Atmospheric Pollution: 15th: International Colloquium Proceedings (''Science of the Total Environment'')

ATMOSPHERIC POLLUTION 1982 Other volumes in this series 1 Atmospheric Pollution 1978 edited by M.M. Benarie 2 Air ...

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ATMOSPHERIC POLLUTION 1982

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. Jsrgensen 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. M6sz6ros 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. Jsrgensen and I . Johnsen 15 Disposal of Radioactive Wastes by Z . Dlouhq 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 HeemstraLequin and W.F. Tordoir 19 Physicochemical Methods for Water and Wastewater Treatment edited by L. Pawlowski

Studies in Environmental Science 20

ATM0sPHER IC POLLUTION 1982 Proceedings of the 15th International Colloquium, UNESCO Building, Paris, France, May 4-7,1982 Organised by the lnstitut National de Recherche Chimique Appliquie, Vert-le-Petit, France, in association with the Commission on Atmospheric Environment of the International Union of Pure and Applied Chemistry (IUPAC), the World Health Organization (WHO), the Gesellschaft fur Aerosolforschung (GAeF) and the Fraunhofer Gesellschaft (FhG) edited by

Michel M. Benarie

These papers have been published as a special issue of The Science of the Total Environment, Volume 23, 1982

ELSEVIER SCIENTIFIC PUBLISHING COMPANY Amsterdam - Oxford - New York 1982

E L S E V I E R S C I E N T I F I C P U B L I S H I N G COMPANY Molenwerf 1, P.O. B o x 21 1, 1000 A E Amsterdam, The Netherlands Distributors for the United States and Canada:

E L S E V I E R SCIENCE P U B L I S H I N G C O M P A N Y INC. 52, Vanderbilt Avenue N e w York. N.Y. 10017

ISBN 0-444-42083-5 (Vol. 2 0 ) ISBN 0-444-41696-X (Series)

0 Elsevier Scientific Publishing Company, 1982 A l l rights reserved. No p a r t of this publication m a y be reproduced, stored in a retrieval system or transmitted in any f o r m or by any means, electronic, mechanical, photocopying, recording or otherwise, w i t h o u t t h e prior w r i t t e n permission o f t h e publisher, Elsevier Scientific Publishing Company, P.O. B o x 330, 1000 A H Amsterdam, The Netherlands Printed in The Netherlands

V

PREFACE Why a c o l l o q u i u m ?

I n t h e s e t i m e s o f an i n f o r m a t i o n e x p l o s i o n , o f a

mushrooming number o f s c i e n t i f i c j o u r n a l s , and when we a r e a t t h e t h r e s h o l d o f e l e c t r o n i c p u b l i s h i n g , why g a t h e r p e o p l e t o g e t h e r , a t c o n s i d e r a b l e expense and

loss o f t i m e f o r them, s i m p l y so t h a t t h e y n a y l i s t e n t o o r a l p r e s e n t a t i o n s ? I can p u t f o r w a r d two reasons.

The f i r s t reason i s d e r i v e d f r o m my v i e w t h a t t h e purpose o f a l l s c i e n t i f i c communication i s i n t e r a c t i o n .

To i n t e r a c t means t o spread o n e ' s own ideas,

r e s u l t s , e t c . , as w i d e l y as p o s s i b l e

t o g a t h e r i n as many comments, c r i t i -

cisms, novel p o i n t s o f view and, perhaps, applause as p o s s i b l e .

I f a measure

o f t h e " s t r e n g t h o f i n t e r a c t i o n " can be o b t a i n e d f r o m t h e number o f r e f e r e n c e s t o work done and p u b l i s h e d , t h e n I can propose some c o n c l u s i o n s I have o b t a i n e d from examining a sample o f papers w i t h i n t h e f i e l d o f t h e atmospheric e n v i r o n ment.

I n any paper, on average, t h e papers most f r e q u e n t l y quoted a r e those of

t h e author himself, t h e so-called self-references.

Second i n frequency a r e

r e f e r e n c e s t o papers o r i g i n a t i n g f r o m t h e same l a b o r a t o r y , work group o r i n s t i t u t e as t h e a u t h o r .

Then f o l l o w , w i t h about t h e same frequency, r e f e r e n c e s

t o a u t h o r s who c o - p a r t i c i p a t e d w i t h i n t h e p r e v i o u s 10 y e a r s a t a c o l l o q u i u m o r o t h e r k i n d o f m e e t i n g and r e f e r e n c e s t o papers t h a t appeared i n t h e same j o u r n a l as t h e a u t h o r ' s paper i s p u b l i s h e d . Please do n o t s m i l e a t t h e frequency o f s e l f - r e f e r e n c e s .

They a r e n o t

Nobody i s n e a r e r t o t h e r e c e n t h i s t o r y o f a v e r y

evidence o f a u t h o r s ' v a n i t y .

s p e c i f i c t o p i c , t o a g i v e n t r a i n o f t h o u g h t s , t o t h e p a r t i c u l a r method o f i n v e s t i g a t i o n o f a s c i e n t i s t , than the author himself.

With t h i s i d e a i n mind,

i t i s c l e a r t h a t t h e above-mentioned o r d e r o f f r e q u e n c i e s o f r e f e r e n c e s , i . e .

s e l f , group, c o - p a r t i c i p a n t ,

same j o u r n a l , s i m p l y express t h e i n c r e a s i n g l y

l a r g e r s e t s o f s c i e n t i s t s who a r e i n v o l v e d w i t h , understand, and a r e i n t e r e s t e d i n , t h e work t h a t t h e a u t h o r i s c u r r e n t l y doing.

This order o f reference

f r e q u e n c i e s proves how e f f e c t i v e l y a c o l l o q u i u m enhances s c i e n t i f i c i n t e r a c t i o n . I n o u r s p e c i f i c s i t u a t i o n , when t h e Colloquium papers a r e a t t h e same t i m e a s p e c i a l volume o f The Science o f t h e T o t a l Environment, a well-known and w i d e l y a v a i l a b l e j o u r n a l i n t h e . f i e l d , t h e d i f f u s i v e i n t e r p e n e t r a t i o n o f ideas i s even more enhanced. The second reason why people come t o a c o l l o q u i u m i s so t h a t t h e y can f o l l o w o r t a k e p a r t i n t h e d i s c u s s i o n s , t h e remarks, and t h e q u e s t i o n s which f o l l o w each o r a l p r e s e n t a t i o n .

U n f o r t u n a t e l y , t h e p r e s e n t volume, f o r t h e

convenience o f t h e p a r t i c i p a n t s , had t o be ready a t t h e opening o f t h e Colloquium, and t h u s c o u l d n o t i n c l u d e t h e d i s c u s s i o n s h e l d d u r i n g t h e

Colloquium i t s e l f . Such discussions are nevertheless a very e s s e n t i a l component of any meeting. Every author l e f t the podium enriched with some suggestion o r , a t l e a s t , with t h e i m p l i c i t judgement of a p o l i t e b u t sparse applause not followed by any p e r t i n e n t question - perhaps because h i s work o r h i s manner of presentation f a i l e d t o arouse s u f f i c i e n t i n t e r e s t . No j o u r n a l , no r e f e r e e , no e d i t o r i a l committee i s able t o a c t as such a multiheaded, e f f e c t i v e , and quick j u r y . Vox populi, vox Dei. Why t h i s colloquium? My s t a r t i n g point i s once more t h e information explosion. Every year new s u b - s p e c i a l i t i e s and sub-sub-specialities a r e born. There a r e s p e c i f i c gatherings, not only f o r atmospheric modellers, b u t a l s o separately f o r urban, f o r meso-scale, f o r long-range, e t c . modellers. Every atmospheric p o l l u t a n t , whether i t be sulphur, nitrogen, p e s t i c i d e s , o r n i t r o samines, draws together i t s s p e c i a l i s t s somewhere. Aerosol science i s branching out i n t o a dozen t o p i c s , each one with i t s annual, or even more frequent, meeting . Ours i s a h o l i s t i c approach. The divergences r e s u l t i n g from growing s p e c i a l i z a t i o n require increased e f f o r t s i n synthesis. Our purpose i s t o draw together individual s c i e n t i s t s who a r e in danger of becoming c l o i s t e r e d within t h e i r narrowly limited f i e l d . We wish t o t r y a n d maintain l i n k s , develop a common language, s t r e s s points o f common i n t e r e s t , and f u r t h e r i n t e r a c t i o n among t h e ever-widening branches of atmospheric environmental science. New shoots nourish a t r e e , b u t they cannot support themselves in t h i n a i r without a sustaining stem. A t a time when science i s looking with more and more accuracy a t l e s s and l e s s , we must a l s o s u s t a i n t h e s p i r i t of t h e whole. To f u l l y understand t h e p a r t s of our subject we must occasionally t r y and look a t the whole in a s p i r i t of comprehensiveness. Such an approach i s the basis of the scope of The Science of the Total Environment. This h o l i s t i c tendency notwithstanding, we a r e always receptive t o new extensions. Since i t s beginnings, a i r pollution science has been urban-

industrial/temperate-zone o r i e n t a t e d .

The problems were the most acute and

t h e most perceptible in t h i s geographical context. Now, gradually, we a r e becoming increasingly aware t h a t a r i d and t r o p i c a l regions a l s o have t h e i r problems. We a r e almost t o t a l l y ignorant about wet-subtropical a i r chemistry. The t r o p i c a l agroindustry i s an enormous, d i f f u s e source of a i r p o l l u t a n t s . Last, b u t not l e a s t , t h e problems of d e s e r t a i r have barely been touched. Therefore, a s f i r s t point on our programme t h i s y e a r , we included a session dealing with the pollution problems of hot and d e s e r t regions, and we hope t o follow t h i s topic u p i n a f u t u r e Colloquium i n more depth. covered in t h e programme were:

The o t h e r topics

w - Atmospheric flow and dispersion; modeling.

-

Health e f f e c t s , i n d u s t r i a l hygiene and t h e control of a i r pollution in

industry. - Aerosols: t h e i r c h a r a c t e r i z a t i o n , techniques of measurement. - Aerosol physics.

-

Air chemistry; wet and dry deposition of p o l l u t a n t s . Field r e s u l t s ; monitoring and surveys. This volume contains t h e accepted papers selected from the 80 t h a t were submitted t o t h i s 15th International Colloquium held in t h e Palais des C0ngrS.s ( P o r t M a i l l o t ) i n P a r i s . The international character of the meeting i s evident from the o r i g i n o f the papers received. They were contributed by s c i e n t i s t s from 22 countries.

Michel

BENARIE

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CONTENTS

Preface .............................................................

V

POLLUTION PROBLEMS OF HOT AN0 DESERT REGIONS Air pollution i n t r o p i c a l areas E. Sanhueza, M. African0 and J . Romro

.......................

3

Trends i n ozone concentrations i n Jerusalem E . H . Steinberger .............................................

11

Background continental ozone l e v e l s i n the rural U.S. Southwest desert T.E. Hoffer, R.J. Farber and E.C. E l l i s ......................

17

Atmospheric contamination of archeological monuments i n t h e Agra Region ( I n d i a ) J.S. Sharrm and D . N . Sharma ..................................

31

Air monitoring program i n Saudi Arabia T. Husain and S.M. Khan ......................................

41

A study of physocochemical c h a r a c t e r i s t i c s of r e s p i r a b l e dust i n an Indian coal mine N.S. Rawat ..................................................

47

Contamination of s o i l s and plants by m r c u r y . a s influenced by t h e proximity o f i n d u s t r i e s i n Alexandria, Egypt I.H. Elsokkary ..............................................

55

Study of atmospheric p o l l u t i o n i n an urban zone deprived o f measurement systems, f o r purposes of l e g i s l a t i o n application t o t h e c i t y o f Tunis M.C. Robe and J . Carbonnelle ............................... 61 MODELING Atmspheric dynamics of NO, emission controls A . Eschenroeder .............................................

71

S i t e and season-speci f i c variations of the atmospheric p o l l u t a n t t r a n s p o r t and deposition on the local and regional s c a l e G. Neumann-Hauf and G. M a l b r i t t e r ...........................

91

Daily forecasting of a i r pollution p o t e n t i a l A. Joukoff and L.M. Malet ...................................

97

The forecasting method of a i r pollution peaks developed and used i n t h e Nord-Pas-de-Calais area P. Allender a n d J . M. Dejardin .............................

103

A

Turbulent d i f f u s i v i t i e s and deposition c o e f f i c i e n t s : application t o calm wind conditions P.J.H. B u i l t j e s ...............................................

107

Measurement o f turbulence p r o f i l e s i n t h e boundary l a y e r and observations o f atmospheric diffusion by smoke plumes emitted near t h e ground and i n a l t i t u d e D. Schneiter .................................................

119

A comparison o f numrical models f o r c a l c u l a t i n g dispersion from accidental releases of p o l l u t a n t s D.W. Pepper, R.E. Cooper and A.J. Baker ......................

127

Detection and impact prediction of hazardous substances released

t o the atmosphere E . E . P i c k e t t , R.G. Whiting and H . L . Kocchiu

..................

141

Modeling p o l l u t a n t dispersion w i t h i n a tornadic thunderstorm D.W. Pepper ..................................................

151

The influence of the emission height on the meso-scale a n d longrange t r a n s p o r t o f reactive p o l l u t a n t s M. Benarie ...................................................

163

HEALTH EFFECTS

-

POLLUTION CONTROL

Mortality and a i r pollution -- lessons from s t a t i s t i c s F.W. L i p f e r t ..................................................

175

Opposite e f f e c t s o f inhaled cadmium microparticles on mouse suscept i b i l i t y t o an airborne b a c t e r i a l and airborne viral infection G . Bouley, C. Chaumard, A.-M. Quero, F. Girard and C. Boudene.. 185 Genetic f a c t o r s and acute carbon monoxide i n t o x i c a t i o n M. S t u p f e l , A. Perramn, V.-H. Demaria-Pesce, P . Merat, V. Gourlet and H . Thierry .....................................

189

Water analogue m d e l achieves optimal design o f furnace f l u e gas c o l l e c t i o n system J . Rigard and M. Milhe ........................................

197

Fluoride deposition through p r e c i p i t a t i o n and leaf l i t t e r i n a boreal f o r e s t i n the v i c i n i t y o f a phosphorous plant S.S. Sidhu ....................................................

205

Study of t h e working of a new multicell scrubber applied i n the f i g h t against pollution L. Perdreau, S . Djerid, C. Belin, A. Laurent and J.-C.Charpentier

215 AEROSOLS Application o f thermal analysis t o the characterization of organic aerosol p a r t i c l e s E . C . E l l i s and T. Novakov .....................................

227

On the problem o f measuring and analysis of chemically changed miner a l f i b e r s i n t h e environment and i n biological materials K.R. Spumy ................................................... 239

XI

Formation o f monodisperse l e a d a e r o s o l s and i d e n t i f i c a t i o n o f p a r t i c l e number c o n c e n t r a t i o n by i c e n u c l e a t i o n Y . Ueno, D.E. Rosner, Rosa G. de Pena and J.P. H e i c k l e n ........ 251 O p t i c a l o b s e r v a t i o n d u r i n g chemical r e a c t i o n s H . S t r a u b e l ....................................................

259

Comparison among s i x d i f f e r e n t i n s t r u m e n t s t o determine suspended p a r t i c u l a t e m a t t e r l e v e l s i n ambient a i r J.G. Kretzschmar and J . B. Pauwels

.............................

265

Some uses o f a d i l u t e r f o r a e r o s o l s J.-C. Guichard .................................................

273

F o r m t i o n and e v o l u t i o n o f s u l f a t e and n i t r a t e a e r o s o l s i n plumes C. Seigneur, P. Saxena and A. B e l l e Hudischewkyj ............... 283 Photography as a t e c h n i q u e f o r s t u d y i n g v i s u a l range T.E. H o f f e r , D.E. Schorran and R.J. F a r b e r

293

E x p e r i m e n t a l s t u d y o n t h e v i s i b i l i t y i n a b s o r b i n g media H. Horvath, J . G o r r a i z and C. Johnson

305

Changes i n l o c a l p l a n e t a r y albedo by a e r o s o l p a r t i c l e s H. Grass1 and M. Newiger

313

.....................

..........................

.......................................

Laser t r a n s m i s s o m e t e r - - a d e s c r i p t i o n P.H. Lee, T.E. H o f f e r , D.E. Schorran, E . C . E l l i s and J.W. Moyer

.

B i p o l a r charge e q u i l i b r i u m f o r s p h e r i c a l a e r o s o l s ( minimum f l u x hypothesis ) C.S. L i u , S . Davisson and J.W. Gentry ..........................

321

337

SURVEYS and tXlNITORING

The t h i r d dimension i n t h e Los Angeles B a s i n R.J. Farber, A.A. Huang, L.D. Bregman, R.L. Mahoney,D.J. L.D. Hansen, D.L. B l u m n t h a l , W.S. K e i f e r and D.W. A l l a r d

Eatough,

............ 345

C h a r a c t e r i z a t i o n o f a l o c a l a e r o s o l on a r u r a l s i t e o f t h e Po V a l l e y S. F u z z i , M. M a r i o t t i and G. O r s i

...............................

361

Comparison o f r e g i o n a l and temporal t r a c e substance d i s t r i b u t i o n i n b u l k p r e c i p i t a t i o n and atmospheric d u s t W . Thomas ......................................................

369

The c h e m i s t r y o f p r e c i p i t a t i o n i n r e l a t i o n t o p r e c i p i t a t i o n t y p e J.A. Warburton

..................................................

379

D a i l y measurements o f atmospheric s u l f a t e s i n P a r i s Y . Le M o u l l e c , F. Coviaux and B. F e s t y ..........................

387

S i z e , shape and e l e m e n t a l a s s o c i a t i o n s i n an urban a e r o s o l R. H a m i l t o n and G. Adie .........................................

393

Subject index Author index

........................................................ ........................................................

403

404


1

POLLUTION PROBLEMS OF HOT AND DESERT REGIONS

Some r e a d e r s w i l l f i n d t h i s s e c t i o n r a t h e r heterogeneous.

It i s .

T o p i c s such as network d e s i g n and v i s i b i l i t y , m o n i t o r i n g and c a r e o f monuments, problems i n c o a l m i n i n g and p l a n t c o n t a m i n a t i o n by mercury seem t o be enmes hed. The common t r a i t l i n k i n g a l l these t o p i c s t o g e t h e r i s c l i m a t e o r , more a c c u r a t e l y , t h e ambient temperature g o v e r n i n q t h e phenomena.

Some elements

o f c l i m a t e , such as wind o r t u r b u l e n c e , have always been seen as s t r o n g l y influencing a i r pollution.

Temperature was c o n s i d e r e d more o r l e s s o f

secondary importance and t h e d i s t i n c t i o n between temperate, a r c t i c a i r c h e m i s t r y was seldom e v e r made. a i r c h e m i s t r y " seems t o be n o n - e x i s t e n t .

tropical or

The s p e c i a l i t y o f " t r o n i c a l T h i s c h a p t e r i s perhaps a modest

beginning t o r e c t i f y t h i s s i t u a t i o n .

A f u r t h e r p o i n t t o be s t r e s s e d i s t h a t owing t o h i s t o r i c a l reasons, t h e d i s c u s s i o n o f which i s beyond o u r scope here, t h e socio-economic frame of r e s e a r c h i n many t r o p i c a l c o u n t r i e s i s q u i t e d i f f e r e n t f r o m t h a t p r e v a i l i n g i n t h e temperate and c o l d zones.

Social p r i o r i t i e s , a v a i l a b i l i t y o f

adequate manpower, t h e r e l a t i v e w e i g h t o f i n v e s t m e n t i n l a b o r a t o r y f a c i l i t i e s , t h e a v a i l a b l e budgets

...

and much more, a r e d i f f e r e n t .

T h e r e f o r e , t h e answers p r o v i d e d by some o f t h e papers w i t h i n t h i s s e c t i o n w i l l n o t be those which i n t e r e s t a l l r e a d e r s .

Some papers seek avenues

o f i n q u i r y r a t h e r than a p a r t i c u l a r destination.

But i n t h i s context, i t

i s o f t e n more i m p o r t a n t t o f o r m u l a t e t h e r i g h t k i n d o f q u e s t i o n than t o p r o v i d e t h e u l t i m a t e answer.

The p o i n t i s l e s s one o f s o p h i s t i c a t i o n ,

of t h e g e o g r a p h i c a l e x t e n s i o n o f t h e f i e l d o f e n q u i r y .

What has a l r e a d y

been accomplished i n N o r t h America and Europe, must s t i l l be done f o r about 2.10

than

9 people l i v i n g w i t h i n d i f f e r e n t c l i m a t i c b e l t s .


3

A I R POLLUTION IN TROPICAL AREAS EUGENIO SANHUEZA, MABELL AFRICAN0 and JOHNNY ROMERO I.V.I.C.

Apartado 1827, C a r a c a s , Venezuela

ABSTRACT Air p o l l u t i o n problems i n t h r e e d i f f e r e n t t r o p i c a l a r e a s a r e p r e s e n t e d .

The

l e v e l s o f v a r i o u s atmospheric contaminants ( i . e . S O i ) i n d i c a t e t h a t t h e o p e r a t i o n o f a l a r g e petroleum r e f i n e r y a f f e c t s a s u b s t a n t i a l p o r t i o n o f t h e i s l a n d o f Curacao.

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 suspended p a r t i c l e s i n Curacao a r e due t o

n o n - t r a d i t i o n a l open s o u r c e e m i s s i o n s a i d e d by t h e predominantly high w i n d s p e e d s . P a r t i c u l a t e e m i s s i o n s from t h e i n d u s t r i a l complex i n Guayana, Venezuela, n o t i c e a b l y a f f e c t t h e s o r r o u n d i n g savannah.

The c o n s t a n t d i r e c t i o n o f t h e Trade Winds i s an

i m p o r t a n t f a c t o r i n t h e high long-term a v e r a g e p a r t i c u l a t e l e v e l s down-wind o f t h e complex.

A s e r i o u s atmospheric c o n t a m i n a t i o n problem ( i . e . TSP) e x i s t s i n The

Valley o f Caracas.

The high e m i s s i o n , p r i n c i p a l l y due t o t h e c i r c u l a t i o n o f v e h i c l e s ,

exceed t h e a v e r a g e d i s p e r s i o n c a p a c i t y o f t h e atmosphere.

INTRODUCTION T r o p i c s i s a term t h a t has no w e l l - d e f i n e d meaning.

I t i s g e n e r a l l y agreed

t h a t t r o p i c a l a r e a s a r e l o c a t e d between t h e 23.5 degree p a r a l l e l s .

However, some

r e g i o n s w i t h t r o p i c a l c h a r a c t e r i s t i c s a r e found a t l a t i t u d e s g r e a t e r than 23.5", and some n o n - t r o p i c a l a r e a s a r e l o c a t e d c l o s e r t o t h e Equator. Nieuwolt ( r e f . 1 ) s u g g e s t s t h a t c e r t a i n c l i m a t i c c h a r a c t e r i s t i c s can be used t o e s t a b l i s h t h e boundaries o f t r o p i c a l a r e a s .

Some o f h i s c r i t e r i a a r e :

i) t h e absence o f a c o l d w i n t e r season

i i ) a l a r g e r diurnal f l u c t u a t i o n i n temperature than t h e y e a r l y variation i n the d a i l y mean t e m p e r a t u r e ( i n t h e m i d - l a t i t u d e s t h e i n v e r s e i s t r u e ) i i i ) s u f f i c i e n t r a i n f a l l t o support a g r i c u l t u r e without i r r i g a t i o n I t i s u s u a l l y c o n s i d e r e d improbable t h a t t h e a i r i n t r o p i c a l a r e a s can become p o l l u t e d t o harmful l e v e l s .

Petersen ( r e f . 2 ) estimated t h a t t h e a i r pollution

p o t e n t i a l ( i n a b i l i t y o f t h e atmosphere t o d i s p e r s e p o l l u t a n t s ) o f most t r o p i c a l r e g i o n s i s low.

The 1972 F l o r i d a S t a t e Air Implementation Plan s t a t e s "Because o f

t h e general p a t t e r n o f t e r r a i n and t h e t r a d e wind c i r c u l a t i o n , m e t e o r o l o g i c a l condit i o n s t h a t a g g r a v a t e a i r p o l l u t i o n do not o f t e n occur a t any p l a c e i n F l o r i d a " .

4 More r e c e n t l y Ng'ang'a ( r e f . 3 ) Concluded t h a t i n t r o p i c a l r e g i o n s " a i r p o l l u t i o n may not become such a s e r i o u s problem u n l e s s o r u n t i l t h e r a t e o f i n d u s t r i a l i z a t i o n

i s dramatically increased". There a r e however a number o f examples o f p o l l u t i o n problems i n t h e t r o p i c s . G e r r i s h ( r e f . 4 ) found t h a t atmospheric c o n d i t i o n s i n " t r o p i c a l " F l o r i d a could l e a d t o s e v e r e a i r p o l l u t i o n e p i s o d e s . NOx ( r e f . 5 ) and Pb ( r e f . 6 ) l e v e l s measured i n Caracas exceed t h e a i r q u a l i t y s t a n d a r d s e s t a b l i s h e d f o r v a r i o u s c o u n t r i e s . This paper d i s c u s s v a r i o u s c i r c u m s t a n c e s under which r e l a t i v e l y l a r g e t r o p i c a l a r e a s may e x p e r i e n c e a i r p o l l u t i o n problems.

THE ISLAND OF CURACAO Curacao i s a Caribbean i s l a n d l o c a t e d a t 12"North l a t i t u d e , 56 Km from t h e South American c o n t i n e n t . 3.2 and 1 2 . 1 Km.

The t o t a l a r e a i s 466.2 Km2.

The t e r r a i n i s r e l a t i v e l y f l a t with

The average annual m e t e o r o l o g i c a l c o n d i t i o n s (1947 t o 1978)

o n l y a few low h i l l s . are:

I t i s 6 1 . 2 Km l o n g , w i t h a width t h a t v a r i e s between

t e m p e r a t u r e 27.5"C, maximum t e m p e r a t u r e 30,8"C, minimum t e m p e r a t u r e 19.8"C,

r a i n 564.2 mm, w i n d d i r e c t i o n 90°, wind speed 7.2 m/s, and wind s t a b i l i t y 96.5%. I t i s i m p o r t a n t t o mention t h a t t h e d i f f e r e n c e between t h e monthly average temperat u r e o f t h e c o l d e s t and t h e warmest month i s o n l y 2.5"C. A t h r e e month d i a g n o s t i c s t u d y was undertaken t o make a p r e l i m i n a r y assessment

of the i s l a n d ' s a i r quality.

Principal sources include a l a r g e o i l r e f i n e r y i n

S h o t t e g a t Bay and a power p l a n t ( w i t h a sea water d e s a l i n i z a t i o n p l a n t ) .

Fig. 1 is

a p a r t i a l map o f Curacao t h a t shows the p o s i t i o n o f t h e s e s o u r c e s and of t h e f i v e monitoring s i t e s .

P i s c a d e r a i s a t o u r i s t complex w i t h beaches, Wishi i s a low-

income r e s i d e n t i a l a r e a , Buena V i s t a i s a r e s i d e n t i a l a r e a , Blauw i s p r e s e n t l y empty l a n d but i t has p o t e n t i a l f o r t o u r i s t i c o r r e s i d e n t i a l development, Soltuna i s an experimental A g r i c u l t u r a l S t a t i o n . wind r o s e f o r 1973.

Figure 1 a l s o i n c l u d e s a r e p r e s e n t a t i v e

Based on t h e wind i n f o r m a t i o n , v a l u e s measured i n Soltuna a r e

c o n s i d e r e d r e p r e s e n t a t i v e o f background l e v e l s . Almost a l l o f t h e i m p o r t a n t a i r q u a l i t y p a r a m e t e r s were monitored d u r i n g t h e diagnostic study.

The l e v e l o f t o t a l suspended p a r t i c l e s r e p r e s e n t s t h e g r e a t e s t

problem and w i l l be d i s c u s s e d i n d e t a i l , i n c l u d i n g t h e chemical c o m p o s i t i o n .

This

a s p e c t i s o f i n t e r e s t t o environmental s c i e n t i s t s because o f t h e p o t e n t i a l l y hazardous n a t u r e o f c e r t a i n components and because t h e ch,emical composition can be used t o i d e n t i f y s p e c i f i c s o u r c e s . The combustion o f r e s i d u a l f u e l c o n s t i t u t e s art i m p o r t a n t s o u r c e o f primary sulfate (ref.7,8).

Since both t h e r e f i n e r y and power p l a n t burn r e s i d u a l f u e l w i t h

2% o r more S, SO; w i l l be used t o e v a l u a t e i n d u s t r i a l e m i s s i o n s .

Atmospheric l e a d

l e v e l s w i l l be used t o e s t i m a t e t h e i n f l u e n c e o f v e h i c u l a r t r a f f i c and C1- f o r t h e sea s a l t c o n t r i b u t i o n .

5

F i g . 1.

P a r t i a l Map o f Curacao

T a b l e 1 summarizes t h e r e s u l t s o f t h e TSP measurements, t h e s i z e c h a r a c t e r i s t i c s and t h e SO;,

C l - and Pb c o n t e n t .

The SO; v a l u e s have been c o r r e c t e d f o r a r t i f a c t

f o r m a t i o n o f s u l f a t e i n t h e f i b e r g l a s s f i l t e r u s i n g t h e f o r m u l a p r o p o s e d by Coutant (ref.9). T a b l e 1 shows t h a t t h e c o n c e n t r a t i o n s o f TSP, SO; and l e a d a t t h e o t h e r f o u r s t a t i o n s are s i g n i f i c a n t l y higher than a t t h e reference s t a t i o n , Soltuna. l e v e l s o f TSP and SO;

a t Wishi a r e v e r y high.

The

The l e v e l s o f C1- a r e v e r y s i m i l a r

a t a l l f i v e s t a t i o n s , s h o w i n g t h e common sea s a l t s p r a y o r i g i n . The c a l c u l a t e d e n r i c h m e n t f a c t o r s (E.F.)

f o r s u l f a t e and Pb a r e :

P i s c a d e r a (201) > Blauw ( 1 2 6 ) > Buena V i s t a ( 1 0 3 ) > W i s h i ( 8 7 ) and

EFsoi : EFpb : W i s h i ( 4 . 2 ) > Buena V i s t a ( 2 . 0 5 ) > B l a u w ( 1 . 5 ) > P i s c a d e r a (1.4)

The E F ' s were c a l c u l a t e d u s i n g EF ( i ) = ( X / T S P ) i / ( X / T S P ) s o l t u n a Where X i s t h e c o n c e n t r a t i o n s o f SO; o r Pb and i i n d i c a t e s t h e m o n i t o r i n g s t a tion. Based o n t h e EF v a l u e s and t h e d a t a i n T a b l e 1, t h e f o l l o w i n g i n f e r e n c e s c a n be made:

6

Piscadera:

T h i s s t a t i o n has the lowest l e v e l s o f TSP, one of the highest absolute

values o f s u l f a t e s and the l a r g e s t E . F . f o r s u l f a t e s . small vehicular t r a f f i c influence.

The EF f o r lead i n d i c a t e s a

Considering t h e high incidence of s u l f a t e s

associated with small p a r t i c l e s (MMO < 1.Ovm)

i t can be concluded t h a t t h i s part of

the island i s s i g n i f i c a n t l y a f f e c t e d by t h e r e f i n e r y and power p l a n t emissions.

TABLE 1 Total Suspended P a r t i c l e s , SO%, C 1 - and Pb in t h e Curacao Air Site

na

Piscadera Wishi Buena Vista B1 auw Sol tuna

6 5 5 8 2

TSP

MMD

7.2 7.2 -3.0 3 . 0 -1.5 1 . 5 -0.95 0.95-0.49 ~0.49 TOTAL a)

average of 3 days;

b)

56ma

B(a)PC 5mb

21.6 18.0 7.3 5.5 6.2 36.6

10.9 15 .O 8.6 5.7 5.2 31.6

0.18 0.094 0.11 0.083 0.10 6.99

0.096 0.094 0.102 0.079 0.102 5.88

95.2

77.0

7.56

6.35

average of 6 days. c )

x

lo3.

THE CARACAS VALLEY Caracas i s l o c a t e d a t 10.30"N and 66.7"E a t an a l t i t u d e o f 996 m above sea l e v e l i n a v a l l e y sorrounded by mountains w i t h peaks a s high a s 2600 m . The p o p u l a t i o n There a r e i s a p p r o x i m a t e l y 2.5 m i l l i o n w i t h a c a r d e n s i t y o f %I000 vehicles/Km

.

v e r y few i n d u s t r i e s .

The a v e r a g e t e m p e r a t u r e r a n g e s from 18" t o 23°C.

Almost

e v e r y day, a t e m p e r a t u r e i n v e r s i o n forms i n t h e v a l l e y a t n i g h t and b r e a k s u p between 10 and 11 i n t h e morning. Previous p a p e r s have shown t h a t t h e p r i n c i p a l a i r p o l l u t i o n problems i n Caracas a r e r e l a t e d t o the a t m o s p h e r i c c o n c e n t r a t i o n o f primary p o l l u t a n t s ( r e f . 5 , 6 , 1 9 ) . Since t h e i n v e r s i o n b r e a k s u p b e f o r e noon a l l the s t e p s condusive t o t h e p r o d u c t i o n o f p r i n c i p a l components i n t h e c l a s s i c a l photochemical smog do n o t o c c u r . The r e p o r t e d l e v e l s o f TSP a r e r e l a t i v e l y h i g h .

The annual geometric mean f o r Since t h e formation

t h e sampled y e a r i n downtown Caracas was 95.7 ug/m3 ( r e f . 2 0 ) .

o f l a r g e amounts o f secondary p a r t i c l e s i s n o t p r o b a b l e , most o f t h e suspended p a r t i c l e s found were e m i t t e d t o t h e atmosphere (mainly by v e h i c u l a r c i r c u l a t i o n ) . I t i s o f i n t e r e s t t o i n v e s t i g a t e the s i z e d i s t r i b u t i o n o f t h e p a r t i c l e s .

Using a high volume c a s c a d e impactor t h e p a r t i c l e s i z e o f suspended p a r t i c u l a t e has been d e t e r m i n e a t two d i f f e r e n t h e i g h t s (5 and 56 m ) . The B(a)P c o n t e n t a l s o has been e v a l u a t e d .

Table 2 summarizes t h e r e s u l t s .

Ta bl e 2 shows t h a t s i m i l a r r e s u l t s a r e o b t a i n e d a t both h e i g h t s .

This i n d i c a t e s

t h a t t h e suspended p a r t i c l e l e v e l s based on a 24 hour c o l l e c t i o n p e r i o d a r e independent o f t h e sampling h e i g h t .

Hence i n Caracas t h e r e i s r a p i d t u r b u l e n t mixing

d u r i n g the p e r i o d o f most abundant e m i s s i o n ( t r a f f i c ) . The lognormal f u n c t i o n i s w i d e l y used t o r e p r e s e n t t h e size d i s t r i b u t i o n o f the p a r t i c l e s t h a t compose t h e a t m o s p h e r i c a e r o s o l s ( r e f . 2 1 ) . Figure 2 shows the r e s u l t s o f t h i s s t u d y p l o t t e d on a l o g p r o b a b i l i t y s c a l e .

The MMD's o b t a i n e d

9 compare w e l l w i t h t h o s e f o r o t h e r c i t i e s ( r e f . 2 1 ) . l i n e a r i t y f o r p a r t i c l e s g r e a t e r t h a n 3 . 0 pm.

There i s a marked l o s s o f

T h i s i m p l i e s t h a t i n Caracas t h e r e

i s a s i g n i f i c a n t source o f l a r g e p a r t i c l e s o t h e r t h a n combustion sources.

Most

p r o b a b l y t h e l a r g e p a r t i c l e s a r e e m i t t e d f r o m n o n - t r a d i t i o n a l open s o u r c e s such as t h e c i r c u l a t i o n o f v e h i c l e s o n d u s t - f i l l e d s t r e e t s and c o n s t r u c t i o n a c t i v i t i e s . I t i s i m p o s s i b l e t o c a l c u l a t e t h e MMD o f t h e p a r t i c l e s c o n t a i n i n g B ( a ) P s i n c e

93% o f t h e m were n o t s e p a r a t e d ( p a r t i c l e s O

DQ -

kVQ.n = UnQ, l.n 1.5 urn. In some favourable cases, where analytical profiling along an extended fiber was possible, LAMMA analysis revealed that the

244

Nq-leaching was rather nonhomogeneous along the fiber axis. Very similar results could be obtained also by the application

Fig. 4. LAMMA spectra (mass spectra) for positive ions obtained from standard UICC asbestos fibers

(+)

and negative

Fig. 5. Element spectra obtained by bukl analysis of chrysotile and crocidolite fibers.Virgine material ( 1 ) and after extraction in H C 1 solution (2).

245

Yi

: A BINDINC ENERGY. EV

PROBE 2 UTE ERHCILTEN DETRIL

183.5 EV IKORRIGIERTI

ISILIKRT, 5102 U.RC.1

02s

B 0

-225

-200

-175

-150

-125

-108

-75

-58

-2s

e

BIHDIHC EHERCY, EV

6. Analyses of small amounts of chrysotile fibers by ESCA: standard UICC chrysotile before (A) and after ( B ) extraction in HC1 solution. Differences in the element composition are evident.

Fig.

246

Fiq. 7. Scanninq electron microqraph of fine q l a s s fibers (type JM 104) used in animal experiments.

23

2a

LO

No

dl

Ca

15L

00 G

HH Sr

157

d Fiq. 8. LAMMA spectrum for positiv ions of one single fiber. The method is very sensitive (ppm and ppb range).

Pig. 9. SEM-micrographs and element spectra of single glass fibers: XRF analyses of original fibers ( I ) , EDXA analysis of single fibers ( 2 - 4 ) after an exposition (5 years) in rabbit lungs.

Fig. 10. XRF bulk analysis of glass and slag fibers: original probe ( 1 ) and after exposition in H C 1 solutions (2). The leaching effect is very evident.

248

of TEM + EDXA + SAED or also in some cases of SEM + EDXA. TEY can be used for the observation and analysis of very thin (fiber diameter < 0.1 urn) fibers, while the LAMMA-method is limited for fibers with a diameter of with a diameter

>

0.2 pm. Also SEM

+

EDXA is limited for fibers 0.2 urn. A fast extraction of Yg and other elements >

from chrysotile in acids can be also followed by XRF (Figure 5.: bulk analyses). Not only AF, but also PDDlF, primarily qlass fibers, can be changed chemically under different environmental conditions and after long residence in animal tissue. Our experimental results with glass fibers have shown that these inorganic fibers undergo similar chemical and physical changes as do chrysotile fibers. They are not resistant to basic solutions, they lose some elements (e. g. Na, K, Ca, Zn) upon exposure to acids and their surface becomes corroded. Changes of chemical composition have been found in glass fibers after 5 years deposition in animal tissue (instillation experiments done on rabbits). Analysis by LAMMA revealed that also in glass fibers a preferential leachinq of elements occur. But also the original chemical composition as well as the leaching of elements in glass fibers are inhomogeneous. Analyses done along the fiber axis demontrate that their chemical composition was different at different locations of the same fiber. Similarly, the chemical leaching of glass fibers was not constant for all fibers, but differed from one fiber to another. These conclusions are also documented by some examples of analyses done by LAMMA, SEM + EDXA and XRF (Figures 7-10.).

CONCLUSION Both AF and MYMF are chemically not inert when subjected to different environmental conditions or when measured in biological liquids. The proved analytical methods seem to be suitable for the analyses of fiber bulks as well as for the analyses of single fibers.

249

REFERENCES F. Pott, Staub-Reinhalt.Luft 38(1979)490-494. M.C. Jaurand, J. Bignon, P. Sgbastien and J. Goni, Environ.Res. 14(1977)245-251. 3 N. Kohyama, K. Kawai, S. Aita, M. Suzuki and H. Hayashi, Ind.Health (Japan)15 (1977)159-1 68. 4 A. Morgan, P. Davies, J.C. Wagner, G . Berry and A. Holmes, Brit.J.Exp.Pathol.58(1977)465-479 5 J. Harrington, A.G. Allison and D. Badami, Adv.Pharmacol.Chemother.12(1975)291-403. L.D. Palekar, C.M. Spooner and D.C. Coffin: Ann.N.Y.Acad.Sci.330 (1979)673-687 H. Tiesler, Glastechn.Ber.54(1981)136-143 and 369-381. K.R. Spurny, W. Stober, G . Weiss and H. Opiela, Atmos.Pollution 8 (1980)31 5-322 9 K.R. Spurny, J. Schormann and R . Kaufmann, Fresenius 2.Anal.Chem. 308(1981)274-279. 10 H. Malissa and J.W. Robinson, Analysis of Airborne Particles by Physical Methods. CRC Press 1nc.Palm Beach,FL,USA(1978) 1 2


251

FORMATION O F MONODISPERSE L E A D AEROSOLS AND IDENTIFICATION O F P A R T I C L E NUMBER CONCENTRATION BY I C E NUCLEATION

YASUO UENO* a n d DANIEL E . ROSNER D e p a r t m e n t of E n g i n e e r i n g a n d Applied S c i e n c e , Y a l e U n i v e r s i t y , 9 H i l l h o u s e Avenue, New Haven, Connecticut 06511, U . S. A. ROSA G . d e P E N A D e p a r t m e n t of M e t e o r o l o g y , T h e P e n n s y l v a n i a S t a t e U n i v e r s i t y , U n i v e r s i t y P a r k , P e n n s y l v a n i a 1 6 8 0 2 , U . S. A. JULIAN P. HEICKLEN D e p a r t m e n t of C h e m i s t r y a n d A e r o c e n t e r f o r E n v i r o n m e n t , 152 Davey L a b o r a t o r y , The Pennsylvania State University, U n i v e r s i t y P a r k , P e n n s y l v a n i a 16802, U. S. A.

ABSTRACT L e a d a e r o s o l s w e r e g e n e r a t e d t o i n v e s t i g a t e the conditions f o r the f o r m a t i o n of m o n o d i s p e r s e a e r o s o l s in n i t r o g e n s t r e a m . A e r o s o l s of high m o n o d i s p e r s i t y could b e o b t a i n e d by v a p o r i z i n g l e a d a t a t e m p e r a t u r e i n the r a n g e of 1000° t o 1150°C a n d by flowing n i t r o g e n at a r a t e of 1. 5 l l m i n . In o r d e r to p r o d u c e "lead iodide a e r o s o l s " p o r t i o n s of the l e a d a e r o s o l s w e r e conducted into a t e s t c h a m b e r i n which the a t m o s p h e r e of iodine vapor had previously been p r e p a r e d . T h i s m i x t u r e containing the a e r o s o l s with low c o n c e n t r a t i o n w a s m o d e r a t e l y s t i r r e d u n d e r d i f f e r e n t t e m p e r a t u r e s . "The l e a d iodide a e r o s o l s " w e r e s a m p l e d with a s y r i n g e to be i n j e c t e d T h e a e r o s o l s injected into a m o d i f i e d B i g g ' s t e s t d e v i c e f o r i c e nucleation. r a p i d l y changed into i c e c r y s t a l s , which could g r o w in s i z e . A s the n u m b e r of i c e c r y s t a l s could give t h a t of l e a d iodide a e r o s o l s , the r e a c t i v i t y of l e a d a e r o s o l s with iodine v a p o r w a s i n v e s t i g a t e d u n d e r v a r i o u s t e m p e r a t u r e s . An i n c r e a s e in t e m p e r a t u r e d u r i n g the a g e i n g of l e a d a e r o s o l s with iodine vapor promoted t h e i r reactivity.

INTRODUCTION F o r m a t i o n of h e a v y m e t a l a e r o s o l s ( l e a d e. g. ) with m o n o d i s p e r s e s i z e d i s t r i b u t i o n is of g r e a t i m p o r t a n c e to inhalation toxicology e x p e r i m e n t s or air pollutionlaerosol studies. In t h i s p a p e r , p h y s i c o - c h e m i c a l c o n s i d e r a t i o n i s given on the m e c h a n i s m of l e a d a e r o s o l f o r m a t i o n a n d t h e conditions f o r the f o r m a t i o n of m o n o d i s p e r s e a e r o s o l s a r e experimentally investigated. F u r t h e r e x p e r i m e n t s h a v e a l s o b e e n p e r f o r m e d o n the f o r m a t i o n of "lead iodide a e r o s o l s " b y u s i n g g a s - s o l i d i n t e r f a c e r e a c t i o n between iodine vapor 'KPresent a d d r e s s : D e p a r t m e n t of C h e m i s t r y , T e x a s A & M U n i v e r s i t y , C o l l e g e S t a t i o n , T e x a s 77840.

252

and lead a e r o s o l s obtained. The e x p e r i m e n t a l r e s u l t s of t h e i r reactivity u n d e r v a r i o u s t e m p e r a t u r e s a r e evaluated by a n ice nucleation method.

EXPERIMENTAL PROCEDURES L e a d a e r o s o l s w e r e g e n e r a t e d by a condensation method. The operating t e m p e r a t u r e s and flow r a t e s for a e r o s o l generation ranged f r o m 9500 to 1150°C and f r o m 1 . 0 l i m i n to 4 . 5 l / m i n , respectively. The a e r o s o l s w e r e collected with a n e l e c t r i c a l p r e c i p i t a t o r ( r e f . 1) and thoroughly washed away with a known amount of distilled w a t e r containing a s m a l l amount of n i t r i c acid. The amount of l e a d i n the washed solution was t i t r a t e d with EDTA. The mass concentration was calculated f r o m the a e r o s o l volume having passed through the e l e c t r i c a l p r e c i p i t a t o r and the t i t r a t e d amount of l e a d ( r e f . 2 ) . P a r t i c l e s i z e distribution was a l s o m e a s u r e d by sizing and counting l o t s of p a r t i c l e s in the photos taken by e l e c t r o n m i c r o s c o p e to d e t e r m i n e a v e r a g e particle size. P a r t i c l e number concentration could be known by calculating f r o m m a s s concentration and p a r t i c l e s i z e . "Lead iodide a e r o s o l s " w e r e obtained b y introducing a s m a l l amount of l e a d a e r o s o l s for 30 seconds into a t e s t c h a m b e r , in which the a t m o s p h e r e of iodine vapor had a l r e a d y been p r e p a r e d ( r e f . 3 ) . After lead a e r o s o l s r e a c t e d with iodine vapor under m o d e r a t e s t i r r i n g , s m a l l portions of the

2 \

0 ZE

15-

z

0

2

K I-

z

10-

z 0

0 u) u)

a

5-

FLOW RATE, L/MIN

Fig.

1. Influence of flow r a t e on m a s s concentration.

253 a e r o s o l s w e r e s a m p l e d f r o m t h e c h a m b e r to b e f u r t h e r d i l u t e d i n a n o t h e r c h a m b e r , t h e i n s i d e of w h i c h w a s u n i f o r m l y s t i r r e d . T h e f i n a l dilution f a c t o r i n e a c h e x p e r i m e n t w a s 1:12000 o r m o r e by u s i n g c l e a n n i t r o g e n . A small a m o u n t of t h e a e r o s o l s t h u s d i l u t e d w a s slowly i n j e c t e d into t h e In a d v a n c e , t h e m o d i f i e d B i g g ' s a p p a r a t u s which i s shown i n F i g . 5. a t m o s p h e r e of a cold c h a m b e r i n i t w a s m a i n t a i n e d at a t e m p e r a t u r e of -10. 5' o r -7OC by s t i r r i n g c o o l t a n t i n t h e o u t e r c e l l s ( e t h y l e n e g l y c o l t d r y The t e m p e r a t u r e s of t h e c e l l s a n d t h e c h a m b e r w e r e i c e o r ethyleneglycol). frequently examined, T h e t e m p e r a t u r e s of t h e c h a m b e r w e r e c h e c k e d a t t h r e e d i f f e r e n t p o i n t s i n h e i g h t (top, c e n t e r a n d b o t t o m ) . The temperature of t h e c h a m b e r w a s d e f i n e d a t the c e n t e r w h i c h is shown i n t h e f i g u r e . About o n e m i n u t e l a t e r a f t e r i n j e c t i n g t h e a e r o s o l s , t h e y u s u a l l y s e t t l e d down onto t h e c o l d s u r f a c e of a q u e o u s s u g a r solution. T h e a p p a r e n c e of t i n y i c e c r y s t a l s a s w e l l a s t h e i r g r o w t h i n s i z e could b e o b s e r v e d t h r o u g h a t r a n s p a r e n t t h i c k window f r o m t h e c e i l i n g .

R E S U L T S AND DISCUSSION T h e i n f l u e n c e s of the flow r a t e of n i t r o g e n s t r e a m o n mass c o n c e n t r a t i o n and M a s s c o n c e n t r a t i o n and p a r t i c l e o n p a r t i c l e s i z e a r e g i v e n i n F i g s . 1 a n d 2. s i z e v a r y w i t h t h e flow r a t e of n i t r o g e n a n d t h e t e m p e r a t u r e of l e a d v a p o r . Both of t h e m r e a c h a p e a k a t a c e r t a i n flow r a t e u n d e r a n y of t h e t e m p e r a t u r e s

%

5-0.20 IW

-5

n W

0152 t U

U

a

:W

0.10

>

U

FLOW RATE, L/MIN

Fig.

2. I n f l u e n c e of flow r a t e o n p a r t i c l e s i z e .

254

f r o m 950° to 115OoC, making a c o n t r a s t to the n u m b e r concentration passing through a t r o u g h ( F i g . 3 ) . In o r d e r to calculate the h e a t of evaporation f o r f u s e d l e a d f r o m t h e s e e x p e r i m e n t a l r e s u l t s , p r o p e r a s s u m p t i o n s w e r e m a d e and Clausius -Clapeyron's Equation was applied to e x p e r i m e n t a l data in both regions of slower flow r a t e s ( 1 . 0 and 1. 5 l / m i n ) and f a s t e r flow r a t e s ( 3 . 5 and 4. 5 l / m i n ) . Table 1 In f a c t , indicates the a v e r a g e values of heat of evaporation for fused lead. The values in the table do a l i t e r a t u r e shows the value of 47 k c a l / m o l e . not always m a k e a n a g r e e m e n t with this value a s a h e a t of evaporation. T h i s i s why the calculation was m a d e on b a s i s of the a s s u m p t i o n that the efficiency of t h e r m a l precipitation of the a e r o s o l s i s constant, r e g a r d l e s s of the t e m p e r a t u r e s of f u s e d lead. In f a c t , it m a y possibly be r e a s o n a b l e that the a e r o s o l m a s s concentration in the region of s l o w e r flow r a t e s cannot always be controlled by only t h e r m a l precipitation. The t e m p e r a t u r e s f o r nuclei formation w e r e calculated u n d e r the condition of s u p e r s a t u r a t i o n r a t i o of 5 o r 10. Table 2 shows the t e m p e r a t u r e s f o r A s we can e a s i l y observe from the a p p a r e n c e of the nuclei formation. p a r t i c l e s in the photo shown in Fig. the p a r t i c l e s look round. A S the

50001

s, 0

-

0

I

I

I

1

1000 500

.

-

2-

0 + a

U

I-

2

W

50 -

100

0 2 0

0 U

10-

m

5-

W

3z W

A

0 I-

a

d

10.5

FLOW R A T E , LIMIN

Fig.

3 . Influence of flow r a t e on p a r t i c l e n u m b e r concentration.

255 TABLE 1 A v e r a g e e v a p o r a t i o n heat of f u s e d l e a d f r o m e x p e r i m e n t a l d a t a Flow r a t e ( l / m i n )

H e a t of e v a p o r a t i o n ( k c a l / m o l e )

1.0 1. 5 3.5 4. 5

31. 3 25. 1 33.4 31. 1

TABLE 2 T e m p e r a t u r e s f o r n u c l e i f o r m a t i o n b y t h e s u p e r s a t u r a t i o n r a t i o s of 5 a n d 10 T e m p e r a t u r e (OC)

Supersaturation ratio

F o r lead vapor formation

1150

5 950

10 1150

10 950

F o r nuclei formation

1020

860

980

820

5

r).

Fig.

7. L e a d p a r t i c l e s i n n i t r o g e n ( a v e r a g e d i a m e t e r 0. 11

Fig.

8. A p p a r e n c e of i c e c r y s t a l s i n a modified B i g g ' s a p p a r a t u s .

256 melting point of l e a d i s 327OC, it may be suggested that the p a r t i c l e s w e r e actually in a liquid s t a t e while they w e r e s t i l l growing by mutual collision o r coagulation a f t e r fir s t p a r t i c l e formation. L e t us a s s u m e t h a t p a r t i c l e s i z e m a y be influenced by mutual collision while the a e r o s o l s a r e in a liquid s t a t e a t high t e m p e r a t u r e s , the following equation can ba obtained.

k: rl:

p:

71

:

K:

Boltzmann constant v i s c o s i t y coefficient of nitrogen gas vapor p r e s s u r e of fused l e a d a v e r a g e t e m p e r a t u r e while p a r t i c l e formation, coagulation and growth of p a r t i c l e s a r e undergoing constant

Assuming that nitrogen i s a n i d e a l g a s , the viscosity coefficient i s i n

4

5

5

4

4

F i g . 5. Modified Bigg's t e s t device f o r i c e nucleation. 1. T h e r m a l l y insultaing m a t e r i a l , 2. Ethyleneglycol and d r y i c e , 3. Ethyleneglycol, 4. S t i r r e r , 5. Thermocouple, 6. Inlet for t e s t a e r o s o l s , 7 . Aqueous s u g a r solution, 8 , T r a n s p a r e n t window.

257

- 112 The v a p o r p r e s s u r e of fused lead i s a l s o in proportion proportion to T . to the t e r m of exp (-AH/RT)!/' T h e s e t e r m s c a n be introduced into Eq. ( 1 -112 d 3 = K ' T

( e

- b H I R T 112

1

( 2 )

i s obtained and futher t r a n s f o r m e d .

E q . ( 3 ) c a n finally be derived.

In c a s e In ( K ' 'i: ' I 2 ) is constant, t h e r e m a y be a l i n e a r relationship between In d and 1/T. The slope of s t r a i g h t line can give the value of h e a t of evaporation. Applying Eq. ( 3 ) to e x p e r i m e n t a l r e s u l t s , a plot of In d against 1 / T should be l i n e a r and this i s found to bP actually the c a s e , a s i s shown i n F i g . 4. T h e s e plots a r e a l l s t r a i g h t lines p a r a l l e l with one another a s might be expected of Eq.( 3 1. The heat of evaporation f o r fused lead has been obtained a s the value of 47 k c a l / m o l e . T h e r e h a s been a good a g r e e m e n t between the values calculated f r o m e x p e r i m e n t a l data and the l i t e r a t u r e value with r e s p e c t to heat of evaporation f o r fused lead.

I

I

I

-4.

-4

I k t3 0 -5. J

- 5. 0 2.5

/'

0 3.5 0 4.5

"

7.0

.

/,

1

I

7.5

8.0

I/T,

10-4/0~

F i g . 4. P l o t of log d a g a i n s t 1 / T .

1.

258

Fig. 6 shows the influence of t e m p e r a t u r e and flow r a t e on a e r o s o l monodispersity. T h e n u m b e r s in the f i g u r e show the m o n o d i s p e r s i t y of l e a d aerosols. A e r o s o l s of high m o n o d i s p e r s i t y could be obtained by vaporizing l e a d a t a t e m p e r a t u r e i n the r a n g e of 1000° t o 115OOC and by flowing nitrogen s t r e a m a t a r a t e of 1. 5 l / m i n . A s s o m e e x p e r i m e n t s w e r e p e r f o r m e d on i c e nucleation by using r e a l l e a d iodide a e r o s o l s g e n e r a t e d f r o m fused l e a d iodide ( r e f . 41, this p r e s e n t e x p e r i m e n t i s c a r r i e d out by u s i n g two different l e a d a e r o s o l s : d = 0. I l p ( t e m p e r a t u r e 95OoC, flow r a t e 4. 5 l / m i n , m o n o d i s p e r s i t y 0. 31) and d = 0. 78,&(temperature 1000°C, flow r a t e 1. 5 l / m i n , m o n o d i s p e r s i t y 0. 17). As a r e s u l t , i t s e e m s t h a t the c o a r s e r l e a d a e r o s o l s r e a c t with iodine to produce l e a d iodide a e r o s o l s m o r e r e a d i l y than f i n e r ones. The reactivity i s T h e a p p a r e n t h e a t of activation a c c e l e r a t e d by the t e m p e r a t u r e of reaction. could a l s o be e s t i m a t e d . F u r t h e r d i s c u s s i o n will be d e m o s t r a t e d on the effect of r e a c t i o n t e m p e r a t u r e o n t h e r e a c t i v i t y of l e a d a e r o s o l s with iodine v a p o r and t h e i c e nucleation t e m p e r a t u r e s . F i g s . 7 and 8. show t h e photos of l e a d a e r o s o l s and i c e c r y s t a l s in the modified B i g g ' s a p p a r a t u s , r e s p e c t i v e l y .

1150

-

.

1100-

036

Y 10503

I-

4

.

a w

2w

1000-

+ 951

o;. "' ;o 1 0.27

1.0 1.5

25

35

4.5

FLOW RATE, L/MIN

Fig.

6. Influence of t e m p e r a t u r e and flow r a t e on a e r o s o l m o n o d i s p e r s i t y .

REFERENCES 1. Y . 2 Y. 3 Y. 4 Y.

Ueno Ueno Ueno, Ueno,

and I. Sano, Bull. C h e m . SOC.Japan, 44(1971) 908-911. and I. Sano, Bull. Chem. SOC.J a p a n , 45(1972) 975-980. Atmos. E n v i r o n . , lO(1976) 409-413. the 56th Colloid & I n t e r f a c e Sci. S y m p . , Virginia, in J u n e ,

1982.

259

OPTICAL OBSERVATIONS DURING CHDTICAL REACTIONS

H. STRAUBEL Vorderhindelang (G.F.R.

)

AE S TRACT Droplets or solids freely suspended in a three-plate-capacitor and illuminated by a laser beam yield a characteristic diffraction pattern. Assumed an exactly shaped sphere, this diffraction pattern consists in a system of concentric equidistant fringes of equal intensity. Each deviation from geometry or/and intensity in this system indicates a change of the refractive index n. This may be effected by impurities, by a mixture of two components, by an evaporating gradient, by crystalization of solutions or by chemical reactions. Using the electrical voltages connected with the capacitor and by optical evaluating the diffraction patterns, the whole running off can be investigated.

INTRODUCTION In the atmosphere chemical reactions occur between aerosol particles f.e. NaC1, NH C1, Pe 0 in presence of anthropogenic gases such as 4 2 3 C1, SO2, NOx and H2S. Due to these very diluted gases, the reactions run off in minutes to many hours. Therefore it is impossible to investigate such reactions with usual light scattering instruments, as their retention time is shorter (ca 1/100 s) than the time required for the chemical reaction. Besides this the particle is lost having passed the device. Possible reactions are known, however, they could not yet be observed on single particles at any state. Only integral measurement with a big number of particles was possible until now. In a three-plate-capacitor, described by the author previously, droplets or single solid particles can be freely suspended for more than 100 hours, undisturbed by boundaries except the surrounding air (ref. 1 ) Illuminated by a laser beam ( A = O , 6 3 2 8 / u m ) , radii of

.

260

the droplets can be calculated by the distance of the interference fringes, provided the droplet’s shape is exact spherical. The voltages a.c. and d.c., connected with the capacitor, work as a balance. Through it changes of mass are recorded at any time. To evaluate the optical data during the chemical reaction, the process under investigation must ~ n c elead to a spherical shape of the product. (ref. 2). Only in this state it is possible to calculate the radius r of the particle. By using the spheres data as starting point, now all changes during the process can be derived forward and backward at each time. If the specific weight of the sphere is unknown, it can be determined by two different voltages at the cahacitor (ref. 3 ) .

EXPERIMENTS 1). Disturbed ring system Droplets consisting of uniform substances as f.e. water, benzene, glycerine, yield as diffraction pattern a system of concentric, equidistant fringes, easy to evaluate. Fig. 1 shows the possible interferences between the beams 1 and 2 for a transparent sphere. The path difference between 1 and 2 is defined by equation (1) with the radius r and refractive index n: n A = 2r sin Y If the sphere is containing some small impurities (non transparent, monodisperse) the fringes become disturbed and dissimilar, dependent from number and size of these impurities. Fig. 2.

Fig. 1. Possible path difference between beams 1 and 2 for a transparent sphere.

Fig. 2. Disturbed fringes by small particles inside a sphere. Diameter 1 7 , l p .

261

The particles composition was 5% MoS2 ( d< l w ) in 95 % oil. For the particles inside the droplet Rayleigh-scattering can be assumed. The same phenomena will be observed if a frozen homogeneous sphere with a shrinked surface is illuminated by a laser beam. In this case essentially the reflected beam 2 of the surface is influenced.

2). Optical inhomogeneities By suspending a clear transparent droplet in the beam, another appearence can be seen. The fringes are very fine smoothened, however, a series of different diameter, thickness and intensity spreads out in radial direction, indicating a I1modulation1lof the whole system. Fig. 3. Such a phenomenon cannot be explained by Fig. 1, as the relation between reflected and permeating beam is only valid for a uniform refractive index n. This relation is also valid during evaporation o r condensation of the droplet (diminution o r growing). However, smallest deviations of n inside the sphere lead to optical inhomogeneities which appear in the diffraction pattern.,The droplet under research was a mixture of 80% oil with 20% benzene. As the vapour pressure of benzene is higher than that Fig. 3. Modulated interference of oil, the benzene evaporates fringes due to evaporation at the surface and effects a of one component in a mixture. radial gradient of the mixture Diameter 4 2 p . inside the sphere. (noil>nbenzene). This produces a modulation of the system. By evaporation o r condensation of one component of a mixture o r by a more or less concentration of a salt solution, the same phenomenon is developped. Generally, each change inside a particle will be visible as a change of refractive index n.

3).

Chemical reaction Chemical reactions lead always to changes of n. To irivestigate this relation, fixing salt (Na2S203 5 H20) was chosen. A dry crystal freely suspended in the capacitor, is dissolved by increasing relative

262

humidity (r.h.) of the surrounding air. Pig. 4a shows the dry crystal, 4b the initial water film on the crystal's surface. Gradually the crystal is dissolved, deviations in the ring diameters 4c indicate still undissolved small crystal particles (d< 1 w ) within the droplet (d = 2 9 , 3 6 m ) . Now injecting HC1-vapour in the capacitor leads to the reaction, Fig. 4d. The fringes of the diffraction pattern break open, 4e, forming a structure like llcellslt. We detect bright and dark spots, quickly traveling. New formed products NaCl and S are separated. Electrical control of the particle's weight shows that the whole portion of H2S03 5 H20 is expelled from the droplet, Fig. 5. At last a zone of preferred forward scattering appears in the middle of the pattern, and the contours of a NaC1-crystal emerges Fig. 4f During and after the reaction we see a strong turbidity of the NaC1-solution, due to the liberated S-molecules. After a few minutes, however, the pattern is cleared, as the S-molecules have formed greater agglomerates with smaller light scattering.

.

Fig. 4 a-f. Reaction between Na S 0 2 2 3 Compare Fig. 5 and 6

5 H20 + 2 HC1

263

/ i

L

:loo "

( H,O +SO,) .5H,O

(Y

8 0,

Fig. 5. Weight changes during the reaction

4). Fluid crystals Fluid crystals are organicsubstances with a temperature-dependent opacity, but without chemical change. They are used for displays, controled by temperature or electric fields (ref.$). The so called 0 Wf3BAtf substance is solid and turbid below 21 C, however, it becomes clear above 44 OC. In this interval the molecules have only degrees of freedom for translation and rotation. They arrange in domains of 105 molecules. Due to the walls between these regions, differences in refractive index n arise. Fig. 7a shows a droplet's ring system above 44 O C . Below this temperature there are confused regions and fringes of unequal distances in droplets with 2 0 0 . This may be due to the rotational sywnetric diameters d whirling of the molecules and simultaneous changes of refractive index n.

Fig. 7.

a

above 44

OC

b

between 21 and 44

OC

264

CONCLUSIONS The described method enables the observation of smallest optical deviations in solids o r fluids, freely suspended in electric fields. By two-beam-interference it is possible to differentiate between the properties of clear o r mixed fluid-droplets and of evaporating solutions.

x

tW3BAlf N-(p-Methoxy-bemyliden)-p-n-butylanilin

REFERENCES 1 H,Straubel, in Atmospheric Pollution 1978, Proceedings of the 13th International Colloquium, Paris, France, April 25-28, 1978, M.M.Benarie (Ed.), Studies in Environmental Science, Volume 1 Elsevier Scientific Publishing Company, Amsterdam 2

H.Straube1, in Atmospheric Pollution 1980, Proceedings of the 14 International Colloquium, Paris, France, May 5-8, 1980, M.M.Benarie (Ed.), Studies in Environmental Science, Volume 8 Elsevier Scientific Publishing Company, Amsterdam

3

H.Straube1, “Elektro-optische Messung von Aerosolen” Technisches Messen 48.Jahrgang 1981 Heft 6 tm 199-210 Verlag Oldenbourg, Miinchen

4. H.Kelker, “History of Liquid Crystals”, in: Molecular Crystals and Liquid Crystals, 1973, Vol. 21, pp. 1-48, Copyright 1973 Gordon and Breach Science Fublishers, Printed in Great Britain

265

COMPARISON BETWEEN S I X DIFFERENT INSTRUMENTS TO DETERMINE SUSPENDED PARTICULATE MATTER LEVELS IN AMBIENT AIR

J.G. KRETZSCS.MAR and J.B. PAUWELS

Studiccer.trum voor Kernenergie, B-2400 Mol, Belgium

ABSTRACT Over a period of six months simultaneous suspended particulate matter measurements with two different high volume samplers, two different low volume samplers, an automated dichotomous particulate system and an integrating Nephelometer were carried out at the same semi-rural monitoring site in the vicinity of the Nuclear Energy Research Centre, Mol, Belgium.

Except for the nephelometer all SPY-deter-

minations were done gravimetrically. The entire experiment was based on the comparison of daily averages. A reasonable to good correlation was found between the different instruments although the daily levels as well as the overall statistics of the SPM-situation over a period of six months showed large deviations.

For certain instruments the

deviations seemed to be systematic. The experiment will be repeated over another period of six months in order to control the present findings.

INTRODUCTION During the past years suspended particulate matter (SPM) levels in ambient air were determined with many different systems in a rather impressive number of short term projects or more permanent monitoring networks.

This paper reports the pre-

liminary results of the intercomparison under field conditions of six different systems used or in use under the previously mentioned conditions for the determination of SPM-levels in Belgium. comparison

The aims of the project are first of all the

of individual short-term (daily averages) measurements, simultaeously

obtained under field conditions with each of the systems, and secondly the analysis of the possible influence of the choice of a specific measuring system upon the evaluation of the actual SPM-situation when collectinq a sufficient number of individual measurements, and comparing some specific statistical parameters (means, percentiles or maxima) with the specifications of air quality guidelines, recommendations or standards.

266

DESCRIPTION OF THE MONITORING SITE AND SYSTEMS Figure 1 shows the semi-rural monitoring site in the vicinity of the Nuclear Energy Centre, Mol (SCK/CEN) with the following measuring systems

1 and 1'

:

:

two versions of the high volume LIB-Filterverfahren (LIB-HI1 and LIB-HI1' as described in ref. 1).

Fig. 1. Monitoring site (SCK/CEN, Mol) with different sampling systems.

2

:

the low-volume sequential sampler of the Instituut voor Hygiene en Epidemiologie, Brussel (IHE-LO, ref. 2).

3

:

the Beckman Dichotomous Particulate Sampler (DVI-LO, refs. 3-5). ment separates the collected dust in a fine and coarse fraction.

This instru-

267 The concentration corresponding to the sum of both fractions is used in the comparison with the other systems.

4 : a low-volume version of the LIB-Verfahren (LIB-LO). 5 :the SCK/CEN high volume sampler (SCK-HI, ref. 6).

6 :the MRI Integrating Nephelometer (NEPH, not represented on fig. 1 ) .

The main characteristics of the sampling systems for the gravimetric determination of the SPM-levels are summarized in Table 1.

done on conditioned filters (20 "C, 54 averages.

% RH).

All gravimetric determinations are Reported SPM-levels are daily

For the Nephelometer analogue recording was used.

TABLE 1 Main Characteristics of the sampling systems for gravimetric determination of SPM System

Fig. 1

filter

filtered volume/day

loaden surface LIB-HI1 LIB-HI 1 ' IHE-LO DVI-LO LIB-LO SCK-HI

450 500 15 24 80 550

m3 m3 m3 m3 m3 m3

Whatman 41, Whatman 41, Sartorius, Sartorius, Whatman 41, Whatman 41,

87 cm2 77 cm2 12,6 cm2 6,6 cm2 15 cm2 104 cm2

cellulose cellulose membrane 0,45 !Jm membrane 0,80 Um cellulose cellulose

1 1' 2 3 4 5

COMPARISON OF THE SIMULTANEOUS MEASUREMENTS Over a period of six months 77 simultaneous valid determinations of the SPMlevels were obtained. day-by-day LIB-LO.

Of the six systems three showed a very good agreement on a

base namely the SCK-HI, the LIB-HI (in bath versions 1 and 1') and the

The IHE-LO sampling system Predominantly followed the pattern of these

three systems although some prolonged deviations in both directions (lower or higher) were noted during the experiment.

The dichotomous virtual impactor (DVI-LO)

systematically gave lower levels than all the other instruments while the Nephelometer (NEPH) recorded the hiqhestpeak values.

Full details of the time series of

the simultaneous measurements are given in reference 7. The results of a linear regression analysis on the simultaneous measurements of each time two different systems are summarized in Table 2 (r cient, to the left of the diagonal

;

a/b

=

=

correlation coeffi-

coefficients of the equation y = a x + b ,

to the right), while Figure 2 gives the correspondinq scatter diagrams with respect to the SCK-HI sampler.

268

0 0 N

L

I

2 _J

R=O. 95 0

0

100

0

200

100

200

SCK-HI lug/rn31

SCK-HI ( ~ g / m ~ I

7

0

0

0

100

100

0

200

SCK-HI (ug/m31 0 0

0 0

N

N

I

u

0

I

200

SCK-HI h g / m 3 1

N=77 A=O. u B=2 R = O . 66

R=O. 86 0

0

1 0

100

SCK-HI

200 (4m31

0

100

200

SCK-HI [ ~ ~ g / m ~ 1

Fig. 2. Scatter diagrams of the simultaneous measurements with respect to the SCK-HI system.

269

TABLE 2 Correlation between the different measuring systems

SCK-HI LIB-HI 1 LIB-HI 1 ' LIn-Lo IHE-LO DVI-LO NEPH

SCK-HI

LIB-HI1

LIB-HI1'

LIB-LO

IHE-LO

DVI-LO

NEPH

-

0.9/10

0.94 0.95 0.94 0.71 0.66 0.86

-

1.0/-2 1.0,'-9

0.6/44 0.7/40 0.7/47

0.4/2 0.5/-3

-

1.0/1 1.1/-8 1.0/4

0.97

-

0.6/47

0.4/0

0.76 0.77

0.73 0.74 0.90

-

0.4/-11

0.96 0.97 0.71 0.71 0.89

0.92

0.67

-

1.4,'-24 1.6/-38 1.4/-17 1.4/-22 1.3,'-45 2.0/11

0.73

0.76

-

0.5/0

Table 2 and Figure 2 confirm the very good agreement between the SCK-HI, the LIB-HI'S and the LIB-LO samplers. The Nephelometer has a good correlation with these devices too but the regression equations confirm the tendacy of the Nephelometer for too hi.gh readinqs once the SPM-levels exceed a certain value. shows an acceptable correlation (r

=

The ME-LO

0 . 7 1 to 0 . 7 6 for n = 77) with the previous

systems. With respect to SCK and LIB the regression equations show a tendacy for overestimation of the lower SPM-levels measured in this test.

The SPM-levels given

by the dichotomous virtual impact are systematically too small over the entire SPMrange, and the correlation varies between 0.66 and 0.77.

COMPARISON OF THE GLOBAL STATISTICS Cumulative frequency distributions of the 77 simultaneously obtained daily averages are given on Figure 3 for each of the systems. The main statistical parameters are summarized in Table 3. in very good agreement.

As before the LIB'S and the SCK-HI sampler are

The IHE-LO device gives a significantly larger arithmetic

average, 87 1.1g/m3 against 6 1 to 6 7 ug/m3, and larger percentiles except above P90 where the SPM-levels are within the range of the LIB'S and the SCK-HI device. This results in a smaller u

9

( 1 . 4 against 1 . 6 to 1 . 8 ) for IHE-LO.

The Nephelo-

meter gives the inverse picture namely arithmetic average and lower percentiles (beneath P80) are comparable with the LIB'S and the SCK-HI but the higher percentiles, and consequently the geometric standard deviation,are larger ( u = 2 . 4 against 9

1 . 6 to 1 . 8 ) .

On the average the results of the dichotomous virtual impactor are a

factor 2 to 2 . 5 smaller than the corresponding results of the LIB-HI, the LIB-LO and the SCK-HI.

270

/ 1.;.

SC K - H,I,,, .. ..

................ .. .. .. .. .. .. ... ... ... ... ... ... . . . . . .

. . ... ...

i..i..i...l..i..l.... .. .. .. .. .. .. I . ... .I ..

LIB-HI 1

200

100

i . .

GO 50 40

.?.H E.

.. .. . . . . . .. .. ...................... ... . ... . ... . . . . . . . . .... . . ... .. .. . . . . . . . .. .. ,............ . .......... .. ... .. . .. . .. . .. ... ... ..................... .. .. . .. ... .. . . .. .. .. . . . .... , .. . .. . ... . . ......... .. .. .. .. .. . . . . . .. .. . . . . . .. .. . . ., . .. . . ,. ..... ,. ...... .. .. ,........ .. .. .. .. .. ... ... .. . .. . .. . .. ... ... . . . . . . ;..: .: . : :.. : , . i . . I ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . . . . . . .

' ?

30

20

:

. . .. . .. .. . . . . . .. ...; . ..

"E

100

GO

50

z

ti0 30

GO 50 UO

-

:lo 50 70 85 9598 PROBRBILITY . . . .

Fig. 3.

. . . . .. . . .. . .. . . .. . . .. . .. ... . .... .. .. . .. .. .. .. .. . ... . . .. . . . . . . . .

60 50

' 7

20

:

.

l

j

110 30 20

10

I

200

) . . _ ...........

. . . . . .

100

,.:.

i

.. ... .. ... . ... .. ,:

50 70 85 9598 PROBRBILITY

Cumulative Frequency Distributions.

.I 1 0 0

.....

.....

30 .. .. .. .. .. .. .. . . , . , . , .. ...................... . . . . . . .. ... ... ... ... ... ... ... ... ... ... ... ... ... .. .. .. .. .. .. .. .. .. .. .. .. .. .. . . . . . . . j

,

m~

....... . . . . ... . .. .. .. .. .. .. .. .. .. . . . . . . . .

UO

j

.


50

j

.

.. .. . . . . . .. .. .. . . . . . . . . .....................

G O "e

"E

I

.

NEPH.?

.. .. . . . . . . . . . . .:..;..;.. . . . . .. . . .;. ..: .. .. .. :..;..: .. .. .. .. .. ... ... . .. . .. . .. . .. .. .. . . . . . . i. N. 4 7 3 i 1 .. .. .. .. . . . . . . . ... . . .... . . ... . . ... . . .. . . ... . . . . . . . . .. .. .. .. .. .. .. .. , ...... ,......, . . . . . . . . . . . . . . . . .

30

20

100

... ... ... ... ... ... ... ... .. .. .. . . . . . . . . :..:..: . :. :...:. . . .:. . . . ; ... ... . . . . . .. . . . . .. .. ... ... ... ... ... ... ... ... ... ... ... ... . .. . .. . .. .. ... ... ... ... ... ... ... ... .. .. . . . . . .. ..

DVI-LO

100

.

. , ,

i i

. . , ..... ............. .. .. .........., ............. .. .. .. .. .......................... .. .. .. .. .. .. .. .. ,. ........................... .. ... ... ... ... ... ... ... ......................... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .,. ..,.... ,........ . , ........... . . . . .. .. .. ... ... ... ... ... ., ......................... . . . . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . . . . . ;..:...;...:..;..: .. .. .. .. .. . . ... .; ... . i.. .. .. .. .. .. .. .. .. ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .. .. .. .. .. .. .. .. . . . . . . .

.

.. .. .. .. .. .. .. ..

PROBRBILITY

200

.

.. . ... . ... . .. . . . . .. . . . ... . ... . .. . .. .. . . . . . . . .. . ... ... . . . . .. . . .. . .. . . . ......................... .

"!

50 70 85 9598

LO

. . . . -.. . ... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . . . . . . .:,.:..;,..:.:..: . . . . . .. .. .. .. .. . . ... .; .... . .j.. . . . . . . . .

.

m10

10

50 70 85 9598 PROBRBILITY ,,

//

N s77

%... . . . . . . .

. . . . . . . .. .. .. . ... ... ... ... ... .. .~. . ... . ... . ... . ... . ... . ... 200 .. .. .. .. .. .. .. ..

200

:. N. =77 : I . . .. .. ..

.......................... .. . . . . . . . . . . .. .. .. .. .. .. .. .. . . . .. .. .. .. .. .. ........................ .. .. .. .. .. .. .. .. ... ... ... ... ... ... ... ... ......................... .. .. .. .. .. .. .. .. ... ... ... ... ... ... ... ... .. .. .. .. .. .. .. ..... .,. ....... . /................. . . . . . .. .. .. ... ... ... ... ... .. .. .. .. .. .. .. .. ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . . . . . . .

L I.. B. . -. .L.9.. . . . .

....... . ... ... . .

20

10

' 7

. . . . . . . .:

.. .. .. .. . .:. ... .

:.

.. .. .. .

60 "E

. . . . . . . .. .. ... . . . . . . . . . .,.... ,. ....... , ..... ;. . . j . . . . . . . .. .. .. . . . . . . :. i .. . . !.. i . .. I . ... .I .. . . ..I 30 ... ... ... ... . .. . .. .. .. .. .. .. .. .. .. :,. :...:..;..: . . . .:. . . . .: 20 . .. .. .. .. .. .. ... ... ... ... ... ... ... ... ... ... ... ... ... ... . . . . . . . .. .. .. .. .. .. .. .. .. .. .. . . . . . : 10

uo

.. ..

.


271

TABLE 3 Global statistics of the 7 7 simultaneous daily averages System

m

P50

P60

P70

SCK-HI LIB-HI1 LIB-HII' LIB-LO IHE-LO DVI-LO NEPH

66 67 61 64 87 28 69

59 59 54 58 80 24 51

65 68 58 61 89 30 63

73 72 63 67 96 33 73

with

P80 77 78 72 77 110 37 83

P90 92 98 91 90 124 47 128

m

:

arithmetic average

P50...P98

:

percentiles

max .

:

maximum value

U

:

geometric standard deviation

9

P95

P98

max

0

125 132 137 140 141 73 214

164 148 149 158 155 80 221

180 162 172 171 164 87 227

1.6 1.6 1.8 1.6 1.4 2.0 2.4

g

based on P98 and P50

These ratios are even larger than the 1.2 and the 1.8 reported for two different sites in reference 8.

It's obvious that more detailed studies of the DVI are

needed.

CONCLUSIONS The first phase of an intercomparison under field conditions of several commonly used methods for the determination of SPM-levels in ambient air leads to the following preliminary conclusions. Simultaneously determined daily SPM-levels are systematically in excellent agreement for certain sampling systems while others show random or systematic deviations.

Correlations ranged from acceptable to excellent while linear regression

techniques confirmed functional differences over the entire measured concentration range or over parts of it. Taking into account that normally the main purpose of measuring SPM-levels is to make a statement with respect to air quality recommendations, guidelines or standards, the obtained data sets of 77 simultaneous daily averages were analized from this point of view too.

If the WHO-Guidelines of 60 to 90 ug/m3 for the year-

ly average, and 150 to 230 ug/m3 for the 98-percentile of the gravimetrically determined daily average SPM-levels (ref. 9) are taken as reference this leads to the following observations. One system (DVI) gave results significantly smaller than the reference levels (approx. a factor 2).

The statistics of all the other systems

were within the specified range for respectively the mean and the 98-percentile level.

The results of the LIB'S and SCK-HI were rather around the lower limit of

the specified ranges while IHE-LO was high for the mean, low for the 98-percentile and vice versa for NEPH.

212

ACKNOWLEDGMENT This research was carried out under contract with the Ministry of Public Health.

REFERENCES 1 VDI-Richtlinien, Messen der Massenkoncentration von Partikelen in der Aussenluft, VDI 2463, August 1974. 2 IHE, Jaarrapport 1980. IHE Meetnet Zware Metalen, Brussel, 1981. 3 B.W. Loo, J . M . Jaklevic and F.S. Gouldinq, in B.Y.M. Lin (Ed.), Fine Particles, Aerosol Generation, Measurement, Sampling and Analysis, Academic Press Inc. N.Y., 1976, pp. 311-350. 4 W. John, G.P. Reisahl and J. Wesolowski, PB 80-113731, NTIS, 1978. 5 H. van Duuren, Kema 6792-79, 1979. 6 J.G. Kretzschmar, I. Delespaul and Th. De Rijck, The Science of the Total Env., 14 (1980) 85-97. 7 SCK, Onderzoek naar de niveaus van de luchtverontreiniging door Zware Metalen in Belgie, Mol, 1981. 8 R.K. Stevens et al., Atm. Env., 1 2 (1978) 55-68. 9 WHO, Environmental Health Criteria 8, Geneva, 1979.

213

SOME USES OF A DILUTER FOR AEROSOLS J.C. GUICHARD I n s t i t u t N a t i o n a l de Recherche Chimique Appliquee

-

I R C H A - VERT-le-PETIT - ( F r a n c e )

AB ST RA CT To d i l u t e an a e r o s o l i s a u n i t o p e r a t i o n which i s m m a n d n n r e f r e q u e n t i n the everyday work o f a l a b o r a t o r y o f p h y s i c s o f a e r o s o l s . We proposed a s o l u t i o n and have been d e v e l o p i n g i t s i n c e 1966. The I R C H A d i l u t i o n system i s h e r e d e s c r i b e d , and i t s main c h a r a c t e r i s t i c s are g i v e n . P r e s e n t l y commercialized, i t has p r o v e d e f f i c i e n t i n v a r i e d a p p l i c a t i o n s - a choice o f which i s h e r e o r e s e n t e d .

INTRODUCTION

To d i l u t e an a e r o s o l i s a u n i t o p e r a t i o n o f p h y s i c e n g i n e e r i n g which r e q u i r e s t o be more c a r e f u l t h a n i n t h e case o f t h e simDle m i x i n g gas-gas. T h i s s p e c i f i c c h a r a c t e r of t h e p r o b l e m o f t h e d i l u t i o n o f an a e r o s o l was d e f i n e d i n t h e l a t e 1 9 5 0 ' s and t h e c o m m e r c i a l i z a t i o n o f t h e o p t i c a l c o u n t e r s o f p a r t i c l e s has l e d t o t h e s t u d y o f o r a t i c a l systems, o a r t i c u l a r l y a t t h e I R C H A . We d e s c r i b e d t h e f i r s t " d i l u t i o n system" i n

1966 ( 1 ) and o r e s e n t e d i t t o t h e general o u b l i c t h e same y e a r ( 2 ) . That i n s t r u m e n t has r a o i d l y become an e s s e n t i a l t o o l which i s mentioned i n q u i t e a number o f o u r p u b l i c a t i o n s , f o r i n s t a n c e i n ( 3 ) where we show how u s e f u l i t can be f o r t e s t i n g a i r

f i 1 t e r s . O t h e r teams have a l s o worked on such r e a l i s a t i o n s w i t h o u t always o u b l i s h i n g t h e i r r e s u l t s . The l a t e s t s t u d i e s seem t o be those o f F e l i x and h i s colleagues ( 4 ) . F o r many y e a r s t h e p r o d u c t development o f these d i l u t i o n systems has been n u r e l y e m p i r i c which l i m i t e d t h e i r d i f f u s i o n . But, i n 1976 we managed t o work c u t a semiq u a n t i t a t i v e t h e o r y w h i c h now enables us t o c a l c u l a t e these anparatus a c c o r d i n g t o each p a r t i c u l a r case. A system o f c o m m e r c i a l i z a t i o n has t h e n been s e t t l e d i n s a t i s f a c t o r y c o n d i t i o n s , t h e r e s u l t o f which was t o show us t h a t these d i l u t i o n systems had o t h e r a p p l i c a t i o n s t h a n t h e ones o r i g i n a l l y t h o u g h t o f , as we s h a l l see now.

P r i n c i p l e s o f t h e I R C H A d i l u t i o n ' systems and d i f f e r e n t types o f r e a l i s a t i o n P r i n c i p l e s . Because o f t h e l a r g e dynamic o f usual c o n c e n t r a t i o n s i n t h e f i e l d o f a e r o s o l ( l o 4 and beyond) t h e system must reach d i l u t i o n r a t i o s o f

and beyond,

which imposes t o d i l u t e a s m a l l q u a n t i t y o f a e r o s o l i n a l a r g e volume o f c l e a n a i r .

274

The p r i n c i p l e of resolution chosen c o n s i s t s i n making a progressive d i l u t i o n i n a t u r bulent medium i n a dynamic system ( s e e f i g u r e 1 ) . For t h a t we use a cone perforated with rings of blowing holes which are supplied with clean a i r . The aerosol i s s e n t t o the top of the cone and finds i t s ' way out by d i l u t i n g i t s e l f gradually. There e x i s t two types of apparatus whether the mean airflow velocity in the cone i s constant o r

n o t . I t i s the constant tyoe apparatus t h a t we s h a l l now study.

clean air

porous media FIGURE 1 : General schema of the d i l u t e r model A The p r i n c i p l e above mentioned must come i n t o operation in a p r a c t i c a l system answering a c e r t a i n number of c r i t e r i o n s which define the ideal d i l u t i o n . There are three c r i t e r i o n s : - the aerosol should be homogeneous i n concentration and p a r t i c l e s i z e d i s t r i b u t i o n a t the output.

-

the system should be " l i n e a r " t h a t i s t o say the concentrations of aerosol a t the

e n t r y Co and a t the way-out C should be linked by q c = c0 Q + q Q clean a i r flow '

q aerosol flow

c

dilution ratio

CO

Whatever be Q and q between the ooerational l i m i t s appropriate f o r each d i l u t e r . - The l o s s e s i n the cone, which a r e i n e v i t a b l e s i n c e we have t o go through a t u r b u l e n t phase, should be, as much as p o s s i b l e , reduced. The theory a t our disposal enables us t o cone e n t i r e l y with the f i r s t two problems B u t the losses cannot be q u a n t i t a t i v e l y delimited a p r i o r i . Experience showed us

275 which types o f c o n s t r u c t i o n c o u l d g i v e r a t i o s g o i n g beyond 10 %.So we know how t o a v o i d t h a t problem b u t , f a c e d w i t h a new c o n s t r u c t i o n f o r which we p r e c i s e l y want t o know t h a t r a t i o , we must r e s o r t t o a d i r e c t d e t e r m i n a t i o n through a s i m p l e enough experiment. E v e n t u a l l y , l e t us m e n t i o n t h a t , uo t o now, o u r systems have been used w i t h a continuous a e r o s o l f e e d i n g . We a r e D r e s e n t l y s t u d y i n g t h e i r r e a c t i o n under an impuls i o n a l f e e d i n g i n o t h e r words we a r e t r y i n g t o q u a n t i f y t h e d e f o r m a t i o n which a s h o r t a e r o s o l p u f f undergoes d u r i n g i t s d i l u t i o n . B u i l d i n g o f d i l u t i o n systems. The d i l u t i o n system i s e s s e n t i a l l y d e f i n e d by i t s i n t e r n a l cone ( t h e o u t p u t d u c t i s meant t o smooth down t h e t u r b u l e n t f l o w coming o u t from t h e cone). The b u i l d i n g parameters a r e t h e a n g l e o f t h e cone and i t s o u t p u t diameter, t h e number and p o s i t i o n o f t h e r i n g s o f b l o w i n g h o l e s , t h e number o f h o l e s i n a r i n g and t h e i r own d i a m e t e r s . I t f o l l o w s t h a t t h e number o f p o s s i b l e cones i s v e r y l a r g e , b u t t h e t h e o r y enables t o s e l e c t s o l u t i o n s which answer t h e c r i t e r i o n s above mentionned ( s e e p r i n c i p l e s ) . Faced w i t h a problem which we a r e asked t o s o l v e , we can t h u s propose an apparatus t h e p e r f e c t f u n c t i o n i n g o f which we can a s c e r t a i n , b u t we do n o t p r e t e n d t o d i s c o v e r a l l t h e p o s s i b l e s o l u t i o n s . Indeed we happened t o c r e a t e systems d i v e r g i n g f r o m t h e t h e o r e t i c a l s o l u t i o n b u t we had t o check t h e i r good f u n c t i o n i n g by r a t h e r c o s t l y experiments, f o l l o w i n a procedures t h e g e n e r a l l i n e o f which has a l r e a d y been mentioned i n ( 1 ) . Another i m p o r t a n t p o i n t i s t h e area s u r r o u n d i n g t h e cone and which c o n s t i t u t e s a plenum where t h e f l o w s h o u l d be s u f f i c i e n t l y u n i f o r m so as t o have t h e same f l o w i n g speed f o r each o f t h e h o l e s i n t h e cone. There a r e two main ways t o s o l v e t h e problem; t h e y a r e governed by t h e acceptance o r n o t o f a s t r a i g h t f o n v a r d e n t r y l e n g t h f o r t h e aerosol p i p e . I n model A ( f i g u r e 1) t h e c l e a n a i r i s blown t a n g e n t i a l l y i n t o a f i r s t compartment t h e n t h e f l o w i s s t a b i l i z e d by p a s s i n g t h r o u g h a porous l a y e r b e f o r e p e n e t r a t i n g i n t o t h e plenum s u r r o u n d i n g t h e cone. T h a t d i s p o s i t i o n which g i v e s D a r t i c u l a r l y cheap c o n s t r u c t i o n s n e c e s s i t a t e s t h a t t h e f i r s t compartment s h o u l d have a p i g e g o i n g across i t and l e a d i n g t h e a e r o s o l . T h i s s t r a i g h t f o r w a r d l e n g t h i s n o t a c c e p t a b l e f o r c e r t a i n problems, because o f t h e l o s s e s i t may provoke ( f o r i n s t a n c e an a e r o s o l o f s m a l l drops t o be d r i e d ) . We t h e n use model B ( f i g u r e 2 ) i n which t h e a i r i s i n t r o d u c e d i n t o a compartment s u r r o u n d i n g t h e o u t p u t p i p e b e f o r e i t be blown towards t h e cone t h r o u g h a f i n e g r i d o f d i f f u s i o n . T h a t s o l u t i o n which p e r m i t s t h e i n t r o d u c t i o n o f t h e a e r o s o l p r a c t i c a l l y a t t h e l e v e l o f t h e f i r s t b l o w i n g r i n g , gives apparatus much more c o s t l y and b u l k y .

276

clean air

FIGURE 2 : General schema of the d i l u t e r model B General c h a r a c t e r i s t i c s of d i l u t i o n systems. A f i r s t p r a c t i c a l apnroach consists i n

giving t h e i r dimensions. The smallest d i l u t i o n system which i s t h e o r e t i c a l l y possible to conceive i s 7 cm i n diameter a n d t r e a t s 100 l/mn and more of clean a i r . I t i s f e a s i b l e t h a t systems 5 cm i n diameter should function b u t t h e i r perfecting will have

t o be made through an experimental approach. Picture 1 shows asystma little 1-r

which i s of a model B type and whichis special i n t h a t i t was devised t o sample aerosols a t

high temperature. There are no t h e o r e t i c a l l i m i t s t o l a r g e s i z e s b u t we have never had the occasion t o check i t beyond 1 m in diameter. The l a r g e s t we a r e personally using i s 60 cm i n diameter and i t s t o t a l length i s 3 m . I t can be seen o n p i c t u r e 2 . There e x i s t , of course, a l l the intermediary s i z e s w i t h a model of output diameter measuring 20 cm which i s often requested by the laboratory o f ohysics of aerosols f o r i t covers most of t h e needs. The next parameter t o be considered i s the airflow through the d i l u t i o n system o r the mean airflow velocity a t the output. I n general the minimal airflow corresponds t o an output velocity i n f e r i o r t o 1 m/s ( t e c h n i c a l reasons). The maximum airflow i s limited t o the value which gives a pressure drop i n the cone o f 60 mm of water (pract i c a l reason); the corresponding output velocity i s then 8,5 times the minimal veloc i t y . This r a t i o 8,5 a l s o represents the dynamic of the flows currently used. The pressure drop o f the cone i s given by

2 = 0,1326 V P in which V i s , i n m/s, the output airflow velocity common t o every hole. A A

P

t h e pressure drop i n mm o f water

217

A more c o n v e n i e n t f o r m u l a i s = 0,1326 ( K Us)’ where Us i s , i n m/s, t h e a i r f l o w v e l o c i t y a t the P o u t p u t and K a c o n s t a n t c h a r a c t e r i s t i c o f t h e cone. T h a t c o n s t a n t , g i v e n w i t h each

h

system, i s always > 2,5 Another i m p o r t a n t c h a r a c t e r i s t i c i s t h e c a o a c i t y o f d i l u t i o n . F o r an o r d i n a r y system o p e r a t i n g a t a g i v e n a i r f l o w , t h e r e i s a maximum v a l u e o f t h e aerosol a i r f l o w which can be a d m i t t e d . T h i s v a l u e depends on t h e c o n s t r u c t i o n c h a r a c t e r i s t i c s ; i t can be a d e t e r m i n a n t element f o r c e r t a i n a p p l i c a t i o n s such as t h e p r o d u c t i o n o f d u s t l a d e n f l o w s . I n o t h e r i n s t a n c e s ( t o measure a e r o s o l s f o r i n s t a n c e ) i t can be

gnored.

F i g u r e 3 i l l u s t r a t e s t h i s p o i n t f o r systems 23 cm i n diameter designed f o r d i f e r e n t a p p l i c a t i o n s . On t h e c o n t r a r y t h e r e i s no i n f e r i o r l i m i t t o t h e a i r f l o w t o d i Ute;

dilution ratio x

lo-*

I/mn 100

1000

clean air flow

FIGURE 3 : Examples o f t h e maximum r a t i o f o r two d i l u t e r s o f t h e same d i a m e t e r (pi 23 cm)

however, i n t h e case o f an a e r o s o l , p r a c t i c a l l i m i t s can be found, f o r i f t h e a i r f l o w i s too low

t h e l o s s e s , i n t h e c a r r y i n g p i p e s , b e f o r e r e a c h i n g t h e d i l u t i o n system

become s i g n i f i c a n t . T h a t i s why t h e g e n e r a l r u l e i s t o work on as much aerosol as p o s s i b l e so as t o o b t a i n e v e n t u a l l y a qood p r e c i s i o n . T h i s leads t o use i m p o r t a n t a i r f l o w o f c l e a n a i r f e e d i n g s e r i a l l y disposed systems (we s h a l l see an example of

t h a t application t o medical n e b u l i z e r s ) . Finally another c h a r a c t e r i s t i c , with which we s h a l l deal b r i e f l y , concerns the l i m i t a t i o n s of the s i z e s of the p a r t i c l e s which can be t r e a t e d . A few common sense recommendations, which our experience taught us as w e l l , are here very useful t o know. The d i l u t i o n operation i t s e l f can function without problems f o r n a r t i c l e s of 100 u ( d e n s i t y 2 ) b u t losses with local concentration decreases can be the consequence of thc natural sedimentation o r of centrifugation e f f e c t s due t o the turbulence in the cone and i n the straightforward length a t the outout. I n a l l the cases, when the s i z e s are s u p e r i o r t o 10 p ( d e n s i t y l ) , i t i s b e t t e r t o work with systems equipped with a v e r t i c a l a x i s , which prevents l o s s e s i f we do not go beyond 20 p . Beyond t h a t p o i n t , according to the model of the d i l u t e r and i t s operating flow, we can come across problems which i t i s b e t t e r t o discover and quantify during an i n i t i a l study o f q u a l i f i c a t i o n from which t a b l e s of correction of t h e observed defects may be drawn. Examples of a p p l i c a t i o n of d i l u t i o n systems Measuring aerosols. A d i l u t i o n system i s an often indispensable i n t e r f a c e between the real aerosols, o r the ones made i n l a b o r a t o r i e s , and the various o p t i c a l counters (Royco, S a r t o r i u s e t c . . ) , b u t we a l s o happened t o use i t f o r l e s s recent instruments, such as the cascade impactor, when the smoke t o be studied was highly concentrated. I t would seem cheaper t o use small models b u t , as we already noticed, the d i l u t i o n c o e f f i c i e n t s sought being and below, we would then t r e a t small airflows of aerosols and losses would a l t e r the measuring accuracy. That i s why we generally recommend t o use d i l u t e r s 20 t o 23 cm i n diameters and operating around 1000 l/mn. There a r e , however, cases i n which high d i l u t i o n r a t i o s a r e sought and we have a permanent apparatus which c l e a r l y i l l u s t r a t e s t h i s point ( s e e p i c t u r e 2 ) . I t i s used t o study the clouds produced by medical nebulizers. (pneumatic nebulizers, u l t r a s o n i c nebulizers o r "spray cans") The i n i t i a l concentrations a r e usually of some millions of p a r t i c l e s per cm3 and they must be reduced t o r a t i o s i n f e r i o r t o 50/cm3 which n e c e s s i t a t e s d i l u t i o n s of 105 times and more. I n the i n s t a l l a t i o n presented, the nebulizer i s enclosed i n a t i g h t box i n t o which s t a i n l e s s s t e e l ( p = 10 cm) The whole of the droplets aerosol i s s e n t i n t o t h a t f i r s t s t a g e where i t i s mixed with 300 l/mn of hot a i r (temperature of 120°C) so a s t o dry i t up t o obtain a penetrates the e n t r y of a d i l u t i o n system model B made of

cloud of nuclei which will be the o b j e c t of the measuring. The output of the d i l u t e r i s p u t under pressure thanks t o a g r i d , so t h a t one p a r t of the airflow should be send towards a second stage (@=60cm)through an o r i f i c e p l a t e . This d i l u t e r operates around 10.000 l/mn and i s followed by a terminal level (@=23cm)i n which the airflow of clean a i r i s 1000 l/mn.

219

The r e a l i s a t i o n of dust laden flows. We had t h e occasion t o present such a n applic a t i o n a t the 1 2 t h colloquium of the I R C H A ( 5 ) . Since then the same basic principles have been applied t o the r e a l i s a t i o n of flows a t a g r e a t e r velocity ( 2 0 m/s) obtained i n i n s t a l l a t i o n s t h a t we f i t out when asked, according t o a common scheme. A fluidized bed aerosol generator of the " n u l d o u l i t " tyne model B sends a concentrated aerosol i n t o the e n t r y of a special d i l u t e r capable of operating a t a high airflow velocity. A t the output, the homogeneous phase obtained a t t a c k s a second f l u i d i z e d bed where the aerosol undergoes i f necessary a f u r t h e r disnersion and where the flow acquires turbulence c h a r a c t e r i s t i c s which can be regulated a t will ( f l a t velocity c h a r t , uniform turbulence r a t i o e t c . .) Another obvious application i s in the f i e l d of a i r - f i l t e r s t e s t i n g f a c i l i t y . The d i l u t e r , j o i n t l y operating with a f l u i d i z e d bed aerosol generator enables t o create an "entry s e c t i o n " which can be very e f f i c i e n t and whose reduced s i z e i f compared t o the straightforward lengths necessary t o have a c o r r e c t aerosol i n c l a s s i c a l i n s t a l l a t i o n s (ASHRAE t e s t , Na C1 t e s t e t c . . . ) T h a t disposition proves p a r t i c u l a r l y e f f i c i e n t when we want t o s e t u p a permanent i n s t a l l a t i o n enabling t o measure the f r a c tional e f f i c i e n c y of f i l t e r s and of f i l t e r i n g l a y e r s . Moreoverin the domaine of f i l t e r s , t h a t same technology enabled us t o find a good s o l u t i o n to the t r i c k y problem of t e s t i n g c a r t r i d g e f i l t e r s with c i r c u l a r l y opened s u c t i o n . I t i s well known t h a t we generally have t o deal with cylindrical nleated paper i n a housing where polluted a i r i s admitted t h r o u g h a c i r c u l a r s l o t opened near the top of the housing. The nroblem of t e s t i n g i s t o make the aerosol penetrate uniformly i n t o the s l o t , while avoiding as much as possible the deposits on the housing i t s e l f . We have b u i l t and studied a n i n s t a l l a t i o n accordinq t o the diagram in figure 4. The f i l t e r t o be t e s t e d i s s e t t l e d on the f l o o r of a c y l i n d r i c tank in which i s f i t t e d the outnut of a d i l u t i o n system which sends the t e s t aerosol uniformly dispersed i n a flow representing, on a n average, half of the one aspirated by the f i l t e r being t e s t e d . The complementary flow comes from the outside and goes t h r o u g h the ring s i t u a t e d between the two cylinders where i t i s transformed i n t o a p r o t e c t i v e flow meant t o minimize the dust l o s s e s . With t h a t system, the quantity of dust which penetrates i s exactly i d e n t i c a l i n a l l points of the a s p i r a t i n g s l o t and the deposits ( t h a t can be released i n suspension a t the end of the t e s t ) do n o t exceed 10 % of the q u a n t i t y s e n t . Applications i n the f i e l d of the mixinq of gases. The homogeneous mixing of two o r more gases can be done by methods well known in chemical engineering and practised i n apparatus which may be simpler than those here described. That i s why we did n o t think a t f i r s t t h a t our d i l u t e r s could have an onening in t h a t f i e l d and y e t they

280

dust .-c

.-- clean air

ambiant air

FIGURE 4 : Schema o f a f a c i l i t y t o t e s t c a r t r i d g e f i l t e r have n o t ceased t o develo? i n t h a t a p p l i c a t i o n . The reasons a r e many b u t v e r y o f t e n

i t i s t h e i r c h a r a c t e r i s t i c o f b e i n g a b l e t o make r a p i d l y , i n a reduced space, a p e r f e c t m i x i n g w h i c h i s p a r t i c u l a r l y a p p r e c i a t e d as p r o v e d by t h e two f o l l o w i n g examples The f a b r i c a t i o n o f g r e a t f l o w s o f gaz o n l y s l i g h t l y p o l l u t e d , f o r i n s t a n c e by t o x i c s , can be done almost c o r r e c t l y i n v e s s e l s which a r e expensive because o f t h e i r volume. The d i l u t i o n system i s a v e r s a t i l e and cheap s o l u t i o n . Thus, i t was p o s s i b l e t o m i x 50 cc/mn o f gas i n 15.000 l/mn o f c l e a n a i r , g i v i n g c o n c e n t r a t i o n s o f 3 ppm i n volume. The c l e a n i n g o f gases and noxious vapours by making them r e a c t w i t h a n o t h e r gas which t r a n s f o r m s them i n t o aerosol i s a o o s s i b i l i t y which arouses g r e a t i n t e r e s t . We have made a d e m o n s t r a t i o n i n t h e case o f t h e phosgen. I t i s a dangerous t o x i c which chemical i n d u s t r i e s r e j e c t , more and more f r e q u e n t l y , under t h e f o r m o f d i l u t e d e f f l u e n t s , which l i m i t s p u r i f y i n g e f f i c i e n c y and makes i t expensive t o use c l a s s i c a l systems such as t h e washers ( w i t h a l i m e s o l u t i o n t h e b e s t ones reach an e f f i c i e n c y o f 90 % on c o n d i t i o n o f t o l e r a t i n g 200 t o 300 mm o f w a t e r o f p r e s s u r e d r o p ) . B u t t h e phosphogene can r e a c t w i t h t h e ammoniac by g i v i n g an aerosol o f u r e a . Thus, f o r

281

e f f l u e n t s a t 650 ppm, i n t r o d u c e d i n t h e main c i r c u i t o f t h e d i l u t e r ( f l o w o f 2500 l / m ) a f l o w o f ammoniac o f 8 l/mn s e n t by t h e a e r o s o l c i r c u i t enables t o p u r i f y a t 95 % whereas t h e p r e s s u r e drop accepted w i t h t h e c i r c u i t o f e f f l u e n t s i s o f 40 mm o f w a t e r . Even i f t h e a e r o s o l produced must t h e n be stopped, t h i s means o f o u r i f i c a t i o n seems t o be cheaply c o m p e t i t i v e . L e t us m e n t i o n t h a t t h e c o m m e r c i a l i z a t i o n o f d i l u t e r s f o r t h a t t y p e o f a p p l i c a t i o n i s c a r r i e d o u t by EUROPOLL l t d ( 6 ) . Sampling h o t a e r o s o l s . The g r e a t m a j o r i t y o f t h e measuring apparatus f o r a e r o s o l s p a r t i c u l a r l y t h e most e l a b o r a t e ones, h a r d l y e v e r f u n c t i o n beyond 50 o r 6 0 " . I f we have t o s t u d y d u s t s u b m i t t e d t o h i g h temoeratures (400 t o 800°C),

t h e y have t o be

c o o l e d . The use o f an exchanoer i s a s o l u t i o n e n t a i l i n g heavy l o s s e s o f a e r o s o l , moreo v e r t h e a e r o s o l can a l s o be d e t e r i o r a t e s . Combining b o t h t h e c o o l i n g and t h e d i l u t i o n i n one o f o u r apparatus i s a s o l u t i o n w h i c h gave e x c e l l e n t r e s u l t s , f o r i n s t a n c e when we s t u d i e d t h e e x h a u s t fumes o f i n t e r n a l combustion e n g i n e s . I t was t h e d i l u t e r model B, i n s t a i n l e s s s t e e l , p r e s e n t e d i n p i c t u r e 2 which was used. A n o t i c e a b l e c h a r a c t e r i s t i c o f t h e method i s t h a t t h e f l o w o f h o t qas which e n t e r s i n t o t h e appar a t u s i s measured by a t h e r m i c method. F o r t h a t , thermocouples w i t h r e c o r d e r s a r e p l a c e d a t t h e e n t r y o f t h e h o t gas ( T 2 ) , a t t h e e n t r y o f t h e d i l u t i o n c i r c u i t ( T o ) and a t t h e o u t p u t o f t h e d i l u t e r (T1). I f we draw t h e e n t h a l o i c balance o f t h e system, t h e r e s u l t o b t a i n e d , i n a f i r s t a p n r o x i m a t i o n i n t h e case o f t h e a i r i s :

5

Q

=

1 ;

-

To

2_- T 1

With a d i l u t i o n r a t i o o f

lo-[,

= dilution ratio

w i t h gas a t 600°C, whereas c l e a n a i r i s a t 22°C t h e

r i s e i n temperature a t t h e o u t p u t i s 5,8"C. Thus equipped, t h e d i l u t e r i s v e r y c o n v e n i e n t f o sampling and measurinq h o t a e r o s o l s whether these be a t a s u f f i c i e n t o v e r p r e s s u r e o r whether we de-pressure t h e d i l u t e r by a s p i r a t i n g a t i t s o u t p u t . The examples o f a p p l i c a t i o n s above mentioned have been chosen among o t h e r s because t h e y a r e p a r t i c u l a r l y s i g n i f i c a n t . They show t h a t these d i l u t e r s c o n s t i t u t e an operat i o n a l s o l u t i o n f o r most o f t h e problems o f a e r o s o l d i l u t i o n and o f t h e f a b r i c a t i o n o f d u s t l a d e n f l o w s w h i c h can a r i s e i n t h e l a b o r a t o r y o r i n i n d u s t r y . REFERENCES 1 J.C. Guichard e t J.C. Ney, C o n s t r u c t i o n e t etude d'une chambre d d i l u t i o n pour a e r o s o l s . I R C H A , n o t e i n t e r i e u r e NO32 (1966) 2 J.C.

Guichard, Chambre

a

d i l u t i o n p o u r a e r o s o l s . Conference a l a s e s s i o n 1966 d

Munich de " A r b e i t k r e i s F u r Reine Riume" ( S t u g g a r t )

282

3 J.C. Guichard e t J . TGsio, Performance of a i r f i l t e r s f o r clean rooms. The t e s t f a c i l i t y of I R C H A . F i l t r a t i o n a n d se9aration Sent/Oct. 1370 n.577 B 585. 4 L.G. F e l i x , R . L . t l e r r i t t , J.D.Uc Cain e t J.W. Ragland, S a m l i n g a n d d i l u t i o n system design f o r measurement o f submicron o a r t i c l e s i z e and concentration i n stack emission a e r o s o l s . TSI q u a t e r l y Oct/Dec. 7 1 9 8 1 N O 4 D . 3 B 1 2 . 5 J . C . Guichard, A . Saint-Yrieix e t J.L. Magne, E h d e s oreliminaires a la construc

t i o n d'une cheminee d ' e s s a i . lZPme Colloque International orqanisi! par 1 ' I R C H A in Atmosoheric Pollution e d i t e d by PI. Benarie, 0 . 325 B 338. 6 EuroDoll, 2 Rue Amorteaux 78730 Saint-Arnoult-en-Yvelines - France

Picture 2

283

FORMATION AND EVOLUTION OF SULFATE AND N I T R A T E AEROSOLS I N PLUMES C h r i s t i a n Seigneur, Pradeep Saxena, and A. Be1 l e Hudischewskyj Systems A p p l i c a t i o n s , Inc.,

San R a f a e l , C a l i f o r n i a

94903

ABSTRACT A mathematical model i s p r e s e n t e d t h a t d e s c r i b e s t h e b e h a v i o r o f gaseous and a e r o s o l s p e c i e s i n plumes.

The processes r e p r e s e n t e d b y t h e model i n c l u d e

a d v e c t i v e t r a n s p o r t , t u r b u l e n t d i f f u s i o n , s u r f a c e d e p o s i t i o n , gas-phase c h e m i s t r y , a e r o s o l c o a g u l a t i o n and s e d i m e n t a t i o n , and gas-to-aerosol s i o n f o r b o t h n i t r a t e and s u l f a t e species.

conver-

The model p r e d i c t i o n s a r e compared

w i t h measurements o b t a i n e d i n t h r e e power p l a n t plumes having d i f f e r e n t environments.

INTRODUCTION The s t u d y o f secondary a e r o s o l f o r m a t i o n i n t h e atmosphere i s a s u b j e c t o f p a r t i c u l a r i n t e r e s t i n a i r p o l 1 u t i o n r e s e a r c h because secondary a e r o s o l s c o n t r i b u t e t o v i s i b i l i t y impairment, a c i d p r e c i p i t a t i o n , and p o s s i b l y a f f e c t human h e a l t h a d v e r s e l y .

Secondary a e r o s o l s a r e formed i n t h e atmosphere when

gaseous s p e c i e s e i t h e r n u c l e a t e t o form new a e r o s o l s o r condense on t h e surface o f e x i s t i n g aerosols.

Chemical s p e c i e s i n v o l v e d i n t h e s e gas-to-

a e r o s o l c o n v e r s i o n processes i n c l u d e s u l f a t e , n i t r a t e , and o r g a n i c species. The p r i m a r y p o l l u t a n t s e m i t t e d from power p l a n t s i n c l u d e SO2,

NO,

and p r i m a r y

a e r o s o l s ; s i n c e small amounts o f hydrocarbons a r e e m i t t e d , o r g a n i c a e r o s o l f o r m a t i o n i n power p l a n t plumes can be c o n s i d e r e d t o be n e g l i g i b l e .

In this

paper, we c o n s i d e r t h e f o r m a t i o n and e v o l u t i o n o f secondary s u l f a t e and n i t r a t e a e r o s o l s i n power p l a n t plumes. I n r e c e n t y e a r s , s e v e r a l e x p e r i m e n t a l programs have been undertaken t o s t u d y secondary s u l f a t e and n i t r a t e a e r o s o l f o r m a t i o n i n plumes.

Conversely,

t h e o r e t i c a l s t u d i e s have been conducted t o q u a n t i t a t i v e l y d e s c r i b e t h e processes i n v o l v e d i n aerosol f o r m a t i o n and dynamics and, u l t i m a t e l y , t o s i m u l a t e a e r o s o l b e h a v i o r i n t h e atmosphere.

To t h i s end, s e v e r a l mathematical models f o r s u l f a t e f o r m a t i o n have been developed ( r e f s . 1-2-3).

Comparisons o f model p r e d i c t i o n s w i t h a i r b o r n e

measurements performed i n power p l a n t plumes have shown s a t i s f a c t o r y agreement ( r e f s . 1-3).

N i t r a t e a e r o s o l c h e m i s t r y i n t h e atmosphere has a l s o been

s t u d i e d ( r e f s . 4-5-6-7).

However, t o o u r knowledge, t h e r e has been no a t t e m p t

t o model n i t r a t e aerosol f o r m a t i o n i n plumes.

Since t h e r e i s i n c r e a s i n g

e v i d e n c e o f i t s f o r m a t i o n i n power p l a n t plumes ( r e f s . 8 - 9 ) , i t i s c l e a r l y i m p o r t a n t t o i n c l u d e n i t r a t e aerosol dynamics i n t h e mathematical t r e a t m e n t o f plume a e r o s o l f o r m a t i o n . T h i s paper p r e s e n t s t h e e x t e n s i o n o f a s u l f a t e a e r o s o l plume model t o i n c l u d e n i t r a t e aerosol formation.

We f i r s t p r e s e n t a b r i e f d e s c r i p t i o n o f

t h e model and t h e c h e m i s t r y o f secondary aerosol f o r m a t i o n a t l o w humidities.

The f o l l o w i n g s e c t i o n d i s c u s s e s t h e model s i m u l a t i o n o f secondary

a e r o s o l f o r m a t i o n i n power p l a n t plumes f o r t y p i c a l cases i n v o l v i n g d i f f e r e n t background c h e m i s t r y and compares model s i m u l a t i o n s w i t h e x p e r i m e n t a l data. F i n a l l y , t h e s t u d y r e s u l t s a r e d i s c u s s e d i n terms o f model a p p l i c a t i o n s and o f a d d i t i o n a l work needed t o understand and s i m u l a t e atmospheric aerosol formation.

D E S C R I P T I O N OF THE MODEL

Formation o f s u l f a t e a e r o s o l s S u l f a t e a e r o s o l s a r e formed i n t h e atmosphere from t h e o x i d a t i o n o f SO2

on soot aerosol s u r f a c e s o r i n l i q u i d c o a t e d a e r o s o l s o r l i q u i d d r o p l e t s . A r e v i e w o f t h e v a r i o u s chemical pathways ( w h i c h can o c c u r i n t h e gas phase)

t h a t l e a d t o t h e f o r m a t i o n o f s u l f a t e s i n t h e atmosphere has been presented by B u r t o n e t a l . ( r e f . 10).

A f t e r a b r i e f o v e r v i e w o f t h e s e processes, we

address i n more d e t a i l t h o s e chemical processes o f i n t e r e s t t o t h e p r e s e n t study. The most i m p o r t a n t chemical pathways o f gas-phase o x i d a t i o n o f SO2 i n t h e

A

atmosphere i n v o l v e t h e r e a c t i o n o f SO2 w i t h OH, CH3O2, and H02 r a d i c a l s . r e v i e w o f t h e k i n e t i c d a t a a v a i l a b l e f o r t h e s e r e a c t i o n s suggests t h a t t h e

r e a c t i o n w i t h OH i s t h e most s i g n i f i c a n t gas-phase o x i d a t i o n pathway f o r SO2 ( r e f . 1 1 ) ; t h e r e f o r e , i n t h i s s t u d y , i t w i l l be t h e o n l y pathway c o n s i d e r e d ( r e f s . 3-12):

SO2

+

OH

----+

HS03

----+

H SO

2 4

k = 1320 ppm-' m i n - l

(11

285

Because t h e vapor p r e s s u r e o f H2SO4 i s low, i t w i l l condense i n t h e presence o f H20 ( r e f . 13).

Another g a s - t o - p a r t i c l e c o n v e r s i o n process f o r H2SO4

i n v o l v e s t h e r e a c t i o n o f H2SO4 w i t h NH3 t o form NH4HS04 and (NH4)2S04.

This

process i s b e l i e v e d t o p r e v a i l o v e r t h e f o r m a t i o n o f H2SO4 s o l u t i o n a e r o s o l s i n t h e t r o p o s p h e r e ( r e f s . 14-15-16).

The f o r m a t i o n o f ammonium s u l f a t e s i s

i n v e s t i g a t e d i n g r e a t e r d e t a i l a t t h e end o f t h i s s e c t i o n . The o x i d a t i o n o f SO2 a l s o o c c u r s on t h e s u r f a c e o f soot a e r o s o l s and i n t h e l i q u i d phase o f l i q u i d - c o a t e d a e r o s o l s o r l i q u i d d r o p l e t s .

The l i q u i d -

phase o x i d a t i o n processes i n c l u d e o x i d a t i o n by 02, 03, and H202, and o x i d a t i o n b y O 2 c a t a l y z e d by t r a n s i t i o n metal i o n s ( r e f . 10).

Liquid-phase o x i d a t i o n o f

SO2 has been i n c l u d e d i n aerosol plume models e i t h e r as a parameterized

process ( r e f . 3 ) o r as a m e c h a n i s t i c component ( r e f . 2 ) .

The model s i m u l a t i o n

p r e s e n t e d here i n v o l v e d cases w i t h l o w r e l a t i v e h u m i d i t i e s (below 60 p e r c e n t ) f o r which l i q u i d - p h a s e o x i d a t i o n o f SO2 i s u n i m p o r t a n t ( r e f .

17); therefore,

we c o n s i d e r o n l y gas-phase o x i d a t i o n o f SO2. An i m p o r t a n t component o f an aerosol model i s t h e g a s - t o - p a r t i c l e convers i o n process.

It d e t e r m i n e s t h e k i n e t i c s o f a e r o s o l f o r m a t i o n , as w e l l as t h e

chemical c o m p o s i t i o n o f t h e a e r o s o l s .

F i r s t l e t us c o n s i d e r t h e case o f H2SO4

and NH3 i n e q u i l i b r i u m w i t h a d r y a e r o s o l .

The f o l l o w i n g e q u i l i b r i u m

r e l a t i o n s h i p s hold:

“H31[H2SO41 NH3(g) + H2S04(g)=NH4HS04(s)

= 2.0

K1 =

“H31 NH3(g) + NHqHSO4(S)=(NH

) SO 4 ( S )

4 2

ppm2

(2)

x

K 2 = ___ - 3.8 x

Y

x

ppm

(3)

when ( 9 ) and ( s ) r e f e r t o t h e gas phase and s o l i d phase, r e s p e c t i v e l y , and K1 and K2 a r e t h e e q u i l i b r i u m constants.

The chemical c o m p o s i t i o n o f t h e aerosol i s charac-

t e r i z e d b y t h e mole f r a c t i o n s x and y o f NH4HS04 and (NH4)2S04, r e s p e c t i v e l y . We can c a l c u l a t e t h e c o m p o s i t i o n o f t h e a e r o s o l f o r a c l o s e d chemical system i f

t h e i n i t i a l gas-phase c o n c e n t r a t i o n s [NH31° and [H2SO4I0 a r e known. t i o n leads t o t h e f o l l o w i n g r e l a t i o n s h i p s :

Mass conserva-

286 x + y = l [ N H 3 I 0 = [NH31 + (2x + Y) M [H2S04]0

= CH2S041 + ( x + Y) M

where M i s t h e t o t a l c o n c e n t r a t i o n o f aerosol s u l f a t e and b i s u l f a t e . This system o f equations can be solved t o g i v e t h e e q u i l i b r i u m composition o f t h e aerosol f o r v a r i o u s gas-phase concentrations.

Several s i m u l a t i o n s were

performed f o r an i n i t i a l c o n c e n t r a t i o n o f H2SO4 o f 5 x c o n c e n t r a t i o n s o f NH3 r a n g i n g from 10-1 ppm t o

ppm.

ppm, and i n i t i a l The r e s u l t s showed t h a t

t h e mole f r a c t i o n y o f NH4HS04 was always l e s s than 0.01. Alternatively,

we can c a l c u l a t e t h e gas-phase c o n c e n t r a t i o n o f H2SO4 and NH3,

f o r which an a p p r e c i a b l e amount o f NH4HS04 w i l l be present. percent o f NH4HS04 and 90 percent o f (NH4)$04 t i o n s o f 3.4 x

lo-'

For instance,

ppm f o r NH3 and H2SO4, r e s p e c t i v e l y .

and 5.8 x

10

would r e q u i r e gas-phase concentraThe

s u l f u r i c a c i d c o n c e n t r a t i o n t h a t i s r e q u i r e d t o produce an appreciable amount o f ammonium b i s u l f a t e i s f a i r l y h i g h and such c o n c e n t r a t i o n s have n o t been observed i n t h e atmosphere, except p o s s i b l y i n t h e f l u e gases c l o s e t o t h e stack.

Thus,

i t i s safe t o assume t h a t i n atmospheric plumes, H2S04 and NH3 w i l l l e a d t o t h e

f o r m a t i o n o f (NH4)2S04,

and t h a t n e g l i g i b l e amounts o f NH4HS04 w i l l be formed.

I n t h i s model, we t h e r e f o r e assume t h a t H2SO4 condenses w i t h NH3 t o form (NH4)2S04,

which i s s o l i d a t r e l a t i v e h u m i d i t i e s below 80 percent.

Formation o f n i t r a t e a e r o s o l s N i t r i c a c i d and n i t r a t e are formed i n t h e atmosphere m a i n l y by t h e o x i d a t i o n

o f NO2.

The most i m p o r t a n t chemical pathways i n v o l v e d i n t h e f o r m a t i o n o f HNO3

a r e t h e gas-phase o x i d a t i o n o f NO2 by OH r a d i c a l s , which occurs d u r i n g t h e daytime, and t h e gas-phase o x i d a t i o n o f NO2 by NO3 r a d i c a l s t o form N2O5, which then r e a c t s on wetted aerosol surfaces t o heterogeneously form HNO3.

This second

process occurs m a i n l y a t n i g h t because d u r i n g t h e daytime NO3 i s r a p i d l y photolyzed t o NO2 and 0 ( r e f . 18).

Since t h e s i m u l a t i o n s t h a t were conducted

correspond t o daytime c o n d i t i o n s , t h i s chemical pathway i s unimportant and i s n o t considered i n t h e model; however, t h e model c o u l d e a s i l y t a k e i n t o account t h i s heterogeneous r e a c t i o n i f necessary. o x i d a t i o n o f NO2 b y

For t h e study simulations,

OH i s t h e main pathway t o HN03 formation.

therefore, the (Some n i t r i c a c i d

i s a l s o formed when HS04 r e a c t s w i t h NO2 t o form H2S04 and HNO3): NO2 + OH - - - - +

HN03

k = 1.4 x

lo4

ppm-' min-'

(7)

287

The s a t u r a t i o n vapor p r e s s u r e o f HN03 i s h i g h , so t h a t HN03 does n o t condense i n a p p r e c i a b l e amounts and remains m a i n l y i n t h e gas phase.

The main process

l e a d i n g t o t h e f o r m a t i o n o f i n o r g a n i c n i t r a t e a e r o s o l s i n daytime i s t h e r e a c t i o n o f NH3 w i t h HN03 a t r e l a t i v e h u m i d i t i e s below 62 p e r c e n t when t h e r e a c t i o n p r o d u c t NH4N03 is s o l i d . NH3(g) + HN03(g)=NH

4 NO 3 ( s )

(8)

The e q u i l i b r i u m parameters f o r t h i s two-phase e q u i l i b r i u m have been e v a l u a t e d u s i n g thermodynamic and e x p e r i m e n t a l d a t a ( r e f s . 6-7) and depend on t h e ambient temperature.

I n t h i s study, t h e f o l l o w i n g e q u i l i b r i u m parameter was chosen ( r e f .

6) :

K3 = [NH3][HN03]

= 70.68

-

--,--24090

-

6.04

in

T

m

(9)

where t h e t e m p e r a t u r e T i s expressed i n K, and K j i n ppm2. T h i s e q u i l i b r i u m between gaseous ammonia and n i t r i c a c i d and aerosol ammonium n i t r a t e constitutes the gas-to-particle f o r m a t i o n i n t h i s model.

c o n v e r s i o n process f o r aerosol n i t r a t e

U n l i k e t h e c o n v e r s i o n o f H2S04 t o aerosol s u l f a t e ,

which can be c o n s i d e r e d t o be i r r e v e r s i b l e i n a power p l a n t plume because o f t h e l o w vapor p r e s s u r e o f H2SO4, t h e f o r m a t i o n o f ammonium n i t r a t e i s a r e v e r s i b l e process; ammonium n i t r a t e w i l l decompose i n t o i t s p r e c u r s o r s i f t h e i r c o n c e n t r a t i o n p r o d u c t i s below t h e s a t u r a t i o n v a l u e g i v e n by Equation ( 9 ) . F o r m u l a t i o n o f t h e aerosol plume model The mathematical model t h a t has been developed t o d e s c r i b e t h e f o r m a t i o n o f s u l f a t e and n i t r a t e a e r o s o l s and t h e e v o l u t i o n o f t h e aerosol s i z e d i s t r i b u t i o n i n plumes i n c l u d e s t h r e e components: c h e m i s t r y , and a e r o s o l dynamics.

plume t r a n s p o r t and d i s p e r s i o n , gas-phase

These components have been d e s c r i b e d i n d e t a i l

elsewhere ( r e f . 3). The plume i s d e s c r i b e d i n a Lagrangian frame o f r e f e r e n c e .

It c o n s i s t s o f

s i x c o n t i g u o u s p u f f c e l l s t h a t a r e v e r t i c a l l y w e l l mixed and t h a t expand as t h e plume i s d i s p e r s e d by t h e atmospheric t u r b u l e n t eddies.

I n e r t species a r e

d i s p e r s e d a c c o r d i n g t o a Gaussian 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 , whereas t h e d i f f u s i o n o f c h e m i c a l l y r e a c t i n g s p e c i e s i s t r e a t e d by means o f a K-theory formulation.

The plume model t a k e s i n t o account t i m e - v a r y i n g wind speed, m i x i n g depth,

288

e n t r a i n m e n t o f gaseous chemical s p e c i e s and a e r o s o l s from t h e background i n t o t h e plume, and d e p o s i t i o n o f gases and a e r o s o l s on t h e ground ( r e f . 19). The gas-phase c h e m i s t r y mechanism uses t h e Carbon-Bond Mechanism developed by Whitten, K i l l u s , and Hog0 ( r e f . 20).

M o d i f i c a t i o n s t o t h e mechanism t o make i t

s u i t a b l e f o r plume c h e m i s t r y have been d i s c u s s e d by Seigneur ( r e f . 3 ) and t h e c h e m i s t r y o f ammonium s u l f a t e and ammonium n i t r a t e f o r m a t i o n has been d i s c u s s e d i n t h e previous sections.

The mechanisms c o n s i s t o f 7 5 r e a c t i o n s among 37

chemical species. The a e r o s o l dynamics component d e s c r i b e s t h e c o a g u l a t i o n o f a e r o s o l s , t h e gas-to-particle

c o n v e r s i o n processes t h a t govern t h e f o r m a t i o n o f ammonium

s u l f a t e and n i t r a t e , and t h e thermodynamic e q u i l i b r i u m between NH3, HN03, and NH4N03.

The aerosol s i z e d i s t r i b u t i o n i s r e p r e s e n t e d by a s e c t i o n a l d i s t r i b u t i o n

t h a t c o n s i s t s here o f 7 s e c t i o n s i n t h e a e r o s o l d i a m e t e r s i z e range o f 0.01 t o 2.15

@I. This

d i s t r i b u t i o n corresponds t o t h e a c c u m u l a t i o n mode where most o f

t h e secondary a e r o s o l mass i s formed.

L a r g e r aerosol s i z e s (coarse-mode

a e r o s o l s ) can a l s o be t r e a t e d by t h e model as i n e r t a e r o s o l s .

The e v o l u t i o n of

t h e a e r o s o l s i z e d i s t r i b u t i o n i s governed b y t h e s e c t i o n a l General Dynamic Equation t h a t i s presented elsewhere ( r e f s . 3-21). t o c o n d e n s a t i o n o f H2SO4 and HN03 as (NH4),S04

Condensational growth i s due

and NH4N03 monomers.

If the

c o n c e n t r a t i o n p r o d u c t o f NH3 and HNO3 i s below i t s s a t u r a t i o n value, NH4N03 decomposes and l e a v e s t h e a e r o s o l phase. The model i s a p p l i e d i n cases f o r which (NH4)$04 f o r r e l a t i v e h u m i d i t i e s below 62 p e r c e n t .

and NH4NO3 a r e s o l i d , i.e.,

It i s assumed t h a t (NH4)2S04 and

NH4N03 e x i s t as an e x t e r n a l m i x t u r e i n t h e a e r o s o l phase. MODEL APPLICATIONS The model s i m u l a t e d t h e f o r m a t i o n o f s u l f a t e and n i t r a t e a e r o s o l s i n power p l a n t plumes i n t h r e e d i f f e r e n t environments:

a c l e a n background w i t h l o w NH3

c o n c e n t r a t i o n s , a c l e a n background w i t h h i g h NH3 c o n c e n t r a t i o n s , and a p o l l u t e d background w i t h h i g h NH3 c o n c e n t r a t i o n s . Clean environment w i t h l o w NH2 c o n c e n t r a t i o n s The 1979 VISTTA f i e l d programs were conducted, i n p a r t , t o s t u d y t h e p h y s i c s , c h e m i s t r y , and o p t i c a l p r o p e r t i e s o f t h e plume o f t h e Navajo power p l a n t l o c a t e d i n n o r t h e r n A r i z o n a ( r e f . 22).

A t t h i s l o c a t i o n , t h e background a i r i s g e n e r a l l y

v e r y c l e a n , w i t h l o w NH3 c o n c e n t r a t i o n s ( r e f . 16).

The s i m u l a t i o n s o f plume

c h e m i s t r y , s u l f a t e a e r o s o l f o r m a t i o n , and t h e e v o l u t i o n o f t h e aerosol s i z e

289

d i s t r i b u t i o n on f o u r d i f f e r e n t days o f t h e VISTTA programs have been presented elsewhere ( r e f . 3).

The p o s s i b l e f o r m a t i o n o f a e r o s o l n i t r a t e was i n v e s t i g a t e d

w i t h t h i s model and

t appeared t h a t background NH3 c o n c e n t r a t i o n s and plume HN03

c o n c e n t r a t i o n s were t o o l o w t o l e a d t o t h e f o r m a t i o n o f NH4N03 a e r o s o l s .

This

f i n d i n g i s i n agreement w i t h t h e a i r b o r n e plume measurements, which showed l i t t l e f o r m a t i o n o f NH4N03 i n t h e plume.

These r e s u l t s a r e shown i n t a b l e 1.

I n two

cases o n l y - - 9 and 13 December 1979--the measured gas-phase c o n c e n t r a t i o n s o f NH3 and HN03 a r e above t h e s a t u r a t i o n v a l u e ; f o r one o f t h e cases--9 December--some n i t r a t e a e r o s o l was measured i n t h e plume. t h a t K3

>

[HN03][NH3].

I n a l l cases, t h e model p r e d i c t e d

The r e s u l t s o f t h e plume s i m u l a t i o n s a r e t h e r e f o r e

i d e n t i c a l t o t h o s e a l r e a d y presented.

The reader i s r e f e r r e d t o Seigneur ( r e f .

3 ) f o r a d e t a i l e d p r e s e n t a t i o n o f t h e comparison o f model p r e d i c t i o n s and measurements f o r s u l f a t e a e r o s o l c o n c e n t r a t i o n s and a e r o s o l s i z e d i s t r i b u t i o n s . TABLE 1 C o n c e n t r a t i o n Product o f NH3 and HN03 i n t h e Navajo power p l a n t plume

P1 ume S i m u l a t i o n

Measured

13 J u l y 1979, 58 km downwind 13 J u l y 1979, 88 km downwind 5 December 1979, 33 km downwind 5 December 1979, 80 km downwind 9 December 1979, 30 km downwind 13 December, 25 km downwind

2.1 2.8 5.4 5.9 8.3 5.0

10-5 x 10-5 x x loe8 x lom7 x

Predicted

(ppm‘)

4.7 1.1 2.0 5.3 1.3 2.0

3.0 5.0 4.2 7.3 2.3 4.0

10-6 10-5

x x x x

lom8

10-5 10-5

x x x x

Clean environment w i t h h i g h NH3 c o n c e n t r a t i o n s The K i n c a i d power p l a n t i n I l l i n o i s i s l o c a t e d i n an area where background NH3 c o n c e n t r a t i o n s a r e h i g h e r t h a n t h o s e i n n o r t h e r n Arizona.

The February 1981

VISTTA f i e l d program was conducted t o s t u d y t h e chemical and p h y s i c a l processes and t h e v i s u a l e f f e c t s o f t h e K i n c a i d power p l a n t plume ( r e f . 9).

On 25 February

1981, t h e Meteorology Research, Inc. a i r c r a f t performed one-hour sampling o r b i t s i n t h e plume a t 60 km downwind, and i n t h e background.

A plume s i m u l a t i o n was

performed w i t h t h i s model f o r a p u f f r e l e a s e d a t 1150 CST f r o m t h e stacks. a wind speed o f 6.25 m.sec-l,

t h i s p u f f t r a v e l e d 60 km i n 160 minutes, which

With

290 corresponds t o t h e a i r b o r n e measurement p e r i o d o f 1400-1500 CST.

I n p u t d a t a were

deduced from t h e VISTTA d a t a base and t y p i c a l v a l u e s were assumed f o r t h e background hydrocarbon c o n c e n t r a t i o n s . plume SO2 c o n c e n t r a t i o n s . t e m p e r a t u r e was 10°C.

Plume d i s p e r s i o n was determined from t h e

The r e l a t i v e h u m i d i t y was about 60 p e r c e n t and t h e

Measured and p r e d i c t e d c o n c e n t r a t i o n s o f secondary aero-

sols a r e p r e s e n t e d i n t a b l e 2, where plume excess c o n c e n t r a t i o n r e p r e s e n t s t h e plume c o n c e n t r a t i o n minus t h e background c o n c e n t r a t i o n .

The model u n d e r p r e d i c t s

t h e amount o f a e r o s o l s u l f a t e and n i t r a t e formed, p o s s i b l y because t h e background OH c o n c e n t r a t i o n s o r t h e plume t r a v e l t i m e a r e underestimated.

However, t h e

model p r e d i c t s w e l l t h e r e l a t i v e amounts o f s u l f a t e , n i t r a t e , and ammonium. TABLE 2 P r e d i c t e d and measured c o n c e n t r a t i o n i n t h e K i n c a i d power p l a n t plume

Chemical Species

Background C o n c e n t r a t i o n (Pg m-3) Measured

P1 ume Excess C o n c e n t r a t i o n (!4 m-31 Measured Predicted

so42-

2.26

2.22

0.39

NO3-

0.47

1.54

0.25

NH~+

1.06

1.19

0.22

Pol 1 u t e d environment The c h e m i s t r y and d i s p e r s i o n o f t h e common plume o f t h e Haynes steam p l a n t and t h e A l a m i t o s power p l a n t i n t h e Los Angeles b a s i n were s t u d i e d on s e v e r a l days i n t h e w i n t e r o f 1974 ( r e f s 2-3).

The plume model s i m u l a t e d t h e case s t u d y

o f 7 November 1974, f o r which g r o u n d - l e v e l measurements o f plume c o n c e n t r a t i o n s were conducted a t 18 km downwind between 1400 and 1500 PST. were o b t a i n e d from Richards e t a1 ( r e f .

23).

Model i n p u t d a t a

T y p i c a l v a l u e s were assumed f o r t h e

background c o n c e n t r a t i o n s o f gaseous s p e c i e s t h a t were n o t a v a i l a b l e .

Plume

d i s p e r s i o n was determined from t h e plume c o n c e n t r a t i o n of t h e i n e r t t r a c e r SF6. The wind speed was 5 m.sec-l, t e m p e r a t u r e was 23OC.

t h e r e l a t i v e h u m i d i t y was 34 p e r c e n t , and t h e

The p r e d i c t e d and measured s u l f a t e and n i t r a t e c o n c e n t r a -

t i o n s a r e compared i n t a b l e 3.

291

TABLE 3 P r e d i c t e d and measured c o n c e n t r a t i o n i n t h e HayneslAlamitos p l a n t s plume

Chemical Species

Background C o n c e n t r a t i o n (ug m-3) Mea s u red

P1 ume Excess C o n c e n t r a t i o n (ug m-3) Measured Predicted

so42-

3.0

+6.2

+2.8

NO3-

8.0

-3.3

-0.8

The s u l f u r i c a c i d e m i t t e d from t h e s t a c k s i s c o n v e r t e d t o (NH4)2S04 as i t r e a c t s w i t h t h e background NH3 e n t r a i n e d i n t o t h e plume.

The p r e d i c t e d concen-

t r a t i o n o f s u l f a t e i s l e s s t h a n t h e measured v a l u e ; t h i s d i s c r e p a n c y i s p o s s i b l y due t o u n c e r t a i n t i e s i n t h e measurements, s i n c e t h e model p r e d i c t i o n s correspond w e l l w i t h t h e t o t a l c o n v e r s i o n o f e m i t t e d H2SO4 t o (NH4)2S04, and s i n c e l i t t l e

SO2 o x i d a t i o n t o o k p l a c e i n t h e plume.

The d e p l e t i o n o f NH3 i n t h e plume due t o

(NH4)2S04 f o r m a t i o n l e a d s t o t h e displacement o f t h e NH3-HN03-NH4N03 e q u i l i brium.

Thus, NH4N03 decomposes i n t o NH3 and HNO3 i n t h e plume t o r e e s t a b l i s h t h e

equilibrium.

T h i s e f f e c t appears i n b o t h t h e measurements and t h e model p r e d i c -

tions. CONCLUSION

A model has been p r e s e n t e d t h a t d e s c r i b e s t h e f o r m a t i o n o f ammonium s u l f a t e and n i t r a t e a e r o s o l s and t h e e v o l u t i o n o f t h e aerosol d i s t r i b u t i o n i n plumes a t h u m i d i t i e s below 6 2 percent.

The model was a p p l i e d t o t h e s i m u l a t i o n o f aerosol

f o r m a t i o n i n power p l a n t plumes f o r t h r e e d i f f e r e n t t y p e s o f background e n v i r o n ments and appeared t o reproduce w e l l t h e p r i m a r y c h a r a c t e r i s t i c s o f aerosol plume c h e m i s t r y under v a r i o u s c o n d i t i o n s .

F u r t h e r work should be d i r e c t e d toward t h e

s t u d y o f a e r o s o l f o r m a t i o n a t h i g h r e l a t i v e h u m i d i t i e s f o r which t h e c h e m i s t r y o f t h e l i q u i d - c o a t e d a e r o s o l s must be t a k e n i n t o account. ACKNOWLEDGMENTS Thanks a r e due t o Dr. L. W. Richards f o r p r o v i d i n g v a l u a b l e i n f o r m a t i o n r e g a r d i n g t h e e x p e r i m e n t a l d a t a and t o C.

J. Lawson f o r e d i t o r i a l a s s i s t a n c e .

REFERENCES

1 M.W. E l t g r o t h and P.V. Hobbs, Atmos. Environ., 13(1979)953-975. 2 M. Basset, F. Gelbard and J.H. S e i n f e l d , Atmos. Environ., 15 ( 1981 ) 2395-2406. 3 C. Seigneur, Atmos. Environ., i n press. 4 A.E. Ore1 and J.H. S e i n f e l d , Environ. Sci. Techol., ll(1977)lOOO1007. 5 T.W. Peterson and J.H. S e i n f e l d , Am. I n s t . Chem. Eng. J., 25( 1979)831-838. 6 A.W. S t e l s o n , S.K. F r i e d l a n d e r and J.H. S e i n f e l d , Atmos. Environ.. 13 (1979)369-371. Doyle, E.C. Tuazon, R.A. Graham, T.M. Mischke, A.M. Wine and J.N. P i t t s , Jr., Atmos. Environ. Sci. Techno1 13(1979)1416-1419. 8 D.A. Hegg and P.V. Hobbs, Atmos. Environ., 13(1979)1715-1716. 9 L.W. R i c h a r d s , J.A. Anderson, D.L. Blumenthal, A.A. Brandt, S.Z. Hynek, J.A. McDonald, and N. Waters, Report 81-DV-1806, 1981 Meteorology Research, Inc., Santa Rosa, C a l i f o r n i a . 10 C.S. B u r t o n , M.K. L i u , P.M. Roth, C. Seigneur and G.Z. Whitten, Proc. 1 2 t h NATO/CCMS I n t . Techn. Meeting 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 s , Palo A l t o , C a l i f o r n i a , August 25-28, 1981. 11 R. A t k i n s o n and A. C. L l o y d , J. Phys. Chem. Ref. Data, lO(1981) i n press. 12 0.0. Davis, A.R. Ravishankara and S. F i s c h e r , Geophys. Res. L e t t . ,

7 G.J.

.,

6(1979)113-116. 13 J.I. R n i t r o and T. Vermeulen, Am. I n s t . Chem. Eng. J., 10(1969)740746. C a t t e l l , Atmos. Environ., 13( 1979)307-317. 14 W.D. S c o t t and F.C.R. 15 P.K. Dasgupta, Atmos. Environ., 14(1980)267. 16 L.W. R i c h a r d s , J.A. Anderson, D.L. Blumenthal, A.A. Brandt, J. A. 17

McDonald, N. Waters, E.S. Macias, and P.A. Bhardwaja, Atmos. Environ., 15(1981)2111-2134. P.H. McMurry, D.J. Rader and J.L. S t i t h , Atmos. Environ.,

15( 1981)2315-2328 18 L.W. R i c h a r d s , s u b m i t t e d t o Atmos. Environ., 1982. 19 D.A. Stewart and M.K. L i u , Atmos. Environ., 15(1981)2377-2394. 20 G.Z. W h i t t e n , J.P. K i l l u s and H. Hogo, Report EF79-129, Systems A p p l i c a t i o n s , Inc., San R a f a e l , C a l i f o r n i a , 1980. 21 F. Gelbard and J.H. S e i n f e l d , J. C o l l o i d I n t e r f . Sci., 78(1980)485501. 22 D.L. Blumenthal, L.W. Richards, E.S. Macias, R.W. Bergstrom, W.E. Wilson and P.S. Bhardwaja, Atmos. Environ., 15(1981)1955-1970. 23 L.W. Richards, E.L. Avol, and A. B. Marker, Report SC593-5 FRD, 1976, Rockwell I n t e r n a t i o n a l , A i r M o n i t o r i n g Center, Newbury Park, California.

293

PHOTOGRAPHY AS A TECHNIQUE FOR STUDYING VISUAL RANGE

T.E.

HOFFER, D.E.

SCHORRAN

Desert R e s e a r c h I n s t i t u t e , U n i v e r s i t y of Nevada System R. J. FARBER

S o u t h e r n C a l i f o r n i a E d i s o n Company

ABSTRACT

A t e c h n i q u e i s d e s c r i b e d t h a t u s e s b l a c k and w h i t e a n d c o l o r photography t o s t u d y v i s u a l r a n g e , a n d t h e e f f e c t s o f c l o u d s and h a z e on a s c e n e . w h i t e f i l m i s u s e d f o r q u a n t i t a t i v e measurement of v i s u a l r a n g e .

Black and

Film density

measurements are d i g i t i z e d u s i n g a f l y i n g s p o t s c a n n e r t o a s s u r e t h a t t h e meas u r e m e n t , a n a l y s i s a n d i n t e r p r e t a t i o n are r e p r o d u c i b l e and a c c u r a t e .

The p r o c e d u r e and a n example are

s i t y wedges a n d t h e n e g a t i v e s are d i g i t i z e d . presented.

Color f i l m is used t o q u a l i f y

The den-

t h e b l a c k a n d w h i t e measuremenw.

The t e c h n i q u e s a p p l i e d i n a n a l y s i s and some r e s u l t s of

t h e f i e l d measurement

program a r e p r e s e n t e d .

INTRODUCTION

Koscmeider ( r e f . y e a r s ago.

1) p u b l i s h e d a p i o n e e r i n g work on v i s i b i l i t y a l m o s t s i x t y

I n t h i s p a p e r , h e d e r i v e d t h e f u n d a m e n t a l r e l a t i o n s h i p between t h e

v i s u a l range,

contrast,

and t h e b a c k s c a t t e r i n g c o e f f i c i e n t ,

t h e p a r t i c l e number a n d s i z e .

a term r e l a t e d t o

U n t i l 1977, o b j e c t i v e r e p r o d u c i b l e measurement

t e c h n i q u e s f o r v i s u a l r a n g e a n d c o l o r c o n t r a s t were n o t mandated. t h e United

S t a t e s Congress

p a s s e d amendments t o

Under a new s e c t i o n of t h a t A c t ;

areas

was

to

be

protected.

In t h a t y e a r

t h e C l e a n A i r Act of

1970.

v i s i b i l i t y i n n a t i o n a l p a r k s and w i l d e r n e s s

The

act

also

specified

that

the

scientific

294

community was t o d e v e l o p methods of a c c u r a t e l y measuring v i s i b i l i t y . perception

s t u d i e s were s t a r t e d t o c o r r e l a t e i n s t r u m e n t measurements o f v i s u a l

range w i t h how p a r k v i s i t o r s p e r c e i v e v i s i b i l i t y . have

Recently,

tried

to

Furthermore,

these

studies

a s s e s s t h e r o l e of v i s i b i l i t y on a e s t h e t i c a p p r e c i a t i o n of t h e

wilderness. I n a recent experimental visibility

conditions

in

work,

hydrosols

have

demonstrated

p e r c e p t i o n of d e t a i l .

that

simulated

atmospheric

and showed t h a t t h e r e l a t i o n s h i p between

c l a r i t y and v i s u a l range i s n o t l i n e a r . (ref. 4 )

(ref. 2 )

Stankunas

A l l a r d and Tombach ( r e f . 3 )

color

the

is

dominant

and

parameter

These f a c t o r s must b e c o n s i d e r e d i n t h e

Malm i n the

measurement

of

v i s u a l range. Measurement

techniques

can

b e c l a s s i f i e d i n t o two broad c a t e g o r i e s ; t h o s e

t h a t m o n i t o r v i s u a l r a n g e a t a p o i n t and t h o s e t h a t i n t e g r a t e over a l o n g p a t h . Point source techniques include various nephelometers,

and

samplers

for

measurements

include

techniques.

Transmissometers,

measuring

transmissometers,

measure p a r a m e t e r s r e l a t e d t o techniques

types

integrate

of

particle

particle

sizing

counters,

absorption.

Long p a t h

telephotometers

nephelometers extinction.

and

and

photographic

p a r t i c l e s i z e counters a l l

Telephotometers

and

photographic

t h e v a r i a b l e s o f sun a n g l e and t h e s t a t e o f t h e sky i n t o

t h e measurement. A

photographic

simultaneously paper.

technique

exposed

black

for

assessing

and

white

visibility

that

makes

which

of

and c o l o r f i l m i s d e s c r i b e d i n t h i s

The t e c h n i q u e i n c o r p o r a t e s a q u a n t i t a t i v e a n a l y s e s o f b l a c k

negatives

use

and

white

y i e l d s v i s u a l r a n g e measurements and a q u a l i t a t i v e assessment

of c o l o r s l i d e s t o c a t e g o r i z e and q u a l i f y v i s u a l r a n g e measurements.

PHOTOGRAPHIC ASSESSMENT OF VISIBILITY The d e s e r t a r e a s o f t h e s o u t h w e s t e r n United S t a t e s are an i d e a l e v a l u a t i n g d i f f e r e n t methods of measuring v i s i b i l i t y . region

varies

from

locale

for

The v i s u a l r a n g e i n t h i s

i n e x c e s s o f 200 k i l o m e t e r s i n t h e w i n t e r t o l e s s t h a n 7 5

k i l o m e t e r s d u r i n g t h e summer.

The t o p o g r a p h i c r e l i e f

provides

many

mountain

295 targets

at

varying

distances.

Some

of

the

valleys

have

small

s e t t l e m e n t s , which can be t h e s o u r c e o f s p a t i a l inhomogenities i n

A

distribution.

the

urban aerosol

p a t h measurement w i l l b e s t r e p r e s e n t t h e v i s i b i l i t y i n

long

such a n environment. A f t e r c o n s i d e r i n g many f a c t o r s , photography measuring

technique

for

characterizing

was

visibility

selected in

as

our

primary

t h e r e g i o n 100 miles

southwest of t h e Grand Canyon.

. .

.

D t m i z a t i o n o f t h e Dhotonrabhic t e c h n i q u e The p h o t o g r a p h i c d e t e r m i n a t i o n of v i s u a l r a n g e and a t m o s p h e r i c

clarity

has

been o p t i m i z e d i n t h r e e ways. F i r s t , a b l a c k and w h i t e f i l m was chosen t h a t y i e l d s a l a r g e change i n f i l m density

for

a s m a l l change i n e x p o s u r e .

The v i s u a l r a n g e c a l c u l a t i o n s remain

t h e same a s d e s c r i b e d by S t e f f e n s ( r e f . 5 ) . Second, a f t e r development, t h e b l a c k and w h i t e n e g a t i v e s a r e d i g i t i z e d film

density.

This

minimizes

handling

o f t h e f i l m and e l i m i n a t e s o p e r a t o r

e r r o r i n p o s i t i o n i n g t h e n e g a t i v e on a manual d e n s i t o m e t e r . resolution

is

increased

because

than those permitted

using

densitometers.

resolution

The

the

for

In

addition,

the

t a r g e t areas a r e d i g i t i z e d t h a t a r e smaller apertures acheived

commonly

associated

with

manual

with t h i s technique i s g r e a t e r than

t h a t of t h e human e y e . T h i r d , s i m u l t a n e o u s l y exposed c o l o r s l i d e s o f t h e same v i s t a qualify

and

categorize

the

black

and

white

are

used

c o n t r a s t measurements.

p r o v i d e background i n f o r m a t i o n about sky and t a r g e t c o l o r a t i o n , c l o u d i n e s s

to

These and

shadow o r i e n t a t i o n .

Camera system A

range

two

camera

adjacent

i s l o c a t e d on t o p of a mountain peak i n t h e Newberry

system to

the

Lake

Mead

National

Recreation

Area.

t o p o g r a p h i c f e a t u r e s a t s e v e r a l azimuth a n g l e s a r e used f o r t a r g e t s . white

exposures

are

made

with

a

35

Discernible Black and

mm camera equipped w i t h a 600 mm l e n s

296 Color e x p o s u r e s a r e made w i t h a 35 mm camera equipped w i t h

system. lens.

Both

cameras

feature

automatic

exposure

control

100 mm

a

and f i l m advance.

Exposures a r e made i n t h e morning, a t midday, and d u r i n g t h e a f t e r n o o n .

.

Black and w h i t e f i l m

The b l a c k and w h i t e f i l m s e l e c t e d i s Kodak Linagraph

S h e l l b u r s t 2476.

A t y p i c a l exposure v e r s u s d e n s i t y p l o t i s shown i n

and

the

illustrates

large

change

s e n s i t i v i t y p e r m i t s t h e r e s o l u t i o n o f s m a l l changes i n v i s u a l r a n g e . r e p r e s e n t a t i v e o f Plus-X

film

.

1

i n d e n s i t y o b t a i n e d f o r a s m a l l change i n

The p l o t i s f o r f i l m exposed a t ASA 200 and developed n o r m a l l y .

exposure.

Color

Figure

A

The curve

f i l m i s a l s o shown f o r comparison.

The c o l o r f i l m i s Eastman 5 2 4 7 , a c o l o r n e g a t i v e f i l m t h a t i s

p r o c e s s e d commercially.

A c o l o r c h a r t i s photographed a t t h e b e g i n n i n g o f each

r o l l t o p r o v i d e f o r c o r r e c t i o n o f t h e f i l m p o s i t i v e by f i l t r a t i o n t o

the

true

c o l o r of t h e s c e n e .

Film d i g i t i z a t i o n We have developed t h e f o l l o w i n g t e c h n i q u e t o d e t e r m i n e t h e v i s u a l r a n g e from

the

black

and

white

photographs.

On

each r o l l o f f i l m a d e n s i t y wedge is

d i g i t i z e d u s i n g a s p o t s i z e o f 0 . 1 mm i n x by 0.4 mm i n y, measurement

parallel

t o the film breadth.

Where x

refers

to

t o t h e f i l m l e n g t h and y r e f e r s t o measurements p a r a l l e l Two s i d e by s i d e s c a n s are averaged f o r

precision.

The

s m a l l s p o t s are averaged over a s u i t a b l e increment i n x , u s u a l l y 20 v a l u e s , and tabulated

by

a

computer.

The d e n s i t y v a l u e s a s r e l a t e d t o exposure a r e t h e n

g r a p h e d , a s shown i n F i g u r e 1. I n p r a c t i c e t h e f i l m i s exposed so t h a t t h e d e n s i t y is i n t h e l i n e a r p o r t i o n of t h e c u r v e .

The exposure can t h e n b e d e t e r m i n e d from an e q u a t i o n of t h e form

297

Step Number 3.0

I

I

I

I

I

I

1

1

I

August 5, 1980 I

0

2.5

2 .a

c .-

u)

f

1.5

0

.-E -

LL.

I.a

-----

Plus X Film Linogroph Shellburst Film, Monuol Densitometer Linograph Shellburst Film, Digitized

--

0.5

/r

0

/' I

0.3

I

I

1

1

I

1

I

I

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

:

Log E

Fig. L Film characteristic curves for Linagraph Shellburst and Plus-X hlack and white f i l m s . D a t a from manually reduced densitometer measurements and digitized measure ments are shown f a a w e roll of Linagraph Shellburst. where d i s t h e f i l m

density,

m

is

the

slope

and

a

is

the

extrapolated

intercept. Photographs of each v i s t a a r e d i g i t i z e d w i t h a s p o t s i z e of 0 . 1 mm by 0.lmm. For

35

mm f i l m 360 v a l u e s would b e d i g i t i z e d p e r s c a n in t h e x d i r e c t i o n , and

240 in t h e y d i r e c t i o n .

can

be

averaged

The d e n s i t y v a l u e s o b t a i n e d w i t h t h i s s m a l l s p o t

over i n t e g r a l v a l u e s of x and y.

and y v a l u e s are a v e r a g e d .

(60,40).

This reduces t h e

matrix

size

In p r a c t i c e six a d j a c e n t x size

from

(360,240)

to

298

Coordinates

o f t h e t a r g e t and background a r e a s a r e d e t e r m i n e d by p r o j e c t i n g

t h e n e g a t i v e on a l i n e d s c r e e n .

These c o o r d i n a t e s are

used

as

inputs

to

a

program t h a t c a l c u l a t e s t h e v i s u a l r a n g e . In

routine

measurements,

t h e c o o r d i n a t e s o f t h e t a r g e t and an a r e a i n t h e

sky a d j a c e n t t o i t a r e used.

A f t e r t h e exposure i s

calculated,

the

contrast

between sky and t a r g e t i s found from t h e e x p r e s s i o n

(2)

C’E(tar)-E(back)/E(back) where

E(tar)

is

the

exposure

similar quantitity for calculated

using

a

the

a s s o c i a t e d w i t h t h e t a r g e t and E(back) i s t h e

background.

suitable

The

threshold

value

visual and

range

is

subsequently

an assumed v a l u e f o r t h e

inherent contrast of the t a r g e t . T h i s p r o c e d u r e p e r m i t s comparison o f any a r e a on t h e t a r g e t w i t h any element of t h e background, F i g u r e 2 shows an example; h e r e a s i n g l e area on t h e was

used

background.

to

calculate

four

visual

ranges.

Four

sky

The r e s u l t s o f t h e s e c a l c u l a t i o n s a r e p r e s e n t e d

target

a r e a s were used a s in

Table

1.

A

s i m i l a r c a l c u l a t i o n i s shown f o r two o t h e r t a r g e t s .

F i g . 2 . T a r g e t and sky a r e a s u t i l i z e d i n t h e c o n t r a s t d e t e r m i n a t i o n s o f v i s u a l r a n g e shown i n Table 1.

299 TABLE 1

V i s u a l r a n g e s from d i g i t i z e d n e g a t i v e s f o r t h r e e t a r g e t s u s i n g a r e a s of s k y f o r c o n t r a s t d e t e r m i n a t i o n . I n h e r e n t c o n t r a s t = -1.

four

different

Threshoid c o n t r a s t = 0 . 0 2 .

V i s u a l Range (Km)

Sky Area

Target 1

Target 2

Target 3

1

95

85

85

2

109

106

107

3

113

101

109

4

112

103

105

is

There

a

change i n t h e c a l c u l a t e d v i s u a l range f o r d i f f e r e n t sky a r e a s .

The c a l c u l a t i o n u s i n g t h e background a r e a c l o s e s t t o t h e peak (Area 1) in

all

cases,

a

lower

visual

range.

c o n s i s t e n t l y higher v i s u a l ranges. calculations

the

results

are

yields,

The o t h e r c o n t r a s t measurements g i v e

I f d i f f e r e n t t a r g e t a r e a s a r e used

similar.

The

technique

gives

in

the

reproducible

r e s u l t s , p a r t i c u l a r l y when t h e sky and t h e h o r i z o n are c l e a r . V i s u a l range i s a f u n c t i o n o f t h e practice,

this

quantity

inherent

assumption,

several

d i s t a n c e s o r e a c h view. dark

in

increases.

color

and

of

the

target.

i s g e n e r a l l y assumed and r a r e l y measured.

c a n g r e a t l y e f f e c t t h e computed v i s u a l r a n g e . by

contrast

I n o u r work, t o

In

I t s value

minimize

error

c o n t r a s t i n g measurements a r e made a t d i f f e r e n t t a r g e t

A s t h e t a r g e t approaches t h e v i s u a l r a n g e

it

appears

t h e j u s t i f i c a t i o n f o r assuming an i n h e r e n t c o n t r a s t o f -1

T h i s i s e s p e c i a l l y i m p o r t a n t i n t h e d e s e r t southwest where much

of

the terrain i s light i n color. To

reiterate,

these

calculations

are

for

a c l e a r hor zon and sky.

The

on

the

e f f e c t of f a c t o r s such as h o r i z o n b r i g h t n e s s , c l o u d i n e s s v i s u a l range i s n o t incorporated i n t o t h e c a l c u l a t i o n .

and

shadows

300 Color f i l m a n a l y s i s Color

photographs

provide

a medium f o r i n v e s t i g a t i n g how t h e v i s u a l range

a p p e a r s t o change w i t h d i f f e r i n g e n v i r o n m e n t a l this

subjective

measurement

from

a

conditions.

To

differentiate

measurement we have c a l l e d it

physical

V i s u a l a i r q u a l i t y i s dependent upon many a s p e c t s o f t h e

"visual a i r quality".

photographed s c e n e w i t h shadows, c l o u d s , haze and

sun

angle

being

the

most

important. Color

photographs

taken

during

s p r i n g of 1980 were a n a l y z e d . of

the

p e r i o d e x t e n d i n g from w i n t e r through

The p a r a m e t e r s o f p e r c e n t

cloudiness,

presence

shadows o r h a z e , and v i s u a l a i r q u a l i t y were t a b u l a t e d f o r m u l t i p l e t a r g e t s

on e a c h photograph.

The v i s u a l a i r q u a l i t y was

catagorized

for

each

target

according t o t h e following.

1.

C l e a r , no p e r c e p t i b l e h a z e .

2.

P e r c e p t i b l e haze b u t t h e f e a t u r e s a r e d i s t i n c t .

3. Moderate h a z e w i t h many d e t a i l s o b s c u r e d . Target o u t l i n e v i s i b l e . 4 . Dense h a z e , o u t l i n e i s b a r e l y d i s c e r n i b l e . Details a r e o b s c u r e d .

5. The

Target is obscured. t h i r d c a t e g o r y w a s s e l e c t e d a s a good estimate o f t h e d i s t a n c e t h a t c a n

be e a s i l y seen.

It i s not a q u a n t i t a t i v e value of t h e threshold of perception,

b u t i t s e r v e s a s an e s t i m a t o r much reported

at

airports.

This

will

in

the be

same

manner

that

visibility

is

referred t o as the qualitative visual

range. F i g u r e 3 shows t h e q u a l i t a t i v e v i s u a l r a n g e f o r t h i s p e r i o d . d i s c u s s e d , d e g r a d a t i o n o c c u r s as t h e summer a p p r o a c h s . air

quality

is

previously

In addition, the visual

b e t t e r i n t h e morning h o u r s b e f o r e t u r b u l e n c e h a s s t i r r e d t h e

s u r f a c e l a y e r , and l i f t e d it t o t h e h e i g h t o f t h e mountain a r e located.

As

where

the

cameras

0 z

y e ZZE

a. o

$&

0 0 0 0

a : ?

0

0

g d

0

a

4 a 4

?

8 a .

4 4

o o a

0 0

0

. a .a

0

a

t

0

0

d

gg 4

d a

oa

8

0 - 0

‘3

0

80

4

4 0

a 0

a :

a 80 a.

a

a

3

-8

-w N

-8

-R m

2

a

-“g N -

- 9

0

m (0

f N

0 N

m

-R

N

-8 -5

-i? -%I

=

- s Ir V a -9

301

302

CLEAR HORIZON

WHITE CLOUD DARK CLOUD ON HORIZON

Fig. 4. The frequency of occurrence of standard and non-standard horizon conditions during the winter 1980. The region 100 m&s southwest of the Grand Canyon is represented.

ON TARGET

Fig. 5. The frequency of Occurrence of shadow conditiom on visibility tat-gets during t h e w i n t e r of 1980. The r e g h 100 miles southwest of the Grand Canyon is represented.

Fig. 6. The frequency of occurrence of dlwdiness during the winter 1980. The region u)O miles southwest of the G r a d Canyon is represented.

303

Factors affecting visual a i r quality Allard

and

(ref. 6 )

Tombach

c o n d i t i o n s on v i s i b i l i t y .

have

summarized t h e e f f e c t s o f non-standard

Our d a t a b a s e h a s been s o r t e d

into

the

conditions

l i s t e d i n Table 2 .

TABLE 2 . Sort parameters Horizon Clear Horizon White Cloud Dark Cloud

The

Shadows No Shadows Topographic Shadows Cloud Shadows

frequency

Cloudiness < 5 Percent > 5 < 30 P e r c e n t > 3 0 < 60 P e r c e n t > 6 0 90 P e r c e n t

of o c c u r r e n c e of h o r i z o n , shadow, and c l o u d i n e s s c o n d i t i o n s ,

5,

which i n f l u e n c e v i s i b i l i t y p e r c e p t i o n , a r e p r e s e n t e d as F i g u r e s 4 ,

The

maximum v a l u e cannot b e found by a s i m p l e s o r t because t h e s o r t p a r a m e t e r s

can

a

non-standard

6.

c o n d i t i o n s e x i s t f o r t y p e r c e n t of t h e t i m e .

As

minimum,

and

be inter-related.

The q u a l i t a t i v e a n a l y s i s of t h i s c o l o r f i l m p r o v i d e s a means

for

the

categorizing

c o n t r a s t measurements from t h e b l a c k and w h i t e f i l m and

a s s e s s i n g t h e c l a r i t y of t h e atmosphere.

SUMMARY I n t h i s paper measurements

we

from

have

presented

photographic

a

means

photometry

for

on

optimizing

black

and

visual

range

white film.

This

t e c h n i q u e i s a p p l i c a b l e w i t h s t a n d a r d a t m o s p h e r i c c o n d i t i o n s , i . e . , a c l e a r sky and t a r g e t s o f known i n h e r e n t c o n t r a s t .

The t e c h n i q u e a l s o

feature

path

of

integrating

over

a

long

comparable

D i g i t i z a t i o n o f t h e b l a c k and w h i t e f i l m l e n d s i t s e l f measurements. the future.

to

has

positive

t o t h e v i s u a l range. repeatable

The permanency of t h e medium p e r m i t s r e - a n a l y s i s

I n a d d i t i o n , t h e method i s i n e x p e n s i v e , h a s a

the

contrast

a t any t i m e i n

variable

field

of

view, and p r o v i d e s f o r r a p i d d a t a a n a l y s i s . Yet

visual

r a n g e may b e o n l y a p a r t o f what w e a r e a t t e m p t i n g t o q u a n t i f y .

A v i s i t o r t o a N a t i o n a l Park

or

Wilderness

Area

perceives

the

visual

air

304 quality or the scenic beauty of the setting. Visual range is one attribute of visual air quality. Other attributes are general amounts

of

clouds, haze,

measurement.

types

and

foreground features, and time of day. Eventually,

color photography may be used to objective criteria by

topography, the

transform

these

subjective qualities

into

relating color contrast measurements to an extinction

The semi-quantification of our calibrated color

photographs may

be an important first step in quantifying visual air quality and scenic beauty.

ACKNOWLEDGEMENT This

research was supported by Southern California Edison as a part of its

environmental research program.

REFERENCES

1 H. Atm.

Koschmieder, Theorie der 12(1924)33-53; 171-181.

horizontalen

sichtweite, Beitr. Phys. freien

2 Alexander R. Stankunas, An initial investigation of the relationship between visual acuity and haze, Proc. View on Visibility, November 1979, Denver, 70-77. 3 Douglas Allard and Ivar Tombach, Intercomparison of visibility measurement methods, Proc. View on Visibility, November 1979, Denver, 197-221.

4 William Malm, Considerations in the measurement of visibility, J. of the Air Pol. Control Assoc.

29(10)1042-1052.

5 Carsten Steffens, Measurement of visibility by photographic photometry, Industrial and Eng. Chem. 41(1949)2396-2399. 6 Douglas Allard and Ivar Tombach, The effects of non-standard visibility measurement, Atmos. Environ. , 10(1981)1847-1857.

conditions on

305

EXPERIMENTAL STUDY ON THE VISIBILITY I N ABSORBING MEDIA

H. HORVATH, J . GORRAIZ and C. JOHNSON I n s t i t u t fiir E x p e r i m e n t a l p h y s i k d e r U n i v e r s i t a t Wien, Vienna ( A u s t r i a )

ABSTRACT An a b s o r b i n g atmosphere has been s i m u l a t e d by means o f a m i x t u r e o f a hydrosol and a p a r t i c l e f r e e dye. T h i s model a l l o w s an easy d i s t i n c t i o n between a b s o r p t i o n and s c a t t e r i n g . F o r t h i s s i m u l a t e d atmosphere t h e i n f l u e n c e o f a b s o r p t i o n o f t h e medium on t h e v i s i b i l i t y o f b l a c k and g r e y o b j e c t s was determined. The luminance o f t h e h o r i z o n and o f d i f f e r e n t g r e y t a r g e t s a s w e l l as t h e v i s i b i l i t y o f t h e t a r g e t s has been measur e d w i t h i n c r e a s i n g a b s o r p t i o n under monochromatic i l l u m i n a t i o n . The v i s i b i l i t y o f b l a c k t a r g e t s depends o n l y on t h e t o t a l e x t i n c t i o n c o e f f i c i e n t . The v i s i b i l i t y o f non b l a c k t a r g e t s decreases w i t h i n c r e a s i n g a b s o r p t i o n , and depends n o t o n l y on t h e e x t i n c t i o n c o e f f i c i e n t b u t a l s o , t h r o u g h t h e i n h e r e n t c o n t r a s t o f t h e t a r g e t , on t h e e x i s t e n t a b s o r p t i o n . ivleasurements o f t h e i n h e r e n t c o n t r a s t o f t h e o b j e c t a t t h e e x i s t e n t a b s o r p t i o n a r e necesbary i n o r d e r t o d e t e r m i n e t h e v i s i b i l i t y o f non b l a c k o b j e c t s i n a b s o r b i n g media. The r e f l e c t i v i t y o f t h e ground a l s o i n f l u e n c e s t h e v i b i b i l i t y o f non b l a c k t a r g e t > , e s p e a i a l l y a t l o w c o n c e n t r a t i o n - t h e t a r g e t beeing m a i n l y i l l u m i n a t e d by d i r e c t s u n l i g h t

-

and f o r b r i g h t o b j e c t s . Even i f t h e standard v i s i -

b i l i t y can be k e p t c o n s t a n t (e.g. due t o a d d i t i o n a l a i r p o l l u t i o n c o n t r o l ) t h e v i s i b i l i t y o f non b l a c k t a r g e t s i s s m a l l e r ; i . e . t h e o p t i c a l q u a l i t y o f t h e atmosphere decreases w i t h i n c r e a s i n g a b b o r p t i o n . O n l y when t h e t a r g e t s a r e b r i g h t e r than t h e horizon, t h e i r v i s i b i l i t y w i l l increase w i t h increasing absorption. INTRODUCTION A l t h o u g h t h e c l a b s i c works a b o u t t h e v i s i b i l i t y t h e o r y ( M i d d l e t o n 1952, McCartney 1976, K e r k e r 1969) drew t h e a t t e n t i o n t o t h e i m p o r t a n t r o l e o f a b s o r p t i o n , i t was o f t e n u n d e r e s t i m a t e d o r n e g l e c t e d : The s i m p l e v i b i b i l i t y f o r m u l a o f Koschmieder (1924) - i n v e r s e r e l a t i o n between t h e v i s i b i l i t y o f an o b j e c t and t h e e x t i n c t i o n c o e f f i c i e n t o f t h e atmospheric a e r o s o l

-

i s applied, i n s p i t e o f i t s l i m i t i n g

absdmptionb ( H o r v a t h 1971a), l e a d i n g t o c o n s i d e r a b l e e r r o r s i n d e t e r m i n a t i o n o f v i b i b i l i t y , e s p e c i a l l y i f t h e s c a t t e r i n g c o e f f i c i e n t i t used i n s t e a d o f t h e e x t i n c t i o n c o e f f i c i e n t . The e a r l i e r paper o f Dessens (1944), d e a l i n g w i t h t h e e f f e c t s o f a b s o r p t i o n on v i s i b i l i t y , seems t o have been f o r g o t t e n f o r a l o n g time. However, i n h e a v i l y p o p u l a t e d and i n d u s t r i a l i s e d r e g i o n s , t h e c o n c e n t r a t i o n o f d i e b e l and o t h e r carboneceous a e r o s o l s

-

aerosols predominantly absorbing

306

1i g h t

r a t h e r than s c a t t e r i n g v i s i b l e

-

has c o n s t a n t l y grown. T h e r e f o r e nowadays

more and more a t t e n t i o n i s focused on t h e e f f e c t o f a b s o r p t i o n on v i s i b i l i t y , as i t i s shown by t h e r e c e n t l y p u b l i s h e d papers f r o m Faxvog & R o e s s l e r (1978,1980).

They p r e s e n t formulas f o r t h e v i s i b i l i t y o f b l a c k and o t h e r o b j e c t s viewed h o r i z o n t a l y t h r o u g h a e r o s o l s which may b o t h s c a t t e r and absorb l i g h t . L a b o r a t o r y e x p e r i m e n t s t o d e t e r m i n e t h e e f f e c t o f a b s o r p t i o n on t h e h o r i z o n t a l v i s i b i l i t y o f b l a c k t a r g e t s and f u r t h e r on t h e h o r i z o n t a l v i s i b i l i t y and c o n t r a s t o f g r e y t a r g e t s had n o t been performed. Therefore, a s t u d y i n a s i m u l a t e d atmosphere w i t h a s t r o n g l y and a weakly r e f l e c t i n g ground was made and w i l l be r e p o r t e d i n t h i s paper. T h e o r e t i c a l c o n s i d e r a t i o n s o f t h e v i s i b i l i t y o f b l a c k and g r e y o b j e c t s The b r i g h t n e s s c o n t r a s t o f an o b j e c t i s d e f i n e d a s : C = (B

-

Bh)/Bh

where 6 i s t h e b r i g h t n e s s o f t h e o b j e c t and Bh t h e b r i g h t n e s s o f t h e background o r h o r i z o n . The d i s t a n c e a t which t h e c o n t r a s t o f t h e o b j e c t a g a i n s t t h e h o r i z o n j u b t e q u a l s bhe observe& c o n t r a s t t h r e s h o l d

is

E

t h e v i s i b i l i t y V . Koschmieder's

t h e o r y (1924) g i v e s t h e f o l l o w i n g e q u a t i o n : E

= Co.exp(-bext.V)

where Co i s t h e c o n t r a s t a t d i s t a n c e x = 0, o r i n h e r e n t c o n t r a s t . is : 9 I n lCoO/bext

And t h u s t h e v i s i b i l i t y o f a g r e y o b j e c t V

V = (- I n / E l + 9 F o r a p e r f e c t l y b l a c k o b j e c t Co = -1, and t h e n t h e v i s i b i l i t y Vb i s t : Vb = - I n I E l / b e x t One c a n w r i t e t h e r a t i o o f v i s i b i l i t i e s o f g r e y and b l a c k o b j e c t s as: V /V = 1 g b Laboratory simulations

-

I n ICol/ln

/El

A s c a t t e r i n g h y d r o s o l , such as a m a s t i c h y d r o s o l , has s i m i l a r p r o p e r t i e s as a n

a t m o s p h e r i c a e r o s o l . These h y d r o s o l s a r e produced b y m i x i n g a s o l u t i o n o f m a s t i c i n e t h a n o l w i t h w a t e r and t h e y a r e v e r y s t a b l e . The p a r t i c l e s a r e p o l y d i s p e r s e and have a d i a m e t e r t h e same o r d e r o f magnitude as t h e wavelength o f l i g h t ( H o r v a t h & P r e s l e 1979). F o r t h e s i m u l a t i o n of a n a b s o r b i n g a e r o s o l a m i x t u r e o f m a s t i c h y d r o s o l and a dye w h i c h c o n t a i n s no p a r t i c l e s

-

being therefore responsible o n l y f o r absorption

-

was

used. T h i s a b s o r b i n g h y d r o s o l shows o p t i c a l p r o p e r t i e s s i m i l a r t o a b s o r b i n g atmospheric a e r o s o l s and a l l o w s a n easy d i s t i n c t i o n between a b s o r p t i o n and s c a t t e r i n g . As a b s o r b i h g m a t e r i a l two brands of b l a c k i n k and a w a t e r s o l u b l e b l a c k a n i l i n e dye were used. P r e l i m i n a r y measurements showed t h a t t h e s c a t t e r i n g c o e f f i c i e n t remains c o n s t a n t w i t h t h e a d d i t i o n o f dye and t h e e x t i n t i o n c o e f f i c i e n t b e i n g t h e sum o f t h e s c a t t e r i n g c o e f f i c i e n t w i t h t h e a b s o r p t i o n c o e f f i c i e n t o f t h e employed dye c o n c e n t r a t i o n .

307

The v i s i b i l i t y observations have been performed i n a container of approximately 1,5 x 0,s x 0,15 m 3 s i,z e , f i l l e d with hydrosol. The hydrosol was illuminated by means of 5 sodium lamps of 180 W each, giving a homogeneous illumination of approximately 11000 l x . The bottom of the hydrosol container was black anodized aluminium and simulated a weakly r e f l e c t i n g ground. To obtain a strongly r e f l e c t i n g ground t h i s bottom was covered with a white sheet. Experimental resul t s f o r black t a r g e t s The v i s i b i l i t y of black t a r g e t s was measured f o r a purely s c a t t e r i n g hydrosol and f o r increasingly absorbing hydrosols by two observers. Table 1 l i s t s the average v i s i b i l i t y of the two observers a s well a s the standard deviation ( l i s t e d in

(v)

p a r e n t h e s i s ) . ,Also included a r e t h e e x t i n c t i o n c o e f f i c i e n t s determined by means of the long path photometer and v i s i b i l i t i e s calculated from these e x t i n c t i o n c o e f f i c i e n t s a t two c o n t r a s t thresholds: the standard c o n t r a s t threshold of 0,02 and the mean of the measured c o n t r a s t thresholds of the two observers

I E ~=

0,015.

The v i s i b i l i t y c a l c u l a t e d from the mean of the measured c o n t r a s t threshold i s in good agreement with the average measured v i s i b i l i t y . On the o t h e r hand, the v i s i b i l i t y calculated from t h e standard c o n t r a s t threshold i s an average of l o % smaller than the measured v i s i b i l i t y , since both observers have c o n t r a s t thresholds l e s s than 0,02. V i s i b i l i t y i s inversely proportional t o the e x t i n c t i o n c o e f f i c i e n t , independent of t h e s i z e of the absorption c o e f f i c i e n t . Thus t h e v i s i b i l i t y of ideal black t a r g e t s i n absorbing media i s experimentally proven t o depend only on the t o t a l extinction coefficient.

TABLE 1 Measured and c a l c u l a t e d v i s i b i l i t i e s f o r black t a r g e t s Dye concentration ml/l Hydrosol 0 0,5 0,lO 0,15 0,20

Measured v i s i b i l i t y V cm 60,71 49,75 41,85 37,53 34,05

(2,58) (1,71) (2,23) (1,42) (1,14)

bexf

Calculated

Visibility

cm-

IE/

/EI

0,072 0,090 0,100 0,111 0,124

= 0,02

53,8 43,4 39,l 35,l 31,5

=

0,015

58,3 46,65 42 ,O 37,8 33,9

Experimental resul t s f o r grey t a r g e t s The v i s i b i l i t y was measured by t h r e e observers f o r a purely s c a t t e r i n g hydrosol and then f o r three increasing absorbing hydrosols. First a black t a r g e t B was used, followed by four d i s t i n c t . g r e y t a r g e t s ( G 1 was d a r k e s t and 64 l i g h t e s t ) and then t h e black repeated. The r e s u l t s a r e given

in

Table 2.

The measurements f o r the t a r g e t 64 contains an additional uncertainty since the observers could see t h e dark edges of the t a r g e t b e t t e r than the l i g h t face, t h u s

308

Neawrements o f t h e r a t i o o f t h e i l l u m i n a n c e of t h e h o r i z o n t o t h e i r r a d i a n c e o f the i n c i d e n t l i g h t w i t h i n c r e a s i n g a b s o r p t i o n . The p o i n t s xx

$*.. .W

'

r e p r e s e n t t h e measurements f o r a weakly r e f l e c -

20

2: 8 . Pa

t i n g ground, t h e p o i n t s ooo t h e measurement5 f o r

ra

a s t r o n g l y r e f l e c t i n g one. The continuous and

* 3.

broken l i n e s r e p r e s e n t t h e t h e o r e t i c a l values

OQ

5

L

b-

ABSORPTION COEFFICIENT / EXTINCTION COEFFICIENT

h o r i z o n t o t h e i n c i d e n t i r r a d i a n c e was conbidered instead o f the illuminance o f the h o r i z o n . The r e s u l t s a r e p l o t t e d i n f i g .

1 for

a s t r o n g l y and a weakly r e f l e c t i n g ground. These r e s u l t s show t h e i m p o r t a n t r o l e of t h e r e f l e c t i o n o f t h e ground. The r a t i o o f t h e i n h e r e n t b r i g h t n e s s o f the observed o b j e c t t o t h a t o f the h o r i z o n was measured f o r each s e t of g r e y t a r g e t s i n each h y d r o s o l . The r e s u l t s a r e r e p r e bented f o r b o t h weakly and s t r o n g l y r e f l e c t i n g ground i n f i g u r e 2. From t h i s f i g u r e one concludes t h a t t h e d i f f e r e n c e between t h e weakly and s t r o n g l y r e f l e c t i n g ground

i b

negligible.

From t h e measured r a t i o s Bo/Bh,

t h e i n h e r e n t c o n t r a s t o f t h e g r e y t a r g e t s was

c a l c u l a t e d a t t h e bame c o n d i t i o n s as f o r the measurements of t h e v i s i b i l i t y (see t a b l e 2 ) . The r a t i o s o f t h e v i s i b i l i t y o f t h e g r e y t a r g e t s t o t h a t o f a b l a c k t a r g e t wab t h e n determined u s i n g t h e t h e o r e t i c a l formula:

V /V = 1 - I n ICol/ln I E ~ 9 b Results, c a l c u l a t e d u s i n g t h e standard c o n t r a s t t h r e s h o l d and the mean c o n t r a s t t h r e L h o l d of t h e t h r e e observers

1 ~ =1 0,018 a r e

shown i n t a b l e 2 a l o n g w i t h t h e

d i r e c t meabured r a t i o s o f v i s i b i l i t i e s . The correspondence between t h e average measured r a t i o and t h a t c a l c u l a t e d u s i n g t h e mean c o n t r a s t t h r e s h o l d o f t h e obbervers

ib

v e r y good f o r t h e f i r s t t h r e e g r e y o b j e c t s .

309 F i g . 2:

. 9. W

Behaviour o f t h e r a t i o o f t h e i n h e r e n t b r i g h t ness o f t h e o b j e c t t o t h e b r i g h t n e s s o f t h e

- theoret ica I x x x grey 1 + + + o D o

grey2

bbb

grey 3

h o r i z o n w i t h i n c r e a s i n g a b s o r p t i o n . The L A &

symbols l e f t o f " g r e y " r e p r e s e n t t h e measurements f o r a weakly r e f l e c t i n g ground, t h e symbols r i g h t o f " g r e y " t h e measurements f o r a s t r o n g l y r e f l e c t i n g one.

I n t h e case o f t h e f o u r t h g r e y t a r g e t t h e d i s agreement i s most l i k e l y caused b y t h e exa g g e r a t e d v i s i b i l i t y o f t h e t a r g e t s due t o t h e i r d a r k e r edges. I

.

.

.

. . . . 0.4 0.6 A B S O R P T ION COEFFICIENT/ E X T lN C T lO N COEFFICI E N 1 0.2

Thus t h e p r e d i c t i o n o f t h e v i s i b i l i t y o f g r e y o b j e c t s i n a b s o r b i n g media f r o m t h e t o t a l e x t i n c t i o n c o e f f i c i e n t alone i s n o t s u f f i c i e n t .

The i n h e r e n t c o n t r a s t o f t h e observed o b j e c t s as a f u n c t i o n o f a b s o r p t i o n i s a l s o necessary. A p p l i c a t i o n t o t h e atmosphere and comparison w i t h o t h e r r e w l ts The v i s i b i l i t y o f p e r f e c t l y b l a c k o b j e c t s i n a b s o r b i n g media i s i n v e r s e l y p r o p o r t i o n a l t o t h e e x t i n c t i o n c o e f f i c i e n t , independent o f t h e s i z e o f t h e absorpt i o n c o e f f i c i e n t , a s i t was t h e o r e t i c l y f o r m u l a t e d b y Foaxvog & R o e s s l e r (1978). For non-perfectly black objects, appearing o f t e n i n nature, the e f f e c t o f a b s o r p t i o n must be i n c l u d e d . I n t h i s case t h e f i r s t f a c t o r t o be t a k e n i n t o c o n s i d e r a t i o n i s t h e i l l u m i n a n c e

o f t h e horizon (see f i g . 1 ) .

The t h e o r e t i c a l r e s u l t s f r o m Faxvog & R o e s s l e r (1980)

do n o t correspond w i t h t h e performed measurements, e s p e c i a l l y n o t f o r s t r o n g a b s o r p t i o n and f o r a s t r o n g l y r e f l e c t i n g ground. The a u t h o r 5 suggest t h a t p o s s i b l e 5ource5 o f e r r o r a r e t h e n o t - c o n s i d e r a t i o n o f t h e mu1 t i p l e scattering-mu1 t i p l e s c a t t e r i n g i s i m p o r t a n t i n o p t i c a l l y t h i c k media

-

and t h e n o t - c o n s i d e r a t i o n o f

t h e r e f l e c t i o n o f t h e ground, which i n f l u e n c e s t h e decrea5es o f t h e i l l u m i n a n c e o f t h e horizon w i t h increasing absorption. The second f a c t o r t o be t a k e n i n t o c o n s i d e r a t i o n

i 5

t h e i n h e r e n t b r i g h t n e s s of

t h e observed o b j e c t . The i n h e r e n t b r i g h t n e s s o f t h e o b j e c t i s n o t a c o n s t a n t l i k e i t was assumed by Faxvog & R o e s s l e r (1980) b u t depends on t h e i l l u m i n a t i o n r e c e i v e d

by t h e o b j e c t and t h e r e f o r e depend? on t h e a b s o r p t i o n o f t h e a e r o s o l and on t h e r e f l e c t i o n o f t h e ground. To d e t e r m i n e t h e v i s i b i l i t y , t h e d e c i s i v e f a c t o r i s however t h e r a t i o o f t h e i n h e r e n t brightness o f the t a r g e t t o the brightness o f the horizon. I n our

310

TABLE 2 deasured v i s i b i l i t i e s f o r g r e y t a r g e t s and measured and c a l c u l a t e d r a t i o s o f v i s i b i l i t i e s o f g r e y and b l a c k o b j e c t s w i t h i n c r e a s i n g a b s o r p t i o n ba/bext

Target

B Gi E2

0

G3 64 B

B B1

0,27

G2 G3 G4 B B G1

0,37

62 63 G4 B

0,47

B G1 G2 G3 G4 B

Visibility cm

46,40 45,oG 44.31 42,93 38,67 46,91

V/Vb

ICo

I

E

V/Vb = 0,018

(calculated) E

= 0,02

1 0,97 0,96 0,92 o ,83 1

1 0,89 0,85 0,75 0,46 1

1 0,97 0,96 0,93

1 0,97 0,96

0,81 1

o $0 1

1 0,86

1 0,96 0,945 o,90 0,72 1

0,96 0,94 o ,89 o ,71 1

0,92

1

32,04 30,88 29,69 28,60 25,49 31,95

(1,72) (1,45) (1,77) (1,81) (2,44) (1,53)

1 0,96 0,93 o,89 1

0,675 0,325 1

27,49 25,70 25,57 24,06 20,48 27,39

(1,07) (1,64) (1,44) (2,08) (1,62) (1,78)

1 0,94 0,93 0,87 0,75 1

1 0,83 0,78 0*,625 0,225 1

1 0,95 0,94 0,88 0,63 1

o $8 o ,62 1

24,56 22,56 22,16 20,84

(1,68) (1,26) (1,49) (0,96)

1 0,91 o,90 0,81

25,63

(2,94)

1

1 0,82 0,74 0,60 0,16 1

1 0,95 0,93 0,87 0,55 1

1 0,95 0,92 o ,87 0,53 1

--

-_

0,80

--

0,80

1 0,95 0,93

e x p e r i m e n t a l s e t u p t h e r e f l e c t i o n o f t h e ground had no e f f e c t on t h i s r a t i o ( s e e f i g . 2 ) : t h e e f f e c t o f t h e r e f l e c t i o n o f t h e ground on t h e i n h e r e n t b r i g h t n e s s o f t h e t a r g e t compensates t h a t on t h e b r i g h t n e s s o f t h e h o r i z o n . A l t h o u g h t h e two assumptions, used f o r t h e t h e o r e t i c a l f o r m u l a f r o m Faxvog & K o e s s l e r , c o u l d n o t be proven e x p e r i m e n t a l l y , t h e i r f i n a l formual r e p r e s e n t s a good a p p r o x i m a t i o n , a s shown i n f i g . 2. O n l y a t s t r o n g a b s o r p t i o n t h e t h e o r e t i c a l r e s u l t s i n c r e a s e f a s t e r t h a n t h e e x p e r i m e n t a l measurements. Because o f t h e l a c k o f a good t h e o r e t i c a l l y bahed formula, w h i c h c o u l d g i v e t h e v a r i a t i o n o f t h e i n h e r e n t c o n t m s t w i t h i n c r e a s i n g a b s o r p t i o n , i t i s necessary t o measure t h e r a t i o o f t h e i n h e r e n t brightness o f t h e t a r g e t t o the brightness o f the horizon a t t h e e x i s t e n t absorption i n order t o determine t h e v i s i b i l i t y o f non-perfectly black o b j e c t s i n absorbing media ( s e e t a b l e 3 ) .

311

Table 3 shows t h e v i s i b i l i t y o f b l a c k and g r e y t a r g e t s i n a non a b s o r b i n g atmosp h e r e a n atmosphere w i t h 25 % and 50 % o f t h e e x t i n c t i o n beeing due t o a b s o r p t i o n . We have assumed two p o s s i b l e p a r t i c l e c o n c e n t r a t i o n s , h i g h c o n c e n t r a t i o n mean5 l o w v i s i b i l i t i e s and t h u s a h i g h v e r t i c a l o p t i c a l d e n s i t y and t h e r e f o r e a l a r g e p o r t i o n o f d i f f u s e l i g h t i l l u m i n a t i n g the t a r g e t ( s i m i l a r t o our simulation e x p e r i m e n t s ) ; l o w c o n c e n t r a t i o n means h i g h v i s i b i l i t y and t h e t a r g e t beeing m a i n l y i l l u m i n a t e d by d i r e c t s u n l i g h t . The d i f f e r e n t shades o f g r e y would correspond t o c o n i f e r 5 w i t h t h e sun b e h i n d t h e t a r g e t ( G l ) , c o n i f e r s 90' c o n c r e t e a t 90'

f r o m t h e sun (GZ),

(G3), c o n c r e t e i l l u m i n a t e d b y t h e sun (G4). The v i s i b i l i t y o f t h e

b l a c k t a r g e t was n o r m a l i z e d t o 1. I n p u r e s c a t t e r i n g t h e v i s i b i l i t y o f t h e g r e y t a r g e t s a r e up t o 20 % l o w e r b o t h f o r s t r o n g and w e a k l y r e f l e c t i n g grounds. W i t h i n c r e a s i n g a b s o r p t i o n t h e v i s i b i l i t y o f a l l g r e y t a r g e t s decreases, f o r d a r k t a r g e t s t h e r e f l e c t a n c e o f t h e ground has a minimal i n f l u e n c e , e x c e p t f o r 50 % a b s o r p t i o n and l o w c o n c e n t r a t i o n , where t h e a d d i t i o n a l r e f l e c t i o n o f t h e ground has a marked i n f l u e n c e on t h e luminance o f t h e h o r i z o n . F o r t h e l i g h t e r t a r g e t s (G3, 54) t h e same i s t r u e ,

t h e i n c r e a s e i n v i s i b i l i t y f o r 64 a t 50 % a b s o r p t i o n

and l o w c o n c e n t r a t i o n i s caused b y t h e t a r g e t b e e i n g b r i g h t e r t h a n t h e h o r i z o n . TABLE 3 V i s i b i l i t y i n d i f f e r e n t a b s o r b i n g atmospheres w i t h a s t a n d a r d v i s i b i l i t y o f 1. Target

Pure s c a t t e .

25 % absorp. h i b h concen. weak. s t r o n g r e f l e c t i ng

weak. s t r o n g r e f l e c t i ng Black ~~

1

1 ~

~

25 % absorp. l o w concen. weak. s t r o n g r e f l e c t i ng

50 % absorp. h i g h concen. weak. s t r o n g r e f l e c t i ng

50 % absorp. l o w concen. weak. s t r o n g r e f 1ec t ing

1

1

1

1

1

1

1

1

~~

Grey 1

0,97

0,97

0,96

0,96

0,96

0,95

0,94

0,94

0,91

0,83

Grey 2

0,96

0,96

o,94

0,94

0,94

0,92

0,92

0,91

0,86

o,70

Grey 3

0,92

0,92

o,90

0,89

0,89

0,85

0,84

0,83

0,70

0,43

Grey 4

0,80

0,80

0,71

0,71

0,66

0,41

0,23

0,22

0,80

1,06

G e n e r a l l y one can say: An i n c r e a s e o f t h e a b s o r p t i o n o f t h e atmospheric a e r o s o l ( w i t h t h e e x t i n c t i o n c o e f f i c i e n t r e m a i n i n g c o n s t a n t ) does n o t change t h e v i s i b i l i t y

of b l a c k t a r g e t s . The v i s i b i l i t y o f nonblack t a r g e t s decreases w i t h i n c r e a s i n g a b u e r p t i o n , t h e decrease i s l a r g e r f o r atmospheres w i t h h i g h amounts o f d i f f u s e l i g h t and f o r s t r o n g l y r e f l e c t i n g ground. F o r t h e model c a l c u l a t i o n s o f t a b l e 3, t h e extreme cases, b o t h f o r t h e amount o f d i f f u s e l i g h t and t h e r e f l e c t i o n o f t h e ground have been chosen, so t h a t most o f t h e cases t o be expected w i l l l i e i n between.

312

snow f i e l d s ) w i l l be b e t t e r v i s i b l e i n a s t r o n g l y

O n l y v e r y b r i g h t t a r g e t s (e.g.

a b s o r b i n g atmosphere ( M i d d l e t o n 1952), because t h e p o s i t i v e i n t r i n s i c c o n t r a s t o f the t a r g e t r e l a t i v e t o the horizon increases, since the brightness o f the h o r i z o n decreabes due t o a b s o r o t i o n . REFERENCES Dessenb, H.,

1944, " R e l a t i o n e n t r e 1 ' a b s o r p t i o n p a r 1 'atmosphere e t l a v i s i -

b i l i t 6 " , C.R.

Acad. S c i . 218, pp. 685 - 687

and R o e s s l e r , D.M.,

Faxvog, F.R.,

1978, "Carbon a e r o s o l v i s i b i l i t y vs. p a r t i -

c l e s i z e d i s t r i b u t i o n " , A p p l . Optic. Horvath, H.,

A t m . Environment 4 , pp. 177

Horvath, H.,

17, pp. 2612-2616

1911 a, "On t h e a p p l i c a b i l i t y o f t h e Koschm:edcr b : s i h i i i t y and P r e s l e , G.,

-

formula",

134

1979, "Measuremenbof v i s i b i l i t i e s i n s i m u l a t e d

atmospheres ( h y d r o s o l s ) and a p p l i c a t i o n s t o r e a l atmospheres", Aero-

sols research a t the I n s t i t u t e f o r Experimental Physics o f the U n i v e r s i t y o f Vienna, P a r t I 1 K e r k e r , M.,

1969, "The s c a t t e r i n g o f 1 i g h t and o t h e r e l e c t r o m a g n e t i c r a d i a t i o n " ,

New York: Academic p r . 1924, " T h e o r i e d e r h o r i z o n t a l e n S i c h t w e i t e " , B e i t r . z . Phys.

Koschmieder, H.,

f r e i e n A t m . 12, pp. 33 - 53 and 1 7 1

-

181

1976, " O p t i c s o f t h e atmosphere",

McCartney, E.J., M i d d l e t o n , W.E.K.,

John Wiley, New York

1952 and 1963, " V i s i o n t h r o u g h t h e atmosphere", U n i v e r s i t y

o f T o r o n t o Press, Toronto R o e s s l e r , D.M.,

and Faxvog, F.R.,

1981, " V i s i b i l i t y i n a b s o r b i n g a e r o s o l s " ,

A t m . Environment 15, pp. 151

-

156

ACKNOWLEDGEMENT: T h i s work was s u p p o r t e d i n p a r t by a g r a n t o f t h e "Fonds z u r Forderung d e r w i s b e n s c h a f t l i c h e n Forschung i n U s t e r r e i c h " , g r a n t number 3453.

313

CHANGES OF LOCAL PLANETARY ALBEDO BY AEROSOL PARTICLES HARTMUT GRASSL, I n s t i t u t fur Meereskunde, Universitat of Kiel, F R G MADELEINE NEWIGER, Max-Planck-Institut fur Meteorologie, Hamburg, FRG

ABSTRACT T h e c l i m a t e p a r a m e t e r local p l a n e t a r y a l b e d o i s a f f e c t e d both in c l e a r a n d cloudy a r e a s by a e r o s o l particles. In b o t h cases t h e a l b e d o may i n c r e a s e or d e c r e a s e i f

turbidity

increases, i.e. t h e r e a r e a r e a s w h e r e a n additional pollution l e a d s t o a n energy gain o r loss. While t h e most i m p o r t a n t p a r a m e t e r s in c l e a r a r e a s a r e s u r f a c e albedo a n d t h e mass absorption c o e f f i c i e n t of t h e particles, aerosol p a r t i c l e c o n c e n t r a t i o n v i a t h e number of condensation nuclei a n d a g a i n absorption a r e t h e dominating f a c t o r s i n clouds. A reappraisal of known bulk formulae for c l e a r a r e a s points t o additional p a r a m e t e r s determining t h e crossover from h e a t i n g t o cooling. T h e most i m p o r t a n t additional p a r a m e t e r i s sun elevation, however, a e r o s o l o p t i c a l d e p t h also has to b e considered. T h e weakness of former e s t i m a t e s of cloud a l b e d o c h a n g e w i t h aerosol p a r t i c l e c h a r a c t e r i s t i c s i s demonstrated f o r broad cloud

drop s i z e distributions and for simultaneous c h a n g e s in p a r t i c l e number, size, a n d chemical composition. T h e t e r r e s t r i a l radiation does n o t c o m p e n s a t e f o r t h e partly d r a s t i c changes in t h e solar radiation in c l e a r a n d cloudy a r e a s , a g a i n pointing t o a s t r o n g influence of aerosol p a r t i c l e s o n local p l a n e t a r y albedo.

INTRODUCTION Minor c o n s t i t u e n t s of t h e a t m o s p h e r e c a n play a n important role for climate. If t h e s e 'climatic' minor c o n s t i t u e n t s a r e moreover influenced i n t h e i r c o n c e n t r a t i o n of distribution by human a c t i v i t i e s t h e y become especially important. A s long as many of t h e feedback loops of t h e n a t u r a l c l i m a t e system a r e poorly o r n o t at all understood, o u r c o n c e r n with global

man-made p e r t u r b a t i o n s of t h e c l i m a t e system h a s t o b e speculative, being justified only by potentially dangerous c l i m a t i c changes a n d by obvious regional perturbations, as for i n s t a n c e h e a t islands of c i t i e s a n d acid rain, B e s t , b u t still only p a r t l y understood of a l l t h e possible c l i m a t i c perturbations i s t h e consequence of t h e greenhouse effect of radiatively a c t i v e g a s e s like C O

.

N 0, C H T h e 2' 2 4 e s t i m a t i o n of t h e a e r o s o l p a r t i c l e influence, however, i s much m o r e complicated e v e n for c l e a r a r e a s of t h e a t m o s p h e r e s i n c e 1) t h e seasonal a n d local c o n c e n t r a t i o n , composition and s i z e of t h e p a r t i c l e s v a r i e s tremendously, 2) t h e i n c r e a s e of p a r t i c l e c o n c e n t r a t i o n i s questioned, a n d 3) e v e n t h e sign of t h e local e n e r g y budget c h a n g e equivalent to a change in local p l a n e t a r y a l b e d o is u n c e r t a i n (ref. 1) depending o n s u r f a c e albedo, absorption a n d

314 s c a t t e r i n g c h a r a c t e r i s t i c s of t h e particles.

-

Since aerosol p a r t i c l e s

besides c i r c u l a t i o n p a t t e r n s - d e t e r m i n e t h e microphysics of

clouds, and t h u s a r e responsible for p r e c i p i t a t i o n a n d t h e radiation budget of clouds, t h e r e is n o justification for a n omission of t h e a e r o s o l particles’ influence o n t h e e n e r g y budget i n cloudy areas. A s a c o n s e q u e n c e of t h e u n c e r t a i n t i e s mentioned, t h e following s e c t i o n s will f i r s t give a n assessment of t h e a c c u r a c y of a l r e a d y known bulk formulae f o r c l e a n a r e a s , will show t h e i m p o r t a n c e of t h e p a r t i c l e s for t h e r a d i a t i v e t r a n s f e r i n a n a t m o s p h e r e w i t h clouds, and will also d e p i c t p r e s e n t u n c e r t a i n t i e s in estimating cloud a l b e d o changes just by showing t h e number of a c t i v a t e d p a r t i c l e s f o r given c h a n g e s in number, size, composition and s u r f a c e tension. ALBEDO IN A CLOUDLESS ATMOSPHERE T w o a t t e m p t s h a v e been made (ref. 1, 2) t o d e s c r i b e t h e i n f l u e n c e of aerosol p a r t i c l e s o n t h e r a d i a t i o n budget in cloudless a t m o s p h e r e s by bulk formulae. R a d i a t i v e t r a n s f e r c a l c u l a t i o n s using t h e

6

-Eddington approximation have b e e n c a r r i e d o u t t o test t h e

validity of t h e s e bulk formulae. Comparisons w i t h socalled e x a c t calculations with t h e matrix o p e r a t o r method show a good a g r e e m e n t for i n t e g r a l f e a t u r e s as albedo. For i n s t a n c e t h e a l b e d o d i f f e r e n c e f o r t w o cloud types, a p u r e w a t e r cloud a n d a n aerosol contaminated cloud, a r e 0.1186

a n d 0.1152

6

for t h e matrix o p e r a t o r a n d t h e

-Eddington method

respectively. In a f i r s t s t e p ChGlek and Coackley (ref. I ) derived a relationship b e t w e e n t h e r a t i o absorption-to-backscattering a / b of a n aerosol a n d t h e s u r f a c e a l b e d o A

E (1 -- As)2T

a

S’

>

o

heating

=

o

equilibrium

0

heating

Again n e i t h e r t h e s p e c t r a l d e p e n d e n c e of t h e r a t i o a/b(p) nor t h e variation of optical thickness is considered. Fig. 2 shows t h e resuIts of t h e bulk formula (Eq. 2) a n d o u r c a l c u l a t i o n s i n terms of a/b(p) a n d t h e c r i t i c a l s u r f a c e albedo As f o r f i v e values p = cos 0 from 0.1 t o 0.5 and t h e t w o "extremes" for a / b from Fig. 1. T h e formula (Eq. 2) o v e r e s t i m a t e s t h e dependence o n p;

316

-_

._

zenith angles cos0 0 09

07 05 a03 0

00’

Fig. 2: a/b(p) a s a function of t h e c r i t i c a l s u r f a c e a l b e d o A f o r f i v e d i f f e r e n t z e n i t h a n g l e s p = cos 8 using Eq. 2 (-----) for t w o d i f f e r e n t aerosol siz; distributions. Own calculations T 6 0.5). (-) a l s o show d e p e n d e n c e o n o p t i c a l d e p t h 1 (0.1 t h e d i f f e r e n c e s being l a r g e s t f o r low sun e l e v a t i o n a n d low values a/b. T h e question w e t h e r a n additional aerosol l a y e r c a u s e s cooling o r h e a t i n g of t h e atmosphere-earth system c a n obviously n o t b e a n s w e r e d by t h e formulae (1) o r (2). AEROSOL PARTICLES AND RADIATION PARAMETERS O F WATER CLOUDS

If a e r o s o l p a r t i c l e s a b s o r b solar radiation (mainly i n t h e visible spectrum a n d in ‘windows’ b e t w e e n w a t e r vapour bands in t h e n e a r infrared), t h e r e i s a high probability t h a t t h e o r d e r of magnitude of absorption i s k e p t a f t e r t h e incorporation i n t o cloud air. This should hold w h e t h e r t h e p a r t i c l e s have been used as a condensation nucleus, c a t c h e d by cloud d r o p l e t s o r only grown with r e l a t i v e humidity t o a size normally n o t called a cloud droplet. C a l c u l a t i o n s by o n e of t h e a u t h o r s (ref. 4) a n d a n experimental verification f o r a f e w c a s e s by And& et al. (ref. 5), w h e r e simultaneous samples of cloud w a t e r a n d t h e una c t i v a t e d component w e r e available have confirmed t h i s expectation. If only t h e number of aerosol p a r t i c l e s changes, however, t h e i r chemical composition and r e l a t i v e s i z e distribution does not, t h e number of cloud d r o p l e t s under a fixed circulation p a t t e r n , e q u i v a l e n t t o fixed s u p e r s a t u r a t i o n and liquid w a t e r c o n t e n t , should c h a n g e i n t h e s a m e direction. Then t h e following r e l a t i o n b e t w e e n condensation nuclei number C or optical depth

T and t h e number of aerosol p a r t i c l e

should e x i s t (ref. 6-8):

N under t w o d i f f e r e n t situations

317 c2

N2a

I -

(-)

-

c2

NI

t 2

N2R (--)

-5

N1

-=

a = 0.8 as measured by Warner a n d Twomey (ref. 9) for a s p e c i f i c case

(3)

13 -0.3 if using a= 0.8, assuming narrow d r o p l e t s i z e distribution a n d T = 2 . C * r-z with t; = mean s q u a r e radius a n d C* = condensation nuclei used above unit surface.

(4)

If t h e a e r o s o l p a r t i c l e s a r e not only increasing in number b u t a l s o have a higher mass

absorption c o e f f i c i e n t k , t h e resulting clouds following r e l a t i o n (3) have higher optical d e p t h a n d a b s o r b stronger. S i n c e increasing

T, e n h a n c e s a l b e d o a n d increasing k lowers

albedo, both e f f e c t s additionally depending o n 7; for t h e s t a n d a r d case, t h e r e should e x i s t a n optical depth extent

Tc with no a l b e d o c h a n g e (T "35

- 0.8 km at 0.2

for highly polluted c a s e 2, v e r t i c a l

gmm3 liquid w a t e r conten?). Thinner clouds become brighter, thicker

clouds darker. If t h e absorption c o e f f i c i e n t remains c o n s t a n t , a l l clouds in a n increasingly polluted a t m o s p h e r e r e f l e c t more solar radiation, leading t o a n energy loss for t h e atmosphere-earth

system. This discussion of cloud albedo c h a n g e w i t h aerosol p a r t i c l e

changes included a n albedo e n h a n c e m e n t d u e t o a f l a t t e n i n g of t h e s c a t t e r i n g o r phase function which a l w a y s accompanies a decreasing mean d r o p l e t size. T h e variations of absorption, r e f l e c t i o n and transmission i n t h e i n t e g r a t e d

solar spectrum (0.3-3.7

vm

wavelength) c a u s e d by v a r i a t i o n s of a n a l y t i c a l cloud d r o p l e t s i z e distributions within observed limits have been presented e l s e w h e r e (ref. 10). Before questionning r e l a t i o n (4),which may b e necessary f o r simultaneous changes in size, c h e m i s t r y a n d number of p a r t i c l e s , in t h e n e x t section, w e will answer t h e question: Does longwave r a d i a t i o n compensate t h e e f f e c t s of aerosol p a r t i c l e variations o n shortw a v e cloud p a r a m e t e r s ? Again using t h e matrix-operator method f o r r a d i a t i v e t r a n s f e r c a l c u l a t i o n s f o r a n azimutally a v e r a g e d , plane parallel a t m o s p h e r e a n d accounting f o r t h e inhomogeneous s o u r c e extension by Wiscombe (ref. 1 I), our answer is: t h e longwave radiation d o e s n o t c o m p e n s a t e t h e e f f e c t s in t h e s h o r t w a v e domain. In Fig. 3 t w o cloud transformations

covering

t h e conceivable r a n g e from maritime (typical d r o p l e t

size

distribution C 5 a f t e r Deirmendjian (ref. 12) to c o n t i n e n t a l ( C l ) a n d c o n t i n e n t a l to strongly polluted (C3) l e a d to nearly t h e same n e t flux d i f f e r e n c e

A Fnet

= Fnet (C5)

-

Fnet (C1)

i n t h e s h o r t w a v e domain. N o i n c r e a s e i n t h e mass absorption c o e f f i c i e n t k is included. Additional absorption

A Fn e t in t h e longwave p a r t a r e a t l e a s t o n e o r d e r of

i n t h e s t r o n g e r pollution case would lower b o t h curves. T h e

values i n c r e a s e w i t h sun elevation.

A Fnet

magnitude lower a n d f o r t h e C5-C1 transformation e v e n a d d t o t h e s h o r t w a v e effect T h e s e small

a Fnet

a r e caused by t w o competing mechanisms. By adding p a r t i c l e s T is

increased lifting t h e e m i t t i n g l a y e r t o lower t e m p e r a t u r e s , causing r e d u c e d emission. This would f a v o r a compensation. T h e single s c a t t e r i n g albedo, however, i s lowered at t h e same time, bringing cloud emission n e a r e r t o blackbody emission, t h e r e f o r e increasing emission t o space.

318

AFnet

200

i -

100 : 50 -

-

optical depth at 0.55pm 26(C1) mean liquid water content = 0.2 gm-3

20 -

---

c1 -c3 continental 3 highly polluted

-

10 :

C5-Cl

continent a1 ---------

maritime

521

3

K

1

LW

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 cos 0 fig. 3. Radiative n e t f l u x d i f f e r e n c e A F = F (C5) - F function of solar zenith angle; upper &%es f0"rt shortwa%?

'

- F (C3) as a and lower (constan"e$alues) for

(1) or Fnet(C1)

long wave radiation. These results apply t o high lying clouds as well. An influence of pollution for high clouds is, however, much more uncertain because pollution by aerosol particles is f i r s t of all a problem of t h e planetary boundary layer. Since t h e location, t h e type and t h e height of a cloud determine, whether a n increase in cloud cover causes a n energy loss or gain for t h e earth-atmosphere system (for details

see Hartmann and Short (ref. 13)), additional aerosol particles without strongly increasing absorption favor a still more dominating albedo e f f e c t and thus enhanced energy losses if cloud amount should increase. ACTIVATED PARTICLES FOR DIFFERENT AEROSOL POPULATIONS T h e foregoing discussion avoided a n explicit t r e a t m e n t of changes in chemical composition and s i z e distribution of aerosol particles. Also changes in liquid water c o n t e n t and maximum supersaturation, which

-

even at fixed circulation p a t t e r n s

particle characteristics, have been neglected.

-

would vary with

T h e following example shows possible

variations of t h e number of a c t i v a t e d particles as a consequence of varying aerosol

319 p a r t i c l e parameters. T h e equations used stem from Hanel (ref. 14) a n d t h e example shown should only give a n impression of t h e possible reactions. T h e p a r a m e t e r c h a n g e s in Fig. 4 a r e at t h e margin of applicability of t h e r e l a t i o n s used, s i n c e Hanel's assumption of only minor c h a n g e s i n liquid w a t e r c o n t e n t

-

if comparing basic a n d new state - a r e already

stressed. Variations i n s u r f a c e tension a n d w a t e r u p t a k e with r e l a t i v e humidity, resulting from c h a n g e s i n chemical composition a r e n o t shown explicitly in Fig. 4, because r e a c t i o n s t o a 10% i n c r e a s e in p a r t i c l e numbers (n /n =1.1) a r e equivalent t o a lowering of s u r f a c e 1

0

tension by 6% or a n i n c r e a s e of t h e exponential mass i n c r e a s e c o e f f i c i e n t by 6.6%. T h e exponent

y

i n t h e r e l a t i o n b e t w e e n t h e r a t i o of cloud d r o p l e t s a n d t h e r a t i o of aerosol

p a r t i c l e numbers CCN1/CCNo =(NI/No)Y

, which

i s t h e r e s u l t of a l l t h e influences,

t h e r e f o r e h a s t o b e known for d i f f e r e n t a e r e a s a n d aerosol types.

16

I

I

.-c 121

0

I I I I I I I I I I I 1

2

3

4

5

6

7

8

9

10.10-5

liquid water mass mixing ratio

Fig. 4. A c t i v a t e d p a r t i c l e s in p e r c e n t as a funFtion of liquid w a t e r mass mixing ratio. T h e s u p e r s a t u r a t i o n at t h e basic state is 5 . 10- ; c( a n d 0: a r e t h e exponents of t h e power l a w s i z e distributions within t h e 0.01-0.1 a n d t h e 0.1-6.0 pm p a r t i c l e s i z e range. N /N is t h e r e l a t i v e p a r t i c l e number, n /n - 1.1 IS equivalent t o a 10 p e r c e n t i n c r e a s e 1 0 inlpa?ticle numbers. DISCUSSION Aerosol p a r t i c l e s play a n i m p o r t a n t r o l e f o r s h o r t w a v e r a d i a t i v e t r a n s f e r both i n c l e a r a n d cloudy areas. T h e e r e a r e only t w o p a r a m e t e r s grossly determining t h e sign of t h e energy-budget variation. In c l e a r and cloudy a t m o s p h e r e s o n e of t h e s e main parameters is t h e imaginary p a r t of t h e r e f r a c t i v e index of p a r t i c l e s , while t h e second o n e is s u r f a c e a l b e d o i n c l e a r a r e a s a n d o p t i c a l thickness of clouds i n cloudy areas. High s u r f a c e albedo a n d mean v a l u e s of t h e imaginary p a r t f o r c o n t i n e n t a l aerosol p a r t i c l e s favor energy gain

320 of t h e a t m o p s h e r e - e a r t h system. On t h e o t h e r hand thin w a t e r clouds under conditions w i t h

m e a n imaginary p a r t f a v o r a n e n e r g y loss. T h e s e p a r t l y o v e r simplified s t a t e m e n t s h a v e t o be modified in b o t h areas. T h e crossover from e n e r g y loss t o e n e r g y g a i n i s a f u n c t i o n of solar z e n i t h a n g l e a n d o p t i c a l d e p t h of t h e a e r o s o l p a r t i c l e s too. T h e crossover in cloudy a r e a s may e v e n n o t b e found, if cloud d r o p l e t s i z e distributions o c c u r i n g b e f o r e a c h a n g e i n p a r t i c l e c h a r a c t e r i s t i c s a r e broad a n d c h a n g e s in p a r t i c l e number a r e accompanied by a n i n c r e a s e in s u r f a c e t e n s i o n or a v a r i a t i o n in t h e s l o p e of t h e a e r o s o l p a r t i c l e s i z e dist r i b u t i o n prior to cloud formation. T h e t h e r m a l i n f r a r e d c a n n o t at all c o m p e n s a t e t h e possible v a r i a t i o n s in t h e s o l a r spectrum. In c l e a r a r e a s t h e longwave o p t i c a l d e p t h t e

i s by a f a r l o w e r t h a n t

in t h e

s h o r t w a v e s p e c t r u m e v e n if only a c c o u n t i n g f o r t h e a b s o r p t i o n o p t i c a l depth. T h e cloud d r o p l e t s i z e v a r i a t i o n s c a u s e d by c h a n g e s in a e r o s o l p a r t i c l e number a n d s i z e as well as chemical composition, which s h i f t t h e e m i t t i n g l a y e r s upwards t o l o w e r t e m p e r a t u r e s if a r e d u c t i o n i n m e a n d r o p l e t s i z e should o c c u r , a r e a c c o m p a n i e d by a n i n c r e a s e i n single s c a t t e r i n g a l b e d o fully compensating for r e d u c e d emission a t l o w e r temperatures. T h e o v e r a l l e f f e c t of human a c t i v i t i e s c a n only b e a s s e s s e d if reliable v a l u e s of p a r t i c l e c o n c e n t r a t i o n depending on l a t i t u d e a n d h e i g h t f o r n a t u r a l a n d disturbed cases a r e available. We hope t h a t w e c a n give t h i s a s s e s s m e n t r e f e r i n g t o a two-dimensional global a e r o s o l t r a n s p o r t model which i s now t e s t e d by our group. ACKNOWLEDGEMENT This work i s mainly s u p p o r t e d by t h e Environmental P r o t e c t i o n Agency of t h e F R C under G r a n t 104 02 621 a n d t h e European Commission under G r a n t CL I-044-D(B). REFERENCES 1 P. Ch$lek a n d J.A. C o a c k l e y , S c i e n c e , 183 (19741, 75-77. 2 J.A. C o a c k l e y a n d P. ChGlek, J. Atm. Sci., 32 (1975), 409-418. 3 K. Fischer, Contr. Atm. Physics, 46 (1973), 89-100. 4 H. Grassl, Contr. Atm. Physics, 48 (1975), 199-210. 5 K. Andrg, R. Dlugi a n d G. S c h n a t z , J. Atm. Sci., 38 (1981), 141-155. 6 T.S. Twomey, in G A R P C l i m a t e Dynamics Sub-programme, R e p o r t of IOC-Study C o n f e r e n c e o n p a r a m e t e r i z a t i o n of e x t e n d e d cloudiness, Appendix E, WMO, G e n e v a , 1978. 7 H. Grassl, R e i h e A, H e f t 37, Hamburger Geophysik. Einzelschriften, 1978, pp., 136. 8 H. Grassl, i n W. Bach, J. P a n k r a t h a n d W.W. Kellogg (Eds.), Man's Impact o n c l i m a t e Elsevier, Amsterdam, 1979, 229-241. 9 3. Warner a n d T.S. Twomey, J. Atm. Sci., 25 (19671, 704-706. 10 H. Grassl, Idoj&&s, in press (1982). 11 W.J. Wiscombe, J. Quart. Spectrasc. Radiat. T r a n s f e r , 16 (1976), 477-489. 12 D. Deirmendjian, E l e c t r o m a g n e t i c s c a t t e r i n g on s p h e r i c a l polydispersion; Elsevier, Amsterdam (1969), 290 pp. 13 D.L. H a r t m a n n a n d D A . Short, J. Atrn. Sci., 37 (1980), 1233-1250. 14 G. Handel, Contrib. Atm. Physics, 54 (19811, 159-172.

321

LASER TRANSMISSOMETER --A DESCRIPTION P.H. LEE University of California at Santa Barbara T.E. HOFFER, D.E. SCHORRAN Desert Research Institute, University of Nevada System E.C. ELLIS AND J.W. MOYER Southern California Edison

ABSTRACT A

laser

atmospheric

transmissometer is

described

extinction measurements.

that

The

is

suitable

for

instrument design

long path

incorporates

several unique features which greatly enhance the signal to noise ratio of the system. These are apodization of controlled beam

aiming

and

the

output

automatic

beam

beam

by

conical

width measurement

intervals. The system is completely automated and

utilizes

scan, servo at

regular

a micro-computer

designed by the DRI for data acquistion and s e r v o control.

INTRODUCTION The

optical

transmission of a particular medium is defined as the ratio of

t.he initial intensity to the final intensity of light after the medium.

Clearly

it

has

traversed

this number will vary with the path length through the

medium as well as the characteristic extinction of the medium. For a uniEorm medium, the transmission, T, is given by the equation: T=exp(-kL)=I/Io

,

(1)

where L is the path length and k is the extinction coefficient. The extinction

322 coefficient is, in

turn, the

sum

of

the

absorption coefficient and

the

scattering coefficient. In

the

atmosphere, the transmission in the visible portion of the spectrum

is affected principally by scattering. As a consequence, the transmission is a weak function of color and any convenient wavelength

can be

for

used

such

measurements. We have conceived and built a transmissometer that uses a red He-Ne laser to measure

atmospheric

extinction over

long paths.

The instrument has several

unique design features which allow the accurate measurement of small changes in transmission.

INSTRUMENT ARCHITECTURE The instrument has two paths, one for the reference and one for the This

is

a

conventional way

to

eliminate

sample.

the errors due to changes in the

sensitivity of the detector or in the intensity of the source. We have tested the instrument over a sample length of about two In

practical

planned.

field

operation, path

These path

lengths

are

lengths as

singly

folded

kilometers.

long as ten kilometers are by

the use

of

a

remote

retroreflector that requires no input power. The

optical

plan

of

this

instrument

is

shown

in Figure 1.

With the

exception of the retroreflector array, all of the components are mounted single rigid plate. and

the

on

a

The data paths between the components on the optical table

other major electronic components associated with the transmissometer

are illustrated in Figure 2 . Some of the block names are abbreviated as listed in the following table.

323 TABLE 1

Abbreviations S SM RSFM CSM VSM HSM SCM IRET IREF DME

SOURCE SPLITTING MECHANISM REFERENCE SIGNAL FOCUSING MECHANISM CONICAL SCAN MECHANISM VERTICAL SERVO MECHANISM HORIZONTAL SERVO MECHANISM SIGNAL C O M B I N I N G MECHANISM RETURN SIGNAL INTENSITY REFERENCE SIGNAL INTENSITY DEMODULATING ELECTRONICS

The remainder o f t h i s s e c t i o n on i n s t r u m e n t a r c h i t e c t u r e w i l l

describe

the

f u n c t i o n and s t r u c t u r e o f t h e s e b l o c k s and components. helium neon l a s e r i s used a s t h e s i g n a l s o u r c e .

Laser--A has

an

output

operates in a

of 10 m i l l i w a t t s a t a wavelength o f 6 3 3 nanometers.

power single

The l a s e r s e l e c t e d

transverse

mode

with

a

Gaussian

intensity

It

profile.

Angular

d r i f t o r beam p o i n t i n g s t a b i l i t y i s l e s s t h a n 0.050 m i l l i r a d i a n s a f t e r

warmup.

The beam d i v e r g e n c e i s about one m i l l i r a d i a n .

The

output

is

light

plane polarized. Source

Splitting

Mechanism

(SSM)--A

p e r c e n t as i n t e n s e as t h e main beam polarizing

beam

splitter.

The

is

r e f e r e n c e s i g n a l i n i t i a l l y about t e n split

reference

off signal

a d j u s t e d by r o t a t i n g t h e l a s e r about i t s a x i s . turned

to

as semb 1y

.

be

parallel

L i g h t Chopper--The

to

the

main

beam

The

used

are

this

block

by

a

i n t e n s i t y can b e c o a r s e l y reference

beam

is

then

f o r e n t r y i n t o t h e l i g h t chopper

l i g h t chopper i s a c o m e r c i a l l y a v a i l a b l e component

u s e s a r o t a t i n g d i s c w i t h a x i a l l y spaced s l o t s . radii

inside

that

Two sets o f s l o t s a t d i f f e r e n t

t o modulate t h e main beam and t h e r e f e r e n c e beam a t d i f f e r e n t

frequencies. R e f e r e n c e S i g n a l Focusing Mechanism (RSFM)--In reference

this

block,

the

modulated

s i g n a l i s focused by a l e n s o n t o t h e end of a f i b r e o p t i c bundle.

In

a d d i t i o n , mounting space i s provided ahead o f t h e l e n s f o r f i l t e r s t h a t f u r t h e r attenuate the reference signal provided

strength.

by f i x e d a b s o r p t i o n f i l t e r s .

a rotatable polarizer.

Coarse

steps

in

attenuation

are

F i n e a t t e n u a t i o n c o n t r o l i s provided by

324

PRIMARY MIRROR RETROREFLECTOR HORIZONTAL SERVO WEDGE PRISMS

VERTICAL SERVO WEDGE PRISMS

I

I

\"/

/

/ LASER'

POLARIZING BEAMSPLITTER

CONICAL SCANNER WEDGE PRISMS

LASER TRANSMISSOMETER OPTICS LAYOUT

Fig. L Laser transmissometer optics layout.

--I RETURN -._/SIGNAL

--

/ PHOTOMULTIPLIER TUBE

RECEIVING TELESCOPE

&--

TRANSMITTED

'

t

LL W

a

n z a I-

ki I

1

II I CONICAL SCAN

-VOLTAGE CONTROL AMP

HORZ. ERROR

Fig. 2. I n f o r m a t i c m signal links between the c o m p n e n t s on the optical table and the peripheral electronics.

325 C o n i c a l Scan Mechanism (CSM)--This rotate

c o n t i n u o s l y a t f i v e Hz.

block contains

time-averaged

apodization

properties

of

wedges

scan

is

twofold:

results

It

that

beam

toward

the

this

in

a

retreoreflector.

a r e t h e most u n u s u a l f e a t u r e o f t h i s i n s t r u m e n t .

and implementation of

that

t h e o u t p u t beam and i t p r o v i d e s a r e t u r n s i g n a l

of

s u i t a b l y modulated f o r s e r v o - p o i n t i n g These

pair

T h i s r o t a t i o n r e s u l t s i n a conical scan of the

The purpose o f t h i s c o n i c a l

main beam.

a

conical

scan

are

described

in

The t h e o r y

detail

in

the

d e s c r i p t i o n o f t h e t r a n s m i s s o m e t e r f e a t u r e s below. a d j u s t a b l e m i r r o r is used for the initial alignment

Mirror--This

Alignment

of t h e t r a n s m i t t e d s i g n a l beam. V e r t i c a l and H o r i z o n t a l Servo Mechanism (VSM, HSM)--These driven

by

the

are

the

devices

o u t p u t o f t h e s e r v o e l e c t r o n i c s t o d i r e c t t h e main beam toward

the retroreflector.

The d e t a i l s o f t h e s e r v o p r i n c i p l e s a r e a l s o c o n t a i n e d

in

t h e s e c t i o n on f e a t u r e s . Output

Mirror--This

mirror

launches

the

main

beam o n t o t h e a x i s o f t h e

receiving telescope. R e t r o r e f l e c t o r Array--This measuring

path.

The

component i s s i t e d a t t h e f a r

end

of

a

folded

c u r r e n t l y used c o n s i s t s o f f i f t e e n 2 . 5 cm c o r n e r

array

cubes. R e c e i v i n g Telescope--A laser

light.

component

is

with

eyepiece

This

reflecting telescope

t e l e s c o p e i s used t o c o l l e c t and f o c u s t h e

the

a

reflected

commercially a v a i l a b l e 1 2 . 5 cm d i a m e t e r replaced

by

the

signal

combining

mechanism. S i g n a l Combining Mechanism (SCM)--Within signals

are

combined

and

t h i s b l o c k t h e r e t u r n and r e f e r e n c e

d i r e c t e d toward t h e p h o t o m u l t i p l i e r t u b e .

A small

f r a c t i o n o f t h e combined l i g h t i s d i r e c t e d toward an a u x i l i a r y e y e p i e c e t o h e l p i n aligning t h e instrument.

The remainder o f t h e l i g h t

is

passed

series of s t o p s , c o l l i m a t o r s and f i l t e r s t o t h e p h o t o m u l t i p l i e r t u b e .

through

a

Care h a s

been t a k e n i n t h e d e s i g n of t h i s s i g n a l combining b l o c k t o make s u r e t h a t t h r e e i m p o r t a n t c r i t e r i a are m e t : 1)

The

light

from

both

beams must f a l l on e x a c t l y t h e same a r e a of t h e

326 photocathode. 2 ) The combined beams must be c o l l i m a t e d when p a s s i n g through t h e p o l a r i z e r

and t h e narrow band p a s s f i l t e r .

3 ) The f i e l d and a p e r t u r e s t o p s must be o p t i m i z e d f o r f u l l

suppression

of

any s t r a y l i g h t . Photomultiplier tube i s used.

Tube--A

commercially

available

high gain photomultiplier

I t h a s an end-on c a t h o d e w i t h a h i g h quantum e f f i c i e n c y

wavelength o f t h e He-Ne

at

the

laser.

Chopper Frequency Control--A

commercially a v a i l a b l e motor speed c o n t r o l t h a t

p r o v i d e s a s t a b l e chopping f r e q u e n c y . S i g n a l C o n d i t i o n i n g Electronics--A

commercially a v a i l a b l e u n i t t h a t performs

t h e f o l l o w i n g f u n c t i o n s : a d j u s t s t h e s i g n a l g a i n ; demodulates and d i s c r i m i n a t e s t h e r e t u r n and r e f e r e n c e s i g n a l s ; and r a t i o s t h e r e t u r n s i g n a l t o t h e r e f e r e n c e signal. Servo

Control

Electronics--Interface c i r c u i t r y t h a t processes conical scan

p o s i t i o n s i g n a l s from t h e CSM and t r a n s m i s s i o n measurements i n t o e r r o r

signals

t h a t p r o v i d e beam p o s i t i o n i n f o r m a t i o n . Field

Data

A c q u i s i t i o n Computer--A CMOS computer used f o r d a t a a c q u i s i t i o n

and t h e c o n t r o l o f a l l t r a n s m i s s o m e t e r f u n c t i o n s . proper

control

strategy

to

drive

The

computer

develops

the

s t e p p e r m o t o r s i n t h e VSM and HSM through

i n t e r r o g a t i o n o f t h e e r r o r s i g n a l s from t h e s e r v o c o n t r o l e l e c t r o n i c s i n

order

t o minimize p o i n t i n g e r r o r .

UNIQUE FEATURES OF THE TRANSMISSOMETER Our

transmissometer

has

several

unique

features.

The most i m p o r t a n t o f

t h e s e i s t h e a p o d i z a t i o n o f t h e beam. The o t h e r f e a t u r e s o f importance are

beam

width

measurement

and

uniform

intensity.

A p o d i z a t i o n by c o n i c a l s c a n

A l a s e r beam t y p i c a l l y h a s a Gaussian d i s t r i b u t i o n as i t s i n t e n s i t y p r o f i l e .

327 Thus,

if

t h e i n t e n s i t y , I , i s p l o t t e d a g a i n s t d i s t a n c e from t h e c e n t e r of t h e

beam, y , t h a t f u n c t i o n t a k e s t h e form

I=Io exp(-by2)

(2)

where t h e c o n s t a n t 10 d e f i n e s t h e i n t e n s i t y on t h e beam a x i s , and t h e c o n s t a n t , The e x p r e s s i o n i s e x a c t b o t h c l o s e t o t h e l a s e r ( i n

b , d e f i n e s t h e beam w i d t h .

In

t h e n e a r f i e l d ) and f a r away from t h e l a s e r ( i n t h e f a r f i e l d ) . field,

the

near

c o n s t a n t , b , i s a l i n e a r measurement u s u a l l y g i v e n i n m i l l i m e t e r s .

the

I n t h e f a r f i e l d , t h e c o n s t a n t , b , i s an a n g u l a r measurement normally g i v e n

milliradians.

3

Figure

in

i l l u s t r a t e s t h e c o n t o u r s o f i n t e n s i t y through such a

beam. When such a beam i s a p o d i z e d , some d e l i b e r a t e s t e p s

this

Gaussian

intensity

distribution,

c o n s t a n t independent of p o s i t i o n i n

the

i.e.,

to

beam,

y.

are

make

taken the

That

to

flatten

intensity, I, a

constant

intensity

d i s t r i b u t i o n s h o u l d p r e v a i l f o r some u s e f u l d i s t a n c e away from t h e beam a x i s . If

symmetrical Gaussian beam i s r o t a t e d about i t s own a x i s , t h e r e i s , o f

a

c o u r s e , no change i n i t s however,

the

intensity

profile

anywhere

along

the

beam.

If,

beam i s scanned smoothly about a n o t h e r a x i s somewhat i n c l i n e d t o

i t s own, t h e peak i n t e n s i t y a t t h e c e n t e r of t h e o r i g i n a l laser beam w i l l t r a c e o u t a cone i n s p a c e .

This i s i l l u s t r a t e d i n Figure 4 .

a t a p o i n t , p, i n t h i s f i g u r e . It

be

will

maximum

when

Consider t h e

intensity

Here t h e i n t e n s i t y w i l l f l u c t u a t e p e r i o d i c a l l y .

t h e l a s e r p o i n t s c l o s e s t t o i t and minimum when i t

p o i n t s f a r t h e s t away. The time averaged v a l u e of t h e p e r i o d i c a l l y v a r y i n g i n t e n s i t y o f f

the

scan

a x i s ( a t p i n F i g u r e 4 ) can b e made n e a r l y e q u a l t o t h e i n t e n s i t y sensed on t h e axis.

By

properly

selecting

the

scanning angle.

I n o t h e r words, t h e t i m e

averaged beam p r o f i l e can be shaped t o be remarkably f l a t i n

the

vicinity

of

the distant target. A p l o t o f t h e t i m e averaged i n t e n s i t y as a f u n c t i o n of p o s i t i o n with r e s p e c t t o t h e c e n t r a l a x i s o f c o n i c a l s c a n t h r o u g h such an F i g u r e 5.

apodized beam

i s shown a s

328

Fig. 3. Contours of normalized intersity for a laser beam of G a d a n Shape. The contour interval equals 0 1 units. Beam axis is directed through the paper at the onqh. X and Y represent distances measured in meters perpendicular to this axis. The eras section typifies a certain 1;Lser beam at a distance of sL5 K m from the source.

SCAN ABOUT THE LASER / RETRO REFLECTOR AXIS

-,,

I

...’.,.

DIRECTION OF

EZ’. LASER

Fig. 4. Conical Scan with a laser beam of G a d a n shape.

%-:*

329

GAUSSIAN PROFILE BEAM

APODIZED BEAM PROFILE

0.7

/

t

/

\

\

a

/ ;,'

3 v)

APODIZED BEAM

'

10.3

\

I

i\

DISTANCE PERPENDICULAR TO CENTRAL AXIS OF CONICAL SCAN (meters)

Fig. 5. An apodized beam prof& at a distance of %L5 K m from the laser s)uTce. The normalized time averaged inte&ty is plotted as a function of distance as measured perpendicular to the conical scan axis. Averaging time is greater than 10 scan cycles. The half width of the profile is shown. A nori-amized Gaussian beam profile is shown as a dashed line fur comparison. BEAM AT START OF SCAN TO LEFT t = t 2

BEAM JUST COMPLETING SCAN TO RIGHT t = t

y--\ \

/ /

\

I

I

\

fi SCAN DlREC /

&AM JUST COMPLETING SCAN TO LEFT t = t 3

BEAM AT START OF SCAN TO RIGHT t = t ,

THE INPUT SIGNAL TO THE SERVO CONTROL ELECTRONICS vo ( t ) IS PROPORTIONAL TO THE RATIO OF THE RETURN SIGNAL INTENSITY IRET ( 1 ) AND THE REFERENCE SIGNAL INTENSITY IREF

Yo I t )

k 11

13

'2

i v t2 o(t)

-

[v,(t) 13

HORIZONTAL ERROR SIGNAL = I

2

Fig. 6. Scan of the retrorefkctor array for beam steering feedback. The integrated return signal received during the scan to the right of the retroreflectck- is electronically m the signal returned during the scan to the bft. This difference is subtracted m propor+ional to the beam aiming error in the horizontal plane.

330 Conical

scan

and

a p o d i z a t i o n have been p u t i n t o p r a c t i c e i n

t r a n s m i s s o m e t e r by mounting two matched wedge prisms i n t o a

In

the

mount,

one

prism

the laser

cylindrical

c a n be r o t a t e d w i t h r e s p e c t t o t h e o t h e r .

tube.

In t h i s

c o n f i g u r a t i o n , t h e wedges a r e a d j u s t a b l e f o r an optimum s c a n n i n g a n g l e and correct

apodization

conical scan

of

the

When t h e t u b e i s r o t a t e d about i t s a x i s , a

t h e beam.

and as a r e s u l t a p o d i z a t i o n o f t h e main beam.

OCCUKS

In a d d i t i o n t o a p o d i z a t i o n , t h i s c o n i c a l s c a n t e c h n i q u e p r o v i d e s a means pointing

the

laser

beam a t t h e r e t r o r e f l e c t o r .

of

Feedback s i g n a l s are d e r i v e d

from t h e p e r i o d i c a l l y v a r y i n g i n t e n s i t i e s o f t h e r e t u r n s i g n a l i n

conical

its

sweep.

C o n i c a l s c a n p o s i t i o n s i g n a l s from t h e CSM t i m e t h e i n p u t o f t h e r e t u r n

signal

intensity

into

a

pair

of

differential

amplifiers.

s u b t r a c t s t h e r e t u r n s i g n a l i n t e n s i t y a s t h e beam p a s s e s t o retroreflector

from

the retroreflector. return

signal

retroreflector. zero,

the

left

the

The o t h e r a m p l i f i e r i s used t o compute d i f f e r e n c e s i n

as

intensity

the

beam

the

p a s s e s o v e r t h e t o p and bottom o f t h e

This i s i l l u s t r a t e d i n Figure

6.

If

both

differences

are

I f t h e two d i f f e r e n c e s a r e

o t h e r t h a n z e r o , t h e s i g n s of t h e d i f f e r e n c e s i n d i c a t e t h e d i r e c t i o n the

of

t h e i n t e n s i t y r e t u r n e d as t h e beam p a s s e s t o t h e r i g h t o f

beam i s c e n t e r e d on t h e r e t r o r e f l e c t o r .

the

One a m p l i f i e r

in

which

beam i s o f f - t a r g e t ( r i g h t o r l e f t , up o r down) and t h e magnitudes i n d i c a t e

t h e d e g r e e of p o s i t i o n i n g e r r o r .

These e r r o r s i g n a l s a r e used t o c o n t r o l s e r v o

mechanisms which steer t h e beam i n t h e

horizontal

(left-right)

and

vertical

(up-down) p l a n e s , r e s p e c t i v e l y . Aiming

of t h e beam i s accomplished by t h e alignment o f matched p r i s m s as i t

p a s s e s through t h e h o r i z o n t a l and principle

involved

in

this

vertical

adjustment

mechanism, t h e beam p a s s e s through a p a i r opposite

directions.

s t e p p e r motor. change

The

amount

of

servo

mechanisms.

The

is i l l u s t r a t e d i n Figure 7 . of

wedges

that

are

physical

In each

rotatable

in

r o t a t i o n i s c o n t r o l l e d by a f i n e a n g l e

As t h e wedges r o i a t e , t h e magnitude of t h e beam d e f l e c t i o n

can

from a minimum o f z e r o t o a maximum o f t w i c e t h e d e v i a t i o n a n g l e of t h e

wedge prism.

-

331

MATCHED WEDGE PRISMS

U

u

SIDE VIEW OF STEERING WEDGES

FRONT AXES OF VIEW DEFLECTION OF PRISMS SHOWN

PRISMS ROTATED THROUGH ANGLE e

'I

Yl

VECTOR COMPONENTS OF DEFLECTION

Fig. 7. Beam steering with matched wedge prisms. A light beam incident to the p r k m s shown at the top experiences no net deflection. The right wedge cancels the deflection affected by the left wedge. If the wedges are corstrained to rotate o b t e to each other through an angle, as shown above, the net deflection is to the right This can be represented as the vector sum of A + B. V e r t i c a l components of deflection cancel, horizontal components add.

332 Beam w i d t h

The i n t e n s i t y of t h e r e f l e c t e d l i g h t c o l l e c t e d by t h e t e l e s c o p e i s dependent n o t o n l y on a b s o r p t i o n and

atmospheric

established.

medium

The

transmission

beam

spreading

we

periodic

have beam

selected

is

normalization

width measurements.

the

main

to

It i s i l l u s t r a t e d on F i g u r e 4

beam.

.

of

the

Beam w i d t h , i n t h i s

a p p l i c a t i o n , i s d e f i n e d as t h e h o r i z o n t a l width between h a l f of

due

and i t s c o n t r i b u t i o n t o changing t r a n s m i s s i o n must be

technique

through

on

also

but

T h i s beam d i s p e r s i o n i s an i n h e r e n t f e a t u r e c r e a t e d by

atmospheric turbulence. the

scattering

intensity

points

It can b e measured by a

c o n t r o l l e d d e f l e c t i o n o f t h e beam from i t s c e n t e r e d p o s i t i o n . I n p r a c t i c e , t h e wedges o f t h e h o r i z o n t a l s e r v o mechanism a r e

the

centered

position

in

one

from

d i r e c t i o n u n t i l the returned signal i n t e n s i t y

f a l l s t o one h a l f i t s i n i t i a l v a l u e . opposite

rotated

The

prisms

are

then

rotated

in

the

d i r e c t i o n past t h e center point t o the opposite half i n t e n s i t y point.

The wedges a r e t h e n r e t u r n e d t o calculated

from

the

central

position.

The

beam

width

is

t h e p u l s e count needed t o d r i v e t h e h o r i z o n t a l servomechanism

between t h e h a l f i n t e n s i t y p o i n t s and t h e i n i t i a l

alignment

position

of

the

h o r i z o n t a l s t e e r i n g prisms. A

subroutine

i n t h e f i e l d d a t a a c q u i s i t i o n computer i s a c t i v a t e d h o u r l y t o

i n t e r r u p t t h e t r a n s m i s s i o n measurement and make The

transmission

data

are

normalized

to

the

beam

width

measurement.

an a v e r a g e beam width d u r i n g d a t a

processing.

Uniform i n t e n s i t y A p o d i z a t i o n c r e a t e s a beam of uniform i n t e n s i t y when i n t e g r a t e d This

means

beams

sections.

time.

t h a t w i t h i n t h e beam volume, a l l p a r t i c l e s w i t h i d e n t i c a l p h y s i c a l

c h a r a c t e r i s i t i c s w i l l a b s o r b and s c a t t e r l i g h t t h e same. light

over

that

have

Gaussian

or

other

shape

to

This i s not

true

of

their intensity cross

333

This uniform

intensity

transmissometers and

feature

all

eliminates

a

common

deficiency of

laser

other long path transmissometers that do not use an

apodized beam.

ELECTRONIC FEATURES The electronic signals that carry information to and from the optical table They are also enumerated in Table 2 below.

are illustrated i n Figure 2 . TABLE 2

-..Electronic information signals to and from the optical table.

INPUT

OUTPUT

VERTICAL SERVO CONTROL HORIZONTAL SERVO CONTROL CHOPPER SPEED CONTROL

P.M.T. SIGNAL (1) CONICAL SCAN POSITION SIGNALS ( 2 ) CHOPPER SPEED FEEDBACK

(1) Combined return and reference signal. ( 2 ) The four position signals from the conical scan mechanism. A

schematic

illustration of the electronic components associated with the

transmissometer are components with

shown as

Figure

8.

The

interconnections of

the optical table are shown on Figure 2 .

from the optical table are the combined return and conical

scan

The signal outputs

reference

signals, four

position signals,and the chopped frequency, The combined signal

is intially discriminated by demodulating electronics which lock in on chopped

these

signals

at discrete frequencies. These signals are then electronically ratiod

to obtain the transmission, T.

This information is passed

on

to

the

servo

control electronics (SCE) and the computer. The

SCE

serves

as an electronic interface between the electro-optical and

electromechanical components located on computer.

the

optical

table

and

the

control

Four scan position signals from the (CSM) indicated the position of

the beam in its scan about the retroreflector. These signals are used to the

input

of

the

transmission signal

to

two

differential amplifiers.

Differences in the transmission signals computed during top and scans

are

integrated

to

develop

a beam

aiming

time

bottom

sector

error signal in the plane

334 v e r t i c a l t o the scan a x i s . and

left

S i m i l a r l y , d i f f e r e n c e s computed

during

the

right

s e c t o r s c a n s a r e i n t e g r a t e d t o develop a beam aiming e r r o r s i g n a l i n

the plane horizon tal t o t h e scan a x i s . CH0PPI NG

ELECTRONICS

lRET RATIOMETRIC AMPLIFIER

PHOTOMULTIPLIER TUBE

SCAN SIGNALS FROM CSM

ELECTRONICS VERTICAL ERROR

HORIZONERROR

FIELD DATA ACQUISITION COMPUTER CONTROLS BEAM AIMING

- 11

OUTPUTS TO CONTROL VSM AND HSM

ACCUMULATES DATA MEASURES BEAM WIDTH

F i g . 8. Block diagram of t h e major e l e c t r o n i c components a s s o c i a t e d w i t h transmissometer.

and h o r i z o n t a l e r r o r s i g n a l s g e n e r a t e d i n t h e SCE a r e fed i n t o t h e

Vertical computer.

the

The

interrogation

of

computer

generates

the error signals.

servo

control

signals

based

upon

These c o n t r o l s i g n a l s are t h e n o u t p u t t o

t h e a p p r o p r i a t e servomechanism.

SUMMARY We have developed and put i n t o features

that:

provide

for

practice continually

a

laser pointing

transmissometer the

laser

at

beam

r e t r o r e f l e c t o r , t h e r e b y e l i m i n a t i n g t h e e r r o r s a s s o c i a t e d w i t h changes beam

with

in

a the

d i r e c t i o n due t o r e f r a c t i v e index changes; p r o v i d e a means o f n o r m a l i z i n g

t h e t r a n s m i s s i o n d a t a t o minimize t h e e f f e c t s of atmospheric t u r b u l e n c e on d i s p e r s i o n o f t h e beam; and p r o v i d e a beam of uniform i n t e n s i t y .

the

335 Experiments

are

in progress

to compare the transmission measurement with

other instruments that measure extinction parameters. The transmissometer is designed to operate in a field folded

path

of

ten kilometers.

installation with

Field installation is facilitated by using a

passive retroreflector. All functions have been successfully controlled by computer during

the development

anticipated that

it

interventions, and

will that

a

operate

period. for

In

at

a

least

field a

a

installation it is

week

without

operator

the data will be accessed by telephone using remote

terminals that can be indefinitely far away.

ACKNOWLEDGEMENT The authors wish to acknowledge the project

possible.

assistance of

Clarence Fought who

designed

and

others who made

the

built all the analog

circuitry, Rick Brown who designed the CMOS computer and wrote all the software to control the transmissometer, and Malcolm Barr who machined all the parts for the instrument. The development of this transmissometer was supported by Southern California Edison as a part of its environmental research program.


337

BIPOLAR CHARGE EQUILIBRIUM FOR SPHERICAL AEROSOLS (MINIMUM FLUX HYPOTHESIS)

L i u , S. Davisson and J.W.

C.S.

Gentry*

Department o f Chemical E n g i n e e r i n g , " I n s t i t u t e f o r P h y s i c a l Science and Technology,

U n i v e r s i t y of Maryland, Cot l e g e Parh, Maryland 20742,

U.S.A.

ABSTRACT An a l g o r i t h m based on t h e "minimum f l u x h y p o t h e s i s " f o r d e t e r m i n i n g t h e r e l a t i v e charge d i s t r i b u t i o n o f s p h e r i c a l p a r t i c l e s has been developed. l a t i o n s were c a r r i e d o u t f o r b o t h equal and unequal

ion mobil i t i e s .

Ca cu-

The

a l g o r i t h m was used t o d e t e r m i n e e x p e r i m e n t a l c r i t e r i a f o r t h e p r o d u c t i o n o f monodisperse a e r o s o l s and f o r t h e i n t e r p r e t a t i o n of measurements w i t h u l t r a

I ne

aeroso I s.

I NTRODUCT I O N P a r t i c l e s w i t h d i a m e t e r s j e s s than 0.05 Llm ( u l t r a f i n e a e r o s o l s ) must be measured i n d i r e c t l y .

One such method i s based on The e l e c t r i c a l m o b i l i t y o f t h e

p a r t i c l e i n which o n l y t h e charged p a r t i c l e s a r e measured.

Such a measurement

r e q u i r e s an a c c u r a t e t h e o r y f o r d e t e r m i n i n g t h e r a t i o o f uncharged t o charged p a r t i c l e s as a f u n c t i o n o f p a r t i c l e size.

Presented i n t h i s paper i s a d e s c r i p t i o n

o f a method based on t h e mean charge h y p o t h e s i s ,

i t s use i n d e t e r m i n i n g experimental

c o n d i t i o n s f o r o b t a i n i n g m n o d i s p e r s e a e r o s o l s by e l e c t r o s t a t i c c l a s s i f i c a t i o n , and i t s appl i c a t i o n i n i n t e r p r e i a t i o n of experiments.

CALCULATION OF CHARGE DISTRIBUTION The charge d i s t r i b u t i o n i s c a l c u l a t e d on t h e b a s i s o f two assumptions:

I. (ref.

The i o n f l u x t o t h e p a r t i c l e s a r e g i v e n by t h e "minimum f l u x " c r i t e r i o n

I ,2).

The e l e c t r o s t a t i c p o t e n t i a l ,

a t a reduced r a d i u s ;=r/a

i n c l u d i n g the image term,

obtained from t h e s o l u t i o n o f :

where +o i s t h e d i m e n s i o n l e s s charge parameter

2.

i s evaluated

(E

2

/akT).

The charges a r e assumed t o be i n d e t a i l e d e q u i l ibrium.

That is,

338

where NJ i s t h e number o f p a r t i c l e s w i t h J charges and F ( J , k )

i s the flux o f a

p a r t i c l e w i t h J charges changing t o k charges. In o u r f i r s t simulations, symmetrical --a

i t was assumed t h a t t h e charge e q u i l i b r i u m was

d i r e c t consequence o f assuming t h a t p o s i t i v e and n e g a t i v e i o n s

have t h e same m b i I i t y . In F i g .

I , t h e p a r t i c l e r a d i u s i s p l o t t e d a s a function o f t h e normalized

number r a t i o NJ Exp ( J

2

$,)/No

IW

( t e m p e r a t u r e @ 30O0K) f o r 1-4 charges.

I 10

I

RATIO

2 10

NJ E X P (

3

10

4 10

J2 Po

NO

F i g . I . P a r t i c l e r a d i u s a s a f u n c t i o n o f normal i z e d number r a t i o f o r p a r t i c l e s w i t h J e l e m e n t a r y charges.

Were t h e Boltrmann charge d i s t r i b u t i o n appl i c a b i e , t h e normal i z e d r a t i o would be e x a c t l y one.

W i t h i n c r e a s i n g charge number and d e c r e a s i n g charge, t h e

d i s c r e p a n c y between t h e two t h e o r i e s increase. (ref.

New p a r t i a l l y e m p i r i c a l t h e o r i e s

3 , 4 , 5 ) a g r e e w i t h t h e d i r e c t i o n o f our t h e o r y which c o n t a i n s no a d j u s t a b l e

parameters b u t suggests t h a t t h e t r u e c h a r g i n g d e n s i t y I i e s between t h e two t h e o r i e s a1 though c l o s e r t o t h e "mean charge h y p o t h e s i s " .

A p o s s i b l e s o u r c e o f e r r o r I i e s i n t h e assumption t h a t p o s i t i v e and n e g a t i v e i o n s have t h e same m o b i l i t y - - a

c o n c l u s i o n n o t i n agreement w i t h c l o u d p h y s i c s

experiments o r w i t h t h e recent studies o f Porstendorfer.

Our approach has been

t o examine t h e e f f e c t o f asymmetric d i s t r i b u t i o n s by assuming t h e r a t i o o f p o s i t i v e t o n e g a t i v e ion mobil i t y .

339 EXPERIMENT SELECT I ON Recent e x p e r i m e n t s by Heyder and Madelaine suggested an o p p o s i t e c o n c l u s i o n t o t h a t found by P o r s t e n d o r f e r i n t h a t p a s s i n g a p o l y d i s p e r s e aerosol t h r o u g h a TSI e l e c t r o s t a t i c c l a s s i f i e r d i d n o t r e s u l t i n a monodisperse a e r o s o l .

In

r e t r o s p e c t , t h e i r r e s u l t s c o u l d be e x p l a i n e d i n t h a t t h e c l a s s i f i e r s e l e c t s p a r t i c l e s by t h e i r m b i l i t y r a t h e r t h a n by s i z e .

The somewhat h i g h e r experimental

v a l u e s f o r p a r t i c l e s w i t h two o r m r e charges c o u l d be e x p l a i n e d by t h e erroneous use o f t h e Boltzmann d i s t r i b u t i o n . However, t h e r m r e i n t e r e s t i n g q u e s t i o n is: on t h e i n i t i a l p a r t i c l e d i s t r i b u t i o n ( i . e .

can one s e t t h e a p r i o r i c r i t e r i a

mean s i z e and s t a n d a r d d e v i a t i o n )

necessary t o d e t e r m i n e a m n o d i s p e r s e d i s t r i b u t i o n ?

To answer t h i s question,

a

computer code was designed and t e s t e d c h a r a c t e r i z e d by parameters d e s c r i b i n g t h e i n l e t aerosol and parameters d e s c r i b i n g t h e l o c a t i o n and w i d t h o f t h e window i n A t y p i c a l r e s u l t i s shown i n F i g . 2.

t h e EAC.

1.0

- 0.04

-

u)

K

& W

B 0

w

w

K

-0.02

g

5

t, a

E -I

0

3

6

Fig. 2. S i m u l a t i o n o f EAC performance: f r a c t i o n o f o u t 1 i e r s and f r a c t i o n o f p a r t i c l e s recovered as a f u n c t i o n o f t h e d i f f e r e n c e i n mean d i a m e t e r s o f t h e d i s t r i b u t i o n and EAC.

The i n i t i a l s i z e d i s t r i b u t i o n i s l o g normal w i t h equal t o D I .

&

LnB=o=l .O and w i t h a mean

The s e l e c t e d d i a m e t e r o f p a r t i c l e s f r o m t h e EAC i s 0.075 pm w i t h

t h e r e l a t i v e range o f mobil i t i e s b e i n g 10 and 20%.

The f r a c t i o n o f t h e i n i t i a l

d i s t r i b u t i o n w i t h p a r t i c l e s i n t h e s p e c i f i e d m b i l i t y range ( i . e . l e a v i n g t h e EAC) i s d i s p l a y e d on t h e r i g h t h a n d s i d e .

the particles

On t h e l e f t h a n d side, t h e

340 f r a c t i o n of charged p a r t i c l e s w i t h more t h a n one c h a r g e i s d i s p l a y e d .

An optimum

e x p e r i m e n t a l d e s i g n would r e q u i r e t h a t t h e f r a c t i o n o f p a r t i c l e s l e a v i n g t h e EAA be as l a r g e as p o s s i b l e w i t h as few o u t l i e r s a s p o s s i b l e .

The s i m u l a t i o n s i n d i c a t e d t h a t as t h e p a r t i c l e s become l a r g e r , t o have a n a r r o w e r d i s t r i b u t i o n .

i t is necessary

B e s t r e s u l t s a r e o b t a i n e d when t h e c l a s s i f i e r

s i z e i s n e a r t h e maximum o f t h e d i s t r i b u t i o n .

When t h e mean d i a m e t e r o f t h e

d i s t r i b u t i o n i s l a r g e r t h a n t h e EAC d i a m e t e r , t h e number o f o u t l i e r s i n c r e a s e dramat i c a l I v.

APPL ICAT ION TO EXPERIMENTAL MEASUREMENTS One t e s t o f t h e method i s whether t h e s i z e d s t r i b u t on o f a t e s t a e r o s o l t h e same f o r d i f f e r e n t c l a s s i f i e r s ( i . e . pore sizes).

GCAF d f f us i o n b a t t e r i e s w i t h d i f f e r e n t

In t h e "apparent diatneter method" ( r e f .

o f a h y p o t h e t i c a l monodisperse aerosol

6

, the

diffusion coefficient

h a v i n g a t heo r e t c a l p e n e t r a t i o n equal t o

t h e e x p e r i m e n t a l p e n e t r a t i o n i s p l o t t e d as a f u n c t i o n o f p e n e t r a t i o n . curve,

can be determined unambiguously.

where N

From t h i s

t h e parameters o f a log norma I d i s t r i b u t ion d e s c r i b i n g t h e measurements

diffusion coefficient

and NJti,

is

(T)/NJ(c) and WJ(')

6*(Q)

S p e c i f i c a l l y , t h e "apparent v a l u e " o f t h e

f o r a f l o w r a t e Q would be q i v e n b y :

i s t h e number o f p a r t i c l e s o f mobi I i t y J per measured charge, a r e t h e measured charge b e f o r e and a f t e r t h e g l a s s f i l t e r .

F o r each s i z e o f f i l t e r , one would e x p e c t t h a t increasinq flow rate. I

theoretical r a t i o

6*(Q) would

increase w i t h

A1 I t h e p o i n t s should f a l l on t h e same c u r v e i f t h e

NJ(T)/NJ(c)

i s calculated correctly;

f o r t h e d i s t r i b u t i o n does

n o t change o n l y t h e e x p e r i m e n t a l v a l u e s W J ( I ) and

W,"'.

v a l u e s f o r a s i l v e r a e r o s o l generated a t 650

The s o l i d c u r v e r e p r e s e n t s a

OC.

c a l c u l a t e d d i s t r i b u t i o n based on parameters o f 0=1.3

F i g . 3 shows t y p i c a l

and D*=1.6 x 10-4(cm2/sec).

The t h r e e symbols r e p r e s e n t t h e d i f f e r e n t p o r e s i z e s o f t h e GCAF and f a l l on t h e same c u r v e as would be expected i f t h e number t o charge r a t i o were c o r r e c t . contrast,

In

were t h e Boltzmann charge d i s t r i b u t i o n used, a sequence o f t h r e e d i f f e r e n t

curves a r e obtained (Fig. 4.).

The c o n s i s t e n t t r e n d i n t h e d a t a a r e due t o t h e

f a c t t h a t w i t h t h i s d i s t r i b u t i o n , t h e Boltzmann charge d i s t r i b u t i o n c o n s i s t e n t l y o v e r e s t i m a t e s t h e number o f p a r t i c l e s w i t h a s t r o n g b i a s toward y i e l d i n g e s t i m a t e s o f t h e d i f f u s i o n c o e f f i c i e n t which a r e t o o l a r g e . w i t h t h e d a t a i n F i g . 4.

T h i s i s i n accord

For t h e 50 urn, most p a r t i c l e s p e n e t r a t e , and t h e

e x p e r i m e n t i s n o t skewed toward srnal l e r p a r t i c l e s where t h e number/charge r a t i o i s inaccurate.

Consequently,

agreement w i t h t h e o r y .

the calculated d i f f u s i o n c o e f f i c i e n t i s in

341

o 0

L A

-

lo 0

5 0.5

1 1.0

0.5

lo -5 0

PENETRATlON

10um FILTER 25um FILTER 5 0 p m FILTER SIMULATION

F i g . 3. Apparent d i f f u s i o n c o e f f i c i e n t (crn2/sec) a s a f u n c t i o n of p e n e t r a t i o n f r o m EM measurements u s i n g minimum flux criteria.

1.0

PENETRATION

F i g . 4. Apparent d i f f u s i o n c o e f f i c i e n t (cm2/sec) a s a f u n c t i o n o f p e n e t r a t i o n f r o m E A A measurements u s i n g Boltzmann charge d i s t r i b u t i o n .

B o t h Koj irna and Haaf have proposed a s e m i - e m p i r i c a l

charge d i s t r i b u t i o n

A p p r o x i m a t e l y 50 e x p e r i m e n t s

d i f f e r i n g f r o m t h e Boltzmann c h a r g e d i s t r i b u t i o n .

were a n a l y z e d w i t h t h e s i z e d i s t r i b u t i o n c a l c u l a t e d u s i n g t h e s e c h a r g e d i s t r i b u tions,

t h e "minimum charge" h y p o t h e s i s , and t h e B o l t z m n n d i s t r i b u t i o n .

"minimum f l u x " model and t h e t w o s e m i - e m p i r i c a l a e r o s o l s whose mean d i a m e t e r i s l e s s t h a n 0.02

methods agreed w i t h i n 5%.

urn,

The For

t h e d e p a r t u r e i n t h e mean

c a i c u l a t e d w i t h t h e b i t z r n a n n c h a r g e d i s t r i b u t i o n was 25% whereas f o r a e r o s o l s whose mean d i a m e t e r s were g r e a t e r t h a n 0.02 was w i t h i n 8%.

urn,

agreement armng a l l f o u r t h e o r i e s

These r e s u l t s a r e c o n s i s t e n t w i t h o t h e r e x p e r i m e n t s which show

t h e Boltzniann d i s t r i b u t i o n o v e r e s t i m a t e s t h e number/charge r a t i o f o r smal I p a r t i c l e s .

CONCLUSION The "minimum f l u x c r i t e r i a " has been used t o d e v e l o p a code f o r p r e d i c t i n g f r a c t i o n r e c o v e r y and t h e p e r c e n t a g e o f o u t 1 i e r s ( d e g r e e o f m o n o d i s p e r s i t y ) t o s i m u l a t e p e r f o r m a n c e o f an E l e c t r i c a l A e r o s o l C l a s s i f i e r . ments a r e c o n s i s t e n t w i t h t h e o r y .

E x p e r i m e n t a l rneasure-

342 ACKNOWLEDGEMENTS

T h e a u t h o r s would I i k e t o r e c o g n i z e t h e s u p p o r t o f t h e N a t i o n a l Science Foundat ion under Grant # CPE-80-1 1269-AOI and t h e S t a t e o f Mary1 and Department o f N a t u r a l Resources under G r a n t #

P 678004.

REFERENCES

I 2 3 4

5 6

J. Gentry, J. Aerosol Science, 3(1972)65-76. C. L. , L i u and J.W. Gentry, J. Aerosol Science, 15(1982). W. Haaf, J. Aerosol Science, I I (1979)201-212. H. Kojirna, Atomspheric Environment, 12( 1978)2363-2368. J P o r s t e n d o r f e r , Pr i v a t e Commun i c a t ion, G o t t ingen , I 9 8 1 Y.O. Park, W. King, J r . and J. Gentry, I&EC P r o d u c t R&D, 19(1980)151-157.

.

.

343

SURVEYS AND MONITORING

Surveys were, and remain, the mainstay of a i r pollution science.

Their

methodology may range from simple h i s t o r i c a l recording t o the most s o p h i s t i c a t e d i n t e r p r e t a t i o n s and presentations. They may cover many p o l l u t a n t s and s i t e s , o r deal with one s i n g l e t o p i c , e . g . , p a r t i c u l a t e matter. T h e above proves t h a t surveys s t i l l cannot be made by completing some printed form. I n t h i s section a t l e a s t no routine or y e a r l y record and r e p o r t - l i k e survey has been included. Each one has some s p e c i f i t y , i t s own approach, i t s own outlook o r i n t e r p r e t a t i o n .


345

THE THIRD DIMENSION IN THE LOS ANGELES BASIN

R.J.

FARBER, A.A. HUANG, L.D.

BREGMAN, and R.L. MAHONEY

Southern California Edison Company, Rosemead, California (U.S.A.) D.J. EATOUGH and L.D. HANSEN Brigham Young University, Provo, Utah (U.S.A.) D.L. BLUMENTHAL and W.S. KEIFER Meteorology Research, Inc., Altadena, California (U.S.A.) D.W. ALLARD Aerovironment, Inc., Pasadena, California (U.S.A.)

ABSTRACT Airborne measurements were made during the summer and early fall seasons of 1978-1980 to characterize the third dimension of the Los Angeles Basin during air

pollution days.

One to three aircraft were employed per flight day to measure the

vertical profile of meteorology and air quality continuously, and to collect aeros o l samples for the various chemical analyses across the Basin.

sis was placed in the nighttime measurements.

Particular empha-

This was done because relatively

little nighttime third dimension data are available to date, and because they are important in defining the initial conditions f o r the following photochemically active days.

It was found that the physical and chemical characteristics with-

in the two meteorological regimes, i.e., mixed and stable layers, are distinctively different.

The mixed layer is characterized by uniformly low O3 and rela-

tively high NOx at night, while the stable layer has stratified high O3 but low NO

.

Aerosol size distribution in the mixed layer is found to be tri-modal,

while that in the stable layer is nearly bi-modal.

Based on the collected data,

the nighttime sulfur, nitrate and ammonia chemistry is discussed. INTRODUCTION During the past three decades, several research groups using a variety of techniques have sampled the vertical distribution of pollutants and meteorological parameters in the Los Angeles Basin.

Vertical pollutant and meteorological profiles

have been obtained by blimp (Refs. 1, 21,

small aircraft (Refs. 3-5) and helicop-

346 ter

(Ref.

_ et _ al.

6).

The most e x t e n s i v e

(Ref. 5),

set o f measurements were made by Blumenthal

i n 1972 and 1973.

The t h i r d dimension i n t h e Los Angeles B a s i n i s t y p i c a l l y c h a r a c t e r i z e d d u r i n g t h e s p r i n g , summer and e a r l y f a l l months by a s t a b l y s t r a t i f i e d atmosphere w i t h a strong,

persistent

well-defined

temperature

inversion.

There

is

a

pronounced

boundary between t h e P a c i f i c Ocean marine mixed l a y e r and a d r y , w a r m , c a p p i n g s u b s i d e n c e l a y e r above.

stable or

Mixing h e i g h t s d u r i n g t h e a f t e r n o o n summer months

t y p i c a l l y r a n g e from a b o u t 500 t o 1500 f e e t above ground l e v e l (AGL) i n t h e c o a s t a l sections increasing

Basin. hours,

The

capping

t o 1500 t o 2500 f e e t AGL i n t h e i n l a n d

inversion,

typically

2000 f e e t

portions

t h i c k during

the

of

the

nighttime

i s formed by a c o m b i n a t i o n o f m e t e o r o l o g i c a l p r o c e s s e s s u c h as s u b s i d e n c e Above t h i s s t a b l e a i r mass,

and r a d i a t i o n .

t h e atmosphere i s c o n d i t i o n a l l y sta-

b l e , o f t e n t o 10,000 f e e t mean sea l e v e l (MSL). The above c i t e d r e s e a r c h programs have p r i m a r i l y f o c u s e d on summertime daytime and e p i s o d i c s t u d i e s ( 0 3 h o u r l y a v e r a g e d peaks

>350

s e a b r e e z e d r i v e n "smog f r o n t " a c r o s s t h e Basin.

ppb),

often following

the

With t h e advancement d u r i n g t h e

p a s t few y e a r s of measurement t e c h n i q u e s i n g e n e r a l and a i r b o r n e sampling methodology i n p a r t i c u l a r ,

an increased

understanding

of

m e t e o r o l o g i c a l and

chemical

p r o c e s s e s i s now f e a s i b l e . Realizing

this,

the

Research

and

Development

E d i s o n (SCE) h a s embarked upon a m u l t i - y e a r dimension i n t h e Los Angeles Basin.

group

of

Southern

California

r e s e a r c h program t o e x p l o r e t h e t h i r d

The e l e v a t e d plumes from s e v e r a l l a r g e power

p l a n t s l o c a t e d a l o n g t h e immediate c o a s t i n t h e Los Angeles B a s i n p e n e t r a t e i n t o the stable layer.

T h i s r e s e a r c h program i s e x p l o r i n g t h e l o c a t i o n ,

sembled w i t h a long-range three-dimensional

t r a n s p o r t pro-

A s u f f i c i e n t d a t a b a s e i s b e i n g as-

cesses a n d u l t i m a t e f a t e of t h e s e e f f l u e n t s .

g o a l of a p p r o p r i a t e l y modeling t h e B a s i n u s i n g complex

E u l e r i a n and Lagrangian g r i d models.

s i m u l a t i o n s are p l a n n e d b e c a u s e of

Where p o s s i b l e ,

multi-day

t h e p o t e n t i a l " c a r r y over" e f f e c t and p e r s i s -

t e n c e of " e p i s o d e " p e r i o d s i n t h e Los Angeles Basin.

A s a f i r s t s t e p toward r e a l i z a t i o n of t h i s modeling g o a l , a g e n e r a l understandi n g of

t h e t h i r d dimension i s n e c e s s a r y .

meteorological

questions,

including

T h i s p a p e r a d d r e s s e s some fundamental

transport

t r a n s p o r t of p o l l u t a n t s i n t o t h e s t a b l e l a y e r ;

processes

in

the

inversion;

the

d e c o u p l i n g of t h e mixed and s t a b l e

l a y e r s ; and t h e p o t e n t i a l i m p o r t a n c e of c a r r y o v e r from one day t o t h e n e x t . p h a s i s i n t h i s p a p e r i s p l a c e d on t y p i c a l summer and f a l l non-episode m e t e o r o l o g y f o r which few d a t a have been p r e v i o u s l y a v a i l a b l e .

Em-

nighttime

The c h e m i c a l and

p h y s i c a l t r a n s f o r m a t i o n of p o l l u t a n t s i n t h e B a s i n and t h e a e r o s o l s i z e d i s t r i b u t i o n s r e s u l t i n g from t h e s e p r i m a r y and s e c o n d a r y p r o c e s s e s are a l s o examined. DESCRIPTION OF RESEARCH PROGRAM, EXPERIMENTAL PROCEDURES AND DATA BASE During

t h e summer

s e a s o n s of

1978-1980

a i r b o r n e measurements

were

conducted

347 t h r o u g h o u t t h e Los Angeles Basin, e x t e n d i n g from t h e ocean e a s t w a r d t o t h e mountains.

Sampling d u r i n g t h e f i r s t two

w i t h two t h r e e - h o u r f l i g h t s and

s e a s o n s emphasized n i g h t t i m e measurements The emphasis i n 1980 s h i f t e d t o daybreak

f l i g h t s per night.

afternoon flights.

T h i s paper

will

d i s c u s s mainly

1978-1979

the

n i g h t t i m e measurements. T h i s r e s e a r c h program r e p r e s e n t s s e v e r a l advances i n b r e a d t h and q u a l i t y of data collected. of-the-art

Continuous p a r t i c l e s i z e measurements have been made u s i n g s t a t e -

a i r b o r n e techniques.

A i r b o r n e p a r t i c u l a t e l i d a r d a t a , c o l l e c t e d by an

i n d e p e n d e n t g r o u p , a r e a v a i l a b l e as w e l l as s i z e s p e c t r a of s t r a t u s c l o u d s u s i n g t h e K n o l l e n b e r g forward s c a t t e r i n g probe.

A t y p i c a l t h r e e - h o u r a i r b o r n e f l i g h t would c o n s i s t of s e v e r a l v e r t i c a l s p i r a l s from c l o s e t o t h e s u r f a c e t o 5000 f e e t MSL a t s t r a t e g i c a l l y s e l e c t e d p o i n t s a c r o s s t h e B a s i n and o v e r t h e ocean.

S p i r a l s were connected by t r a v e r s e s a t

a l t i t u d e i n e i t h e r t h e mixed o r s t a b l e l a y e r s .

Twenty- t o t h i r t y - m i n u t e

constant orbits i n

b o t h t h e mixed and s t a b l e l a y e r s were conducted n e a r t h e s p i r a l s t o c o l l e c t aero-

s o l s u s i n g a wide v a r i e t y of f i l t e r d e v i c e s . From one t o t h r e e a i r c r a f t c o l l e c t e d d a t a s i m u l t a n e o u s l y d u r i n g e a c h sampling period. (AV)

D i f f e r e n t t y p e s of small, i n s t r u m e n t e d a i r p l a n e s from AeroVironment,

and Meteorology Research,

Inc.

(MRI)

collected

airborne data.

Inc.

Additional

ground based m e t e o r o l o g i c a l and chemical d a t a were c o l l e c t e d s i m u l t a n e o u s l y by t h e N a t i o n a l Weather S e r v i c e and SCE r e s e a r c h s t a f f . B e e c h c r a f t Queen A i r .

MRI used e i t h e r a Cessna 206 o r

The Cessna 206 had a f u l l complement of c o n t i n u o u s meteoro-

l o g i c a l i n s t r u m e n t s i n c l u d i n g t e m p e r a t u r e and t u r b u l e n c e equipment and c o n t i n u o u s gas analyzers, elometer.

i n c l u d i n g 0 3 , NOx,

and

SO2 m o n i t o r s

plus

an

i n t e g r a t i n g neph-

The Queen A i r i n c l u d e d i d e n t i c a l gaseous and m e t e o r o l o g i c a l i n s t r u m e n t s

as were a b o a r d t h e Cessna,

p l u s a e r o s o l and f o g measuring d e v i c e s t o provide a

complete a r r a y of p a r t i c l e s i z i n g from n u c l e i t o d r o p l e t s .

These d e v i c e s i n c l u d e d

a n e l e c t r i c a l a e r o s o l a n a l y z e r , K n o l l e n b e r g a c t i v e and forward s c a t t e r i n g probes and a Royco o p t i c a l p a r t i c l e c o u n t e r .

The Queen A i r a l s o i n c l u d e d a Volker Mohnen

fog d r o p l e t c o l l e c t o r f o r s t r a t u s clouds.

For a d d i t i o n a l d e t a i l e d i n f o r m a t i o n ,

t h e Cessna 206 i s d e s c r i b e d i n Blumenthal e t a l . Richards

st. (Ref.

8).

(Ref.

7) and t h e Queen A i r i n

AeroVironment used a P i p e r Turbo Navajo and P i p e r Aztec

i n s t r u m e n t e d w i t h a s i m i l a r complement of m e t e o r o l o g i c a l and gaseous a n a l y z e r s . I n t e r p r e t a t i o n of t h e i n s t r u m e n t s '

r e s p o n s e s i n v o l v e d d a t a a d j u s t m e n t s based on

(1) s t a n d a r d c a l i b r a t i o n of a n a l y z e r r e s p o n s e t o r e f e r e n c e s t a n d a r d s , and ( 2 ) det e r m i n a t i o n of s p e c i a l d a t a c o r r e c t i o n s n e c e s s a r y t o a c c o u n t f o r e a c h a n a l y z e r ' s r e s p o n s e and l a g t i m e , pressure day.

(altitude).

and changes i n a n a l y z e r r e s p o n s e w i t h changes i n ambient Analyzer

c a l i b r a t i o n s were performed

before

every

flight

S p e c i a l c a l i b r a t i o n f a c t o r s were d e r i v e d s e p a r a t e l y and were a p p l i e d t o t h e

s t a n d a r d c a l i b r a t i o n f a c t o r s t o a l l o w computation of

meters a s f u n c t i o n s of t i m e and p o s i t i o n .

the

values for

a l l para-

A d d i t i o n a l d e t a i l s have been d e s c r i b e d

348 by B l u m e n t h a l s & .

(Ref.

7) and R i c h a r d s %&. (Ref. 8).

An a r r a y of f i l t e r s were deployed t o c o l l e c t p a r t i c u l a t e analyzed f o r s u l f a t e ,

nitrate,

chloride,

o t h e r c a t i o n s s u c h as l e a d and sodium.

organic sulfur I V species,

s a m p l e r (0.3 p pore f i l t e r ) o r sequen-

t i a l tandem two s t a g e s a m p l e r s ( 8 pm and 0.3

and a l s o on a c i d

p pore f i l t e r s )

washed P a l l f l e x q u a r t z f i l t e r s u s i n g a high-volume

sampler.

c l u d e d i o n chromatography

proton

(IC),

ammonium and

These samples were c o l l e c t e d on n u c l e p o r e

membrane f i l t e r s u s i n g e i t h e r a low-volume

s p e c t r o s c o p y (PIXE).

samples s u b s e q u e n t l y

calorimetry,

and

Aerosol analyses ininduced

x-ray

ct. (Ref.

c h e m i c a l a n a l y s i s t e c h n i q u e s are g i v e n i n Eatough

Gaseous hydrocarbon samples were a l s o c o l l e c t e d .

emission

Details on t h e

S t r a t u s f o g samples were a n a l y z e d u s i n g I C .

9).

P o l i s h e d s t a i n l e s s s t e e l can-

i s t e r s , s u p p l i e d by Washington S t a t e U n i v e r s i t y , were f i l l e d w i t h ambient samples and w i t h i n 48 h o u r s a n a l y z e d f o r s p e c i a t e d hydrocarbons versity

u s i n g g a s chromatography

necessary,

mass s p e c t r o s c o p y .

by Washington S t a t e Uni-

(GC) w i t h f l a m e i o n i z a t i o n d e t e c t i o n and when d a t a are a n e c e s s a r y

These s p e c i a t e d hydrocarbon

i n p u t f o r modeling a p h o t o c h e m i c a l l y a c t i v e atmosphere. Aircraft

f o r a wide v a r i e t y

have c o l l e c t e d d a t a

of

m e t e o r o l o g i c a l c o n d i t i o n s d u r i n g t h e p a s t t h r e e summers. done on b a d l y p o l l u t e d d a y s d u r i n g t h e "smoggy" s e a s o n .

i s severely

and f a l l months v e r t i c a l mixing B a s i n d u r i n g a n e n t i r e 24-hour

time.

period.

air quality

ambient

Sampling was t y p i c a l l y During t h e s p r i n g , summer

restricted

across

the

This condition persists

Los Angeles

f o r days a t a

The mixed l a y e r i s capped by a v e r y s t r o n g t e m p e r a t u r e i n v e r s i o n ,

degrees

i n magnitude.

With v e r y

light

winds

night

and

through

morning

several

hours

and

s t r o n g s o l a r i n s o l a t i o n , t h e Los Angeles B a s i n behaves as a c l a s s i c a l photochemic a l smog chamber.

Furthermore,

s t r a t u s c l o u d s o r marine m o i s t u r e

are normally

p r e s e n t to promote h e t e r o g e n e o u s aqueous d r o p l e t c h e m i s t r y .

A l l this results i n

summer d a y s c h a r a c t e r i z e d by c o m b i n a t i o n s of e l e v a t e d ozone,

a e r o s o l and s u l f a t e

and a e r o s o l l e v e l s .

l e v e l s and f a l l d a y s c h a r a c t e r i z e d by h i g h NO

AND

CHEMICAL

PHYSICAL

CHARACTERISTICS OF

GASES AND

AEROSOLS

IN

THE

VERTICAL

DIMENS I O N A i r b o r n e measurements were conducted f o r a v a r i e t y of ambient a i r q u a l i t y and meteorological conditions during the past

three years.

v e r t i c a l p r o f i l e o f t h e Los Angeles B a s i n a t n i g h t , d i f f e r e n c e s between t h e s t a b l e a n d mixed l a y e r s .

Figure 1 i l l u s t r a t e s the

showing t h e marked chemical

These f i g u r e s a l s o i l l u s t r a t e

t h e maximum mixing h e i g h t d u r i n g t h e p r e v i o u s daytime hours. completely eroded, uniform a c r o s s result, layer.

masses.

the

even i n t h e

i n l a n d areas.

t h e e n t i r e Basin,

stable

in

spite

of

The mixing intense

The i n v e r s i o n i s n o t height

solar

i s remarkably

insolation.

As a

a i r mass r e m a i n s m e t e o r o l o g i c a l l y d e c o u p l e d from t h e mixed

T h i s i s r e f l e c t e d i n c h e m i c a l and p h y s i c a l d i f f e r e n c e s between t h e two a i r

349

Fig. 1. Vertical profile of meteorological and air quality data collected by light aircraft over the L.A. Basin; (top) from 2007-2248 PST, August 2, 1978; and (bottom) from 2020-0258 PST, October 24-25, 1979.

350 Gases ___ polluted,

being

characterized

by

These ozone c o n c e n t r a t i o n s are months) and because o f multiple

thin

is surprisingly quite

i n F i g u r e 1, t h e i n v e r s i o n ( s t a b l e ) l a y e r

As depicted

elevated

often

ozone

i n excess

levels,

t h e s t a b l y s t r a t i f i e d n a t u r e of

horizontal

l a y e r s e x t e n d i n g westward

p a s t t h e c o a s t l i n e s e v e r a l miles o v e r t h e ocean.

but

200 ppb

of

low

values.

NOx

(during

the inversion,

from

the

summer

the

occur i n

mountains

to

Above t h e i n v e r s i o n l a y e r ,

out

O3

values decrease rapidly. By c o n t r a s t , t h e mixed l a y e r i s a f r e s h a i r mass and c o n t a i n s h i g h v a l u e s of NOx

and v e r y

the year NOx

03.

low v a l u e s of

toward

the

fall,

Higher v a l u e s

of

NOx

are

observed

c o i n c i d i n g w i t h d e c r e a s i n g mixing

later

heights.

in

Highest

v a l u e s are u s u a l l y o b s e r v e d from t h e E l Monte area westward t o t h e c o a s t .

S p a t i a l c o n c e n t r a t i o n s of NOx v a r y n i g h t l y depending on t h e sea-land culation pattern.

The r a t i o of NO t o NO

breeze c i r -

a l s o v a r i e s seasonally.

C o n c e n t r a t i o n s o f SO2 m o n i t o r e d by t h e a i r c r a f t were low a c r o s s t h e Basin i n E x c e p t i o n s are immediately downwind of p o i n t

b o t h t h e mixed and s t a b l e l a y e r s . sources

s u c h a s power

p l a n t s and

refineries.

Otherwise,

nighttime

SO2 v a l u e s

a r e t y p i c a l l y 10 t o 25 ppb i n t h e mixed l a y e r and 10 t o 15 ppb i n t h e i n v e r s i o n . Aerosols

A s outlined previously,

a i r b o r n e p a r t i c u l a t e f i l t e r samples were c o l l e c t e d i n

t h e Los Angeles B a s i n as p a r t of t h i s r e s e a r c h program. i z e d i n T a b l e 1 and F i g u r e 1.

less a e r o s o l t h a n does layer.

These r e s u l t s a r e summar-

These d a t a show t h a t a l t h o u g h t h e s t a b l e l a y e r has

t h e mixed

layer,

substantial aerosol

is i n t h e s t a b l e

I n t h i s section, the nighttime chemistry i s described.

Nighttime

sulfur

chemistry.

Table

1 shows

the

highest

c o n c e n t r a t i o n s of

p a r t i c u l a t e s u l f u r s p e c i e s t o be i n t h e i n l a n d p o r t i o n s of t h e B a s i n i n t h e mixed layer.

The c o n c e n t r a t i o n s found w i t h i n t h e i n v e r s i o n l a y e r , b o t h i n l a n d and a l o n g

t h e c o a s t , are comparable.

The l o w e s t c o n c e n t r a t i o n s are observed a l o n g t h e c o a s t

i n t h e mixed l a y e r , which i s r e a s o n a b l e c o n s i d e r i n g t h e s t r e n g t h of t h e sea b r e e z e d u r i n g t h e summer months.

T a b l e 1 a l s o shows t h a t ,

s u l f a t e i s i n t h e f i n e s i z e range

( l e s s t h a n 2.5

s u l f a t e c o n c e n t r a t i o n s d e t e r m i n e d by hi-volume

and low-volume

a r e i n good agreement a s i n d i c a t e d by t h e low-volume

are a t l e a s t two r e a s o n s f o r t h e c o m p a r a b i l i t y .

on t h e a v e r a g e , p~ p a r t i c l e

90% of

diameter).

the The

sampling t e c h n i q u e s

t o hi-volume

ratio.

There

First, particulate sulfate i n the

atmosphere i s thermodynamically s t a b l e because t h e s u l f a t e s a l t s have low vapor pressures (Ref.

10).

Second,

since there was little sulfate i n larger particles,

t h e d i f f e r e n c e i n c u t p o i n t s among t h e sampling systems d i d n o t markedly a f f e c t t h e measured s u l f a t e c o n c e n t r a t i o n s .

351 TABLE 1

Summary of a i r b o r n e nighttime a e r o s o l samples in the Los Angeles Basin i n 1979

Locallo"

*nversran Layer, CDOStale

On sampling n i g h t s following days with s t r a t u s a s f a r inland a s t h e E l Monte a r e a , s u l f a t e l e v e l s i n t h e mixed l a y e r a r e n e a r l y twice a s high a s those on the days without

stratus.

This r e s u l t

i s c o n s i s t e n t with previous work suggesting

that heterogeneous SO2 t o s u l f a t e conversion occurs more r a p i d l y i n the presence

of c o a s t a l moisture and higher r e l a t i v e humidities than do slower homogeneous conv e r s i o n processes (Refs. 11-13). Perhaps t h e most i n t r i g u i n g chemical r e s u l t i s the l a r g e f r a c t i o n of particul a t e s u l f u r bound t o organic compounds.

i s r e f e r r e d t o a s organic S(IV) c o n c e n t r a t i o n s of

organic

s p e c i e s (Ref.

S(IV)

Figure 1) have been observed.

This f r a c t i o n of the p a r t i c u l a t e s u l f u r 14).

a s high a s 6

The e x i s t i n g d a t a base shows

pg/m3 expressed a s

s u l f a t e (see

In general, organic S(1V) i s observed in the d r i e r

p o r t i o n s of t h e Basin, both i n l a n d and throughout t h e i n v e r s i o n from the coast t o inland areas.

Figure 2 shows t h a t a t times,

more than 50% of

the p a r t i c u l a t e

s u l f u r is in t h e form of organic S(1V). Figure 2 i n d i c a t e s a very good c o r r e l a t i o n between organic and t o t a l particul a t e s u l f u r f o r days with warm a i r masses. open p o i n t s f o r a i r masses c o o l e r than 2 2 ° C .

Figure 2 a l s o includes data denoted by Excluding days when the average day-

time temperature of t h e a i r mass i s l e s s than 2 Z 0 C , obtained:

t h e following r e l a t i o n s h i p i s

352

A

Fig.

2.

R e l a t i o n s h i p between a i r b o r n e t o t a l f i n e p a r t i c u l a t e s u l f a t e and organic i n t h e L.A. Basin f o r s e v e r a l summer and f a l l days i n 1979. Solid data p o i n t s a r e f o r warmer a i r mass while open d a t a p o i n t s a r e f o r cooler a i r mass. The l a t t e r a r e not included i n the r e g r e s s i o n a n a l y s i s .

S(1V)

2-

+

[So4 ] = 1.10 [Org. S(IV)] where ground

all

concentrations a r e

level

of

inorganic

a l s o suggests t h a t i n warm,

in

SO-:

nanomoles/m in

the

3

17.7

.

Basin

Equation of

about

(1)

2

suggests pg/m

3

.

a

back-

Figure

dry a i r masses SO2 conversion t o inorganic

2

sulfate

and organic S(IV) occur a t similar r a t e s . These r e s u l t s a r e complicated by the f a c t

that

these data were

n i g h t when photochemical homogeneous processes were a t a minimum.

collected a t Furthermore, a

d i f f e r e n c e i n residence times and a i r mass age between the mixed and s t a b l e l a y e r s m u s t a l s o be considered.

Additional sampling and d a t a a n a l y s i s a r e needed t o un-

r a v e l t h e d i f f e r e n c e s between daytime and nighttime chemistry w i t h i n and between each l a y e r .

Nighttime n i t r a t e

chemistry.

Proper

sampling

of

nitrate

in

the

atmosphere

353 i n the data s c a t t e r n e s s shown i n Fig-

continues t o be a challenge a s r e f l e c t e d ure 3.

From t h e c o a s t

to the inland areas,

l e v e l s i n c r e a s e a s the dry a i r masses aged. tions

of

particulate

nitrate

to

occur

measured

fine particulate nitrate

The trend is f o r higher concentra-

toward

the

fall

months

as

NO2

values

increase.

100

fn

0 INVERSION A MIXED L A Y E R

W

-

c

a

0

U

n

60 -

W

5

LL

40

z 0"

z

E

2o A

0

I

0

A

20

I

I

I

,

,

I

40

60

80

100

120

140

[NO;] IN FINE PARTICLES

, nanomol/m3

Fig. 3. R e l a t i o n s h i p between the percent of t o t a l p a r t i c u l a t e n i t r a t e i n the f i n e S o l i d data mode ( < 2 . 5 pm Dp) and ambient c o n c e n t r a t i o n of f i n e p a r t i c l e n i t r a t e . p o i n t s a r e samples where evidence e x i s t s f o r gaseous HNO3. The percentage of p a r t i c u l a t e n i t r a t e in t h e fine size range i s d i r e c t l y proportional

t o the

fine

particle

concentration

as

shown i n Figure

3.

Figure

3

suggests t h a t the background p a r t i c u l a t e n i t r a t e is about 30% f i n e p a r t i c l e and

70% c o a r s e p a r t i c l e .

These concentrations

a r e derived from the regression

line

obtained i n Figure 3: % NO;

where

NO;

suggests

( f i n e s ) = 0.334 [NO;]

concentration that

is

t h e background

in

nanomoles/m

nitrate

+

fines

3

.

31.0

This

concentration

in

(2) regression

the

Basin

pg/m3 f o r t h e 2 . 5 pm p a r t i c l e diameter (Dp) range and about 2 . 3

relationship

is about

1.0

pg/m3 f o r the

2.5 pm Dp range. The d a t a obtained i n t h i s study lead t o believe t h a t f o r n i g h t s when s t r a t u s clouds a r e not p r e s e n t i n the mixed l a y e r inland and i n the inversion a substant i a l p o r t i o n of n i t r a t e might be i n the form of

gaseous HN03.

The i n t e r p r e t a -

t i o n of t h e i n l a n d and i n v e r s i o n p a r t i c u l a t e n i t r a t e concentrations is d i f f i c u l t

354 because

of

t h i s g a s e o u s HN03.

The

c o n s i d e r i n g c h a n g e s i n t h e C1volume and high-volume The

presence

of

presence

of

g a s e o u s HN03 was

concluded

by

p a r t i c l e s i z e d i s t r i b u t i o n and comparing t h e low-

sampling r e s u l t s .

should

g a s e o u s HN03

result

in

release

of

coarse

particle

C1- as g a s e o u s HC1 a c c o r d i n g t o t h e r e a c t i o n (Ref. 1 5 ) :

I t h a s been s u g g e s t e d by Moskowitz

(Ref.

16) t h a t t h i s r e a c t i o n is i m p o r t a n t i n

t h e p r o d u c t i o n of c o a r s e p a r t i c l e n i t r a t e i n t h e Basin.

Evidence t o s u p p o r t t h i s

c h e m i s t r y i s shown in F i g u r e 4 , which p l o t s t h e % C1% NO;

the

in

coarse

particles.

While

p a r t i c l e s l e s s t h a n and g r e a t e r t h a n 2.5

the

i n coarse particles versus

of

distribution

pm Dp i s r e l a t i v e l y

NO;

constant,

between t h e C1-

d a t a c a n be d i v i d e d i n t o two g r o u p s as denoted by t h e two c i r c l e s .

100

1

I

,/

v)

w

I _----_ -.

,

-

0 l-

\

A

/ I

80 -

0

\

\\

-0

,tiI

A

0

I I'

0

/'

A

0

-

',..-?--*.#' A /----A,

60 -

0

', i

o

\, O

a a a w v) a a

I

A'

40 -

z

\, 1 I

! I \\,

m

a

-

0 :

;

'\ A ,,' '\..e----.-.,'

20 -

-

-

OlNVERSlON

aQ

AMIXED LAYER 0 0

I

I

I

I

20

40

60

80

100

F i g . 4 . R e l a t i o n s h i p between p e r c e n t o f t o t a l c h l o r i d e in c o a r s e mode and p e r c e n t o f t o t a l n i t r a t e i n c o a r s e mode. S o l i d d a t a p o i n t s are samples from l o c a t i o n s of g r e a t e r photochemical a c t i v i t y .

The

samples having

the

majority

c o l l e c t e d i n t h e mixed l a y e r a t

c l e NO;

and

SO:-

levels

ures 2 and 3) a n d / o r

were

of

the

t h e coast. close

to

C1-

in

At

this

the

expected

t h e r e was no m e a s u r a b l e a c i d i t y

coarse

location

background i n the

particles

were

b o t h fine p a r t i levels

samples,

(Figso

that

355 gaseous HN03 c o n c e n t r a t i o n s would be u n i m p o r t a n t ( T a b l e 1). Table 1 s u g g e s t s t h a t i n t h e mixed l a y e r a t t h e c o a s t , c e n t r a t i o n i n t h e s i z e r a n g e of > 2 . 5

pm Dp i s a b o u t 1 pg/m

The samples having t h e m a j o r i t y of

t h e C1-

i n the

t h e background C13

con-

.

f i n e p a r t i c l e s were c o l -

i n t h e i n l a n d areas and from t h e s t a b l e l a y e r

l e c t e d from t h e mixed l a y e r

The s h i f t t o smaller p a r t i c l e C1-

the coast.

An examination of

in

i s c o r r e l a t e d w i t h g r e a t e r photo-

c h e m i c a l a c t i v i t y ( h i g h e r O3 and gaseous HNO ) as w e l l a s h i g h e r f i n e p a r t i c u 3 l a t e NO;, SO:a n d a c i d i t y and presumably r e s u l t s from d i s p l a c e m e n t of from c o a r s e p a r t i c l e s as shown i n E q u a t i o n ( 3 ) .

C1-

c a t e t h a t a b o u t one-half

i n l a n d mixed l a y e r samples by way of E q u a t i o n ( 3 ) . inland

coarse particle

levels

NO;

the experimental value

3.9

of

pg/m

of 3

about

4

of

t o form 2 pg/m3 of NO;.

The

the

pg/m3

from

of CI-

present

2

study

i s displaced i n the drier

1,

(Table

background

indicates

that

NO;

T h i s would l e a d t o p r e d i c t e d

pg/m

3

,

agrees w e l l

with

"mixed l a y e r ,

in-

which

row l a b e l l e d

l a n d , no i n l a n d low c l o u d s t h e p r e v i o u s day"). comes

The d a t a i n F i g u r e 4 i n d i -

t h i s c o a r s e p a r t i c l e C1-

of

T h i s p r e d i c t e d v a l u e of 4 pg/m and

elevated

the

displacement

particle

1 pg/m3

of

concentrations

NO;

3

can

o c c u r a t n i g h t n o t o n l y when t h e a i r mass was w a r m and d r y on t h e p r e v i o u s day ( T a b l e 1) b u t a l s o when t h e a i r mass was c o o l e r and m o i s t d u r i n g t h e n i g h t (Refs. 18).

17,

P e r h a p s NO2 i s c o n v e r t e d p h o t o c h e m i c a l l y d u r i n g t h e warmer,

d r i e r day-

t i m e h o u r s t o g a s e o u s HN03 and t h e n w i t h t h e o n s e t of c o o l e r n i g h t t i m e temperat u r e s and i n c r e a s i n g r e l a t i v e humidity to particulate nitrate.

t h e gaseous HN03 i s g r a d u a l l y converted

Thermodynamically, t h e f o r m a t i o n of

particulate nitrate

i s f a v o r e d by c o o l e r t e m p e r a t u r e s and h i g h e r r e l a t i v e h u m i d i t i e s (Ref.

A p r i n c i p a l a t m o s p h e r i c r o l e f o r ammonia is as a n e u t r a l -

Ammonia chemistrll. izer for

s u l f u r i c and n i t r i c a c i d .

i n t h e f i n e p a r t i c l e mode. i s bound

t o Na

The

Table

two

a c i d i t y of

columns

+

i n Table

the aerosol.

1 shows t h a t n e a r l y a l l t h e NH;

is

This again suggests t h a t the coarse p a r t i c l e n i t r a t e

t o some c a t i o n o t h e r t h a n NH4,

+.

19).

as d i s c u s s e d above,

and,

1 a d d r e s s t h e abundance of

+

the

NH4

concentration,

From examining t h e H+

age a e r o s o l a c i d i t y i s observed i n t h e i n l a n d samples.

most

ion

likely

and

the

t h e h i g h e s t aver-

However,

t h e h i g h e s t con-

c e n t r a t i o n s of a c i d i t y o c c u r i n samples c o l l e c t e d a t t h e c o a s t .

T h i s i s reason-

able

NH3

s i n c e most

inland aerosols.

NH;

was

in

sources The

t h e

Atmospheric Pollution: 15th: International Colloquium Proceedings (''Science of the Total Environment'')

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Atmospheric Pollution