
8 (A) hours.
705 influx of protein in BALF as can be seen in Table 1. Multivariate regression analysis of the data resulted in the following function, that accounted for 88.6% of the variance of the data: log protein
-+
4.68 - 0.17 C + 0.049 Ca + 0.13 CxT 0.028 A 0.0005 As + 0.0013 TXA
-
0.11 T
-
This function enables the calculation of the influence of T on the influx of protein in BALF for every possible combination of C, T and A within the tested ranges. Figure 2 displays the calculated cuwes for 1.5 mg/m3 and exposure times of 0 , 1, 2, 4 , and 8 h.
TABLE 1 Influence of exposure time on the protein concentration in bronchoalveolar lavage fluid of day-time exposed rats at 22 h from the start of the ozone exposure. Values are given as percentage of control (n
Concentration (mg/ms ozone)
3).
Exposure time (hours) 2 4
1 94 138 120 277
0.75 1.50 2.50 4.00
-
100 180 209 497
119 267 499 1336
8
137 543 2003 8468
7m
600
600-
m-
+
+..."""
,,,,,,,,,....
"'
+............+...,.,_,,,,
'.t......,,
"".+
xa&---4--Q---
en
Fig. 2. Calculated time course of the protein concentration (mg/l) in bronchoalveolar lavage fluid (ng/l) after day-time exposure of rate to ozone for 0 (A), 1 (+), 2 (A), 4 ( O ) , OK 8 (+) hours. 1.5 &ma
706 Fxueriment 2. CxT. The time course of albumin influx in BALF after a single exposure of active rats to ozone differed from that of the protein influx in sedentary rats, since the increase and decrease of the albumin concentration was much more gradual and the maximum response shifted towards a later moment viz. 36 in stead of 22 h for exposure times of 8 and 12 h.(Fig. 3). The absolute changes were large with respect to the relatively low ozone concentrations. Ozone induced effects were detectable for the smallest investigated CxT product of
-
0.25 x 4 1.0 mg.h/d. 72 h after the start of an 8 or 12 h exposure to 0.50 and 0.75 mg/ms, albumin concentrations in BALF were still elevated. The maximum albumin concentration in BALF in ozone exposed rats was proportional to the length of T. The impact of T increases with increasing C (Fig. 4). Furthermore it appeared that e.g. an 80% increase in albumin in BALF was caused by CxT products of 3.0, 2.0, and 1.5 mg h/ma for concentrations of 0.25, 0.50, and 0.75 ng/d and exposure times of 12, 4. and 2 h respectively. Multivariate regression analyaia of the data resulted in the following function, that accounted for 73.2% of the variance of the data: log albumin
-
-
3.89 0.81 C + 1.31 Cz + 0.018 A 0.00024 A'
-
+
0.21 CxT
-
0.044 T
DISCUSSION Ozone can cause permeability changes in the epithelium and endothelium of the respiratory tract in man and animals (refs. 10, 13). It has been demonstrated that these changes are paralleled by inflamnatory processes in the lung (refs. 7, 13). Protein and albumin in BALF are indicators of the degree of pulmonary permeability. Consequently increases in protein and albumin concentration in BALF after ozone exposure are of great significance for the evaluation of health riska aosociated with public ozone exposure. The moment at which the maximum increase in protein and albumin in BALF occurs has not been properly investigated. C as well as T may have influence on this moment. Therefore we chose to study the time course of protein and albumin influx in BALF caused by various CxT products. This enabled the statistical analysis of all data of the c u n w instead of relying on the supposed moment of maximum response. Protein concentrations were increased at 54 h especially for T's of 4 and 8 h of all CxT products. Thia indicates that the lung ia still in a state of repair and that T s e e m to govern the extent of this proces. Experiment 1 demonstrates that the degree of the more than proportional contribution of T progressively on C. Thus the in provoking ozone induced lung injury, &pen& simple product of C and T c u m o t be applied to predict the reaponse for all possible combinations of a given product. A polynomial function demonstrates
707
Fig. 3. Time course of albumin concentration (percentage of control) in bronchoalveolar lavage fluid (BALF) after a single night-time exposure of rats to 0.25 (top), 0.50 (middle), or 0.75 (bottom) mg/ma ozone for 4 (+), 8 (A), or 12 ( 0 ) hours.
708 quantitatively the progressive influence of T with higher C's. This response model can be used to calculate the effect in terms of protein influx in BALF for a single ozone exposure to an arbitrary combination of CxT. For example an 1 h exposure to 2.0 mg/ms causes the same effect as an 8 h exposure to 0.425 mg/ms ozone. These findings are almost in complete accordance with the findings of Costa and coworkers (ref. 14). The model is based in part on experimental data with relatively high CxT products resulting in extreme lung injury. This renders a model that is suitable for generalizations on ozone CXT relationships but is of less value for the evaluation of risk involved with ambient ozone exposure. For this reason similar information for lower ozone concentrations was warranted. It has been shown in h w a n and animal experiments that minute volume exerts a strong positive influence on ozone induced effects (refs. 8, 15). We have observed a twofold increase in effect when rats were exposed to ozone during the night-time compared to day-time exposure (ref. 16). Preliminary data from our laboratory show two periods during the night in which animals displayed an increased breathing frequency. We therefore performed a second CxT experiment in which active animals were exposed during the dark period to ambient concentrations, to compare the results from our animal experiments with data from exposure of exercising humans. The observations of experiment 1 were largely confirmed for lower ozone concentrations by the results of experiment 2. The difference in the shape of the time-reponse curves in both experiments may be caused by the difference in the permeation velocity of protein and albumin and/or by qualitative changes in the ozone dosimetry of sedentary and active rats in terms of the localisation and the extent of the tissue affected by ozone. A seemingly proportional influence of T on the ozone response was observed for these low concentrations. The influence of T again being greater for higher C, but a strong impact of T still exists at 0.25 mg/mr. Koren et al. (ref. 6) measured a significant 120% increase in the albumin concentration of BALF from humans exposed to 0.4 ppm ozone for 2 h during intermittent exercise. Almost identical exposure conditions, 0.75 mg/ms for 2 h, caused an 80% increase in the albumin concentration in active rats. Remarkably the same response wan induced by a 4 h exposure to 0.50 m g / d or a 12 h exposure to 0.25 &ma
(Fig. 4.). So ozone exposure conditions that
normally occur on a large number of day8 during the summer season, will cause injury in rat lungs. Preliminary results from Koren et al. (ref. 6) and HOrStYMM et PI. (ref. 17) point to similar exposure-reponse dynamics for humans. In conclusion ozone exposure-response relationships for single exposures cannot simply be described by the product of C and T. A quadratic polynomial function suitably models the response and demonstrates a significant
709
-,..yo
E w l effect foc
600-
a-
-
o ...-are npmu
.’--O , ,
,/0 . -
,..~*b /./ -.----
.&--,: 0
/.----
-0.-
200-
/-Ll
*--
0.12 ppm a t l e a s t once per ozone season as they engage i n heavy exercise. population.
These exercisers c o n s t i t u t e 9.3% o f t h e t o t a l U.S.
MSA
I f the c u r r e n t NAAQS o f 0.12 ppm i s attained, o n l y 600,000
people (0.3% o f t h e t o t a l urban population) would experience t h a t l e v e l o f ozone as they h e a v i l y exercise. The f i n a l Table presented t o i l l u s t r a t e 03-NEM outputs i s concerned w i t h very h e a v i l y e x e r c i s i n g cohorts. These people are e x e r c i s i n g a t 64 L/min o r higher a t some time d u r i n g a t y p i c a l week. urban U.S.
Only 441,800 people i n t h e
are estimated t o undertake such an exercise r a t e f o r an hour o r
longer d u r i n g t h e ozone season.
O f these people, we estimate t h a t about
100,000 people experience an ozone l e v e l > 0.12 ppm d u r i n g a t l e a s t one o f t h e i r heavy exercise regimes.
While o n l y 0.06% o f t h e U.S.
population, t h e
combination o f high ozone exposure and very high exercise l e v e l (and v e n t i l a t i o n r a t e ) makes them a p a r t i c u l a r l y s e n s i t i v e group from a p u b l i c h e a l t h perspective.
I f any o f t h e a l t e r n a t i v e NAAQS analyzed i n Table 6 a r e a t -
tained, we estimate t h a t no one would experience an ozone exposure > 0.12 ppm during very heavy exercise.
834 TABLE 5 Estimate o f t h e cumulative number o f heavy e x e r c i s e r s i n t h e U.S. urban population exposed t o one-hour average ozone d u r i n g t h e ozone season a t heavy exercise under a l t e r n a t i v e a i r q u a l i t y scenarios ( m i l l i o n s o f people)
A i r Q u a l i t y Scenario 03 Conc. Equaled o r Exceeded (ppm)
The Current Situation
A l t e r n a t i v e NAAQS ( i n ppm) 0.12
0.10
0.08
0.361 0.341 0.321 0.301 0.281
0
0 0 0
0 0 0
0 0 0
0.1 0.2
0
0 0
0 0
0.261 0.241 0.221 0.201 0.181
0.4 0.7 1.2 2.1 3.0
0 0 0 0 0
0 0 0
0 0 0 0 0
0.161 0.141 0.121 0.101 0.081
6.2 10.4 16.2 24.4 39.9
0 0 0.6 3.0 16.7
0 0 0 0.2 8.2
0.2
0.061 0.041 0.021 0.001 0.000
49.1 59.4 61.2 62.2 62.2
41.0 56.7 62.1 62.2 62.2
32.3 49.3 62.0 62.2 62.2
14.5 43.2 61.3 61.6 62.2
* *
0
0 0
0 0 0
*
*Fewer than 50,000 people. Note: These are "best estimate" projections.
CAVEATS AN0 LIMITAT IONS The 03-NEM model described above i s undergoing review by t h e public. Undoubtedly, t h i s review w i l l uncover several shortcomings t h a t w i l l r e s u l t i n m o d i f i c a t i o n s t o t h e model.
Two such shortcomings already noted by one
reviewer i s t h a t heavy and very heavy exercise seems t o be o v e r l y concent r a t e d i n o n l y a few hours per day, which seems u n r e a l i s t i c ; i n addition, t h e r e a r e inconsistencies among exercise groups w i t h respect t o sequence o f exercise ( r e f 7).
Another shortcoming i s a l a c k o f u n c e r t a i n t y analyses
regarding both model i n p u t s and p r e d i c t i o n s ( r e f 8). These shortcomings are c u r r e n t l y being addressed.
I n t h e meantime, EPA
i s i n v e s t i g a t i n g another ozone exposure model t h a t can accomnodate t h e c a l c u l a t i o n of sequential h o u r l y exposures t o t h e p o l l u t a n t .
Thus, f u t u r e
835 EPA ozone exposure estimates may be d i f f e r e n t than those presented i n t h i s
paper. TABLE 6 Estimate o f t h e cumulative number o f heavy exercisers i n t h e U.S. urban population exposed t o one-hour average ozone d u r i n g t h e ozone season a t very heavy exercise under a l t e r n a t i v e a i r q u a l i t y scenarios (thousands o f people) A i r Qua1it y Scenario
03 Conc. Equaled o r Exceeded ( ppm 1
The Current Situation
A l t e r n a t i v e NAAQS ( i n ppm)
0.12
0.10
0.08
0 0 0 0 0
0 0 0 0 0
0.361 0.341 0.321 0.301 0.281
1.8 2.8
0 0 0 0 0
0.261 0.241 0.221 0.201 0.181
2.8 3.5 5.0 7.1 11.2
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0.161 0.141 0.121 0.101 0.081
25.3 75.3 100.0 162.8 258.7
0 0 0 27.7 148.7
0 0 0 0 49.7
0 0 0 0
0.061 0.041 0.021 0.001 0.000
343.0 387.9 431.8 441.8 441.8
305.6 379.8 434.5 441.8 441.8
266.1 337.1 431.8 441.8 441.8
0
* *
*
154.1 349.2 426.2 437.4 441I8
*kewer than 1,000 people. Note: These a r e "best estimate" projections. REFERENCES
1
2 3 4 5 6
7 8
42 U.S. Code 7408-9 (Sections 108 and 109 o f t h e Clean A i r Act as amended ) U.S. EPA. "Revisions t o t h e National Ambient A i r Q u a l i t y Standards f o r 44 Fed. Reg. 8202 (February 8, 1979). Photochemical Oxidants." W.F. B i l l e r , e t a l . "A General Model f o r Estimating Exposures Associated Paper presented a t t h e 74th annual meeting o f w i t h A l t e r n a t i v e NAAQS." t h e A i r P o l l . Control Assoc.; Phila., June 1981. R.A. Paul, e t a l . National Estimates o f Exposure t o Ozone Under A l t e r n a t i v e National Standards. Durham, NC: P E I Associates, 1986. A. Ferdo. "Ozone Microenvironment Factors." Memo t o T. McCurdy; 1985. T. Johnson and J. Capel. The Use o f t h e EKMA Model f o r A d j u s t i n g Hourly Average Ozone Data t o Simulate Attainment o f Proposed A i r Q u a l i t y Standards. Durham, NC: P E I Associates, 1985. W. Ollison. L e t t e r t o T. McCurdy; October 14, 1987. Flaak; January 26, 1988. G. Morgan. L e t t e r t o A.R.
.
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T. Schneider et aL (Editors),Atmospheric Ozone Reeeorch and its Policy Z m p h t b n e 0 1989 Elsevier Science Publiihem B.V., Ameterdam -Printed in The Netherlands
837
RISK ANALYSIS AND EVALUATION FOR DEVELOPMENT OF AN OZONE CONTROL STMTEGY
K.R. KRIJGSHELD and S. ZWERVER Ministry of Housing, Physical Planning and Environment, Air Directorate, P.O. Box 450, 2260 ME Leidschendam, The Netherlands ABSTRACT A risk assessment is presented by comparing current concentrations of ozone in Europe with suggested "no-effect-levels" derived from the presently available effect data. Clearly, the prevailing ozone concentrations are at an unacceptable level. Very drastic reductions of more than 75% in both NOx and VOC emissions are needed in order to significantly reduce the ozone levels. INTRODUCTION The atmospheric ozone problem relates, on the one hand, to excessive ozone formation in the boundary layer and the free troposphere and, on the other hand, to ozone breakdown in the stratosphere. The risk evaluation in this paper is directed primarily at the increased ozone concentrations in the ambient air. The formation, prevalence and dispersion of ozone have been part of Dutch research into air pollution for more than 15 years. In the beginning much effort has been put into smog-chamber research concerning the mechanism of the chemical reactions. Later, the step was taken towards models for the open air; first a box model, then the EKMA model and finally the large-scale model for Europe which was used in the Dutch - West-German PHOXA project Ozone was monitored regularly at several locations in the Netherlands for a long time. In addition, ozone has been monitored systematically for the last ten years at 29 points in the dense air pollution monitoring network in the Netherlands. The availability of monitoring statistics is thus increasing rapidly.
.
838 In the Netherlands, inhalation-toxicological research of ozone also got off the ground several years ago. In addition, the impact of ozone on plants is receiving increasing attention as part of the Netherlands' acidification-related research program. Research in the area of effects has already led to a tightening of the levels at which negative effects on humans and the ecosystem must be feared. EXPOSURE ASSESSMENT Photochemical ozone formation Until1 recently, risk assessment has devoted attention primarily to 1-hour average peak concentrations. In the past few years, research into the effects of sub-acute and chronic exposure to ozone has provided sufficient reason, both for hurnan health and vegetation, to devote more attention to long term average concentrations. Therefore, it is good to realize that ozone formation takes place on various spatial and temporal scales (TABLE 1). The large-scale background of ozone is determined in the free troposphere. This ozone level is caused by emissions of NO, and low-reactive hydrocarbons, but also methane and carbonmonoxide. Ozone peak values during episodes arise from reactions in the mixing layer. Here the transport on the national and the European scale does play a role. The very reactive hydrocarbons may cause locally increased ozone concentrations.
TABLE 1 Photochemical ozone formation rpakl usla
tinw mala
pncum
LOCAL
HOURS
NO., , highly reactive VOC
REGIONAL (nationallEuropeen)
DAYS
MONDW
%Zzi
NO,, VOC
SEASON. YEARS
No,, Voc (vscy low -41. CO, CH,
839
Current concentrations Concentrations have exhibited a considerable increase in the course of this century, particularly in the years between 1950 and 1970 when NO, and VOC emissions also grew substantially. There has been no clear trend in peak ozone concentrations over the past ten years. This is generally explained by the increase of NO,emissions through which ozone is quenched or eliminated on the local scale. Fig. 1 presents the daily maximum ozone concentrations for the period 1980-1985 (ref.1). It is striking that the maximum 8-hour
Fig. 1. Frequency distribution of measured ozone concentrations for all Dutch monitoring stations (ref. 1). average concentrations are only slightly lower than the maximum 1-hour values. The 8-hour averages range from 190-350 pg/m3. The 1-hour averages range from 230-430 pg/m3. Even the ozone concentrations during the growing season in the Netherlands on average amounts to 80-95 pg/m3 (average of &hour values, between 9 a.m. and 5 p.m., over the period May-September). When looking at the frequency distributions of 1-hour values in the Netherlands, then the highest 98-precantiles for ozone are found in the southern part of the country. This is illustrated in F i g . 2 for the year 1985. However, the highest 50-percentiles are measured in the north, in relatively clean areas. A great part of the year winds come from northern directions. The ozone concentrations in the north, therefore, are determined preponderantly by the tropospheric background level, present in
840
Fig. 2. The 50 and 98 percentile for ozone Netherlands (Jan Dec 1985) (ref.2).
-
(pg/m3) in the
the air masses coming from overseas. The average concentration of ozone decreases towards the south of the country due to dry deposition and reaction with NO from polluted air. The occurrence of peak concentrations usually involves episodes lasting several days. The seriousness 05 effects will presumably be influenced by the average duration of a period during which a certain maximum 1-hour or 8-hour average concentration is exceeded. The number of consecutive days that a certain ozone
Fig. 3. Average length of a period (in days) during which a maximum 1 hr (---) or 8 hrs (-) average concentration of ozone has been exceeded (station Den Helder; 1980-1985) (ref.3).
84 1
level is exceeded will usually decrease with increases in the considered concentrations of ozone (Fig. 3). HEALTH EFFECTS
To make possible a risk assessment for ozone in the Netherlands the National Institute for Public Health and Environmental Hygiene (RIVM) recently drew up - by order of the Ministry - a criteria document for ozone (ref. 1). In the document the effects both on human health and on crops and vegetation have been evaluated. The most critical effects on humans evident from the epidemiological and clinical research are decreased lung function, increased airway reactivity and an increase in chance and severety of attacks among asthmatics. Based on research with laboratory animals, it is also likely that other effects can occur as a result of exposure to ozone, such as increased sensitivity to respiratory infections and structural lung damage with repreated or chronic exposure. Unfortunately, the information regarding the exposure-response relationships for ozone is still very inadequate, also because of the disproportionate attention there has been in the past to peak exposures. The need for a better insight into the exposureresponse relationships for ozone is emphasized by recent research. The factors that govern this relationship may be separated in factors related to dose, and factors related to the intrinsic sensitivity of exposed persons:
* dose: - ozone concentration - duration of exposure in - number of days exposed - level of exercise * intrinsic sensitivity: - "responders" (people
-
hours per day
exhibiting reaction to ozone) persons with respiratory problems
stronger
than
average
Based on the factors noted above, we can distinguish various risk groups in the population:
8 of Dutch population Risk qroup * Persons whose work involves physical 3.5 exercise in the open air * Children (up to and including 14 years) 20 * "Responders" 5-15 ( ? ) * Persons with respiratory problems 7
042 This means that an estimated 30 to 40 percent of the Dutch population will fall into one of these categories and thus, are potentially at risk for exposure to ozone. So-called no-effect-levels to protect human health have been derived in the ozone criteria document (Table 2). They agree with the recommendations drawn up recently by the World Health Organization (ref. 4). TABLE 2 No-effect levels for ozone in relation with human health Dutch crlterladocument marginal effect level
neeffect level
WHO guideline value
1 hour average
240 p g h 3
160 pglm3
150-200 kglrn3
8 hour average
160 pg/rn3
110 pg/rn3
100-120 pg/rn3
A safety margin of 1.5 was applied in deriving the no-effectlevel from marginal effect levels. This factor is fairly arbitrary, but - nevertheless - is necessary to cover a degree of uncertainty in a number of aspects, like extrapulmonary effects, the effects caused by combined exposure to ozone and other air pollutants, and sufficient protection of populations at risk. The possible carcinogenic, co-carcinogenic and/or promotor activity of ozone is still a matter of debate. For the time being, in the Netherlands, we are not considering ozone as a carcinogenic substance. ECOLOGICAL EFFECTS With respect to the effects of ozone on plants, one can also make a distinction between acute toxicity at short-term exposure (visible leaf injury) and harmful effects from prolonged exposure to lower concentrations (growth inhibition, yield reduction, and increased susceptibility to biotic and abiotic stress). Harvest reduction in the Netherlands resulting from air pollution in general was estimated at 5 percent in 1983. Ozone is considered the most important component of air pollution in this matter,
043
accounting for nearly 70 percent of the harvest reduction. The concern about acidification has provided in recent years an important impulse for further research into the effects of ozone on plants. It is very likely that ozone contributes significantly to the decline in forest vitality which is observed in the Netherlands and elsewhere in Europe. In the Dutch Criteria Document for Ozone no-effect-levels have also been derived for plants, forests and crops (Table 3). The desired ozone air quality in this case has been differentiated into 1-hour, &hour and growing season averages in order to do justice to the influence of the exposure pattern. TABLE 3 No-effect-levels for ozone in relation with vegetation, forests and crops.
RISK ASSESSMENT. In order to get a sense of the extent of the risks presented by current ozone concentrations, we can compare these concentrations to the advised no-effect-levels. As can be judged from figure 2 the maximum 1-hour and 8-hour average concentrations in the Netherlands amply exceed the respective no-effect-values. If we look at the average number of days per year that a no-effect-level is exceeded, we see that this occurs in five percent of the days when compared with the 1-hour limit value, on five to ten percent of the days for the &hour level related with human health effects, and on even more than 50 percent of the days, when comparing with the 8-hour no-effect-level for vegetation. The average concentration of ozone during the growing season, being
844 80-95 pg/m3, will exceed the suggested no-effect-level of 50 pg/m3 during the entire season. A similar picture emerges from model calculations for the European situation, as performed in the PHOXA-project. This project is a collaboration of the Netherlands and the Federal Republic of Germany. Up till now it has been directed at calculating European ozone concentrations during summer episodes. The Dutch research institute TNO participates in the project and some of their results will be discussed here. The data represent model calculations based on an episode that occurred in 1982. The curves shown in Fig. 4 and 5 show the cumulative frequency distribution for the percentage of the
Fig. 4. Calculated frequency distributions of exposure to ozone during an episode. population in the considered area, that is exposed above a certain ozone concentration. In these calculations exceedence of 240 pg/m3 as a 1-hour average - the current ambient air quality standard in the USA and also the provisional limit value in the Netherlands - appears to occur only limitedly (Fig. 4). The model tends to underpredict the observed ozone levels. T h i s is mainly due to the fact that the ozone concentrations have been calculated as an averaae over fairly large surface units, grids of 60 x 60 km. Local variations in ozone levels therefore don't become visible. For example, 240 pg/m3 was exceeded at almost all of the stations in the National Monitoring Network in the Netherlands during this particular period: the highest value measured even reached 430 microgram/m3.
845
However, the suggested no-effect-level of 160 pg/m3 (1-hour average) is being amply exceeded. Taken these calculated concentrations, it is estimated that this involves 9 percent of the total population, that is 23 million inhabitants, for the area under consideration. The 6-hour no-effect-level, again, appears to be much more critical than the 1-hour value. The calculations indicate at least in this episode about 140 million people, that is more than half of the total number of inhabitants in the area, are exposed at ozone concentrations above the 6-hour no-effect-level. Only one conclusion is possible: for ozone we clearly have come into the range of unacceptable concentrations. CONTROL STRATEGY To develop a control strategy to reduce ozone to acceptable levels, models like the one used in PHOXA can become an important tool. In the PHOXA-project calculations with 50 percent less NO,
Fig. 5. Calculated frequency distributions of exposure to ozone duriong an episode: effect of emission reductions. emissions, 50 percent less hydrocarbon emissions, and the combination of both were also carried out (fig. 5). At this stage results should be interpreted as very preliminary. The effect of emission reductions on the ozone concentrations occurs especially in the high concentration ranges. Limiting hydrocarbon emissions clearly has a positive effect. NO. reduction appears to have a negative effect. This is particularly the case in the areas of dense NO,-emissions, as in the Netherlands.
846
However, elsewhere in Europe, reduction has a positive effect.
in
less NO,
rich
areas,
NO,
Model calculations with a more limited design indicate that very large emission reductions are needed in order to reach the no-effect-level in the Netherlands (Table 4). Only the ozone concentration in the Netherlands has been calculated in these studies although emissions in all of Europe were included. Emission reduction of NO, and VOC on a European scale is needed to limit the 1-hour average peak concentrations; reductions on a global scale may be needed to limit the 8-hour average and are certainly needed to reduce the seasonal average.
TABLE 4 Emission reductions needed to prevent all adverse effects on human health and vegetation.
Despite the many uncertainties in model calculations, all available studies tend to the same conclusion that very high emission reductions are needed to cause a significant decrease in ozone levels. We have to be realistic, this can only be achieved in the long run. Therefore, setting an interim-goal will be helpful Thus, it makes sense to research the emission reductions necessary to prevent, in any event, the more serious human health and environmental effects (Table 5). The existing provisional limit value in the Netherlands, which is comparable to the current standard in the USA of 240 pg/m3 (1-hour average) can be
.
847
considered the marginal-effect-level. If we take this level as the point of departure, an emission reduction of 40% is required for both NO, and VOC, on a European scale (if exceedence is allowed 3 times per year). Similarly, the marginal effect-level for the 8hour average at least in relation with human health may be set at 160 pg/m3. The associated emission reduction then is 75% for both NO, and VOC. TABLE 5 Interim-goal for ozone ambient air quality, and related emission reductions, to prevent serious effects on human health and vegetation.
ozone is concerned, it would be too speculative to conclude on the basis of the presently available model calculations, what emission reduction of NO,, hydrocarbons, CO and/or CH, are necessary to arrive at lower ozone levels. As far as the growing season average for
CONCLUSIONS To conclude, it is evident there are still many uncertainties in the effects of ozone that need further clarification:
* * * *
the relationship between exposure pattern and the effects on human health; similarly the effects of chronic exposure on the environment; the risk for sensitive groups in the population; why are "responders" extra sensitive to ozone; the effects of combined exposure to ozone and other air pollutants.
1348
To properly assess the risk of occurring concentrations of ozone we need better knowledge regarding the extent of the actual human exposure. Personal monitoring and modelling of exposure, based on human aqtivity patterns both indoors and oudoors, have to provide more insight in this respect. Despite the uncertainties it is clear that actions should be taken to reduce the ozone concentrations, the more so since we must acknowlegde that: 1. effects occur at much lower ozone levels than has been assumed thus far, also due to the importance being attributed to 8hour average ozone concentrations, in addition to the 1-hour peak values. 2. the prevailing concentrations are at an unacceptable level. To arrive at a control strategy, the development and use of models is an important tool for ascertaining which factors have a determining influence. Also in this area it is clear that our knowledge is far from complete. Next to validation of the models, there is a need to expand the models to include long-term average ozone concentrations. A good international infrastructure for monitoring ozone would be very useful for this purpose. In addition, it is essential that we improve our information about the levels and emissions of ozone precursors. The models indicate that the effectiveness of NO, emission reductions is slight in areas with high NO, emissions. However, NO, emissions need to be reduced, on the one hand because NO,, in low NO, areas and in the free troposphere, is a driving force In ozone formation and on the other hand because of the role of NO, in acidification. It is clear that very drastic reductions of more than 755 in both NO, and VOC emissions are needed in order to significantly reduce the ozone concentrations. Reductions that are planned in the Netherlands at the moment for the year 2000 are 33% and 50% for NO, and VOC, respectively. These appear not sufficient. In the Netherlands, this year an evaluation will take place of the present policy concerning the acidification. Especially for NO, further reduction measures are under consideration. The large scale origin of the problem emphasizes the need to give - in addition to policy development on a national scale-
a49
also internationally high priority to abatement o f photochemical air pollution, on both the European and the global level. In this respect the development of protocols within the ECE containing agreements concerning emission reduction of NO, and VOC will mean an important step ahead. REFERENCES National Institute of Public Health and Environmental Protection, Integrated Criteriadocument on Ozone (report nr. 758474002): Bilthoven, September 1987. F.A.A.M. de Leeuw, in R. Guicherit, J. van Ham and A.C. Posthumus (Eds.) , Proceedings Symposium on ozone, Ede, The Netherlands, November 13-14, 1986, Kluwer, Deventer, 1987, pp. 40-44. J.W. Erisman, National Institute of Public Health and Environmental Hygiene, Report nr. 758474001: Bilthoven, June 1987. World Health Organization, Air Quality Guidelines for Europe. WHO regional publications, European series: No.23. WHO, Regional Office for Europe, Copenhagen, 1987.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Zmplicntions 0 1989 Elsevier Science Publishers B.V., Amsterdam Printed in The Netherlands
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051
A HEALTH RISK ASSESSMENT FOR USE I N SETTING THE U.S. PRIMARY OZONE STANDARD
S. R. Ha es,' A. S. Rosen aum,' Winkler,4 and H. Richmond
!
T. S. Wallsten,'
R. 6. Whltfielde3 R. L.
'Systems Applications, Inc., 101 Lucas Valley Road, San Rafael, C a l i f o r n i a (USA) 2L.L. Thurstone Psychometric Laboratory, University o f North Carolina, Chapel ill, North Carolina (USA) !Argonne National Laboratory, Decision Analysis and Systems Evaluation Section, Pgonne , I 111no1s (USA) Fuqua School o f Business, Duke University, Durham, North Carolina (USA) 'U.S. Environmental Protection Agency, O f f i c e o f A i r Q u a l i t y Planning and Standards, Durham, North Carolina (USA)
ABSTRACT This paper describes the r e s u l t s o f a U.S. assessment o f the ozone-induced acute pulmonary health r i s k s associated w i t h attainment o f three a l t e r n a t i v e 1hour average ozone standards: 0.12 pprn (current U.S. standard), 0.10 ppm, and 0.08 ppm. Risk r e s u l t s are presented f o r pulmonary function and r e s p i r a t o r y symptoms i n heavy exercisers, the group thought t o be a t highest r i s k t o acute ozone exposure. To examine two a l t e r n a t i v e d e f i n i t i o n s o f response adversity, ozone-induced pulmonary function change i s measured as F E V l decrements o f 210 and 220 percent; respiratory symptoms are characterized by cough, chest discomfort, o r lower respiratory symptoms as a group, a t two d i f f e r e n t severity levels--any (including mild) and moderatelsevere. Rlsk estimates are presented f o r up t o ten U.S. c i t i e s : Chicago, Denver, Houston, Los Angeles, M i a m i , New York, Philadelphia, S t . Louis, Tacoma, and Washington, D.C.
INTRODUCTION The Clean A i r Act requires periodic review and possible r e v i s i o n o f U.S.
pri-
mary (health-based) and secondary (welfare-based) national ambient a i r q u a l i t y standards (NAAQS) to' assure that standards are based on the l a t e s t s c i e n t i f i c information and t h a t primary standards protect p u b l i c health w i t h an adequate margin o f safety. During NAAQS review, t o evaluate whether a l t e r n a t i v e primary NAAQS provide such an adequate margin o f safety, the U.S. Environmental Protect i o n Agency (EPA) assesses such factors as the nature and severity o f the health effects associated w i t h p o l l u t a n t exposure, the degree o f t o t a l human exposure (both indoor and outdoor), and the r i s k s o f adverse health e f f e c t s when the
NAAQS Is attained.
To assist i n i t s review o f the primary NAAQS f o r ozone, the EPA Office of A i r Q u a l i t y Planning and Standards has sponsored an ozone health r i s k assessment. To date, the i n i t i a l p o r t i o n o f the r i s k assessment, which addresses acute ozoneinduced lung effects, based on c l i n i c a l response data from 1- and 2-hour cont r o l l e d human exposure studies, has been completed. Results are discussed by Hayes e t al. (ref.1) and the EPA's ozone s t a f f paper (ref. 2). which i n t e r p r e t s the standard-setting implications o f the e x i s t i n g s c i e n t i f i c data base (described i n the EPA's ozone c r i t e r i a document--ref. 3 ) . Results were reviewed by the U.S. Science Advisory Board's Clean A i r S c i e n t i f i c Advisory Comnittee ( r e f . 4). The EPA i s currently planning t o address subchronic (6-8 hour) and chronic (several month) ozone e f f e c t s i n subsequent phases o f the ozone NAAQS r i s k assessment, and t o examine the e f f e c t o f a l t e r n a t i v e d e f i n i t i o n s o f heavy exercise. The r e s u l t s o f the r i s k assessment w i l l be an important input t o the EPA's overa l l review o f the U.S. ozone primary standard.
RISK ASSESSMENT SCOPE This paper describes the r e s u l t s o f the acute pulmonary function and symptom portion o f the ozone NAAQS health r i s k assessment. Results are presented f o r the attainment o f three a l t e r n a t i v e 1-hour average ozone primary standards: 0.12 ppm (current U.S. Standard), 0.10 ppm, and 0.08 ppm, a l l o f the same s t a t i s t i c a l single expected-exceedance form as the current standard. Risk i s calculated f o r pulmonary function, as measured by FEV1* decrement, o r respiratory symptoms, as measured by cough, chest discomfort, and lower respiratory symptoms taken as a group. To compare a l t e r n a t i v e d e f i n i t i o n s o f response adversity, r l s k i s calculated f o r two response levels: f o r pulmonary function, F E V l decrements o f 210 and 220 percent; and f o r respiratory symptoms, any symptoms (mild, moderate, o r severe) and moderate o r severe only. Two d i f f e r e n t kinds o f r i s k are calculated: benchmark (the r i s k posed by e l evated ambient ozone levels, without reference t o the number o f people exposed) and headcount (the r i s k due t o actual personal exposures, accounting f o r indooroutdoor differences, population a c t i v i t y and m o b i l i t y patterns, and physical act i v i t y ) . I n a l l cases, r i s k r e s u l t s are f o r heavy exercisers, t h a t p o r t i o n o f the population thought t o be most a t r i s k due t o ozone exposure because o f high, exercise-induced v e n t i l a t i o n rates. Benchmark r i s k r e s u l t s are presented f o r 10 U.S. urban areas: Chicago, Denver, Houston, Los Angeles, M i a m i , New York, Philadelphia, St. Louis, Tacoma, and Washington D.C. Headcount r i s k r e s u l t s are pre*A standard spirometric measure o f lung function, the forced expiratory volume i n one second (FEVl) i s defined as the volume o f a i r t h a t can be expelled from the lungs i n the f i r s t second o f a maximal expiration.
053
sented f o r eight c i t i e s ( a l l but Chicago and New York, for which population exposure r e s u l t s were being refined by the EPA a t the time o f the r i s k assessment). Exposure-response relationships are developed from c l i n i c a l data obtained i n three controlled human exposure studies: Avo1 e t a l . (1984) (ref. 5), K u l l e e t al. (1985) (ref. 6), and McDonneli e t al. (1983) (ref. 7). These studies, which are selected from studies reviewed i n the EPA ozone c r i t e r i a document according t o c r i t e r i a described i n r e f . 1, measured acute pulmonary function and symptom response i n heavy exerci s e n . R I S K MODELS
Two types o f r i s k are calculated: benchmark ( r i s k posed by ambient a i r ) and headcount ( r i s k due t o personal exposure). The r i s k o f a harmful health e f f e c t as posed by ambient a i r (benchmark r i s k ) may be thought o f as a hazard (i.e., a source o f potential danger, a c l i f f f o r example). A hazard i s the presence o f a danger, without reference t o the number o f people who come i n contact w i t h it. The r i s k posed t o an individual by personal exposure t o ozone (headcount r i s k ) may be thought o f as the chance that, having encountered the hazard (elevated ozone levels i n t h i s case), a harmful health event w i l l occur (analogous t o a climber on the c l i f f f a l l i n g o f f ) . The development of the r l s k models used i n the r i s k assessment closely follows previous work by Feagans and B i l l e r (refs. 8 and 9). Benchmark r i s k model The benchmark r i s k model calculates the p r o b a b i l i t y t h a t upon j u s t a t t a i n i n g the ozone standard, ambient ozone levels w i l l occur s u f f i c i e n t t o t r i g g e r a health endpoint o f concern (e.g., an FEVl decrement o f 210 percent) i n a l e a s t a
**
specified excess f r a c t i o n (the most sensitive portion) o f the sensitive popul a t i o n (heavy exercisers), one o r mare times during the period o f i n t e r e s t (usua l l y the ozone season). Two sources o f uncertainty enter i n t o benchmark r i s k calculation: (a) uncertainty i n the concentration l e v e l C* t h a t would a f f e c t an
*t
The term "excess" i s used throughout t h i s paper t o r e f e r t o response i n excess o f that which would have occurred under background ozone a i r q u a l i t y conditions. Risk i s measured from t h i s baseline because (a) only concentrations above background are susceptible t o human control and (b) i t i s d i f f i c u l t , given c u r r e n t l y available c l i n i c a l response data, t o characterize the very small, hypersensitive fraction o f the population t h a t a l g h t respond a t ozone levels a t o r below background. While background ozone levels fluctuate during the day, from day t o day, and seasonally, f o r the purposes o f the r i s k assessment, i t i s assumed t h a t 0.04 p p i s a generally representative surrogate f o r the l e v e l o f background ozone.
854
R* excess f r a c t i o n o f the population and (b) uncertainty as t o the value o f the ambient concentrations t h a t would occur when the NAAQS i s j u s t attained. Combining these two sources o f uncertainty y i e l d s the equation used t o compute benchmark r i s k : B(S,R:K,N)
-
[hax 0
f(C*lR*)
P('ob
2 '** Or wre) dC* times i n N periods
where B i s the benchmark r i s k , C* i s the concentration t r i g g e r i n g the health endpoint o f concern i n an R* excess f r a c t i o n o f the sensitive population (heavy exercisers), cobs are the hourly ambient concentrations projected t o occur upon j u s t exactly a t t a i n i n g the standard, K i s the number o f times C* i s equalled o r exceeded during the period o f i n t e r e s t (N averaging periods, e.g., 8,760 hours i n a f u l l year o r less f o r the ozone season), S i s the concentration l e v e l o f the standard, and Cmax i s a concentration value chosen t o be c l e a r l y above the range o f observed values. The exposure-response r e l a t i o n s h i p i s expressed i n the benchmark model by the which i s determined from c l i n i c a l data conditional p r o b a b i l i t y density f(C*lR*), (see refs. 1 and 10). Ambient ozone a i r quality, under conditions o f exact NAAQS attainment, i s represented by the second p r o b a b i l i t y d i s t r i b u t i o n i n eqn. 1. The required d i s t r i b u t i o n i s derived from the time series o f hourly ambient concent r a t i o n values thought t o represent ozone a i r q u a l i t y under conditions o f exact NAAQS attainment, and considers ozone concentration autocorrelation and nonsta-
t i o n a r i t y . Ozone time series projected f o r exact NAAQS attainment are provided t o the r i s k assesment from the EPA's ozone NAAQS population exposure p r o j e c t by Paul e t al. (1986) ( r e f . 11). Headcount r i s k model The headcount r i s k model calculates the expected excess number o f additional health endpoint incidences, o r people affected, w i t h i n a specified period (usua l l y the ozone season). Calculation of headcount r i s k takes i n t o account persona l exposure as people move about, from indoors t o outdoors, and from one place t o another. Sources o f uncertainty entering i n t o headcount r i s k c a l c u l a t i o n i n clude uncertainty i n (a) the exposure-response relationship, (b) indoor and outdoor a i r quality, and (c) population a c t i v i t y and m o b i l i t y patterns. For r i s k assessment purposes, headcount r i s k i s expressed as expected headcount (see r e f .
1 f o r f u r t h e r discussion).
H
=
1'
N N p e 0
i ( C ) dE(CIS)
Expected headcount may be w r i t t e n as follows:
*
855
where i? i s the expected headcount, Np i s the number o f people i n the sensitive popu1a t ion (heavy exercisers), Ne i s the number o f possible exposures per person during the period o f i n t e r e s t (8,760 hours f o r a year, o r less f o r the ozone season), ii i s the expected excess exposure-response function obtained from c l i n i c a l response data (see refs. 1 and lo), and d i i s the nomalized population exposure d i s t r i b u t i o n expected when the area under consideration j u s t a t t a i n s the standard S and i s derived from population exposure d i s t r i b u t i o n s generated by the EPA's ozone NAAQS Exposure Model (03-NEM). Exposure d i s t r i b u t i o n s calculated with the 03-NEM model were developed i n the EPA's ozone NAAQS population exposure project by Paul e t al. (1986) (ref. 11). The OJ-NEM i s an urban-scale population exposure model t h a t calculates ozone exposure f o r up t o 54 d i f f e r e n t population groups, which are distinguished on the basis o f age, occupation, and conmuting patterns. Individual population subgroups, o r cohorts, which are defined on the basis of c o m n age-occupation group and home and work location, are tracked by the 03-NEH f o r the ozone season (9 months t o a year, depending on the urban area), as they move each hour among f i v e d i f f e r e n t microenvironments: indoors-residential, indoors-other, motor vehicle, outdoors near a roadway, and outdoors-other. To characterize uncertainty i n the expected headcount, 90 percent credible intervals about the mean value are estimated based on uncertainty I n the exposure-response relationship (see l a t e r discussion). Results are expressed i n two ways: (a) the number o f times that a response occurs i n heavy exercisers (with possibly more than one response per person) and (b) the number o f people affected (each person i s counted only once). EXPOSURE-RESPONSE RELATIONSHIPS
The EPA ozone c r i t e r i a document and s t a f f paper i d e n t i f y the following sensit i v e groups thought t o be p o t e n t i a l l y a t r i s k t o ozone exposure: (a) i n d i v i d u a l s with pre-existing respiratory disease and (b) the general population o f normal, healthy individuals, p a r t i c u l a r l y those who f o r reasons c u r r e n t l y unknown are unusually responsive t o ozone, and those whose a c t i v i t i e s out o f doors r e s u l t i n increased lung v e n t i l a t i o n (refs. 2 and 3 ) . With regard t o the f i r s t o f these groups, while a given decrement i n lung function may be more serious i n persons with already impaired lung function, the ozone c r i t e r i a document concludes t h a t available data indicate s i m i l a r response i n both healthy groups and those w i t h pre-existing respiratory disease (ref. 2). Therefore, f o r the purposes o f the r i s k assessment, notwithstanding the p o t e n t i a l l y greater seriousness o f a given lung function decrement i n those individuals w i t h chronic r e s p i r a t o r y disease, i t i s assumed t h a t the exposure-response behavior o f the more heavily studied
856
normal, healthy population (as characterized by FEVl decrement and respiratory symptoms) can be used to characterize the response of both groups. Further, the criteria document identifies exercise, which strongly affects 'lung ventilation and thus dosage rate, as an important factor Influencing the effects of ozone exposure. Thus, it is reasonable to presume that the individuals potentially most at risk from such exposure are those who exercise most heavily, with those heavy exercisers who are unusually responsive to ozone (so-called "responders") the most at risk. Applying criteria described in ref. 1, three controlled human exposure studies are judged sufficiently similar in terms of subject population, exercise level, and exposure protocol for use in the risk assessment: Avol et al. (1984) (ref. 5). Kulle et al. (1985) (ref. 6). and McDonnell et al. (1983) (ref. 7). All three studies are of healthy, heavily exercising adults. Avol et al. exposed 50 well-conditioned, mostly male (80 percent) athletes (competitive bicyclists), two of whom had histortes of mild asthma, to ozone concentrations of 0.00 ppm (clean air), 0.08, 0.16, 0.24, and 0.32 ppm. Forty-one subjects had never smoked regularly, 3 were current smokers, and 6 were ex-smokers. Data for 48 subjects were available to the risk assessment. Kulle et al. exposed 20 healthy, nonsmoking, male subjects to ozone concentrations of 0.00, 0.10, 0.15, 0.20, and 0.25 ppm. Eight of the 20 subjects were also exposed at 0.30 ppm. McDonnell et al. divided 135 healthy male subjects into six exposure groups o f approximately 20 subjects each, exposing groups to ozone concentrations of 0.00, 0.12, 0.18, 0.24, 0.32, or 0.40 ppm. In the Kulle and McDonnell studies, subjects were exposed for 2 hours under heavy, intermittent exercise (alternating 15-minute periods of exercise and rest) at 68 L/min (Kulle) and 65 L/min (McDonnell); subjects in the Avol study exercised continuously for 1 hour at 57 L/min. The Avol and Kulle studies exposed the same subjects at all concentration levels; McDonnell et al. exposed different subject groups at each concentration. Spirometric measurements (including FEV1) and symptom response were reported for each study. The Kulle and McDonnell studies reported Individual symptom data (e.9.. cough and chest discomfort), ranked as either none, mild, moderate, or severe. Avol et al. grouped symptoms as either lower respiratory (including cough and chest discomfort), upper respiratory, or nonrespiratory. Individual responses for each symptom within a group were recorded as none, mild but noticeable only upon questioning, mild, moderate, severe, or incapacitating. Responses were reported by symptom group score, which were obtained by sumning the ratings for individual symptoms within the group.
a57
Probabilistic exposure-response relationships are developed for risk assessment purposes according to a methodology described in ref. 1. The effects of ozone are isolated by correcting for the effect of exercise alone, using response data obtained during clean-air exposures. Exposure-response uncertainty is represented in terms of sampling error due to small siunple size using a beta probability distribution constructed according to Bayesian statistical methods (e.g., see ref. 12). Continuous exposure-response curves (with 90 percent credible intervals) are estimated by fitting constrained four-parameter logistic functions to the fractile values of the beta probability distributions. The distributions are forced through the origin since, by definition, ozone-induced response must be zero when the ozone concentration equals zero. Exposure-response uncertainty is represented In two ways. Interlaboratory differences are recognized by separate calculation of risk results f o r all three clinical data sets, with no averaging or other aggregation performed. Intralaboratory uncertainty is accounted for by statistical techniques for calculating sampling error due to small sample size as outlined above. Figs. 1 and 2 present probabilistic exposure-response relationships for acute ozone-induced pulmonary function response in heavy exercisers (FEVl decrements of 210 and 220 percent). Similar relationships for cough and chest discomfort (Kulle and McDonnell) and lower respiratory symptoms as a group (Avol) are contained in ref. 1 for two symptom severity levels: any (including mild) and moderatehevere. As a final step, the exposure-response relationships are adjusted for response under exposure at background ozone levels, taken to be 0.04 ppm. The figures demonstrate a range of response among the three clinical data sets. As shown in ref. 1, the differences among data sets are also present for respiratory symptoms, with the McOonnell subjects reporting systematically greater response than the Avol and Kulle subjects. Although response differences may represent intrinsic variation in subject populations or may be attributable to experimental protocol differences, the reasons for the response variation are currently unknown. RISK RESULTS AND FINDINGS Probabilistic exposure-response relationships are utilized in the benchmark model (risk due to ambient air) and the expected headcount model (risk posed by actual personal exposure) to estimate acute ozone-induced pulmonary function and respiratory symptom risk. Risk results are calculated (ref. 1) for three alternative 1-hour ozone standards (0.12, 0.10, and 0.08 ppm), for ten urban areas, for each o f three clinical data sets (Avol, Kulle, and McDonnell).
858 Benchmark r i s k r e s u l t s and findings I l l u s t r a t i v e benchmark r i s k r e s u l t s f o r FEVl decrements o f 210 and 220 percent are presented i n Fig. 3 f o r S t . Louis. Results for the three a l t e r n a t i v e standards are s i m i l a r t o those f o r S t . Louis across a l l the other n h e urban areas. Results are presented i n the form o f bar charts, w i t h three groups o f bars per figure, corresponding t o the three exposure-response data sets. Each group i s comprised o f four bars. One bar i s f o r as-is conditions, w i t h one each f o r the three a l t e r n a t i v e standards. Each bar i s i t s e l f subdivided i n t o three parts, each corresponding t o a d i f f e r e n t excess percentage o f the exposed heavy exercisers responding. The t o t a l height o f a bar i s the r i s k f o r the 1%-benchmark case, t h a t i s , the p r o b a b i l i t y t h a t a t least an excess 1 percent o f heavy exercisers would respond. It should be noted t h a t t h i s measure o f benchmark r i s k focuses on the r i s k posed by ambient a i r t o the most sensitive individuals. The top o f the v e r t i c a l l y shaded portion o f the bar corresponds t o the r i s k f o r the 5%-benchmark case, t h a t i s , an excess 5 percent o f exposed heavy exercisers responding; s i m i l a r l y , the top o f the slant shaded p o r t i o n corresponds t o the 10%-benchmark case. Interpretation o f the f i g u r e depends on s p e c i f i c a t i o n o f (a) endpoint d e f i n i t i o n (the severity o f health response thought t o be a matter o f regulatory concern, e.g., an F E V l decrement o f 210 o r 220 percent); (b) n%-benchmark d e f i n i t i o n (the minimum excess percentage o f the sensitive population [heavy exercise r s l that must exerience the designated health endpoint before i t becomes a matt e r o f standard s e t t i n g concern); and (c) degree o f r i s k (the magnitude o f the event p r o b a b i l i t y thought t o represent a l e v e l o f concern). The EPA has not endorsed any s p e c i f i c values f o r these three quantities. However, assuming f o r i 1 l u s t r a t i o n purposes only t h a t we are interested i n a 5%-benchmark (the chance o f an excess 5 percent o r more exposed heavy exercisers responding) and an 0.2 degree-of-risk (a chance o f a given health endpoint occurring no more o f t e n than once every f i v e years, on average), Table 1 presents the number o f urban areas whose projected degree o f r i s k i s less than o r equal t o 0.2, f o r each health endpoint, f o r as-is conditions and the three a l t e r n a t i v e standards. Based on the r e s u l t s i n Table 1, the following findings may be stated: (1) Importance o f decision parameters. As can be seen through examination o f Fig. 3 (also see r e f . 1 f o r a more comprehensive demonstration), t h e choice o f decision parameters (health endpoint, nX-benchmark, and degreeo f - r i s k ) i s c r i t i c a l l y important i n the i n t e r p r e t a t i o n o f benchmark r i s k results. (2) S i m i l a r i t y o f r e s u l t s f o r the >10 percent FEVl decrement and any-symptoms Jincludlng mild) cases. Benchmark r i s k r e s u l t s are roughly s i m i l a r f o r three health endpoints: 210 percent F E V l decrement, any (Including mild) cough, and any (including mild) chest discomfort. I n none o f the three
859 cases do many o f the ten urban areas studied achieve the degree-of-risk considered, upon the attainment o f a 0.12 ppm standard. A few additional areas do so upon a t t a i n i n g a 0.10 ppm standard; i n general, nearly a l l areas achieve the specified degree-of-risk f o r a 0.08 ppm standard. (3) S i m i l a r i t y o f r e s u l t s f o r the >20 percent FEVl decrement and moderate/severe symptoms case. Benchmark r i s k r e s u l t s are roughly s i m i l a r f o r the remaining three health endpoints: 220 percent FEVl decrement, moderate/ severe cough, and moderately/severe chest discomfort. I n contrast t o (2). many, i f not a l l , o f the ten urban areas are projected t o achieve the degree-of-risk considered f o r a l 1 three standards, including the current 0.12 ppm NAAQS (with the exception o f r e s u l t s f o r the McDonnell symptom exposure-response data sets, which y i e l d systematicaly higher cough and chest discomfort r i s k estimates than w i t h the Avol and K u l l e data sets). A number o f urban areas also achieve the specified degree-of-risk under as-i s conditions. Headcount r i s k r e s u l t s and findings Headcount r i s k i s characterized i n the r i s k assessment by expected headcount, the number o f people ( o r incidences) i n which a health endpoint i s expected t o occur during the ozone season, given t h a t the ozone standard i s j u s t attained. Expected headcount i s calculated by combining ozone exposure-response r e l a t i o n ships with ozone population exposure d i s t r i b u t i o n s generated f o r heavy exercisers by Paul e t al. (1986) (ref. 11) using the EPA's 03-NEM urban-scale ozone population exposure model. Fig. 4 presents the aggregate expected headcount f o r e i g h t o f the ten study c i t i e s . (Chicago and New York are omitted because EPA ozone exposure calculations f o r those urban areas were being refined a t the time o f the r i s k assess-
TABLE 1 Number o f urban areas (up t o 10) whose projected 5%-benchmark degree-of-risk i s less than o r equal t o 0.2, f o r d i f f e r e n t acute ozone-induced pulmonary effects, f o r as-is conditions and attainment o f alternative 1-hour ozone standards. Number o f urban areas achieving 0.2 degree-of-risk 0.08 ppm Health AS-IS 0.12 PDln 0.10 ppm Endpoint A K M A K M A K M A K M bFEVl
->10%
Cough
>20% Any
Chest discomfort
Mod/Sev Any M/Sev
_ _ _ _ _ _ --- 5 2 -- -- -7 5 --- -- -7 4 --
--
8 - 10 9
-- -- -10 10 --- -- -lo lo
where A = Avol, K = Kulle, and M = McDonnell;
--
--lo-4
10 10
1 -lo lo
3 3 10 10
"--" =
---
---
3 10 3 10 10 10 9 5 -10 10 --
lo lo
10 10
0 (for clarity).
---
860 ment.) Results, which are aggregated by sumning the expected number o f people exposed across the eight urban areas, are presented f o r pulmonary function (represented by F E V l decrements o f 210 and 220 percent). Though not shown, expected headcount was also calculated f o r cough, chest discomfort, and lower resp i r a t o r y symptoms taken as a group. Mean expected headcount i s shown f o r each alternative standard, f o r each c l i n i c a l data set. Exposure-response uncertainty i s represented by 90 percent credible intervals, which are calculated on the basis o f sampling e r r o r introduced by small-sample size. The t o t a l number o f people l i v i n g i n the e i g h t areas i s approximately 25.9 million; the number o f individuals i n population groups exercising heavily enough t o reach the 03-NEM heavy exercise regime used (three o r more 10-minute periods i n an hour, a t heavy o r very heavy exercise) a t l e a s t once during the ozone season t o t a l 9.3 m i l l i o n (or about 36 percent). Primary headcount r i s k findings are as follows: (1) Number o f people responding under NAAQS attainment, aqgregated f o r e i g h t U.S. urban areas. As shown i n Table 2, while there i s p o t e n t i a l l y s i g n i f icant uncertainty i n the absolute value o f the r i s k estimates, a s i g n i f i TABLE 2 Range o f mean number o f heavy exercisers responding (millions) across c l i n i c a l exposure-response data sets * under NAAQS attainment (expected headcount), f o r various acute ozone-induced pulmonary effects, f o r a l t e r n a t i v e 1-hour ozone standards, aqqregated f o r 8 U.S. urban areas. Health Mean number o f people responding under attainment ( m i l l i o n s ) Endpoint AS-IS 0.12 ppm 0.10 ppm 0.08 ppm A F E V ~ 210% -*20% Cough Any Mod/Sev Chest Any discom- Mod/Sev
0.46 0.15 1.22 0.18 0.78 0.06
- 1.72
- 0.95 - 2.73 - 1.43 - 1.30 - 1.15
0.06 0.03 0.20 0.02 0.20 0.02
- 0.22 - 0.12 - 1.34 -- 0.26 0.61 - 0.51
0.05 0.02 0.14 0.01 0.14 0.01
- 0.21 - 0.08 - 1.07 - 0.18 - 0.50 - 0.40
0.04 0.01 0.05 0.01 0.05 0.01
-
0.15 0.05 0.75 0.10 0.36 0.28
TABLE 3 Range o f mean percentages o f heavy exercisers responding across 8 U.S. urban areas (expected headcount), under NAAQS attainment, f o r various acute ozoneinduced pulmonary effects, f o r a l t e r n a t i v e 1-hour ozone standards. Health Range of mean percentages respondinq under attainment 0.10 ppm Endpoint As-1~ 0.12 ppm 0.08 ppm 210% ->20% Cough Any Mod/Sev Chest Any discom- Mod/Sev
bFEVl
1.1 0.5 3.1 0.2 2.7 0.2
-
-
36.3 20.7 41.8 27.7 20.4 18.7
0.5 0.2 0.9 0.1 0.8 0.1
- 4.2 - 2.1 - 18.8 - 4.8 - 8.5 - 7.1
0.1 0.0 0.2 0.0 0.1 0.0
-
3.0 1.3
0.0
15.2 2.9
0.1 0.0 0.1 0.0
7.0
5.8
0.0
-
1.9 0.7 10.1 1.4 4.8 3.8
cant reduction i n the number o f heavy exercisers responding i s projected t o occur, going from as-is conditions t o NAAQS attainment, f o r any o f the three a1ternative standards examined including the current 0.12 ppm standard. (2) Percentages o f heavy exercisers responding under NAAQS attainment, across eight U.S. urban areas. As shown i n Table 3, consistent w i t h (1). a sign i f i c a n t reduction i n the percentage o f heavy exercisers responding i s projected t o occur going from as-is Conditions t o NAAQS attainment. (3) Comparabi 1 it y o f percentages o f heavy exercisers responding. The percentage o f heavy exercisers responding under as-is conditions ranges widely across the eight urban areas. However, f o r a given standard and c l i n i c a l data set, the percentage projected t o respond under attainment i s o f t e n comparable across urban areas. F u l l supporting data f o r t h i s f i n d i n g are provided i n ref. 1. APPLI CAB I LITY A number o f assumptions are made i n the r i s k assessment, each o f which should be kept i n mind when i n t e r p r e t i n g results. Extrapolation o f r i s k r e s u l t s f o r the Avol, Kulle, and McDonnell studies t o the heavily exercising population a t large i s affected by a number o f considerations, including the following: (1) Interaction between ozone and other pollutants. It i s assumed t h a t the health endpoints o f i n t e r e s t are due solely t o ozone. This i s consistent with the r e s u l t s o f Avol e t al. (1984) and conclusions i n the EPA ozone c r i t e r i a document. (2) Reproducibility o f ozone-induced responses. It i s assumed t h a t ozone-induced pulmonary responses are reproducible i n individuals. Such an assumption i s supported by the EPA c r i t e r i a document and analyses o f study data sets conducted by Hayes e t al. (1987b) (ref. 13). (3) @. The r i s k assessment i s assumed t o apply t o a l l heavily exercising individuals regardless o f age. However, research studies discussed i n the ozone c r i t e r i a document have reported pulmonary function decrement, b u t not symptomatic response i n children under ozone exposure. Therefore, headcount r i s k , which r e l l e s on exposure estimates t h a t include children, may overstate t r u e symptom r i s k . However, pulmonary function r i s k e s t i mates are not affected, nor does any lack o f symptoms necessarily i n d i cate t h a t the b i o l o g i c a l processes associated w i t h ozone symptoms i n adults are not also present i n children. (4) Sex. It i s assumed t h a t exposure-response data obtained i n the Avol, Kulle, and McDonnel1 studies apply t o both males and females. To the extent t h a t females are more responsive than males (there i s some l i m i t e d evidence t o t h i s e f f e c t f o r lung function impairment as measured by
862
the r i s k estimates may be understated i n r e l a t i o n t o the percentage o f heavy exercisers who are female. (5) Smoking status. The r i s k assessment i s assumed t o apply t o a l l heavy exercisers, regardless o f t h e i r smoking status. There i s some l i m i t e d e v i dence t h a t smokers may be less responsive t o ozone exposure than nonsmokers. To the extent t h a t t h i s i s SO, the r i s k estimates may be overstated i n r e l a t i o n t o the percentage o f heavy exercisers who are smokers. (6) Exercise group. The r i s k assessment assumes t h a t the exposure-response relationships obtained from the Avol, Kulle, and McDonnell studies apply t o a l l heavy exercisers. The ozone c r i t e r i a document defines heavy exercise as lung v e n t i l a t i o n rates o f 44-63 L/min and very heavy exercise as ->64 L/min. The Avol study (57 L/min) corresponds t o the mid-to-upper port i o n o f the heavy exercise range (54 L/min i s the midpoint). The McDonn e l l study (65 L/min) f a l l s j u s t i n the lowest p o r t i o n o f the very heavy exercise range, w i t h the K u l l e study (68 L/min) some 5 percent higher. To the extent t h a t exercise rates among any p a r t i c u l a r heavy exercisers are lower than i n the subject studies, pulmonary f u n c t i o n and symptom r i s k s m a y be less than estimated. The extent t o which t h i s i s the case i s unknown and must be regarded as an additional source o f uncertainty. To further address t h i s uncertainty, EPA plans i n subsequent work t o examine the e f f e c t o f a l t e r n a t i v e d e f i n i t i o n s o f heavy exercise on r i s k assessFEVl),
ment results. (7) Attenuation o f response. The r i s k assessment assumes t h a t ozone-induced
response i s not affected by previous ozone exposure history. The extent o f attenuation and/or enhancement o f ozone response due t o previous exposures cannot be addressed q u a n t i t a t i v e l y i n the r i s k assessment and must, therefore, be regarded as an additional uncertainty. ACKNOWLEDGMENTS The authors wish t o g r a t e f u l l y acknowledge the assistance, comnents, and suggestions o f a l l who contributed t o t h i s work, p a r t i c u l a r l y the following: a t EPA, Mr. Bruce Jordan, Mr. Thomas McCurdy, and O r . David McKee; health researchers, Drs. Edward Avol, Thomas Kulle, and William McDonnell, whose c o n t r o l l e d human exposure data are the basis o f the ozone exposure-response r e l a t i o n s h i p s used; an independent consultant t o EPA, O r . William B i l l e r : a t P E I Associates Inc., Mr. Roy Paul and Mr. James Capel; and a t Systems Applications, Or. C. Shepherd Burton, O r . Thomas Permutt, and Ms. Marianne Dudik.
863
REFERENCES S.R. Hayes, A.S. Rosenbaum, T.S. Wallsten, R.G. Whitfield, and R.L. Winkler, Assessment o f Lung Function and Symptom-Health Risks Associated w i t h Attainment o f Alternative Ozone NAAQS (Draft Final), Systems Applications, Inc., San Rafael , California, 1987 (SYSAPP-87/171).
U.S. Environmental Protection Agency, A i r Q u a l i t y C r i t e r i a f o r Ozone and Other Photochemical Oxidants, Research Triangle Park, North Carol ina, 1986 (EPA-600/8-84/020a-ef). U.S. Environmental Protection Agency, Review o f the National Ambient A i r Qua1i t y Standards f o r Ozone: Preliminary Assessment o f S c i e n t i f i c and Technical Information (Revised Draft), Research Triangle Park, North Carolina, 1987.
Clean A i r S c i e n t i f i c Advisory Cornittee, Transcript o f the December 1987 Meeting o f the Clean A i r S c i e n t i f i c Advisory Cornittee, U.S. Science Advisory Board, Washington, D.C., 1987. E.L. Avol, W.S. Linn, T.G. Venet, D.A. Shamoo, and J.D. Hackney, Comparative Respiratory Effects o f Ozone and Ambient Oxidant P o l l u t i o n Exposure During Heavy Exercise, J. A i r Pollut. Control Assoc., 34 (1984) 804-809.
T.J. Kulle, L.R. Sauder, J.R. Hebel, and M.D. Chatham, Ozone Response Relationships i n Healthy Nonsmokers, Am. Rev. Respir. Dis., 132 (1985) 36-41. W.F. McOonnell, D.H. Horstman, M.J. Hazucha, E. Seal, Jr., E.D. Haak, S. Salaam, and D.E. House, Pulmonary Effects o f Ozone Exposure During Exercise: Dose-response Characteristics, J. Appl. Physiol.: Respir. Environ. Exercise PhySiOl. , 54 (1983) 1345-1352. T.B. Feagans and W.F. B i l l e r , Risk Assessment: Describing the Protection Provided by Ambient A i r Q u a l i t y Standards, Environ. Profess., 3 (1981) 235-247.
T.B. Feagans and W.F. B i l l e r , A General Method f o r Assesslng Health Risks Associated w i t h Primary National Ambient A i r Q u a l i t y Standards, U.S. Environmental Protection Agency, Office o f A i r Q u a l i t y Planning and Standards, Research Triangle Park, North Carolina (May 1981 d r a f t ) . 10 S.R. Hayes, M. Moezzi, T.S. Wallsten, and R.L. Wlnkler, An Analysis o f Symptom and Lung Function Data from Several Controlled Ozone Exposure Studies, Systems Applications, Inc., San Rafael , Cal ifornia, 1987 (SYSAPP-86/120).
11 R.A. Paul, T. Johnson, A. Pope, and A. Ferdo, National Estimates o f Exposure t o Ozone Under Alternative National Standards (Draft), P E I Associates, Inc. , Durham, North Carolina, 1986. 12 R.L. Winkler, An Introduction t o Bayesian Inference and Oecisfon, Holt, Rinehart and Winston, New York, 1972.
13 S.R. Hayes, M. Moezzi, T.S. Wallsten, and R.L. Winkler, An Analysis o f Symptom and Lung Funciton Data from Several Controlled Ozone Exposure Studies, Systems Applications, Inc., San Rafael , California, 1987b (SYSAPP-86/120).
PROBABILISTIC EXP.-RESP. RELAT. (Kulle Data)
PROBABILISTIC EXP.-RESP. RELAT. (Avol Data) _-D(FEV1) >= 1% 1.01.
n
.
Heavy Exercise.Variws Credii Levels 3
__ D(FEV1)>= 10%. Heavy Exercise,Various CmdiMe Levels --
-
- O.%(upper)
- .!5O(middle)
n
E
-
0.4
w
U Y
U
2
%
h
e2
0
2
0.2
a U
U
0.1
0.00.0
0.0
0.1
0.2
0.3
.05(bWer)
0.6
IA
\L
0.4
OZO~CONCE~AlDN@pn)
0.2
0.3
PROBABILISTIC EXPrAESP. RELAT. (McDonnell Data) -- D(FEV1) >= 10%. Heavy Exercise, Various Credble Levels 1.O-r
0.0
0.1
0.2
P
0.3
0.4
OZONE COWCENTRATKm(ppm)
Fig. 1. Probabilistic exposure-response relationships (with 90 percent credible intervals) for acute ozone-induced pulmonary function change i n heavy exercisers (FEV1 decrement 2 10 percent).
0.4
PROBABILISTIC EXP.-RESP. RELAT. (4
__ D(FEV1)
>= 20%. Heavy Exercise. Various Cred
, Levels --
-- D(FEV1)>= 20%. Heavy Exercse. Various Credlble Levels --
I
I-
-
Y
.os(lOmw)
06
Y
0 0
01 0 2 03 OZONE C0NcEHTRATK)N @pm)
4
0.2
0.1
0.0
OZONE C
O
N
C
0.3 0.4 E (p(nn) ~ ~
PROBABILISTICEXPAESP. RELAT. (McDonnell Data)
-- D(FEV1) >= 209c. Heavy Emmse. Various Credible Levels -I
1.0,,
n
E Y Y U.
a
o.81 0.6
e Y
a
E 0.0
0.1 0.2 0.3 OZONE CONCENTRATION (ppm)
0.4
Fig. 2. Probabilistic exposure-response relationships (with 90 percent credible intervals) for acute ozone-induced pulmonary function change in heavy exercisers (FEV1 decremnt 2 20 percent).
866
BENCHMARK RISK => ( O X . Haavy Exarclma
-- D(fEV1)
Avo1
*Ul*
--
YcDonndl
Alhmattvr Ozona Standordm (ppm)
BENCHMARK RISK
-- D(TfV1)
I> Z O X , Haavy Erarclra
Arol
--
YcOonndl
Alkmaltvr Ozone Standard@(ppm)
St.Lou1r
Fig. 3. Benchmark risk in St. Louis for three alternative U.S. ozone standards, (probability of F E V l decrements of 2 10% and 2 20 percent occurring at least once during the ozone season If exposed under heavy exercise): for three clinical exposure-response data sets (Avo1 , Kul le, and McOonnell).
23.0
z
I
Am-b
L c4
2
20.0
X
W
I
c
3
tS.0
-
0
P
I
4.4
10.0
2
.I0
-
c
0
an T
.I1
a W
A#
d,
-
HEADCOUNT RISK (Pooplo)
-- D(FEV1) E> 20%. Weoq Enerclrr --
-
CI
0 X
W
c
C
au
U 0
I
P
c
e
n W
lull8
YcDonnall
Altomoth Ozone ttondordr (ppm)
Eight City Aggrogation
Fig. 4. Expected headcount for three a l t e r n a t i v e U.S. ozone standards, aggregated for eight U.S. urban areas, for FEVl decrements of 10 and 2 20 percent (number of heavily exercising people respondlng durlng the ozone season).
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T. Schneider et al. (Editors), Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Am~terdam-Printed in The Netherlands
ESTIMATED ECONOMIC CONSEQUENCES OF OZONE ON AGRICULTURE: THE U.S.
869
SOME EVIDENCE FROM
R.M. Adams Department o f A g r i c u l t u r a l and Resource Economics, 220 B a l l a r d Extension H a l l , Oregon State University, C o r v a l l i s , Oregon 97331-3601 ABSTRACT Tropospheric ozone a t ambient l e v e l s reduces crop y i e l d s . These reduct i o n s imply economic costs t o society. T h i s paper r e p o r t s estimates o f the economic consequences o f ozone changes on U.S. a g r i c u l t u r e , using recent data and procedures from an i n t e g r a t e d assessment program. Results suggest t h a t reductions i n ozone w i l l l e a d t o economic b e n e f i t s o f from $1 t o $3 b i l l i o n U.S. d o l l a r s p e r year. I m p l i c a t i o n s f o r s t r a t o s p h e r i c ozone changes are also discussed. INTRODUCTION An adequate supply o f a g r i c u l t u r a l products i s fundamental t o t h e welfare o f most societies. I t i s n o t s u r p r i s i n g then t h a t p o t e n t i a l adverse e f f e c t s o f environmental change on a g r i c u l t u r e generates considerable i n t e r e s t . The e f f e c t s o f a c i d deposition, gaseous a i r p o l l u t a n t s , and s t r a t o s p h e r i c ozone d e p l e t i o n on a g r i c u l t u r a l p r o d u c t i v i t y are being evaluated i n t h e U.S., Europe and elsewhere. I n t h e U.S., t h e economic consequences o f such e f f e c t s are a l s o assessed as i n p u t i n t o the process o f r e g u l a t i n g a i r p o l l u t a n t s . The a g r i c u l t u r a l e f f e c t s o f tropospheric ozone were r e c e n t l y studied by t h e U.S. Environmental Protection Agency’s National Crop Loss Assessment Network (NCLAN). The structure, p r o t o c o l s and f i n d i n g s o f t h i s program are w e l l documented [see, f o r example, r e f . 1 and 21. Results i n d i c a t e t h a t tropospheric ozone i s one o f the major p o l l u t a n t s i n terms o f y i e l d losses. Related a r t i c l e s r e p o r t p r e l i m i n a r y estimates o f t h e economic e f f e c t s o f these y i e l d changes on U.S. a g r i c u l t u r e [ r e f . 31. Improved estimates o f the economic e f f e c t s o f troposphere ozone are now a v a i l a b l e , based on f i n a l f i n d i n g s from NCLAN research [ r e f . 41. The o v e r a l l o b j e c t i v e o f t h i s paper i s t o summarize these more recent NCLAN estimates o f t h e economic e f f e c t s o f ozone on U.S. a g r i c u l t u r e . Procedures, r e s u l t s and p o l i c y i m p l i c a t i o n s o f a1 t e r n a t i v e tropospheric ozone l e v e l s and standards are b r i e f l y discussed. These f i n d i n g s i n d i c a t e the economic e f f e c t s o f emissions o f ozone precursors i n t o t h e troposphere. There i s also a p o s s i b l e l i n k between s t r a t o s p h e r i c ozone depletion, tropospheric ozone l e v e l s and crop p r o d u c t i v i t y , which we explore a t t h e conclusion o f t h i s paper.
METHODOLOGY A bioeconomic assessment r e q u i r e s c r i t i c a l i n p u t from several d i s c i p l i n e s i n order t o l i n k physical and b i o l o g i c a l phenomenon t o an economic v a l u a t i o n model. The s t a r t i n g p o i n t i n t h i s assessment i s d e f i n i t i o n o f a l t e r n a t i v e scenarios concerning tropospheric ozone changes, and s p e c i f i c a l l y how changes i n ozone w i l l r e s u l t i n changes i n items t h a t people value, i.e., t h e q u a n t i t y and q u a l i t y o f food and f i b e r . T h i s i n f o r m a t i o n i s obtained from appropriate crop y i e l d response models t h a t l i n k y i e l d changes t o changes i n ozone. Such crop y i e l d changes were estimated from data generated i n t h e NCLAN program. The f i n a l step o f the assessment process i n v o l v e s applying an appropriate model t o measure t h e economic a f f e c t s o f these y i e l d changes. The assessment model used here i s an updated v e r s i o n o f t h e economic model used i n e a r l i e r economic analyses o f tropospheric ozone [ r e f . 3 1 . I n general, t h e model and i t s a p p l i c a t i o n i s conceptually s i m i l a r t o t h e numerous induced change analyses found i n t h e a g r i c u l t u r a l economics l i t e r a t u r e . S p e c i f i c a l l y , the economic model i s a s p a t i a l e q u i l i b r i u m model formulated as a mathematical programming problem t o represent production and consumption o f 24 primary a g r i c u l t u r a l commodities i n t h e U.S., i n c l u d i n g both crop and l i v e s t o c k products (see Table 1). Processing of a g r i c u l t u r a l products i n t o secondary commodities (e.g., d a i r y products, meat products) i s a l s o included. The production and consumption sectors a r e made up o f a l a r g e number o f i n d i v i d u a l s , each o f whom operates under c o m p e t i t i v e market conditions.
This
leads t o a model which maximizes t h e area under t h e demand curves l e s s t h e areas under t h e supply curves. T h i s area, known as economic surplus o r net s o c i a l benefit, i s an accepted measure o f s o c i a l w e l f a r e i n market o r i e n t e d economies. Both domestic and f o r e i g n consumption (exports) are considered. Exports (foreign consumption) are p a r t i c u l a r l y important f o r many U.S. crops, i n c l u d i n g maize, soybeans and o t h e r feed g r a i n s . The assumptions and p r o cedures of t h i s methodology are discussed i n more d e t a i l i n Adams, Hamilton, and McCarl [ r e f . 41. TABLE 1 Primary commodities included i n t h e economic model, Cotton Corn Soybeans Wheat Sorghum Oats Bar1ey Rice
Sugar Cane Sugar beets Silage Hay Milk Culled d a i r y cows Culled d a i r y calves Culled beef cows
L i v e heif e r s L i v e calves Nonfed calves f o r slaughter Fed calves f o r slaughter Calves f o r s l a u g h t e r Hogs f o r slaughter Feeder p i g s
871
The model consists of two components, a set of micro or farm level models integrated with a national (sector) level model. Producer level behavior is captured in production relationships that portray the physical and economic environment of agricultural producers in 63 homogeneous production regions, encompassing the 48 contiguous states. The farm level supply response generated from the 63 individual regions are linked to national demand through the sector model objective function which features demand relationships for various market outlets for the modeled commodities. The model simulates a long-run, perfectly competitive equilibrium as reflected in 19801983 economic and environmental parameters. EXDOSUre ResDonse Functions Yield response data are needed to predict crop yield changes from ozone changes. NCLAN ozone exposure-response experiments on cultlvars of 14 distinct crops are used to estimate response functions for eight major field crops; alfalfa, barley, corn, cotton, hay (a clover-fescue mix), sorghum, soybeans, and wheat. In addition, data from a non-NCLAN rice experiment were used to estimate yield effects for rice [ref. 51. Ozone levels are transformed into a seasonal 7- or 12-hour average exposures for each experimental treatment. Functional correspondence between seasonal exposures and yields is estimated using the Weibull function. The flexible, nonlinear Weibull function is biologically reasonable and captures aspects of plant response to ozone that linear forms do not, with important economic consequences [ref. 61. Response functions were obtained from field experiments for each cultivar and site for each crop, as well as combinations across crop cultivar experiments. The parameter estimates used in the analysis are presented in Table 2, along with the standard errors and correlations. For this analysis, only the aggregate of all sites and cultivars of a crop (e.g., soybeans) are used. It should be noted that the use of pooled response is conservative (understates yield effects) because slightly larger yield effects would result from a given reduction in ozone if producers shifted cultivars in the face of differential response to ozone. Ozone Data and AssumDtions Use of the NCLAN response functions requires estimates of ozone levels in agricultural areas consistent with the NCLAN exposure measure (7- or 12-hour daily maximum). Using EPA's Storage and Retrieval of Aerometric Data System (SAROAD) ozone readings for rural areas, Lefohn et al. [ref. 71 calculated monthly averages on both a "maximum seven hour' and a "maximum twelve hour' basis for a five-year period. This was accomplished through use of the kriging spatial interpolation procedure.
872
The estimated regional seasonal 7- and 12-hour mean ozone levels for each year define the actual base or benchmark level for use In the economic analysis. Since the model is intended to represent equilibrium behavior over a recent period, the average 1981-1983 ozone levels are used as the base ambient ozone. This base ozone level is then altered to develop changes in ozone for use in the response function, as described subsequently. TABLE 2 Weibull Model Parameter Estimatesa Cropb c A1 fa1 fa Corn Cotton Forage Soybeans Rice Sorghum Spring Wheate Winter Wheat
Ud 178 124 111 139 107 202 314 186 137
(28) ( 2) ( 5) (15) ( 3) (50) (162) (40) ( 5)
C
2.07 2.83 2.06 1.95 1.58 2.47 2.07 3.20 2.34
( .55) ( .23) ( .33) ( .56) ( .16) (1.10) (1.22) (1.86) ( .34)
aThe Weibull is y = a exp [-x/oIc. The a parameter is normalized to unity. bThe pooled responses of all crop cultivars have been used. c12 hour averages have been used except for rice, sorghum, spring wheat and winter wheat, which use 7-hour averaging times. dStandard errors are in parentheses. Erowina Windows The growing season for each crop and region is modeled to approximate crop exposure to ozone. Growing seasons vary because producers have flexibility on planting (and hence harvesting) dates. There are also phenological periods when plants are more sensitive to ozone, e.g., during flowering of soybeans, or when growth rates differ. This results in a distribution of plant growth (yield sensitivity) between the planting and harvesting dates. The development of differentially weighted growing windows explicltly accounts for the distribution of planting dates and growth rates for each crop in concert with the experimental details which give rise to the exposure-response relations. By adjusting these dates and weights on a state-by-state and crop-by-crop basis, the estimated ozone exposures provide a good approximation to real world conditions. Moisture Stress An important issue in analyzing pollutant stress on crops is the interaction with moisture stress, as moisture stress is one of the primary factors
a73 a f f e c t i n g crop y i e l d s . A number o f NCLAN experiments t e s t e d p o t e n t i a l i n t e r a c t i o n s between ozone and moisture stress. To address t h i s r e l a t i o n ship, King [ r e f . 81 modeled drought e f f e c t s w i t h a p l a n t process model f o r major crops (maize, soybeans, cotton, wheat, and forage) i n t h e Corn B e l t and adjacent areas. This simulation process p r o j e c t s diminished s e n s i t i v i t y t o ozone when y i e l d s are reduced concurrently by moisture stress. The d e t a i l s o f the procedure can be found i n Adams, Glyer and McCarl [ r e f . 41. Scenarios for Chanaes i n Ozone A l t e r n a t i v e ozone l e v e l s (scenarios) are r e q u i r e d t o simulate t h e economic e f f e c t s o f changes from c u r r e n t l e v e l s . Previous assessments use a range o f assumptions i n developing ozone changes, i n c l u d i n g p r o p o r t i o n a l changes (from a base year) and s p e c i f i c seasonal averages. I n t h i s analysis, both proport i o n a l changes and changes t i e d t o seasonal l e v e l s are evaluated. The proportional changes provide a comparison w i t h t h e r e s u l t s from previous studies. Seasonal standard scenarios are developed t o approximate a standard proposed by t h e U.S. EPA [ r e f . 91. The standard i s a seasonal average i n c o r p o r a t i n g a three-month average o f d a i l y 7-hour averages. The 7-hour average i s the d a i l y average o f the seven (consecutive) one hour periods i n a day w i t h the highest average. The three-month average i s t h e t h r e e consecutive months w i t h t h e highest average. Any proposed seasonal standard must recognize t h e s t o c h a s t i c nature o f a i r p o l l u t i o n and t h e weather and human elements which cause i t . Because o f p o l l u t i o n v a r i a b i l i t y , c u r r e n t standards f o r ozone i n t h e U.S. use t h e highest one hour average on t h e second highest p o l l u t i o n day. To a l l o w f o r t h i s v a r i a b i l i t y , scenarios need t o r e f l e c t d i f f e r e n t p r o b a b i l i t i e s t h a t the seasonal standard w i l l be exceeded i n a given year. Development o f these s t o c h a s t i c p r o p e r t i e s f o r each seasonal standard i s presented i n Adams, Glyer and McCarl [ r e f . 41. RESULTS AND IMPLICATIONS Successful v a l i d a t i o n provides one i n d i c a t i o n t h a t t h e economic model i s acceptable f o r evaluating t h e e f f e c t s o f ozone on a g r i c u l t u r e . To e s t a b l i s h t h a t t h e model i s a reasonable approximation t o t h e a g r i c u l t u r a l sector over t h e period o f i n t e r e s t , we t e s t the model outputs w i t h actual values f o r the base years, 1981-1983. Table 3 provides a comparison o f actual average p r i c e s and q u a n t i t i e s w i t h those determined by t h e model a t 1981 t o 1983 average ambient ozone and moisture s t r e s s conditions. As i s evident, t h e p r i c e s for a l l commodities match reasonably w e l l ( w i t h i n 5 percent) w h i l e the q u a n t i t i e s g e n e r a l l y understate actual l e v e l s by.5 t o 10 percent.
874 Levels and Seasonal Standards The economic e f f e c t s o f a l t e r n a t i v e ozone l e v e l s o r standards are captured by t h e chanqes i n t h e o b j e c t i v e f u n c t i o n values f o r each ozone scenario when compared with t h e base s o l u t i o n . Table 4 presents t h e changes i n economic value (economic surplus) from t h e base f o r 10, 25 and 40 percent changes i n ozone from 1981-1983 ambient l e v e l s . The t a b l e a l s o contains some example seasonal standards. TABLE 3 t!lodel
Prices and Ouanti t i e s vs. Actual: Prices Cornnod t Y Model Actual (S per u n i t ) 281.90 Cotton 284.97 Corn 2.68 2.68 5.73 5.65 Soybeans Wheat 3.56 3.50 Sorghum 2.53 2.50 Rice 8.13 8.01 Bar1ey 2.23 2.20 1.55 1.67 Oats 65.76 Hay 62.08
1981-1983
Ouantities ode1
Actual (nlillions)
10.24 6,452.28 2,018.02 2,260.78 662.00 120.00 425.18 503.04 76.82
11.79 6,839.00 1,915.00 2,419.00 730.00 145.00 498.00 526.00 82.00
1,283.61 139.38 135.81 87.60
1,359.80 151.70 156.25 18.37
..................................................................
Milk Pork Fed beef Wonfed beef
13.35 169.54 232.27 131.44
13.65 165.90 239.70 145.15
Prices f o r a l l crops are d o l l a r s per bushel, except f o r c o t t o n (S per 480 pound bale), r i c e (S per hundredweight), and s i l a g e and hay (S p e r ton). Meat p r i c e s are S per cwt. and are average r e t a i l p r i c e s f o r f i n i s h e d meat products. Source:
USDA, ERS, S t a t i s t i c a l B u l l e t i n No. 715, Washington, D.C. USDA, A a r i c u l t u r a l S t a t i s t i c s , 1984. Washington, D . C .
I n aggregate terms the economic e f f e c t s o f ozone changes are substant i a l . For example, when ozone i s reduced u n i f o r m l y by 25 percent i n a l l regions, t h e estimated economic b e n e f i t s are $1.890 b i l l i o n ( i n 1982 U.S.$) f o r t h e c u r r e n t assessment. The 40 percent ozone r e d u c t i o n increases benef i t s t o s o c i e t y t o $2.780 b i l l i o n . To place these values i n perspective, the n e t value o f a l l crops included i n t h e model was approximately $65 b i l l i o n (U.S.)
i n 1982. Thus, these changes i n economic value a r e from 3 t o 5
percent o f gross crop value. This study d i f f e r s from previous analyses by e v a l u a t i n g p o t e n t i a l seasonal standards f o r tropospheric ozone i n t h e U.S.
One seasonal stan-
dard used here represents ozone c o n d i t i o n s which would p r e v a i l i f s t a t e s d i d n o t exceed t h e seasonal standard most o f t h e time (95 percent, o r 19 years o u t o f 20).
By i n c l u d i n g t h e p r o b a b i l i s t i c aspects o f t h e standard, the
a75 analysis captures both average levels and year-to-year variability in ozone. The focus here is on a seasonal standard of 50 ppb (parts per billion). This standard falls midway in the range of potential seasonal standards 140-60 ppb) suggested by OAQPS [ref. 91. The 50 ppb standard is sufficiently high that some states do not violate the standard, while other states must reduce pollution levels. To test the sensitivity of the seasonal standard to the extent and nature of ozone reductions, the probability of compliance is also varied to represent both 90 and 50 percent compliance levels. The benefits of a 25 percent reduction and a 50 ppb standard with 95 percent compliance (50/95) are similar, $1.890 and $1.674 billion, respectively. In aggregate terms, producers gain relatively more with the seasonal standard than with the constant 25 percent rollback (46 vs. 30 percent of total benefits). This difference is due to the regions (and hence the crops) which are most affected. The distribution o f consumer gains is constant across the two scenarios, with domestic consumers obtaining over half (5659%) of the benefits. At the regional level the effects on producers differ markedly between the seasonal standard and the constant percentage reduction. Producers in higher ozone areas, especially those with greater variability, gain most with the 50/95 standard. This is due to relatively low ozone levels in these regions (and hence little yield improvement), while crop prices decline by the same amount across all regions. As noted before, the 50 ppb standard is a "midpoint" seasonal standard. Alternative seasonal levels can be tested by varying the compliance parameter. Referring back to Table 4, for 90 and 50 percent compliance with a 50 ppb standard (50/90, 50/50), respective increases in economic surpluses of $1.465 and 5.853 billion result. In all cases, the gains of small ozone reduction accrue mainly to producers (over half for the 50/90 standard), while greater reductions consistently favor consumers. Consumer benefits favor the domestic sector. An implication o f these evaluations is that the degree o f compliance is an important element in setting a standard. Ignoring year-to-year variability in implementing a seasonal standard would be similar to choosing a standard with only a 50 percent o f not exceeding that seasonal level. Further, from a regulatory perspective, it is unreasonable to assess the impact of a standard by assuming that all regions exactly equal the proscribed level. lmpact o f Ozone Reductions on the Cost of U.S. Farm P r o a r m Due to government intervention, the agricultural industry in the U.S. (and the EEC) typically responds to a mix of market and institutional signals. Since agriculture is also affected by other government policies such as air
876 TABLE 4 Changes i n Economic Surplus A r i s i n g from A l t e r n a t i v e Ozone Scenarios: Constant Percentage Reduction vs. Seasonal Standardsa
-10% -25% -40%
808 1,890 2,780
Producers’ Surol us S Millions 286 572 683
50/95b 50/90 50/50
1,674 1,465 853
769 738 63 1
Ozone tion
Total Surol us
Consumers’ SurDl us
Consumers ’ Sum1us Exoort Domest 1c
A
522 1,318 2,097
313 738 1,127
209 580 970
905 727 222
53 1 473 186
374 254 136
.........................................................................
“Changes i n economic surplus are t h e changes from t h e base s o l u t i o n . bThese numbers r e f e r t o scenarios f o r changes i n ozone l e v e l s . 50/95 i s a 50 ppb seasonal standard w i t h 95 percent p r o b a b i l i t y o f n o t exceeding the l e v e l i n any given year, as explained i n t h e t e x t . qua1 i t y standards, i t s s t a t u s as a revenue-supported i n d u s t r y has imp1 i c a t i o n t i o n s when examining e f f e c t s o f ozone changes. For example, i f ozone reduct i o n s increase crop y i e l d s and hence output, c o s t t o government farm support programs may increase. Past estimates o f b e n e f i t s from ozone reductions t y p i c a l l y have n o t included such farm program costs because o f t h e d i f f i c u l t y i n modeling i n t e r a c t i o n s between long-term environmental p o l i c i e s and t h e s h o r t term p r o v i s i o n s o f U.S. farm programs as w e l l as t h e complexities and y e a r - t o - y e a r v a r i a t i o n s i n farm support p r o v i s i o n s . The procedure we use t o address t h e e f f e c t s o f ozone r e d u c t i o n s on U.S. Farm Program costs c o n s i s t s o f t h r e e stages. I n t h e f i r s t stage t h e t a r g e t p r i c e s are introduced f o r crops covered i n t h e 1985 Farm Program (cotton, corn, wheat, r i c e , barley, sorghum and oats).
Producers are presumed t o use
t h e t a r g e t p r i c e s as t h e i r expected market prices. Stage two f i x e s t h e q u a n t i t i e s o f program crops i n t h e model a t t h e l e v e l s determined by producer response t o t h e t a r g e t p r i c e s i n t h e f i r s t stage. Market c l e a r i n g p r i c e s f o r these new q u a n t i t i e s r e s u l t from t h e Stage two s o l u t i o n . The d i f f e r e n c e between the t a r g e t p r i c e (Stage 1) and t h e market c l e a r i n g p r i c e (Stage 2), times t h e q u a n t i t y produced (Stage 2), i s equal t o t h e d e f i c i ency payment f o r each program crop. These steps are then repeated using the y i e l d adjustments associated w i t h changes i n ozone l e v e l s . Comparison o f the Farm Program solutions, i n c l u d i n g d e f i c i e n c y payments, b e f o r e and a f t e r t h e ozone adjustment provides an estimate o f t h e p o s s i b l e impact o f t h e 1985 Farm Program on t h e b e n e f i t s from changes i n ozone l e v e l s . The r e s u l t s o f i n c l u d i n g farm program costs are r e p o r t e d i n Table 5. These increased costs t o s o c i e t y reduce t h e b e n e f i t s o f ozone c o n t r o l reported i n Table 4 by 15 percent. This i m p l i e s t h a t t h e a g r i c u l t u r a l
077
b e n e f i t s t o s o c i e t y o f ozone c o n t r o l are reduced when farm programs are i n place. However, i t may be inappropriate t o ascribe t h i s r e d u c t i o n i n b e n e f i t s from ozone c o n t r o l t o the cost o f t h a t environmental c o n t r o l program
[lo]. Rather, i t i s t h e increased cost o f t h e c u r r e n t Farm Program under the new "techno1 o g i c a l 'I conditions. TABLE 5 I n t e r a c t i o n Between Ozone Reductions and 1985 U.S. Farm B i l l Provisions
Scenario
25x
Change i n Economic SurDl us IS m i l l i o n s )
With 1985 Farm B i l l
1,621
Without 1985 Farm B i l l
1,890
Chanqe i n Estimates
lsJwhsl 269
A With 1985 Farm B i l l
1,438
Without 1985 Farm B i l l
1,674
236
THE EFFECTS OF STRATOSPHERIC OZONE DEPLETION ON AGRICULTURE Stratosphere ozone d e p l e t i o n has the p o t e n t i a l t o adversely a f f e c t a g r i c u l t u r a l p r o d u c t i v i t y . Reduction i n s t r a t o s p h e r i c ozone increase u l t r a v i o l e t f l u x i n t h e "Bll range (UV-B), which reduces y i e l d s o f some c u l t i v a r s o f soybeans and wheat [ r e f . 111. I n addition, increased UV-B r a d i a t i o n w i l l increase tropospheric ozone formation (USEPA). Thus, s t r a t o s p h e r i c ozone reductions are l i k e l y t o impose a g r i c u l t u r a l costs t o s o c i e t y v i a some o f the same mechanisms discussed above. Using t h e same model as defined e a r l i e r , we explored t h e p o t e n t i a l economic e f f e c t s o f s t r a t o s p h e r i c ozone d e p l e t i o n on U.S. a g r i c u l t u r e . The d e t a i l s o f t h i s assessment are reported i n Rowe and Adam [ r e f . 121. While the b i o l o g i c a l data on UV-B e f f e c t s on crop y i e l d s a r e l e s s w e l l researched then f o r tropospheric ozone, y i e l d reductions have been observed a t UV-B enhancements 1i k e l y t o occur under a 15 percent s t r a t o s p h e r i c ozone reduct i o n . A 15 percent s t r a t o s p h e r i c ozone reduction i s a l s o expected t o g i v e r i s e t o a 13 percent increase i n tropospheric ozone l e v e l s . Together, these e f f e c t s w i l l r e s u l t i n a y i e l d reduction f o r soybeans o f up t o 10 percent. A 15 percent reduction i n s t r a t o s p h e r i c ozone i s evaluated by using estimated reductions f o r soybeans, corn and wheat y i e l d s from UV-B, along w i t h the e f f e c t s o f increased tropospheric ozone on o t h e r crops i n t h e economic model.
078
Under these yield changes, the estimated economic cost of a 15 percent stratospheric ozone reduction is $2.6 billion. Of this total, about $1.6 billion is from direct UV-B effects, while the remaining $1 billion is due to the 13 percent increase in tropospheric ozone. This link between stratospheric and tropospheric ozone points to the complexities involved in setting atmospheric pollution regulations. Specifically, regulating pollutants in isolation ignores the interactive aspects of most pollution phenomenon. Similarly, assessing the agricultural yield or economic consequences of only one pollutant ignores these interactions and potentially understates the benefits of controls, given that reductions of pollutant precursors are likely to have a range of indirect benefits that may equal or increase the direct consequences. CONCLUSION Results from our current assessments of ozone effects on U.S. agriculture indicate substantial economic costs. Specifically, increases in the yields of eight NCLAN crops associated with a 25 percent reduction in ambient ozone from 1981-1983 levels results in a benefit of approximately $1.9 billion (in 1982 U.S. dollars). Rollbacks of ozone by 40 percent reveal net benefits of almost $3 billion. Including the increased cost of Farm Program payments reduces the magnitude of these estimates by 15 percent. A unique feature of the analysis reported here is the evaluation of seasonal, rather than hourly, standards for vegetation that reflect alternative exceedance rates arising from the stochastic nature o f pollution events. Analysis of a seasonal standard indicates that the magnitude of potential benefits are similar to those achieved with constant percentage rollbacks but the distributional consequences are substantially different. For example, a seasonal standard of 50 ppb with 9 5 percent probability o f not exceeding the level in each region would produce approximately $1.7 billion (in 1982 dollars) in benefits, about the same amount as in the 25 percent rollback. However, the regional implications are quite different, with areas with the greatest air quality improvement realizing the greatest gain. Producers in areas already in or near compliance may actually lose due to a decline in crop prices nationally from increased supply. This suggests the importance of using economic models that capture effects across the many facets that make up economic markets, whether that be in case in the U.S. or EEC countries. Finally, a companion study of stratospheric ozone depletion effects on agriculture indicates that stratospheric ozone reductions of IS percent will have costs to society of about $2.6 billion. These costs arise from both the
079 d i r e c t e f f e c t o f UV-B r a d i a t i o n on crop y i e l d s and t h e increases i n tropospheric ozone a r i s i n g from increased UV-B r a d i a t i o n . T h i s 1inkage between t h e two ozone phenomenon p o i n t s t o t h e need f o r i n t e g r a t e d environmental assessments t h a t r e f l e c t t h e i n t e r a c t i o n between p o l l u t i o n emissions and t h e i r various e f f e c t s . REFERENCES
1 Heck, W.W.,
W.W. Cure, J.O. Rawlings, L.J. Zaragoza, A.S. Heagle, H.E. Heggestad, R.J. Kohut, L.W. Kress and P.J. Temple. "Assessing Impacts o f Ozone on A g r i c u l t u r a l Crops: I.Overview." J. A i r P o l l . Cont. A s s o ~ .
34(1984) :729-735. 2 Heck, W.W., W.W. Cure, J.O. Rawlings, L.J. Zaragoza, A.S. Heagle, H.E. Heggestad, R.J. Kohut, L.W. Kress and P.J. Temple. "Assessing Impacts o f Ozone on A g r i c u l t u r a l Crops: I.Crop Y i e l d Functions and A l t e r n a t i v e Exposure S t a t i s t i c s . " J. A i r P o l l . Cont. Assoc 34 (1984):810-817. 3 Adams, R.M.. S.A. Hamilton and B.A. McCarl. "The B e n e f i t s o f P o l l u t i o n Control: The Case o f Ozone and U.S. A g r i c u l t u r e . " Amer. J. Aari. Econ. 68[19861:886-893. ,- - - - ,.- - - - ... 4 Adams, R.M., J.D. Glyer and B.A. McCarl. "The NCLAN Economic Assessment: Approach, Findings and Implications." I n t e r n a t i o n a l Symposium on Assessment o f Crop Loss from A i r P o l l u t a n t s . Raleigh, N.C., October 25-
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29, 1987. 5 Katz, G., P.J. Dawson, A. Bytnerowicz, J. Wolf, C.R. Thomson and D. Olszyk. " E f f e c t s o f Ozone o r S u l f u r Dioxide on Growth and Y i e l d o f Rice." Aari. Ecosvs and Envi r 14 ( 1985) :103-117. 6 Rawlings, J. and W.W. Cure. "The Weibull Function as a Model f o r Plant Response." Croo Sci. 1985. 7 Lefohn, A.S., H.P. Knudsen, J.A., J. Simpson, and C. Bhumralkar. "An Evaluation o f t h e K r i g i n g Method t o P r e d i c t 7-Hour Seasonal Mean Ozone Concentrations f o r Estimating Crop Losses." 3. A i r P o l l u t . Cont. Assoc.
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37(1987) :595-602. 8 King, D. "Influence o f Moisture Stress on Crop S e n s i t i v i t y t o Ozone," 9
10 11
12
I n t e r n a t i o n a l Symposium on Assessment o f Crop Loss from A i r Pollutants, Raleigh, N.C., October 25-27, 1987. U.S. EPA, O f f i c e o f A i r Q u a l i t y Planning and Standards. 1986. Review o f t h e National Ambient A i r O u a l i t v Stand ards f o r O a n e : P r e l i m i n a r y Assessment o f S c i e n t i f i c and Technical I n f o r m a t i m . Research T r i a n g l e Park, N.C. Segerson, K. "Economic Impacts o f Ozone and Acid Rain: Discussion.' Amer. J. o f Aari. Econ. 69(1987):7900-791. "Current Understanding o f t h e E f f e c t s o f Increased Levels Teramura, A.H. of Solar U l t r a v i o l e t Radiation t o Crops and Natural Plant Ecosystems." Testimony before U.S. Senate. May, 1987. Rowe, R.D. and R.M. Adams. 1987. "Economic Impacts Lower Crop Yields Due t o Stratospheric Ozone." Final P r o j e c t Report t o USEPA. Washington, DC, September.
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801
ESTIMATING THE COSTS OF CONTROLLING AMBIEHT OZONE I N THE UNITED STATES
T. McCURDY1, W. BATTYEZ, M, SMITH2, and M. DEESE2 1Ambient Standards Branch, U.S. T r i a n g l e Park, NC 27711
Environmental P r o t e c t i o n Agency, Research
2A1 l i a n c e Technologies Corporation; Chapel H i l l , NC
ABSTRACT Under contract t o t h e U.S. Environmental P r o t e c t i o n Agency, a l e a s t cost model was developed t o estimate annualized s o c i e t a l costs associated w i t h a t t a i n i n g a l t e r n a t i v e n a t i o n a l ambient a i r q u a l i t y standards (NAAQSs) f o r ozone. Costs are c a l c u l a t e d separately f o r s t a t i o n a r y , mobile, and area sources f o r t h r e e time periods: 1990, 1995, and 2000. Study areas included i n t h e modeling e f f o r t a r e 192 metropolitan s t a t i s t i c a l areas (MSAs) having v a l i d ozone data. Because most ozone c o n t r o l s t r a t e g i e s are based on reducing VOC emissions, t h e a n a l y s i s focuses on v o l a t i l e organic compounds (VOC) controls. Nitrogen oxides (Nox) l e v e l s a r e assumed t o remain constant unless otherwise specified. Emission c o n t r o l options studied i n t h e model i n c l u d e "reasonably a v a i l a b l e " and "best a v a i l a b l e " c o n t r o l technology f o r p o i n t and area sources. For mobile sources, basic and enhanced i n s p e c t i o n and maintenance ( I I M ) programs and other t r a n s p o r t a t i o n c o n t r o l measures (TCMs) are studied. A mixed-integer least-cost program i s used t o s e l e c t c o n t r o l s t r a t e g i e s t o achieve t h e required VOC emission reduction. S t r a t e g i e s are selected t o minimize t o t a l annualized costs o f c o n t r o l f o r each study area, w i t h some constraints. The c o n s t r a i n t s on s t r a t e g y s e l e c t i o n are designed t o emulate d i f f e r e n t s t a t e r e g u l a t o r y strategies.
OVERVIEW The U.S. o f a NAAQS. currently
Clean A i r Act, as amended i n 1977, r e q u i r e s p e r i o d i c review
In accordance w i t h t h i s requirement, t h e NAAQS f o r ozone i s being reviewed.
As p a r t o f t h i s review procedure, h y p o t h e t i c a l
Impacts t h a t changes i n t h e standard would have on nationwide c o n t r o l costs and on ambient a i r q u a l i t y i n various m e t r o p o l i t a n areas are analyzed. While these impacts data are n o t used by EPA t o s e t a NAAQS, they are provided t o t h e p u b l i c as background i n f o r m a t i o n regarding t h e regulatory action.
882 Control costs required t o achieve t h e c u r r e n t and a l t e r n a t i v e NAAQSs are presented i n t h i s paper.
The a l t e r n a t i v e l e v e l s studied are 0.10 ppm and
0.08 ppm, d a i l y maximum one-hour averages.
Costs and a i r q u a l i t y impacts
are analyzed f o r 1990, 1995, and 2000, b u t o n l y 1995 impacts a r e shown below. U n l i k e many a i r p o l l u t a n t s , ozone i s n o t e m i t t e d t o t h e a i r as a primary p o l l u t a n t .
Rather, ozone i n t h e troposphere i s produced by a complex
chain o f photochemical reactions i n v o l v i n g oxygen, n i t r o g e n oxides (Nox), v o l a t i l e organic compounds (VOC),
and o t h e r c o n s t i t u e n t s i n ambient a i r
( r e f . 1). Thus, ozone concentrations cannot be modeled d i r e c t l y from emissions data.
However, given a s t a r t i n g ozone concentration, changes i n ozone
concentrations can be estimated using t h e Empirical K i n e t i c Modeling Approach (EKMA) from expected changes i n VOC and NOx emissions.
Current EPA p o l i c y regarding ozone reductions i s t h a t VOC c o n t r o l i s t h e p r e f e r a b l e strategy f o r a t t a i n i n g NAAQS l e v e l s ( r e f . 2).
Thus, t h e
analyses discussed i n t h i s paper focus on VOC c o n t r o l s . I n order t o estimate precontrol ozone concentrations i n t h e t h r e e years o f a n a l y s i s (1990, 1995, and 2000). f u t u r e VOC emissions a r e p r e d i c t e d u s i n g s t a t e - s p e c i f i c growth indices.
Except i n t h e South Coast A i r Basin o f C a l i f o r n i a , NOx emissions
and ambient l e v e l s are assumed t o remain constant i n t h e f u t u r e and t o be independent o f a l l VOC c o n t r o l s t r a t e g i e s studied. I f EKMA does not p r e d i c t attainment o f an a l t e r n a t i v e ozone NAAQS, VOC emission reductions needed t o a t t a i n a r e estimated.
VOC c o n t r o l s t r a t e g i e s
are selected using an approach designed t o emulate t h e S t a t e Implementation Plan (SIP) process, by which S t a t e s f o r m a l l y develop and adopt emission c o n t r o l strategies. For s t a t i o n a r y and area sources, p o t e n t i a l emission c o n t r o l s s t u d i e d i n t h e cost a n a l y s i s i n c l u d e "reasonably a v a i l a b l e " c o n t r o l technologies
(RACT) and "best a v a i l a b l e " c o n t r o l technology (BACT).
"Lowest achievable emission r a t e " (LAER) technology i s n o t included i n t h e ozone c o s t analysis. For mobile sources, motor v e h i c l e i n s p e c t i o n and maintenance ( I & M ) programs and t r a n s p o r t a t i o n c o n t r o l measures (TCMs) are studied. Control s t r a t e g i e s a r e selected i n t h e c o s t model t o minimize t o t a l annu a l i z e d costs o f c o n t r o l f o r each study area, w i t h some c o n s t r a i n t s .
Controls
are not applied on an i n d i v i d u a l source basis, b u t are a p p l i e d t o e n t i r e source categories, as they would be under a t y p i c a l SIP.
Moderate-stringency
I&M can be applied before o t h e r c o n t r o l s t o simulate an EPA requirement t h a t I&M be i n s t i t u t e d wherever an area requests an extension o f time t o a t t a i n t h e ozone standard.
TCMs, such as d i f f e r e n t i a l p r i c i n g p o l i c i e s and increased
gasoline taxes, a r e assumed t o be applied as a l a s t r e s o r t a f t e r a p p l i c a t i o n o f a l l o t h e r p o t e n t i a l controls.
Controls i n s t a l l e d a t new p l a n t s t o meet New Source Performance Standards (NSPS) and c o n t r o l s required under t h e Federal Motor Vehicle Control Progam (FMVCP) are t r e a t e d as baseline c o n t r o l s i n t h e cost analysis.
Costs o f
these c o n t r o l s are considered t o be a t t r i b u t a b l e t o NSPS and FMVCP.
Reductions
i n gasoline vapor pressure and onboard emission c o n t r o l s f o r automobile refueling, which would be required under proposed gasoline marketing regulations, are a l s o t r e a t e d as p a r t o f t h e c o n t r o l baseline. The cost analysis covers 192 geographic study areas f o r which c u r r e n t ozone monitoring data are available.
These areas comprise 218 U.S.
Bureau Metropolitan S t a t i s t i c a l Areas ( B A S ) .
Census
Since t h e cost a n a l y s i s does
n o t cover t h e e n t i r e nation, i t i s p o s s i b l e t h a t t o t a l U.S. c o n t r o l costs have been underestimated, e s p e c i a l l y f o r more s t r i n g e n t NAAQS a l t e r n a t i v e s . The analysis described here i s explained i n more d e t a i l i n Ref. 3. THE COST METHODOLOGY
I n t h e ozone cost model, emission source categories are grouped together i n "cost pods;" a cost pod i s defined as a category o f emission sources t h a t have s i m i l a r emission c h a r a c t e r i s t i c s which can be c o n t r o l l e d by t h e same type o f c o n t r o l device. Cost pods correspond roughly t o source categories regulated under a t y p i c a l S I P .
I n analyzing VOC c o n t r o l scenarios, t h e cost
model applies c o n t r o l s a t a cost pod l e v e l .
Thus, w i t h i n a given study area,
a l l members o f a given pod are t r e a t e d equally, as they would be under a t y p i c a l SIP.
S t a r t i n g w i t h t h i s c o n s t r a i n t , and others t h a t can be s p e c i f i e d
by t h e analyst, t h e model i d e n t i f i e s t h e l e a s t expensive s e t o f c o n t r o l s t h a t would achieve t h e t o t a l VOC emission reduction t a r g e t f o r a given study area. Although some study areas cross S t a t e boundaries, i t i s assumed t h a t t h e same l e v e l o f VOC c o n t r o l would be a p p l i e d over t h e e n t i r e study area. Controls t h a t are applied t o e x i s t i n g sources w i t h i n a cost pod are a l s o applied t o a l l new sources i n t h a t pod t h a t might be b u i l t , even i f t h e study area i s projected t o a t t a i n an a l t e r n a t i v e NAAQS i n t h e year t h a t c o n s t r u c t i o n occurs. The c o s t model i s implemented on t h e Sperry-UNIVAC mainframe computer a t EPA's National Computer Center. The model comprises a number o f separate modules, each o f which performs a s p e c i f i c task. There a r e s i x major modules (besides j o b run c o n t r o l modules). 1. data i n p u t 2. growth p r o j e c t i o n s
3. baseline EKMA model 4. c o n t r o l costs 5. l e a s t - c o s t model 6. post-control EKMA model
They are:
The modules a r e interconnected as shown i n F i g u r e 1.
A b r i e f discussion o f
t h e modules follow. The main purpose o f t h e i n p u t module i s t o develop a data base o f emissions and c o n t r o l e f f i c i e n c i e s f o r t h e base y e a r o f analysis.
The base
year i s defined t o be t h e most recent year f o r which ambient ozone data a r e available.
The main source o f data on base year emissions and c o n t r o l s i s
t h e National Emissions Data System (NEDS).
The i n p u t module processes NEDS
data t o g i v e a s i m p l i f i e d f i l e o f e s s e n t i a l data f o r each s t a t i o n a r y , area, and mobile source category included i n the ozone c o s t model.
I n addition t o
base year emissions and c o n t r o l information, t h e i n p u t module modifies and s t o r e s i n f o r m a t i o n regarding source l o c a t i o n , production capacity u t i l i z a t i o n , emission source c l a s s i f i c a t i o n code (SCC),
and Standard I n d u s t r i a l C l a s s i f i -
c a t i o n (SIC) code.
INPUT MODULE
CONTROL COSTS MODULE
GROWTH PROJECTIONS MODULE
LEAST-COST MODULE (FMPS)
BASELINE EKMA MODULE
a
POST-CONTROL EKMA MODEL
Figure 1.
M a j o r modules comprising t h e ozone cost model.
885 The i n p u t module performs q u a l i t y assurance checks on S I C and emissions c o n t r o l information.
I n addition, depending on run c o n t r o l s p e c i f i c a t i o n s , a
S I P c o n t r o l f i l e " can be used t o a l t e r c o n t r o l l e v e l s given I n NEOS f o r
s t a t i o n a r y sources so t h a t they correspond roughly t o c u r r e n t S I P c o n t r o l levels.
S i m i l a r adjustments can a l s o be made t o r e f l e c t c u r r e n t I I M programs.
Source-specific base-year capacity u t i l i z a t i o n r a t e s a l s o are assigned i n t h e module, using a f i l e o f SIC-specific i n d u s t r y capacity factors.
Finally,
the i n p u t module performs a number o f f i l e management operations, such as assigning study area and cost pod numbers and aggregating VOC emissions f o r sources t h a t do n o t f a l l i n t o any defined cost pod. The growth p r o j e c t i o n module estimates changes i n t h e emission i n v e n t o r y over time. For t h e t h r e e analysis years, t h e module assesses growth i n emissions from e x i s t i n g sources, closure o f e x i s t i n g sources due t o market conditions, and new source construction. P r o j e c t i o n s are stored i n a new source growth f i l e and a f u t u r e baseline emissions f i l e .
The basis
f o r these p r o j e c t i o n s i s a set o f annual growth estimates from 1980 t o 2000 f o r each S I C group w i t h i n each State. (from various U.S.
These are based on external p r o j e c t i o n s
federal government agencies) o f population and employment
growth, but t h e p r o j e c t i o n s can be v a r i e d by an analyst using t h e cost model t o perform s e n s i t i v i t y analyses. Emissions and c o n t r o l data i n t h e f u t u r e baseline emissions f i l e correspond t o t h e baseline l e v e l o f c o n t r o l .
T h i s f u t u r e baseline i s defined as
t h e emissions s i t u a t i o n t h a t would be achieved i f e x i s t i n g c o n t r o l s a r e maintain a t t h e i r current level.
For t h e primary case, whose r e s u l t s are shown
below, i t i s assumed t h a t no a d d i t i o n a l VOC c o n t r o l s are i n s t a l l e d as p a r t of t h e f u t u r e baseline o t h e r than those i n h e r e n t l y associated w i t h FMVPC and NSPS. Baseline ozone concentrations a r e modeled using EKMA. The b a s e l i n e EKMA module i s run separately f o r each NAAQS a l t e r n a t i v e , year o f analysis, and study area.
Inputs t o t h i s module i n c l u d e t o t a l baseline emission
p r o j e c t i o n s f o r each study area (from t h e f u t u r e baseline emissions f i l e ) and a f i l e o f ozone c,oncentrations o r "design values" by study area, determined from recent ambient ozone data. A major output o f t h e baseline EKMA module i s a f i l e o f emission reduction requirements b y study area. I n addition, t h e module produces a f i l e o f f u t u r e baseline design values. The c o n t r o l cost module i s a l s o r u n f o r each year o f analysis. The module uses a f i l e o f cost equations t o c a l c u l a t e costs and emission reductions o f p o t e n t i a l add-on controls.
These a r e assigned t o each i n d i v i d u a l
s t a t i o n a r y source, area source, and mobile source c o s t pod based on t h e source o r group size. A c o n t r o l c r e d i t f i l e determines whether c o s t s of NAAQS c o n t r o l s applied i n a previous year o f a n a l y s i s a r e t o be c r e d i t e d toward
886 t h e cost o f any a d d i t i o n a l r e q u i r e d controls.
The c o n t r o l c o s t module outputs
a f i l e o f t o t a l pod-level costs and emission reductions f o r each study area and a f i l e o f i n d i v i d u a l source costs and emission reductions. The least-cost module uses a mixed i n t e g e r l i n e a r program t o i d e n t i f y t h e l e a s t c o s t l y s e t o f emission c o n t r o l s t h a t w i l l achieve a s p e c i f i e d emission reduction. The user can s p e c i f y c o n t r o l s t h a t are t o be a p p l i e d f i r s t , regardless o f cost, and c o n t r o l s t h a t are t o be a p p l i e d as a l a s t resort. For instance, I&M c o n t r o l s f o r motor vehicles are a p p l i e d i n t h e module b e f o r e a d d i t i o n a l s t a t i o n a r y source controls, t o r e f l e c t c u r r e n t EPA SIP-development policy.
Least-cost modellng i s conducted separately f o r each study area,
each year o f analysis, and each NAAQS a l t e r n a t i v e . Inputs t o t h e l e a s t cost module are t h e pod-level cost and emission r e d u c t i o n and emission reduction requirements f i l e s . The module output i s a f i l e o f l e a s t cost s o l u t i o n s f o r each study area. A f t e r s e l e c t i o n of emission c o n t r o l s i n t h e l e a s t c o s t module, t h e EKMA model i s re-run t o estimate post-control ozone concentrations t h a t may be achieved using a l l i d e n t i f i e d controls. post-control EKMA module.
T h i s i s accomplished i n t h e
LEAST-COST MODELING The least-cost model used i n t h e ozone cost a n a l y s i s i s t h e UNIVAC Functional Mathematical P r o g r a m i n g System (FMPS). It operates on a s e t o f pod-level annualized costs and emission reductions.
For each c o s t pod, t h e r e i s a t l e a s t one emission c o n t r o l o p t i o n t h a t w i l l achieve a given l e v e l
o f c o n t r o l a t a given cost.
When t h e l e a s t - c o s t model i s run, a t o t a l pod-
l e v e l annualized cost o f c o n t r o l and a corresponding pod-level emission reduction are i n p u t f o r each c o n t r o l o p t l o n w i t h l n a pod.
The pod-level t o t a l s i n c l u d e c o n t r o l costs and p o t e n t i a l emission reductions f o r a l l sources w i t h i n t h a t pod. For a given study area, t h e l e a s t - c o s t model i d e n t i f i e s t h e s e t o f c o n t r o l optlons t h a t h y p o t h e t i c a l l y achieves t h e t o t a l emisslon reduction t a r g e t a t t h e lowest t o t a l annual cost. Annual c o s t s used i n t h e model i n c l u d e annualized c a p i t a l costs, annual o p e r a t i n g and maintenance and insurance and taxes costs, and product- o r fuel-recovery c o s t c r e d i t s . basic a l g o r i t h m f o r t h e mixed-integer l e a s t - c o s t model can be w r i t t e n as follows: Minimize:
AjXj
Such t h a t :
EHjXj
The
(1)
2 ERT
(2)
aa7 A j = pod-level annualized c o s t o f c o n t r o l o f o p t i o n j, f o r a p a r t i c u l a r study area, a n a l y s i s year, and NAAQS a l t e r n a t i v e ($/year),
where:
X j = 0 i f option j i s n o t selected and 1 i f o p t i o n j i s selected, E R j = pod l e v e l VOC emission reduction f o r o p t i o n j (tonslyear), and,
t a r g e t t o t a l emission reduction f o r t h e study area.
ERT
Pod-1 eve1 annualized c o n t r o l costs, A j , a r e c a l c u l a t e d by adding annualized c o n t r o l costs f o r a l l sources, i, i n t h e study area using c o n t r o l o p t i o n j. Thus,
n Aj
Z Aij i=1
(3)
A i j f o r each source i s c a l c u l a t e d by adding o p t i o n - s p e c i f i c c a p i t a l costs ( C C j )
t o t y p i c a l - y e a r operating and maintenance (OMj) costs and s u b t r a c t i n g any product o r f u e l recovery c r e d i t (RCj), i f any.
Annualized c a p i t a l costs a r e
calculated from i n s t a l l e d r e t r o f i t equipment costs, a 10% f l a t i n t e r e s t rate, an equipment l i f e o f 10 t o 15 years (depending upon t h e cost pod i n question), and a y e a r l y charge f o r insurance and taxes equal t o 4% o f i n s t a l l e d c a p i t a l costs.
Therefore, f o r each source w i t h i n a pod:
The independent variables i n Eq. 3 a r e obtained from f i t t i n g l i n e a r o r m u l t i p l i c a t i v e regression equations ( o f t h e general form: and y = a
*
y = a + bx
xb, r e s p e c t i v e l y ) t o c o n t r o l c o s t data from various s i z e d plants.
These data come from EPA cost analyses o f NSPS and RACT regulations.
The
regression equations t a k e t h e f o l l o w i n g form, removing some s u b s c r i p t s
on t h e regression parameters t o simp1 i f y presentation:
S t a t i o n a r y Sources Capital Costs OPM Costs Recovery C r e d i t
a * (Ui**b) a * (Ui**b) a + (b * U i )
Area Sources a a a
* Ui * Ui
*
Ui
888 U i i s t h e u n c o n t r o l l e d VOC emissions l e v e l from source i ( i n c o n t r o l pod j,
of course).
The m u l t i p l i c a t i v e regression equation c o e f f i c i e n t , b, f o r area
sources i s assumed t o be 1.0,
and hence i s n o t shown.
EXAMPLE OF DATA FOR A COST PO0 There are over 40 cost pods i n t h e ozone cost model f o r p o i n t and area sources, More are belng developed. To i l l u s t r a t e t h e t y p e o f data developed f o r each o f t h e pods, Pod 1 w i l l be f u l l y described. Pod ID:
001.
Solvent Metal Cleaning
SCCs Included:
4-02-002-02 t o -06 4-01-002-97 4-01 -002-99
Associated SICs:
Oegreasing ( M u l t i p l e SICs)
Cost Documentation:
NSPS ( r e f . 4)
Control Options ( j ) : 1. CCI:
OM1: RC1:
Freeboard Cover, E f f i c i e n c y :
23%
a = b a = b a =
$2,033/ton = 0.418 $21.70/ton = 0.550 $0.25 b = $147/ton
2. R e f r i g. Freeboard; E f f i c i e n c y : 42% CC2: OM2: RC2:
a = b a = b a = b
$4,72O/ton = 0.451 f165lton = 0.496 $0.92 = $266/ton
3. Carbon Absorbers; E f f i c i e n c y 54% CC3: OM3: RC3:
a = 114,989lton b = 0.368 a = 62931ton b = 0.623 a = $3.62 b = $340/ton
RESULTS Results o f applying t h e cost methodology t o one set o f c o n t r o l s t r a t e g i e s appear i n Table 1. 1995.
For ease o f presentation, o n l y one year o f a n a l y s i s i s shown:
The a l t e r n a t i v e ozone NAAQS analyzed are t h e c u r r e n t 0.12 ppm standard and
two a l t e r n a t i v e s :
0.10 and 0.08 ppm. Costs are aggregated i n t o f o u r major categories: point, area, ( I & M ) , and t r a n s p o r t a t i o n c o n t r o l measures, which i n v o l v e
such programs as r i d e - s h a r i ng and t r a n s l t system improvements.
889
TABLE 1 Emission reductions and v a r i a b l e costs a t t r i b u t a b l e t o a l t e r n a t i v e NAAQS f o r 1995
Case
VOC Reduction
C a p i t a l Cost
Annual Cost
(1000 tons)
(f m i l l i o n )
(f million)
PRIMARY CASE (NAAQS = 0.12 ppm)
Point source c o n t r o l s Area source c o n t r o l s ISM Transportation c o n t r o l measures
456 1,144 303 78
3,794 17,686 1,400 384
909 4,699 704 (1,207)
Totals Residual Nonattainment Areas
1,982
23,264 37
5,105
P o i n t source c o n t r o l s Area source c o n t r o l s ISM Transportation c o n t r o l measures
602 1,595 430 126
5,621 25,634 2,039 619
1,336 6,796 994 (1,940)
Totals Residual Nonattainment Areas
2,753
33,913 90
7,178
Point source c o n t r o l s Area source c o n t r o l s ISM Transportation c o n t r o l measures
697 1,969 504 167
5,910 32,119 2,594 82 1
1,510 8 ,542 1,175 (2,583)
Totals Residual Nonattainment Areas
3,336
41,444 167
8,639
NAAQS = 0.10 ppm
NAAQS = 0.08 ppm
Associated w i t h each a l t e r n a t i v e analyzed i s t h e number o f r e s i d u a l non-attainment areas.
T h i s i s t h e number o f geographic areas
(%As
or
combinations o f contiguous MSAs) t h a t cannot a t t a i n t h e ozone NAAQS being analyzed using the s e t o f cost pods included i n t h e model.
The number o f residual
non-attainment areas increases d r a m a t i c a l l y as t h e a l t e r n a t i v e ozone NAAQS becomer tighter.
For instance, t h e cost model p r e d i c t s t h a t 167 o f t h e 192 areas analyzec
(87%) would not a t t a i n a 0.08 ppm ozone NAAQS i n 1995. S e n s i t i v i t y analyses have been undertaken on t h e model ( r e f . 3). As might be expected, varying t h e i n p u t s used and t h e assumptions made makes a l a r g e impact on model results.
The i n t e r e s t e d reader i s d i r e c t e d
t o Ref. 3 f o r a more thorough dfscussion of s e n s i t i v i t y analyses t h a t have been undertaken.
890 CAVEATS AND LIMITATIONS Despite t h e complexity and comprehensive nature o f the' c o s t model, EPA considers t h e work done t o date t o be p r e l i m i n a r y i n nature.
Significant
u n c e r t a i n t i e s remain regarding t h e baseline VOC emission i n v e n t o r y a v a i l a b l e from each S t a t e on EPA's computer system (i.e.,
NEDS).
Past analyses have
I n d i c a t e d t h a t NEDS can be d i f f e r e n t by 2 200% f o r aggregated source categories when compared t o supposedly more d e t a i l e d i n v e n t o r i e s done by i n d i v i d u a l S t a t e s f o r S I P development work ( r e f . 5).
Another source
o f considerable u n c e r t a i n t y I s t h e VOC/NOx r a t i o needed f o r t h e EKMA model. R a t i o data a r e d i f f i c u l t t o o b t a i n and are a v a i l a b l e f o r o n l y a few MSAs.
(A d e f a u l t r a t i o h a d ' t o be used f o r most MSAs.)
F i n a l l y , area-
s p e c i f i c (and n a t i o n a l l y aggregated) growth r a t e s a r e always a source o f u n c e r t a i n t y regarding f u t u r e conditions.
Growth r a t e s e n t e r t h e ozone
c o s t model f o r numerous p r o j e c t i o n s : population, c a r sales, i n d u s t r i a l growth (by S I C ) , and v e h i c l e miles traveled. Any one o f these items obviously a f f e c t s f u t u r e emission estimates due t o t h e compounding phenomenon. I n addition, i f one r a t e i s o f f r e l a t i v e t o another, a s i g n i f i c a n t imbalance among sectors included i n t h e model can occur. There i s no i n t e r n a l check a t present t o determine if such an imbal ance is occurring. I n sum, t h i s paper described t h e ozone c o s t model t h a t EPA has developed t o analyze s o c i e t a l costs o f a t t a i n i n g a l t e r n a t i v e NAAQS. The model i s considered t o be a p r e l l m i n a r y method a t present, and w i l l be developed f u r t h e r over t h e next two years p r i o r t o EPA's t a k i n g formal a c t i o n regarding t h e ozone NAAQS review.
REFERENCES Environmental C r i t e r i a and Assessment O f f i c e . A i r Q u a l i t y C r i t e r i a f o r Ozone and Other Photochemical Oxidants, Volume I. Research T r i a n g l e Park, NC: U.S. EPA, 1987. E.L. Meyer. Review o f Control S t r a t e g i e s f o r Ozone and T h e i r Effects on Other Environmental Issues. Research T r i a n g l e Park, NC: U.S. EPA, 1986. W.H. Battye, M.G. Smith, and M. Deese. Cost Assessment o f A l t e r n a t i v e National Ambient A i r q u a l i t y Standard f o r Ozone, D r a f t Report. Chapel H i l l , NC: A l l i a n c e Technologies Corporation, 1987. Emission Standards and Engineering Division. Organic Solvent Cleaners Background Information o f Proposed Standards. Research T r i a n g l e Park, NC: U.S. EPA, 1979. W.T. Harnett. "Memo: Comparison o f S I P and NEDS Emission Inventories." Chapel H i l l , NC: GCA Corporation, June 15, 1983.
T.Schneider et d (Editore),Atmospheric Ozone Research and ite Policy Zmplicotions 0 1989 Elsevier Science Publiehere B.V.,Amsterdam Printed in The Netherlande
-
891
ESTIMATED COSTS AND BENEFITS OF CONTROLLING CHLOROFLUOROCARBONS
DAVID DULL1, STEPHEN SEIDELl, and JOHN WELLS2 loffice of Air and Radiation, U.S. Environmental Protection Agency, ANR-445, 401 M Street, SW, Washington, D.C. 20460 (U.S.A.1 2The Bruce Company, Suite 410, 3701 Massachusetts Avenue, NW, Washington, D.C. 20016 (U.S.A.) ABSTRACT The Montreal Protocol on Substances that Deplete the Ozone Laver requires a 5 0 percent reduction in consumption of fullyhalogenated chlorofluorocarbons (CFCs) within ten years and a freeze on consumption of halons. In December 1987, the U.S. Environmental Protection Agency (EPA) proposed to implement the Protocol requirements by allocating production and consumption quotas to CFC producers and importers based on their 1986 market shares. The quotas would be reduced over time according to the staged reduction schedule in the Protocol. As the supply of CFCs is directly reduced by regulation, rising CFC prices would serve as the mechanism which would allocate CFCs to the highest valueadded end-uses. EPA has completed simulations of the costs of control of the Montreal Protocol in the United States1. In addition, it has estimated the benefits resulting from stratospheric ozone protection. EPA's benefit-cost comparison shows that the benefits of stratospheric protection are far greater than control costs. METHODOLOGY -- ESTIMATING CONTROL COSTS while economic theory would hold that such a market system would achieve the Protocol reductions at the least possible cost, significant economic effects would still be felt in terms of higher prices of final products that use CFCs (social costs), and transfer payments from CFC users to CFC producers. EPA recently estimated these costs in the Regulatory Impact Analysis which accompanied its regulatory proposal. EPA used a bottom-up approach in analyzing the costs of meeting the proposed regulation. Studies were initiated in eight major CFC and halon use categories -- flexible foam, rigid polyurethane foam, rigid non-urethane foam, refrigeration and air conditioning, aerosols, solvents, fire extinguishing, and miscellaneous uses. These groupings were then further divided
892
into 82 specific applications. For example, refrigeration was divided into 18 categories including retail food, home refrigerators, refrigerated transport, etc. Finally, cost and emission reduction estimates were developed for over 6 5 0 distinct control options covering the full range of use applications. The control options included engineering controls (such as improved design to reduce leakage), chemical substitutes (such as aqueous cleaning and HCFC-l34a), product substitutes (such as fiberglass), recovery and recycling, and work practices (such as use of alternative leak testing agents). Cost estimates were developed and included capital and operating expenses (including,where applicable, any energy penalty). Technologies were assessed in terms of the date at which they would become available (0-3 years, 4-7 years, or longer), and the rate and limits for achieving market penetration. Documentation of the control options was reviewed by industry sources and published in December 1987. The cost estimates for these Dptions were used as inputs into EPA’s Integrated Assessment Model (IAM) which provided estimates of the total cost of meeting a regulatory goal. The model operates by prioritizing the potential reductions on the basis of least cost and the judgment of EPA’s contractors based on discussion with industry representatives concerning the likely response of specific industry sectors to CFC limits. The model estimates the resulting CFC and halon price increases, and the costs associated with these price increases. Two types of costs are computed: social costs and transfer costs. Social costs represent the real resource costs involved in meeting regulatory requirements. Transfer costs represent the transfer of income from consumers of CFC-using products to other segments of society. In computing transfer costs, decreases in income to one sector of the economy are usually offset by increases in income to a competing sector. For example, a shift in electronic cleaning from CFC-113 to terpene-based solvents results in decreases in income to CFC-113 manufacturers, but this loss is offset by an increase in income to manufacturers of terpene-based solvents. IMPACT ANALYSIS COST ESTIMATES FROM EPA’S -0RY The aggregate demand for CFCs in the absence of regulatory controls is one important determinant of CFC prices. Based on
893
econometric and market-based studies of CFC demand completed for a series of UNEP workshops, EPA projected that in the absence of regulatory controls, demand for CFCs -11, -12, -114, and -115 would rise at approximately 2.5 percent per year until 2050 and remain constant thereafter. Demand for CFC-113 is projected to rise at 3.75 percent per year from 1986 to 2 0 0 0 ; 2.5 percent from 2000 to 2050; and remain constant thereafter. As our companion paper for this symposium discusses, the rate at which available controls are adopted plays a large role in determining total control costs. Early adoption of controls reduces aggregate demand for CFCs and thus moderates the CFC price rises that are induced by the reduced supply as quotas are tightened. Figure 1 shows the projected price rises for two sets of assumptions about the rate at which firms shift to alternatives. Figures 2 and 3 show the accompanying Social costs and transfer costs.
as :::: 0
14.0
W 0
a8
12.0
P
9 9 Y c
10.0
t
P f" E
O-O 4.0 2.0 0.0
$/
Fig. 1. Diagram showing the projected CFC price increases for Montreal Protocol implementation in the United States'.
894
1989 THROUQH2075
c
0
30
Leaat Coat
Moderate
Moderate/ Major Major Stretchout Ca8.8
Fig. 2. Diagram showing the estimated social costs for Montreal Protocol implementation in the United States1.
10 I
1988THROUQH207S
I
9
1 0
Leaat Coat
Moderate I
Moderate/ Major Malor I Stretchout Caaer
Fig. 3. Diagram showing estimated transfers to producers for Montreal Protocol implementation in the United Statesl.
895
The "least costg1scenario assumes that all reductions are taken as soon as they are technologically available and as soon as the cost of the CFCs or halons exceeds the costs of making the reduction. In the "least cost8tscenario, CFC price rises are minimal in early years, rise to $3.77 per kilogram around the turn of the century, and plateau around $5.48 per kilogram Well before 2075 when chemical substitutes have penetrated major markets. The low initial cost increases reflect the large quantity of CFC and halon reductions that are available with current technologies and which either will save firms money (e.g. through CFC recovery and reuse) or which are competitive. In the latter years of the analysis, the $5.48 price ceiling represents the anticipated costs of substitute chemicals (primarily HCFC-134a replacing CFC-12 and HCFC-123 replacing CFC-11 in foam applications). In the "least costll scenario, social costs were calculated to be $689 million through 2000 and $27 billion through 2075. Transfer costs were calculated to be $2.0 billion through 2000 and $6.2 billion through 2075 (social costs are discounted at 2 percent per year and transfer costs at 6 percent per year). While the "least costttsimulation assumes no resistance to technological change, the Ilmoderate stretch out^^ simulation contains a number of assumptions that slow the rate or extent to which available technologies would be adopted. The assumptions primarily involve slower penetration rates for new products and production processes into the marketplace. In addition, manufacturers of products for which CFCs comprise only a minor share of the final product price (e.g. mobile air conditioning) are assumed not to adapt to increases in CFC prices. Finally, switches to alternative chemicals are assumed to be much slower. The other simulations -- "moderate to major stretchout" and "major stretchoutll -- assume additional delays in introduction of CFC alternatives. The social costs for the stretchout scenarios ranges from $1.1 billion to $1.8 billion by 2000 and $7.15 billion to $9.4 billion by the year 2075. Transfer costs range from $2.5 billion to $5.7 billion by 2000 and $7.1 billion to $9.4 billion by 2075. Thus, the rate at which firms implement low cost reductions is an important determinant, particularly in the near-term, of the
896
costs and transfer payments involved in meeting the proposed regulation. METHODOLOGY -- ESTIMATING BENEFITS FROM REDUCTIONS In addition to estimating the costs of control, EPA’s latorv ImDact (RIA) contains a description of the potential benefits that would result from actions to limit the risks from ozone depletion. The response of stratospheric ozone to increases in CFC and halon emissions was estimated based on a parameterized version of a one-dimensional atmospheric model developed by the Lawrence Livermore National Laboratory (LLNL). A United Nations Environment Workshop (UNEP) workshop on atmospheric modelling in Wurzburg, Federal Republic of Germany, found that the LLNL parameterization produces results that are within the range of estimates of the more complex models, although slightly on the low side (1.e. underestimating ozone depletion) in some cases2. The projected ozone depletion for the ItNo Controlsttcase and a simulation of the Montreal PrOtoCO1 controls is shown in Figure 4 . Note that the Montreal protocol results in significantly less depletion. To compute the health and environmental benefits of this reduced depletion, EPA relied on the scientific analysis that was completed earlier for its comprehensive risk assessment3. This assessment was peer-reviewed and approved by EPA’s independent Science Advisory Board, and summarizes the scientific basis for EPA’s decisionmaking. Benefits are computed only in those areas in which sufficient research has been completed to provide a basis for a quantitative dose-response relationship. The strongest dose-response relationships have been developed for basal, squamous, and melanoma skin cancer; and for cataracts. Sufficient case studies have been completed to allow development of extrapolated doseresponse relationships for effects on plants, aquatics, outdoor materials, ground-level oxidants, and sea level rise. In several areas, however, quantification of benefits for the RIA was not possible. These areas include suppression of the human immune system and climate-related impacts on water resources, agriculture and forests.
897
Fig. 4 . Projected ozone depletion for No Controls and tne 2.7 Montreal Protocoll. Assumes baseline growth in CFCS of percent per year; and that 94% of developed and 6 5 % of developing nations join the Protocol. To express benefits in common terms with control costs, benefits were monetized and discounted at the rate of 1 percent per year. BENEFIT ESTIMATES FROM EPA’SM IP -A C T A N A L S Y IS Estimates of the economic benefits in the United States which would result from implementation of the Montreal Protocol are shown in Table 1. These benefits reflect the difference between the base case of no controls and the simulated implementation of the Montreal Protoco1. It should be noted that projecting benefits out to the year 2075 is a speculative exercise, but is required because of the long atmospheric lifetimes of CFCs and halons. The estimates are subject to substantial uncertainties both in the calculation of the dose-response effects and in the economic values placed on such effects. Due to this uncertainty, the benefits are expressed in ranges. The total benefits through the year 2075 are estimated to be between $29 billion and $340 trillion Based on this analysis, it would appear that the estimated benefits of the mntrea 1 protocol would far exceed the control costs under any reasonable Set of assumptions.
898
Effects Skin Cancer Cases Skin cancer Deaths Cataract Cases
154.43 million cases 3.14 million deaths 17.60 million cases avoided Monetarv Effects (S)
Skin Cancer Cases Skin Cancer Deaths cataract cases crop Damage from W - B Loss of Fish harvests Crop Damage from Smog Polymer Damage Sea Level Rise Damage to Major Ports Total Monetary Benefits
61.3 6.4 2.6 23.4 5.5 12.4 3.1 4.3
billion trillion billion billion billion billion billion billion
6.3 trillion
Assumptions: Shows value of avoided damage relative to "NO Controlsn for populations alive today and born before 2075. Valuation assumes a 2 percent discount rate. The value of life is assumed to be $3 million and is increased at 1.7 percent per year. Dose-response e timates are based on models summarized in EPA's risk assessment
1.
Table 1. Estimated economic benefits of the Montreal Protocol in the United States1
899 REFERENCES 1
U.S. Environmental Protection Agency (EPA), -to rv ImDact vsis: Protection of Stratomheric O z a , U . S . EPA, Washington, D.C., 1987.
2
United Nations Environment Programme, Bd Hoc s c i e n t m ina to ComDare M o d e l G e n e r a t e d o o f Ozone Laver ae for Various Stratecries for CFC Control, UNEP/WG.167/INE'.lf Wurzburg, Federal Republic of Germany, 910 April, 1987.
3
U.S. EPA, Assessins the m k s- of m T m e S t r a t o s m , EPA400/1-87/001, U.S, EPA, Washington, D.C., 1987.
. .
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T.Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
COST-EFFECTIVENESS OF SPECIFIC CONTROL OPTIONS FOR VOC EMISSIONS OIL INDUSTRY ASSESSMENT
301
-A
EUROPEAN
R. J.Ellis CONCAWE, Babylon-Kantoren A, Koningin Julianaplein 30-9, 2595 AA The Hague (The Netherlands)
ABSTRACT The paper VOC emissions that could be VOC emissions
introduces the subject by briefly reviewing the significance of as an ozone precursor and suggesting general control policies followed. An overall European inventory of man-made and natural is included In order to put the subject into perspective.
Some possible control measures are identified for VOC emissions originating from motor gasoline during its manufacture, distribution, dispensing and use. The capital and operating costs and cost-effectiveness of a number of these measures are discussed including, reduction of storage tank losses, vapour recovery systems for primary distribution modes, on-board car systems for evaporative refuelling emissions, Stage I1 controls for refuelling emissions and fuel volatility controls. The results show significant differences in cost-effectiveness of some of the options. A form of presentation of the results is used which allows authorities a clear choice of options for control measures.
INTRODUCTION It is generally accepted that tropospheric ozone is created from chemical reactions involving largely nitrogen oxides (NO ) and volatile organic X
compounds (VOC). Ozone soformed, supplements that which has been transported down from the stratosphere. Ozone formation is a photo-chemical reaction and therefore it can only occur in daytime. Actual measurements of tropospheric ozone concentrations in Europe show that episodes of high concentrations occur frequently normally in the hotest summer months. Such peak concentrations can contribute to damage to forests, vegetation, material and human health, and impair visibility. There is still a lack of adequate scientific understanding of the relationship between emissions and their ultimate contribution to observed damages whether they be via acidification or ozone attack. No rigorous criteria exist on which to base emission, air quality or pollutant deposition standards. For this reason the proposals to reduce NO
X
and VOC emissions are of
an arbitrary nature, and can be seen as necessary insurance against irretrievable damage if action were delayed indefinitely to await a complete scientific understanding.
902 Against this background CONCAWE strongly supports the view that:
-
control policies are required but should be balanced with respect to the state of evidence available relating cause with effect effective control regulations should begin with the largest significant sources
-
adoption of specific control measures should be preceded by adequate evaluation of the various technologies available to identify the most cost-effective ones.
Accordingly with respect to VOC emissions CONCAWE has gathered together inventory, control technology and cost information to assist in assigning priorities in the development of any regulatory activities felt to be necessary. VOC EMISSIONS INVENTORY CONCAWE's best estimates of anthropogenic and natural source VOC emissions to the atmosphere in Western Europe 1986 are s h a m in Appendix 1. The data have been compiled from a combination of emission factors
-
calculated from well established formulae and from actual measurements e.g. in the case of evaporative emissions from vehicles. The VOC data reported exclude methane basically because of the lack of reliable data and because initially it was felt that the low reactivity of methane would not have a significant effect on ozone production. This view is now undergoing some change since the large amount of methane in the atmosphere still has a significant effect on background ozone formation. Looking to the data some clear conclusions can be drawn:
- VOC emissions from mobile sources represent about 41% of total anthropogenic VOC emissions which include 37% from gasoline vehicles.
- VOC emissions from solvents represent another 40%. - The
oil industry contribution is only 6.5% of which 1.7% is from
refineries and 3.1% from gasoline distribution.
- Emissions
from natural sources such as forests leaf litter and
pastures are estimated to be of the same magnitude as those from man-made sources. There is some considerable uncertainty about the size of natural emissions, a number of other studies quoting eignificantly lover totals. A recent study of the US situation (1) has produced a figure for natural emission in the USA somewhat higher than man-made emissions there. An important aspect is that the rate of natural emissions ie temperature dependant
60
that the maximum emiesion occurs in the summer. Recent modelling
studies (OECD sponsored) have highlighted the importance of natural emissions.
903 The mobile source sector being one of the largest VOC emitters, is analysed in more detail. Gasoline vehicles contribute three categories viz.
- Exhaust
- Evaporative
- Refuelling
2.5 million tlyr 1.0 million t/yr 0.18 million t/yr
GASOLINE ENGINED VEHICLE EXHAUST EMISSIONS Without controls, exhaust is the largest source of vehicle VOCs. Since 1970 exhaust emission limits for gasoline engined cars hsve been steadily tightened in Europe (2). The so-called ECE 05 regulations (Luxembourg Accord) can be met by a combination of engine modification,
agreed on 21.7.87
oxidation catalysts or three-way catalysts depending upon the car model. A further tightening of controls for csrs with engine capacity below 1.4 litres is under discussion. Even more severe exhaust controls could be envisaged 1.e. to meet the standards now current in the USA, Japan and Australia involving all cars equipped with advanced catalyst systems. CAR EVAPORATIVE EMISSIONS These VOC emissions originate from: 0
vehicle fuel systems (as a result of fuel evaporation through vents open to the atmosphere). They occur:
- during a
period when the vehicle is stationary with the engine hot
(hot-soak losses)
- when - when
being driven (running losses) standing and subjected to temperature changes (diurnal losses)
displacement of vapours during car refuelling Evaporative emissions can be controlled by three routes:
-
the use of small carbon canister system installed in the vehicle. These have already been fitted to vehicles throughout the USA for some time and are beginning to find their way on to cars in Europe. By enlarging these canisters the refuelling losses could be captured as well.
- Reduction
of gasoline volatility which affects both vehicle fuel
system and refuelling emissions.
- Vapour recovery during vehicle refuelling which involves the transfer of vapours displaced from the vehicle tank to the service station tank during refuelling by use of specially designed filling nozzles, hoses and lines (so-called Stage 2 controls). In order to evaluate the effect of some of these measures CONCAWE has carried out a number of studies including come experimental work.
904 The conclusions were:
- vehicle and fuel system design has the greatest influence on evaporative emissions from vehicles. Fuel volatility has a significant but smaller effect
- under
standard test conditions (26-3OoC) small carbon canisters reduce
evaporative emissions by some 90%
- enlarged carbon -
canisters would enable refuelling losses to be reduced
by more than 95% a reduction in vapour pressure (RW) of 10 kPa under the standard test conditions would only reduce emissions by some 23%. However, under typical ambient temperatures in the market, which are for a large part of the year below 26-30°C, a 10 kPa vapour pressure reduction would give a lower emission reduction and would lead to unacceptable low volatility if applied to the lower R W summer gasolines. A smaller reduction in RVP to the 60 kPa level in summer would only reduce emissions by 10%. Furthermore RVP controls would have little or no effect when VOC emissions control equipment such as carbon canisters are in place.
COST-EFFECTIVENESS ASPECTS CONCAWE has carried out a number of studies (3) to evaluate the costeffectiveness of a number of control measures applicable to VOC emissions. Most of the control options require capital investment for new equipment and some maintenance and operating costs are incurred. In line with common industrial practice the capital costs are converted into an annual capital charge which reflects the required return on capital, lifetime of equipment (technical and economical), taxation required and inflation
-
if any. A
capital charge of 25% is normally applied by CONCAWE for oil industry
-
investment. A more detailed account of these costing aspects is given in (4). The costs shown below are in 1986 USD i.e.
1 USD
-
2.5 NLG
-
2.2 DM
0.65 GBP
In principle the following controls could be applied to vehicle evaporative emissions. (a) enlarged carbon canister (b) RVP plus Stage 2 (c) small carbon canister plus Stage 2 Re. (a), there is a large range of costs being quoted for the enlarged carbon canister, ranging from USD 20 by EPA to USD 80 and even higher from US car industry. On the basis of a range of USD 20-80 per canister and a conservative estimate of 90% vapour retention the cost-effectiveness can be calculated at USD 335-1340/ton VOC recwered. The potential European recovery
905 is 1.1 million t/yr when the complete European car population is fitted out with the enlarged canister. Re. (b), reduction of gasoline RVP means removal of butaae which is a high octane component and replacing it by lower RVP components of the same octane number. This will mean a downgrading in value of butane, finding a new outlet for it and the installation or modification of gasoline upgrading capacity such as catalytic reforming. For a 10 W a RVP reduction to European summer gasoline to give an emission reduction of lo%, some 0.1 million t/pr, a cost-effectiveness of USD 2100/t VOC is calculated. Stage 2 vapour recovery of refuelling emissions at service stations means the installation of special delivery hoses and new dispensing nozzles. Based on US experience and an average of 6 nozzles for European service stations with a throughput of 1200 ms/yr, a cost-effectiveness of USD 5000/t VOC is calculated. This assumes a capital cost of USD 17 000 per service station and 902 recovery of refuelling emissions i.e. 0.16 million t/yr if all 150 000 European service stations would be equipped with Stage 2 equipment. This recovery rate is significantly more optimistic than the 56-86% efficiency quoted by EPA depending upon the levels of maintenance and enforcement. Clearly alternative (b) is much less attractive both from potential VOC recovery and cost points of view, also illustrated in Appendix 2. Re. (c). CONCAWE has considered this option at an early stage but has discarded it because of the high incremental costs of Stage 2 (USD 5000/t VOC) compared with the cost of enlarging the canister. EPA has estimated this cost to be USD 1460/t VOC (ex-refuelling) compared with USD 770/t VOC (ex-evaporation/refuelling) which is in the middle of the CONCAWE range. As mentioned already EPA considers Stage 2 to have a lower efficiency to recover VOCs than canisters. TRENDS ON EXHAUST AND EVAPORATIVE EMISSIONS FROM GASOLINE ENGINED CARS CONCAWE has developed a computer model which can prwide data on the potential of various VOC control strategies to reduce emissions over a time period when there is a growing European car population. The results of the application of such a model are shown in Appendix 3. Comparison of Case 1 (do nothing) and Case 2 highlights the benefits that have followed from the progressive implementation of ECE standards up to and including ECE 04. However, despite this progress, growth in car population beyond the mid 80s exceeds the ability of the ECE 04 regulations to restrict growth in VOC emissions.
306
The Implementation of ECE 05 regulations (Case 3) will prevent growth in VOC emissions but the effect of car population growth especially in the muall car sector limits the long term benefits. The addition of controls to reduce vehicle evaporative and refuelling emissions show that enlarged carbon Canisters (Case 5) give a significant further improvement overall. RVP plus Stage 2 (Case 4) is clearly less efficient for recovery of these emissions. Finally, the best result ie achieved by a combination of applying US standards to exhaust emissions and enlarged carbon canisters to vehicle evaporative and refuelling emissions (Case 6). REFINERY AND DISTRIBUTION EMISSIONS Refinery emissions from crude oil receipt, refining and product dispatch are discussed in (5). In the case of crude oil receipt, the changeover to segregated ballast with tanker fleet renewal over time (prescribed in the MARPOL 74/78 Convention) will have the complementary effect of virtually eleminating hydrocarbon emissions at crude oil discharge locations by the equivalent of 1.5% of the total 10 million t/yr from man-made sources. Refinery emissions, based on the study of a hypothetical refinery, represent 1.7% ot total emissions. Principal sources considered were:
- process plant fugitive emissions; - waste water treatment fugitive emissions; - crude oil and relevant component and product
tankage.
Available controls include formal programmes of monitoring and maintenance for process plant fugitives, floating covers for waste water separator bays, and the installation of rim-mounted secondary seals in selected floating roof tanks. These controls could reduce the total emissions of 0.17 million tlyr by 0.07. 0.02 and 0.02 million t/yr respectively at cost of 100, 500 and up to 3000 USD/t. Emissions in the distribution sector occur when discharges are made from tanks of road and rail cars, barges and ships, and also when tank filling occurs at depots and service stations. Control measures that can be taken depending upon the particular situation include vapour balanclng/collecting and avoidance of splash loading e.g. by bottom loading. A further step could be the installation of vapour recovery units at distribution depots. Discharge of gasoline into underground tanks at service stations gives rise to vapour loss. This can be contained by some 90% if the displaced vapours are returned to the bulk road tanker by an additional hose connection. These facilities are normally referred to in the USA as "Stage 1" vapour recwery at service stations. Retention of the VOCs is only effected if the
907
road tanker loading terminal has a vapour recovery system and therefore in Europe, Stage 1 is taken to include these facilities. The cost-effectiveness of Stage 1 controls has been estimated as USD llOO/t VOC for a recovery of 0.2 million t/yr. CONCLUSIONS The state of knowledge concerning the role of VOC emirsions as ozone precursors is sufficient to require that VOC control measures should be introduced. There is still debate concerning an acceptable level particularly when taking account of natural VOC emissions. The largest sources of man-made VOC emissions are from the gasoline vehicle sector and from solvents. Within the gasoline vehicle sector exhaust VOC emissions are the largest contributor. European legislation already in place will prevent a further increase in these VOC emissions from increasing vehicle population. A further drastic decrease could be obtained by applying US and Japanese type legislation, resulting in the extension of advanced catalyst systems to all cars in Europe. Such measures of course also reduce very significantly NOx and CO emissions. Vehicle evaporative and refuelling emissions, the next largest source, can most efficiently and at lowest cost be reduced by enlarging the carbon canisters which are already a well-proven trouble-free and cheap control for evaporative VOCs on vehicles. Other alternatives involving gasoline volatility controls and so-called Stage 2 controls have either a low recovery efficiency and/or a poor cost-effectiveness. Experience with Stage 2 controls in the USA has shown that enforcement of maintenance and upkeep of the equipment is essential if the claimed 90% VOC recovery rate is to be maintained, a formidable task in an European context of 150 000 service stations. VOC emissions from the refinery and gasoline distribution sectors represent only some 5% of man-made emissions. These emissions can be reduced by half by a combination of additional refinery maintenance and inspection measures and Stage 1 vapour recovery with a cost-effectiveness comparable to that of enlarged carbon canisters for reducing evaporative emissions.
903 REFERENCES
1.
A national inventory of biogenic hydrocarbon emissions. Lamb, Guenther, Gay and Westberg. Atmospheric Environment Vol 21, No. 8 pp. 1695-1705, 1987 (GB)
2.
CONCAWE Report No. 87/53 Trends in motor vehicle emission and fuel 1987 update. CONCAWE, The Hague. 1987 consumption regulations
3.
CONCAWE Report No. 6/87 Volatile organic compound emissions in Western Europe. Control options and their cost-effectiveness for gasoline vehicles, distribution and refining. CONCAWE, The Hague, 1987
4.
CONCAWE Report No. 88/51 Capital and operating cost estimating aspects of environmental control technology residue hydrodesulphurization as a case example. CONCAWE, The Hague, 1988
5.
CONCAWE Report No, 87/52 Cost-effectiveness of hydrocarbon emission controls in refineries from crude oil receipt to product dispatch. CONCAWE, The Hague, 1987
-
-
Appendix 1 Emissions of volatile organic compounds in Western Europe (OECD) (tonnes x lo3)
(X)
1010 180 2500
10.1 1.8 25.0
Mobile sources Gasoline vehicles
- Evaporative - Refuelling
emissions
- Exhaust
Sub total
Diesel vehicles Aircraft Railways Coastal and inland shipping
3690 300 40 40
3.0 0.4 0.4 0.1
10
Sub total
36.9
4080
40.8
Oil industry Production Marine transport and crude terminals Refineries Gasoline distribution
20 150 170 310
Sub total Solvents Manufacturing industry Natural gas (non-methane) Solid waste disposal Stationary combustion Total Anthropogenic Natural (Trees, etc.) Grand Total Note: -
All values exclude methane
0.2 1.5 1.7 3.1 650
6.5
4020 410 650 110
40.2 4.1 6.5 1.1
90
0.9
10 010 10 000 20 010
100
-F-
EVAPORATIVE LOSS CONTROL COST-tw tCTlVENESS AND RECOVERY POTENTIAL,
-1-
STAGY 2 ALONE
4600
s / t
R E C 0 V E R E
IARQE CARBON
D
1.1Mt
0.-
0.1Mt
0.1-
0.2Mt w
0 10
W.EUROPE HYDROCARBON EMISSIONS FROM MOGAS VEHICLES 7500 NO EEC CONTROLS
7Ooo
6100 (ooo
T SIQO 0 T5ooo A
4100 ECE UPTO 01
E M
a
I
f
3100 Kt 0s
I 0 N
s
ECEOS + RVP +SllAGE 2
2100 ECE 05 + URGE CANISTERS
loo0 CANISTERS
100
0 1970
1990
2010
T. Schneider et aL (Editors),Atmospheric Ozone Research and its Policy Implications 0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
911
OPTIONS FOR VOC-REDUCTION I N THE MECHANICAL AND ELECTRICAL ENGINEERING INDUSTRY
J . Nobel Association o f the Mechanica Zoetermeer (The Netherlands]
and Electrotechnical Industries FME,
INTRODUCTION In this paper I will go into the situation regarding the control1 and reduction of the emissions of hydrocarbons in the mechanical and electrical engineering industries in the Netherlands. In the first place I will give attention to the origin and extent of the hydrocarbon emissions. Thereafter I will consider the technical process and corporate economical consequences of steps to reduce these emissions. These reduction measures can be split up between methods of prevention at the source (by means of the use of alternative raw materials) and alternately the use of control1 and purification techniques. Both of these methods of controll and prevention have advantages and disadvantages. It will become clear, that the choice between these methods is dictated by the extent to which the reduction or prevention has to be realised within the shorter or longer term. THE ASSOCIATION FIE The Association of the Uechanical and Electrotechnical Industries FIE is an independant, private law organisation of industrial enterprises. The FUE cares for the collective and individual social, economic and technical interests of her members. The membership of FUE consists of some 1 . 1 8 0 industrial enterprises that achieved a collective turnover in 1987 of some 60 billion guilders. The products manufactured by the members of the associatioh know a great diversity (for example aeroplanes, bicycles, electronical apparatous, ships, steel mills, trucks, etc.). A number of the members are engaged in the field of environmental equipment. number of employees
0.2 ppm) f o r much s h o r t e r durations (i.e.,
A d d i t i o n a l s t u d i e s r e p o r t e d a t t h i s Symposium have
62 h r ) .
confirmed t h e above f i n d i n g s a t 0.8 and 0.10 ppm, as w e l l as a t 0.12 ppm ozone, w i t h t h e 0.8 and 0.10 ppm exposures producing smaller changes t h a t a l s o p r o g r e s s i v e l y increased w i t h each succeeding hour o f exposure.
Thus, t h e t r a n s i e n t r e s p i r a t o r y
f u n c t i o n decrements seen w i t h ozone exposure worsen as a f u n c t i o n o f i n c r e a s i n g time o f exposure and can be observed a t lower concentrations (0.8,
0 . 1 ppm)
than the present EPA 1-hr 0.12 ppm ozone standard w i t h more prolonged exposure d u r a t i o n s (6 t o 8 h r ) .
These new f i n d i n g s are very i m p o r t a n t f o r c u r r e n t
evaluations o f ambient ozone standards o r g u i d e l i n e s , as a r e new f i n d i n g s from animal t o x i c o l o g i c a l s t u d i e s t h a t demonstrate a v a r i e t y o f e f f e c t s o f ozone on l u n g defense mechanisms and morphological s t r u c t u r e . Accumulating evidence from animal s t u d i e s reviewed d u r i n g t h i s Symposium p o i n t s toward m u l t i p l e d e l e t e r i o u s e f f e c t s being associated w i t h c h r o n i c ozone exposure.
The c o n s t e l l a t i o n o f e f f e c t s includes, f o r example:
changes i n
r e s p i r a t o r y f u n c t i o n ; airway inflammatory responses; a l t e r e d p a r t i c l e clearance; p e r s i s t i n g changes i n l u n g s t r u c t u r e p o s s i b l y associated w i t h l u n g f i b r o s i s and emphysema; slowed lung development; and reduced a b i l i t y t o fend o f f r e s p i r a t o r y infections.
Much s t i l l remains t o be e l u c i d a t e d w i t h r e g a r d t o many o f these
types o f e f f e c t s ; t h i s i n c l u d e s t h e C x T dose-response r e l a t i o n s h i p s t h a t may apply and r e l a t i v e e f f e c t i v e n e s s o f v a r i o u s ozone exposure p a t t e r n s i n producing various types o f e f f e c t s .
For some e f f e c t s , repeated h i g h e r l e v e l peak exposures,
956
analogous t o ambient episode c o n d i t i o n s , may be more d e l e t e r i o u s t h a n c h r o n i c continuous exposures. e.g.,
Also o f importance i s t h e f a c t t h a t some o f t h e changes,
e p i t h e l i a l damage and inflammatory responses, seem t o be cumulative and
are p e r s i s t e n t even i n animals t h a t have a t t e n u a t e d r e s p i r a t o r y responses. Also o f growing concern a r e new d a t a r e p o r t e d here based on ambient a i r m o n i t o r i n g and new human exposure models m i l l i o n s , o f members o f t h e U.S.
-
data which i n d i c a t e t h a t many, even
and Dutch p o p u l a t i o n a r e exposed t o ozone
concentrations found t o be associated w i t h i d e n t i f i a b l e h e a l t h e f f e c t s .
A l l of
t h i s accumulating new evidence p r o v i d e s a s t r o n g impetus toward c o n s i d e r a t i o n o f p o s s i b l e longer-term ozone standards, perhaps averaged over 8 hours, i n o r d e r t o p r o v i d e f u r t h e r p r o t e c t i o n f o r human h e a l t h beyond t h e c u r r e n t U.S. 1-hour ozone NAAQS.
The need f o r a longer averaging time standard and t h e
a p p r o p r i a t e l e v e l s , I am sure, w i l l be c a r e f u l l y considered i n b o t h t h e U.S. and t h e Netherlands i n t h e coming months o r years.
I n each case, t h e u l t i m a t e
determination o f what c o n s t i t u t e s s u f f i c i e n t a l t e r a t i o n s i n normal f u n c t i o n t o c o n s t i t u t e adverse h e a l t h e f f e c t s w i l l be a key i s s u e t o be d e a l t w i t h . We have a l s o learned much here about s u r f a c e l e v e l ozone e f f e c t s on a g r i c u l t u r a l crops, f o r e s t s , and n a t u r a l ecosystems.
When developing an ozone
c o n t r o l p o l i c y t o p r o t e c t a g a i n s t v e g e t a t i o n e f f e c t s , t h e long-term average ozone c o n c e n t r a t i o n appears t o be i m p o r t a n t , as w e l l as s h o r t - t e r m peak l e v e l s d u r i n g consecutive episode days.
P a r t i c u l a r l y d u r i n g t h e growing season,
r e l a t i v e l y low l e v e l s o f ozone appear t o cause a g r i c u l t u r a l crop l o s s by growth i n h i b i t i o n and increased s u s c e p t i b i l i t y o f v e g e t a t i o n t o a b i o t i d b i o t i c s t r e s s . I n a d d i t i o n , c h a r a c t e r i s t i c i n d i c a t o r s o f f o r e s t d e c l i n e observed i n Europe and North-America have been a l s o associated w i t h ozone exposure.
I t becomes
i n c r e a s i n g l y c l e a r e r t h a t economic losses due t o reduced c r o p p r o d u c t i v i t y and f o r e s t damage are q u i t e l a r g e and a r e o f growing importance i n determining a p p r o p r i a t e l e v e l s f o r ozone standards i n o r d e r t o minimize r e g i o n a l ozone impact.
For many developing c o u n t r i e s these types o f e f f e c t s may be o f even
g r e a t e r importance, where extensive d e f o r e s t a t i o n and inadequate a g r i c u l t u r a l p r o d u c t i o n due t o o t h e r f a c t o r s are already serious problems.
I t i s noteworthy
t h a t long-term ozone l e v e l s necessary t o minimize n e g a t i v e e f f e c t s on v e g e t a t i o n approach background t r o p o s p h e r i c c o n c e n t r a t i o n s o f t e n p r e s e n t over c o n t i n e n t s i n t h e Northern Hemisphere. We have a l s o heard extensive d i s c u s s i o n here w i t h regard t o e x t e n s i v e c o m p l e x i t i e s and d i f f i c u l t i e s i n developing e f f e c t i v e ozone c o n t r o l p o l i c i e s and s t r a t e g i e s .
L a t e s t modeling r e s u l t s and r e a l - w o r l d experience, as r e p o r t e d
957
here, show that no simple solutions are at hand. Several factors complicate the situation. The formation of ozone (03) and other photochemical oxidants of importance in producing so-called urban smog effects involve photochemical (UV light-enhanced) reactions between hydrocarbons or volatile organic compounds (VOC) and inorganic (nitrogen oxides; NOx) air pollutants. The VOC and NO, emissions are associated with both stationary sources (e.g., electrical power generation plants and petrochemical facilities) and mobile sources (automobiles, trucks, and other transportation devices), especially those involving fossil fuel combustion or utilization of oil components in production of commercial products. Also of very major importance are numerous small, widely dispersed sources of hydrocarbon emissions that are associated with many different everyday human activities. Besides the multiplicity and diversity of emission sources, the relevant atmospheric processes are also extremely complex. Several notable developments with regard to our understanding of photochemical oxidant/ozone air pollution phenomena and their effects were highlighted: (1) Organic emissions differ widely in ozone-forming potential, a finding that has led to the concept of discriminate VOC control for ozone reduction; (2) Ozone and related air pollution problems are regional-scale (not just urban-scale) phenomena resulting from multi-day pollutant transport and precursor transformation enroute; and (3) the mechanisms of atmospheric chemical processes that produce ozone have been elucidated in great detail, with hundreds of elementary chemical reaction steps being necessary to describe the mechanisms as now understood. Overall, VOC controls are likely needed as one common measure for reducing ozone formation but NOx reduction may only be applicable in certain situations depending upon VOC/NOx ratios and other factors in given locations. These facts all point toward the need for much flexibility and care in developing control strategies appropriate for particular situations in various countries. The one clear generally mandatory element o f such strategies appears to be the use of catalytic converters on motor vehicles. These have been used, of course, f w many years in the United States, and the Netherlands is now well on the way toward implementing catalytic converter use as a major step toward reducing mobile source contributions to ozone formation. It is important that other nations in the European community do this and countries in other areas, as well - if control of surface level ozone as a regional air pollution problem that does not respect national boundaries is to be accomplished. Even with such technology-based control efforts, large increases in numbers o f motor vehicles
958
may o f f s e t gains from c a t a l y t i c converters, so t h a t reduced c a r use may be needed. As f o r VOC-emissions from s t a t i o n a r y sources, t h e l a r g e v a r i e t y o f sources and substances i n v o l v e d hampers t h e development o f c o n t r o l p o l i c y .
Advances
were noted here i n NOx c o n t r o l technology f o r l a r g e combustion i n s t a l l a t i o n s , e.g.
low NOx burners, two stage combustion processes, and f l u e gas treatment.
There i s an i n c r e a s i n g understanding o f t h e chemistry i n v o l v e d i n NOx f o r m a t i o n as t h e r e s u l t o f combustion processes.
New data suggest t h a t a s i g n i f i c a n t
p a r t o f NOx-emissions i n many combustion processes may c o n s i s t o f N20 (up t o
25%).
This i s o f a d d i t i o n a l environmental s i g n i f i c a n c e , because N20, w i t h i t s
l o n g atmospheric l i f e t i m e , i s i n v o l v e d i n s t r a t o s p h e r i c ozone d e s t r u c t i o n and i n t h e s o - c a l l e d 'greenhouse e f f e c t " .
A t t h i s symposium, s p e c i a l a t t e n t i o n was
a l s o focussed on emissions from t h e use o f p a i n t s , b o t h i n i n d u s t r y and i n households.
I n t h e p a i n t i n d u s t r y , a l t e r n a t i v e products have a l r e a d y been
developed i n which organic s o l v e n t s a r e e l i m i n a t e d o r reduced. The c o s t s o f these and o t h e r c o n t r o l measures, as we have heard here, w i l l be l a r g e , b u t nevertheless necessary.
Also, as noted here by speakers
and p a n e l i s t s , our a b i l i t y t o e x p l a i n t o t h e p u b l i c t h e reasons f o r needing such c o n t r o l s and, p o s s i b l y , f o r a l t e r e d l i f e s t y l e s w i l l be one key t o our accomplishing t h e i r cooperation i n d e a l i n g w i t h t h e ozone problem.
Public
communication w i l l be an i n c r e a s i n g challenge f o r a l l o f us i n t h e coming years; and c r e a t i v e new approaches must be developed and t r i e d ( f o r example, t h e use o f i n c e n t i v e programs t o encourage cooperation w i t h ozone c o n t r o l programs).
The need t o accomplish b e t t e r t r o p o s p h e r i c ozone c o n t r o l takes on
even f u r t h e r importance i n view o f s t r a t o s p h e r i c ozone d e p l e t i o n b e i n g expected t o enhance surface l e v e l ozone f o r m a t i o n as one o f many n e g a t i v e e f f e c t s . STRATOSPHERIC OZONE Turning t o s t r a t o s p h e r i c ozone, d u r i n g t h i s Symposium we have heard much i n t e r e s t i n g b u t , also, very d i s t u r b i n g i n f o r m a t i o n r e g a r d i n g t h e d e p l e t i o n o f s t r a t o s p h e r i c ozone and i t s l i k e l y f u t u r e impacts.
As noted here, t h e n a t u r a l
d i s t r i b u t i o n o f ozone i n t h e E a r t h ' s atmosphere, concentrated most h e a v i l y i n a r e l a t i v e l y t h i n l a y e r i n t h e stratosphere, i s c r u c i a l i n h e l p i n g t o p r o t e c t humans, b i o l o g i c a l organisms, and man-made m a t e r i a l s from t h e harmful e f f e c t s o f c e r t a i n wavelengths o f Sun l i g h t .
S t r a t o s p h e r i c ozone e x e r t s i t s b e n e f i c i a l
e f f e c t s by p a r t i a l l y b l o c k i n g u l t r a v i o l e t r a d i a t i o n i n t h e 295 t o 320 nm (ultraviolet-6,
UV-6) range from reaching t h e E a r t h ' s surface.
Also, t h e
v e r t i c a l d i s t r i b u t i o n o f s t r a t o s p h e r i c ozone and t h e r e l a t i v e dryness o f t h e
953
a i r i n the stratosphere help t o maintain the r a d i a t i v e balance o f t h e earth. Depletion of t h e s t r a t o s p h e r i c ozone l a y e r can, therefore, be expected t o l e a d t o damaging e f f e c t s on human h e a l t h and t h e environment: (1) d i r e c t l y by increased penetration o f UV-B r a d i a t i o n t o t h e E a r t h ' s surface and (2) i n d i r e c t l y by the influences o f changes i n t h e v e r t i c a l d i s t r i b u t i o n o f s t r a t o s p h e r i c ozone and water vapor t h a t c o n t r i b u t e t o global warming e f f e c t s and a l t e r e d c l i m a t i c conditions. Also, as we have learned here, many gases emitted due t o man's i n d u s t r i a l and a g r i c u l t u r a l a c t i v i t i e s can accumulate i n t h e atmosphere and u l t i m a t e l y c o n t r i b u t e t o a l t e r a t i o n s i n t h e v e r t i c a l d i s t r i b u t i o n and concentrations o f stratospheric ozone. Among the most important are t r a c e gases having long residence times i n t h e atmosphere, a l l o w i n g f o r t h e i r accumulation i n t h e troposphere and gradual upward m i g r a t i o n i n t o t h e stratosphere where they c o n t r i b u t e t o d e p l e t i o n o f s t r a t o s p h e r i c ozone. Trace gases o f p a r t i c u l a r concern include: (1) c e r t a i n l o n g - l i v e d chlorofluorocarbons ( o r CFC's) such as CFC-11, CFC-12 and CFC-113, t h a t have atmospheric residence times o f approximately 75 t o 110 years; (2) carbon t e t r a c h l o r i d e (CC14), w i t h a 50 year residence time; and (3) Halon-1301 and Halon-1211, w i t h 110 and 25 year residence times, respectively. Given t h e long periods o f time i n v o l v e d i n t r a n s p o r t o f these gases t o the stratosphere, t h e i r l o n g residence-times there, and slow removal processes, any e f f e c t s already seen on s t r a t o s p h e r i c ozone are l i k e l y due t o atmospheric loadings o f these t r a c e gases due t o anthropogenic emissions several decades ago; and those gases already i n t h e atmosphere w i l l continue t o e x e r t s t r a t o s p h e r i c ozone d e p l e t i o n e f f e c t s f a r i n t o t h e f u t u r e - - t h a t i s , w e l l i n t o the next century. That stratospheric ozone d e p l e t i o n i s f u r t h e r advanced than e a r l i e r p r o j e c t e d and c l e a r l y t i e d t o chlorofluorocarbon emissions became very evident as we heard speakers discuss the A n t a r c t i c ozone hole and t h e chemical/atmospheric processes underlying it. We a l s o heard information t h a t p o i n t s toward l i k e l y f u r t h e r spread o f the p o l a r ozone d e p l e t i o n and i t s expansion beyond t h e South P o l a r Region i n the coming decade; and o t h e r information p o i n t s toward t h e p o s s i b i l i t y of an analogous (though smaller) d e p l e t i o n zone developing over t h e North Polar Region. What are the types of e f f e c t s t h a t can be expected due t o s t r a t o s p h e r i c ozone depletion? The u l t i m a t e f u l l range of impacts cannot y e t be d e f i n i t e l y estimated. However, as heard a t t h i s Symposium, a t l e a s t some very major impacts on human h e a l t h and t h e environment can be reasonably p r o j e c t e d even now. Probably the best defined human h e a l t h e f f e c t s a r e increases i n s k i n
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cancer cases expected as t h e r e s u l t o f even small increases i n UV-B r a d i a t i o n reaching t h e E a r t h ' s surface. E x c e l l e n t summaries o f i n f o r m a t i o n on t h e subject have been provided as p a r t o f t h i s Symposium. O f various s k i n cancer types (non-melanoma and melanoma), t h e most d e f i n i t i v e evidence e x i s t s f o r nonmelanoma basal and squamous c e l l carcinomas o f the s k i n being l i n k e d t o UV-B r a d i a t i o n and, therefore, being l i k e l y t o increase due t o ozone l a y e r depletion. Cutaneous basal and squamous c e l l carcinomas occur most f r e q u e n t l y on sun-exposed body s i t e s of l i g h t - s k i n n e d Causasion peoples, and t h e i r incidences increase w i t h age. These and other data on geographic d i s t r i b u t i o n o f r a t e s f o r such cancers i n r e l a t i o n s h i p t o t h e e x t e n t o f l i k e l y sun exposure a l l suggest t h a t cumulative l i f e t i m e exposure t o Sun l i g h t p l a y s an e s s e n t i a l r o l e i n the i n d u c t i o n o f these s k i n cancers. Increases o f s k i n cancers d u r i n g t h e p a s t several decades i n t h e U.S. are probably p a r t l y due t o i n c r e a s i n g exposure t o both natural and a r t i f i c i a l sources o f UV-B r a d i a t i o n (e.g.
, with
more sunbathing
a t younger ages i n b a t h i n g s u i t s covering l e s s body surface and use o f u l t r a v i o l e t tanning salons, r e s p e c t i v e l y ) and g r e a t e r l o n g e v i t y a l l o w i n g f o r appearance o f such cancers a f t e r t y p i c a l long l a t e n c i e s (several decades) before t h e i r manifestation.
Given such l o n g latency associated w i t h UV r a d i a t i o n , i t i s
u n l i k e l y t h a t already observed increases i n s k i n cancer r a t e s can be a t t r i b u t e d t o any o f t h e small measurable decreases i n s t r a t o s p h e r i c ozone observed d u r i n g the p a s t decade o r so. Extensive other evidence e x i s t s , however, which permits f o r reasonable p r e d i c t i o n s t o be made o f l i k e l y increases i n basal and squamous c e l l s k i n cancer r a t e s (above higher r a t e s seen d u r i n g t h e p a s t few decades) i f s t r a t o s p h e r i c ozone d e p l e t i o n occurs a t an increasing r a t e .
As noted d u r i n g t h i s Symposium, i f s t r a t o s p h e r i c ozone i s depleted, t h e g r e a t e s t increase i n UV-B r a d i a t i o n w i l l be nearer t h e 295 nm versus the 310 upper end o f t h e a f f e c t e d wavelength range. The subject s k i n cancers are most a f f e c t e d by UV l i g h t around 300 nm, as w e l l demonstrated by experimental animal studies; and t h e percent incidence o f tumors i s a f u n c t i o n of dose (0) times exposure d u r a t i o n o r time (TI, i.e., D x T, w i t h no evidence f o r any threshold. That i s , t h e p r o b a b i l i t y o f cancer i n d u c t i o n
increases w i t h any degree o f exposure t o UV l i g h t (even low d a i l y doses can have strong effects) and t h e number o f new s k i n cancer p a t i e n t s can be p r e d i c t e d t o increase a t a greater-than-linear r a t e due t o several f a c t o r s . Such f a c t o r s include both (1) o p t i c a l a m p l i f i c a t i o n and (2) b i o a m p l i c a t i o n e f f e c t s . The o p t i c a l amplication e f f e c t s a r e p a r t l y geographically dependent, w i t h greater increases i n s k i n cancer r a t e s p r o j e c t e d i n human populations as a
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function o f t h e i r distance from t h e equator t o t h e poles due t o higher amounts of UV-B r a d i a t i o n expected t o reach the E a r t h ' s surface nearer the poles. Both o p t i c a l and b i o a m p l i f i c a t i o n f a c t o r s w i l l c o n t r i b u t e t o d i f f e r e n t i a l increases i n r a t e s f o r t h e two types o f non-melanoma s k i n cancers, although greater than proportional increases i n each are l i k e l y i n r e l a t i o n t o percentage ozone depletion. Thus, i f both a m p l i f i c a t i o n f a c t o r s are taken i n t o account, then the f o l l o w i n g q u a n t i t a t i v e consequences can be expected: (1) With a 1% decrease i n stratosphere ozone, e f f e c t i v e UV-B i r r a d i a n c e w i l l increase by 2% and, i n t u r n , lead t o increases i n t h e incidence o f basal c e l l carcinomas by 4% and o f squamous c e l l carcinomas by 6%; and (2) With a 5% decrease i n stratospheric ozone, increases can be expected i n incidences o f basal c e l l carcinoma by 22% and o f squamous c e l l carcinomas by 33%. The above p r o j e c t i o n s (combined with population s t a t i s t i c s and a d j u s t i n g f o r geographic gradients noted e a r l i e r ) l e a d t o estimates t h a t markedly increased numbers o f cases o f non-melanoma s k i n cancers w i l l eventually occur due t o s t r a t o s p h e r i c ozone depletion. The lighter-skinned White populations o f t h e w o r l d are expected t o be most affected, w i t h 70,000 new cases o f non-melanoma s k i n cancer per year (worldwide) p r o j e c t e d w i t h 1% s t r a t o s p h e r i c ozone d e p l e t i o n and 360,000 new cases annually w i t h 5% ozone depletion. I t was a l s o noted t h a t s u f f i c i e n t evidence e x i s t s f o r s u n l i g h t p l a y i n g a r o l e i n t h e much more dangerous ( o f t e n f a t a l ) melanoma forms o f s k i n cancer and t h e i r higher incidence i n persons w i t h non-melanoma tumors t o r a i s e t h e issue o f p o t e n t i a l f u t u r e increases i n melanomas due t o s t r a t o s p h e r i c ozone depletion. The key u n c e r t a i n t y i s t h e extent t o which UV-B r a d i a t i o n , versus o t h e r sun1 g h t components, may s p e c i f i c a l l y c o n t r i b u t e t o i n d u c t i o n o f cutaneous melanomas; and the l a c k u n t i l very r e c e n t l y o f any v i a b l e experimental animal model i n which t o study these l i g h t - a c t i v a t e d s k i n pigment c e l l cancers impeded resea ch progress. Two new animal study f i n d i n g s noted d u r i n g t h i s Symposium may, however, be harbingers o f f u t u r e advances i n t h i s area: (1) demonstration o f UV-B r a d i a t i o n increasing both squamous c e l l carcinomas and melanomas i n an animal model having photoactivated s k i n c e l l s and (2) o t h e r new data showing much greater growth o f ,melanomas transplanted i n t o skins o f UV-radiated animals , suggesting t h a t UV r a d i a t i o n may n o t o n l y t r i g g e r growth o f melanomas b u t a l s o have promotor e f f e c t s as w e l l . I t i s t h u s l y c l e a r t h a t appropriate c a u t i o n must be taken n o t t o prematurely r u l e o u t p o s s i b l e increases i n melanoma-type s k i n cancers due t o s t r a t o s p h e r i c ozone depletion. Another important h e a l t h endpoint 1i k e l y t o be a f f e c t e d by s t r a t o s p h e r i c ozone depletion--with p o s s i b l e much more extensive impacts on more diverse
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human populations o f t h e w o r l d than t h e s k i n cancer e f f e c t s - - i s immune suppression. As h i g h l i g h t e d d u r i n g t h i s Symposium, UV-B r a d i a t i o n appears t o be able t o modify immune f u n c t i o n i n several d i f f e r e n t ways, i n c l u d i n g changes o c c u r r i n g l o c a l l y a t t h e p o i n t o f s k i n i r r a d i a t i o n and o t h e r systemic e f f e c t s a t d i s t a l s i t e s away from exposed areas. L o c a l l y induced e f f e c t s i n c l u d e UV-B impairment of Langerhans c e l l s , those macrophage-like s k i n c e l l s mainly responsible f o r e n g u l f i n g antigens and presenting them t o helper T - c e l l lymphocytes i n v o l v e d i n mediation o f immune responses t h a t destroy antigens ( i . e . , f o r e i g n substances e n t e r i n g the body) and abnormal endogenous cancer c e l l s . A f t e r exposure t o UV-B r a d i a t i o n , Langerhans c e l l s no longer present antigens t o t h e helper T-lymphocytes and, when contact a l l e r g e n s a r e a p p l i e d t o UV-B exposed skin, no contact a l l e r g y ensues. Instead, suppressor lymphocytes a r e a c t i v a t e d which prevent any subsequent immune response t o t h e same antigen. UV-B r a d i a t i o n induced a c t i v a t i o n o f suppressor T - c e l l lymphocytes, which are normally i n v o l v e d i n r e g u l a t i o n o f the magnitude and d u r a t i o n o f immune responses, prevents devel opment o f n a t u r a l immune responses against UV-B induced s k i n cancers and thereby c o n t r i b u t e s t o t h e i r growth and spread t o o t h e r p a r t s o f t h e body. Besides the above e f f e c t s , c i r c u l a t i o n o f UV-B a c t i v a t e d suppressor lymphocytes throughout t h e body and an associated r e d u c t i o n i n numbers o f helper lymphocytes r e s u l t s i n a general, systemic suppression o f c e r t a i n immune functions. Thus, n o t o n l y do UV-B i r r a d i a t e d mice f a i l t o e x h i b i t c o n t a c t a l l e r g y responses t o chemicals a p p l i e d t o i r r a d i a t e d skin, b u t they a l s o have impaired a b i l i t y t o respond t o chemicals a p p l i e d t o non-radiated s k i n and decreased lymphocytemediated immune responses t o f o r e i g n substances i n j e c t e d under the s k i n ( i . e . , delayed h y p e r s e n s i t i v i t y reactions).
The systemic suppression o f immune
f u n c t i o n due t o UV r a d i a t i o n has been demonstrated t o occur i n several animal species, t o increase as a f u n c t i o n o f increasing UV-B dosage, and t o p e r s i s t beyond t h e i n i t i a l p e r i o d o f UV exposure. Very importantly, as noted d u r i n g t h i s Symposium, t h e above f i n d i n g s r a i s e the p o s s i b i l i t y t h a t suppression o f c e r t a i n lymphocyte-mediated immune responses by UV r a d i a t i o n may a l s o r e s u l t i n impairment o f analogous immune responses t o some i n f e c t i o u s agents. For example, t h e p a r a s i t e Schistosoma and t h e leprosy b a c i l l u s g a i n e n t r y v i a the skin, and such e n t r y o f these disease-producing organisms through UV-irradiated s k i n may l e a d t o a c t i v a t i o n o f suppressor lymphocytes and impaired immune r e a c t i o n s t h a t would otherwise counter the i n f e c t i o n s . Also, noted was t h e f a c t t h a t many o t h e r i n f e c t i o u s agents (e.g.
some viruses, b a c t e r i a , fungi, e t c ) produce s k i n diseases, and
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other organisms are normally h e l d i n check by delayed h y p e r s e n s i t i v i t y immune reactions.
I n each case, UV-6 induced immune suppression may increase s e v e r i t y of i n f e c t i o n s and impair development o f immunity against r e i n f e c t i o n . Consistent w i t h t h i s hypothesis are f i n d i n g s f o r t h e two i n f e c t i o u s agents s t u d i e d thus f a r :
(1) the demonstration t h a t i n j e c t i o n o f Herpes simplex v i r u s i n t o t h e s k i n o f mice exposed t o UV-B r a d i a t i o n r e s u l t e d i n suppressed immune response t o t h e v i r u s which l a s t e d f o r several months; and (2) t h e demonstration t h a t UV-6 i r r a d i a t e d mice i n f e c t e d w i t h Leishmania (a protozoan p a r a s i t e ) f a i l e d t o e x h i b i t delayed h y p e r s e n s i t i v i t y immune responses induced i n n o n - i r r a d i a t e d mice. The f u l l s i g n i f i c a n c e o f o f f i n d i n g s reviewed above f o r human h e a l t h remains t o be b e t t e r elucidated. However, evidence does e x i s t s f o r UV-B exposure i n humans producing analogous impairments i n immune system function, including:
(1) damage t o Langerhans c e l l s i n the s k i n and depressed a l l e r g i c
reactions t o f o r e i g n substances applied t o UV-irradiated skin; (2) decreases i n immune system k i l l e r c e l l a c t i v i t y and increases i n t h e number and a c t i v i t y o f suppressor lymphocytes w i t h human exposure t o UV-B r a d i a t i o n o r Sun l i g h t ; and (3) the persistence o f some o f these e f f e c t s beyond two weeks a f t e r exposure.
Thus, although much s t i l l has t o be learned through f u r t h e r research, prudence argues f o r viewing immune suppression e f f e c t s and any associated increased incidences o f some i n f e c t i o u s diseases as being l i k e l y t o occur w i t h s t r a t o spheric ozone depletion. Various o t h e r p o t e n t i a l h e a l t h e f f e c t s o f s t r a t o s p h e r i c ozone d e p l e t i o n l i k e l y t o be mediated v i a increased UV-B r a d i a t i o n were a l s o i d e n t i f i e d i n Symposium presentations. Probably most notably among these o t h e r e f f e c t s are adverse ocular e f f e c t s of UV-B r a d i a t i o n . One p o s s i b l y increased o c u l a r e f f e c t o f s o l a r UV r a d i a t i o n , snowblindness, i s t y p i c a l l y t r a n s i e n t ( i . e . , l a s t i n g f o r o n l y a few days); b u t i t s p o s s i b l e increase may be o f i n t e r e s t e s p e c i a l l y i n view of a n t i c i p a t e d greater UV-B i r r a d i a t i o n a t higher (snowier) l a t i t u d e s as t h e r e s u l t of ozone l a y e r depletion. O f much more concern, however, are t h e prospects o f increased incidence o f c a t a r a c t s cases.
New evidence i n d i c a t e s
t h a t small percentages o f UV-B r a d i a t i o n can penetrate i n t o t h e l e n s o f t h e eye and t h a t UV-6 r a d i a t i o n increases c a t a r a c t formation. The ozone l a y e r d e p l e t i o n would be expected t o increase t h e incidence o f c a t a r a c t s (a permanent clouding o f t h e lens o f the eye most o f t e n seen i n t h e e l d e r l y ) i n exposed populations, regardless of r a c i a l o r e t h n i c o r i g i n s . O f much concern i s t h a t , even i n developed countries where s u r g i c a l operations prevent most c a t a r a c t s from causing blindness, cataracts s t i l l remain as a leading cause o f blindness;
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and, i n less-developed c o u n t r i e s w i t h much more l i m i t e d s u r g i c a l c a p a b i l i t i e s , c a t a r a c t s represent an even g r e a t e r t h r e a t . Human h e a l t h e f f e c t s a r e n o t t h e o n l y concerns associated w i t h s t r a t o s p h e r i c ozone d e p l e t i o n .
I n f a c t , as some speakers have noted d u r i n g t h i s Symposium,
t h e environmental e f f e c t s t h a t can be hypothesized as l i k e l y t o occur, may be even more d e v a s t a t i n g than t h e d i r e c t h e a l t h e f f e c t s .
Increased UV-B r a d i a t i o n ,
f o r example, can be p r o j e c t e d t o a f f e c t b o t h phytoplankton and zooplankton i n our oceans.
These microscopic a q u a t i c organisms, o f course, form t h e base o f t h e
food chain f o r many marine species and decreases i n t h e i r number would i n v a r i a b l y l e a d t o reduced commercially a v a i l a b l e s u p p l i e s o f e d i b l e f i s h and o t h e r seafoods, as w e l l as o t h e r negative e f f e c t s .
I t i s a l s o hypothesized
t h a t increased UV-B r a d i a t i o n i s l i k e l y t o reduce t h e y i e l d s o f many food crops (e.g.,
r i c e ) and a l s o t h a t i t may l e a d t o s e r i o u s f o r e s t and o t h e r t e r r e s t r i a
ecosystem damage.
L a s t l y , we have a l s o heard t h a t increased UV-B l e v e l s due t o
s t r a t o s p h e r i c ozone d e p l e t i o n can be l i k e l y expected t o exacerbate o r worsen tropospheric ozone f o r m a t i o n and associated h e a l t h and enviornmental problems. Appropriate steps t o be taken t o deal w i t h s t r a t o s p h e r i c ozone d e p l e t i o n were e x t e n s i v e l y discussed d u r i n g t h i s Symposium.
The general concensus a t t h i s
meeting was: (1) t h a t e f f e c t i v e i n t e r n a t i o n a l cooperation i s necessary t o reduce f u t u r e s t r a t o s p h e r i c ozone d e p l e t i o n and (2) t h a t r a t i f i c a t i o n and implementation o f t h e Montreal Protocol i s u r g e n t l y needed as a f i r s t i m p o r t a n t i n t e r n a t i o n a l cooperation step. However, t h e r e d u c t i o n o f CFC-use as planned under t h e Montreal Protocol (50% r e d u c t i o n by 1998) w i l l be i n s u f f i c i e n t t o p r e v e n t a t l e a s t some f u r t h e r d e t e r i o r a t i o n o f t h e ozone l a y e r .
Emission c u t s o f a t l e a s t 80-90% a r e
necessary and the c u r r e n t l y a v a i l a b l e maximum c o n t r o l p o t e n t i a l i s expected t o be about 50-70%.
I n t h a t case, several c o n t r o l approaches w i l l need t o be f o l l o w e d
The f i r s t p r i o r i t y i s t o f i n d s u b s t i t u t e s f o r t h e CFC's i n chemicals w i t h lower ozone d e p l e t i n g p o t e n t i a l .
I n a d d i t i o n , products and equipmen
developed t h a t r e q u i r e l e s s o r no CFC's.
have t o be
Also, t h e technology f o r emission
c o n t r o l i n p r o d u c t i o n processes, as w e l l as recovery and recyc i n g o f used CFC's need f u r t h e r development. CLOSING
These p o i n t s should be s u f f i c i e n t t o capture t h e general f l a v o r o f t h i s Symposium.
Both M r . Wolters and I have g r e a t l y enjoyed c o - c h a i r i n g t h i s meeting
and having t h e o p p o r t u n i t y t o see many o l d f r i e n d s and t o make many new ones. We l o o k forward t o seeing such f r i e n d s again i n t h e f u t u r e , b o t h a t t h e n e x t U.S.-Dutcl Symposium t o be planned f o r 1991 i n t h e U . S and i n t h e i n t e r v e n i n g years as w e l l .
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Znplicatwns 0 1989 Elsevier Science PublishersB.V., Amsterdam - Printed in The Netherlands
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OZONE AGGRAVATES HISTOPATHOLOGY DUE TO A RESPIRATORY INFECTION IN THE RAT
H. VAN LOVEREN, P.J.A. ROMBOUT, and J.G.VOS National Institute of Public Health and Environmental Protection, P.O.Box 3720 BA
1,
BILTHOVEN, The Netherlands,
INTRODUCTION Epidemiologic observations have suggested that exposure to air pollutants is linked with increased susceptibility to respiratory infections. Although definite
correlation
has
not yet been
shown
a
(1,8,9,15,32,43,45) the
association of air pollution with excessive hospitalization seems valid (3). The interpretation of this association as mediated through host defense mechanisms and pulmonary infection is however conjectural. In inhalation toxicological studies much emphasis has therefore been placed on animal infectivity models. In general, these models comprise exposure of laboratory animals to noxious gases or aerosols, and subsequent challenge of the animals with infectious agents causing only marginal mortality in non-exposed animals. Excess mortality or differences in bacterial growth in the lungs, induced by exposure to gases, are the indicators of adverse effects. Many animal species have been used in such studies, including mice, hamsters, squirrel monkeys (17) and rats (41). The infectious agents that have been used include bacteria such as U e D t o c W u s D V eO or~ a e b s i a D n e m (17), but also viruses such as Influenza A (48). With some exceptions (41,48), numerous studies using infectivity models have revealed that exposure to oxidant gases has an adverse influence on the host defense to respiratory infections (6,10,12,13,16-19,23,26,33.34). The infectivity models are therefore very useful to hosts
to
defend
show
the
inability of
the
themselves against opportunistic pathogens as a result of
exposure to noxious gases. However, although these models may aid in understanding how the defense mechanisms are affected, the models cannot discriminate between the various aspects of pulmonary defense mechanisms. Roughly, pulmonary defense mechanisms to pathogens can be divided into three main categories, comprising mechanic
defense mechanisms, non-specific
defense mechanisms (ingestion by phagocytic cells) and specific immunity. Exposure to oxidant gases can, dependent on concentration and duration of the exposure, impair ciliary activity (7) and ciliated cells (39). Suppression of
phagocytic activity of macrophages by
exposure
to
oxidant
gases has
been
reported (l), as well as suppression of the digestive activity of lysosomal enzymes (20,21,25,28), and of leakage of lysozomal enzymes into the cell
(5). Regarding specific immunity exposure to oxidant to interfere with the humoral immune response (11,35,36,42). The cellular immune response in the lung is important in that it regulates the magnitude of the humoral response to various antigens, and thus the efficacy of the humoral immune defense mechanisms (4). Moreover, it is also important in recruiting and activating alveolar macrophages (27). Effects of exposure to oxidant gases on cellular immune responses have not been studied very extensively. Hillam et al. (24) found that lymphocytes from lung draining lymph nodes from rats that were intratracheally immunized with sheep red blood cells showed an exaggerated reactivity to antigens when the rats were exposed to nitrogen dioxide. We have described experiments in the rat that were aimed to investigate the effect of exposure to ozone on the cellular immune response to Listerb monocvtonenes (47). Apart from mechanic defense mechanisms in the lung, the relevant mechanisms of defense against Listeria in the lung include phagocytosis by macrophages. and T cell dependent lymphokine production that enhances phagocytosis (30,31,37,44,46). Humoral immunity, in contrast to T cell dependent immunity, is not relevant in terms of protection against the infection in this Listeria model. We found an inhibitive effect of ozone exposure on the clearance of Listeria by the lungs and spleen of intratracheally infected rats. Besides effects of ozone on the capacity of alveolar macrophages to ingest and kill Listeria also effects on ratios of T and B cells in lung draining bronchial lymph nodes, on proliferative responses to Listeria antigen of lymphocytes from bronchial lymph nodes and spleen of immunized rats, and on delayed-type hypersensitivity responses to Listeria cytoplasm and gases has
tissue
been
reported
antigen in immunized rats were
found
(47).
Pathological
lesions
following
intratracheal infections with m c v t o eenea appeared as inflammatory foci, comprising macrophages and lymphoid cells. Since both cell types seem to be
affected by
exposure
to
ozone, we also studied the influence of ozone
exposure on these lesions. For this purpose rats were continuously exposed
to
0, concentrations ranging from 0.25 to 1.5 mg/ms for a period of 1 week. TIME COURSE OF HISTOPATHOLOGIC EFFECTS OF A PUIMONARY INFECTION WITH
LISTERIA
MONOCYTOGENES Lungs of rats were examined at various
time points
infection with
infection (10 bacteria instilled
after
a pulmonary
6
Listeria.
One
day
after
observed; diffusely in lung interstitial histiocytes and lymphoid cells were noted, and a slight
intratracheally) very mild pathological changes were the
969 increase of alveolar macrophages could
be
established.
These
lesions were
observed associated with bronchi or bronchioli, but not preferentially. By day 3 after infection multiple foci, consisting of lymphoid cells, accompanied by histiocytes,
and
occasionally
an
influx of neutrophilic granulocytes with
areas of local cell degeneration could be seen. These lesions did not show a clear association with bronchi or bronchioli. These foci sometimes included alveolar lumina, where also granulocytes could be located. By day 5 the histopathological alterations in the lung were similar to those found 3 days after infection, but more severe and also more or less diffuse. By day 7 the inflammation was somewhat less severe. By day 10 after infection the lung had practically recovered from the infection, illustrated by the absence of major histopathological lesions. Some foci of histiocytes and lymphoid cells were still present. By day 15 after infection only sporadically lesions
could
be
observed. EFFECTS OF OZONE EXPOSURE ON PATHOLOGICAL LESIONS DUE TO LISTERIA 8
The lesions, that were observed in rats that were exposed to 1.5 mg/m I3 ozone for one week prior to intratracheal infection with 10 Listeria were more pronounced as compared to those in unexposed animals. Especially at 5 days after infection, the lesions in ozone exposed rats were most severe. Diffusely throughout the lung large inflammatory
infiltrates were
observed,
that were characterized by predominantly lymphoid cells and to a lesser extent also by histiocytes. Locally cell degeneration could be observed, and the entire aspect of the lesions were suggestive of granulomatous alteration (Fig.
1). The cells involved seemed
to
spread
in
the
lung parenchyma.
In the
alveolar spaces many macrophages were present. In contrast to non-exposed rats, the lungs of rats exposed to ozone still showed these pathologic lesions at later time points after infection. Whereas 15 days after infection the inflammatory noduli had disappeared in lungs of non-exposed rats, in the interstitium of exposed rats increased numbers of inflammatory cells could still be noted, and in the alveolar lumina clusters of alveolar macrophages were still observed. There were only minimal differences between rats that belonged to the same group. DISCUSSION Ozone exposure of rats decreased the resistance
to pulmonary
infection
with Wsteria m o n o c v t o m (47). In part this decreased resistance was due to an impaired capacity of alveolar macrophages to ingest and kill Listeria. Decreased phagocytic and lytic activity of alveolar macrophages due to exposure to oxidant gases is in agreement with many other studies, using other models (1,19,20,21,28). Besides non-specific defense mechanisms, mediated by macrophages, a crucial &fenso mchanimr i n t a r u of protection to ud control of raopiratory
Fig. 1. Granuloma in lung of ?At, 5 day8 aftor king continilauly oxpoaed to 0, for 1 week and subsequently infoctod intratrachoally w i t h loe (HE x 400).
ia
infection with
wdiatod by
cellular
immunity
(30,31,37,44,46).We have shown that also tho d e w l o p a n t of Icell mdiated immunity to Listeria appears to be suppressed in ozone exposed rats (47). The conclusion, that ozone exposure can have an influence on development of T cell dependent immune responses to Listeria indicates that potentially
hazardous with
respect
to
ozone must
The pulmonary changes in the rat that can be well
documented
judged
bacterial, viral
challenges of the lung, where T cell dependent immunity is crucial role in the defense. levels are
be
(2,14,38). In
and neoplastic known to play a
induced by
ambient
ozone
those studies damage was mainly
restricted to the transition zone from terminal bronchiole to
alveolar
duct.
Here, desquamation of type I pneumocytes of the alveolar lining, having a denuded basement membrane, was followed by a proliferation of type I1 cells, urd
together with
an
influx of interstitial inflammatory cells resulted in
thickor proximal alvoolar aopta. h incream of alvmolar ucrophasoa
waa
the
971 alvoolar component of tho infl-tory roaction. Loss of cilia and hypertrophy of tho bronchiolar epithelium has been deacribed in the t e I d M 1 conducting
d A h 8 t C ~ h t Wrphological O rocovery Of oxidant-induced lesion8 illustrates the e x t o ~ i v erepair capacity of the rat lung tissue. airvAy8. Rapid
Within a recovery period of one week nearly all lesion8 induced by continuous a exposure to 1.6 mg/m 0 , (22) or 20 mg/m NO, (40) had disappeared. Gross and White (22) described a nearly complete recovery of morphological lesions in a
rat lung 4 weeks after a continuous exposure to 1.4 mg/m 0 , for 4 weeks. In our model we made similar observations (data not shown). Within 5 days after termination of a one week period of continuous ozone exposure the lungs had recovered; by
that time hardly any lesions could be found, except some minor
lesions in the lungs of rats exposed to the higher s
concentrations of ozone
.
used, i.e. 1.5 mg/m Pulmonary infection with mnocvtlesions, that were characterized by foci of
induced histopathological inflammatory cells such as
lymphoid and histiocytic cells, accompanied by local cell degeneration and influx of granulocytes. The maximal histopathological effects due to a Listeria infection were observed at 5 and 7 days after infection. If rats were exposed t o ozone for one week prior to infection, the lesions found 5 and 7 days after infection were much more severe than in non-exposed animals. At that time the changes by exposure to ozone itself, without an infection, would virtually have disappeared. This indicates therefore, that the increased severity of lesions due to infection with Listeria after prior exposure to ozone was not an addition of ozone lesions, but
induced lesions and Listeria
induced
rather represented synergism between effects of ozone and
Listeria. This was illustrated also by the fact that at 15 days after infection, and thus also 15 days after the end of a one week period of exposure to 1.5 mg/m
s
ozone, at a time that both challenges of
the
rat
lung
were no longer seen as histopathologic lesions, lesions could still be seen if the challenges occurred in the same rat. Besides the severity and duration of the histopathology after
infection, also
the quality of the lesions was
influenced by prior exposure to ozone. Nature granulomas were Listeria infected rats that were also exposed to ozone. We interpret these data by macrophages after ozone exposure
found in
the diminished phagocytic activity of and the diminished cellular immunity to
Listeria after ozone exposure. Infection with Listeria caused an influx of macrophages. These macrophages ingested and killed the bacteria, and also gave rise to induction of Listeria-antigen specific T cells, that could produce lymphokines that activated macrophages to more effectively ingest and kill the bacteria. These defense mechanisms were visualized in the lungs by the inflammatory sites, where macrophages (histiocytic cells) and lymphoid cells were localized. In ozone exposed animals, as a consequence of diminished activity of u c r o p h g o s and of tho collular
upocts of tho dofeme, the
972 numbers of bacteria that could be recovered from the lung after infection were increased, thus effective
leading
to
an
even more
pronounced attxaction of
-
less
-
inflammatory cells. The frustrated efforts of both macrophages and lymphocytes resulted in granuloma formation.
CONCLUDING REMARKS In conclusion this report shows that ozone exposure, by diminishing the cellular immune and non-specific defense mechanisms with
Listeria, can
greatly
add
to
pulmonary
infection
to the pathological alterations due to the
infection, and, as a consequence, enhance the loss of lung functions caused by the
pulmonary
infection. These findings are underscored by the results that
indicate that systemic effects of a respiratory infection with Listeria, i.e. alterations in the liver, were more profound after exposure of the rats to the oxidant gas ozone (47). REFERENCES 1. Acton, J.D. and Myrvik. Q.N. (1972). Nitrogen dioxide effects on alveolar macrophages. Arch. Environ. Health 24, 48-52. 2. Barry, B.E., Miller, F.J. and Crapo, J.D. (1985). Effects of inhalation of 0.12 and 0.25 ppm ozone on the proximal alveolar region of juvenile and adult rats. Lab. Invest. 52, 692-704. 3. Bates, D.V. and Sitzo, R. (1983). Relationship between air pollutant levels and hospital adminissions in Southern Ontario. Canad. J. Publ. Health &, 117-122. 4 . Bienenstock, J., Befus, A.D. and McDermott, M. (1980). Mucosal Immunity. 1-18. Monogr. Allergy. 5. Castleman, W.L., Dungworth, D.L. and Tyler, W.S. (1973). Lung acid phosphatase reactivity following ozone exposure. Lab. Invest. 2,310-319. 6. Coffin, D.L., Gardner, D.E. and Blommer, E.J. (1966). Time-dose response for nitrogen dioxide exposure in an infectivity model system. Environ. Health Perspect. Q, 11-15. 7. Dalhawn, T. and Sj6holm, J. (1963). Studies on SO,, NO, and NH,: Effect on ciliary activity in rabbit trachea of single vitrQ exposure and resorption in rabbit nasal cavity. Acta Physiol. Scand. 287-292. a . Dohan, F.C., Everts, G.S. and Smith, R. (1962). Variations in air pollution and the incidence of respiratory disease. J . Air Poll. Contr. ASS. u , 418-436. 9. Durham, W.H. (1974). Air pollution and student health. Arch. Environ. Health 2,241-254. 10. Ehrlich, R. (1966). Effect of nitrogen dioxide on resistance to respiratory infection. Bacteriol. Rev. Zp, 604-614. 11. Ehrlich, R., Silversteyn, E., Maigetten, R. and Fenters, J.D. (1975). Immunologic response in vaccinated mice during long-term exposure to nitrogen dioxide. Environ. Res. 217-223. 12. Ehrlich, R., Findlay, J.L. and Gardner, D.E. (1979). Effects of repeated exposure peak concentration of nitrogen dioxide and ozone on resistance to streptococcal pneumonia. J. Toxicol. Environ. Health 5, 631-642. 13. Ehrlich, R. (1980). Interactions between environmental pollutants and respiratory infections. Environ. Health Perspect. 89-100. 14. Evans, M.J., Johnson, L.V., Stephens, R . J . and Freeman, C. (1976). Cell renewal in the lungs of rats exposed to low levels of ozone. Exp. Mol. Pathol. &, 70-83. 15. French, J.C., Lowrimore. G., Nelson, W.C., Fincklea, J.F. and Hertz, M. (1973). Effect of sulfur dioxide and suspended sulfates on acute reapiratory disease. Arch. Environ. Health 2,129-133.
u,
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973 16. Gardner, D.E., Miller, F.J., Blomer, E.J. and Coffin, D.L. (1979). Influence of exposure mode on the toxicity of NO2. Environ. Health Perspect. 2,23-29. 17. Gardner, D.E. (1982). Use of experimental airborne infections for monitoring altered host defenses. Environ. Health Perspect. 41. 99-107. 18. Gardner, D.E. (1984). Oxidant-induced enhanced sensitivity to infection in animal models and their extrapolation to man. J. Toxicol. Environ. Health 2,423-439. 19. Goldstein, E., Eagle, C. and Hoepreich, P.D. (1973). Effect of nitrogen dioxide on pulmonary bacterial defense nechanisms. Arch. Environ. Health 26, 202-205. 20. Goldstein, E., Lippert, W. and Warshauser, D. (1974). Pulmonary macrophage. Defences against bacterial infection of the lung. J. Clinic. Invest. &, 519-528. 21. Goldstein, E., Bartlema, H.L., Van der Ploeg, H., Van Duyn, P., Van der Stap, J.G.M.M. and Lippert, W. (1978). Effect of ozone on lysozomal enzymes of alveolar macrophages engaged in phagocytosis and killing of inhaled S t a D h v w aurew J. Infect. Die. 299-311. 22. Gross, K.B. and White, H.J. (1986). Pulmonary functional and morphological changes induced by a 4 week exposure to 0.7 ppm ozone followed by a 9 week recovery period. J. Toxicol. Environ. Health 143-157. 23. Henry, M.C., Findlay, J., Spangler, J. and Ehrlich, R. (1970). Chronic toxicity of NO, on squirrel monkeys. 111. Effect on resistance to bacterial and viral infection. Arch. Environ. Health 2p, 566-570. 24. Hillam, P., Bice, D.E., Hahn, F.F. and Schnizlein, C.T. (1983). Effect of acute nitrogen dioxide exposure on cellular immunity after lung immunization. Environ. Res. =,201-211. 25. Holzman, R.S., Gardner, D.E. and Coffin, D.L. (1968). Jn vivQ inactivation of lysozyme by ozone. J. Bacteriol. 1562-1566. 26. Illing, J.W., Miller, F.J. and Gardner, D.E. (1980). Decreased resistance to infection in exercized mice exposed to NO2 and 0 , . J. Toxicol. Environ. Health 6, 843-851. 27. Keller, R.H., Fink, J.N., Lyman, S. and Pedersen, G.M. (1982). Immunoregulation in hypersensitivity pneumonitis. I. Differences in T cell and macrophage suppressor activity in symptomatic and asymptomatic pigeon breeders. J. Clin. Immunol. 2, 46-51. 28, Kimura, A. and Goldstein, E. (1981). Effect of ozone on concentration of lysozyme in phagocytizing alveolar macrophages. J. Infect. Dis. 247251. 29. Lawther, P.J. (1958). Climate, air pollution and chronic bronchitis. Proc. Roy. SOC. Med. 3, 262-267. 30. Mackaness, G.B. (1969). The influence of immunologically committed lymphoid cells on macrophage activity b vivQ. J. Exp. Med. 973-992. 31. McGregor, D.D., Hahn, H.H. and Mackaness, G.B. (1973). The mediator of cellular immunity. V. Development of cellular resistance to infection in thymectomized irradiated rats. Cell. Immunol. 6 , 186-199. 32. Melia, R.J.W., Florey, C.V., Altman, D.G. and Swan, A.V. (1977). Association between gas cooking and respiratory disease in children. Br. Med. J. 2, 149-152. 33. Miller, S. and Ehrlich, R. (1958). Susceptibility to respiratory infections of animals exposed to ozone. 1. Susceptibility to Klebsiella 145-149. pneumoniae. J. Infect. Dis. 34. Miller, F.J., Illing, J.W. and Gardner, D.E. (1978). Effect of urban ozone level on laboratory-incurred respiratory infections. Toxicol. Letters 2 , 163-169. 35. Osebold, J.W., Owens, S.L., Zee, Y.C., Dotson, W.M. and Labarre, D.D. (1974). Immunological alterations in the lungs of mice following ozone exposure. Changes in immunoglobulin levels and antibody containing cells. Arch. Environ. Health &, 258-265.
m,
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u,
s,
m,
m,
m,
974 36. Osebold, J.W., Gershwin, L.J. and Zee, Y.C. (1980). Studies on the enhancement of allergic lung sensitization by inhalation of ozone and sulfuric acid aerosol. J. Environ. Pathol. Toxicol. 2, 221-234. 37. Pennington, J.E. (1985). Immunosuppression of pulmonary host defense. Adv. in Host Defense Mechanisms 4, 141-164. 38. Plopper, C.G., Chow, C.K., Dungworth, D.L., Brummer, M. and Nemeth T.J. (1978). Effect of low levels of ozone on rat lungs. 11. Morphological responses during recovery and reexposure. Exp. Mol. Pathol. 2,400-411. 39. Rombout, P.J.A., Dormans, J.A.M.A.,.Danse, L.H.J.C., Van Esch, E., Van Leeuwen, F.X.R. and Marra, M. (1982). Correlation between morphological and biochemical alterations in the rat lung exposed to nitrogen dioxide. In: Air pollution by nitrogen dioxides (Eds. Schneider, T., and Grant, L.). pp. 457-466. 40. Rombout, P.J.A., Dormans, J.A.M.A., Marra, M . and Van Esch, G.J. (1986). Influence of exposure regimen on nitrogendioxide induced morphological changes in rat lung. Environ. Res. 41, 466-480. 41. Sherwood, R.L., Kimura, A.. Donovan, R. and Goldstein, E. (1981). Effect of 0.64 ppm ozone on rats with chronic pulmonary bacterial infection. J. Toxicol. Environ. Health 893-904. 42. Schnizlein, C.T., Bice, D.E., Rebar, A.H., Wolff, R.K. and Beethe, R.L. (1980). Effect of lung damage by acute exposure to nitrogen dioxide on lung immunity in the rat. Environ. Res. u , 362-370. 43. Speizer, F.E., Ferris, B., Bishop, Y.M.M. and Spengler, J. (1980). Respiratory disease rats and pulmonary function in children associated with NO, exposure. Am. Rev. Respir. Dis. 3-10. 44. Takeya, U., Shimotori. S., Tanaguchi, T. and Nomoto, K. (1977). Cellular mechanisms in the protection against infection by u t e r i a -om in mice. J. Gen. Microbiol. ULp, 373-379. 4 5 . Thomson, D.J., Lebowitz, 1. and Cassell, E.J. (1970). Health and the urban environment. Air pollution, wheather and the common cold. Am. J . Publ.Health 731-739. 46. Van Loveren, H., Postma, G.W., Van Soolingen, D., Kruizinga, W., Groothuis, D.G. and Voe. J.G. (1987). Enhanced macrophage activity and s in nude rats. In: deficient acquired resistance to Immune-deficient animals in biomedical research. Eds. Rygaard, J . , BrUnner, N., Graem, N., Spang-Thomson, M., pp. 108-111. Y.Karger, Basel. 47. Van Loveren, H., Rombout, P.J.A., Uagenaar, Sj.Sc., Walvoort, H.C., Vos, J.G. Effects of ozone on the defense to a respiratory Listeria monocytogenes infection in rat, Suppression of macrophage function and cellular immunity and aggravation of histopathology in lung and liver during infection. Toxicol. Appl. Pharmacol, $&, in press, 1988. 48. Wolcott, J.A., Zee, Y.C. and Osebold, J.W. (1982). Exposure to ozone reduces influenza disease severity and alters distribution of influenza viral antigens in murine lung. Appl. Environ. Microbiol. &, 723-731.
n,
u,
a,
T.Schneider et al. (Editors),Atmpheric Ozone Research and ita Pollcy Implications 0 1989 Eleevier Science Publishers B.V.,Amstardam -Printed in The Netherlands
975
ADAPTATION UPON OZONE EXPOSURE IN KICE AND RATS
T.S. VENINGA Central Animal Laboratory, University of Groningen, Ant. Deusinglaan 50, 9713 AZ Groningen, The Netherlands
ABSTRACT Changes in the activity of the enzymes creatine kinase and glucose-6-phosphate dehydrogenase observed in blood plasma and alveolar macrophages (AM) respectively, as well as changes in AM adherence caused by 0, concentratiom of 40 pg/ms and higher reveal activation of this pulmonary defense system after 0, exposure. Such an activation creates a certain threshold. If the defence can fully cope with an offending irritant the state of adaptation may have been reached. INTRODUCTION Studying the effect of air pollutants on living organisms you may expect to observe 3 types of reactions: 1. defensive
2. injurious 3. reparative We examined 3 aspects of alveolar macrophage (AM) activity in mice and rats after exposure to ozone (0,) in concentrations of 0.02 to 0.4 ppm (40 to 800 pg/ms) namely: 1. AM adherence to nylonwool, 2. their intracellular glucose-6-phosphatedehydrogenase (G-6-PD)-activity, 3. activity of the enzyme creatine kinase (CK) in blood plasma, which is suggested to originate from AM'S (ref. 1).
METHODS Young adult male C57BL mice and young adult male Wistar rats were used. These conventional clean animals were bred in own facilities. Mice were housed 5 to a cage and rats 2 to a cage. The animals had free access to pelleted feed and acidified water. Feed was removed 8 h before and during 0, exposure. Experiments were performed according to a staggered schedule. The exposure facilities have been described previously (ref. 2). In all series of experiments a comparable number of control animals were exposed to filtered air. The exposure time for mice was 2.h, for rats either 2 h in the CK experiment or 16 h in the adherence and G-6-PD study. AM'S were isolated by
976 pulmonary lavage immediately after exporure. Only 2 washes were performed by intratracheal injection of physiological saline. These were treated separately. The An adherence was measured by counting the number of A n ’ s before and after passing 1 ml samples through a nylonwool column (ref. 2). C-6-PD was histochemically determined (ref. 3). The number of positively stained cells, counted under the microscope, was related to the number of cells present in small samples. Blood was taken by orbital puncture. Mice were punctured only after exposure, rats before and after exposure. Plasma CK was determined with CK test combinations of Boehringer (W. Germany) (refs. 4 - 5 ) . The determination of CK isoenzymes was performed by gelelectrophoresis (ref. 1). A range of 0, concentrations was used for each of the 3 variables studied. At each concentration at least 20 mice and in general at least 10 rats were used.
RESULTS Typical dose-response relationships were obtained for all 3 variables (Fig. 1, 2 ) .
CK rats(.) Median in relation to control
CK mice(0) Mean : per cent of control
-40
- 20 -0
- -20
Fig. 1. Activity of the enzyme CK in blood plasma of rats and mice exposed to a range of 0, concentrations for 2 h. Solid line: activity in rats, dashed line: activity in mice.
977
I
A 02 05 01
Low200
02 WM
B
04
02 a5 01
02
ppn
0.4
800
urn m
wx)
pg/w
1)oo
Fig. 2. Activity of the enzyme G-6-PD in AM'S (solid lines) and adherence of A M ' S (dashed lines) of rats exposed to a range of 0, concentrations for 16 h.A. First wash A M ' S , B. second wash AM'S
Except for the adherence where the lowest concentration was not tested, the curves start with one or two values negative in relation to the controls, then rise to positive values and then show a decline to values as or below those of controls. Lavages contained 98 per cent A M ' S ; 96 per cent of the cells were vital as demonstrated by dye-exclusion. AM'S of first washes showed a somewhat greater adherence than AM'S of second washes. Morphological variations were present between first- and second wash AM'S (Fig. 3): the majority of the first-wash A M ' s were larger and more rounded, with a foamy cytoplasm; the majority of the
second-wash AM'S were compact cells with a dense cytoplasm. The percentage G-6-PD positive AM'S in the washes varied between 10 and 40. In contrast to adherence no difference was found between first- and second wash A M ' S . Regarding CK activity in blood plasma rats turned out to be less sensitive to 0, exposure than mice. CK-BB in murine plasma demonstrated significantly higher activity in 0, exposed animals. CK-MM showed no difference, whereas CK-
MB was absent. DISCUSSION AM's represent a pulmonary defence system which as shown in this study, is and lower. Concentraactivated by 0, in concentrations of 0.1 ppm (200 &ma) tions higher than 0.1 ppm lead to decreasing activity. This may point to a deficit in defensive capacity and therefore may be the consequence of a detrimental effect. All 3 variables studied react in a similar way and give rise to comparable curves. The observed increase of CK-BB may originate from the lungs
9 78
F i g . 3. First-wash (left) and second-wash (right) An's from non-exposed rats. May-Grilnwald Giemsa stain. Magnification 1000 x.
(ref. 6). CK is present in An's
(ref. 7); it is necessary for their mobiliza-
tion. Activated AM'S move to foreign substances and adhere (Fig. 4). As indicated previously AM adherence is an expression of their (increased) activity (ref. 2). Stimulation of G-6-PD supports the defensive potential of the cells. Also Rietjens et a1 (ref. 8) reported increased G-6-PD activity in rat An's grown in vitro after exposure to 1.5 0, for 4 days. We did not observe large amounts of neutrophils in the lavage fluid of rats
muma
exposed for 16 h to 0, as has been reported by others in this symposium. The reason might be that we lavaged the animals only twice. In general it is done serveral times in order to obtain larger numbers of An's. The presence in living organisms of defence systems wich become activated upon 0, inhalation, creates a threshold. If the defence becomes disabled no threshold will be observed. Activation of the defence may occur with some delay. Therefore, we can not exclude the possibility that even a small amount of 0, causes a lesion in the respiratory system beit of a minor order. Besides morphological it could be of biochemical on physiological nature. Such a lesion may be unnoticed because it is rapidly repaired and the defence systems
Fig. 4. Adherenco of M ' m to
A
foreign particle lavaged from a non-exposed rat.
have started their activity. In this relation distinction between defence and repair reactions is not always possible. Our results indicate that we observed elevated AM activity as an expression of an increased defensive capacity caused by 0, concentrations of 0.1 ppm (200
pg/ms) and lower. With 0, concentrations of 0.2 ppm (400 pg/ms) and higher the defensive capacity becomes deficient. We suggest that if the defence can cope with an offending stimulus like 0,, the state of adaptation is achieved. REFERENCES T.S. Veninga, Variations in pulmonary macrophage and enzymatic activity characteristics in animals exposed to photochemical oxidants, Proceedings Clean Air Congres, Sydney, 1986, 2 , pp. 293-299. T.S. Veninga and P. Evelyn, Activity changes of pulmonary macrophages after in vivo exposure to ozone as demonstrated by cell adherence, J . Toxicol. Environm. Health, 18 (1986) 483-489. C.J.F. Van Noordsn, I.M.C. Vogels, J. James and J. Tar, A sensitive cytochemical staining method for glucose-6-phosphate dehydrogenase activity in individual erythrocytes, Histochemistry, 75 (1982) 493-506. T.S. Veninga, J. Wagenaar and W.Lemstra, Distinct enzymatic reponses in mice exposed to a range of low doses of ozone, Environm. Health Persp., 39 (1981) 153-157. T.S. Veninga and V. Fidler, Ozone - induced elevation of creatine kinase activity in blood plasma of rats, Environm. Res., 41 (1986) 168-173. R.B. Coolen, D. Pragay, J . S . Nosanchuk and R. Belding, Elevation of brain type creatine kinase in serum from patients with carcinoma, Cancer, 44 (1979) 1414-1418. J . D . Loyke, V.F. Kozler and S.C. Silverstein, Increased ATP and creatine phosphate turnover in phagocytosing mouse peritoneal macrophages, J . Biol. Chem., 254 (1979) 9558-9564. I.M.C.M. Rietjens, L. Van Bree, M. Marra, M.C.M. Poelen, P.J.A. Rombout and G.M. Alink, Glutathione pathway enzyme activities and the ozone sensitivity of lung cell population derived from ozone exposed rats, Toxicol., 37 (1985) 205-214. ACKNOWLEGMENT The skilful technical assistance of R.A. Wieringa is gratefully acknowledged.
981
ORGANIZATION
SYMPOSIUM CHAIRMEN Environmental Protection Agency, United States o f America L. D. Grant M i n i s t r y o f Housing, Physical Planning and Environment, G.J.R.Wolters The Nether1ands
ORGANIZING COMMITTEE United Stat e s o f America S.D. Lee, chairman K. Barry B.Dimitriades L. D. Grant F.Mi 1l e r
PARTNERS PROGRAMME Mrs.M.Schneider-Ferrageau de S t .Amand
ADVISORY COMMITTEE
L.D.Grant, chairman G .Hueter B. Long V. A. Newi 11 J.O*Connor D.H. S t r o t h e r
REGISTRATION AND INFORMATION CENTRE Mrs.O.van Steenis
The Nether1ands T.Schneider, chairman J.van Ham, secretary Mrs .O. van Steen is Mrs P. W .A.M. Veni s-Pol s S. Zwerver
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T.Schneider, chairman J.van Ham, secretary E .H Adema J .H. Blom L.J.Brasser N. C. van Lookeren Campagne G. Schaap C. J. E. Schuurmans J.F.van de Vate K.Verhoeff G. H. Von kernan W .H. J .M.Wi entjens S, Zwerver
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INTERNATIONAL SECRETARY J.van Ham
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LIST OF PARTICIPANTS R.M.van A a l s t National I n s t i t u t e of Pub1i c Health and Environmental P r o t e c t i o n P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l e x : 47215 t e l : 030-742025 J.M.M. Aben N.V. KEMA P.0.Box 9035 6800 ET ARNHEM The Netherl ands t e l : 085-562383
B. Achermann Federal O f f i c e f o r Environmental Protection Hallwylstrasse 4 CH-3003 BERN Switzerland t e l : 031-619978 t e l e x : 912304 R.M. Adam Oregon State University, Dept. o f A g r i c u l t u r a l and Resource. Economics CORVALLIS, OR 97331-3601 USA t e l : 503-754-2942 Adam U n i v e r s i t y o f California, Human Performance Laboratory DAVIS CA 95616 USA W.C.
E.H. Adema A g r i c u l t u r a l University, Department o f A i r P o l l u t i o n P.0.Box 8129 6700 EV WAGENINGEN The Netherl ands t e l : 08370-82100
K. Ahmed
NRDC 122 East 42nd Street NEW YORK NY 10017 USA G.J.A. A1 VROM P.0.Box 450 2260 MB LEIDSCHENDAM The Netherl ands t e l e x : 32362 t e l : 070-209367 A.T. Alexander AECI Limited, Research and Development Dept. P.0.Box x2 PO MODDERFONTEIN 1645 Rebl .South A f r i c a t e l : 605-2324
984
G.M. A l i n k Department o f Toxicology, A g r i c u l t u r a l U n i v e r s i t y De Dreyen 12 6703 BC WAGENINGEN The Netherl ands t e l : 08370-14294
P. A l t s h u l l e r US EPA MD-59 RESEARCH TRIANGLE PARK NC 27711 USA M.A. Amoruso UMDNJ Robert Wood Johnson Medical School 675 Hoes Lane PISCATAWAY, NJ 08854-5635 USA t e l : 201-463-4478 J. F. Anderson
US EPA 2565 Plymouth Rd. ANN ARBOR M I 48105 USA t e l : 313-668-4496 B. Arends Netherl ands Energy Research Foundation, ECN P.0.Box 1 1755 ZG PETTEN The Netherl ands t e l : 02246-4666 t e l e x : 57211 F.M. Beck Hau t s t r a s s e 39 CH-I280 KREUZLINGEN Switzerland t e l : 072-724240
K. Becker h e 1tbundesarnt Bisaarckplatz 1 D-1000 BERLIN 33 FRG t e l : 030-8903390
t e l e x : 183756
L. C. van Beckhoven VROM P.O.Box 450 2260 MB LEIDSCHENDAM The Netherl ands t e l : 070-209367 t e l e x : 32362 S. B i n i a r i s Rheini sch-Westfal isches E l e k t r i z i t a t s w e r k A.G. Kruppstrasse 5 4300 ESSEN 1 FRG t e l : 185-3780
985
L.O. Bjorn U n i v e r s i t y of Lund, Oept. o f Plant Physiology P.0.Box 7007 S-220 07 LUND Sweden t e l : 46-46107797
F.M. Black US EPA MD 46 P.O.Box RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-3039 J.H. Blom N.V. KEMA P.O.Box 9035 6800 ET ARNHEM The Nether1ands t e l : 085-562585
t e l e x : 45016
R.D. Bojkov Atmospheric Environment Service 495 D u f f e r i n Street DOWNSVIEW, Ontario M3H 5T4 Canada t e l e x : 06-964582 t e l : 416-739-4615 J. Bouma-Ellis I n t e r n a t i o n a l Society f o r B i ometeorol ogy Anonenweg 10 2241 XK WASSENAAR The Netherlands t e l : 01751-10969
M. Bovenkerk VROM P.O.Box 450 2260 M8 LEIDSCHENDAM The Netherlands t e l : 070-209367 t e l e x : 32362
J.M. Brand Staatsbosbeheer P.0.Box 20020 3502 LA UTRECHT The Netherlands t e l : 030-852576 L.J. Brasser Tuinstraat 9 2671 BK DE LIER The Netherlands C. Braun-Fahrlander Abt.fur Sozial- und Praventivmedizin St.Alban-Vorstadt 19 CH-4052 BASEL Switzerland t e l : 061-233838
986
L.van Bree National I n s t i t u t e o f Public Health and Environmental P r o t e c t i o n P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l : 030-742843
R.E. Breslau Du Pont de Nemours (Nederland) B.V. P.0.Box 145 3300 AC WRDRECHT The Netherl ands t e l : 078-218893 A.H.M. Bresser National I n s t i t u t e o f Public Health and Environmental P r o t e c t i o n P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l e x : 47215 t e l : 030-743108
H.T. Broer N.V. Nederlandse Gasunie P.0.Box 19 9700 MA GRONINGEN The Netherl ands t e l : 050-212194 t e l e x : 53448 P.A. Bromber University North Carolina, Chapel H i l , Center f o r Environmental Medicine CB 7310, Med.Res.Bldg.C CHAPEL HILL NC 27599 USA t e l : 919-966-2531
03
A.J. Bruin Dow Chemical B.V. P.0.Box 48 4530 AA TERNEUZEN The Netherlands t e l : 01150-72978
t e l e x : 55061
N.A.J.H.C. Brull Province o f Limburg Parkwe 32 6212 MAASTRICHT The Netherl ands t e l : 043-897602
d
B. Brunekreef Department o f Environmental Health, U n i v e r s i t y P.0.Box 238 6700 AE HAGENINGEN The Netherlands t e l : 08370-82080
987
W.J. Bruring VROM P.0.Box 450 2260 MB LEIDSCHENDAM The Nether1ands t e l : 070-209367 t e l e x : 32362 P.J.H. B u i l t j e s MT-TNO P.0.Box 342 7300 AH APELDOORN The Netherlands t e l : 055-773344
t e l e x : 36395
F. C h i a r e l l i Eni r i c e r c h e Via E.Ramarini 32 00015 MONTOROTONDO (Rome) Italy 0. Clay US EPA 401 M S t r e e t S.W. WASHINGTON DC 20460 USA t e l : 202-382-7404 t e l e x : 475-7155 E. Coleman Duke Universitv. Medical Center DURHAM NC 27718’ USA C. Conzelmann Abt.fur Sozial- und Praventivmedizin S t . A1 ban-Vorstad 19 CH-4052 BASEL Switzerland t e l : 061-233838
0.1. Costa US EPA, Toxicolo y Branch MD-52 RESEARCH TRIANGL! PARK NC 27711 USA t e l : 919-506-8755
R.E. Crosthwait Mobil O i l Coro. P.O.Box 1031 PRINCETON NJ 08540 USA t e l : 609-737-5487
F. Cupel i n Service Cantonal d -Ecotoxicologie Case 78 12 GENEVE Swi t z e r l and t e l : 022-287511
988 T.C. Curran US EPA, MD-14 RESEARCH TRIANGLE PARK NC 27711 USA
t e l : 919-541-5467 R.G. Dement Harwell Laboratory P.O.Box 364 OXON OX 11 ORA United K i n dom t e l : 0235-!4141
telex: 83135
B. Dimitriades US EPA, MD 59 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-2706 H.van DOD KNMI P.0.Box 201 3730 AE DE BILT The Netherlands t e l : 030-766451
telex: 47096
J.A.M.A. Dormans National I n s t i t u t e o f Pub1i c Health and Environmental P r o t e c t i o n P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l : 030-743077 telex: 47215
D. D u l l US EPA PD-221 401 M S t r e e t SW WASHINGTON DC 20460 USA R.J. E l l i s Concawe, Babylon-kantoren A Konin i n J u l i a n a p l e i n 30-9 2595 DEN HAAG The Netherl ands telex: 36000 t e l : 070-424511
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A.J. Elshout N.V. KEMA P.0.Box 9035 6800 ET ARNHEM The Netherl ands t e l : 085-562381
telex: 45016
W.L. Eschenbacher U n i v e r s i t y o f Michigan Medical Center 1500 E.Medica1 Center D r i v e ANN ARBOR M I 48109-0026 USA t e l : 313-936-5245
989
Th. Evers National I n s t i t u t e o f Pub1i c Health and Environmental Protection P.O.Box 1 3720 BA BILTHOVEN The Nether1ands t e l : 030-749111 telex: 47215 H. F i o r i n i Enir i c e r c h e Via E.Ramarini 32 00015 MONTEROTONDO (Rome) Italy L.J. Folinsbee CE-Envi ronmental 800 Eastowne D r i v e 200 CHAPEL HIL NC 27514 USA t e l : 919-968-4836 H.D. Freeman Ricardo Consulting Engineers p l c . B r i d e Works SHORfHAM BY SEA, Sussex EN4 5FG En land 273-455611 te!: A. F r i e d r i c h Umwel tbundesamt Bismarckplatz 1 D-1000 BERLIN-33 FRG t e l : 30-8903562
t e l e x : 183756
J. S. Fugl estvedt State P o l l u t i o n Control A u t h o r i t y P.0.Box 8100 0032 OSLO Norway t e l e x : 76684 t e l : 02-659810
E. Gabarain Association Friends o f t h e Earth 14 Av. de St.Germain 78160 MARLY LE ROI France t e l : 33-1-39580091 T.G. G e r r l t y US EPA. HD-58 C1 i n i c a l Research Branch RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-966-6206
L. Gery 22 Pitman Road MARBLEHEAD MA 01945 USA t e l : 617-631-1162
990
H.S. Ghandi Science Research Laboratory, Ford Motor Company P.0.Box 2053 DEARBORN H I 48121 USA J.R. Goldsmith Ben Gurion U n i v e r s i t y o f t h e Negev, US EPA P.O.Box 473 M E R 84965 Israel telex: 5253 t e l : 57-690998
R. Gomez-Zorrilla Empresa de E l e c t r i c i d a d s.a., Control Ambiental Principe de Vergara 187 28002 MADRID Spain t e l : 4167012-4168011 telex: 22917 ene
J.A. Graham US EPA OD/HERL (MD-51) RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-2281 L.D. Grant US EPA, ECAO MD-52 3200 Hwy. 54 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-4173 telex: 510-927-1800
P. Grennfelt Swedish Environment Research I n s t i t u t e P 0 Box 47086 S-402 58 GOTHENBURG Sweden telex: 21400 t e l : 031-460080
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E.C. Grose US EPA, HERL/MD 82 Alexander O r . RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-1498 W.L. Grose NASA Langley Research Center HS 4013 NASA Lan l e y HAMPTON, VA 2366! USA t e l : 804-865-4788 R.F.de Grui jl Department o f Dermatol ogy Cathari jnesingel 101 3511 GV UTRECHT The Nether1ands
991
A. Guicherit TNO D i v i s i o n o f Technology f o r Society P.0.Box 217 2600 AE DELFT The Netherl ands t e l : 015-696034 telex: 38071 N. Haanappel Haarwe 135 6709 UAGENINGEN The Netherl ands t e l : 08370-11121
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J.D. Hackney Rancho 10s hi 0s Medical Center, U n i v e r i s i t y o f Southern C a l i f o r n i a 7601 E.Inperia7 Highway DOWNEY, CA 90242 USA t e l : 213-940-7561 J.van Ham SCM-TNO P.0.Box 186 2600 AE DELFT The Netherl ands t e l : 015-696877
R. Hamann Mobil O i l AG Streinstrasse 5 2 HAMBURG 1 FRG J.C.den Hartog S i ma Coatings B.V., P.8.Box 42 1420 AA UITHOORN The Netherl ands t e l : 02975-41373
C o n t r o l l e r HVGK
G.E. Hatch US EPA, MD-82 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-2658 S. Hayes SAI 101 Lucas Valley Road SAN RAFAEL CAL. 94903 USA t e l : 415-472-4011 t e l e x : 469287 C. Hayes US EPA RESEARCH TRIANGLE PARK NC 27711 USA
932 G.D. Hayman UK Atomic Energy Authority, Env. and Medical Sciences D i v i s i o n Hamel 1 Laboratory UKAEA OXFORDSHIRE OX11 ORA UK telex: 83135 t e l : 0235-24141 H.J. Hazucha Center for Env.Medicine, U n i v e r s i t y o f North Carolina a t Chapel H i l l CB 7310 Hed.Res.Bldg. C. CHAPEL HILL NC 27599 USA t e l : 919-962-0126 H. Heap Energy and Environmental Research Corp. 18 Mason I r v i n CA 92718 USA W.W. Heck USDWARS A i r Qua1i t y Program 1509 V a r s i t y D r i v e RALEIGH NC 27606 USA t e l : 919-737-3311 H. Heida Environmental Research Laboratorv kstelveensewe 80 90 1075 XJ AMSTERIAM The Netherlands t e l : 020-167373
R.A. Henpenius Vakgroep Toxicologie, LU Bornsestee 1-13C 6708 GA HA~ENINGEN The Netherl ands t e l : 08370-84624 P. Hennicke Deut scher Bundest ag Bundeshaus D-5300 BONN 1 FRG t e l : 0228-169345 T. Heyse Greenpeace Waversesteenweg 335 1040 BRUSSEL Be1g i urn t e l : 02-6478765 6. Hoek De artment o f Environmental Health U n i v e r s i t y P.!.Box 238 6700 AE HAGENINGEN The Netherl ands t e l : 08370-82080
993
A.B.M. H o f f Shell I n t e r n a t i o n a l Petroleum Co. PL/l1 SIPC, Shell Centre LONDON SE1 7NA UK t e l : 01-934-5967 telex: 919651
W. Hogsett US EPA 200 SW 35th Street CORVALLIS OR 97333 USA D.H. Horstman US EPA, Health E f f e c t s Research Lab. C1 i n i c a l Research Branch (MD-58) RESEARCH TRIANGLE PARK, NC 27711 USA telex: 510-927-1800 t e l : 919-966-6207
0. Hov NILU
PIOIBQX 46 N-2001 L I LLESTROM Norway t e l : 47-6-841773
telex: 74854
F.G. Hueter US EPA, HERL HD-51 RESEARCH TRIANGLE PARK NC 27711 USA R.A. Hulscher VROn P.0.Box 450 2260 MB LEIDSCHENDAM The Netherlands telex: 32362 t e l : 070-209367
D.M. Hyde U n i v e r s i t y o f C a l i f o r n i a , Dep. o f Anat., DAVIS CA 95616 USA
t e l : 916-752-1174 E.C.Th. Jansen Provincie Zuid-Holl and P 0 Box 90602 2509 LP DEN HAAG The Netherl ands t e l : 070-116686
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M. Janssen-Jurkovicova N.V. KEMA P.0.Box 9035 6800 ET ARNHEM The Netherl ands t e l : 085-563004
School o f Veterinary Medicine
334 H. J e f f r i e s U n i v e r s i t y of North Carolina, Env.Sci. School o f Public Health EigPiL HILL NC 27514 USA
S.M. J o f f r e
Finnish Meteoroloaical I n s t i t u t e Sahaajankatue 22ESF-00810 HELSINK1 Finland telex: 124436 t e l : 358-0-7581320
W. B. Johnson National Center f o r Atmospheric Research BOULDER CO 80307 USA t e l : 303-497-1032 telex: 989764 P. E, Joost i n g Laan van Oostenburg 16 2271 AP VOORBURG The Netherl ands t e l : 070-869418 J. Kagawa Dep. o f Hygiene and Public Health, Tokyo Women’s Medical College 8 - 1 Kawada-cho, Shinjuku-ku TOKYO 162 Japan t e l : 03-353-8111
R.R. Kampen Kerkhofsweg 17 9995 PL KANTENS The Netherl ands t e l : 05995-1903
L.V. Karenlampi U n i v e r s i t y o f Kuopi P.0.Box 6 70211 KUOPI 21 Fin1and t e l : 971-163180
telex: 42218
A. Karpinen M i n i s t r y o f t h e Environment P.0.Box 399 SF-00121 HELSINKI Finland telex: 123717 t e l : 358-0-1991371 H.R. Kehrl US EPA, C l i n i c a l Research Branch MD-58 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-966-6208
995
H. Kelder KNMI P.0.Box 201 3730 AE DE BILT The Netherlands t e l : 030-766472
t e l e x : 47096
H. Kolb U n i v e r s i t y o f Vienna Hoge Warte 38 A-1190 VIENNA Austria
J.van der Kooy N.V. KEMA P.0.Box 9035 6800 ET ARNHEM The Netherl ands t e l : 085-562543 H.S.
t e l e x : 45016
Koren
US EPA. Health E f f e c t s Research Lab.
C1 i n i c a l Research Branch (MD-58) RESEARCH TRIANGLE PARK. NC 27711 USA t e l : 919-966-6254
telex: 510-927-1800
M. Kosters Mari jkweg 3 6 4 6709 PG UAGENINGEN The Netherl ands t e l : 08370-20979 G.H.M. Krause Landesanstalt f u r Immissionschutz des Landes N.R.U. Wallneyerstrasse 6 0-4300 ESSEN FRG t e l : 201-7995395 t e l e x : 8579065 l i s d ~~
K. K r i jgsheld VROH P.0.Box 450 2260 MB LEIDSCHENDAM The Netherl ands t e l : 070-209367 telex: 32362 M.L. Kripke U n i v e r s i t y o f Texas, Anderson Hospital and Tumor I n s t i t u t e 1515 Holcombe Blvd. HOUSTON, Texas 77030 USA t e l : 713-792-8578
R. Kroes National I n s t i t u t e o f Pub1i c Health and Environmental Protection P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l : 030-742310 telex: 74215
996
P. Kroon Netherlands Energy Research Foundation ECN P.O.Box 1 1755 ZG PETTEN The Netherl ands telex: 57211 t e l : 02246-4347 M.C. Kroon VROn P.O.Box 450 2260 MB LEIDSCHENDAM The Netherlands t e l : 070-209367 telex: 32362
S.V. Krupa U n i v e r s i t y o f Minnesota, Department o f Plant Pathology 1991 Buford C i r c l e , 495 Borlang H ST.PAUL MN 55108 USA t e l : 612-625-7294 H. L a t t i l a Finnish Meteorological I n s t i t u t e Sahaajankatu 22E SF -00810 HELSINKI Finland telex: 124436 t e l : 358-0-7581320 T. Leah Environment Canada OTTAWA. Ontario K1A OH3 Canada. telex: 819-997-0547 t e l : 819-953-1670 E. Lebret National I n s t i t u t e o f Public Health and Environmental P r o t e c t i o n P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l : 030-742777 S.D. Lee Harvard University, EEPC 65 Yinthrop S t r e e t CAMBRIDGE, MA 02138 USA t e l : 617-495-1313
J.A.M.van de Lee Acaci a s t r a a t 208 2565 KJ DEN HAAG The Netherl ands F.de Leeuw National I n s t i t u t e o f Public Health and Environmental P r o t e c t i o n P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l e x : 47215 t e l : 030-742806
997
R.van der Lende U n i v e r s i t y o f Groningen Bloensin e l 1 9713 BZ ~RONINGEN The Netherlands t e l : 050-619111 6. Leone IPO P.0.Box 9060 6700 GW WAGENINGEN The Netherl ands t e l e x : 45888 t e l : 08370-19151 C. Leuenber e r Gesundheitsanspektorat der Stadt Zurich Walchestrasse 33 8035 ZURICH Switzerland t e l : 01-216-2801
J.C.van der Leun U n i v e r s i t y o f Utrecht, I n s t i t u t e o f Dermatology Cathari jnesingel 101 3511 GV UTRECHT The Netherlands t e l : 030-372727 telex: 47687 Ph.D. Ling-Yi Cang Duke U n i v e r s i t v Medical Center P.0.Box 3177 DURHAM NC 27710 USA t e l : 919-684-6266
P. Lioy Robert Wood Johnson Medical School PISCATAWAY NJ 08854 USA t e l : 201-463-4547 M. Lippnann New York University, Medical Center P.0.Box 817 TUXEDO, NY 10987 USA t e l : 914-351-2396 N.C.van Lookeren Carnpagne Shell Nederland B.V. P.0.Box 9035 3000 BE ROTTERDAM The Netherlands t e l e x : 36530 t e l : 010-4696036
H .van Loveren National I n s t i t u t e o f Pub1 i c Health and Environmental P r o t e c t i o n P.0.Box 1 3720 BA BILTHOVEN The Netherl ands t e l : 030-742476 t e l e x : 47215
998 N.A. Lukkenaer VROM P.O.Box 450 2260 MB LEIDSCHENDAM The Nether1ands telex: 32362 t e l : 070-209367 W.J. Manning U n i v e r s i t y o f Massachusetts, Department o f Plant Pathology Fernald H a l l AMHERST, MA 01003 USA t e l : 413-545-2289
R. Mansini Ecofuel Spa V i a l e Brenta 15 20139 MILAN0 Italy t e l : 02-52021944
telex: 310246 e n i i
M. Marra National I n s t i t u t e o f Pub1i c Health and Environmental P r o t e c t i o n P.O.Box 1 3720 BA BITLHOVEN The Netherlands t e l : 030-742406 G.B. M a r t i n US EPA, AEERL MD-60 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-2821
T. McCurdy US EPA, MD-12 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-5658 M. McElroy Harvard U n i v e r s i t y , Department o f Earth and P1 anetary Sciences Pierce H a l l , 100 E CAMBRIDGE MA 02138 USA
M.A. Mehlman Mobil O i l CorDoration P.O.Box 1029 PRINCETON. NK 08540 USA t e l : 609-737-5501 0.6. Menzel Duke U n i v e r s i t y , Medical Centre, Department o f Pharmacol. and Medicine DURHAM NC 27710 USA t e l : 919-684-3915
999 E.L. Meyer US EPA 10 Glenmore Drive DURHAM, NC 27707 USA t e l : 919-541-5594 J. Meyer RMNO P.O.Box 5306 2280 HH RIJSWIJK The Netherl ands t e l : 070-985880
F.J. M i l l e r US EPA, MD-66 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-2655 C. Monn
Federal I n s t i t u t e o f Technology, Dep-.of Hygiene and Ergonomics P.O. Box CH-8092 ZURICH Switzerland t e l : 01-256-4629 C.A. Moore Cornittee on Environment and Public Works, US Senate WASHINGTON DC 20510 USA
G.van Muiswinkel Shell Pernis Vondel i n enwe 601 3196 KK f O T T E b 4 The Netherl ands P. Mullenix Forsyth Research I n s t i t u t e , Dental Center 140, Fenway BOSTON MA 021 15 USA t e l : 617-262-5200 M. H u l l e r M i n i s t e r e de 1 -Environnement/SRETIE 14, Bd.du General Leclerc 92524 NEUILLY-SUR-SEINE CEDEX France t e l e x : denvir 620602f t e l : 1-47581212 V. Newill Assistant Administrator, US EPA RD-672 410 M S t r e e t SW WASHINGTON DC 20460 USA
1000
J . Nobel Association o f the Mechanical and E l e c t r i c a l Engineering I n d u s t r i e s P.0.Box 190 2700 AD ZOETERMEER The Netherl ands t e l : 079-531334 S.L. Nolen US EPA, MD-61 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-7607
M. Noordhoek B r i t i s h Petroleum Raff. Nederland N.V. P.0.Box 1033 3180 AA ROZENBURG The Netherl ands t e l : 01819-50361 t e l e x : 23584 A. Novo I t a l i a n E l e c t r i c i t y Board, Thermal and Nuclear Research Centre Via Rubattino 54 20134 MILAN0 Italy t e l : 2-88473975 telex: 310496 U.M. O l l i s o n
American Petroleum I n s t i t u t e 1220 L S t . NU WASHINGTON DC 20005 USA t e l : 202-682-8262
D. Onderdel 1nden
National I n s t i t u t e o f Public Health and Environmental P r o t e c t i o n P.O.Box 1 3720 BA BILTHOVEN The Netherl ands t e l : 030-742880
R. Orthofer Austrian Research Centre Sei bersdorf A-2444 SEIBERSDORF Austria t e l : 02254-80-2166 telex: 014-353
J. Overton US EPA, MD 82 RESEARCH TRIANGLE PARK NC 27711 USA t e l : 919-541-5715 J . Pankrath
Unwel tbundesamt Bismarckplatz 1 0-1000 BERLIN 33 FRG t e l : 030-8903-375
FME
1001
R.T. Paul Motor Vehicle Manufacturers Association 300 New Center B u i l d i n g DETROIT, Michigan 48202 USA telex: 1009770 t e l : 313-872-4311
S.
Penkett U n i v e r s i t y o f East Angl ia, School o f Environmental Sciences NORWICH NR4 7TJ UK L. Perros L.P.C.E.University o f Paris X I 1 Avenue du General de Gaulle 94000 CRETEIL France t e l : 16-148989144 t e l e x : UPVM 211 752 F
A.C. Posthurnus Research I n s t i t u t e f o r Plant Protection Wageningen, Free U n i v e r s i t y Amsterdam Vossenwe 66 6721 BP OENNEKN The Netherlands t e l : 08370-19151 H. Puxbaum Technical U n i v e r s i t y Vienna Getreidemarkt 9 A-1060 VIENNA Austria M. Raizenne National Health and Welfare Tunney-s Pasture OTTAWA, ON KIA OL2 Canada S.T. Rao NYS, Department o f Environmental Conservation 50 Wolf Road, Room 134 ALBANY, NY 12233-3259 USA t e l : 518-457-3200 L. Reijnders Societv f o r Environmental Conservation Donkerhraat 17 3511 KB UTRECHT The Netherlands t e l : 030-331328 t e l e x : 70890
I.M.C.M. Rientjens A g r i c u l t u r a l U n i v e r s i t y , Department o f Biochemistry De D r e i j e n 11 6703 BC WAGENINGEN The Netherlands t e l : 08370-83723
1002
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1003
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D. Simpson Warren S r i n g Laboratory Gunnels i o o d Road STEVENAGE, Herts. UK t e l : 0438-741122
1004
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h
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1005
D. Tingey US EPA 200 S.U. 35th Street CORVALLIS, O r 97333 USA
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#
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1007
J.W. Weenink VROn
PYO..Box 450 2260 MB LEIDSCHENDAM The Netherl ands t e l : 070-209367 telex: 32362 W.H.J.M. Wientjens MT-TNO P.0.Box 217 2600 AE DELFT The Netherl ands t e l : 015-696185 J.van Wieringen Sealed i .r B.V. - .- . - - A . .. - . .. P.0.Box 271 6500 AG NIJMEGEN The Netherl ands t e l : 080-710111
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E. Yokoyama The I n s t i t u t e o f Public Health 4-6-1 Shirokanedai Minato-ku TOKYO Ja an te!: 03-441-7111
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SUBJECT INDEX
Adaptation Age Effects A i r Qua1it y Alfalfa Alveolar Macrophages Asthma Automobi 1it y
805 284 36, 127, 839 233 50 1 493 472
Basis Document Boundary Layer Brundtl and Conmi ssi on
573 608, 657 8
Carbon Cycle Catalytic Cycles Chi 1dren Climate Modification Control Options Strategies Cost -Effectiveness Crop Loss
61, 67 358 319 79 392, 565, 766, 774, 901 623, 660, 671, 683, 837, 845 891, 901 254
Direct Effects Dose-Effect Relationships Dosimetry Dry Depos it i on
240 51, 713, 851 281, 293, 319, 553 583
Economic Effects
869, 881, 891 564 302 57
EKMA Electrocardiography Elemental Cycle Emi s s i on CFC Diesel Evaporative Factors Inventories Mobi 1e Sources Reduction
103, 765, 777, 786, 891 43 1 406, 423, 675, 903 454, 944 85, 111, 637 87, 405, 443, 936 438, 443, 455, 567, 671, 779
1010
Refueling Environmental Protection EPA Exercise Exposure Acute Assessment Chronic Effects Index Indicators Model Population
554, 711 535, 301, 220 207, 825, 83 1
Fibrosis Forest Decline Free Troposphere
529, 750 47 60, 605
Glutathione Greenhouse Effect Guinea Pigs
520 14, 75, 368, 377 545
Hi stami ne Human Health Effects
550 12, 711, 745, 795, 803
Indicator Plants International Cooperation In Vitro
253 496 7, 16 514
Luminescence Lung Structure
264 26
Indomet hac in
413, 423 9 17 23, 345, 757 738, 759 738 321, 975 749, 883 855
Memorandum o f Understanding 3 Mi crodosimetry 287 380, 563, 589, 613, 623, 633, 647, 657, 825, Model simulation Monkey Montreal Protocol Motor Vehicles
869, 886 524 15, 16, 175, 785, 926, 949 387, 405
Nasal Cavity
525
1011 Neutrophil Nitrogen Cycle Oxides Non- a t t a i nment
65 102, 122, 141, 683 13
Ozone Background Episodes Forest Trees Formation Health Effects Toxicity Transport Trends Vegetation Effects Ozonides
127, 575, 607 633, 647 239 35, 130, 172, 579, 590 21, 311, 319, 331, 501, 513, 701, 759, 841 334 134 167, 174, 177, 195, 205 45, 219, 229, 251, 843, 875 518
751
Paint PAN Photochemistry Photosynthesis PHOXA Phytoplankton P1ant Hetabol ism Pol i c y Pollutant Interactions Potent ia t ion Pulmonary Function
691, 913 190, 368 35, 177, 589, 633 262 633 270 46 919, 931, 943, 949 49 24 289, 295, 313, 343, 483, 493, 537, 726, 733, 755, 975
Rat Respiratory Function Risk
301, 501, 536, 553, 723, 733, 967, 975 22, 348, 523, 547, 759, 967 336, 814, 837, 851
Scal es Scenario Skin Cancer Sol vents Spi r e t r y Standards Setting
5 311, 641 796 691 488 21, 701
1012 Stratospheric Ozone Depletion
355, 365, 765, 785, 877, 925, 934
Test Cycl e Threshold Trace Gases Troposphere
435, 461 33 1 73, 159 62, 935
Urban Areas US-Dutch Symposium UV-B Radiation Effects General Imnunesystern He1anoma
195, 206 4, 11 269, 795 18, 261, 803 799, 809 809, 813
Veget a t ion Effects Vitamin E
45 341
voc Emissions /NO, Ratio Volunteers
92, 123, 137, 667, 675, 901, 911 67, 139, 630, 641 311
Zooplankton
272
1013
PAPERS RECEIVED LATE
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T.Schneider et aL (Editore),Ahnospheric Ozone Research and its Policy Implicotiona 0 1989 Elaevier Science Publishem B.V.,Amsterdam-Printed in The Netherlands
1015
STATIONARY SOUIECE CXARACI'ERIZATION AND OONTROL Sl'RATEGIES FOR REACI'IVE VOLATILE ORGANIC COMPOUNDS
G.B.Martin, US EPA, Research Triangle Park NC 27711, USA
ABSTRACT Volatile organic conpounds (Mcs) are emitted t o the atmosphere from a variety of processes. These conpounds may react i n the lower atmosphere as part of the process leading t o ozone generation and/or may be classified as hazardous a i r pollutants (HAPS) which have direct health inpacts. This paper provides a brief overview of the sources of VOCB and of the control technologies which may be used t o control these emissions. INTRoDumroN
Volatile organic conpounds (Mcs) are emitted by a w i d e variety of stationary and mobile sources. The v a s t majority of mobile source VOC emissions are from highway vehicles. The stationary emission sources are extremely varied ranging from large point sources t o numerous relatively small area sources and fugitive emissions. The major stationary source classes of VOCB are: solvent uses; petroleum production; treatment, storage, and disposal f a c i l i t i e s ; combustion; and industrial processes. Solvent uses include: metal cleaning, consumer solvents, and a variety of surfacing coating. Petroleum production includes exploration, refinery processes, d i s t r i h t i o n , and marketing. Combustion includes numerous small fuel combustion processes and agricultural, forest or other open burning. Industrial processes include organic chemical manufacturing and manufacturing of a number of consumer products. The specific process w i t h i n these source categories w i l l determine the applicable control technology. Many of the area and fugitive sources require a collection system of some kind t o duct the VCC emission stream t o the control device.
CONTROL TECHNOLOGY SELECTION
The control technologies applicable t o control of VCC emissions are described i n "Control Technologies for Hazardous Air Pollutants" (ref. 1) and a methodology for matching a specific source w i t h a technology is discussed. Although the report deals w i t h hazardous organics, the discussion of organic control technologies is equally applicable t o a l l VOCB. VOC Emission Characteristics
The characteristics of the VOC emission stream are more inportant i n selection of the control technology than the type of source. These charac
1016
teristics can further be separated into two categories: stream characteristics and Mc characteristics. Stream characteristics. The characteristics of the VOC-containing stream are a primary consideration i n selecting the preferred control technology. The major stream characteristics are: 1. Organic content. The amount of VOC i n the emission stream w i l l determine whether the Mc can be economically recovered or if a destruction technology is preferred. I t may also determine which type of combustion technology is preferred t o most effectively and economically destroy the VOC. 2. Heat content. The heat content (Btu/SCF) of the stream is inportant primarily for those technologies where additional fuel may not be used i n the combustion process (e.g., boilers or f l a r e s ) . 3. Moisture content. This characteristic is of primary importance only for carbon absorption. 4. Flow rate. The various technologies have different limits on the amount of flow that they can effectively handle. Additionally some of the technologies can handle time variant flow rates more effectively. VOC characteristics. The characteristics of specific VOCs i n the stream are important primarily for removal techniques. Molecular weight and adsorption/desorption characteristics are important for carbon adsorption. Solubility i n water or other solvents is key for adsorbers. Vapor pressure as a function of tenperature is the governing characteristic for condensers. Control Technology Characteristics Several control technologies are available t o t r e a t specific VOC streams. These technologies can be divided into two categories: destruction techniques and removal techniques. Destruction techniques. A l l t h e currently available destruction techniques are based on combustion of the VOC stream either alone or w i t h supplementary fuel. By matching the characteristics of the stream t o the capabilities of the technologies, appropriate levels of control can be achieved a t reasonable costs. The characteristics of each technology are: 1. Thermal incineration. This technique is broadly applicable t o continuous VOC emission streams. It can achieve 95 t o over 99% destruction relatively independent of Mc characteristics. Only minor fluctuation i n flows can be tolerated and still maintain residence time and tenperature necessary for high destruction efficiency. Thermal incineration is typically applied t o d i l u t e
1017
l i m i t (LEI,) concentration; however, i f the VOC concentration is too
low, supplemental fuel may be required t o maintain the tenperature necessary for acceptable destruction efficiency. A potential advantage is that systems which recover heat may allow recovery of some economic value. 2. catalytic Incineration. This is another form of thermal incineration, which uses a catalyst t o promote VOC oxidation a t a lower temperature. It can achieve 90 t o over 99% destruction of VOCa for low VOC concentrations. ~ t applicability s is more restricted s i n c e VOC Characteristics have a greater influence on the efficiency of the catalyst than for thermal incinerators. A number of metals, as well as sulfur and halogens, can poison the catalyst and reduce its efficiency. Careful tenperature control is essential since the catalyst l i f e can also be significantly reaced by thermal aging. I n fact, catalyst l i f e is a key factor both i n maintaining control efficiency and i n determining the economic feasibility of the technique. I t has the advantage that the amount of supplemental fuel required may be rehced substantially. 3. Flares. Flares are typically used t o control intermittent emissions Qring process upsets and/or emergencies. Properly designed flares for high heat content waste stream 0300 Btu/SCP or 1.12 megaJoules per normal cubic meter) can achieve up t o 988 VOC control. For lower heat content stream, supplemental fuel may be required. A variety of f l a r e designs can accolrmodate a w i d e range of VOC stream characteristics and/or flow rates. 4. Boilers/Process Heaters. I n many cases existing plant equipment can be used t o destroy VOC streams and t o recover energy a t the same time. Destruction efficiencies of greater than 988 can be achieved. The limitation of the technology is the amount of a d i l u t e Mc w a s t e stream that can be incinerated w i t h o u t adversely affecting the equipment's primary function of supplying steam and/or heat t o the plant.
Removal techniques. These techniques can provide efficient removal of the VOC from t h e emission stream but do not change the chemical form of the VOC. This h a s the advantage that economic pro&ct recovery may be achieved i n addition t o p o l l u t i o n control. Unlike thermal destruction, these processes work on several different principles and can be strongly dependent on the VOC characteristics.
1018
1. carbon Adsorption.
The VOC is selectively removed from the
emission stream by a bed of activated carbon. Removal efficiencies of 50 t o 99% can be achieved for dilute mixtures of Mc and air. Inlet VOC concentrations are limited t o avoid exceeding the adsorption capacity of the bed and/or generating excessive bed tenperatures due t o t h e heat of adsorption. The maxinum concentration is about 10,000 ppmv, and higher concentrations may have t o be reduced by dilution. A further limitation may be placed on concentration of flammable organic vapors for safety reasons. These limits are 25% of LEL for most cases,, although 40 t o 50% of LEL may be acceptable i f proper monitors and controls are present. Furthermore, high molecular weight organics may be d i f f i c u l t t o remove from the bed once adsorbed, Therefore, the application of t h i s technique is generally limited t o conpounds with boiling points less than 400° F (200° C) and/or molecular weights less than 130. On the other hand, conpounds w i t h molecular weights below 50 are not efficiently removed. Finally, the removal efficiency decreases as relative humidity increases and, a t relative humidit i e s above 50%, efficiency may show a significant decrease. I n most systems one bed is used t o adsorb organics from the stream while a second bed is being regenerated t o recover a high VOC concentration stream. 2. Absorbers. This technique has limited applicability t o organic vapors, although removal efficiencies can exceed 99% for specific systems. The primary limitation is the availability of a suitable solvent t o remove the specific VOC. I n addition, disposal of the used solvent can present additional problems. 3. condensers. This technique is frequently used for recovery of raw materials and/or products from a process stream. Condensers are most suited t o streams w i t h more t h a n 5000 ppmv and can achieve removal efficiencies increasing from 50 t o 90% as VOC concentration increases. The VOC removal is limited by the VOC vapor pressure a t the available coolant temperature. H i g h removals require coolant tenperatures below normal water temperature. Condensers can be used as a preliminary resource recovery and pollution control device t o be followed by a destruction technique for high efficiency. These devices are typically applicable t o relatively low flow rates.
1019
Conplter Technique Based on the HAP manual (ref.21, the EPA and the New Jersey Department of Environmental Protection has complterized the design and cost calculations
for eight control devices for permit reviewers.
This program, called
IM conpatible Controlling Air Toxics (CAT), has been designed for use on B conputers. Information supplied on the permit application is entered into
the program, and design parameters and cost estimates are calculated. The program is designed t o easily perform what-if calculations, allowing the reviewer t o change parameters and quickly see the inpact on design and costs. REFERENCES
1 Control Technologies for Hazardous Air Pollutants, EPA/625/6-86/014, September 1986. 2. S. L. Nolen, T. Micai, G. Shareef, and M. T. Johnson, "Controlling Air Toxics, an Advisory System", paper 88-51.14, presented a t the 81st Annual Meeting of APCA, Dallas, TX, June 19-24, 1988.
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T. Schneider et al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
1021
GLOBAL MODELING OF OZONE AND TRACE GASES
W.L.
GROSE, R.S.
ECKMAN, R.E.
TURNER, AND W.T.
BLACKSHEAR
Atmospheric Sciences Division, NASA Langley Research Center, Hampton, V i r g i n i a 23665-5225
ABSTRACT A three-dimensional, global atmospheric model f o r s i m u l a t i o n o f t h e d i s t r i b u t i o n o f ozone and other t r a c e gases i s described. The model extends from the surface t o 60 km, i n c l u d i n g a comprehensive formulation o f the r e l e v a n t chemistry. Simulated d i s t r i b u t i o n s o f some o f t h e c o n s t i t u e n t s important t o understanding the stratospheric ozone budget are presented and discussed w i t h respect t o degree o f agreement w i t h observations. The seasonal e v o l u t i o n o f t h e global d i s t r i b u t i o n o f t h e s t r a t o s p h e r i c ozone column i s discussed. The i n t e r a c t i o n between dynamical and chemical processes i s i l l u s t r a t e d during disturbed winter conditions i n t h e mid-stratosphere.
INTRODUCTION
For much o f t h i s century, s c i e n t i s t s have been engaged i n the study o f atmospheric ozone. However, during the past 2 decades, concern over the p o t e n t i a l d e p l e t i o n o f t h e ozone layer by nitrogen compounds i n h i g h - a l t i t u d e a i r c r a f t emissions, chlorofluorocarbons, and various other chemicals has provided the stimulus f o r a comprehensive program o f observations and t h e o r e t i c a l modeling ( r e f . 11. The d i s t r i b u t i o n s o f ozone and other constituents i n the Earth's atmosphere evolve as t h e r e s u l t o f the complex i n t e r p l a y among r a d i a t i v e , chemical, and dynamical processes.
Our
understanding o f these processes has been hindered by t h e lack o f simultaneous, long-term, global-scale measurements o f winds, temperature, and constituents. Hence, much o f our i n s i g h t must, o f necessity, r e l y upon atmospheric simulation models o f varying complexity. Substantial computational resources a r e required f o r modeling t h e chemistry o f the ozone l a y e r because o f t h e exceedingly l a r g e number ( i n excess of 100, e.g.
ref. 2) o f chemical r e a c t i o n s believed
relevant. For t h i s reason, most o f the modeling studies have been conducted w i t h one- o r two-dimensional models i n which the t r a n s p o r t i s h i g h l y parameterized.
These models r e l y upon various types o f parameterizations
( f r e q u e n t l y ad hoc) o f t h e t r a n s p o r t processes (e.9.
r e f . 3 and r e f . 1).
1022 Although the r a t i o n a l e f o r three-dimensional model studies o f s t r a t o s p h e r i c chemistry and t r a n s p o r t i s w e l l established (e.g. r e f . 1 and included references), r e l a t i v e l y fewer studies have been done w i t h t h e three-dimensional models because of t h e requirement f o r l a r g e computational resources even without i n c l u d i n g chemistry. A t t h e present time, long-term simulations w i t h a general c i r c u l a t i o n model which incorporates a comprehensive and f u l l y i n t e r a c t i v e treatment o f r a d i a t i v e , chemical, and dynamical processes a r e n o t f e a s i b l e and, indeed, may be unwarranted considering known d e f i c i e n c i e s i n our c u r r e n t understanding o f these processes ( r e f . 3). For these reasons, a v a r i e t y o f approaches t o modeling t h e ozone layer w i t h more s i m p l i f i e d three-dimensional models (e.g. see references and discussions i n r e f . 1 and r e f . 3) have developed over the years. Nearly 20 years ago, Hunt ( r e f . 4 ) studied the t r a n s p o r t o f ozone using a three-dimensional, hemispheric, p r i m i t i v e - e q u a t i o n GCM. Despite t h e s i m p l i f i e d nature o f t h e GCM and a much-abbreviated photochemical formulation, he achieved modest success i n t h a t the simulated ozone d i s t r i b u t i o n agreed qua1 i t a t i v e l y w i t h observations.
P a r t i c u l a r l y notable was t h e establishment o f a column
ozone maximum a t high latitudes--a r e s u l t c o n t r a r y t o what one would expect based upon p u r e l y photochemical considerations. Hunt's pioneering e f f o r t s were followed by a succession o f attempts t o model the s t r a t o s p h e r i c ozone l a y e r . An i n t e r e s t i n g example i s t h e study by Cunnold e t a l . ( r e f s . 5 and 61, who conducted a long-term simulation ( 3 years) w i t h a low-resolution quasigeostrophic model w i t h a much s i m p l i f i e d representation o f t h e ozone chemistry. Schlesinger and Mintz ( r e f . 7 ) adopted e s s e n t i a l l y t h e same representation o f t h e ozone chemistry as Cunnold e t al., b u t used a comprehensive p r i m i t i v e equation GCM. The usefulness o f t h i s study was somewhat compromised i n t h a t the s i m u l a t i o n extended o n l y s l i g h t l y more than a month. Mahlman e t a l . ( r e f . 8) studied ozone t r a n s p o r t using a p r i m i t i v e equation GCM extending t o t h e mid-stratosphere. They assumed ozone t o be i n photochemical e q u i l i b r i u m a t t h e t o p model l e v e l and i n e r t below.
This study
was notable i n i t s extensive diagnosis of t r a n s p o r t mechanisms. Examples o f a l t e r n a t e approaches are t h e studies o f Kurzeja e t a l . ( r e f . 91 and C a r i o l l e and Oeque ( r e f . 10). These two groups examined ozone t r a n s p o r t using three-dimensional c i r c u l a t i o n models, b u t adopted a l i n e a r i z e d f o r m u l a t i o n o f the ozone chemistry. Recently, Grose e t a l . ( r e f . 11) used an " o f f - l i n e " ( r e f . 12) t r a n s p o r t model w i t h a very comprehensive f o r m u l a t i o n o f the chemistry o f t h e stratosphere t o simulate t h e d i s t r i b u t i o n o f most o f the relevant cocstituents
.
1023 The present study extends the work of Grose et al. (ref. 11) describing the methodology used in constructing a model of the ozone layer and presenting preliminary results from an annual cycle simulation experiment. DESCRIPTION OF THE MODEL A global, primitive equation GCM (see refs. 11, 13, and 1 4 for details of the model) was used for the studies described herein. The model extends from the surface to approximately 60 km (12 levels) and includes the effects of forcing by orography and land-ocean thermal contrast. Time integration is accomplished with a semi-implicit technique using a 30-minute time step. Transport model simulations are performed with an "off-1 ine" technique (ref. 12) in which wind and temperature fields are generated separately by the GCM and then used as input to the set of mass continuity equations for the constituents. Formulation of the transport model is essentially identical to that of the GCM. A scale-selective, biharmonic diffusion term is included to parameterize horizontal, sub-grid-scale processes. Vertical sub-grid diffusion is not included, following Mahlman and Moxim (ref. 12). However, special attention is given to vertical transport in the model when negative mixing ratios are encountered. Early experiments with inert tracers indicated that vertical transport in the presence of strong gradients was the primary mechanism for producing negative mixing ratios. Generation of such negative mixing ratios resulting from the use of second-order central difference approximations to the vertical transport term was alleviated by switching to upstream differencing only when negative values occur. The switch to upstream differences is accomplished in a mass-conserving manner by addition of a flux divergence term equal to the difference between an upstream difference and a central difference approximation to the vertical advection term. The effectiveness of this technique for suppressing negative mixing ratios is a consequence of the positive definite advection property of this technique. Evaluation of the net chemical source (sink) term required during the integation requires consideration of a large number o f species and chemical reactions (39 and 115, respectively, in this version of the model). The complexity o f the chemistry makes explicit transport of each constituent an unwieldy and expensive option. Also, the extremely fast chemistry characteristic of some species would dictate integration time steps so small as to be impractical for conducting long-time simulations. To circumvent these difficulties, the "family" approach has been adopted i n which related species that undergo relatively fast chemical transformation are grouped into a family with a characteristic chemical lifetime much greater than for the component
1024 members--a concept f r e q u e n t l y used i n one- and two-dimensional models ( r e f . 2). I n t h e present version o f t h e model, mixing r a t i o s o f Ox L O 3 + O(’P) + O(’D)l, NOy [NO + NO;! + NO3 + N + HNOp + HNOkI, CEx [ C i + CgO + CtONOp + CeO2 + H O C i + HCel,
HzO;!,
HNO3, and N205 a r e determined by e x p l i c i t
i n t e g r a t i o n of t h e i r respective mass c o n t i n u i t y equations. Although n o t e x p l i c i t l y transported, t h e chemistry of t h e f a m i l i e s HOx [H + OH + H O 2 l and CHx [HCO + CH3 + CH20 + CH200H + CH30z + CH,OI
i s included i n t h e
formulation. P a r t i t i o n i n g f a m i l i e s for evaluation of t h e net source ( s i n k ) term i s accomplished through various e q u i l i b r i u m r e l a t i o n s h i p s .
I n order t o assess the
impact of using these r e l a t i o n s h i p s , d e t a i l e d production and loss analyses have been performed f o r various z e n i t h angles and l a t i t u d e s and intercomparisons made w i t h more complete mechanisms o f a one-dimensional model.
Largest d i f f e r e n c e s appear i n those i n d i v i d u a l species which have chemical l i f e t i m e s on
the order o f a day or so and deviate s i g n i f i c a n t l y from e q u i l i b r i u m due t o diurnal effects.
Invoking t h e e q u i l i b r i u m assumption f o r most o f these species
has l i t t l e impact on t h e net f a m i l y source term (e.g.
CeONO;!).
I n a r i g o r o u s evaluation o f p h o t o l y s i s r a t e s r e q u i r e d i n t h e chemical code, i t i s necessary t o perform i n t e g r a t i o n s w i t h respect t o wavelength o f t h e
products o f photodissociation cross section, quantum e f f i c i e n c y , and l o c a l solar f l u x . Evaluation o f these i n t e g r a l s numerically consumes a s i g n i f i c a n t f r a c t i o n o f t h e computational time i n a t y p i c a l chemical c a l c u l a t i o n .
As an
a d d i t i o n a l approximation f o r the chemical code used i n the model, a l l r e q u i r e d p h o t o l y s i s r a t e s are parameterized as a f u n c t i o n o f 0 2 and 03 absorber amounts. A s a t i s f a c t o r y degree o f approximation has been ensured by comparison w i t h values determined i n the r i g o r o u s c a l c u l a t i o n . Ordinary r a t e c o e f f i c i e n t s are taken from DeMore e t al. ( r e f . 15) Certain chemical species t r e a t e d i n the model include l o n g - l i v e d constituents, which are e s s e n t i a l t o the ozone problem i n t h a t they represent
Ce,, and odd hydrogen species. These chemicals (H20, H;!, CH,, N20, CH,Ce, CF2Ce3, CH3CCe3, and CO) are s p e c i f i e d as a f u n c t i o n o f a l t i t u d e , l a t i t u d e , and season (as appropriate) based on observations or t h e sources o f NOy,
two-dimensional model r e s u l t s o f Garcia and Solomon ( r e f . 16). D I S C U S S I O N OF RESULTS
The simulation discussed i n the f o l l o w i n g section consisted o f a I-year i n t e g r a t i o n i n i t i a t e d on model day January 1. I n i t i a l c o n s t i t u e n t f i e l d s were e i t h e r i n f e r r e d from monthly mean data (December 1978) from the Limb I n f r a r e d Monitor o f t h e Stratosphere (LIMS) experiment ( r e f . 1 7 ) o r from two-dimensional
1025 model simulations ( r e f . 16). Wind and temperature f i e l d s used i n t h e t r a n s p o r t model simulation were taken from a multi-year i n t e g r a t i o n of t h e GCM. Numerous p r e l i m i n a r y comparisons have been made w i t h observations, but t h e l i m i t e d scope o f the present paper allows o n l y a few i l l u s t r a t i o n s t o be presented.
The r e s u l t s a r e generally encouraging, b u t model/data comparisons
are d i f f i c u l t , a t best, because o f the s c a r c i t y o f simultaneous, g l o b a l data f o r the r e l e v a n t constituents and an incomplete understanding o f t h e interannual v a r i a b i l i t y o f the atmosphere. I n the f o l l o w i n g sections, some representative zonal mean d i s t r i b u t i o n s are discussed w i t h respect t o degree o f s i m i l a r i t y w i t h observations and/or two-dimensional model r e s u l t s i n order t o provide a broad, general perspective o f model performance. Next, t h e e v o l u t i o n o f t h e global, column ozone above 100 mb i s presented t o i l l u s t r a t e seasonal v a r i a t i o n s i n t h e s t r a t o s p h e r i c distribution.
V e r t i c a l p r o f i l e s o f the
CEO r a d i c a l and the temporary r e s e r v o i r
species C i O N O 2 are then presented as examples o f c o n s t i t u e n t s which are important i n the c a t a l y t i c d e s t r u c t i o n o f ozone by f r e e chlorine. F i n a l l y , pressure surface d i s t r i b u t i o n s o f 0% and N205 i n the mid-stratosphere are shown during a disturbed winter c o n d i t i o n t o demonstrate t h e i n t e r a c t i o n s between chemical and dynamical processes. Total column NO2 i s prese ted t o i n t e r p r e t the sequestering o f odd-nitrogen i n the polar night. Zonal mean d i s t r i b u t i o n s o f c o n s t i t u e n t s Zonal mean cross sections o f odd-oxygen (Ox),
t o t a l odd-n trogen (NO,
=
N t NO + NO2 t NO3 + HN03 + 2 x N205 + CiON02 + HN02 + HN04) n i t r i c a c i d (HN03), and hydrogen peroxide (H202) are presented f o r t h e m d-November p e r i o d
i n f i g . 1. These r e s u l t s were selected near the end o f t h e i n t e g r a t i o n period t o allow the c o n s t i t u e n t d i s t r i b u t i o n s t o adjust from t h e i r i n i t i a l s t a t e t o the model climatology. Throughout much o f the stratosphere, the odd-oxygen f a m i l y i s dominated l a r g e l y by ozone.
Only i n the upper stratosphere and above does atomic oxygen
c o n t r i b u t e t o any s i g n i f i c a n t degree t o the t o t a l odd-oxygen abundance.
Hence,
odd-oxygen i s a s u i t a b l e proxy f o r ozone i n much o f t h e stratosphere. Figure l a shows the calculated zonal mean abundance o f odd-oxygen f o r mid-November. The d i s t r i b u t i o n i s g e n e r a l l y s i m i l a r t o observations f o r t h i s period, w i t h peak mixing r a t i o displaced southward from the Equator a t 10 mb. The peak mixing r a t i o i s s l i g h t l y i n excess o f 10 ppmv, w i t h i n t h e range o f values from s a t e l l i t e - d e r i v e d ozone climatologfes ( r e f . 18). Values i n t h e upper stratosphere e x h i b i t the we1 1-known discrepancy between theory and observations t y p i c a l l y seen i n one- and two-dimensional model simulations ( r e f . 1).
The calculated ozone l e v e l s are approximately 30 percent lower than
1026
(a)
,
"290
-60
-30
0
30
60
90
60
90
Latitude (deg)
-
O
10' n
n E
B3 0' v) u)
2 a 10'
lb)
10'
-90
-60
-30
0
30
Latitude (deg)
Fig. 1. Zonal mean f i e l d s f o r mid-November: .(a) Odd oxygen (ppmv); (b) Odd nitrogen (ppbv); ( c ) N i t r i c acfd (ppbv); (d) Hydrogen peroxide (ppbv).
1027
I ) ' - O 1' oo
1 o3
\
-90
I
I
I
I
I
-60
-30
0
30
60
90
Latitude (deg)
l
Latitude (deg)
Fig. 1 continued.
1028 observed values. Examination o f t h e seasonal e v o l u t i o n o f t h e ozone d i s t r i b u t i o n r e v e a l e d t h a t t h e l o c a t i o n o f t h e peak m i x i n g r a t i o t r a v e r s e d t h e Equator f r o m s o u t h t o n o r t h and back s o u t h a g a i n s i m i l a r t o observed b e h a v i o r (e.g.
SBUV r e s u l t s , r e f . 18).
T o t a l o d d - n i t r o g e n shown i n f i g . 20 ppbv a t a p p r o x i m a t e l y 6 mb.
l b e x h i b i t s a peak abundance i n excess o f
T h i s v a l u e i s w i t h i n t h e range o f c a l c u l a t e d
v a l u e s t y p i c a l o f two-dimensional models ( r e f . 1 ) and i n agreement w i t h s a t e l l i t e - and b a l l o o n - b o r n e o b s e r v a t i o n s o f t h e o d d - n i t r o g e n f a m i l y which a r e presently available.
Using LIMS d a t a , C a l l i s e t a l . ( r e f . 19) e s t i m a t e a lower
l e v e l f o r t o t a l o d d - n i t r o g e n of 22.5 k 4 b y summing HN03 and n i g h t t i m e NO2. P r e l i m i n a r y comparisons o f t h e s e r e s u l t s w i t h n i g h t t i m e LIMS NO2 o b s e r v a t i o n s show s u b s t a n t i a l areas o f agreement ( r e f . 1 1 ) . The seasonal e v o l u t i o n o f o d d - n i t r o g e n d i s p l a y s a wide range o f s p a t i a l and temporal v a r i a t i o n s .
In
November, t h e l o c a t i o n of t h e peak m i x i n g r a t i o i s s h i f t e d toward h i g h l a t i t u d e s i n t h e N o r t h e r n Hemisphere, b u t s h i f t s i n t o t h e Southern Hemisphere a f t e r s o l s t i c e i s reached. The HNOB d i s t r i b u t i o n shown i n f i g . l c has a l s o been compared w i t h r e s u l t s f r o m a v a r i e t y o f two-dimensional models and shows agreement b u t , l i k e t h e s e models, does n o t reproduce t h e h i g h - l a t i t u d e h e m i s p h e r i c asymmetry p r e s e n t i n t h e L I M S o b s e r v a t i o n s ( r e f . 20).
LIMS o b s e r v a t i o n s show an i n c r e a s e i n peak
HN03 m i x i n g r a t i o towards t h e w i n t e r p o l e , whereas models t e n d t o p r e d i c t n e a r l y c o n s t a n t m i x i n g r a t i o a t h i g h l a t i t u d e s i n w i n t e r . Based upon t h i s disagreement between o b s e r v a t i o n s and modeling s t u d i e s , A u s t i n e t a l . ( r e f . 21) conclude t h a t gas-phase c h e m i s t r y a l o n e i s n o t s u f f i c i e n t t o e x p l a i n t h e observed h i g h - l a t i t u d e b e h a v i o r i n w i n t e r , and suggest t h a t i n c o r p o r a t i o n o f heterogeneous processes may be r e q u i r e d . The H202 d i s t r i b u t i o n shown i n f i g . I d a l s o agrees w i t h two-dimensional model s i m u l a t i o n s and shows g e n e r a l agreement w i t h v a l u e s i n f e r r e d f r o m LIMS d a t a ( r e f . 22).
However, t h e v a r i o u s model p r e d i c t i o n s v a r y b y a r a n g e o f a
f a c t o r o f 2 o r l a r g e r over much o f t h e s t r a t o s p h e r e .
The H202 c o n c e n t r a t i o n
has a q u a d r a t i c dependence on t o t a l odd-hydrogen (HOx) and w i l l be s e n s i t i v e t o d i f f e r e n c e s i n HO, p r o d u c t i o n f o r t h e v a r i o u s models ( r e f . 1). O n l y 1 i m i t e d d i r e c t o b s e r v a t i o n s a r e a v a i l a b l e ( i n most cases e s t a b l i s h i n g o n l y upper l i m i t s , e.g. r e f . 23 and r e f . 241, so i t i s d i f f i c u l t t o make d e f i n i t i v e comparisons. S t r a t o s p h e r i c column ozone The e v o l u t i o n o f t h e m o n t h l y mean column ozone above 100 mb d u r i n g an annual c y c l e i s shown i n f i g . 2.
P r i o r comparisons o f an e a r l i e r model s i m u l a t i o n
w i t h LIMS r e s u l t s showed good agreement i n most r e s p e c t s .
However, t h e s p a t i a l
1029 90
60
-
30
cn 0,
-0
v
a
U
r
o
3
.c c
4
-30
- 60 -90 Month
Fig. 2.
Variation o f column ozone (Oobson Units) above 100 mb.
1
n
E
v
?
10
ffl ffl
!? a
100
Mixing Ratio (ppbv)
Fig. 3.
V e r t i c a l p r o f i l e o f chlorine monoxide a t (ppbv) 30.5N f o r mid-May.
1030 coverage (84N t o 645) and l i f e t i m e o f t h e LIMS experiment ( 7 months), together w i t h t h e d u r a t i o n o f t h e e a r l i e r simulation (4 months), permitted o n l y l i m i t e d comparison. The present r e s u l t s e x h i b i t a maximum i n s p r i n g a t h i g h l a t i t u d e s i n the Northern Hemisphere (N.H.1,
a lesser f a l l maximum a t h i g h l a t i t u d e s i n
and a minimum i n t h e e q u a t o r i a l region. These the Southern Hemisphere (S.H.), general features are i n reasonable agreement w i t h t h e 20-year average t o t a l column ozone d i s t r i b u t i o n presented by London ( r e f . 251, b u t d i f f e r i n some d e t a i l s . For example, the observed S.H. f a l l maximum shows a d i s t i n c t poleward progression w i t h time. The model r e s u l t s d i s p l a y a s i m i l a r tendency, b u t c e r t a i n l y much less pronounced. U n t i l 3-D model simulations o f s u f f i c i e n t d u r a t i o n (10 years o r more) become p r a c t i c a l and t h e model c l i m a t o l o g y can be developed, i t i s d i f f i c u l t t o assess the importance of some o f t h e d i f f e r e n c e s between models and observations. Constituent v e r t i c a l p r o f i l e s V e r t i c a l p r o f i l e s o f the CkO r a d i c a l and t h e temporary r e s e r v o i r species CEON02, important i n the c a t a l y t i c d e s t r u c t i o n o f ozone by f r e e c h l o r i n e , have been selected as i l l u s t r a t i o n s of species which are not e x p l i c i t l y p r e d i c t e d by the model, b u t are derived from the Ca, assumptions.
f a m i l y through e q u i l i b r i u m
For these species, t h i s assumption i s reasonable f o r most o f the
stratosphere w i t h the important exception t h a t CtONO2 becomes long-lived i n t h e polar n i g h t . The loss o f CaON02 occurs by p h o t o l y s i s i n t h e u l t r a v i o l e t and, t o a lesser extent, by r e a c t i o n w i t h atomic oxygen. For a i r parcels r e s i d e n t i n the polar n i g h t f o r extended periods, CaON02 forms by r e a c t i o n of CaO w i t h NOp.
P r o f i l e s o f CEO and CaON02 a t 30.5N f o r mid-May a r e presented i n f i g s . 3 and 4, respectively. This l o c a t i o n was chosen because i t i s t h e Gaussian l a t i t u d e i n the model c l o s e s t t o 30N, where recent data on these species are a v a i l a b l e . The CaO p r o f i l e i n f i g . 3 f o r l o c a l noon has peak mixing r a t i o o f approximately 0.6 ppbv a t 2 mb.
Waters e t a l . ( r e f . 26) have r e c e n t l y reported C a O
measurements taken a t Palestine, Texas, i n May 1985 and October 1986 using a microwave limb sounder. They present comparisons o f t h e i r data w i t h other observations and a range o f 2-D model p r e d i c t i o n s f o r summer conditions. The CEO p r o f i l e shown i n f i g . 3 i s w i t h i n the range predicted b y t h e various 2-D models. The May 1985 data o f r e f . 26 (average o f values from 2 hours before noon t o 3 hours a f t e r noon) are i n t h e middle o f t h e model range between 26-
30 km.
A t 34 and 38 km, the measured values are lower than the model Values
(both 2- and 3 4 1 , b u t e r r o r bar estimates overlap t h e lower h a l f o f t h e model range, Waters e t al. note t h a t w i t h i n 1-1/2 hours a f t e r sunset, C a O between 26 t o 34 km has v i r t u a l l y disappeared, w h i l e 38 km values are unchanged. This
1031
100
t\
I
_______~~
0
0.2
I
I
0.4
0.6
I
0.8
I
1
1.2
Mixing Ratio (ppbv)
F i g . 4.
V e r t i c a l p r o f i l e s o f c h l o r i n e n i t r a t e (ppbv) a t 30.5N f o r mid-May.
180
GM
F i g . 5. Ozone mixing r a t i o (ppmv) a t t h e 10 mb pressure l e v e l o f t h e Northern Hemisphere, February 7.
1032 r e s u l t i s consistent w i t h t h e d i u r n a l behavior displayed i n t h e present 3-0 model r e s u l t s . V e r t i c a l p r o f i l e s o f CtON02 a t l o c a l noon and noon plus 6 hours are shown i n f i g . 4. A peak mixing r a t i o s l i g h t l y exceeding 1 ppbv occurs a t 20 mb f o r t h e noon p r o f i l e . The p r o f i l e has decreased n o t i c e a b l y a t 10 mb and below w i t h i n 6 hours.
This behavior i s consistent w i t h t h e CEO behavior noted i n r e f . 26.
Measurements o f C l O N O 2 have been reported by Zander e t a l . ( r e f . 27) a t 31N f o r May 1985 f o r the Atmospheric Trace Molecular Spectroscopy (ATMOS) experiment. The observed p r o f i l e has peak mixing r a t i o s between 10-20 mb, w i t h decreasing values above and below, and it i s i n good q u a l i t a t i v e agreement w i t h the model The peak mixing r a t i o i s about 30 percent higher than t h a t f o r t h e
results.
model a t noon.
However, u n c e r t a i n t i e s o f 54 percent are quoted f o r t h e data
( r e f . 27). Mid-stratosphere d i s t r i b u t i o n o f c o n s t i t u e n t s The d i s t r i b u t i o n of 03 and N205 on t h e 10 mb pressure surface o f t h e Northern Hemisphere i s shown i n f i g s . 5 and 6 f o r e a r l y February conditions. These r e s u l t s are selected f o r a disturbed period t o i l l u s t r a t e t h e i n t e r a c t i o n between dynamical and chemical processes. The e v o l u t i o n o f a s t r a t o s p h e r i c sudden warming which occurred during t h i s period has been described by Blackshear e t a l . ( r e f . 131. Minimum ozone concentration ( 5 ppmv) occurs i n the p o l a r vortex, which i s displaced from t h e pole and elongated toward 9OW. The p o l a r vortex i s flanked on the l e f t by an i n t e n s i f y i n g Aleutian anticyclone and on the r i g h t by a weaker, secondary anticyclone over t h e A t l a n t i c .
The
r e g i o n o f low ozone concentration w i t h i n t h e p o l a r vortex has been drawn o u t and wrapped about t h e region where the anticyclone has i n t e n s i f i e d . Note t h e large m a t e r i a l tongue ( i n d i c a t e d by the darkened arrow on f i g . 5) being drawn d i r e c t l y across the pole between t h e main vortex and t h e f l a n k i n g anticyclone. Both t h e q u a l i t a t i v e features and the mixing r a t i o l e v e l s a r e c o n s i s t e n t w i t h t h e behavior noted i n LIMS observations f o r t h e January 1979 warming event b y Leovy e t a l . ( r e f . 28). I s e n t r o p i c diagnostic analysis o f these r e s u l t s has been conducted t o i n t e r p r e t the i n t e r a c t i o n s between chemistry and dynamics b y Turner e t a l . ( r e f . 29). I n the zonal mean, the ozone tendency increases during t h i s p e r i o d a t h i g h l a t i t u d e s (poleward o f 50N), p r i n c i p a l l y i n response t o h o r i z o n t a l advection w i t h weak opposition by chemical destruction. Three-dimensional diagnosis reveals t h a t the increase i n ozone concentration a t high l a t i t u d e s i s p r inc ipa 1l y associated w i t h quas i-hor izonta 1 (on isentropic s u r f aces ) transport, l a r g e s t i n the r e g i o n denoted by t h e darkened arrow ( r e f . 11).
1033
Fig. 6. Dinitrogen pentoxlde mlxing r a t i o (ppbv) a t the 10 mb pressure l e v e l o f Northern Hemisphere, February 7.
10
n
I
I
I
I
I
0
30
60
8
N I
E 6
Y) L
0 F
v
E
-0
4
0
N
0 Z
2
0 -90
-60
-30
Latitude (deg)
Fig. 7.
(10”
L a t i t u d i n a l v a r i a t i o n o f the column abundance o f nltrogen dioxlde 22.5E (Local noon), February 7.
CIII-*),
1034 The N2O5 d i s t r i b u t i o n shown i n f i g . 6 i s a l s o t h e r e s u l t o f t h e i n t e r a c t i o n between dynamics and chemistry.
I n c o n t r a s t t o ozone, however, N 2O5 has a much
shorter l i f e t i m e a t these l e v e l s of t h e stratosphere ( r e f . 2). The highl a t i t u d e d i s t r i b u t i o n o f N2O5 i s much influenced by t r a n s p o r t i n t o and o u t o f t h e p o l a r n i g h t . A i r parcels e n t e r i n g the confluence r e g i o n between t h e main vortex and t h e Aleutian anticyclone (near 70E) tend t o have a low l e v e l o f N2O5 as a r e s u l t o f p h o t o l y s i s i n the s u n l i t atmosphere. A i r parcels e n t e r i n g the confluence region subsequently c i r c u l a t e about t h e Aleutian anticyclone, experiencing increased production of N 205 i n t h e p o l a r n i g h t (note the maximum near 60N, 120W) or e l s e they c i r c u l a t e about t h e main vortex e v e n t u a l l y entering s u n l i g h t where much o f t h e N2O5 i s photolyzed. A t lower l a t i t u d e s , t h e d i s t r f b u t i o n is, t o a l a r g e extent, a f u n c t i o n o f t h e d i u r n a l photochemistry. Minimum mixing r a t i o s o f N2O5 I < 0.5 ppbv) occur near l o c a l sunset (approximately 101E). Mixing r a t i o s increase eastward and westward w i t h a maximum o f approximately 2.9 ppbv near 4 0 N , 4W o c c u r r i n g j u s t before sunrise. Solomon and Garcia ( r e f s . 30 and 31) have demonstrated t h a t the highl a t i t u d e production o f N2O5 i n t h e p o l a r n i g h t i s t h e key element i n t h e development o f the so-called "Noxon c l i f f " ( r e f . 32) i n which t h e column o f NO2 experiences a sharp decrease over a small l a t i t u d i n a l extent during winter. The NO2 column shown i n f i g . 6 corresponds t o the N 205 d i s t r i b u t i o n shown i n f i g . 7 f o r model day February 7. The NO2 column i s shown as a f u n c t i o n o f l a t i t u d e along t h e meridian a t 22.5E ( l o c a l noon). Note t h a t t h e sudden decrease i n t h e NO2 column poleward o f 4 0 N corresponds t o t h e increasing gradient i n N2O5 concentration a t these l a t i t u d e s (see f i g . 6 ) . Thus, N2O5 acts as a r e s e r v o i r f o r sequestering odd-nitrogen i n the p o l a r n i g h t . CONCLUDING REMARKS Some selected r e s u l t s from a three-dimensional, g l o b a l atmospheric chemistry/transport model have been presented f o r t h e s t r a t o s p h e r i c ozone layer. The r e s u l t s are g e n e r a l l y encouraging and compare favorably, i n most instances, w i t h both observations and 2-D models w i t h comparable treatments of t h e r e l e v a n t chemistry. The r e s u l t s suggest t h a t t h e o f f - l i n e t r a n s p o r t approach i s a useful, v i a b l e a l t e r n a t i v e t o a 3-0 model with f u l l y i n t e r a c t i v e r a d i a t i o n , chemistry, and dynamics. A complete assessment o f t h e v a l i d i t y o f such models i s d i f f i c u l t because o f t h e lack o f simultaneous, long-term, .global measurements o f the species and meteorological variables.
1035 REFERENCES World Meterological Organization, "Atmospheric Ozone 1985: Global Ozone Research and Monitoring Project." Report No. 16, (19861. 2. 6. Brasseur and S. Solomon, Aeronomy o f the Middle Atmosphere. D. Reidel and Co., Dordrecht, Holland. (19841. 3. D.G. Andrews, J.R. Holton, and C.B. Leovy, Middle Atmosphere Dynamics, Academic Press Inc., New York, NY, (19871. 4. B.G. Hunt, Mon. Wea. Rev., 97, (19691, 287-306. 5. 0. Cunnold, F. Alyea, N. P h i l l i p s , and R. Prinn, J. Atmos. Sci., 32, (19751, 170-194. 6. D. Cunnold, F. Alyea, and R. Prinn, PAGEOPH, 118, (19801, 329-354. 7. M.E. Schlesinger and Y. Mintz, J. Atmos. Sci., 36, (19791, 1325-1361. 8. J.D. Mahlman, H. Levy 111, and W.J. Moxim, J. Atmos. Sci., 37, (19801, 655-685. 9. R.J. Kurzeja, K.V. Haggard, and W.L. Grose, J. Atmos. Sci., 41, (19841, 2029-2051. 10. 0. C a r i o l l e and M. Deque, J. Geophys. Res., 91, (19861, 10825-10846. 11. W.L. Grose, J.E. Nealy, R.E. Turner, and W.T. Blackshear, i n 6. Visconti and R. Garcia (Eds.), Transport Processes i n t h e Middle Atmosphere, D. Reidel and Co., (19871, 229-250. 12. J. Mahlman and W. Moxim, J. Atmos. Sci., 35, (19781, 1340-1374. 13. W.T. Blackshear, W.L. Grose, and R.E. Turner, Quart. J. Roy. Met. SOC., 113, (19871, 815-846. 14. B.J. Hoskins and A.J. Simmons, Quart. J. Roy. Met. SOC., 101, (19751, 637-655. 15. W.B. DeMore, M.J. Molina, S.P. Sander, D.M. Golden, R.F. Hampson, M.J. Kurylo, C. J. Howard, and A.R. Ravishankara, JPL P u b l i c a t i o n 87-41, Jet Propulsion Laboratory Pasadena, CA, (19871. 16. R. Garcia and S. Solomon, J. Geophys. Res., 88, (19831, 1379-1400. 17. J.C. G i l l e and J.M. Russell 111, J. Geophys. Res., 89, (19841, 5125-5140. 18. J.M. Russell I 1 1 ( E d i t o r ) , MAP Handbook, 22, (19861. 19. L.B. C a l l i s , M. Natarajan, and J.M. Russell 111, Geophys. Res. Lett., 12, (19851, 259-262. 20. J.C. G i l l e , J.M. Russell 111, P.L. Bailey, E.E. Remsberg, L.L. Gordley, W.F.J. Evans, H. Fischer, B.W. Gandrud, A. Girard, J.E. Harries, and S.A. Beck, J. Geophys. Res., 89, (19841, 5179-5190. 21. J. Austin, R.R. Garcia, J.M. Russell 111, S. Solomon, A.F. Tuck, J. Geophys. Res., 91, (19861, 5477-5485. 22. L.B. C a l l i s , M. Natarajan, R.E. Boughner, J.M. Russell 111, and J.O. Lambeth, J. Geophys. Res ., 91, (19861, 1167-1198. 23. R.L. DeZafra, A. Parrish, J. B a r r e t t , and P. Solomon, J. Geophys. Res., 90, (19851, 13087-13090. 24. K.V. Chance and W.A. Traub, J. Geophys. Res., 89, (19841, 11655-11660. 2 5. J. London, i n M. N i c o l e t and A.C. A i k i n (Editors), Proc. o f t h e NATO Advanced Study I n s t i t u t e on Atmospheric Ozone: I t s V a r i a t i o n and Human Influences, Aldeia das Acoteias, Portugal, October 1979, U.S. Dept. o f Transportation, Washington, D.C., 1980, pp. 31-44. 26. J.W. Waters, R.A. Stachnik, J.C. Hardy, and R.F. Jarnot, Geophys. Res. Lett., 15, (19881, 780-783. 27. R. Zander, C.P. Rinsland, C.B. Farmer, L.R. Brown, and R.H. Norton, Geophys. Res. Lett., 13, (19861, 757-760. 28. C.B. Leovy, C.-R. Sun, M.H. Hitchman, E.E. Remsberg, J.M. Russell 111, L.L. Gordley, J.C. G i l l e , and L.V. Lyjak, J. Atmos. Sci., 42, (19851, 230244. 29. R.E. Turner, W.L. Grose, W.T. Blackshear, and R.S. Eckman, Proc. Quad. Ozone Symp., Gottingen, FRG, August 1988, (submitted f o r p u b l i c a t i o n ) . 30. S. Solomon and R. Garcia, J. Geophys. Res., 88, (19831, 5229-5239. 31. S. Solomon and R. Garcia, J. Geophys. Res., 89, (19831, 5497-5501. 32. J.F. NOxon, J. Geophys. Res., 84, (19791, 5067. 1.
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T.Schneideret al. (Editors),Atmospheric Ozone Research and its Policy Implications 1989 Elsevier Science Publishers B.V.,Amsterdam - Printed in The Netherlands
1037
CATALYTIC CONTROL OF HYDROCARBONS IN AUTOMOTIVE WHAUST
H. S. GANDHI and M. SHELEF Research Staff, Ford Motor Company, P . O . Box 2053, Dearborn, Michigan 48121 U.S.A.
ABSTRACT Hydrocarbons in the atmosphere participate in a series of complex reactions leading to the formation of oxidant and therefore their emission is subject to stringent environmental control. The principal means for the control of hydrocarbons from mobile sources is catalytic removal. The catalytic reactivity of hydrocarbons varies widely with their chemical structure, the exhaust composition and the composition of the catalyst. The paper describes the intricate relationship between these factors and explains the processes taking place on the catalyst surface. INTRODUCTION The control of oxidants in the atmosphere which are considered injurious to the environment is based principal
oxidant
generated by These
in
on
the
automotive vehicles
species
are
control of
the atmosphere
is
their precursors.
ozone.
The
The
ozone precursors
are hydrocarbons and nitrogen oxides.
participants
in
a
complex set
transformations which lead to the formation of ozone.
Of
of
atmospheric
these precursors,
nitrogen oxides are considered to be injurious to the environment in their own right as well, while the hydrocarbon emissions
because of
their
are subject
to control
involvement in atmospheric processes resulting in the
formation of photochemical smog and ozone. aromatic hydrocarbons, benzene on
It must
also be
noted that
the one hand and polycyclic aromatic
hydrocarbons on the other, are considered to be adverse to human health and their emissions are undesirable. There are
two sources of hydrocarbons emissions from vehicles equipped
with spark-ignited engines. The vented into
first
source are hydrocarbons
the atmosphere without passing
and are the result of fuel evaporation. controlled by
that are
through the combustion chamber The evaporative emissions are
making the fuel delivery system as leakproof as possible and
by installing absorbent traps which soak-up fuel vapors when the vehicle is at rest or during
idling.
These vapors
are redirected into the air-fuel
stream going to the engine when the vehicle is in a cruising or accelerating mode,
1038 The composition of the evaporative emission is reflective of the more volatile components of the fuel i.e. C4, C5 and c6 alkenes and single ring
aromatics i.e.
alkenes and
benzene, toluene, xylenes and trimethylbenzene
(ref. 1). The second source, of processes are
interest here, which is controlled by catalytic
the hydrocarbons
exiting
from
hydrocarbons originate in part from uncombusted the exhaust
stroke and partly from
residual hydrocarbons
stem
tailpipe.
fuel molecules
from
front in
emerging in
of the
emission system.
the unavoidable presence of small
spaces and other locations in the engine cylinder which are the flame
These
the transformation of these molecules
either in the engine cylinders or in the hot part These
the
inaccessible to
the combustion process such as crevices. oF1 films and in addition
Thus,
hydrocarbon species
in the fuel, the exhaust hydrocarbons introduced into
the catalyst will contain measurable
to
over
70 or
engine deposits.
amounts of
identifiable
so
lighter hydrocarbons not
present in the original fuel; methane, ethane, ethylene, acetylene, propane, propylene and of partially
oxygenated species.
mostly C1-C3 aldehydes and
benzaldehyde, with minute amounts of ketones. Because
of
the
removal of
equipped cars, oxygenated fuel octane enhancers.
These
are
lead
fuels designated for catalystincreasingly used as
tertiary C4 and C5 ethers and short chain
alcohols, mainly methanol and ethanol. operating on
from
additives have been
The catalyst feed gas
from vehicles
fuel containing oxygenated octane enhancers will contain such
species and somewhat elevated amount of aldehydes derived
from the alcohols
in the fuel. The task of the
catalytic converter
is to oxidize all the hydrocarbon
species, including partially oxygenated molecules, to
carbon
dioxide and
water as completely as possible under all operating conditions.
The present
emission standard in the U.S. for hydrocarbons is
(0.25 g/km)
which is
roughly equivalent to 90% reduction compared
vehicle in 1974. g/mile
0.41 g/mile
In present
day vehicles,
hydrocarbons when measured
Procedure driving cycle.
to an uncontrolled
the feed gas will
contain 2-3
over a specially designed Federal Test
Therefore, the overall catalyst
efficiency should
85-90% and be maintained over a long use of the vehicle, presently 50,000 miles (80.000 km).
be
upwards
of
Tightening of the standards to 0.25 g/mile has duty vehicles
been adopted
for light
in California for 1991, which makes the task of the catalyst
still more demanding.
1039 PRINCIPLES OF CATALYST OPERATION In early
catalyst-equipped cars, the removal of hydrocarbons and carbon
monoxide was accomplished in a exhaust by
an
large excess of
auxiliary air pump.
oxygen
supplied
The catalyst contained platinum and
palladium as the active elements, finely dispersed on a high support. mostly
1-Al2O3.
sensors and electronic
Modern catalyst-equipped cars are controlled by feedback to maintain the engine combustion at
the amount of oxygen required to
molecules to water and from
surface area
to stoichiometry, where the air supplied to the engine is
conditions close equivalent to
to the
the engine has
stoichiometry.
convert all
an overall composition which
The
is also close to
residual uncombusted hydrocarbons and
monoxide, which is a product of partial oxygen left over from
the fuel
As a result, the exhaust emerging
carbon dioxide.
the carbon
combustion, are balanced by the
the engine combustion and by nitric oxide formed at
high engine temperatures by the reaction of air nitrogen and oxygen. The present-day catalyst is conditions in order
nitric oxide to Cop, water condition of catalyst
designed
to
operate at
stoichiometric
to convert simultaneously the CO, hydrocarbons and
300-700.C
and molecular nitrogen.
the equilibrium
strongly accelerates the
rate
At
the operating
favors this conversion and the at which
this equilibrium
is
attained. The denomination of such a catalyst is three-way catalyst or TWC. In actual vehicle
operation, the air/fuel ratio oscillates about the
stoichiometric value at frequencies of 0.5-5.0 Herz. extends to
the
fuel-rich side of
partially removed by
When this oscillation
stoichiometry, the hydrocarbons are
reaction with water vapor
in the
exhaust (steam
reforming) which yields hydrogen and Cog. The hydrocarbon removal reactions are:
+ n)
4%
+
2%
+ 4d20
(4m
+
02 + 4mC02+ 2nH20 (oxidation) 2mC02
+
(4m
+
n) H2 (steam reforming)
(2)
The removal of carbon monoxide proceeds in parallel by oxidation to C02 and by
the water
gas shift reaction which is analogous to steam reforming
and leads also to C02 and hydrogen when stoichiometry.
Nitric oxide
the A/F
ration shifts rich of
is reduced either to molecular nitrogen, the
desirable product, or to ammonia by the small amounts of hydrogen present in the exhaust or generated by water-gas shift and steam reforming.
1040 The catalytically active noble metals in TWC's are platinum, palladium and rhodium in varying proportions which depends on the prospective application. The high surface alumina is modified by various stabilizers such as oxides of cerium, lanthanum and barium and other modifiers such as nickel oxide. The role
of rhodium
is mainly
to catalyze selectively the conversion of
nitric oxide to molecular nitrogen in the presence
of partial
pressures of
oxygen which usually exceed those of nitric oxide. The overall performance of the automotive TWC in the removal of oxidant precursors (hydrocarbons) will depend in a complex way on several variables: catalyst composition, residence
time, composition
of
the hydrocarbons,
presence of catalyst poisons, the redox potential of the gas,
inhibition by
other gas constituents, etc. EFFECT OF HYDROCARBON COMPOSITION The catalytic reactivity of hydrocarbons is atmospheric reactions which lead double
and
to
triple carbon-carbon
oxidant bonds
akin to their reactivity in formation. Hydrocarbons with
are
The hydrocarbons
hydrocarbons are less so.
reactive while
in
the
raw
saturated
engine exhaust
contain 20-30% saturated hydrocarbons, depending on fuel composition. reactivity of alkanes increases with chain length (ref. 2). most inert methane
is
species as not
it is
included
in atmospheric reactions.
in emission
standards
for
The
Methane is the For that reason, hydrocarbons
in
California. As a
consequence of
the differing catalytic reactivity of hydrocarbons,
their composition in the
tail pipe
differs considerably
from that
at the
inlet to the catalyst. The tailpipe contains proportionately less aromatics and olefins and more paraffins.
As the emissions standards have become more
stringent, the overall catalyst efficiency has risen and the proportion of saturated hydrocarbons has risen in parallel.
In the time span from 1975 to
1982, the weighted proportion of alkanes in tail pipe emission has increased from 46 to 708, the proportion of olefins has decreased that of
from 21
to 11% and
aromatics from 28 to 18%. The increase of methane was, as would be
expected, the steepest from 7.0 to
24%
(ref. 1).
Thus,
the
10-15% of
hydrocarbons that escape the catalytic treatment are the least reactive part and will accordingly contribute little vehicles designed to meet
0.25 g
methane can be expected to be with
fresh highly
active
hydrocarbons can attain
oxidant
formation.
In future
HC/mile, the proportion of non-reactive
still higher. catalysts,
- 50% (ref. 3).
the stringent regulations if the total hydrocarbons.
to
Indeed,
in vehicles equipped
the proportion of methane to total It will
be very
difficult to meet
the non-reactive methane is not excluded from
1041
The catalytic reactivity of benzene approximates that of the average catalytic reactivity of all exhaust hydrocarbons and its proportion in the tail pipe hydrocarbons remained fairly constant from 2.5 to 3.5% in vehicles from the 1975 model year
to
1982.
The catalyst
is very
efficient in
oxidation of polynuclear aromatic compounds. In the numerous investigations aimed at
the evaluation of automotive
catalysts, the reactive hydrocarbons are usually represented by
ethylene or
propylene and the non-reactive by propane. EFFECT OF CATALYST COMPOSITION in TWC, platinum, palladium
The three noble metals
and rhodium are all
quite active for the oxidation of olefins and aromatics under conditions prevailing
in automotive exhaust.
In one
the operating
study of olefin
oxidation (ref. 4), the specific activity series is given as Pt>Pd>Ir>Ru>Rh. The activity for the oxidation of the slow-burning Ci-Cg alkanes was studied by Yao (ref. 5), both on massive metallic surfaces in the form on supported catalysts.
Large crystallites of noble
supported catalysts are expected wires.
to behave
of wires and
metals in sintered
catalytically similar
to metal
On Pt the catalytic activity increases very sharply with the alkane
chain length in the C1-C4 range, approximately one each increase
in carbon number.
order of magnitude for
The reaction rate is inhibited by excess
oxygen in the reacting gas. Thus, at a large excess oxygen, the rate of methane is higher
than on
Pt wire.
length on Pd is less steep than on faster on
Pt.
oxidation of
Pd wire
Because the dependence of reactivity on chain Pt, propane
and butane
are oxidized
Rhodium wire behaves similarly to Pd wire but the activity Large excess of 02
for each hydrocarbon is lower by one order of magnitude. does not inhibit the reaction of Pd or Rh wires. The
strong effect
related to the metals.
of
oxygen excess
on
thermodynamic stability of
The surfaces
the activity of Pt surface is the
surface oxides
of noble
of Pd and Rh are covered by an oxide layer even at a
slight oxygen excess in the gas
phase and
this coverage
is independent of
increased oxygen concentrations. Platinum oxide is mush less stable and the extent of
the coverage of
Pt by
surface oxygen
concentration of oxygen in the gas phase. active than the metallic
increases with
is especially prominent
surface which
the
The oxidized surface is less in the
oxidation of the least reactive hydrocarbon, methane. It
can be
generalized
that, with
the possible
oxidation, the activity for oxidation of wires or
small
exception of methane
saturated hydrocarbons on
large supported metal crystallites is Pt>Pd>Rh. As mentioned, the
incorporation of rhodium is necessitated by its selectivity in the reduction
1042 of nitric oxide.
Its role in the removal of hydrocarbons is associated with
its high activity in the steam reforming reactions (ref. 6 & 7). EFFECT OF NOBLE KETAL DISPERSION The extent of dispersion of the noble metal over the support is dependent on the nature of
the metal
the surface area of
and support, the metal loading with respect to
the support, the treatment temperature and
the redox
potential of the gas phase at that temperature. It is
stability of the ionic species (higher oxidation
the thermodynamic
states) of the noble metals that determines the metals over
oxide supports.
The
stable higher oxidation states than Pt under
oxidizing conditions at high
dispersion of
and maintain
their high dispersion
temperature.
With increased metal
loading, the dispersion decreases. The metal crystallite under reducing conditions.
the noble
metals. Pd and Rh, have more
less noble
growth is faster
The modification of the support surface by the
addition of ceria to high-surface 7-Al203 stabilizes the highly dispersed. non-crystalline, ionic state of the noble metals. If the treatment under
oxidizing conditions, calcination, is carried out
below 600'C,
the dispersion of Pt and Pd, the noble metals responsible for
hydrocarbon
oxidation, is high
for both
metals.
At higher calcination
temperatures the Pd is still resistant to sintering while the dispersion of Pt
decreases and
metallic
crystallites are
stabilizes the dispersion of both
noble
formed.
metals with
Addition of ceria the effect
of the
stabilization of the Pd dispersion being larger than on Pt dispersion. It has been repeatedly noted in
the evaluation of hydrocarbon oxidation
activity that under the conditions of operation of automotive catalysts, the oxidation of
the fast-burning olefins and aromatics is not dependent on the
dispersion of the noble metals. species, it
is
advantageous to
practice the oxidation of
Therefore,
for
the oxidation of these
maintain a high dispersion.
reactive hydrocarbons
Thus, in
is "structure" insensitive
although at lower temperatures such sensitivity has been noted (ref. 8). The oxidation of short-chain saturated hydrocarbons is, on the other hand, very much dependent on catalysts (ref.
5).
the
dispersion of
the noble metal
in supported
The larger crystallites of noble metals have a higher
specific activity for the oxidation of C1-Cs paraffins.
Depending
on the
hydrocarbon, noble metal, and conditions, the crystallites or metal wires may have a specific activity exceeding that of highly-dispersed noble metals by several orders of magnitude.
Platinum crystallites are more active than
Pd or Rh crystallites parallelfng the activity
of metal
wires discussed
above. The effect
of increased metal dispersion on the oxidation of slow-burning
hydrocarbons is immediately apparent from Figure 1. The figure shows
1043
directly
that
the activity for
strongly inhibited by the addition of 3.7%
containing 0.07% Pt/-y-A1203 is ceria.
the oxidation of propane of a catalyst
The influence of ceria
is to maintain the high initial dispersion
and to prevent the agglomeration of Pt into discrete particles. would enhance
the structure-insensitive reactions such as oxidation of CO
and nonsaturated hydrocarbons, it does
strongly
saturated hydrocarbons.
al.
oxidation at 250'C particle
While this
Tokoro at
inhibit
the oxidation of
(ref. 9 ) . have studied propane
over supported Pt and simultaneously measured the average
size and
found out
that
':I
the increase
in particle
size
is
accompanied by a sharp rise in specific activity i.e. the turnover number. 0
Increasing the average particle size from 20
to
> 1000 A increases the
turnover number by two orders of magnitude.
Y 4 0
L
P 20
0 100
I
200
300
400
500
TEMPERATURE(-1
Fig. 1 Conversion of propane on a 0.07% Pt catalyst support on 1-Al2O3 with and without 3.7% ceria; 1000 ppm C3H8, 2% 02. If the temperature is lowered to permit the measurement of rates structure sensitivity is observed even burning propylene
(ref. 8).
At
130'
low reaction
for the oxidation of fast
the specific reaction rate for the
oxidation of propylene increases sharply when the average Pt particle 0
The absence of the effect of crystallite
size increases from 11 to 144 A.
size on the oxidation of olefins and aromatics above 250'C, range of
interest to
the temperature
automotive catalysis, is apparently due to the fakt
that at these temperatures, the intrinsic surface reaction for the oxidation of
fast burning hydrocarbons is
faster than transport processes such as
diffusion. The structure sensitivity of depends very
much on
the nature
the oxidation of
Saturated hydrocarbons
of catalyst and of the hydrocarbons.
The
1044
oxidation of
n-butane on
supported rhodium was found
to be structure in-
sensitive in contrast to the NO-H2 reaction (ref. 10). It is plausible that the structure sensitivity is
dependent more
on the
oxidation state of the noble metal particles than on their size per se.
As mentioned before, small noble metal
particles are
oxidized under strongly oxidizing conditions and that determines their lower activity. structure sensitivity
in hydrocarbon
it
More work oxidation
more likely to be
is
this circumstance
is needed
over
to study the
noble metals
as a
function of chain length, dispersion, and temperature. EFFECT OF EXHAUST COMPOSITION The exhaust gas composition will influence the oxidation of hydrocarbons in several ways. inhibits the
Firstly, the presence of carbon monoxide
oxidation of hydrocarbons by competing for active sites of the
hydrocarbons. The retarded by
and nitric oxide
oxidation of
the presence
slow-burning, saturated
of carbon monoxide, aromatics
hydrocarbons is
and olefins. The
temperature of removal of saturated hydrocarbons is pushed
upwards when the
more reactive species are also present in the gas stream.
This is important
for the light-off performance of the catalyst. the feedgas
to the
It is beneficial to control
catalyst for obtaining satisfactory conversion of the
slow burning hydrocarbons during light off. Nitric oxide is also adsorbing on atmosphere.
the
catalytic
sites
in
an oxidizing
The inhibition of propylene conversion by nitric oxide can be
very pronounced as seen in Fig. 2.
It is shown that a five-fold increase in
the concentration of nitric oxide shifts the conversion curve to much lower space velocities (ref. 11). oxidation of
Nitric
oxide
is
also
known
CO and hydrocarbons over Pt and Pd wires.
to
inhibit the
The effect of NO on
the light-off behavior of vehicle catalysts is small since during cold start NO concentrations are low.
Space Velocity, Literq(min)(gm cot.)
Fig. 2 Inhibition effect of nitric oxide on propylene conversion at 550'F.
1045
As
mentioned
above, under
reducing conditions the steam
reactions contribute to the conversion of reforming activity
is very
the TWC is active while Pt
the hydrocarbons.
reforming The steam
dependent on catalyst composition. Rhodium in and Pd
inactive (ref. 6).
are relatively
The
steam reforming activity is vulnerable to poisoning by traces of lead. The large amounts of water vapor and carbon dioxide have minimal effect. Excess oxygen accelerates the oxidation of reactive hydrocarbons noble metals and
on all
inhibits the oxidation of saturated hydrocarbons on Pt
crystallites and wires. Finally. the
small amounts of sulfur dioxide will
in generally inhibit
somewhat the oxidation of hydrocarbons on noble metals at temperatures below 500'C
(ref. 2).
The inhibition will be much more
other noble metals because
pronounced on
Pt than on
SO2 chemisorbs on platinum to a greater extent
than on other noble metals. The catalytic behavior is completely altered, however, when supported on an oxide
capable of
forming a
adsorbing sulfur trioxide. Both 1-Al2O3 and CeO2
surface
the Pt is
sulfate layer by
chemisorb sulfur trioxide
and form sulfate groups on the surface. These groups can cover a portion of the exposed surface of ?-A1 (ref. 12).
The catalytic oxidation of
SO2 to
SO3 is structure sensitive in a manner similar to the catalytic oxidation of small saturated hydrocarbons. Platinum has long been known to
be much more
active in SO2 oxidation than other metals (ref. 13) and it is the Pt present as crystallites (or massive metallic Therefore, the
surface of
a
form)
that
is catalytically active.
supported catalyst
is
sulfated much more
effectively if it contains Pt which is not very highly dispersed. It has been noted that the presence of gases containing
20 ppm
SO2 in mixture with other
saturated hydrocarbons, such as propane, and excess oxygen
reacting over a Pt
catalyst
oxidation of
saturated hydrocarbons
the
supported on 1-Al2O3 strongly promotes the (ref.
14).
This promotion is
associated with the creation of new catalytic sites on the junction between the Pt particles
and
the
surrounding sulfated surface of the 1-Al2O3.
Without sulfur dioxide in the gas stream the catalyst oxidizes propylene and propane in two distinct
steps, the propylene reacting at temperatures much
below those at which propane is oxidized. The addition of 20 ppm of
SO2 to
the gas
In the
stream equalizes
the reactivity of propylene and propane.
absence of SO2 there is a large disparity
in the
activity of
Pt catalysts
with different metal loadings for propane oxidation. Addition of SO2 levels out these
activity differences and strongly enhances the activity of all
catalysts (Fig. 3).
1046
Fig. 3 Percentage conversion as a function of temperature for C3Hg oxidation over three Pt/l-A1203 catalysts of different Pt concentrations. The surface aluminum sulfate and sulfur elevated temperatures and
trioxide itself are unstable at
low oxygen partial pressures.
606-C or so. the enhancing effects of SO2 on hydrocarbon catalysts may
not be
observable.
Therefore above
oxidation over Pt
Neither will the effect be noted on
catalysts with a very high metal dispersion. DE-ACTIVATION OF CATALYSTS FOR HYDROCARBON OXIDATION Because the oxidation of hydrocarbons, in particular the carbon number
oxidation of low
alkanes, is structure sensitive it is also more vulnerable to
deactivation by poisons than the oxidation of carbon monoxide (ref. 15).
As
the catalyst is gradually deactivated in prolonged use the activity for the oxidation of C1-C5 alkanes will be amounts of
residual lead
in the
lost
first.
fuel is
The
presence
of small
in particular injurious for this
activity (ref. 16). Here, again the ability of Pt crystallites to oxidize sulfur an indirect,
residual lead. The sulfur trioxide formed interacts with the lead sulfate.
lead to form
Small amounts of lead sulfate do not deactivate the surface
of a noble metal catalyst. an oxide
dioxide has
important effect on the catalyst resistance to deactivation by
or when
it forms
On the other hand, when the lead is
present as
an intermetallic compound with the noble metal,
the deactivation is severe (ref. 17). Due to their composition and their range susceptible to
deactivation by
of
operation, TWC's
residual lead.
When
are more
operating near
stoichiometry, the amount of oxygen present is small and the SO2
+
1/2
O2c*SO3
equilibrium
is
shifted to
formation probability of lead sulfate.
the
left, minimizing the
1047
As the regulations require long term durability at very high hydrocarbon conversion it is necessary to protect the catalyst from contamination. The noble metal composition, state of noble metal dispersion. composition of the high-surface area support will have an effect on the ability of the catalyst to remove the oxidant precursors from the exhaust and to achieve the goal of maintaining a desirable air quality. REFERENCES 1. J. E. Sigsby at al.. Environ. Sci. Technol., 21, 466 (1987). 2. J. T. Kummer, Prog. Energy Combust. Sci., 6, 177 (1980). 3. T. Kornieki. and J. Butler. Ford Motor Company, Private Communication (1988). 4. N. W. Cant, and W. K. Hall, J. Catal, J&, 220 (1970). 293 (1980). 5. Y-F Y. Yao, Ind. Eng. Chem. Prod. Res. Dev., 6. H. S. Gandhi. et al., SOC. Aut. Eng. Paper 770196 (1977). 7. C. J. Kim, J. Catal.. 12. 169 (1978). 8. L. K. Carballo and E. E. Wolf, T. Catal.. 2,366 (1978). 9. Y. Tokoro et al., Nippon Kagaku Kaishi u, 1646 (1979) C.A. 2:180367f. 10. H. C. Yao, Y-F Y. Yao, and K. Otto, J. Catal., Id, 21 (1979). 11. S. E. Voltz et al., Ind. Eng. Chem. Prod. Res. Develop., u, 294 (1973). 12. R. H. HamnerIe and K. Kikkor, SOC. Aut. Eng. Paper 750097 (1975). 13. G. C. Bond, "Catalysis By Metals", Academic Press, London and New York 1962. 14. H. C. Yao, H. K. Stepien and H. S. Gandhi, J. Catal., 62, 231 (1981). 15. H. Shelef, K. Otto and N. C. Otto, Adv. Catal., 2,311 (1978). 16. W. B. Williamson et al., Ind. Eng. Chem. Prod. Res. Dev., 21, 531 (1984). 17. H. S. Gandhi et al., Surf. Interf. Anal.. 6. 148 (1984).
u,
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