Principles of Air Quality Management, Second Edition

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Author: Roger D. Griffin

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PRINCIPLES OF

Air Quality Management SECOND EDITION

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PRINCIPLES OF

Air Quality Management SECOND EDITION

Roger D. Griffin

Boca Raton London New York

CRC is an imprint of the Taylor & Francis Group, an informa business

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CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2007 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-10: 0-8493-7099-X (Hardcover) International Standard Book Number-13: 978-0-8493-7099-1 (Hardcover) This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www. copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Griffin, Roger D. Principles of air quality management / Roger D. Griffin. -- 2nd ed. p. cm. Includes bibliographical references and index. ISBN 0-8493-7099-X (alk. paper) 1. Air quality management. I. Title. TD883.G78 2006 363.739’2--dc22 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

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Dedication Still dedicated to those who seek the Truth in all things, and to Him Who is

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Preface to the Second Edition In the years since the first edition, we have seen new trends that this author did not think possible when he began his environmental career in 1969. Today there are far fewer “smog alerts,” far fewer acute-health impacts, a far greater acceptance of clean fuels and clean technologies, new engine systems, and a far greater understanding of the sources of air emissions — both natural and man-made. (Air quality improvements are detailed in Chapter 10.) On an international scale, air quality issues being addressed include the concern for indoor air quality in developing nations, the push for clean fuels worldwide, and the search for newer, less polluting technologies for industry and control systems. It is worth noting that the stratospheric ozone layer over Antarctica — once predicted as taking decades to improve — is increasing. If the estimated methane reserves of 400 million tcf (trillion cubic feet) discovered in gas hydrates offshore can be accessed, the entire energy paradigm will shift dramatically to clean fuels. While our goal is the same as in our first edition — “giving the reader a firm grasp of the principles that make up the broad field of air quality, its pollution and its management” — we are also celebrating the successes we have seen over the past 40 years of a concerted effort directed toward clean air. I would like to pay tribute to the thousands who have spent myriad hours studying the atmosphere, devising technologies for clean fuels, clean engines and new control systems, investigating health effects, reviewing historical information on climate, monitoring the air, preparing new management strategies, evaluating rules and regulations, and guiding the energies and industries of a modern society in new directions. To you we say thank you.

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Preface to the First Edition In order to understand and manage our air quality resources, it is necessary to gain a fundamental understanding of the principles that govern our ability to do so. From a local perspective, it may be considered desirable to install huge fans in order to “blow the smog away,” but from a technological and scientific perspective it is not feasible. Likewise, from a regional or continental perspective, it is not acceptable to merely transfer air contaminants from one location to another one by dilution or “blowing it away.” It is therefore the purpose of this book to give the reader a firm grasp of the principles that make up the broad field of air quality, its pollution, and its management. Starting from the basic definitions of air and types of air pollution, we will follow some of its history through the present century. From that perspective, we will look at the terms used: air quality, emissions, standards and classifications of pollutants, and the production of secondary air pollution or photochemical smog. We next look at the health effects of the criteria air pollutants and those that are considered toxic or hazardous, and the effects of those contaminants on the human body. Air pollutant damages to materials and vegetation are also reviewed. The standards of acceptable air quality from the perspective of health impacts (chronic through emergency episode concentrations) and the techniques for measuring air quality are also reviewed. We approach the sources of air contaminants from an anthropogenic as well as geogenic and biogenic perspective. Between sources and receptors we look at how contaminants are dispersed into the atmosphere from a local, regional, and global perspective. From these studies come an evaluation of the different models used to calculate dispersion and the models used to predict ambient air quality. Federal laws and regulations as well as regional perspectives are summarized and evaluated. Control technologies that are available for both stationary sources and mobile sources are reviewed. From these, we are able to evaluate the possible management options for limiting emissions and optimizing air pollutant strategies. Global air quality concerns, relative global emissions, and the alternative views are evaluated from the perspective of management options that may be available to society at large. Of particular concern are those that may influence long-term air quality and health. Finally, we will be looking at indoor air quality and the future trends in air quality management approaches, with their limitations.

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The Author Roger D. Griffin has more than 35 years of technical and management expertise as a result of working on numerous environmental problems. He has in-depth experience in the design, evaluation, and testing of existing and planned combustion, air pollution, waste-to-energy, and hazardous waste sources and control technologies, combined with several years of advanced study of pollutant formation and dispersion from point and area sources. He has served as an expert witness in cases involving air toxics, contaminated properties, and remediation. His master’s thesis was a field validation of the Gaussian plume dispersion model; the antecedent of EPA’s ISC and AERMOD dispersion models. He has conducted remedial investigations at Superfund sites. Mr. Griffin has worked with local government agencies throughout his career, including the County of Orange (California), and the South Coast Air Quality Management District and its predecessor agencies. He has held positions with the Ecology Auto companies (director of Environmental Compliance), Converse Consultants (president and managing officer), CH2M-Hill, US Ecology, and KVB Engineering. He has served in various capacities in his career: analyzing air samples for trace pollutants; and as a field inspector, source testing specialist, permit processing engineer, project manager, and principal-in-charge. His projects have included working on secondary aluminum foundries; performing dispersion modeling and health risk assessments for permits to operate combined cycle power systems; providing expert witness testimony for cases involving hazardous air pollutant emissions from a railroad tank car derailment and spill; performing extensive NOx testing and control programs on standard and alternative fuels; and providing on-site reviews and evaluations of operating European and United States incineration facilities, determining hazardous and toxic emission levels, emissions test methods, and best control technologies for toxic air contaminants. Mr. Griffin has worked on biomass fuel systems (rice hull burner and cow manure combustion systems); performed alternative control technologies and process change evaluations for effectiveness and costs to control odors. His other activities have included preparing hearing board cases, testifying as an expert witness, supervising special studies, preparing emission inventories, and evaluating technological and economic impacts of New Source Review regulation. In addition, he has worked for industrial clients in the food preparation, metallurgical, chemical, petroleum, and power generation industries. In his earlier years, Mr. Griffin supervised a source test team, was responsible for ambient air monitoring instrument calibrations, and advised on methods of air sampling analysis. He taught for 10 years at UCLA and UC–Irvine in their Environmental Engineering Extension program, teaching air quality and hazardous materials

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management. He has a master’s degree in engineering, a bachelor’s degree in chemistry, and is a registered chemical engineer in California.

CONTRIBUTOR Benjamin K. Griffin practices law as an associate for Bois & Macdonald, an environmental law firm in Irvine, California. In his practice, he has worked with the South Coast Air Quality Management District (SCAQMD), the California Department of Toxic Substances Control (DTSC), regional water quality control boards, the Los Angeles County Health and Hazardous Materials Division, and the County of San Diego Department of Environmental Health. He works on matters regarding CERCLA, RCRA, USTCF, and NPL listed sites. He also has worked on claims involving construction delay and inverse condemnation. He earned his J.D. degree from Pepperdine University School of Law. While in law school, Mr. Griffin distinguished himself as a member of the Law School Honor Board, serving as prosecutor. During his second year of law school he was selected as a Blackstone Fellow. Mr. Griffin earned his B.A. degree from The Citadel, with department honors, in political science, international politics, and military affairs. Mr. Griffin is a member of the State Bar of California, the U.S. District Court, Central District of California, the American Bar Association, and the Environmental Law Section of the Orange County Bar Association.

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Acknowledgments The following individuals are acknowledged for their contributions to this book and to a greater understanding of the field of air quality management: Dr. Kathryn Kelly of Delta Toxicology, Inc. Michael Oard, Retired Meteorologist Dr. James Pitts of the University of California, Riverside Dr. Scott Samuelson of the University of California, Irvine Dr. Larry Vardiman of the Institute of Creation Research A special acknowledgment is given to my wife, Dr. Avice Marie Griffin, without whose encouragement this book would not have been possible.

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Contents Chapter 1

The Atmosphere and Its Contaminants ...............................................1

History of Air Pollution.............................................................................................1 Medieval Experiences ......................................................................................1 Industrialization................................................................................................2 The Early 20th Century ...................................................................................2 The Great London Smog Disaster — December 1952...................................3 Late 20th and Early 21st Centuries .................................................................4 Terms and Definitions................................................................................................4 Ambient Air......................................................................................................4 Criteria and Noncriteria Air Pollutants............................................................5 Emissions .........................................................................................................6 The Epidemiologic Model ...............................................................................7 Components of the Atmosphere ................................................................................7 Physical Characteristics ...................................................................................8 Standard Conditions.........................................................................................9 Dew Point and Humidity .................................................................................9 States of Air Pollutants............................................................................................10 Pollutant Gas Features ...................................................................................10 Particulate Features ........................................................................................10 Contaminant Classifications ....................................................................................13 Primary Contaminants....................................................................................13 Natural Emissions ..............................................................................14 Anthropogenic Emissions ..................................................................14 Secondary Contaminants................................................................................14 Photochemical Smog ...............................................................................................14 Air Quality Management Aspects of Photochemical Reactions...................18 Chapter 2

Effects of Air Pollution......................................................................21

Time Effects and Sensitivities .................................................................................21 Acute versus Chronic.....................................................................................21 Sensitive Populations .....................................................................................22 Criteria versus Noncriteria Air Pollutants...............................................................22 Criteria Air Pollutant Effects .........................................................................23 Ozone .................................................................................................23 Sulfur Dioxide....................................................................................24 Particulate Matter ...............................................................................26 Nitrogen Dioxide................................................................................26 Carbon Monoxide ..............................................................................27 Lead ....................................................................................................27

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Basic Principles of Toxicology ...............................................................................28 Sources of Health Effects Information ..........................................................28 Dose–Response ..............................................................................................29 Routes of Exposure .................................................................................................30 Inhalation........................................................................................................30 Response to Airborne Chemicals ............................................................................30 The Lungs ......................................................................................................31 The Central Nervous System .........................................................................33 The Liver ........................................................................................................33 The Kidneys ...................................................................................................33 The Blood.......................................................................................................33 The Reproductive System ..............................................................................33 The Cardiovascular System ...........................................................................34 The Skeletal System.......................................................................................34 Other Factors to Consider..............................................................................34 Classes of Health Effects.........................................................................................35 Latency ...........................................................................................................36 Carcinogens ....................................................................................................36 Mutagens ........................................................................................................36 Teratogens ......................................................................................................36 Effects on the Ecosystem ........................................................................................37 Effects on Vegetation .....................................................................................37 Plant Structure....................................................................................37 Leaf Structure.....................................................................................37 Plant Injury.........................................................................................38 Acid Precipitation Effects ..................................................................38 Pollutant Interactions .........................................................................39 Economic Losses Caused by Vegetation Effects...............................39 Effects on Materials .......................................................................................39 Textiles ...............................................................................................40 Building Materials..............................................................................40 Metal Corrosion .................................................................................41 Surface Coatings ................................................................................42 Documents and Manuscripts..............................................................42 Rubber ................................................................................................42 Effects on Animals.........................................................................................43 Economic Losses .....................................................................................................43 Chapter 3

Air Quality Standards and Monitoring..............................................45

Standards..................................................................................................................45 Acceptable Levels ..........................................................................................46 Ambient Air Standards and Exposures ...................................................................48 National ..........................................................................................................48 International Air Pollution Levels .................................................................50

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The Pollution Standard Index..................................................................................51 Episodic Standards.........................................................................................52 Noncriteria Air Contaminant Standards ..................................................................53 Occupational Derived Standards....................................................................53 Risk Assessment ......................................................................................................54 The Risk Assessment Process........................................................................54 Hazard Identification..........................................................................54 Dose–Response Assessment ..............................................................55 Exposure Assessment.........................................................................56 Risk Characterization.........................................................................57 Uncertainties...................................................................................................57 Uncertainties in Toxicity....................................................................57 Uncertainties in Modeled Exposures.................................................58 Screening Level Approaches..........................................................................58 Carcinogen Hazards ...........................................................................58 Acceptable Air Quality ............................................................................................61 Monitoring Ambient Air Quality.............................................................................61 Measurement Techniques ........................................................................................63 Cumulative Samplers .....................................................................................64 Continuous Analyzers ....................................................................................66 Chapter 4

Sources and Measurement Methodologies ........................................69

Global Sources.........................................................................................................70 Geogenic.........................................................................................................70 Biogenic .........................................................................................................70 Anthropogenic ................................................................................................71 Global Emissions ...........................................................................................72 Air Pollution Sinks ..................................................................................................74 Biological Sinks .............................................................................................74 Mechanical Sinks ...........................................................................................74 Photochemical Sinks ......................................................................................75 Anthropogenic Air Emissions .................................................................................76 Combustion ....................................................................................................76 Fuels for Combustion Reactions....................................................................77 Coal ....................................................................................................77 Liquid Fuels .......................................................................................79 Natural Gas ........................................................................................80 Efficiency and Emissions ...................................................................81 Enthalpy Considerations ................................................................................81 Air and Fuel Considerations ..............................................................82 Combustion Chemistry.......................................................................82 Air-to-Fuel Ratio Considerations.......................................................83 Combustion Systems......................................................................................84

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Evaporative Emissions.............................................................................................85 Evaporative Classes........................................................................................87 Fugitive Emissions...................................................................................................88 Waste-Related Emissions.........................................................................................89 Landfills..........................................................................................................89 Treatment-Related Emissions ........................................................................91 Criteria Air Pollutant Formation .............................................................................91 Source Inventories of Criteria Pollutants ................................................................92 Transportation ................................................................................................93 Fuel Combustion ............................................................................................93 Industrial Processes........................................................................................94 Miscellaneous.................................................................................................95 Comparisons by Category..............................................................................95 Hazardous Air Emissions ........................................................................................96 Quantification of Emissions ....................................................................................97 Source Testing................................................................................................97 Continuous Emissions Monitoring ................................................................97 Carbon Balance ..............................................................................................98 Composition ...................................................................................................98 Emission Factors ............................................................................................98 Fugitives .........................................................................................................99 Accuracy and Applicability .....................................................................................99 Chapter 5

Meteorology, Dispersion, and Modeling .........................................101

Earth’s Energy and Radiation................................................................................101 Temperature and Global Air Movements ....................................................103 Global Circulation Cells ..................................................................104 Jet Streams .......................................................................................105 Surface Effects .................................................................................105 Other Forces .................................................................................................107 Patterns of High and Low Pressure .............................................................107 Friction .............................................................................................111 Horizontal and Vertical Air Patterns............................................................111 Atmospheric Stability ......................................................................111 Vertical Mixing ................................................................................113 Horizontal Air Movements ..............................................................113 Regional Air Pollution Meteorology .....................................................................115 Inversions .....................................................................................................115 Types of Inversions ......................................................................................115 Southern California — The Classic Example .............................................117 Sea and Land Breezes..................................................................................117 Other Dispersive Characteristics of the Atmosphere ..................................119 Valley Effects ...................................................................................119 Chimney Effect ................................................................................121 Vegetation Effects ............................................................................121

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Mountain Effects..............................................................................122 Urban Heat Island Effects................................................................122 Local Air Pollutant Dispersion..............................................................................123 Point Sources and Plume Dispersion ..........................................................123 Plume Rise ...................................................................................................124 Plume Shape.................................................................................................125 Line Sources.................................................................................................127 Area Sources ................................................................................................128 Dispersion Modeling .............................................................................................128 Point-Source Modeling ................................................................................129 Model Averaging Time ................................................................................131 Plume Model Modifications.........................................................................131 Line-Source Models.....................................................................................133 Area Modeling .............................................................................................133 Catastrophic Releases ..................................................................................133 Visibility.................................................................................................................134 Mathematical Models ............................................................................................134 Planning Based.............................................................................................134 Receptor Based ............................................................................................136 Statistical Based ...........................................................................................136 Chapter 6

Stationary-Source Control Approaches ...........................................139

Source Reduction...................................................................................................139 Management and Operational Changes ................................................................140 Fugitive Emissions .......................................................................................141 Product Storage Control...............................................................................142 Materials Changes........................................................................................144 Process-Optimizing Actions ..................................................................................145 Combustion Modifications.....................................................................................146 Fuels and Fuel Modification..................................................................................151 Efficiency......................................................................................................151 Secondary Utilization...................................................................................151 Fuel Switching .............................................................................................152 Fuel Blending...............................................................................................152 Fuel Cleaning ...............................................................................................153 Additives.......................................................................................................154 Fuel Modifications .......................................................................................154 Fuel Refining................................................................................................156 Planning and Design..............................................................................................156 Geographic Location....................................................................................156 Lower-Emission Systems.............................................................................157 Greater Efficiency ........................................................................................158 Repowering ..................................................................................................158 Emissions Characterization ...................................................................................158 Collection of Air Contaminants ............................................................................159

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Air Pollution Control Approaches.........................................................................162 Gas Control Technologies............................................................................162 Absorbers .........................................................................................163 Adsorbers .........................................................................................164 Condensers .......................................................................................165 Thermal Oxidation ...........................................................................166 Particulate Control Technologies .................................................................167 Mechanical Collectors......................................................................168 Fabric Filters ....................................................................................169 Wet Scrubbers ..................................................................................171 Electrostatic Precipitators ................................................................172 Combination Units ...........................................................................173 Combustion Gas Control Technologies.................................................................174 Carbon Monoxide and Combustible Carbon Gases ....................................174 Sulfur Dioxide..............................................................................................174 Oxides of Nitrogen.......................................................................................174 Selective Catalytic Reduction ..........................................................176 Selective Noncatalytic Reduction ....................................................176 Oxidative Systems............................................................................177 Technology Comparisons ......................................................................................177 Control System Hardware Considerations ..................................................178 Chapter 7

Mobile Sources and Control Approaches........................................179

Engines and Air Pollutant Emissions....................................................................179 Pollutant Formation in Spark-Ignited Engines .....................................................181 Bulk Gas Pollutant–Formation Region........................................................181 Surface Pollutant–Formation Region...........................................................182 Four-Stroke Pollutant Mechanisms..............................................................183 Lesser Sources of Carbon Gas Pollutant Emissions ...................................183 Fuel Composition and Exhaust Emissions ..................................................185 Diesel Ignition Emission Characteristics ..............................................................185 Pollutant Patterns .........................................................................................188 Hydrocarbon Emissions from Trip Cycles ..................................................188 Engine Thermodynamic Cycles...................................................................189 Hybrid Internal Combustion Engines....................................................................192 ICE Emission-Control Options .............................................................................193 Effects of Operating Conditions ..................................................................193 Spark Timing................................................................................................193 Compression Ratio.......................................................................................193 Engine Speed................................................................................................194 Engine Power ...............................................................................................194 Engine Temperatures....................................................................................195 Engine Cleanliness.......................................................................................195 Design Influences on ICEs ....................................................................................196 Two-Stage Combustion ................................................................................197

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External Control Approaches ................................................................................198 Fuel Recapture Systems...............................................................................198 Catalyst Systems ..........................................................................................198 Diesel Particulate Controls ..........................................................................200 Fuel Change Effects ..............................................................................................200 Diesel Fuels..................................................................................................204 Alternatives and the Future ...................................................................................205 Alternative Fuels ..........................................................................................205 Alternative Mechanical Design and Efficiency Approaches .......................206 Alternative Power Systems ..........................................................................206 Chapter 8

Global Concerns...............................................................................209

The Challenge........................................................................................................210 Data and Records .........................................................................................210 Intercontinental Pollutant Transport......................................................................211 The Data.......................................................................................................212 Conclusions ..................................................................................................213 Stratospheric Ozone...............................................................................................213 Radiation Primer ..........................................................................................213 Stratospheric Ozone Formation ...................................................................215 Early Observations .......................................................................................216 The Response ...............................................................................................216 Other Sources and Variations.......................................................................216 Lab Studies...................................................................................................217 Antarctic Studies ..........................................................................................217 UV Data and Other Impacts ........................................................................218 Alternatives...................................................................................................219 Acid Deposition .....................................................................................................220 Water Plus Air ..............................................................................................220 Water Plus Soils ...........................................................................................220 Acid Rain Studies ........................................................................................221 The NAPAP Findings...................................................................................222 Conclusions ..................................................................................................224 Global Climate Change .........................................................................................224 Historical Perspective...................................................................................225 Current Concerns .........................................................................................227 Measurements...............................................................................................231 Other Considerations....................................................................................235 Feedbacks .....................................................................................................235 Models..........................................................................................................236 Recent Findings............................................................................................237 Alternative Views...................................................................................................238 Increased Yields ...........................................................................................239 Other Agricultural Effects............................................................................240

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Chapter 9

Air Quality Laws and Regulations ..................................................243

General Law Approaches ......................................................................................243 Public Nuisance............................................................................................243 Private Nuisance...........................................................................................244 Recent Approaches.......................................................................................244 The Process of Regulation...........................................................................245 Role of the Public in Rule Making .............................................................245 Environmental Justice ..................................................................................246 Levels of Authority ......................................................................................246 Federal Preemption ......................................................................................246 Federal Laws Affecting Air Quality Management................................................247 Pre-1990 Air Quality Acts and Effects........................................................247 Implementation Plans.......................................................................248 Monitoring and Limiting Emissions................................................248 Prevention of Significant Deterioration ...........................................248 Emergency Episodes ........................................................................249 Hazardous Air Pollutants .................................................................250 Global Concerns...............................................................................250 Federal Environmental Statutes .......................................................250 Toxic Substances Control Act..........................................................250 Resource Conservation and Recovery Act ......................................250 Comprehensive Emergency Response, Compensation, and Liability Act ...................................................................................251 The Clean Air Act..................................................................................................252 Title I — Attainment and Maintenance of the NAAQS .............................253 Ozone Nonattainment Requirements ...............................................254 Additional Ozone Strategies ............................................................256 Carbon Monoxide Nonattainment Provisions .................................258 PM10 Nonattainment Areas.............................................................259 PM2.5 Nonattainment Areas............................................................260 Title II — Mobile Source Provisions ..........................................................260 Light-Duty Vehicle Standards..........................................................260 Tailpipe Toxics .................................................................................261 Emissions Control ............................................................................261 Reformulated Gasoline Fuel Requirements.....................................262 Phase II Reformulated Gasoline Performance Standards ...............262 California Low-Emission Vehicle II Regulations............................263 Title III — Hazardous Air Pollutant Program.............................................263 Toxic Release Inventory Program....................................................264 HAP Sources ....................................................................................264 Area Sources: Urban Air Toxics Strategy .......................................266 SIP Revisions ...................................................................................266 HAP Permits ....................................................................................266 Special Studies .................................................................................266 Clean Air Mercury Rule ..................................................................266

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Prevention of Accidental Releases...................................................267 Solid Waste Combustion ..................................................................268 Title IV — Acid Deposition Program .........................................................268 SO2 Provisions — Clean Air Interstate Rule 2005 Effect ..............268 Market-Based Allowance Program ..................................................269 NOx Provisions — Budget Training Program .................................269 Other Provisions...............................................................................270 Title V — Operating Permits.......................................................................270 Permit Program Requirements.........................................................271 Fees...................................................................................................271 Other Provisions...............................................................................272 Valid Permits ....................................................................................273 Title VI — Stratospheric Ozone Protection ................................................273 Recapture and Recycling .................................................................274 Labeling............................................................................................274 Title VII — Enforcement Provisions...........................................................274 Clean Air Crimes .............................................................................274 Title VIII — Miscellaneous Provisions.......................................................275 Visibility and Source Receptor Concepts........................................275 Grand Canyon Visibility Transport Commission ............................275 International Treaties .............................................................................................276 Montreal Protocol ........................................................................................276 Kyoto Accords..............................................................................................276 The Influence of Nonregulatory Governmental Actions.......................................277 Court Decisions............................................................................................278 Chapter 10 Management, Trends, and Indoor Air Quality ................................279 Elements of Air Quality Management .................................................................280 Nonregulatory Air Quality Management Approaches.................................281 Trends.....................................................................................................................282 Trends in Emissions.....................................................................................282 Trends in the Extreme Ozone Area .............................................................283 Trends in Strategy ........................................................................................286 Fuels and Transportation..................................................................286 Small Sources...................................................................................287 Governance.......................................................................................287 Hazardous Air Pollutants .................................................................288 Lifestyle Impacts..............................................................................289 Stationary Sources............................................................................289 Natural Sources ................................................................................290 The Outlook .................................................................................................290 Indoor Air Quality .................................................................................................291 Environmental Tobacco Smoke ...................................................................294 Radon ...........................................................................................................295

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Radon in Building Sources ..........................................................................297 Soil ...................................................................................................297 Water ................................................................................................298 Building Materials............................................................................299 Measurement and Action Levels .................................................................299 House Characteristics and Radon Gas Entry ..............................................300 Mitigation .....................................................................................................300 Other Indoor Air Contaminant Concerns ....................................................302 Public Buildings ....................................................................................................304 Indoor Air Pollution in Developing Countries......................................................305 List of Acronyms ...................................................................................................307 Glossary .................................................................................................................311 Bibliography ..........................................................................................................325 Index ......................................................................................................................331

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1

The Atmosphere and Its Contaminants

… her Inhabitants breathe nothing but an impure and thick Mist accompanied with a fuliginous and filthy vapour, which renders them obnoxious to a thousand inconveniences, corrupting the Lungs, and disordering the entire habits of their Bodies; so that Catharrs, Phthisicks, Coughs and Consumptions rage more in this one City than in the whole Earth …. Fumifugium, 1661

HISTORY OF AIR POLLUTION Air pollution has been around as long as man has walked the earth. Indeed, in the earliest extant writings, dating from the dawn of civilization, air emissions from forging operations for bronze, iron, and other implements were well known (Genesis, Chapter 4), as were the emissions from smoking fires and blazing torches (Genesis, Chapter 15). Natural emissions from volcanoes and forest fires were well known and a part of everyday life. The usual response was to let nature take its course and blow air contaminants away or else to emigrate to areas with breathable air. It has been known for millennia that people with certain occupations, such as miners, incurred diseases of the lungs and respiratory system. Today we know that many of these effects were not only induced by fine particles and toxic metals but also by carbon monoxide. Radon gas also was one of the contributing factors to miners’ lung disease from the 15th through the 20th centuries in the Erzgebirg Mountains in central and eastern Germany. Emissions from cooking, heating, and fires in general were also well known. Apart from nature, the sources of contamination were simple solid fuels and metal working operations. Odors also were a part of common life. The common approach to air quality management was to stay out of “bad air” (mal aria), or out of areas in which refuse, garbage, and human corpses were deposited in ancient times.

MEDIEVAL EXPERIENCES In the 12th century, Moses Maimonides of Egypt documented the effects of polluted air on child mortality and morbidity in Cairo as it existed in his day. In England in 1228, coal smoke was determined to be “detrimental to human health,” as Queen Eleanor of Aquitaine had complained that it hurt her lungs. She left the palace in Nottingham in favor of the less-polluted countryside. The first known law to clean up air quality in England was the prohibition on burning soft coal in 1273. By the end of the 13th century, there was considerable agitation about the use of “sea-coal,” 1


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Principles of Air Quality Management, Second Edition

and air quality complaints were mounting. In 1306, King Edward I attempted to drastically curtail the use of coal in London by passing a law stating that “no coal was to be burned by industry and artisans during Parliament.” Fumifugium, a classic treatise by John Evelyn, published in 1661, was the first known attempt to provide an acknowledgment of the effects of air pollution on the health of all persons; to point out the industries and fuels that caused the problem; to offer a variety of management strategies to deal with smoke, its deleterious qualities, and its dispersion; and to offer some remedies. Later societal responses included building chimneys as urbanization and population centers grew. These chimneys provided some relief in the immediate vicinity of the pollutants, but they contributed to an overall deterioration of air quality in the surrounding areas.

INDUSTRIALIZATION With the rise of industrialization in the 18th and 19th centuries, the effects of air pollutant emissions were noted on greater portions of the population. Air quality management options (i.e., controls and prohibitions), however, generally lagged behind societal concerns for managing sanitation, water supply, and solid waste. Odors from the Thames River in the late 1850s were reported to make life in London almost intolerable, and industrial centers such as the Ruhr Valley in Germany were known to significantly affect life in general, and health and appearance in particular. The effects of air pollution on vegetation in the United States, primarily sulfur oxides and particulate matter containing heavy metals, were seen first hand in the Copper Hill area of southeastern Tennessee near Ducktown (the hometown of the author’s father). Before 1864, the area was covered with pine forests and shrubs, but following the founding of the copper smelter, vast quantities of air pollutants were emitted directly into the air without controls, and the surrounding countryside was totally denuded. This included 7,000 acres of forest and over 17,000 acres of land that could no longer support vegetation other than a few grasses. It took over 100 years for extremely hardy vegetation to once again come back, and that regrowth occurred only following institution of air pollution controls on the source.

THE EARLY 20TH CENTURY It was not until the 20th century that air quality management approaches (i.e., primarily smoke and odor abatement measures) began to make their appearance. In 1906, Frederick G. Cottrell invented the first practical air pollution control device: an electrostatic precipitator to control emissions of acid droplets from a sulfuric acid manufacturing plant. The term smog, a contraction of the words smoke and fog, was popularized in Great Britain as a result of a report by a Dr. H.A. des Voeux, a London physician who worked in the field of public health, to the Manchester Conference of the Smoke Abatement League in 1911. It concerned conditions in Scotland in which the combination of smoke, sulfurous gases, and fog were believed to have claimed over 1,000 lives in Glasgow and Edinburgh in 1909.



3

Man-made air emissions were generated in the early 20th century from two general sources: industrial operations and the generation of electrical power. Most of these operations were driven by the combustion of solid fuels. Air emissions were without controls and were directly released into the atmosphere through a chimney or stack. Early control efforts were aimed at either recovery of materials (i.e., acid) emitted from the plant or abating smoke emissions. The first method of quantifying smoke density for regulatory purposes, using the Ringlemann visual method, was adopted before World War I. During this era, efforts were made at understanding not only emissions but also their dispersion. The earliest attempts to understand the dispersion of air contaminants were made by observers and meteorologists of the British Army artillery corps during World War I, and afterward by observations of antiaircraft shell bursts. As industrialization proceeded in the early decades of the 20th century, significant air pollutant “episodes” were noted, such as that which occurred in the Meuse Valley in Belgium in 1930. There, meteorological conditions contributed to air stagnation, which led to a build up of pollutant concentrations caused by industrial sites in the vicinity. In this incident, approximately 60 people died and hundreds of others became ill. It was not until the post–World War II era, however, that a better understanding of air pollution was gained and control technology approaches were instituted. In the United States in the 1940s, in addition to efforts by pioneers in understanding air pollutants, changes were also made in the fuels used (i.e., from coal to oil and gas). More significantly, the number and types of sources changed dramatically. However, the most important effect was caused by the dramatic increase in the number of automobiles in the United States following World War II. In the late 1940s and early 1950s in Los Angeles, a new type of air pollution was noted: photochemical smog. We now know this type of air pollution to be made up of photochemical oxidant gases. Since that time, photochemical air pollution has been found in virtually every urbanized area in the world. It results from a combination of weather patterns, sunlight, and specific emissions interacting to form ground-level ozone.

THE GREAT LONDON SMOG DISASTER — DECEMBER 1952 Air pollution reached its worst in the Great London Smog Disaster of December 1952. In this event, all of the worst possible contributing factors of air pollution (air stagnation, a temperature inversion, extreme cold, high usage of dirty fuels, the switch from electric trolleys to diesel buses for public transport, lack of controls on industrial sources, etc.) combined to cause a siege of bad air quality that lasted for about two weeks. Recent research has determined that the mortality estimates of about 4,000 excess deaths in the period immediately following the event were low by a factor of three. Actually about 12,000 people died as a direct result of the Great London Smog Disaster, and thousands more were sickened. Even today that event is being studied and new findings made (i.e., the initial estimate of the excess deaths being only


4


among the elderly was wrong, the majority of deaths were among the 45–65-yearold age group, probably as a result of their higher outdoor exposures).

LATE 20TH

AND

EARLY 21ST CENTURIES

Only in the last decades of the 20th and the first decade of the 21st century have air quality management strategies taken hold. In the last 30 years, there have been significant reversals in earlier air quality trends from increasingly poor air quality to increasingly healthy air quality. This change has come about as a result of dedicated people and of societal decisions to pursue clean air as a priority. Most significant, this change has come at a time when the worldwide population has been increasing.

TERMS AND DEFINITIONS To clarify our understanding of air quality management issues, it is necessary to take a look at the terms that are in use throughout this field of study. Our air is composed primarily of two simple gases: oxygen and nitrogen. It is the one substance without which people cannot survive for more than about three minutes. Occupying less than 1/1,000,000 the mass of the earth, the atmosphere is critical to life as we know it. However, “pure air” is not an easily defined term. Although we may note the average concentrations of gases and other materials that make up the atmosphere, we are called on to make a distinction between the air we breathe, termed the ambient air, and those trace constituents that may be considered pollutants or contaminants. Contaminants may be considered any materials other than the permanent gases seen in Table 1.1. A pollutant, in contrast, has the connotation of being derived from mankind’s activity. Again, this is an artificial distinction, as gases, dust, and particles may be generated by natural processes (e.g., volcanic eruptions), as well as by grinding operations that make a useful product, such as cement. The health, visibility, and materials or vegetation effects may be the same whether the source is natural or man-made. In general, we are mostly concerned with air pollutants. Pollutants are a legitimate concern of society in dealing with air quality and its management, whereas contaminants may be accepted as a part of the natural world in which we live. In one sense, windblown dust may be both a contaminant and pollutant. The distinction is further blurred when adopted air quality regulations are generic; that is, when they are based on concentration measurements regardless of source. Thus, air contaminants may be confused with air pollutants.

AMBIENT AIR The term ambient air refers to that portion of the atmosphere that is in the “breathing zone” of the inhabitants of the earth’s surface. As such, it is limited to the lower several hundred feet of the earth’s atmosphere. The ambient air and, in particular,



5

TABLE 1.1 Composition of the Clean Atmosphere Near Sea Level Constituent

Chemical Formula

Percentage by Volume*

Nitrogen Oxygen Argon Neon Helium Krypton Hydrogen Nitrous oxide Xenon

Permanent N2 O2 Ar Ne He Kr H2 N2O Xe

Water vapor Carbon dioxide Methane Carbon monoxide Ozone Ammonia Nitrogen dioxide Sulfur dioxide Hydrogen sulfide

Variable Gases H 2O 0.01–7 CO2 0.035 CH4 CO O3 NH3 NO2 SO2 H2S

Parts per Million by Volume

Gases 78.084 20.946 0.934 18.2 5.2 1.1 0.5 0.3 0.09

1.5 0.1 0.02 0.01 0.001 0.0002 0.0002

* Dry basis.

those contaminants that may exist in the ambient air are of major concern because they determine the effects on human health, materials, and vegetation.

CRITERIA

AND

NONCRITERIA AIR POLLUTANTS

There are two basic categories of contaminants in the ambient air that are of concern. These two categories are termed criteria pollutants and noncriteria pollutants. Criteria air pollutants are those air contaminants for which numerical concentration limits have been set as the dividing line between acceptable air quality and poor or unhealthy air quality. The national ambient air quality standard is the concentration of a given air pollutant in the ambient air (over a specified period of time) below which the U.S. Environmental Protection Agency believes that there are no long-term adverse health effects. The criteria air pollutants include four gases and two solids:


6


• • • • • •

Nitrogen dioxide (NO2) Sulfur dioxide (SO2) Carbon monoxide (CO) Ozone (O3) Particulate matter (PM10) Lead (Pb)

The criteria pollutants have been studied in some cases (e.g., sulfur dioxide) for over 100 years, and their human health and vegetation effects are well documented. The noncriteria pollutants are those contaminants designated as toxic or hazardous by legislation or regulation. They fall into two further subcategories, depending on the legislation that defines them. In general, the hazardous air pollutants may pose a variety of health effects (irritation, asphyxia, etc.), whereas the toxics focus on one physiological response (i.e., toxicity). Noncriteria air pollutants have been studied in industrial hygiene settings. In the ambient air, noncriteria pollutants tend to be several orders of magnitude lower in concentration than the criteria pollutants. For instance, it would not be uncommon to find ambient carbon monoxide in the parts per million range, whereas ambient concentrations of a hazardous air pollutant, such as benzene, would be in the parts per billion range. The concentrations of ambient air pollutants are expressed in terms of either a mass per unit volume ratio, such as µg/m3 (micrograms per cubic meter), or a pure volumetric ratio (i.e., volumes of contaminant per million volumes of air). The relationship between the two concentration expressions is a function of the molecular weight of the contaminant in question and the standard conditions referenced in the setting of the ambient air quality standards. The conversion between mass units and volumetric ratios at standard temperature and pressure is µg/m3 = ppm × MW ÷ 0.02445 = ppb × MW ÷ 24.45, where µg/m3 ppm MW ppb

= = = =

(1.1)

micrograms per cubic meter parts per million by volume molecular weight of the contaminant parts per billion.

It should be remembered that ambient air quality standards have differing time periods over which the concentration is to be calculated. In some cases (e.g., ozone), these concentrations are expressed as parts per hundred million, or pphm, averaged over either one or eight hours.

EMISSIONS Emissions are air contaminant mass releases to the atmosphere from a source. They may be from a tail pipe, vent, or stack, though some may be airborne, such as those from aircraft.



7

Emission regulations are expressed in one of two ways: the first is by a mass emission rate, such as pounds per hour, tons per year, or milligrams per second. The second is in terms of a concentration in a release, such as parts per million or grains per standard dry cubic foot (gr/SDCF). Standards for either expression are set by regulation, depending on the air contaminant, the source, and the regulatory jurisdiction. Mass emission rates are calculated from a measured concentration and from calculations of total gas flow per unit time. Emission standards expressed in concentration units were derived from early measurements of air pollutants at their sources. In these early efforts to control air pollution, this was the quickest method to determine compliance at a source without having to quantify the mass emission rates.

THE EPIDEMIOLOGIC MODEL Mass emission rates and ambient air quality concentrations are related by the source/transport/receptor model. In the public health field, this is termed the epidemiologic model and relates a source through a mode of transmission to the receptor. Modeling of the transport phenomenon by which diffusion and dispersion occur yields a calculated downwind ambient pollutant gas concentration. Recent air quality management approaches for hazardous air pollutants and air toxics have used the epidemiologic model to relate health effects to emissions by using various dispersion models (see Chapter 5).

COMPONENTS OF THE ATMOSPHERE Fundamental to understanding air quality management is a basic understanding of the atmosphere itself, its composition, functions, movements, and effects. The major components of the atmosphere on a dry basis, as seen earlier, are nitrogen, at about 78%, and oxygen, at about 21%, leaving about 1% for all the other components. Neither nitrogen nor oxygen is passive — they have significant effects of their own, particularly when reacting with each other to form other air contaminants. The gas concentrations seen in Table 1.1 vary somewhat from point to point across the surface of the globe. The major components in the atmosphere function first in bulk transport. This includes the transport of energy from east to west and from pole to equator, as well as the transport of contamination from a source to a receptor. Nitrogen and oxygen also participate in the nitrogen cycle, which is critical for the functions of photosynthesis and food production. Atmospheric temperature and pressure are functions of these bulk gases. The minor components of the atmosphere include the gases water vapor (H2O) and carbon dioxide (CO2). These components vary much more in concentration, by several percent in the case of water and by several parts per million for carbon dioxide. These two gases have major effects in and of themselves. First, water participates in the hydrologic cycle on which life itself depends. In addition, water in the vapor or gaseous state is the most important gas contributing to the earth’s maintaining a livable temperature (the greenhouse effect). It is a unique


8


substance because at the earth’s surface, it exists in all three material states: solid, liquid, and gas. Water performs its major functions in the life processes as a liquid over a narrow temperature range of about 100˚K in a universe that tends to operate either near absolute zero or at millions of degrees. The other unique properties of water are the large amounts of energy per unit mass that are either absorbed or released when water moves between solid and liquid or between liquid and gaseous states. In the atmosphere, these movements have tremendous effects on the energy balance in the atmosphere and are responsible for the weather. Carbon dioxide contributes to the greenhouse effect but has a much lesser contribution. However, CO2 is the key participant in the carbon cycle (photosynthesis and respiration), without which life could not exist. The other materials that exist in the atmosphere at highly variable concentrations are the trace components. These include the carbon gases, carbon monoxide (CO) and methane (CH4); the nitrogen gases, ammonia (NH3), oxides of nitrogen (NOx = NO and NO2), and nitrous oxide (N2O); the sulfur gases, hydrogen sulfide (H2S) and sulfur dioxide (SO2); ozone (O3); and particulate matter (finely divided solid or liquid particles suspended in the atmosphere by mechanical mixing or brownian motion). These trace components appear to be closely intertwined, both in terms of their influence and of their reactions with each other in photochemistry. For instance, methane (CH4) is not an inert gas but appears as a greenhouse gas and participates extensively in reactions with carbon monoxide, oxygen, and hydroxyl radicals to form ozone. These trace contaminants also have a major influence on health, damage to materials, and effects on vegetation and crops.

PHYSICAL CHARACTERISTICS Air is a mixture of all of these gases. It has an approximate molecular weight of 29. As a gas, it follows the physical gas laws. Within a somewhat restricted operating temperature (ambient conditions: typically 0˚–50˚C), it follows the ideal gas law: PV = nRT,

(1.2)

where P V n R T

= = = = =

absolute pressure volume of the gas parcel in question number of moles of gas in the parcel gas law constant absolute temperature.

Air is also a fluid and therefore tends to move under the influence of external forces, as would any fluid such as water. However, because it is a gas, it has no effective shear strength and will change its volume and density as the pressure and temperature change.



9

Each component in the atmosphere has its own partial pressure that is independent of all other gas components. Because of this, the molecular weight of the atmosphere changes slightly as one increases elevation.

STANDARD CONDITIONS Because the atmosphere varies from place to place in terms of temperature (T ), density (ρ), and pressure (P), a reference pressure has been defined as one “standard atmosphere at sea level.” Sometimes the standard atmosphere is considered under “dry” conditions. In these cases, all water vapor is subtracted and the remaining gas constituents are calculated on a “dry basis.” The equivalencies between pressure measurement units are One Standard Atmosphere = 1010 mb = 760 mm of Hg = 14.7 psi,

(1.3)

where m = millibar mm Hg = millimeters of mercury column height psi = pounds per square inch. Standard temperatures tend to vary depending on the reference. For the U.S. EPA, the reference temperature is 20˚C. For other air quality jurisdictions the standard temperature is 60˚F. In other technical fields the standard temperature may be 32˚F or 273˚K. Density is the mass-to-volume ratio of any given parcel of air. The correction of a given density to a standard condition is a straight proportionality between the ambient P and T and the reference density at standard T and P. For 14.7 psi and 60˚F, the dry air density is 0.0763 lb/cubic foot. At 760 mmHg and 20˚C, the dry air density is 1.356 g/L.

DEW POINT

AND

HUMIDITY

As the temperature of a gas parcel increases, its capacity to hold water vapor increases. The measure of the amount of moisture or water vapor in a given parcel of air is called its absolute humidity (i.e., milligrams of moisture per cubic meter of air). If we compare the actual amount of moisture in an air parcel to the maximum that it could hold at a given temperature, we have relative humidity. It is expressed in percentage of the maximum moisture possible for the given temperature and atmosphere pressure being considered. If a parcel of air contains all of the possible water that it could theoretically hold, we term that condition “saturation,” or 100% relative humidity. Because saturation is a function of temperature, if we have a parcel of air that is already saturated at a given temperature (such as 90˚F), and that parcel of air is further cooled, the water vapor will tend to condense out to form droplets of liquid water. The water will then be in the form of a fog. If other constituents are present


10


in that parcel of air (such as particles), larger droplets will precipitate out. To condense water from gas to liquid, a large amount of heat (“the heat of condensation”) must be removed. This latter characteristic has significant effects on the weather and on pollutant transport.

STATES OF AIR POLLUTANTS In understanding the physical state of air pollutants, we realize that we are dealing with all three states of matter: solid, liquid, and gas. Each has its own characteristics and effects.

POLLUTANT GAS FEATURES The major pollutant gases include sulfur dioxide, carbon monoxide, volatile organic compounds, nitric oxide, and nitrogen dioxide. Thus, they obey the gas laws outlined earlier. The major pollutant gases are also reactive — either by way of photochemical reactions or by direct reaction with materials, vegetation, or living tissues. There are significant size features: these gas molecules are on the order of 0.0005 micrometers (µ, or microns) in diameter. They mix in a local environment by diffusion and in the atmosphere at large by convection. There is little visibility effect from the true pollutant gases other than changes to the color of the atmosphere as we view it. For instance, NO2 absorbs light in the ultraviolet end of the visible spectrum. Therefore, when NO2 is present in moderate concentrations, we see a yellow-to-brown coloration. Another salient feature is that these gases are primarily acids, and thus they participate in all of the acid reactions common to the field of chemistry. The health effects of these gases are very important. Finally, there are high annual emission rates (tonnage) in all nations for these anthropogenic emissions. In the United States, about 135 million metric tons per year of gaseous air pollutants are emitted to the atmosphere. Gaseous emissions are well in excess of 95% of all U.S. air pollutant emissions, and about two-thirds of this total is carbon monoxide.

PARTICULATE FEATURES Particles or particulate matter that are suspended in the atmosphere (either solids or liquid droplets) are termed aerosols. Particulate matter in solid form is not particularly reactive unless it encounters liquids (i.e., condensing water vapor or other liquids). Liquid droplets are also termed particulate matter (or particulates in some jurisdictions). The pH of the droplet, as well as its composition and the amount of dissolved material in the droplet, is of concern. Particulate matter represents approximately 3% of the total anthropogenic burden of emissions in the United States, at approximately 4 million metric tons per year. The size of particulate matter in the atmosphere is highly variable, ranging from less than 0.01 µ to over 100 µ. In Figure 1.1, we see the typical ambient air trimodal distribution of particulate diameters versus number density. These three size groupings are generally attributable to different sources.



0.002

0.01

0.1

Nuclei mode

11

1 2 Particle diameter, (µm)

10

100

Accumulation mode

Fine particles

Coarse particles

FIGURE 1.1 Modal distribution of atmospheric particles.

Figure 1.2 indicates the particulate size ranges of various materials as found in urban environments. The largest particles, those with an aerodynamic diameter larger than about 10 µ, are generated either by natural causes (windblown dust) or by attrition or grinding of naturally occurring materials, such as sand, coal, lime, and so on. The largest ones settle out soonest (under quiet conditions) with a constant velocity within a fairly short distance. They are governed by the Stokes law, which relates the settling velocity to the particle density and diameter.

Sea salt Fly ash Carbon black Pollen Tobacco smoke Cement dust Combustion nuclei

Coal dust Oil smoke

Metallurgical dust and fumes Smog Insecticide dusts 0.001 µm

0.01 µm

0.1 µm

1.0 µm

10.0 µm

FIGURE 1.2 Size ranges of common atmospheric particles.

100.0 µm


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At the other end of the size distribution are the ultrafine particles — those in the 0.002–0.1µ range. These particles behave like gas molecules and exhibit Brownian motion; thus, they remain suspended in the atmosphere for long periods of time. These particles are in the condensation nuclei size range because they are generally formed by the condensation of gases or vapors into liquid or solid droplets. Sources of these ultrafine particulates include combustion and fumes from metallurgical operations. Key features of these particles are: (1) they are very reactive on their surfaces, (2) they tend not to remain in that particle size, and (3) they serve as sites for the deposition of heavy metals, such as selenium, arsenic, and lead. The middle distribution, roughly between 0.1 and 2 µ in diameter, forms the accumulation group. These particles are termed accumulation because this size range is the final resting place of particles from the other two regions. Ultrafine particles in the condensation nuclei range agglomerate and grow to an optimum diameter between approximately 0.3 and 0.5 µ under the influence of Brownian motion and condensation processes. The growth tends to stop there because of surface charge and surface tension effects. Coarse particles will continue to break down because of mechanical action and weathering. They tend to accumulate in the 1–2 µ diameter sizes. Particulates in the less than 2.5 µ (particulate matter 2.5) diameter range are considered fine particles primarily because of their deposition sites within the lungs. Those larger than 2.5 µ are termed coarse particles. These diameters do not represent the true physical diameter of the particles. Particles tend to be irregular in shape except for liquid droplets. The aerodynamic diameter is defined as the theoretical diameter of the particle in question which is equivalent to a spherical particle of unit density (1 g per cubic centimeter). Monitoring instruments are calibrated to the unit density spherical particle and, therefore, measure particulate size in terms of aerodynamic diameter. Optical measurements, of course, reveal a wide variety of particle shapes and aspect ratios. Liquid aerosols are less well defined. Several considerations differentiate them from gases and solid particulates. These aerosols are typically classified in the 0.01–1.0 aerodynamic diameter size range. Also, because aerosol diameters exist at the wave lengths of visible light, optical scattering occurs. An aerosol’s ability to interfere with light transmission is also related to its mass concentration. The components of aerosols include soil-derived crustal materials; water; organic compounds; water-soluble acids such as HCl, SO2, and carbon dioxide; ions derived from other, originally gaseous, pollutants such as ammonia; and finally, elements such as soot or black carbon in their elemental forms, mixed with the other materials. As such, aerosols are heterogeneous mixtures, and therefore, their composition varies widely depending on their location, the time of the year, meteorological conditions, and so on. Aerosols are reactive and will participate in the formation of other compounds within the droplet itself. Figure 1.3 shows an idealized schematic of the composition of atmospheric aerosols and their sources. Two of the greatest effects of aerosols are on health and visibility. As a result of the size of aerosols, they are deposited deep in the lungs (in the alveoli), where they accumulate. From there other chemical contaminants are carried across tissue membranes into the body.



13

Gaseous organics

Condensible organics

Combustion process emissions

Primary Secondary organic organic C carbon Elemental Na,+ Cl− carbon metals NO 3−

Gas phase photochemistry

Sea salt + dust

H2O +

NH 4

2−

SO4

HNO3


H2SO4

NH3 emissions

Primary 2−

SO4


NOx SO2

FIGURE 1.3 Idealized schematic of the composition of atmospheric aerosols.

CONTAMINANT CLASSIFICATIONS Air contaminants can be classified in one of two major categories depending on the generation mode — primary or secondary emissions. The latter are produced by further reactions in the air or within liquid aerosols.

PRIMARY CONTAMINANTS Within the primary classification are two major subdivisions: those that are naturally occurring and those that are anthropogenic or derived from the activities of mankind. In the chapter on sources (Chapter 4), we look at the relative contributions of the two classifications. Within the naturally occurring category, we find those that are geogenic, or derived from actions within the earth’s crust, and those that are biogenic, or derived from living organisms.


14


Natural Emissions The geogenic source contaminants include the sulfur gases (SO2 and H2S), methane carbon dioxide, particulates (minerals), chlorides and other ions such as sodium (from volcanos and sea salt aerosols), and the petroleum gases. The latter are derived from within the earth’s crust and contain all of the organic compounds normally found in crude oil systems from methane to the heaviest asphaltic compounds. The biogenic gases include hydrogen and all of the carbon-based gases derived from biological activity. The processes include photosynthesis, metabolic action, decomposition of living matter, and emissions from plants and animals. Among the carbon gases are CO, CO2, methane, CH3Cl, and the terpenes (organic compounds — the basic structures of which are formed from isoprene, a five-carbon olefinic chain compound). Terpenes are photochemically reactive and represent significant emissions, which lead to secondary reactions in the atmosphere. Emission rates of those compounds are a strong function of temperature and are released by land-based plants. Anthropogenic Emissions The anthropogenic pollutants (i.e., those generated by man’s activities) include CO and sulfur dioxide, hydrochloric acid, and NOx, as well as the halogenated solvents such as perchloroethylene. In addition, particulate matter, covering all of the size ranges noted earlier, is generated from anthropogenic activities. Petroleum-related gases are also included in the anthropogenic category, as they are also released into the atmosphere from mankind’s activities in handling, processing, transporting, reacting, and combusting petroleum-based materials.

SECONDARY CONTAMINANTS Secondary air contaminants are those that are produced by reactions either in the gas phase or in aerosols suspended in the atmosphere. “Oxidants” (ozone plus PAN plus NO2) are the most important class of secondary pollutants produced in the gas phase. Particulate matter is produced from primary pollutant gases. For example, NO (from combustion or natural causes) is initially oxidized to NO2 and, ultimately, to nitric acid and ionic nitrates. Likewise, sulfur dioxide is oxidized in the atmosphere to sulfur trioxide, which, in the presence of moisture, forms sulfuric acid and, ultimately, particulate sulfates. Within an aerosol, further reactions occur to change the chemical composition and potential health effects of the droplet. The acid forms of sulfur and nitrogen oxide gases will react with naturally occurring ammonia to form ammonium sulfate and nitrate salts.

PHOTOCHEMICAL SMOG Early 20th century chemists were aware of the nature of photochemical oxidant gases but were unable to determine the reactions of contaminant species with sunlight to form ambient ozone. In Los Angeles, researchers in the 1950s discovered a fairly



15

0.4

Hydrocarbon

Concentration (ppm)

0.3

0.2

Oxidant

0.1

NO2 NO

Aldehydes 0.0 0000

0600

1200 Local time

1800

3400

FIGURE 1.4 Daily variation in air pollutant levels.

common pattern of several of the pollutant gases that were noted during the course of a typical “smoggy” day in Southern California (Figure 1.4). The initial levels of contaminants remained low and fairly constant until about sunrise. During the morning hours, sharp increases in NO and nonmethane hydrocarbon concentrations were noted. It was observed that this rise corresponded to the start up and driving of mobile sources of combustion contaminants — principally NO and hydrocarbons from gasoline-powered automobiles. By late morning, the concentrations of hydrocarbons and NO began to fall at about the same time that NO2 concentrations began to rise. This was followed at midday by declining concentrations of NO2 and increasing concentrations of oxidants, principally ozone. As the afternoon proceeded and the sun dipped, it was noted that oxidant concentrations also began falling off. This drop was followed by a late afternoon surge in NO and NO2 readings, which then dropped off and leveled out as the evening progressed. The researchers concluded that there was a relationship between sunlight, hydrocarbons/volatile organic compounds, NO, and NO2. This deduction led others to investigate the relationship between organic gases and oxides of nitrogen in smog chamber studies in the presence of sunlight to form oxidants and ozone. Carbon monoxide concentrations (Figure 1.5) also showed a diurnal pattern with concentration increases in the early morning and late afternoon periods. CO is not a direct participant in the majority of the reactions producing ozone in the atmosphere — CO competes with the formation of ozone by reacting with OH free radicals to produce a free hydrogen atom. The latter reacts rapidly with oxygen to


16


10 9 8

CO∗ ppm

7 6 5 4 3 2 1 0 12M

4:00 AM

8:00 AM 12 Noon Time of day

4:00 PM

8:00 PM

FIGURE 1.5 Typical urban carbon monoxide levels.

form the hydroperoxy free radical (HO2), which may subsequently participate in the ozone formation. Further investigations of atmospheric reactions led ultimately to the understanding that oxidants (primarily ozone) are formed by two mechanisms: one is a direct photolysis, whereby NO2 is split by blue/violet light to form NO and an oxygen atom free radical. The resulting oxygen atom quickly combines with molecular oxygen in a three-body reaction identical to the one producing ozone in the stratosphere: NO2 + hν ⇒ NO + O*

(1.4)

O* + O2 + M ⇒ O3 + M

(1.5)

where M represents any other molecule (typically N2 or O2) available to carry off excess energy. The two reaction components, NO and O3, will react with each other to form NO2 + O2 once again. Thus, an equilibrium is established under ideal conditions whereby ozone is formed by the action of sunlight on NO2 in the atmosphere. Figure 1.6 shows this simple NO2/O3 cycle. Unfortunately, calculations for these equilibrium concentrations of ozone did not match the higher concentrations measured in the Los Angeles photochemical smog. For example, for an initial concentration of 0.1 ppm NO2, the predicted ozone concentration should be 0.03 ppm, whereas the observed ambient concentration is approximately 10 times higher. Thus, the above simple reaction set is not sufficient to explain the formation of photochemical ozone. Further studies indicated that the key to understanding elevated ground-level ozone levels are found in the chemical reactions that convert NO to NO2 without consuming O3. It was discovered that a critical component of the overall higher production of ozone was the effect of reactive hydrocarbons. These hydrocarbons are generated by the act of volatile organic compounds combining with OH* free



17

Nitrogen dioxide (NO2)

Sunlight energy

Nitric oxide (NO) Oxygen atom (O)

Ozone (O3)

Oxygen (+ O2)

FIGURE 1.6 Photolysis of NO2 and generation of O3.

radicals in the vapor phase. (Volatile organic compounds are hydrocarbon-based molecules.) A simplified reaction sequence then becomes R – C – H + OH* ⇒ R – C* + H2O

(1.6)

R – C* + O2 ⇒ RO2*

(1.7)

RO2* + NO ⇒ NO2 + RO*

(1.8)

and then the original reactions occur: NO2 + hν ⇒ O* + NO

(1.4)

O* + O2 + M ⇒ O3 + M

(1.5)

where hν = ultraviolet radiation R = hydrocarbon fragment X* = any free radical atom. The overall equation then becomes RO2 + O2 + hν ⇒ RO + O3.

(1.9)

A schematic of this overall reaction is given in Figure 1.7. All of the species, including OH, are produced by reactions involving photocatalyzed associations of O3, aldehyde or carbonyl compounds, and HNO2. As noted earlier, CO may also


18


Nitrogen dioxide (NO2)

Sunlight energy

Nitric oxide (NO) Hydrocarbon free (radical) (RO2)

Hydrocarbon (RH) Oxygen

Ozone (O3)

(O2)

Oxygen (O2)

Oxygen atom (O)

FIGURE 1.7 The influence of HCs and free radicals on atmospheric O3 generation.

participate in the formation of HO2 radicals by reaction of OH to form H* + CO2. The OH radicals are typically formed by reactions of O* with water vapor to yield OH* species. The RO2 species [from the original hydrocarbon chain with an acyl (-CO-) unit from a reaction with NO2] forms the peroxyacyl nitrate (PAN) family of compounds: R-CO-O2* + NO2 ⇒ R-CO-O-O-NO2

(1.10)

Typical compounds that give rise to such species would include volatile organic compounds such as acrolein (CH2 = CH-CO-H) and formaldehyde. In summary, the secondary photochemical pollutants derive their energy for breaking and forming new chemical bonds from ultraviolet radiation in sunlight. Thus, if sunlight is absent, photochemical oxidants will not be formed. Oxidants include ozone (O3) and peroxyacetyl nitrate. Minor quantities of NO2 and H2O2 are formed in addition to the radicals OH, HO2, and partially oxidized hydrocarbons.

AIR QUALITY MANAGEMENT ASPECTS

OF

PHOTOCHEMICAL REACTIONS

Knowledge of these reactions provides us with opportunities for implementing strategies for managing or improving air quality in locations subject to photochemical oxidants. The current state of knowledge indicates that both NOx and reactive organic gases are key components. Figure 1.8 is a computerized simulation (the EKMA model) of known chemical reactions from smog chamber studies in which oxides of nitrogen and hydrocarbon species are irradiated with sunlight. From this simulation, we derive a contour map



19

0.28 0.24

0.4 0

NOx, ppm

0.20 0.16 0.12

0.2 4

0.08

0.3

6

0.2

0

0.1

6

0.1

0.04

0 0.3 .34 2 0.3 0.2 0 8

2

0 0

0.2

0.4

0.6

0.8 1.0 1.2 1.4 VOC, ppm carbon

1.6

1.8

2.0

FIGURE 1.8 Modeled ozone generation as a function of NOx and VOC.

of maximum ozone production for differing initial concentrations of NOx and hydrocarbons. This map indicates that with high concentrations of both NOx and hydrocarbons, maximum ozone concentrations of 0.4 parts per million or higher are possible. With decreasing NOx and hydrocarbon concentrations, maximum ozone concentrations will also decrease. If concentrations of both NOx and hydrocarbons are progressively lowered (while maintaining the same ratio), the maximum ozone concentrations may only slowly decrease — or even increase. In contrast, if control strategies are implemented such that the ratio of either one or the other contaminant decreases dramatically from some initial point, the minimum ozone concentration may be attained much more quickly. As an example, if one begins at 0.2 ppm of NOx and 1.3 ppm of hydrocarbons (as C), we find approximately 0.36 parts per million of ozone to be the maximum. This is at an approximate HC-to-NOx ratio of about 6.5. Maintaining this 6.5 ratio while reducing both the NOx and hydrocarbon concentrations after the institution of air quality management strategies would produce ozone levels that are still in excess of 0.24 ppm. However, if all of our strategies are maximized to reduce NOx to 0.1 ppm or less, with no change in hydrocarbon concentrations, we would find the approximate maximum ozone level to be about 0.26 ppm, or slightly higher than the concentration attained by reducing both emissions. Proceeding to reduce ambient NOx concentrations further would more quickly reduce maximum ozone concentrations to lower levels, as we would be “over the hill.” However, starting at a lower HC concentration of about 0.6 ppm with the same initial NOx (0.2 ppm), and focusing on only NOx reductions, would increase maximum ozone concentrations. It must be remembered that this is only a generic output of modeled atmospheric reactions — the shapes of the actual curves are unique to each location. These results,


20


based on evaluations of ambient concentrations and smog chamber studies, point the way toward potential air quality management strategies. The actual strategies may be different for each location. We must also be aware that contaminants such as hydrocarbons and NO2 are pollutants in their own right and have a variety of effects on the ecosystem. They are thus subject to regulation and control resulting from their health effects, as well as from materials damage and their effects on crops and vegetation. These effects are the subject of the next chapter.


2

Effects of Air Pollution

And what may be the cause of these troublesome effects, but the inspiration of this infernal vapour, accompaning the Aer, which … enters by several branches into the very Parenchyma, and substance of the Lungs, violating, in this passage, the Larynx and Epiglottis, … which, becoming rough and drye, can neither be contracted, or dilated for the due modulation of the Voyce. Fumifugium, 1661

The effects noted during the 1952 London Smog Disaster were obvious but not perceived — nearly 1000 deaths per day, where beforehand the normal death rate was a few hundred deaths a day at most. It was reported that the increase of deaths during the London smog siege was not noticed during the event, but the shortage of coffins and flowers was. Today we are much more aware of acute as well as longterm or chronic health effects. Air pollution was known to cause damage to the entire ecosystem even before Fumifugium was published. Such damage includes adverse effects on human health; damage to crops, vegetation, and forests; and finally, damage to materials that we all use. Our goal in this chapter is to review and evaluate the effects on human health of the different air contaminants. Then, we consider contaminants’ effects on vegetation, crops, and finally, other materials.

TIME EFFECTS AND SENSITIVITIES ACUTE

VERSUS

CHRONIC

As seen during the London Smog Disaster, the immediate effect of the air pollution was acute — death. Only in the last few years has there been new research to show the long-term complications of air pollution that occurred months and years earlier. Initial estimates were that about 4,000 people had died as a result of the smog siege; now the epidemiological evidence indicates that about 12,000 died of complications over the course of 6 months following that event. There are two time-related categories of health effects. The first deals with acute effects, that is, those health effects that tend to act immediately on a specific target organ or point of entry into the human body. In the air pollution field, these points of entry are typically the eyes and the lungs, as they are in immediate contact with the ambient air. Burns and asphyxiation are other examples of acute health effects. It is possible for a contaminant to have an acute effect that is different from its chronic effect.

21


22


TABLE 2.1 Population Groups Sensitive to Air Pollution Population Group Cardiovascular disease Chronic respiratory disease Elderly (>65 years of age) Children (15 g/kg 5–15 g/kg 0.5–5 g/kg 50–500 mg/kg 5–50 mg/kg 50 0 0

Commercial Fuel switching and blending Physical coal cleaning Low NOx burners Overfire air Lime/limestone FGD* Dual alkali FGD Spray drying Selective catalytic reduction Reburning

Emerging Advanced coal cleaning Copper oxide FGD * Flue gas desulfurization.

45–60 90–95

0–10 90–95

7099_C006.fm Page 176 Monday, July 17, 2006 11:59 AM

176


Selective Catalytic Reduction Selective catalytic reduction (SCR) reduces NOx emissions using a catalyst bed and ammonia. Ammonia, taken from a storage tank, is vaporized and diluted with air or steam to produce gaseous ammonia. The ammonia is injected upstream of the catalyst and mixed with the flue gas. The flue gas, along with the ammonia, then enters a catalyst reactor, which contains several layers of catalyst elements (a catalyst bed) and is distributed throughout the catalyst bed. The catalyst enhances the reaction of ammonia with NOx. When the proper conditions are obtained, such as a flue gas temperature between 275˚C and 424˚C, a reaction sequence takes place and NOx is reduced to molecular nitrogen (and water), thereby reducing emissions. Increasing the ammonia injection rate leads to an increase in NOx reduction. However, this reduction can also result in an increase of unreacted ammonia (ammonia “slip”), which can cause blockage of gas passages, poor emissions control downstream, and visible ammonia salt plumes. Ammonia slip can be minimized by matching the NOx concentrations profile in the flue gases at the inlet of the catalyst. In addition, an ammonia control system can be used to monitor the ammonia dosage applied to the SCR system. The catalyst configuration is usually of a honeycomb type, with parallel rigid plates and cylindrical pellets. Typical catalyst materials are titanium and zeolite. The lifetime of the catalyst is limited as a result of losses from poisoning, erosion, solid deposition, and sintering by high temperatures. Once the catalyst loses its activity, it must be replaced. The lifetime of a catalyst is important in terms of cost and maintenance. SCR is applicable to gas-, oil-, and coal-fired combustors and results in NOx reductions of 85% to 95%. Unfortunately, the cost for SCR installation and maintenance is high. Selective Noncatalytic Reduction When the reduced nitrogen/NOx reaction takes place entirely in the exhaust gases without the presence of a catalyst, the process is called a selective noncatalytic reduction. Three common chemicals (in effect, additives) used with selective noncatalytic reduction (SNCR) are ammonia, urea, and cyanuric acid, each with a different effective reaction temperature range. The latter two may be in either a liquid solution or a powder/dust form. The additive is injected at various distances downstream of the combustion chamber of the boiler, heater, or other combustor. The objective of SNCR is to inject the chemical or solution at an optimum temperature window (between 900˚C and 1100˚C), at which the reaction will take place to convert NOx into nitrogen and water. If, however, the exhaust gas temperature is too high, ammonia will react with oxygen to form more NOx. If the temperature is too low, the ammonia does not fully react and results in poor NOx reduction and excessive ammonia slip. Good mixing of ammonia and flue gas NOx is essential to achieve a high NOx reduction and low ammonia slip. The solid or liquid spray additives are used to expand the temperature window to lower temperatures. Urea injection has the advantage of not being hazardous, as is the case with ammonia or cyanuric acid.


Stationary-Source Control Approaches

177

SNCR equipment consists basically of sprays, temperature sensors, a chemical feed control system, an additive storage tank, and a chemical vaporizer. Reduction in NOx emissions of up to 75% can be achieved with SNCR. This reduction has the advantage of not requiring the expensive catalyst equipment, but it does require a higher consumption of chemicals. Oxidative Systems Oxidative systems also find their niche in NOx control. In these systems, which are specific to smaller gas flows with relatively high concentrations of oxides of nitrogen, the exhaust gases are processed through an oxidative absorption system. Here, intimate contact occurs between the oxides of nitrogen and solution chemicals in a packed tower. In solution, the oxides of nitrogen are fully oxidized to nitric acid and absorbed. The resultant solutions are neutralized in a wastewater treatment process. In these systems there is a potential safety problem in handling strong oxidizing solutions and in disposing of residual materials such as wastewaters following wet control systems.

TECHNOLOGY COMPARISONS A comparison of the applicability of various control systems is seen in Table 6.4. This table compares the relative applicability of individual control options for the range of criteria and noncriteria contaminants seen in stationary-source emissions. As can be seen, no one technique is uniquely qualified to be a “cure-all” for all

TABLE 6.4 Relative Effectiveness of Stationary Control Technologies* System Absorbers Adsorption Condensers Cyclones Fabric filters Oxidative Catalytic Thermal Reductive Electrostatic Scrubbers a

VOCs

HAPs

PM

++a +++ ++

++b ++ +

+

++

+ +++

+

+ ++ ++

+/– +

NOx

+ +/– +++ ++ ++

+

CO

SO2

+/– ++

+++

Oxygenated organics. Acid gases. * Effectiveness varies over a wide range, depending on system parameters. For general comparisons only. b


178


types of air contaminant emissions. Rather, a comprehensive approach, taking into account contaminant-specific parameters, location parameters, efficiency, and economy, is required to produce the most effective air pollution control system. It should be remembered that regulations will become increasingly stringent. Therefore, new facilities must put a premium on flexibility of control systems, incorporating possibilities such as changing fuels, having tighter emission controls, and accepting higher operating or maintenance costs. Concerns about the management of residual waste must also be addressed. Thus, the emphasis in the future will increasingly be on front-end management, planning, and source reduction, in addition to higher-efficiency back-end control technology.

CONTROL SYSTEM HARDWARE CONSIDERATIONS A final note should be made regarding the selection of hardware and the key factors involved in that hardware. The first two major concerns are the efficiency of the control system to meet the technology- or health-based emission standards and the cost that allows the system to be built. As noted earlier, control efficiency requirements can be expected to increase because tighter emission limitations will be adopted in the years ahead. Therefore, systems designed to attain efficiencies of collection and control that are higher than originally required will be considered better options. Detailed economic studies comparing the various control efficiencies as a function of capital and operating costs, with estimates of potential break-even points, are considered in all capital purchases. Increasing concerns are now expected for the life-cycle cost of any technology. With the increasing emphasis on environmental protection of all media, not just air pollution, the costs of residuals management must also be factored into cost analyses. The ability of any given system to withstand the temperature, process, and concentration excursions along with changing contaminant mixtures is also a factor to be considered. The more durable the system, the less maintenance time and costs are required to keep the system operational. The reliability of any system is high on the list of hardware considerations. It has been noted that “anything will work for a while,” but when large capital outlays and high pollutant-control efficiencies are required, estimates of reliability are a major consideration. Not to be forgotten are the potentials for liability (both corporate and individual) should equipment fail to perform as required or, worse, a release of hazardous air pollutants occur. In general, simplicity of operation and maintenance are rated higher than a nominally equivalent or slightly higher control efficiency of another more complicated system. Potential problems with component part breakdowns that may cause releases above emission limits are also to be considered. In addition, matrix analyses for control systems, bringing into play technological, legal, and economic factors, will increasingly be a tool in control system design and selection for stationarysource air quality management.

7099_C007.fm Page 179 Monday, July 24, 2006 2:54 PM

7

Mobile Sources and Control Approaches

While the sulfurous fogs crept across London in early December 1952, the townspeople were not fully aware of what was happening. But many townspeople were pleased that the conversion of the city’s trolleys from electricity to diesel powered buses was now complete. London, December 1952

Probably the most important change in sources of U.S. air contaminant emissions from the early 20th to the early 21st century was the shift from stationary sources to predominantly mobile sources. Technologies and approaches to reducing mobile source emissions lagged behind approaches applied to stationary sources because of the lag in recognition of the mobile sources’ contribution to the problem. Motor vehicles make up the largest number of sources of air contaminant emissions in the United States. These vehicles include passenger vehicles, light-duty trucks/SUVs (LDTs), and medium- to heavy-duty trucks (M/HDTs). As seen in Table 7.1, passenger and light-duty trucks form the majority (over 95%) of the motor vehicles on the road. The significance of these mobile sources is that they are powered primarily by gasoline-burning combustion systems. Gasoline-powered vehicles are responsible for 78% and 92%, respectively, of the gallons of fuel consumed and miles driven. Diesel fuel oil accounts for the balance. Individual emissions from each source are small; however, because of the large number of sources involved, the aggregate emissions are significant. As a consequence, we need to understand how the major types of engines that drive our mobile sources work, how they can be modified, and the most efficient ways available of controlling the emissions that are ultimately released. Equally important is the effect of the fuels they burn on their respective criteria and toxic/hazardous air emissions. Finally, a word needs to be said about alternatives to traditional engines and fuels and some new approaches.

ENGINES AND AIR POLLUTANT EMISSIONS On a pollutant-specific basis, mobile sources account for varying percentages of air contaminant emission. Figure 7.1 indicates that these percentages vary from 77% of the total national CO emissions to less than 30% of the particulate matter emissions. However, on a specific geographic basis, such as in California, mobile-source emissions are significantly higher. The internal combustion engine (ICE) is the basic power plant for these vehicles, whether spark ignited or compression ignited. 179


180


TABLE 7.1 U.S. On-Road Motor Vehicles — 2003 Number, millions

Vehicle Type

Gallons of Fuel, billions

VMT, billions

Passenger Light-duty trucks, SUVs Medium-/heavy-duty trucks

136 85 8

75 56 38

1659 966 214

Total

228

169

2839

VMT = vehicle miles traveled

Percent mobile sources

100 80 60 40 20 0 CO

NOx US

VOC/HC

PM10

California

FIGURE 7.1 Mobile source emissions. (US data from the 1999 EPA National Air Quality and Emissions Trends. Southern California data from the 2004 California Air Resources Board Emission Inventory.)

There are also a large number of nonvehicular ICEs that may play a significant part in air quality management strategies. It is estimated that between 7 and 8 million outboard engines are in use in the United States at the present time, as well as 8–12 million engines in lawn mowers, leaf blowers, chain saws, and similar applications. The emissions from these devices have been largely uncontrolled up to the 21st century, and therefore their contribution, in addition to that from aircraft, may represent a significant local effect on air quality. The principles involved in understanding air pollutant emissions from ICEs are the same as for mobile vehicular sources. Likewise, stationary-source ICEs have the same pollutant formation patterns; however, they are not subject to the changes in operating modes typical of a mobile ICE. While stationary gasoline- or diesel-powered reciprocating ICEs have the same emission patterns they are usually operated in a “cruise” mode rather than the cyclic pattern of mobile sources. Mobile sources, for instance, change from idle to



181

acceleration to cruise to deceleration to stop and back again. Thus, emissions attributable to changes of operating mode are not significant for stationary ICEs but are important for mobile sources. The most significant difference between mobile sources driven by piston engines and those driven by combustion turbines (Figure 4.6 seen earlier) is that the latter experience continuous combustion. The processes occurring in piston engines are essentially a series of explosions internal to the cylinder so that there are tremendous differences in temperature, pressure, gas composition, and volume occurring throughout its cycle.

POLLUTANT FORMATION IN SPARK-IGNITED ENGINES Formation of air pollutants in spark-ignited ICEs occurs in two regions: the bulk gas region and the boundary layer, or surface region. Each region has unique properties; therefore, the relative amounts of criteria pollutants and their formation mechanisms differ in each region. These regions are illustrated in Figure 7.2.

BULK GAS POLLUTANT–FORMATION REGION The bulk gas reactions for a spark-ignited engine produce both fuel hydrocarbons and CO and are generally formed by similar mechanisms. Oxides of nitrogen formation occurs solely in the bulk gas reactions and is a function of many variables. Particulate matter is a significant contaminant for diesel ICEs and is addressed primarily through back-end controls. Hydrocarbons and CO form through two mechanisms in the cylinder, depending on whether they are in a fuel-rich or the fuel-lean region of the bulk gas at any point in the thermodynamic cycle. In a fuel-rich region, hydrocarbon fuel fragments and CO will be formed as a result of a deficiency of oxygen to support complete combustion. Such fuel-rich regions occur during start-up, deceleration, and warmup operating modes. In the bulk gas in which the fuel/air mixture is in an extremely Spark plug Cylinder wall Bulk gas reactions Flame front Surface effects Piston head

FIGURE 7.2 Regions of ICE pollutant formation.


182


fuel-lean (excess air) condition, oxidized carbon gases will be formed and remain as a result of incomplete flame propagation. In these regions, carbon monoxide levels are high. Carbon monoxide, once formed, is fixed by the chemical kinetics of reactions in the bulk gases. Carbon monoxide is difficult to oxidize without high temperatures; therefore, its formation occurs as a result of thermal quenching. This effect is rapid at high air-to-fuel ratio mixtures. Hydrocarbon levels depend on the amount of oxygen present. The effect of thermal quenching for hydrocarbons is much more severe for a given temperature gradient than it is for CO. Oxides of nitrogen formation is a function of many variables, including the gas temperature (for thermal NOx), the residence time at high temperature, and the availability of excess oxygen. The latter is a function of the air-to-fuel ratio. Most oxides of nitrogen are formed in the hot, turbulent gas regions of the flame. The thermal NOx formation process is termed the Zeldovich mechanism. In these high-temperature regions, molecular oxygen is dissociated into oxygen free radicals, which react very quickly with nitrogen to yield one NO molecule plus a nitrogen free radical. The nitrogen free radical then attacks an oxygen molecule to yield one NO plus an oxygen free radical, and so on. Equations (7.1–7.3) illustrate these steps in the formation of NO by the Zeldovich mechanism. O2 → 2O*

(7.1)

O* + N2 → NO + N*

(7.2)

N* + O2 → NO + O*

(7.3)

Thus, for every oxygen molecule that is cleaved by high temperature, four NO molecules will form while regenerating more oxygen free radicals. There is therefore a near exponential increase of NO with temperature as the percentage of oxygen molecules being cleaved increases.

SURFACE POLLUTANT–FORMATION REGION The other major region of air pollutant formation is on the walls and surfaces of the cylinder. Within the cylinder, a boundary layer of fuel and air will form along the surface of the piston head and cylinder walls, which significantly influences emission formation. The cylinder of a spark-ignited ICE also serves as a very large heat sink, as well as providing high surface areas for physical or chemical reactions. Thus, the walls and head of the cylinder and piston are a major source of hydrocarbons, carbon monoxide, aldehydes, and other products of incomplete combustion (PICs). These result from the quenching of combustion resulting from heat sink temperature losses. It has been estimated that approximately 1% of the entire fuel charge is not burned as a result of these wall effects. Deposits, as well as cracks and crevices in and on the surfaces of the cylinder, will enhance the trapping of fuel hydrocarbons in such deposits or crevices. Deposits are formed in localized hot spots that cause metal corrosion. Localized cold spots may condense out fuel fragments as tar. These carbonaceous deposits act like a fuel



183

vapor “sponge.” During the varying temperature regimes of the cycle, these sponges act to adsorb and desorb fuel components and products of incomplete combustion. As the piston moves up and down in the cylinder, a film of oil forms on the walls, yielding a “wet” effect. This wetted wall serves as an additional location for absorption or desorption of fuel fragments. These factors contribute to hydrocarbon and PIC emissions during operation.

FOUR-STROKE POLLUTANT MECHANISMS An illustration of one cylinder typical of a gasoline-powered ICE during the four “strokes” of normal operation is seen in Figure 7.3. During the compression stroke, when the fuel and air are in the chamber, oil and deposit layers absorb hydrocarbons. Fuel and PICs (from the previous cycle) are forced into cracks and crevices in the cylinder surfaces as the pressure increases. During the combustion stroke, the pressure is still rising as the spark from the spark plug ignites the entire mixture. As the flame front moves through the mixture, NO forms in the high-temperature burning gas. CO, if the mixture is fuel rich, will be present in the high-temperature gases. As a result of the increasing pressure at this point in the cycle, unburned fuel will be further forced into crevices on the surfaces of the piston head and exposed cylinder walls. During the “power” expansion stroke, the piston is forced downward, and the volume begins increasing in the chamber. The temperature begins dropping, and NO formation is frozen as the burned gases cool. This is followed by a freezing of the CO combustion chemistry. Along the walls and from crevices in the cylinder, an outflow of hydrocarbon fuel fragments from those crevices begins. Some portions of those hydrocarbons will form CO and products of incomplete combustion. During the exhaust portion of the cycle, the pressure in the cylinder drops to slightly above atmospheric, and wall effects begin to dominate. Deposits, cracks, and crevices desorb additional hydrocarbons, fuel fragments, and PICs. Desorption of fuel fragments from the oily layers along the walls of the cylinder occur at this point. The cylinder head scrapes more fuel from the wall layers and desorbs those into the exhaust gases before the closure of the exhaust valve. From this we may understand some of the basics of air pollutant formation in an ICE. These steps in the process are a function of the complex interactions of pressure, temperature, volume, combustion kinetics, and mechanical effects in a spark-ignited gasoline-powered engine.

LESSER SOURCES

OF

CARBON GAS POLLUTANT EMISSIONS

The effects of wear and aging on engines may contribute significantly to hydrocarbon and CO emissions. These are partly because of the formation of surface deposits or corrosion building up over the course of time. Poorly seated valves and rings may also cause leaks of fuel or fuel fragments into the exhaust. Likewise, poor or faulty ignition generates pure hydrocarbon emissions during cranking, and scoring and crevice formation on aging engine surfaces lead to high emissions.


184

Principles of Air Quality Management, Second Edition Air Carburetor Fuel-air mixture

Intake valve

Spark plug Exhaust valve

Fuel

Cylinder (combustion chamber) Piston

Connecting rod

Crankshaft (1) Intake stroke

(2) Compression stroke

Burnt fuel mixture

(3) Power stroke

(4) Exhaust stroke

FIGURE 7.3 Combustion in an automobile engine (one cylinder of a typical automobile engine shown).

Blowby, which is the flow of fuel vapors past the cylinder walls into the crankcase, may be a significant source of uncontrolled hydrocarbon emissions. In older, uncontrolled vehicles, these fuel vapors may account for 20%–25% of the total hydrocarbon emissions. Newer vehicles recirculate crankcase gases through positive ventilation systems back into the combustion air intake for reburning. Scavenging losses occur when both intake and exhaust valves are open at the same time. In a two-stroke engine, where both valves must be open for the engine



185

to operate, scavenging losses are a major source of hydrocarbons, as the seating of the valves and the design of the combustion chamber require both to be open during portions of the cycle. For a four-stroke engine, the scavenging losses occur when a supercharged or turbocharged system is in operation. This causes portions of the fuel–air mixture to pass directly from the intake to the exhaust.

FUEL COMPOSITION

AND

EXHAUST EMISSIONS

Figure 7.4 illustrates the variety of air pollutants (organic compounds and fuel fragments) in the exhaust of a spark-ignited gasoline-powered four-stroke engine. The four categories are the paraffins (saturated hydrocarbons), the aromatics or unsaturated ring structures, the olefins or double-bonded carbon systems, and the oxygenates or fuel fragments containing oxygen. These categories are charted by species percentage for each carbon number represented. The actual number of individual compounds in gasoline and its exhaust ranges into the hundreds of discrete chemical species. This figure also illustrates the typical average gasoline composition, listed by species. Oxygenates are the partially burned fragments of fuel left in the exhaust. Interestingly enough, the largest single oxygenate is the single-carbon atom species formaldehyde. The highest two-carbon atom compound is acetaldehyde. A comparison of the fuel composition with exhaust hydrocarbon composition demonstrates the strong correlation between the exhaust species distribution and the fuel species. For paraffins and olefins, there is also a “downshift” to lower carbon numbers, representing fuel fragments. This indicates that, except for the oxygenates, the exhaust hydrocarbon emissions are essentially components of the original gasoline.

DIESEL IGNITION EMISSION CHARACTERISTICS The significant differences between a diesel-ignited system and a spark-ignited system are that the diesel system operates at extremely high pressures (approximately 100 atmospheres) and high (lean) air-to-fuel ratios, producing high excess air in the chamber. The bulk gas temperature range is about the same. One of the more significant differences, though, between diesel- and sparkignited systems is that current diesel engines operate by injecting a measured amount of oil into the cylinder at high compression. With oil injection, the mixing and evaporation of fuel components into the gas phase is significantly different from a carbureted system, which uses gasoline or other low–molecular weight fuels. The significance of the liquid fuel spray cannot be overestimated, as it strongly affects the pattern of air pollutants formed in the diesel system. Another difference is the air-to-fuel ratio in the diesel combustion chamber. This air-to-fuel ratio varies spatially throughout the combustion zone as a result of the fuel spray. Air swirl will also influence the geometry of the flame pattern. Liquid fuel spray, air-to-fuel ratio, and air swirl interact under the high-pressure regimes to influence the combustion contaminants associated with diesel emissions. As the jet of fuel is injected into the combustion chamber, the high temperature and air swirl cause the formation of a fan-shaped pattern of evaporating fuel droplets and vapors.


186


20

10

15

8 6

10

4

5

Exhaust

Fuel

Paraffin content, vol % Gasoline vs. Exhaust

2

0

0 C1

C2

C3

C4

C5 C6 C7 Carbon number

C8

Gasoline

C9

C10 C11

Exhaust

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

14 12 10 8 6 4 2 0 C1

C2

C3

C4


C8

Gasoline

C9

Exhaust

Fuel

Olefin content, % vol Gasoline vs. Exhaust

C10 C11

Exhaust

12 10 8 6 4 2 0

14 12 10 8 6 4 2 0 C1

C2

C3

C4

C5

C6

C7

C8

C9

Exhaust

Fuel

Aromatics content, % vol Gasoline vs. Exhaust

C10 C11

Carbon number Gasoline

Exhaust

1.0

0.5

0.8

0.4

0.6

0.3

0.4

0.2

0.2

0.1 0.0

0.0 C1

C2

C3

C4

Gasoline


C8

C9

C10 C11

Oxygenates

FIGURE 7.4 Exhaust gas distributions versus fuel composition.

Exhaust

Oxygenated content exhaust %



187

4. Impingement area 3. Core Piston head

Injector

2. Flame zone 1. Edge

FIGURE 7.5 Diesel fuel liquid spray pattern.

As a consequence, four major regions have been identified in the compressionignited system. Air contaminant generation varies significantly in each zone. These regions are the fuel spray edge, the flame zone, the core, and the droplet or impingement zone. These four zones are illustrated in Figure 7.5. At the edge of the spray, the air-to-fuel ratio is too lean for flame propagation and good combustion because of the high excess air. This is a zone of formation for carbon monoxide and other PICs, as well as gaseous hydrocarbon fuel fragments. At low or idle conditions, this zone is relatively large, and therefore emissions of hydrocarbons are greater. However, as the pressure and temperature increase with increasing load, this zone decreases, and the overall emission of hydrocarbons, CO, and PICs will decrease. The flame zone is operating at near stoichiometric conditions at the highest flame temperatures. Therefore, this area tends to form high quantities of oxides of nitrogen but very little CO or hydrocarbons. Also, this zone is relatively long lasting, and therefore more NOx is generated as a result of the relatively longer time that the burning parcels exist at those high temperatures. The spray core is that zone in which droplet evaporation is the predominant mechanism. The combustion in this zone is limited because of the relatively slow diffusion of combustible vapors from droplets into the available surrounding air mass. As a result of the diffusion-controlled nature of this combustion, the amount of swirl air interacting in this zone will significantly affect the pollutant mix. At low loads, where a relatively smaller fuel is available, some oxides of nitrogen will be formed here because of the amount of excess air available to the diffusion flame. At higher loads, however, this zone will be responsible for CO, hydrocarbons, and PICs, as well as soot or carbonaceous particles. Diesel particulates, once formed, are not easily oxidized and will therefore be emitted. Soot particulate is a significant problem with diesel fuel and is listed in California as a toxic air contaminant. The fourth zone is the location at which large fuel droplets are responsible for most of the pollutant generation. This occurs in two different portions of the combustor. The first portion is where the relatively larger droplets occur at the end of the fuel injection, close to the injection port. These large drops form as a result of reduced pressure at the end of the injection and the higher combustion chamber pressure.


188


TABLE 7.2 Typical Internal Combustion Engine Cylinder Exhaust Concentrations Contaminant

Cruise Mode

Idle Mode

Diesel Gasoline

NOx, ppm 1400 500

50 100

Diesel Gasoline

HC, ppm 100 6000

200 4,000

Diesel Gasoline

CO, ppm 500 60,000

150 10,000

Diesel Gasoline

PM10 High Low

High Low

These relatively large drops are also responsible for diffusion-controlled combustion and, likewise, form soot particles on the evaporation of volatile components. Hydrocarbon and PICs are also found in the emission. Finally, some of these large drops may impinge on the cylinder head and are responsible for additional hydrocarbon and PIC emissions as well as soot formation and carbonaceous deposits.

POLLUTANT PATTERNS A comparison of the pollutant patterns of gasoline (Otto cycle) engines and diesel engines is shown in Table 7.2 for two operating modes. In this table, we see the differences in emission patterns under idle conditions and under normal cruise conditions for the two engine types. For oxides of nitrogen under cruise conditions, a diesel cycle system produces significantly higher overall NOx emissions than a spark-ignited or Otto cycle engine. At idle conditions, as noted above, the NOx emissions are much lower than for the spark-ignited systems. With respect to hydrocarbons and carbon monoxide, spark-ignited emissions are significantly higher — in some cases by an order of magnitude — than those from diesels because of the excess air and compression conditions noted earlier for diesels. Carbonaceous particulate formation for diesels is significantly greater than for sparkignited systems because of the higher molecular weight and oily nature of diesel fuels.

HYDROCARBON EMISSIONS

FROM

TRIP CYCLES

Quite apart from the comparisons of the two engine types is the influence of “cold start” and “hot soak” hydrocarbon emissions as opposed to those from cruise or



189

TABLE 7.3 Influence of Trip Cycles on HC Emissions* Trip Length Condition

5 Miles

10 Miles

20 Miles

Cold start Hot soak Cruise

9 2 3

9 2 6

9 2 12

14

17

23

Total HC, grams

* Grams total hydrocarbons. Source: California Air Resources Board.

running exhaust. In Table 7.3, the influence of trip length on uncontrolled hydrocarbon emissions is summarized. Cold start emissions are fairly constant at about 9 g of fuel hydrocarbons per start. The end-of-trip period or hot soak generates roughly 2 g of hydrocarbons for the average car equipped with a catalyst. Cold start and hot soak emissions are termed standing emissions. The cruise emissions are approximately 0.55 g per mile and are thus a function of the total miles traveled. The significance of these differences in running versus standing emissions is in the control approach taken. Implementing emission reductions in the first 2–3 minutes of operation, as well as during the hot soak or cool-down at the end of the trip, would significantly lower overall air quality effects. Thus, air quality management strategies will have to identify techniques for controlling evaporative hydrocarbon emissions as a function of the number of individual trips. These standing versus running emissions appear to explain some studies that show greater frequencies of elevated ozone levels on weekends when, presumably, there are a greater number of short trips but a lesser number of total miles traveled in areas such as Los Angeles.

ENGINE THERMODYNAMIC CYCLES The purpose of any mobile source of emissions is to provide useful work to drive a vehicle, whether automobile, truck or airplane, to a different location. To accomplish this, useful work must be extracted from the engine. Useful work from a system is described by its thermodynamic cycle. The three cycles representing mobile sources are illustrated in Figures 7.6, 7.7, and 7.8 by their respective pressure–volume diagrams. In piston engines, the cycles are represented by what happens to the fuel, air, and combustion byproducts mixture in the cylinder. The four steps of the cycle are compression, ignition, expansion or work-producing (step), and exhaust. These four steps are the same whether it is a two-stroke or a four-stroke engine. (The number of strokes refers to the number of times the piston traverses the length of the cylinder for each power step.) Figure 7.6 refers to the spark ignition cycle, commonly called the Otto cycle after the German engineer who built the first successful operating spark-ignited


190


Combustion

40

30

n io ns pa l E x de a I Ac tu a

l

20

Igni tion Comp ressio n

10

0

0

5 Volume – arbitrary

Exhaust

Pressure – atmospheres

50

10

FIGURE 7.6 Otto cycle, compression ratio of 9:1.

80 Combustion 60

Expansion Injection Id ea l A Co ctu mp al res sio n

40 20 0

0

10 Volume – arbitrary

Exhaust


100

20

FIGURE 7.7 Diesel cycle, compression ratio of 19:1.

gasoline engine. This figure illustrates each of those steps on an arbitrary pressure–volume diagram. Beginning in the lower right-hand corner, the fuel and air are compressed to much smaller volume with a slight increase in pressure, at which point ignition occurs. From that point, combustion begins, which dramatically increases the pressure in the system with only slight variations in volume. As the combustion proceeds, expansion of the hot combustion gases increases the volume and decreases the pressure as useful work is accomplished. The last step of the cycle is when the combustion gases are exhausted from the cylinder. This brings us to the point of return at which the cylinder is ready for a fresh charge of fuel and air. Figure 7.7 illustrates the diesel cycle in which much higher compression of the air in the cylinder occurs. At a point near the maximum pressure, liquid fuel is



191

Combustion

3

l

0

al

1

Expansion

a tu Ac

2

ssion Compre

4

e Id


5

Atmosphere 0

5 10 15 Volume – arbitrary

20

FIGURE 7.8 Brayton cycle, pressure ratio 4:1.

injected (sprayed) into the cylinder near the final portion of the compression stroke, after which gas combustion occurs by auto ignition. The hot gases provide work to the drive shaft by expansion against the piston. This increases the volume and lowers the pressure in the cylinder until the gases are exhausted. The thermodynamic cycle for combustion turbines is seen in Figure 7.8. This is the Brayton cycle and operates at significantly lower pressures. In this system, compression is accomplished by compressor blades, and combustion occurs via a standing flame at nearly a constant pressure. Exiting the combustor can, the hot gases expand and drive turbine blades (which power the compressor shaft) and exit the exhaust, providing thrust for the aircraft. Figure 4,7, seen earlier, is a schematic of a combustion turbine. A summary of the significant differences in ignition source, pressure, air-to-fuel ratio, peak temperatures, and peak pressure is seen in Table 7.4. These are useful in evaluating performance-based emission differences.

TABLE 7.4 ICE Operating Parameter Comparisons Otto Cycle* Ignition source Peak pressure, atm Compression ratio Fuel delivery Air-to-fuel ratio Peak temperature (˚R)

Spark 35 6 to 11:1 Aspirated or injected Near ideal 4500–5000

* Reciprocating piston. ** Continuous, combustion gas turbine. N.A. = Not applicable.

Diesel Cycle* Compression 100 14 to 22:1 Injected Lean 4500–5000

Brayton Cycle** Spark 4 N.A. Injected Very lean 2250–2600


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HYBRID INTERNAL COMBUSTION ENGINES Research into hybrid ICEs has continued to find more efficient engines with lower air-contaminant emissions resulting from operating fossil fuels. In the last few years, a new syncretistic engine design has been developed called the HCCI, or homogeneous charge compression ignition engine. Earlier names included the active thermo-atmosphere combustion engine and the hot vapor injection engine. The HCCI is a relatively new combustion technology. It is a hybrid of the traditional spark ignition (Otto engine) and the compression ignition engine (diesel). Unlike the spark-ignited or diesel engine, however, HCCI combustion takes place spontaneously and homogeneously, without flame propagation. This alternative combustion process uses lean mixtures ignited without a spark or flame front, which eliminates heterogeneous air/fuel mixture regions. In addition, HCCI operates as a fuel-lean combustion process. These conditions translate to a lower local flame temperature, which lowers the amount of NOx produced in the process. To achieve the homogeneous charge, fuel and air are well mixed throughout every region of the cylinder before combustion. There is theoretically no localized high-temperature flame front; instead, there are hundreds of evenly distributed points of ignition, indicating spontaneous combustion of the gas volume in the cylinder. High exhaust-gas dilution and lean mixtures greatly reduce peak temperatures and heat-transfer losses, which further reduces NOx formation. As a practical matter, HCCI works better in theory than in practice at this time. Achieving sufficient thermal energy late in the compression stroke to trigger the required auto-ignition consistently is an ongoing challenge. Using a compression ratio beyond 12:1 causes severe knock during full-load operation. Other concerns are excessive rates of pressure rise and the combustion-generated noise associated with very high compression. A more practical avenue being pursued by researchers is using high levels of exhaust gas recirculation by various means to supply the desired thermal energy needed for auto-ignition. One technique, called recompression, traps exhaust in the cylinder by closing the exhaust valve early. Another approach (rebreathing) captures exhaust after it has left the cylinder and draws it back into the chamber. Unfortunately, power density is lower with HCCI combustion engines than with gasoline engines running with stoichiometric air/fuel ratios. A greater problem, however, is that HCCI operation is not yet possible during engine warm-up, at very light loads, or at idle because exhaust energy is too low to trigger auto-ignition during these conditions. Another concern is that peak combustion temperatures well below the threshold of NOx formation result in incomplete oxidation of the fuel and air. As a result, HC and CO emissions may be 50% higher than today’s normal spark-ignited gasoline engines. A third dilemma is that the exhaust temperature is too low for proper catalytic converter function. While the HCCI approach may represent the next generation of practical combustion engines, it is believed that it will take 5–10 more years of research before HCCI systems become a practical reality.



193

ICE EMISSION-CONTROL OPTIONS The two major approaches to minimizing emissions from ICEs are through changing the operating conditions or through changing the design of the engine itself. These options both function apart from changes in fuels composition. The former approaches have received significant attention trying to minimize emissions before back-end, or tailpipe, control technologies.

EFFECTS

OF

OPERATING CONDITIONS

The single most important effect on combustion emissions is caused by the air-tofuel ratio. Figure 4.5, seen earlier, is an illustration of pollutant concentrations versus air-to-fuel ratio for gasoline combustion. The equivalence ratio is the relationship between the fuel-to-air ratio of the operating system and the fuel-to-air ratio at stoichiometric, or ideal, conditions. An equivalence ratio less than 1.0 indicates lean conditions (excess air). An equivalence ratio greater than 1.0 indicates fuel-rich conditions. In fuel-rich regions, hydrocarbon and CO emissions tend to predominate and reach their minimum on the slightly lean side of the stoichiometric ratio. Oxides of nitrogen tend to peak just on the lean (excess air) side of stoichiometric mixtures. It should be noted that at very high air-to-fuel ratios, CO and hydrocarbons again increase as a result of the temperature-quenching effect of excess air. Thus, there is a “balancing act” performed between combustion controls for NOx and those for hydrocarbons/CO. The maximum combustion temperature curve is similar to the NOx curve. Thermal NOx emissions are highly temperature dependent.

SPARK TIMING For spark-ignited ICEs, the influences of changing the spark timing may be significant. If the spark timing is advanced, overall temperatures during the cycle tend to go up, and NOx concentrations will therefore increase. Advancing the spark means that the spark occurs earlier than normal during the compression cycle. Retarding the spark tends to lower oxides of nitrogen but may only marginally reduce hydrocarbon emissions. The effect of spark timing and equivalence ratio is seen in Figure 7.9 on oxides of nitrogen concentrations.

COMPRESSION RATIO The effect of compression ratio will significantly increase both oxides of nitrogen and hydrocarbons in direct proportion. Figure 7.10 shows the hydrocarbon concentrations as a function of compression over a range of equivalence ratios. In Figure 7.11, the influence of compression on oxides of nitrogen concentrations is apparent. The effect is directly proportional to increasing compression ratios. The major effect on NOx is in the excess air or lean regions. For hydrocarbons, the effect is “across the board.” The hydrocarbon trend is reflective of the variation in thickness of the quench zone or boundary layer in which fuel gases are contained.


194


0.6

40° BTC

Nitric oxide concentration – percent

0.5

2500 RPM V-8 engine 26" Hg. man.

0.4 30° ° 20

0.3

10°

0.2

T.C

0.1

0.8

0.9 Lean

1.0

1.1

1.2

1.3

Rich

Equivalence ratio (mixture strength)

FIGURE 7.9 Effect of spark timing and mixture ratio on NO emissions.

At higher compression ratios, a greater quantity of fuel would exist in the boundary layer and would therefore be exhausted with the exhaust stroke. The effect on oxides of nitrogen is clearly one of increased temperatures in the chamber with increasing pressurization.

ENGINE SPEED The effect of engine speed, or revolutions per minute, on emissions is variable. An increase in engine speed tends to reduce hydrocarbon concentrations as a result of an increase in turbulence in the combustion chamber. Thus, a greater percentage of the hydrocarbon fuel fractions near engine surfaces become entrained in the bulk gases and are burned. Likewise, exhaust gas temperatures are increased with speed, which promotes further combustion and reductions of CO and hydrocarbons (if the mixture is lean). This effect, however, causes chamber temperatures to increase, and oxides of nitrogen concentrations therefore also increase with engine speed.

ENGINE POWER The effect of engine power output is a direct function of the amount of fuel being injected into the cylinder. Therefore, the effect of power changes the fuel-to-air ratio. As power is increased, the fuel mass increases through the engine and the air-to-fuel



195

500

9: 400

1

1

7:

1

5:

300

tio Ra

Co mp .

Hydrocarbon, concentration–PPM (as C6 H14)

600

Manifold injection spark 48° BTC 1800 RPM

200

100

0

0.8

1.0 Lean

1.2

1.4

1.6

Rich


FIGURE 7.10 Influence of compression ratio and mixture ratio on hydrocarbons.

ratio decreases. This tends to increase both hydrocarbons and CO. Because of the higher temperatures resulting from the increased amounts of fuel, NOx concentrations increase with load until a rich condition occurs (as under high acceleration demands). At that point, NOx begins to decrease.

ENGINE TEMPERATURES Overall engine temperatures, as measured by the temperature of the cylinder surface walls, also have an influence. Operating in hot ambient air or operating in conditions that cause the engine coolant temperature to increase would increase oxides of nitrogen and decrease hydrocarbons. In one experiment, an increase of the engine surface temperature by 75˚F of generated a 73% increase in overall NOx emissions. In another experiment, an increase in coolant temperature of 100˚F decreased hydrocarbon emissions by one third.

ENGINE CLEANLINESS As mentioned earlier, the effect of deposits will significantly affect carbon gas emissions. Therefore, a cleaner or newer engine will have a positive effect by lowering carbon gas emissions. Deposits serve as “sponges” for fuel fragments (hydrocarbons), which are emitted later in the cycle. In contrast, cleaner engines are responsible for higher temperatures and higher NOx emissions result.


196


0.6

Nitric oxide concentration–percent

0.5 12.0 C.R. 9.5 0.4

Man. press. 29" Hg. spark 15° BTC speed 1500 RPM

6.7 0.3

0.2

0.1

0.8

0.9 1.0 Lean

1.1 Rich

1.2

1.3


FIGURE 7.11 Influence of compression ratio (C.R.) and mixture ratio on nitric oxide.

DESIGN INFLUENCES ON ICES Engine design changes modify the combustion process, which has an effect on air contaminant emissions. By lowering the surface-to-volume ratio of the combustion chamber, more of the hydrocarbons will be in the bulk gas, and therefore, the combustion will be more complete. Thus, designing the combustion chamber to reduce this ratio to as low as possible (considering cost, design, feasibility, and reliability) will improve combustion and lower emissions of hydrocarbons. The influences of exhaust back pressure and valve overlap affect hydrocarbons and NOx emissions by influencing the amount of exhaust gases remaining in the cylinder following combustion. Increasing engine back pressure and overlapping the valve timing will cause a greater quantity of the last stroke’s gases to be retained in the cylinder. This causes the oxides of nitrogen to decrease as a result of lower temperatures (a function of the greater quantity of residual noncombustibles) and a lower air-to-fuel ratio. Hydrocarbon emissions tend to increase, however, as the airto-fuel ratio is reduced. A similar approach, but one that is much less complex than using back pressure and valve timing, is the inclusion of an exhaust gas recirculation system. The recirculation of exhaust gas significantly lowers oxides of nitrogen emissions but causes only minimal changes in CO and hydrocarbons. This is a result of the lower gas temperature (from higher inert gas concentrations) and the lower oxygen content of the mixture.



197

Exhaust gas is recirculated back into the combustion air intake manifold by a control valve. It has been found that a 5% gas recirculation may reduce uncontrolled NOx emissions by more than 50%, depending on other engine parameters. A 15% recirculation may cause controlled NOx emission reductions of more than 75%. Above this percent recirculation, CO and hydrocarbon emission tend to increase. This approach is nominal in cost and complexity. At full-load conditions, or maximum acceleration, exhaust gas recirculation is bypassed because of the increased power requirements and the lower air-to-fuel ratios caused by heavy acceleration. Fuel injection lowers hydrocarbon emissions by allowing more precise fuel control, particularly under cold start conditions and deceleration. This reduces the need for fuel enrichment during start-up and load change as compared to carbureted fuel systems. Computerized engine controls (mandated in 1996 for all U.S. automobiles), coupled with on-board diagnostic systems, provide for optimized operation of the combustion process because of fuel-to-air control, spark timing, and enhanced control settings for engine control devices, such as exhaust gas recirculation valving. This optimization minimizes hydrocarbon and CO emissions as well as oxides of nitrogen.

TWO-STAGE COMBUSTION Without totally redesigning the ICE, it is possible to take advantage of certain aspects of the air-to-fuel emission curves such that low NOx emissions (characteristic of a fuel-rich mixture) can be coupled with the low hydrocarbon and CO emissions in the excess air regions of the fuel-to-air ratio. This has led to the redesign of the top of the cylinder such that the combustion chamber consists of two parts. Figure 7.12 illustrates this two-stage combustion engine, also called a stratified charge.

Third valve Precombustion chamber Plug Lean mixture intake

Rich mixture intake Exhaust valve

Intake valve Piston

FIGURE 7.12 Stratified charge engine.


198


In this system, the combustion takes place in two phases. There is a fuel-rich chamber on the top and a fuel-lean portion in the cylinder itself. In the fuel-rich combustion chamber, from 40%–70% of the combustion air is supplied along with the full charge of fuel. In this fuel-rich combustion, very low oxides of nitrogen are formed; however, large quantities of carbon monoxide, PICs, and fuel fragments occur. The rich, hot combustion gases then pass through a restricted opening into the lean portion of the cylinder. In the lean portion of the process, the balance of the required air is supplied, which causes the overall combustion process to operate in the lean fuel-to-air regions such that burnout is completed. The exhaust gases then drive the piston down, providing power to the system. CO and hydrocarbons are consumed, and the oxides of nitrogen are minimized as a result of operation at higher excess air.

EXTERNAL CONTROL APPROACHES The original approach to automotive emissions control was to literally hang a control device on the tailpipe or other source of fugitive emissions. This approach has given way to a combination of options, including engine redesign, engine operations, and fuel composition changes, along with control devices. As more research is performed to accurately gauge emissions from tailpipes and fugitive sources, pollution control devices will both remain and be enhanced in their effectiveness.

FUEL RECAPTURE SYSTEMS Evaporative emission controls are fairly simple and inexpensive, as they consist of an activated carbon adsorption unit with ducting from the sources of evaporative emissions (fuel tank) to the adsorber. Emissions of hydrocarbons during displacement by refueling have been addressed by stage II vapor recovery systems at gasoline-dispensing facilities. These systems include the “rubber boot” and the vapor-return line, which draws gasoline vapors back into the storage tank. Spillage is minimized by an interlock system, which senses a slug of liquid entering the vapor line and stops the flow of fuel into the tank. Activated charcoal canisters to collect fuel transfer emissions, in addition to vapor recovery, are mandated by the Clean Air Act. A “bottom fill pipe” on older models serves to eliminate the splashing and frothing action during filling that increased hydrocarbon emissions. Blowby gases coming from the engine are typically recirculated back into the combustion air intake and serve to return hydrocarbons to the combustion chamber.

CATALYST SYSTEMS Thermal oxidizers were the first attempt to deal with hydrocarbon and CO emissions. These devices were large, insulated chambers with baffles that, to operate, were raised to temperatures between 800˚C and 900˚C. These units were effective provided



199

that an additional air flow of 20–30% of the stoichiometric air flow was provided by an air pump. Exhaust gases that are operated at overall lean conditions showed a much lower efficiency. The key benefit of thermal systems is that they are not “poisoned” by lead, sulfur, or phosphorus contaminants in the exhaust. Catalyst-based systems are currently tasked with the requirement of significantly reducing hydrocarbon, CO, and NOx emissions under varying modes of operation. These come in two types: the oxidizing system and the dual-stage system of catalysts. The first attempt was the oxidative single-stage system, which dealt with hydrocarbons and CO. These single-stage systems were typically high–surface area cartridges containing a noble metal catalyst. Being catalytic, they could operate at lower temperatures than incinerators and still produce significant reductions in both CO and hydrocarbons. The function of the catalyst, using materials such as platinum and palladium, is to lower the activation energy required to oxidize the fuel and CO to CO2. By lowering the activation energy (Figure 4.4, seen earlier), a lower temperature is required; however, the requirement for oxygen still remains. An exhaust gas high in CO or hydrocarbons (such as from a cold start or high acceleration) has poor conversion efficiency, as oxygen or air-injection systems are required. In stoichiometric or lean conditions, the catalyst may work without an air pump for CO and hydrocarbon control. Potential problems with oxidizing catalysts are that they may be sensitive to poisoning by other trace elements in the fuel or exhaust gases and, second, that all fuel elements will be fully oxidized. These may form materials such as sulfur dioxide and sulfuric acid aerosol. Oxides of nitrogen were not addressed in oxidizing or single-bed catalytic converters. Two-stage or dual-bed catalytic systems attempt to get around the problem of oxides of nitrogen emissions by providing a second stage. In these systems, the oxides of nitrogen are eliminated first by operation of a catalyst under fuel-rich conditions such that reducing gases, such as hydrogen, CO, and fuel fragments combine with NO to produce molecular nitrogen (N2), plus some additional CO2. As the exhaust gases pass over to the oxidation bed, additional air is injected to complete the oxidation of CO and hydrocarbon fragments. As a result, the dual-bed systems are larger, heavier, and more expensive than the single-bed systems. Other concerns are for lowered fuel economy, as the engines must be run in a fuel-rich condition. Problems with a dual-bed system include potential poisoning of the catalysts as a result of the presence of other elements. Also, ammonia may be produced in the first stage and will then be more easily oxidized to NOx in the second stage, should the reducing conditions of the first stage be too efficient. Another problem is that catalytic systems only heat up after several minutes of operation. Therefore, the bulk of those emissions tends to be emitted initially without being affected, because the catalyst is not up to temperature. Table 7.5 lists the typical emissions from a three-way catalyst-equipped vehicle. The three ways, of course, refer to the CO, NOx, and hydrocarbon emissions addressed by these systems. The catalysts are still packaged in two-stage operating units.


200


TABLE 7.5 Typical Gasoline Exhaust Emissions Pollutant

Emissions (gm/km)*

Total hydrocarbons Oxides of nitrogen, total NO N2O NO2 Carbon monoxide Toxics, total Benzene 1,3 butadiene Formaldehyde Acetaldehyde

0.14 0.38 0.35 0.031 0.005 1.8 0.0094 0.0069 0.00052 0.0011 0.00077

* Three-way catalyst vehicles.

DIESEL PARTICULATE CONTROLS For diesel fueled systems, major concerns have existed about the carbonaceous soot or particulate emissions commonly associated with such compression ignition systems. Therefore, attempts to provide better emissions control for diesel systems have focused on the diesel particulate trap. Soot particulates may be emitted at rates of 0.1%–0.5% of the total fuel input mass by weight. Because of the low density and small size of carbonaceous soot, regular filters are not appropriate, as they plug quickly. So, two different approaches have been tried for the diesel particulate controls. These include oxidizing ceramic packing filters, which attempt to burn off the carbonaceous soot during operations, or change-out filters, which must be periodically regenerated. Research is continuing on such diesel particulate filter systems. Eventually, all catalyst systems may be heated before the start of the engine, as engines under cold start conditions emit a high level of air contamination. Other possibilities are to mount the catalyst very close to the engine such that radiative cooling will be minimized. Regeneration of the catalysts with hydrogen is on the horizon, and thus catalyst trade out or replacement will become another tool in emissions reduction.

FUEL CHANGE EFFECTS Because combustion in internal engines is kinetically driven, the composition of the fuels will significantly affect the emissions. The major benefit of fuel changes is that all vehicles on the road would be using lower-emission gasolines or diesel fuel; therefore, emissions improvements would begin immediately rather than over a 5–10-year period for replacement by newer, lower-emitting engines.



201

100.0

50.0

Disub. internal olefins Class 6 Cyclopentenes Monosub. internal olefins Unsub. internal olefins

Photooxidation (ppb/min)

10.0

5.0

Class 5

Cyclohexenes Tri- & tetraalkylbenzenes Diolefins Dialkylbenzenes

Class 4

Terminal olefins Class 3

1.0

0.5

C4+ paraffins

Monoalkylbenzenes Class 2

Propane 2,2-dimethylpropane Benzene Ethane Methane

0.1

Class 1

FIGURE 7.13 Hydrocarbon reactivity as indicated by the rate at which NO is oxidized.

In general, fuel changes have been required to lower the volatility and evaporation rate of the fuel and to provide cleaner-burning gasolines that will lower engine deposits. A more recent emphasis has been to lower air toxic emissions (such as benzene) and to lower the percentages of those components of gasoline that are photochemically reactive (those that promote greater ozone production per unit mass). Figure 7.13 indicates the photochemical oxidation potentials for different classes of organic compounds that contribute to such photochemical ozone production. In recent research programs, the effects of changing the compositions of five different fuel parameters (olefins, aromatics, 90% distillation temperature, percentage sulfur and oxygenates) were measured on the exhaust emission species. The exhaust emission species were nonmethane hydrocarbons, carbon monoxide, NOx, benzene, 1-3, butadiene (1,3 Bd), formaldehyde (HCHO), and acetaldehyde (C2H4O). The effects of reducing olefin content from an average of approximately 20% in the test gasoline to 5% resulted in the emissions changes noted in Figure 7.14. In this study, no significant changes were found in CO, formaldehyde, acetaldehyde,


202

Principles of Air Quality Management, Second Edition Olefin and Aromatic HC Reductions 20 10

% Change

0 −10 −20 −30 −40 −50

NMHC

CO

NOx

Benzene

Olefins

1,3Bd

HCHO

C2H4O

Aromatics

FIGURE 7.14 Fuel change effects, olefin and aromatic HC reductions.

or benzene, but the 1,3 butadiene fractions were reduced by approximately onethird. In addition, oxides of nitrogen had a slight reduction of about 6%. The overall total mass of nonmethane hydrocarbons (primarily fuel fragments) increased by approximately 7%. Thus, reducing overall olefin content of gasoline could provide some decreases in ozone potential by virtue of the 1,3 butadiene emission decreases. Reductions of the aromatic content from 45% to 20% led to dramatic decreases in benzene (45% reduction), CO, and nonmethane hydrocarbons (at about 12% each), with no significant increases in NOx. Although effective in reducing the above, however, this fuel change resulted in emission increases of formaldehyde, acetaldehyde, and the ozone-forming 1,3 butadiene. Reducing the “high boiling fractions” (T90 = 90% distillation temperature) in gasoline, as seen in Figure 7.15, produced significant reductions in all carbon species except for CO, which showed no significant change. Oxides of nitrogen showed a nominal increase of about 5%. This change was accomplished by reducing the boiling point of the 90th percentile fractions of gasoline from 360˚F to 280˚F. Probably the most significant emission reductions are a result of lowering the average fuel sulfur content from 450 to 50 ppm, as seen in Figure 7.15. In this experiment, all contaminant emissions were reduced significantly except for 1,3 butadiene, which showed no effect, and formaldehyde, which showed a 45% increase. The purpose of adding oxygenated compounds (ethanol) to gasoline is to force lower CO emissions. The addition of oxygenated fuel components to gasoline also helps to provide better “anti-knock” characteristics to engine performance. Figure 7.16 indicates the change in emissions by using a 15% oxygenated gasoline. No significant changes were found in oxides of nitrogen, benzene, or acetaldehyde. Reductions of CO and nonmethane hydrocarbons were found, as well as reductions in 1,3 butadiene. Formaldehyde emissions, however, increased by approximately 27%.



203

T90 and Sulfur Reductions 50 40 30 20 % Change

10 0 −10 −20 −30 −40

NMHC

CO

NOx

Benzene T90

1,3Bd

HCHO

C2H4O

Sulfur

FIGURE 7.15 Fuel change effects, T90 and sulfur reductions.

15% Oxygenated Compound Addition 30 Oxygenates

% Change

20

10

0

−10 −20 NMHC

CO

NOx

Benzene

1,3Bd

HCHO

C2H4O

FIGURE 7.16 Fuel change effects, 15% oxygenated compound addition.

As a result of recent research, California has mandated the gasoline composition requirements seen in Table 7.6 for 2006. Significant among these are changes in the overall average composition of the fuel. Note that the fuel sulfur content must now average 15 ppm. Should other states opt into the “California approach,” these fuel requirements could become more widely spread.


204


TABLE 7.6 2006 California Gasoline Composition Limits Component

Average

Absolute Limit

22 4.0 0.7 15 295 203

35 10 1.1 30 330 220

Aromatics* Olefins* Benzene* Sulfur, ppm 90% Boiling point, ˚F (T90) 50% Boiling point, ˚F * Percentage by volume.

DIESEL FUELS Composition changes for diesel fuel focus on sulfur content, aromatic hydrocarbon content, and particulate emissions. The latter are addressed by oxidative particulate traps and by lowering the ash or mineral content of diesel fuels. In addition to mandating lower sulfur contents, regulations increasingly are focusing on lowering the aromatic content of diesel fuels. Figure 7.17 indicates the mandated changes for California, which will lower the diesel sulfur content to a maximum of 30 ppm (0.003%) and a maximum aromatic content of 10%. These mandated cleaner diesel regulations force an approximately 99% reduction in total sulfur emissions and approximately a 68% reduction in aromatic hydrocarbon emissions.

35 31 30

Legal limit, %

25 20 15 10

10 5 0

0.003

0.3

Before controls Aromatics

2006 California Sulfur

FIGURE 7.17 Mandated changes to aromatic and sulfur contents in California diesel fuel.



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ALTERNATIVES AND THE FUTURE ALTERNATIVE FUELS Other options to reformulated gasoline and diesel are the oxygenated fuels such as ethanol. The lighter end components of crude oil, such as liquid petroleum gas and compressed or liquefied natural gas, are also contenders for the fuel of the future. Pure methanol fuels were expected to have significantly lower evaporative emissions and running losses. However, one problem associated with methanol was the difficulty in starting the engine. Overall, photochemical modeling studies indicate that although methanol had a lower ozone-forming potential than gasoline, methanol fueled engines had high emissions of formaldehyde. Other problems were that both methanol and formaldehyde are listed hazardous air pollutants and represent increased risks to public health; hence the move to ethanol as the main fuel oxygenate. Pure ethanol raises concerns similar to those for methanol because of its vapor pressure at low temperatures and the formation of acetaldehyde during combustion. Ethanol and acetaldehyde both present concerns for adverse effects on public health because of their toxicological effects. Ethanol is an expensive fuel because it is made from fermentation processes and then distilled into a fuel. Its major contribution is as a blending compound for lowering CO emissions. For liquefied petroleum gas, the nonmethane tailpipe emissions can be relatively high; however, there appears to be a significant reduction in ozone-forming potential for liquefied petroleum gas relative to gasoline. Olefin emissions, however, appear to be somewhat higher than for current gasolines. Compressed natural gas appears to be the best candidate from an emissions standpoint because the combustion kinetics can be more easily optimized (as it is essentially a one-component fuel); however, there are some concerns for safety. Being the required “clean” fuel of choice for many stationary sources, compressed natural gas is unlikely to be a near-term substitute for solid or liquid fuels based on an availability basis. Biodiesel is an alternative to the petroleum-based diesel fuel made from renewable resources such as vegetable oils or animal fats. Peanut oil, the first biodiesel, was the fuel used by Rudolf Diesel in his first diesel engine in 1893. Chemical processing is used to remove acids and convert the oil to the desired esters. After this processing, unlike pure vegetable oil, biodiesel has combustion properties very similar to those of petroleum diesel and can replace it in most current uses. Biodiesel is most often used as an additive to petroleum diesel (in proportions of 5%–30% biodiesel), improving the low lubricity of pure ultralow-sulfur petroleum-based diesel fuel. It does have low sulfur dioxide, particulate matter, and CO emissions, but it produces more NOx because of the fuel nitrogen concentrations. On the supply side, the available amount is far below U.S. requirements, with potential production in the range of 3 billion gallons per year as opposed to the national requirements for transportation fuel and home heating oil of 230 billion gallons. On the economic side, the value of the biological-based oils is far higher in producing other products such as soap rather than being used as a fuel.


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ALTERNATIVE MECHANICAL DESIGN

AND

EFFICIENCY APPROACHES

Another approach to mobile source emissions is to increase fuel efficiency regardless of the combustion system or fuel supply. Increases in fuel efficiency are made possible by design changes to the mechanical system delivering useful work to the drive shaft on the vehicle. Two mechanical design changes coming to the forefront are the variable activated cylinder engine and the continuously variable transmission. The variable activated cylinder engine system uses the advent of high-speed computers and engine sensors to continuously sense the requirements demanded for specific operation (such as speed or horsepower). When the engine achieves the required speed or torque, it automatically shuts off one or more cylinders on a rotating basis, thus saving on fuel consumption (and lowering emissions). Continuously variable transmission systems use the same approach — computerized sensors and continuous interaction with the power train — to drive a belt driven transmission, which replaces the traditional individual gear system. This makes possible lower vehicle weight and optimum efficiency in delivering power to the drive train, thus lowering fuel consumption and air emissions.

ALTERNATIVE POWER SYSTEMS Other means of providing power to the automobile include hydrogen as a fuel, solar power, and fuel cells. Hydrogen is currently made from natural gas and steam via a water gas reaction. Using hydrogen in cars would generate few reactive hydrocarbon emissions. However, as these experimental power plants burn air, the oxides of nitrogen emissions may be significant. Likewise, the production of hydrogen has emissions associated with it at the production facility; therefore, hydrogen fuels may merely shift direct emissions from vehicles to the hydrogen production plant. Thus, hydrogen is not a serious candidate as a transportation fuel for the foreseeable future because it must be made from other fossil fuels at a considerable cost in additional energy. In addition, there are concerns for safety and, on the design side, concerns for the lack of sufficient storage density for onboard vehicle tanks. Fuel cells have the potential to fill a small niche because they produce DC current directly from a low-temperature “combustor.” This current drives an electric motor. However, the power density of fuel cells is limited to approximately 10 watts per pound. Therefore, these systems would only be available for very–low weight transportation. Price is a serious concern as fuel cell–powered vehicles cost about six times as much as a conventionally powered car. A purely electric auto propulsion system appears to be an attractive long-term transportation power system; however, it suffers from two major deficiencies. First of all, the electrical power must be generated at a power plant, which has its own associated air pollutant emissions. Second, the power must be stored in a battery system. Most of today’s research centers around attempts to provide energy storage in a battery system to provide power and range comparable to that seen in ICEs.



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1000 1.0 Gas turbines

Engines Stirling

Available batteries

10

m

id

0.1 Lithiu

ac

Zinc

Le a d–

Ex p ba erim tte e rie nta s l

Fuel cells

Horsepower per pound

Steam

100

Silver

Specific power–watts per pound

Reciprocating internal c ombustion

0.01

Chlorine

Air

Zinc

1 1

10

100

1000

Specific energy–watt hours per pound

FIGURE 7.18 Comparative performance of various power systems.

Figure 7.18 indicates the energy and power ranges of all of the potential power systems for automobiles. In the long run, the limitations on electrical systems center around the search for batteries, sufficient energy storage, and power density to come close to ICEs. Until both power and energy densities for alternative systems are found to approximate that of ICEs, ICEs will remain the propulsion system of choice, using some form of fossil fuel. In the near term, it appears that alternative fuels and better overall vehicle mechanical efficiency may hold the best hope for lowering air pollution emissions from mobile sources.



8

Global Concerns

When you first look into climate change, you realize how little you know. The more you look into it, the more you realize how little anyone knows. Dr. Ralph Cicerone, UC Irvine, March 1992 Mercury from China, dust from Africa, smog from Mexico — all of it drifts freely across U.S. borders and contaminates the air millions of Americans breathe … USA Today, March 14, 2005 In ancient times the Earth had periods when maximum CO2 concentrations were 6,000 ppm (in the Carboniferous period). But life still goes on. There is no proven link between human activity and global warming. Yury Izrael, IPCC vice president, June 2005

The earth and its atmosphere are a dynamic system of which human activities form only a small part. Meteorology and long-range transport of pollutants, geogenic versus biogenic versus anthropogenic emission sources, air pollution control strategies, ocean temperatures, volcanoes and sunspots, as well as their second order effects, make for a system too complex to truly understand. In no other area of air quality management is there greater uncertainty than in some aspects of global issues. Other issues — such as intercontinental pollution transport and stratospheric ozone impacts — are clearer because observation and measurement methods have improved with time and there is a longer record of such measurements. However, proven facts are still few and opinions are many regarding human air pollutant impacts on issues such as climate and acid rain. Popular concerns for intercontinental pollution transport deal with chronic health effects and fairness issues; stratospheric ozone concerns are for potential surface UV light penetration and fears of cancer; climate change concerns include the potential for rising sea levels or impacts on agriculture; acid rain issues include possible effects on vegetation and food supplies. In each case we know some things well, such as temperatures and gas concentrations at various points and times. In other cases, the best we have are various theories and computer models. The concerns are many, and the potential costs are high. This is not unexpected since the impacts of any global air quality management approach will potentially affect virtually every area of society. The implications and fears are many: agriculture, health, economics, business and international relations are at stake.

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It is certain that no one has all the answers, but we will investigate what is known in this section.

THE CHALLENGE It is appropriate to speak of change in measurable parameters and calculations. However, terms such as loss or fluctuation reveal different levels of knowledge, or, more appropriately, theories and presuppositions. When speaking of change, it can be said that there are mathematical differences in measurable parameters versus time. Thus, differences are measured in physical parameters, so conclusions can be based on the scientific method and evidence. Terms such as loss imply an irrevocable or irretrievable diminishment in some quantity that may not be verifiable. Fluctuation denotes a dynamic process over time, which may be a better term to use when dealing with changing data whose true cause is unknown. The challenge is to evaluate changes accurately without becoming advocates. One goal is to be fully cognizant of the accuracy of our measurements. Parameters that can only be modeled, estimated or assumed are based upon presuppositions. An open-minded appraisal of measurable facts is the best approach. At all times, researchers need to be fully cognizant of the uncertainties and potential discrepancies in such models as new evidence becomes available. The reason that one must be careful of the information that models yield is that they are, at best, approximations based on limited data sets. Therefore, small changes in input data, factors, or other “constants” may produce significant changes in modeled output. Of course, direct measurements, such as satellite photographs of the transcontinental transport of air pollution from a source location to a receptor location, are proof of a source/receptor relationship. Pollutant profiling (determining a pollutant’s chemical concentrations and ratios) at such a receptor is another strong proof of the source of the air pollutant.

DATA

AND

RECORDS

With respect to scientific measurements, there is only a very limited period of time during which accurate real-time measurements of the physical world have been taken. For some parameters (pH), the maximum time period over which we have accurate measurements is about 150 years. In other cases, such as the existence of methane, our quantitative knowledge dates back barely 200 years. Therefore, to evaluate potential air quality management strategies for global impact, one must take into account other evidence available for time periods prior to real-time scientific measurements. This allows for model calculations to be put into perspective. It must be remembered, for instance, that the CO2 concentrations measured at Mauna Loa, Hawaii, and used as illustrative of the trends of carbon dioxide in the atmosphere, have only been made since 1958. All other CO2 data purporting to represent long-term concentrations is inferred and subject to interpretation. Also, changes in calibration method alone may introduce dicontinuties in data sets even though an instrument remains the same.


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When concerned with long-term issues in which we do not have consistent mathematical data, written historical records are our initial source of information. For example, historical accounts of climate experienced by various population groups allow us to make general statements relating to climate, such as the “little ice age” that began in 1306 AD and peaked in Europe in the late seventeenth century. Likewise, agricultural patterns may allow us to see the general trend of climate in a location. For example, during the height of the Roman Empire, North Africa was considered the granary of the Empire since wheat was grown throughout that region. This indicates that there once was a much wetter climate in that area than at present time. Recent NASA satellite observations show river channels with complete riverine tributary systems buried beneath the sands of the Sahara desert, verifying greater rainfall in the past. Core sediments from the Dead Sea indicate that rainfall was abundant in the Middle East until about the fifth century AD, whereas today only salt is mined; so modern research is a valuable tool. Indirect evidence, such as tree rings or gas compositions of microbubbles in ice cores, may or may not point to climate changes as well. However, it is important to realize that indirect records are open to interpretation. The degree of accuracy of indirect evidence compared to present levels of instrumentation and real-time data is limited at best; however, these records do allow for qualitative trend analyses over periods of centuries. Our focus must therefore be on what is known to be true from: (1) observable facts, (2) historical records, and (3) indirect evidence. From this information, one may develop models, “what if” scenarios, and alternate views of the same data. With these approaches, different societal management options may be developed. In all events, we must be aware of the uncertainties in any theory beyond that which is verifiable by measurement techniques. And we must be careful not to hold onto theories or models so tightly that it blinds us to the truth of measured data.

INTERCONTINENTAL POLLUTANT TRANSPORT The movement of air contaminants from one location to another has been fairly well known on a local or statewide level, but it has only been in the last five years — with the advent of air quality instrumentation capable of measurements in the low part per billion levels, high speed telemetry, and satellites — that the phenomenon of intercontinental pollutant transport has come to the attention of the scientific community. Popular articles in the United States indicated that in 1998 a plume of smoke drifted north from fires that had been set by farmers in Central America to clear fields. It blanketed cities from Texas to Pennsylvania. The plume was so thick that it caused partial closure of the main airport in St. Louis, Missouri. That same year dust from the Gobi Desert in China headed for North America. It was reported in USA Today that “you could actually see it like yellow ink snaking across the Pacific.” The particulate matter in the cloud was so dense that when it reached the United States, officials in Washington and Oregon issued warnings of unhealthful air quality.


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FIGURE 8.1 A NASA satellite photograph of a dust plume traveling from North Africa to the Caribbean, Central and South America.

Evidence of intercontinental pollutant transport can be seen in a NASA satellite photograph of a dust plume traveling from North Africa to the Caribbean, Central and South America (Figure 8.1). Other photographs are available from NASA on the World Wide Web.

THE DATA Transcontinental movement of air pollution is a serious issue because it threatens the ability of nations to achieve their own air quality objectives. Among those concerns are chronic health impacts and attainment of the national ambient air quality standards. Recent studies have indicated that transcontinental movement of criteria and toxic air contaminants, particularly from developing nations to the United States, is serious and threatens the progress made in attaining our air quality goals. Among the recent reported findings are: •

• • •

Mercury emitted by power plants and factories in China, Korea, and other parts of Asia travels to the United States and settles into the nation’s lakes and streams. EPA estimates that 40% of the mercury in the air in the United States comes from overseas. Aerial- and ground-based sensors have detected the chemical fingerprints of air pollutants floating across the Pacific and Atlantic oceans. Particulate matter and dust from Africa’s Sahara Desert blows west across the Atlantic Ocean, which raises particulate levels above federal health standards in Miami and other Southern cities.


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•

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Ozone and visibility reducing aerosols from factories, power plants, and fires in Asia and Mexico impact pristine spots, such as California’s Sequoia National Park and Texas’s Big Bend National Park. Los Angeles may get as much as 50 parts per billion of the ozone it monitors in the summer from overseas. According to researchers from NOAA, air pollution wafting into the United States accounts for 30% of the nation's overall ozone problem.

By the year 2020, “imported air” pollution will be the primary factor degrading visibility in our national parks. U.S. law requires the restoration of natural visibility in places such as Arizona’s Glen Canyon National Recreation Area. But haze caused by Asian dust storms sometimes obscures the landscape in the parks. The haze could make it difficult, if not impossible, to reach federal visibility goals, and it impacts people’s health due to the ultrafine particle size of the haze.

CONCLUSIONS Intergovernmental cooperation in reducing air pollutants at their source is no longer restricted to local authorities; it is now needed between nations and continents. If national long-term air quality goals are to be achieved, it will take the type of cooperation seen when the problem of stratospheric ozone was addressed, as noted in the following section.

STRATOSPHERIC OZONE Probably the most significant success story in global air quality management is the issue of stratospheric ozone (the ozone hole) and the improvements seen and measured to date. Human health, and the flora and fauna of a remote location — Antarctica — were threatened by increased ultraviolet (UV) radiation. To deal with the threat, reasoned scientific data was applied to a real world problem and a solution was chosen which worked in an amazingly short time period of less than 20 years. This issue represents the highest fusion of scientific research, data analysis, and application of a global management decision to ameliorate a threat to the environment.

RADIATION PRIMER The reason for the concern for stratospheric ozone change lay in the fact that certain simple molecules absorb incoming sunlight, which contributes to decreases in surface radiation. As seen earlier, there are significant differences between the high altitude intensity of incoming solar radiation and the intensity measured at sea level. While it is true that ozone at the earth’s surface is a deleterious material, at high altitudes it has a beneficial effect by blocking certain wavelengths of harmful solar radiation as we saw in Figure 5.1 earlier. In Figure 8.2, we see a comparison of radiation curves over the entire wavelength of incident sunlight, from 0.1 to 100 microns (on a logarithmic scale) and that generated by two surface temperatures: 5800˚ and 245˚K. The curve on the top left is the incident radiation from the sun’s


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Intensity (normalized)

Black body curves

5800°K

245°K

Absorption %

(a) 100 80 60 40 20 0

Ground level

100 80 60 11 km 40 20 0 0.1 0.15 0.2 0.3 0.5

(b)

1

1.5 2 3 5 10 Wavelength (microns)

15 20 30 50

(c) 100

FIGURE 8.2 Radiation emission and absorption curves.

surface (at 5800˚K) as a function of wavelength. The curve on the top right is the emission characteristic of the earth’s surface temperature as a function of wavelength. Incident solar radiation appears in the higher energy (shorter) wavelengths, whereas that of the earth and its re-radiation is concentrated in the longer or infrared regions. The overall effect of altitude on radiation absorption is seen in Figure 8.3. All of the gases from ground level to stratospheric levels contribute to light absorption (dark areas). A comparison of the radiation absorption at higher altitudes (11 kilometers) to that at the surface indicates the significant absorption due to the depth of the atmosphere and its constituent gases. Figure 8.3 illustrates the relative absorptivities of different gases in the top five bands with a summary in the bottom band. All of the gases in these five bands are energy-absorbent gases and each has its own characteristic absorption wavelength. Water is the greatest greenhouse gas of all because of its strong absorption from 0.8 to over 15 microns, which spans the infrared region. Water, while varying dramatically, exists in the atmosphere in the range of 0.1 to 7%. Of significant concern for stratospheric ozone is the third band in Figure 8.3. It shows the very strong absorption characteristics of oxygen and ozone in the ultraviolet regions between approximately 0.2 and 0.3 microns. Ozone is primarily responsible for this absorption. The absorption characteristics of oxygen, while lower


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CH4 N2O Absorption %

100 O2 and O3 100 CO2 100 H2O 100 Total 0 0.1

0.2 0.3 0.4

0.6 0.8 1 1.5 2 3 4 5 6 8 10 Wavelength (microns)

20

30

FIGURE 8.3 Molecule-specific absorption curves.

than ozone, is significant due to its roughly 21% concentration in the atmosphere. (It is interesting to note that the 6% greater density and oxygen partial pressure of the atmosphere at the 1,400 foot [below sea] level of the Dead Sea filters out nearly all of the incident UV radiation such that its beach is a health spa for people with skin diseases.) Stratospheric ozone, therefore, serves as a protective layer for the surface of the earth, since it is known that ultraviolet radiation may have harmful effects not only on human health, such as skin cancer, but potentially on the phytoplankton in the earth’s oceans as well.

STRATOSPHERIC OZONE FORMATION The ozone in the upper atmosphere was assumed to be in a steady state condition. Equations 8.1 through 8.3 indicate the general chemical reactions occurring in the upper atmosphere. (8.1) O2 + hν → 2O* O* + O2 → O3

(8.2)

O3 + hν → O2 + O*

(8.3)

These gases are normally in a natural equilibrium, absorbing ultraviolet radiation to form ozone and then reforming oxygen with absorption of additional ultraviolet radiation. The formation and equilibrium concentrations found in various parts of


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the earth’s atmosphere vary according to latitude, wind velocity, sunspot activity, and temperature.

EARLY OBSERVATIONS The above reactions were not of concern until measured observations indicated a disturbance of the ozone–oxygen equilibrium over the Antarctic in the 1980s. It appeared that certain man-made chemicals had a correlation with decreases of the stratospheric ozone column during October (the Southern Hemisphere’s springtime). The theory was that anthropogenic emissions of chlorine containing compounds, including certain gases, chlorofluorocarbons (CFCs), contributed to the perturbation of the stratospheric ozone equilibrium. Lab studies indicated they had a part in scavenging the ozone radicals, which depressed the overall formation rate. The CFCs and related bromine containing compounds were used as refrigerants, solvents, and fire-extinguishing agents, as well as industrial foam blowing agents.

THE RESPONSE Regulations were implemented which phased out these CFCs in the United States by 1996. Other nations agreed to phase out the use of CFCs by the year 2000. Because the diffusion rate of CFCs into the stratosphere is not instantaneous and there are latitudinal variations in concentration, there was a suggested lag time of 20 to 30 years for the maximum effect of CFCs to the depletion of ozone in the stratosphere.

OTHER SOURCES

AND

VARIATIONS

Natural sources of chlorine such as volcanoes were thought to have a significant impact quite apart from the impact of CFCs in terms of ozone-depletion potential. Scientists estimate that volcanoes annually dump 12 million tons of hydrochloric acid into the atmosphere, but only a portion reaches the stratosphere. The 1976 eruption of Mount St. Augustine in Alaska emitted more than 175,000 tons of chlorine compounds into the stratosphere. Some scientists recall that the 1982 eruption of El Chicon in Mexico thinned the ozone column by 20% as the chlorinecontaining volcanic cloud mixed with the lower portions of the ozone layer. There were historical disputes as to whether the ozone column changes noted in the last 15 to 20 years were truly a result of anthropogenic emissions. For instance, the amount of ozone depends directly on the flux of ultraviolet light from the sun, which varies with the 11-year solar cycle. There are shorter cyclic periods in solar output, which will also change stratospheric ozone concentrations. Increases in sunspot activity, therefore, could be expected to and do indeed contribute to higher ozone levels in the stratosphere. Satellite data show variations between 0.25 and 0.65% in the stratospheric ozone content every 13.5 days. These variations correspond to changes in ultraviolet emission from the sun, thus verifying that there are shorter time periods of solar output variability, which also contribute to ozone variations.


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LAB STUDIES The reactions that were found to occur in the laboratory and appeared to show correlations with ozone depletion in October in the Antarctic are summarized in Equations 8.4 through 8.6: CF2Cl2 + hν → Cl* + CF2Cl*

(8.4)

Cl* + O3 → ClO + O2

(8.5)

ClO + O* → Cl* + O2

(8.6)

These lab studies indicated that CFCs slowly migrate to the upper atmosphere and absorb incident radiation to generate a free radical chlorine atom plus free radical CFC fragments. In the next step, the free radical chlorine attacks ozone molecules to yield chlorine monoxide (ClO) and molecular oxygen. The chlorine monoxide further reacts by scavenging atomic oxygen (free radicals) to yield, once again, the free radical chlorine atom plus oxygen. The overall effect, therefore, is for the chlorine free radical to destroy the ozone as well as oxygen free radicals, which disrupts the normal equilibrium state. This reaction was held to be responsible for diminishment of ozone concentrations in the stratosphere. The reason CFCs were found to be important is that they are virtually nonreactive in the lower atmosphere and slowly diffuse to the stratosphere, where ultimately they are exposed to high altitude ultraviolet radiation. That ultraviolet radiation is sufficient to split the molecule, yielding the free radical chlorine atoms. Laboratory studies indicate that the ozone destruction effectiveness of a chlorine free radical is between 10,000 and 100,000 oxygen free radicals before it is ultimately removed from the process by reactions with hydrogen-containing molecules to yield HCl.

ANTARCTIC STUDIES The effect on stratospheric ozone was originally noticed as a short-term phenomenon in the extreme Southern Hemisphere in early spring rather than a continuous depletion process. Some salient facts on the characteristics of the atmosphere over Antarctica are helpful in the attempt to understand these phenomena. First, the air over Antarctica is isolated from the rest of the global circulation patterns during the winter. The patterns are the result of the lack of air disturbances in the higher southern latitudes due to fewer continental land masses in that hemisphere. This leads to the formation of an isolated polar vortex in which the local atmosphere is cut off from other air currents. Also significant is the 10 to 20˚K colder temperatures over Antarctica than over the Arctic. This condition causes stratospheric ice clouds, which are not seen to the same extent over the northern high latitudes.


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The key appears to be the sudden release of reactive chlorine at the end of the Antarctic winter (September/October). Nitrogen dioxide reacts in the gas phase with chlorine monoxide to yield chlorine mononitrate (ClONO2). This compound can convert other chlorine species into chlorine gas, which readily dissociates into chlorine free radicals. Chlorine mononitrate, when condensed, reacts rapidly with heterogeneous materials on the surface of an ice particle but not in the gas phase. Thus, at the very cold air temperatures above Antarctica, virtually nothing happens during the winter months, except to convert chlorine mononitrate into a solid form on an ice particle surface. With the first appearance of sunlight in the Southern Hemisphere springtime, chlorine free radicals are readily formed to enter into reactions with ozone, causing a drop in ozone concentrations during those early springtime weeks. This sequence, coupled with the breakdown of the polar vortex and heating of the atmosphere in the springtime, causes mixing and dilution of the polar vortex gases with ozone-containing atmospheric parcels from the Southern Hemisphere to reestablish the ozone layer over the Antarctic. It has been observed that the tremendous gradients in concentration of ClO and chlorine mononitrate appear to shift by as much as 5˚ in latitude from one day to the next. This illustrates the importance of the disturbances of the polar vortex in determining the chemical compositions of the Antarctic air. With respect to the Northern Hemisphere, these effects are not seen due to the warmer temperatures, better atmospheric mixing and lack of available ice particles to create the sudden loss of stratospheric ozone.

UV DATA

AND

OTHER IMPACTS

One of the major concerns for potential stratospheric ozone depletion was that UV radiation would increase. During the period when CFC concentrations in the stratosphere were increasing, the ground level UV radiation was monitored. From these monitored data, it has been found that ultraviolet radiation over the United States decreased. Figure 8.4 shows the measurements of decreasing UV radiation of as much as 7%. In fact, it was found that ultraviolet radiation over the United States decreased during the whole monitoring period. This was a clue that there were more parameters involved than just ozone concentrations. The sites in Figure 8.4 illustrate the natural variation in UV radiation to be found at various locations representative of different latitudes and elevations. Tallahassee (FL) and Oakland (CA) are at sea level, Minneapolis (MN) is at 255 meters above sea level, and El Paso (TX) is at 1194 meters. El Paso and Tallahassee are at about the same latitude (approx. 31˚ north). Oakland is at about 38˚ and Minneapolis is at about 45˚ north latitude. General trends can be seen in this monitored data. From Figure 8.4 it appears that the higher the elevation (El Paso versus Tallahassee), even at about the same latitude, the higher the UV radiation. Also, the higher the latitude (all sites), the lower the incident UV radiation. Location, thus, appears to be the most significant factor in UV radiation dose.


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250

UV−RB counts

200

150

100

50 74

76

78

80 Year

82

85

Mpls: 255 m; 45°N

Oakland: 2 m; 38°N

Talla, FL: 2 m; 31°N

El Paso: 1194 m; 31°N

FIGURE 8.4 U.S. ground level UV radiation, 1974 to 1985.

Other natural influences that were proposed as factors in explaining these variations included sunspot activity, atmospheric turbidity, humidity, and cloud cover. In other studies, National Oceanic and Atmospheric Administration scientists indicated that in the mid latitudes of the Northern Hemisphere, rural ultraviolet radiation declined between 5% and 18% during the 20th century. At the same time, the Journal of Physical Research used NASA data to demonstrate that global stratospheric ozone levels have increased in recent years at an average rate of approximately 0.28% per year. Thus, measurements of ozone concentrations in the Antarctic were not giving a clear picture of global ozone trends. Likewise, average effects and measurements for different locations yield significantly different patterns, or patterns with no statistical significance.

ALTERNATIVES With the phase out of CFCs, the challenge has been one of finding substitutes that could be used for refrigeration and air conditioning. Alternative gaseous chemicals, some of which are water-based systems, replaced uses of CFCs and other chlorine containing organics for solvents and foam blowing agents. Substitute refrigerant gases — HFCs (hydrofluorocarbons) — were the chosen candidates since they have a zero ozone-depleting potential. The net result of these U.S. and international actions has been measurable increases in the ozone column over the last four years over the Antarctic — the most heavily impacted area.


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ACID DEPOSITION All rainfall is acidic. Pure water has a neutral pH of 7.0 and is the universal solvent. Consequently it will dissolve all of the gases next to its surface. Thus, raindrops forming from condensation nuclei will have some dissolved nitrogen, dissolved oxygen, and all of the gases noted in Chapter 1, including carbon dioxide. With the exception of ammonia, hydrogen, and the noble gases, atmospheric gases all have an acidic property. That is, when they are dissolved in pure water, they will lower the pH into the acid region (pH less than 7). Pollutant gases, such as sulfur dioxide and chlorine, will also form acids when dissolved in pure water by reaction with water molecules.

WATER PLUS AIR One of the major considerations when discussing the effect of gases dissolved in water is the chemistry of the droplet itself. When there is a dissolution of a gas, such as carbon dioxide, in water we find not only the dissolved gas, carbonic acid (H2CO3), but also an equilibrium between the dissolved gas and its ionized form. One bicarbonate ion and a free proton are generated from CO2. Protons give water its acidic characteristics. The solution pH in this case is 5.6, in the acid range. Equation 8.7 (dissolution), therefore, gives rise to Equation 8.8 (dissociation): H2O + CO2 → H2CO3 H2CO3 → H+ + HCO3-

(pH 5.6)

(8.7) (8.8)

Where other gases (such as ammonia) are present, other reactions are possible in the aqueous phase. If the acid protons are neutralized by an alkali (Equation 8.9), the bicarbonate will react further to yield a second proton and a carbonate ion: HCO-3 + NH4OH → NH4+ + CO=3 + H2O

(8.9)

On the other hand, if more protons are added, the equation shifts back to give more carbonic acid, which will be free to liberate gaseous CO2. The overall effect is a buffering action that acts to keep the pH from changing drastically.

WATER PLUS SOILS Probably the most significant element of the debate on acid deposition is the influence of acidic water once it reaches ground level. (This does not take into account acid fogs, which are a different end product and may have health effects of their own.) Once rainwater reaches soil, the key element in that new matrix is the relative percentage of minerals in that soil. In particular, the relative abundance of calcium, magnesium, and aluminum ions in the soil largely determine the pH of the water contained therein.


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Alkaline earth minerals (calcium and magnesium) act as basic compounds to present another buffering action to any acid elements in deposited rain. Thus, an effect such as Equation 8.10 may be seen: CaCO3 + 2H+ → Ca++ + H2CO3

(8.10)

In this case, the hydrogen ions are neutralized by calcium carbonate (a typical component of many soils and rock formations) to yield the calcium ion plus carbonic acid dissolved in the water. So, the relative abundance of a number of minerals in the soil has a large effect on pH. The effects of mineral content, as well as humus and organic acids from plant decay, will reduce soil water pH to between 4.5 and 5.5. One would expect, therefore, that the more granitic the soil and the fewer dissolved alkali minerals present, the more likely it is that precipitation pH values will be unbuffered and more likely to show acid water levels in the pH 4.5–5.5 range. Greater concentrations of alkaline ions in the soil will, therefore, significantly buffer or neutralize acid components originating in rain.

ACID RAIN STUDIES Concerns exist for receptor areas downwind of major anthropogenic sources of acidic gases, such as sulfur dioxide. A number of studies have been performed in the last few decades reviewing the entire field of anthropogenic acid gas emissions and receptors such as lakes and streams in North America. A statistical analyses of early studies (1964 through 1977) on acid deposition indicated, among other things, that: 1. The annual pH of precipitation showed no long-term significant change over the period. 2. A linear regression of the data indicated no statistically significant trends in H+ deposition. 3. There has been a decrease in SO4= but an increase in NO3- over the same time period. Over 80 sites were studied for the follow-up period (1979-1984) for pH, H+ strength, ion concentrations and precipitation in the northern United States. Table 8.1 summarizes the median concentrations at three of those sites representing a range of receptor locations with differing upwind air pollution source strengths. From this study it appeared that the pH and calcium concentrations are directly related — when the pH is high, the calcium ion strength is high and vice versa. No obvious correlation appeared between pH and either sulfate, nitrate or ammonium ions. A different study (1986) made the following conclusions: (1) The eastern half of the United States experienced ion concentrations of SO4 and NO3 that are greater by a factor of 5 than those levels found in remote parts of the world, and (2) data on the chemistry of precipitation before 1955 should not be used for trend analysis,


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TABLE 8.1 Median Variable Ionic Concentration (mg/L) 1979-84 of Atmospheric Deposition Program (NADP) sites Ion pH SO42– NO3– NH4+ Ca2+

Lamberton, Minnesota

N. Atlantic Lab, Massachusetts

Kane, Pennsylvania

6.00 1.88 1.74 0.81 0.49

4.67 1.54 0.73 0.08 0.13

4.27 3.48 2.08 0.28 0.16

primarily due to the difficulties in establishing a correlation with present methods of measurement and those used previously. Other investigators indicated that a pH of 5.6 may not be a reasonable reference value for unpolluted precipitation pH. Some have questioned the validity of using pH 5.6 as the background reference due to naturally occurring acids. Likewise, the times when the rain was collected varied in pH because of the scavenging efficiencies of rainfall and the times between storms. pH values of rainfall between 4.5 and 5.6 may be due to those natural variabilities alone.

THE NAPAP FINDINGS The ten-year, $500 million National Acid Precipitation Assessment Program (NAPAP) was completed in 1990 and then extended under the Clean Air Act Amendments. NAPAP found some significant but similar trends and effects as seen above. NAPAP employed 700 of the world’s top aquatic, soil, air, and atmospheric scientists in an exhaustive study on the effect of acid rain on receptor areas as a result of anthropogenic emissions. As a part of the NAPAP program, EPA scientists performed an exhaustive study of correlations between acid precipitation and acidity levels in various receptor waters. Table 8.2 summarizes the results of that study for two areas that were suspected of experiencing the highest impact due to high sulfur dioxide emissions. These two sites were the northeastern United States and the southern Blue Ridge province in the Appalachian mountain region. Of the five factors that were investigated for their correlations to surface water acid neutralizing capacity, acid rain had virtually no correlation in either location. The highest correlation factor was found to be with the receptor soil’s chemistry followed by weaker correlations to depth to bedrock (alluvial materials) and geology (strata). Land usage had only a weak correlation in the northeast and no correlation in the southern Blue Ridge area. Acid rain had no correlation in either case. Other evaluations performed during the NAPAP study indicated that Ohio, which had the highest acid gas emissions in the entire United States, had virtually no acidic lakes or streams. On the other hand, Florida, which had one of the lowest levels of


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TABLE 8.2 NAPAP Acid Deposition Correlation Summary: Area Factors Factor Soil chemistry Depth to bedrock Geology Land use Acid rain (SO2)

Northeast U.S.

S. Blue Ridge

Fairly strong Moderate Weak Weak None

Fairly strong Weak Moderate None None

acid deposition, had the highest percentage of acidic lakes in the nation at 20%. These studies indicate that while acid gases such as SO2 have something to do with aquatic acidity, they are the least influential factor studied. As another aspect of the NAPAP study the EPA evaluated pH measurements taken in lakes over the last 140 years (from historical and secondary data). The measurements included a comprehensive core sediment analysis of all acidic lakes (lakes with a pH less than 5.5) in the Adirondack mountains. This evaluation indicated that not only were 90% of the lakes acidic in 1850, but the average acidity today is virtually unchanged from preindustrial times. Table 8.3 indicates the changes of pH over time in the Adirondack mountains and in the Florida acidic lakes. The lakes were grouped into those that had a pH of less than 5.5 and those that had a pH of less than 5.0. The apparent pH change in all cases was lower by 0.35 pH unit or less. However, it should be noted that the standard error of the measurement pH was ±0.30 pH units. Except for the most acidic Florida lakes, there was no statistical change in pH levels measured 140 years ago from those measured today. One of the key factors that did occur over this period of time was a dramatic change in land use patterns and widespread forest clearing. In the mid-19th century, forests covered many of these areas, and the surface water pH values were relatively

TABLE 8.3 NAPAP Historical Assessment: Lake Acidity vs. Time Lake Categories

1850 pH

1986/1988 pH

pH Shift

Actual Shift*

pH less than 5.5 pH over 5.0

Adirondack Acid Lakes 4.95 4.78 4.78 4.63

–0.17 –0.15

None None

pH less than 5.5 pH over 5.0

Florida Acid Lakes 5.11 4.81 5.00 4.65

–0.30 –0.35

None >S.E.

* Standard Error (S.E.) of pH measurement = 0.3 pH units


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low (i.e., approximately 5.0). Over the course of approximately 50 to 60 years, the land was cleared. In each of these cases, the soil chemistry changed due to changes in the naturally occurring acidic conditions in soil structures. Fires raise soil alkalinity by replacing acidic forest floor organic compounds with alkaline ash materials. These alkaline ash materials include the cations calcium, magnesium, and aluminum. Fires release them from the soil matrix so that they more quickly and easily neutralize naturally acidic rain. Other soil analyses show that clear cutting of fir forests raises the pH of the soil from 5.0 to 7.0, and slash-and-burn fires raise it from 4.95 to 7.6. The National Research Council commented in a paper during the NAPAP study period that core sediment analyses suggest that acidic lakes were relatively common in the Adirondack mountains and in New England before the Industrial Revolution. Woods Lake in that region of New England has a current pH of approximately 4.9. That is more acidic than the pH 5.6 found in 1915 but practically unchanged from the 1850s value of pH 5.0. In other words, lakes have been returning to their natural acidic state from a temporarily more alkaline condition during the period from 1900 to 1940 due to land development by clearing and burning.

CONCLUSIONS Is there no effect due to acid gas emissions? There are assuredly two effects, one of which is the addition of gases to the environment, which may have a direct impact on human health (SO2 and NO2) or indirectly by formation of additional sulfate and nitrate particulate in condensation nuclei. These have other indirect effects through particulate matter interactions in the lung. There are also some indications that cloud layers and fogs tend to concentrate acid gas droplets, which have a detrimental effect on human health and forests at high elevations where fog and cloud interactions are more common. The highest correlation between forest damage and acid deposition from fogs or clouds is altitude. The decline of red spruce forests at high altitudes has been found to be correlated with greater percentages of the time when clouds or fogs encircled these regions. As noted in Chapter 2, direct plant impact in lab studies using acid mists have been noted due to leeching of nutrients from tree foliage and the plant crown. Thus, the more concentrated forms of acidic components in fogs or clouds appear to be better correlated to plant damage. Natural wash out of soluble soil ions will occur at higher altitudes by gravity over the course of time. This leads to increasingly poorer nutrient loadings for vegetation at those elevations. The net effect is increasingly sparse soil with ongoing reductions in yearly growth, sap flows, and resin. Deficiency in essential nutrients reduces a plant’s ability to fight disease and to resist insects. The result is an apparent dying environment.

GLOBAL CLIMATE CHANGE One of today’s concerns is the suspected impact of anthropogenic air pollutant gases on global climate. Other concerns are for potential secondary impacts such as rises


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in sea level, flooding of low-lying wetlands, and impacts on agriculture if there is a proven long-term atmospheric temperature rise or greenhouse effect. To address this we must first ask, is there a greenhouse effect that causes a warming of the earth’s surface? The answer is yes, for without a greenhouse effect due to gases in the atmosphere, the average temperature of the earth’s surface would be 0˚F. As a consequence of greenhouse gases, the average temperature of the earth’s surface is approximately 60˚F. Thus, we do experience a global warming impact as a result of greenhouse gases. The next question is, does the scientific data show an effect due to anthropogenic gases? Also, what are the greenhouse gases and what are their sources? Finally, are all of the greenhouse effects “bad”? We will investigate these items in the following sections. Most of the effects attributed to anthropogenic gas emissions are based on computer models attempting to predict temperatures and temperature effects. The difficulty lies in the fact that weather forecasting computers cannot truly project what any given location’s temperatures will be within the next week or month, much less decades in the future. Thus, projections for temperatures in the next century are even less sure, particularly as a result of air pollutant generated global climate change. The controversy lies in attempting to verify trends in small temperature changes (less than 1˚C) while experiencing day to night fluctuations as high as 15˚C. Summer to winter variations may be as high as 30˚C or more. The other problem lies with perception, i.e., if it is snowing in Jerusalem and New York City is having its hottest summer on record, it is hard not to believe that we are facing severe climate changes. As Steven Schneider of the National Center for Atmospheric Research once said, “It’s possible that everything in the last 30 years of temperature records is no more than noise.”

HISTORICAL PERSPECTIVE Direct measurements of the factors influencing our global climate over time are restricted to the immediate past few decades. Precise measurements of air temperatures and surface sea temperatures have been made for only a few hundred years. Accurate measurements of certain atmospheric parameters, such as stratospheric ozone and chlorofluorocarbons concentrations, go back less than 40 years. The first recorded quantitative measurements of methane in the atmosphere were only made in 1948. Consequently, a consideration of historical records is in order since, presumably, whatever climate changes occurred in the past were without the influence of significant anthropogenic air emissions. It is known that prior to about 1800 BC, the entire Middle East experienced a cool, wet climate and forested terrain. By 100 BC, North Africa was functioning as the grain-growing “breadbasket” for the Roman Empire. The implication that this geographic area experienced a much cooler, wetter climate over a time period of 2,000 years is considered valid. Satellite photos that are able to penetrate the surface sands of North Africa verified that this did occur. These surface penetrating photos show widespread riverine courses beneath the sands, which indicate much more extensive runoff and ongoing wetter climates in previous


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millennia. As indicated earlier, core sediments from the Dead Sea indicate that rainfall was abundant in that area until about the fifth century AD. In the tenth to thirteenth centuries AD, Europe experienced the Medieval Warm Epoch or “Little Optimum,” in which for several hundred years, the climate was milder, warmer, and more conducive to civilization in general. Wine grapes were grown in England, which is not possible today. At the beginning of the fourteenth century, however, dramatic climate changes occurred worldwide. The Baltic Sea froze over in the years 1303 and 1306–1307. Beginning in 1310, cold storms and rises in the Caspian Sea levels were noted throughout the century. In 1350, in northwest India, the river Mihran disappeared because of extensive droughts. Monsoons in that era were so weak that droughts led to widespread starvation. In 1372, Chinese records indicate that sunspot activity increased to its maximum over a two-century period. Also in the fourteenth century, the Viking settlement of southern Greenland provided a well-attested fact of the influence of climate change and its historical effects. Having been settled in the tenth century during the “Little Optimum,” the climate in Greenland (hence the name) turned severe with the start of the fourteenth century. The sites of old farms, now buried in ice, indicate the extent of the settlers’ colonial effort, and the graves of the farmer settlers contain thick masses of plant roots, which formerly grew under less severe temperatures than those of today. They are now frozen in soil. The temperature lowering is further verified by records indicating that marauding bands of Eskimos, who lived by hunting seals near the edge of the Greenland ice pack, moved southward attacking and destroying the farming settlements throughout the fourteenth century. The Eskimos’ southerly movements and records of attacks indicate that the ice was spreading southward during that era. This was the beginning of the “Little Ice Age,” which lasted for hundreds of years and was virtually a global event that reached its maximum between the mid-sixteenth and mid-nineteenth centuries. However, from approximately 1850 (at the tail end of the Little Ice Age) and on into the twentieth century, a warming trend has been experienced. Indeed, certain glaciers have been found to be retreating in Europe. But glaciers in central Greenland were found to be growing in the earlier half of the 20th century. Figure 8.5 is an illustration of the known and estimated temperatures in Great Britain for approximately the last 10,000 years compared to the average for the first half of the twentieth century. Approximate departures from the twentieth century average temperature are shown for summer, winter and annual averages. Over all of these historical events have been the geogenic factors, such as large volcanic eruptions, which are proven to dramatically affect climate worldwide for several years. The 1815 eruption of Mount Tambora in Indonesia, which gave rise to the “year without summer” in 1816 in America, is an example. The eruption of Mount Pinatubo in 1991 depressed worldwide temperatures a full degree or more for two years. Recent studies on the late Roman/early Byzantine Empire indicate harsh conditions suddenly showing up early in the first decade of the sixth century. This period corresponds very closely to geologic investigations of Krakatoa, which appears to have “blown off” in a gigantic explosion about the year 506 AD.


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Temperature (°C) Departures from 1900–1950 average

2

1

0

−1 Pre-boreal

Atlantic

Sub-boreal

SubAtlantic

Little optimum

Little ice age

8300– 7000 BC

6000– 3000 BC

3000– 1000 BC

1000– 500 BC

900– 1200 AD

1500– 1850 AD

Summer

Winter

Year

FIGURE 8.5 Estimated England and Wales temperature for selected periods during the last 10,000 years.

CURRENT CONCERNS Concerns are usually expressed for emissions of greenhouse gases, which contribute to absorption of infrared radiation and potential “global” warming. The greenhouse gases are seen in Figure 8.6 by their approximate contributions to atmospheric infrared radiation absorption at current average concentrations.

CO2

CFCs CH4

NOx Others

Water vapor

FIGURE 8.6 Greenhouse gas contributions.


228


350

Billions of tons/year of CO2

300 250 200

331

150 223

216

100 50 28 0 Oceans

Vegetation

Soil microbes

Anthropogenic

FIGURE 8.7 A recent calculation of nongeogenic sources of CO2.

While there is no small controversy with this issue, it must be remembered that the major infrared radiation absorbing gas is water. Therefore, discussions that ignore water vapor do so at the risk of losing a true understanding of the causes of the greenhouse effect. Most popular estimates of greenhouse gases refer only to anthropogenic sources of the nonwater vapor gases. This is a serious flaw, since mankind contributes at most 3% of the nongeogenic CO2 emissions to the atmosphere on a global budget basis. Water vapor, at 0.1 to 7% of the total atmosphere, is the largest single contributor and is not counted in most global climate change scenarios. Most of the interest to date has focused on anthropogenic emission sources and the rise in atmospheric carbon dioxide (CO2) levels. Figure 8.7 shows a recent calculation of nongeogenic sources of CO2. The graph indicates that of the roughly 800 billion tons of CO2 accounted for, only 28 billion can be attributed to human activity worldwide. This does not even consider the geogenic sources of carbon dioxide. (Mount St. Helens alone averaged 1.8 million tons of CO2 per year over the year following the 1980 eruption. Mammoth Mountain, in California, currently emits between 800 and 1200 metric tons per day of CO2 or about 0.5 million tons CO2 per year on an ongoing basis.) Even more interesting is the distribution of anthropogenic CO2 emissions by location. Figure 8.8 shows the percentage of total man-made CO2 by global location calculated for 2000, 2010, and 2020 based on present and estimated global fossil fuel consumption. This indicates that Asian and Pacific Ocean nations are responsible for the majority of global CO2 emissions, ranging from 36% in 2000 to 46% in 2020. The North American (United States and Canada) contribution is calculated to drop from 28% to 22% by 2020. Methane is also a greenhouse gas and its concentration is slowly rising. Global methane budgets, as seen in Table 8.4, indicate that anthropogenic source emissions


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Worldwide CO2 emissions - 2000 AD Central & South America 3% North America 28% Asia & Oceania 36%

Europe 30%

Africa 3%

Worldwide CO2 emissions - 2010 AD Central & South America 5% North America 25% Asia & Oceania 41%

Europe 26%

Africa 3%

Worldwide CO2 emissions - 2020 AD Central & South America 5% North America 22% Asia & Oceania 46% Europe 24% Africa 3%

FIGURE 8.8 Percentage of total man-made CO2 by global location based on present and estimated global fossil fuel consumption.

of methane are approximately 12% of the total, with over half coming from swamps, marshes, lakes, and rice paddies. Thus the anthropogenic contribution is only a small player in the methane scenario. There is also a gradient of methane as a function of latitude on the earth’s surface, as indicated in Figure 8.9, which shows higher


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TABLE 8.4 Global Methane Emissions Source

Tons/Year*

%

146.6 142 72 62 60 25

28.8 28 14 12 12 5

Swamps, lakes, and marshes Rice paddies Animals Anthropogenic Jungles and forests Biomass burning (all) * Millions

Source: Dr. Don Blake, Ph.D. Dissertation, UC Irvine, 1984.

CH4 March–May, 1983

1.70

ppmv

1.60

1.50

1.40

60 N

30

0 Equator

30

60 S

FIGURE 8.9 Global atmospheric methane distribution versus latitude.

concentrations of methane measured in the Northern Hemisphere decreasing to lower concentrations in the Southern Hemisphere. This indicates that methane emissions are associated primarily with land masses in the Northern Hemisphere. Not considered are the enormous quantities of geogenic methane locked in methane hydrates (“methane ices”) on the continental shelves of every major land mass worldwide. Seepage of geogenic methane may be the dark horse of greenhouse gases due to the lack of investigation of its emission rate to the atmosphere.


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Nitrous oxide (N2O) has strong absorption in the infrared radiation band. However, as seen earlier, N2O is the primary NOx species given off “by nature.” Indeed, N2O is ubiquitous in the atmosphere and occurs at concentrations of approximately 330 ppb worldwide. The biggest single problem is that we have essentially no control over the majority of the emissions of carbon dioxide and no control whatsoever over water vapor, nitrous oxide, and methane. Thus, our approaches on a global basis must take these facts into account in any air quality management strategies. Some researchers have indicated that high altitude clouds or jet aircraft condensation trails are responsible for more of the greenhouse effect than even claimed by the IPCC in 2001.

MEASUREMENTS Direct measurements are best for attempting to make projections based upon shortterm fluctuations in emissions. For instance, the eruption of Mount Pinatubo in June 1991 cooled the earth’s average surface temperatures by 1–2˚F, which overwhelmed projections based upon the anthropogenic gases in the atmosphere. Thus, short-term natural phenomena may cause significant variations that cannot be accounted for in climate models. Most of the recent concern for carbon dioxide has been generated by reviewing CO2 concentration data over the last 45 years. Typical of these measurements are those at the Mauna Loa observatory in Hawaii. In Figure 8.10, the atmospheric CO2 levels at this site since 1958 are plotted. There has been an upward concentration slope over that period. Attempts at correlations between gas concentrations and measured average temperatures are more difficult however. The difficulty in justifying human activities as the source of the change arises from the fact that observations of temperatures at the earth’s surface do not track the same rises in CO2 concentrations. In Figure 8.11 are the temperatures over 500 450 400

ppm CO2

350 300 250 200

Mauna Loa observatory

150 100 50 0 1950

1960

1970 1980 1990 Year of measurement

2000

2010

FIGURE 8.10 The atmospheric CO2 levels at the Mauna Loa observatory in Hawaii.


232

Principles of Air Quality Management, Second Edition 0.4 (a) 0.2

C°

0.0 −0.2 −0.4 −0.6 0.4 (b) 0.2

C°

0.0 −0.2 −0.4 −0.6

1870

1890

1910

1930 Year

1950

1970

1990

FIGURE 8.11 Observations of temperature variation from the mean in the (a) Northern and (b) Southern Hemispheres.

130 years in the Northern and Southern Hemispheres, which indicate that the majority of the temperature increase (approximately 0.6˚C to 0.7˚C) occurred prior to 1940. This indicates little correlation of temperature increase in the Northern Hemisphere with the rises in CO2 noted in Hawaii. Closer inspection of the temperatures indicates greater variability from year to year than in average trends. Both hemispheres have noted increases over this period. Other problems, of course, are that even with the best temperature records, the numbers are “fuzzy” by plus or minus several tenths of a degree. On a regional basis, Figure 8.12 shows the observed temperatures for approximately the last 100 years in the continental United States. There has been virtually no change in average temperatures for the past century when corrected for the urban heat island effect, as noted earlier. When one is looking at a shorter time frame, the uncertainty becomes greater. By taking smaller increments of time, greater fluctuations are seen and pattern recognition becomes even more difficult. While the Northern Hemisphere had a slight temperature increase over the last 50 years (which corresponds to the greatest


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55.0

12.7

Temperature (°F)

12.1 11.8

53.0

11.5 11.2

52.0

10.9 10.6

51.0 50.0 1895

Temperature (°C)

12.4

54.0

10.3 10.0 1905

1915

1925

1935 1945 Year

1955

1965

1975

1985

FIGURE 8.12 Annual average temperature for the contiguous United States from 1895 to 1990.

increases of anthropogenic gas emissions, such as CO2), the United States experienced a slight cooling trend. Of course, the year-to-year variability is much greater than the calculated variation of temperatures over a mean value. Other trends in maximum daily and minimum nighttime temperatures in the contiguous United States over the last 100 years indicate that the maximum daily temperatures increased up until about 1935 and since then have been decreasing. At the same time, the minimum temperature has been rising. Thus, if a short period trend analysis conclusion was drawn, it would be that both the daytime high temperatures and nighttime low temperatures were approaching an equilibrium value and the overall climate was becoming more moderate. Apart from temperatures, a look at the changes in sea level on a global basis yields a different pattern. If global warming is truly occurring, a clear pattern of rising sea levels would be expected at all locations worldwide. Figure 8.13 is an illustration of changes in worldwide sea levels between 1960 and 1979 around the world. What has been observed is that the sea level is rising in some locations and falling in others. Indeed, at some locations in close proximity, such as southern West Africa, both sea level rises and falls have been observed. It is therefore impossible to say that any overall sea level rises have in truth occurred. Changes in sunspot activity have been alluded to with respect to potential climate change on a historical basis. The sun’s brightness, a measure of its radiation intensity, affects global temperatures. Likewise, changes in the magnetic field flux of the sun could impact the earth’s atmosphere and therefore the global heat balance. Indeed, these may be the events resulting in natural climatic variability. As noted earlier, the measured changes in air temperature do not match the emission rates of man-made greenhouse gases. However, it appears that the pattern of temperature change does match (correlation coefficient of 0.95) the pattern of changes in the sun’s solar activity for over the last 125 years. Figure 8.14 is a comparison of solar activity and average global temperatures from 1860 to 1985. When solar activity increased in the first half of the twentieth century, global


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0

0

−3

+3

−3

−3 +3 0

−3

+3

0 +3

+3

0 0 0

0

+3 0

0

0 +3

0 0

Rising

Falling

0−3 mm/yr

0−3 mm/yr

>3 mm/yr

>3 mm/yr

FIGURE 8.13 Average annual rates of change in worldwide sea level between 1960 and 1979 (as determined from data supplied by the Permanent Service for Mean Sea Level, Bidston Observatory, UK).

0.3

Cycle length (years)

0.1 0.0 −0.1 11.0 −0.2 Solar activity Temperature 12.0 1880

1900

1920

1940

1960

1980

−0.3

Temperature anomaly (°C)

0.2

10.0

−0.4 −0.5 2000

Year

FIGURE 8.14 Comparison between global temperatures and solar activity, measured by the length of the solar cycle.


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temperatures also increased. Likewise, temperatures declined when solar activity declined. Solar activity is measured by cycle length.

OTHER CONSIDERATIONS A retrospective analysis of historical records and other evidence indicate that significant climate changes are caused by changes in the sun’s brightness over longterm time scales (centuries). An analysis of climate records for England (alluded to earlier) indicates that during the last 1,000 years, protracted periods of cold weather occurred roughly every 200 years. As noted, this included the Little Ice Age, when the average temperatures in Europe were roughly 1˚C lower than they are today. The 1690s were the coldest on record in the history of Europe. There have been correlations of solar activity with carbon-14 content of tree rings. The rings yield an integrated long-term record of apparent temperature changes corresponding to carbon-14 content. (They may also correlate with rainfall.) Comparing carbon-14 records to climate history, one group of researchers found that six of the last seven most severe decreases in solar activity (as measured by carbon-14 content tree rings) corresponded closely to cold spells in the climate record. One of these was the period of about 50 years of very low solar activity in the 17th century which corresponded with the coldest period of the Little Ice Age. Sunspot records confirm that a minimum of solar activity occurred in the nineteenth century followed by a rise in the twentieth century, as noted earlier, to the current levels. If past cyclic trends continue, we can expect that the rising solar activity of the twentieth century will be followed by a decline of solar sunspot activity in the twenty-first century. This decline would not lead to a temperature rise, but to a temperature cooling as a result of natural forces.

FEEDBACKS Feedbacks are those natural phenomena that act to oppose wild swings in temperature in the atmosphere. One feedback element that moderates global temperature changes is the water content of the atmosphere. Any phenomenon that increases air temperatures will increase moisture due to greater driving forces for evaporation over the ocean. When this occurs, warm moist air will rise until it meets cooler temperatures at higher altitudes, which will give rise to clouds. Clouds, due to their high reflectivities, act in the opposite direction to a global warming scenario. Any increases in cloud cover above normal would increase the reflectivity of the earth. This would cause cooler temperatures in the lower regions of the atmosphere, thus acting as a natural “brake” to anticipated global warming scenarios. Other researchers have found unambiguous evidence that the presence of clouds reduces the earth’s mean surface air temperature. In fact, they found that the size of the observed net cloud forcing (climate change) is about four times as large as the expected value of radiative forcing from a doubling of CO2 concentrations. Increasing clouds act in the opposite direction to increasing CO2. Thus an increase in planetary cloud cover would offset much of the effect from doubling or even tripling the earth’s CO2 concentration.


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MODELS Extensive attempts have been made to mathematically model all of the physical, meteorological, and other impacts that may lead to overall global climate change. These models are called general circulation models (GCMs) and are designed to simulate temperature impacts due to the physics of the atmosphere. The difficulty with global climate models is that they can only grossly approximate conditions known to be occurring, and they only handle large (continental size) land masses. Unfortunately, the biosphere is so vast and complex that even advanced computers can only deal with approximations. Due to these limitations, the GCMs have serious defects, notably that they fail to predict the present based on historical input data. That is, when GCMs are run in reverse, they are not able to duplicate what is known to have occurred. For instance, researchers have set global models to the conditions of 1880 and found that the models indicate a rise in global temperatures by as much as 5 degrees Celsius. However, the actual increases in the last century are, at best, only 1 degree Celsius. Thus, climate modelers are forced to retune or adjust their models to calculate projected warming trends. At best, these models may come only within 2 degrees Celsius of what has actually occurred. Figure 8.15 indicates the results of one such model that was set to start in 1880 and ran through the mid 1980s. The problem is that the true temperatures did not match the observed temperatures except at the initial and final points (which were set when the model was begun).

Calculated greenhouse effect Observations

Temperature change (°C)

0.8

0.6

0.4

0.5°C

0.2

0 1880

1900

1920

1940 Year

1960

1980

FIGURE 8.15 Calculated warming due to the increase in greenhouse gases (dashed line) compared with observed temperatures (solid line) over 100 years.


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Predicted sea level rise (feet)

30 25 20 15 10 5 0 1979

1981

1983

1985 Year

1987

1989

1991

FIGURE 8.16 Predictions of the rise in seal level resulting from the greenhouse effect plotted against the year in which the prediction was made. The predictions decreased from 25 feet in 1980 to 3 feet in 1985 to 1 foot in 1989. Today predicted rises are given in centimeters.

As noted earlier, the major problem is in dealing with water in the atmosphere. Early models assumed that water behaved the same as either vapor or ice crystals. When a British meteorological office adjusted its global climate models to take into account actual experiments (which indicated large differences between the two states of water), the predicted greenhouse warming fell from about 10 degrees to approximately 3 degrees. Other difficulties, which at the present time are not factored into most models, are the impacts of contaminants, such as sulfur dioxide and fine particulate matter. Sulfur dioxide forms particulate sulfate and sulfuric acid aerosols; both have been found to act as additional radiation reflectors. Sulfates and aerosols will lower overall temperatures if found in the atmosphere. Thus, one control approach, i.e., reducing sulfur dioxide, may contribute to global warming (if it is occurring) by removing the additional reflectivity. With respect to sea level changes, the predicted rises have gotten smaller over the years. In Figure 8.16 are the results of models calculating greenhouse effects and the predictions for sea level rise. Original attempts modeled sea level rises at approximately 25 feet, whereas today these predicted sea level rises range from a few inches to less than 3 feet. These rises are less than the normal, natural, daily variation in tides.

RECENT FINDINGS A consortium of researchers from around the world formed the Model Evaluation Consortium for Climate Assessment (MECCA). This group has attempted to evaluate modeling results for a variety of greenhouse gas concerns through the present and


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balance them with the levels of uncertainties mentioned here. Some of MECCA’s model findings to date are: 1. As CO2 increases, the rate of global warming decreases. Increases in CO2 in the atmosphere produce a less than linear increase in mean temperatures in the mid latitudes. This “leveling off” effect on temperatures appears to be more related to saturation of the model’s water vapor absorption than of the CO2 absorption window. This indicates the key importance of water in global climate change. 2. Thirty years of observation do not detect a warming trend in the north polar regions, which is where current GCMs indicate that temperatures should have risen even more. 3. The manner in which each of the other greenhouse gases control the global radiation balance is different from CO2. This alone will change assessments of global warming potentials. 4. Modeling on regional scales is critical for creating realistic understandings of the greenhouse gas issue. To provide this level of detail, a tenfold increase in currently used computing capacity would be required. The United Nations sponsored the Intergovernmental Panel on Climate Change (IPCC) to study global warming. The report, “Climate Change 2001,” stated, “The fact that the global mean temperature has increased since the late 19th century and that other trends have been observed does not necessarily mean that an anthropogenic effect on the climate has been identified. Climate has always varied on all time scales, so the observed change may be natural” (p. 97).

ALTERNATIVE VIEWS Adapting to higher CO2 levels and its effects may be the most socially effective management approach to some of the climate change effects dreaded by some people. Among these adaptive approaches may be living with the effects of CO2 on sea level and agriculture. World leaders have stated that relocating a few population groups in the path of less than a 3-foot rise in sea level may be a better approach than attempting to eliminate all anthropogenic air emissions. A number of researchers have indicated that increasing levels of CO2 and moisture content would have positive benefits, even if accompanied by slight temperature rises, particularly with respect to agriculture. For instance, a doubling of the carbon dioxide concentration in the atmosphere would increase plant productivity by almost one-third. In higher CO2 concentrations, most plants grow faster and bigger with increases in leaf size, thickness, branching, and seed production. The number and size of fruit and flowers would also rise. In addition, root to top ratios would increase, giving many plants better root systems for access to water and nutrients. The positive effects from higher CO2 are due to: (1) a superior efficiency of photosynthesis; and (2) a sharp reduction in water loss per unit leaf area. A related benefit comes from the partial closing of pores and leaves associated with higher


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CO2 levels. Closing of the pores is a major source of moisture retention. Thus by closing them, higher CO2 levels will greatly reduce plants’ water loss, which may be a significant benefit in more arid climates. A major benefit of closing stomata cells due to higher CO2 concentrations would be less damage due to air pollutants.

INCREASED YIELDS Increased yields have been proven in greenhouse studies, including tomatoes, cucumbers, and lettuce. The studies showed earlier maturity and larger fruit size, greater numbers of fruit, a reduction in cropping time, and yield increases averaging 20 to 50%. Cereal grains showed yield increases from 25 to 64% with corn, sorghum, and millet. Sugar cane showed increases from 10 to 55% (resulting primarily from superior efficiency of water usage). Figure 8.17 shows the rise in photosynthesis activity for a rise in carbon dioxide concentrations from 340 to 640 ppm, thus illustrating the effect noted earlier. A rise in temperature would also increase net photosynthesis as seen in Figure 8.18 for three other crops. Trees, which cover approximately one-third of the earth’s land area, account for two-thirds of global photosynthesis. They likewise respond favorably to higher 640

Water lily 25

Individual net photosynthesis (µmol CO2 m−2s−1)

20 340 15

10

5 0 20

640

Water fern

µ mol CO2 mol−1air

15 340

10 5 0

0

5

10

15 °C

20

25

FIGURE 8.17 Photosynthesis increases with CO2 and temperature.

30


240


l pe Bel

Relative CO2 assimilation rate

1.4

pp

er

1.3 wo on t t o

od

C

1.2

to ma To

1.1

1.0

0.9

6

10

14

18

22

26

30

34

Leaf temperature (°C)

FIGURE 8.18 Relative CO2 assimilation rate (net photosynthesis) as a function of leaf temperature.

concentrations of CO2. Fruit tree production is verifiably enhanced. When concentrations of CO2 are increased by a factor of 2, orange trees yield 2.8 times more biomass in 5 years and 10 times more oranges in their first 2 years of production.

OTHER AGRICULTURAL EFFECTS Rising CO2 levels also compensate for lower light intensities in high latitudes. Flowers and vegetables grown in CO2-enriched greenhouses experience higher percentage boosts in plant productivity under very low light intensities than when under normal light conditions. Enrichment of the air by CO2 also appears to offer some protection to plants against both extremely hot and cold temperatures. There is also evidence that increased CO2 levels would raise the optimal temperature for plant growth. If significant global warming occurs, and if the higher CO2 world of the future leads to higher temperatures, plants could be expected to respond favorably to increases in both CO2 and temperature. Increases in CO2 and in water retention would provide stress relief to plants and less ethylene gas (and photochemical ozone) production. Fewer diseases due to stomata closure could be expected. Secondary effects of higher CO2 are that as crop yields rise with CO2, the amount of land devoted to agriculture could decline. This would allow for fewer fertilizers and pesticides to be used for crop production. Plants, such as trees, which use a C3 metabolism (so called because the first photosynthesis step produces three carbon atoms per molecule) benefit more in high CO2 atmospheres than C4 metabolism plants; hence a more rapid reforestation and an expansion in forest biomass could be expected. Of the 21 most important food crops, 17 have C3 metabolic pathways.


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These crops include rice, wheat, barley, oats, soybeans, potatoes, sweet potatoes, casabas, sugar beets, and coconuts. On the other hand, 14 of the 18 most noxious weeds are C4 metabolic pathway plants that are not as favored in a high CO2 atmosphere. Thus, rising levels of atmospheric CO2 would generally favor crop production over weeds. A boost in plant production due to major increases in CO2 would provide more food for birds, fish, and mammal populations as well. Also listed as benefits would be soil stabilization, lowered soil erosion, and greater subsoil productivity. These factors would provide more organic matter to the soil matrix, which would provide for soil enrichment, increases in the microbial population, increases in earthworms, and increases in salt tolerance. Decreases in insect foraging would occur due to lower nitrogen to carbon ratios and greater biomass. This would decrease the soil nutritive value somewhat and result in fewer insects. Insects would also decrease generally due to increased mortality and longer larval development times as observed when such insects had been fed CO2-enriched foliage. Lab tests at 650 ppm CO2 found reduced populations of leafhoppers, predaceous flies, and pink bollworms on crops grown under those conditions. The potential positive effects of a CO2 increase should perhaps be considered before attempts to substantially decrease those concentrations as an air quality management strategy.



9

Air Quality Laws and Regulations

Whereas the Columns and Clowds of Smoake, which are belched forth from the sooty Throates of those Works, are so thick and plentiful. … I propose therefore, that by an Act of this present Parliament, this infernal Nuisance be reformed; enjoyning, that all those Works be removed five or six miles distant from London below the River of Thames. Fumifugium, Part II (1661)

Historically, a general law approach to air quality concerns has been taken. Outright prohibitions against certain activities generating air contaminants have been adopted for centuries, beginning as early as the 13th century (see Chapter 1). These prohibitions were for those actions that harmed, or that potentially harmed, the health or safety of the citizenry. At present, many international efforts are being attempted to control criteria emissions, as well as hazardous air pollutants, utilizing treaties among nations.

GENERAL LAW APPROACHES The legal framework for air quality management in the United States consists of dual federal and state statutes; case law, including common law; and regulations. These laws and regulations are at the heart of our air quality management strategies, even as health and environmental effects are the justification for those laws and regulations.

PUBLIC NUISANCE One approach has been to allow for lawsuits as a result of public nuisance complaints. In general, public nuisance complaints, originally based on the principle of “discomfort to the sovereign,” have been among the oldest legal approaches used to abate air pollution emissions. Today, these complaints are still used when odors or emissions occur that may affect more than one person. Nuisance is defined in the common law as anything injurious, indecent, or offensive to the senses and that obstructs or otherwise interferes with the free use or enjoyment of life or property. The legal concept of a public nuisance, as developed in the common law, refers to a nuisance that affects the entire community, or any considerable number of persons, at the same time, even though the extent of the annoyance or damage

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inflicted may not be equal. Because a public nuisance is one that affects the community at large, the attorney general of the state or other authorized government legal representative must bring the action on behalf of the community. In certain states, a private individual who has been specially injured by a public nuisance may bring an action for recovery of damages or for the abatement of the nuisance. Therefore, these provisions have been used in some jurisdictions as a legal approach to combating excess cancer risks from noncriteria pollutants, with actions brought by both private individuals and government entities.

PRIVATE NUISANCE The private nuisance complaint, brought by a private individual who has been specially injured, stands in contrast to the public nuisance complaint. A private nuisance lawsuit is brought against the person causing it by a property owner and covers anything that is indecent or offensive that interferes with the free usage of property. There is no requirement of particular or special injury, as in public nuisance complaints, but merely a showing that the defendant’s actions are causing the interference with the free enjoyment of the owner’s property. Thus, a real property owner may bring an action for nuisance against the owners of a neighboring industrial facility, factory, or any other business that emits fumes or smoke. The fumes, smoke, or particulate matter that waft onto the plaintiff’s property interferes with their use and enjoyment of the property. In public and private nuisance complaints, the available remedies for these types of airborne nuisances would typically include injunctive relief.

RECENT APPROACHES Other approaches that are used to lower air emissions, and thus enhance the general air quality, include taxation, land-use controls, source-specific emission standards, and standards based on health risk. Taxes do not abate or reduce emissions in and of themselves. Instead, they form an indirect (economic) approach in which, if the tax is too high, source owners will voluntarily reduce emissions to avoid paying them. The control of land use, or zoning, is typically administered at the local county or municipal level and attempts to separate sources of air contaminants from receptors (people) by a distance sufficient for natural air dispersion and dilution to lower contaminant concentrations to levels that will not generate a public nuisance. This was the solution advocated in Fumifugium in 1661. Fumifugium also suggests controlling growth, and thereby limiting emissions creation. The backbone of current air quality management strategies has been the socalled command and control approach. In this approach, specific mass emission rate limitations are placed on sources. Receptors experience lowered concentrations of contaminants and, therefore, better air quality. Indirect source controls attempt to change societal patterns or personal behavior (driving gasoline automobiles with only one occupant) that indirectly contribute to air emissions. This change is generally accomplished by requiring employers to institute



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incentives for employees to use alternate transportation, to use ride-sharing, to shift work hours, to telecommute, or to stagger work days. These incentives are assumed to work by limiting the vehicle miles traveled in an area and thus to reduce mobile source emissions. The most recent approach to individual source controls has been to evaluate health risks and to set, by regulation, acceptable levels of health risk for the receptors. Area or point sources are required to implement whatever controls or limitations on emissions are necessary to avoid exceeding established excess health risks. These health risk–based approaches are primarily directed toward the noncriteria hazardous air pollutants.

THE PROCESS

OF

REGULATION

Within the U.S. federal system of laws and regulations, with respect to air quality, there are specific procedures that must be followed. The initial step, of course, is the establishment of the laws governing air quality. In this system, elected officials adopt legislation, and, on signature by the chief executive, the law takes effect. The laws set direction and goals and identify those branches of government responsible for implementation. The agencies involved are mandated to formulate specific regulations that implement the goals, outlines, and intent of the law. The process of implementing regulations is one in which the public has an opportunity to review, comment on, and influence such regulations. In general, regulations identify the specific mandates of law and the particular problems and sources of those problems, such as air pollution. The problem could be nonattainment of a health-based air quality standard.

ROLE

OF THE

PUBLIC

IN

RULE MAKING

Draft regulations proposed by U.S. government agencies are published in the Federal Register. This is the federal government’s daily newspaper of all actions and activities of a regulatory nature, along with relevant background information, sources, and so on. Draft regulations set time frames and dates for public hearings and provide written comment on such regulations. Within the federal government, this is a process in which the proposed regulations undergo public review in three stages. These are the prerule, proposed rule, and final rule stages. At each stage, the proposed regulation outlines its significance and legal authority, mandated deadlines, abstracts of the regulations, entities affected, and responsible agency. At each stage, the public is invited to comment on the draft or redrafted regulations. Once a final rule has been published, a deadline for a final public hearing is set, at which time the last public comments are received. Following the close of public comment, the agency promulgates the new regulation in the Federal Register. At that point, the regulation is final and takes effect. The most recent emerging concept in rule making is that of the stakeholder. In this vision, all potentially affected members of society are invited to participate at the earliest possible time in any proposed regulation. This concept is further advanced


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through the stated goals of the U.S. Environmental Protection Agency (EPA) regarding the implementation of environmental justice in its decision-making process.

ENVIRONMENTAL JUSTICE According to the EPA, the emerging concept of environmental justice refers to the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies. The EPA states that it has this goal for all communities and persons across the United States. The goal will be achieved, according to the EPA, when everyone enjoys the same degree of protection from environmental and health hazards and equal access to the decisionmaking process needed to have a healthy environment.

LEVELS

OF

AUTHORITY

Historically, the levels at which air quality regulatory authority existed has varied. In some municipalities, attempts at air pollution control under local health departments were in effect before World War II. The immediate post–World War II era saw a rapid increase in the number of regional and statewide air pollution authorities, with varying degrees of responsibility. With the establishment of the EPA in 1970 and the passage of the first comprehensive federal Clean Air Act, and its successive amendments, the focus of air quality control authorities has been increasingly federalized. The EPA has nationwide authority in all areas of air quality management. In addition to setting air quality standards and maximum levels of emissions, the federal government has been extensively involved in monitoring, research, and funding local programs. Historically, states have possessed the widest possible latitude in regulating their own environment. However, constitutional interpretation requires states to defer to the federal government when Congress makes a clear decision to preempt state laws and set up a nationwide regulatory system. Therefore, under federal environmental laws, states have been given specific authority to implement their own air quality management programs. Enabling legislation at the state level is required to set up a statewide program. To enforce federal laws, state legislation must be adopted and approved by the EPA to give federal enforcement authority to the state. Otherwise, the federal government is the enforcing authority.

FEDERAL PREEMPTION With respect to specific provisions, states must be at least as stringent, or in cases of a waiver may be more stringent, in their regulations than the equivalent federal regulations and laws. Because Congress has specifically provided for a nationwide scheme of regulating air quality, the federal preemption doctrine of the U.S. Constitution mandates that any inconsistent state laws or regulations must be struck down. However, states may also adopt their own ambient air quality standards and provide for their own implementation plans. They possess independent legal authority



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to manage air quality within their jurisdiction. For example, California has its own Clean Air Act in the state’s Health and Safety Code. In certain jurisdictions, there is no permitting authority at the state level. This may be delegated to local authorities. In addition to the State Implementation Plan (SIP), local authorities in areas not in attainment of air quality standards are required to establish air quality management plans, which detail those activities and regulations that will demonstrate reasonable further progress toward attaining the ambient air quality goals. Reasonable further progress regulations are a part of the state implementation plan and are legally enforceable as a part of the SIP at the federal level once they have been approved by the EPA. In some areas, the regional or local air pollution control or management authorities were the first government agencies regulating air pollution in their areas. As a consequence, many of these departments have a long history of air monitoring, regulations, emission standards, local enforcement, and permitting. In general, the regional or local air pollution authorities carry the burden of day-to-day activities with respect to implementation of air quality legislative mandates and regulatory requirements of both federal and state agencies. Municipalities may also implement their own ordinances governing emissions of air contaminants within their jurisdiction, provided they are not preempted by or in conflict with other levels of government. For example, before the 1990 Clean Air Act Amendments, some cities adopted local ordinances that banned emissions, or even the use, of chlorofluorocarbons (CFCs). Frequently, the local governments that have demonstrated the most environmental involvement are located in air pollution– affected areas. However, the fact remains that every level of government may be involved in air quality management to a greater or lesser degree.

FEDERAL LAWS AFFECTING AIR QUALITY MANAGEMENT There are a number of laws that affect our approaches to air quality management. They include those that are media specific (water, solid waste) or that have an air quality component (toxic substances, nuclear materials). The former deal with some other aspects of environmental contamination that may have an effect on some aspect of air quality. The Clean Air Act and its predecessors are the most direct federal laws affecting air quality management.

PRE-1990 AIR QUALITY ACTS

AND

EFFECTS

Before the formation of the EPA in 1970, a number of federal laws dealt with air quality. These laws primarily dealt with the criteria pollutants but did make attempts to address noncriteria air contaminant issues. A number of these major concepts were modified and incorporated into the most recent amendments to the Clean Air Act. The primary national ambient air quality standards (NAAQS) for the six criteria pollutants are the driving force for federal regulatory action because of their known health effects. The NAAQSs are periodically reviewed and subject to change as more information becomes available.


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Implementation Plans The concept of a SIP with federal oversight is the basic approach to air quality management. SIPs are ongoing documents that provide a regulatory framework for each state to demonstrate to the federal government that they are on a path to attaining and maintaining the national ambient air quality standards. Plans for the states that are not in attainment with those standards form a significant portion of each SIP. Federal law does provide for the preparation of a federal implementation plan by the EPA if state implementation plans are not approved or are deficient. Clean Air Act §176(c)(1) requires that federal actions conform to applicable state implementation plans for achieving and maintaining the NAAQS for the criteria air pollutants. To ensure conformity among the states, the EPA maintains the requirement that all federal actions not have the effect of contributing to new violations of air quality standards, increase the frequency or severity of existing violations, or delay timely attainment of standards in the area of concern. Monitoring and Limiting Emissions Monitoring ambient air quality and limiting emissions of criteria pollutants within each air quality region are key requirements under all federal air quality legislation passed since 1970. In general, these requirements are delegated to the respective states, as local agencies have a better understanding of the sources of contaminants and are responsible for providing monitoring, inspection, and enforcement of air pollution laws. The federal government has in effect new source performance standards (NSPS) for new sources of criteria pollutants in specified industries. These new sources are required to meet national emission standards. The focus of the NSPS requirements is criteria pollutant emissions from the largest stationary source categories in the country. These include fossil fuel–fired electric utility generating plants, Portland cement plants, nitric and sulfuric acid plants, petroleum refineries, asphalt concrete plants, secondary metal smelters, iron and steel plants, fertilizer plants, and so on. One of the dominant areas of federal authority in terms of performance standards is the setting of “tailpipe” emission standards for motor vehicle emissions, as well as overseeing fuels and additives for those sources. This is in recognition of the fact that mobile sources emit the criteria pollutants NOx, carbon monoxide, and ozone precursor hydrocarbons. Prevention of Significant Deterioration Federal regulations also require that the air quality does not deteriorate further in those areas in which the air is already cleaner than the NAAQS. Under the prevention of significant deterioration (PSD) regulations, all the nation’s air quality control regions with a NAAQS were divided into three classes of ambient air quality. Class I areas receive the highest degree of protection, with only a small amount of certain kinds of additional air pollution allowed. In class I areas — primarily national parks and wilderness areas — few effects are allowed, and some types of nearby industrial development are severely restricted.



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Mandatory federal class I sites are areas that may not be reclassified to class II or class III. These include international parks (such as Waterton Glacier International Peace Park and Roosevelt-Campobello International Park), national wilderness areas, and national memorial parks larger than 5,000 acres or national parks larger than 6,000 acres that were in existence (or authorized) on August 7, 1977. The 1990 amendments to the Clean Air Act specified that acreage added to these areas after 1977 must also receive class I designation. Therefore, in class I areas, only very small incremental increases of air contaminant concentrations are permitted. Class II areas are those in which the air pollution is in excess of national standards and in which different levels of incremental addition to existing air contaminant levels are allowed. In class II areas, limited amounts of new emissions are allowed, and in class III areas, greater amounts of new emissions are permitted. No class III areas have been designated to date. The PSD program initiated the concept of new source review. This concept is one in which limited degrees of incremental additional air pollutants are allowed in the air quality regions. Stationary sources are the focus. For a major source to be built, the new source in a PSD-regulated area was not allowed to increase the existing total emissions in that area. Thus, the concept of offsetting emissions was established. In this approach, other emissions are required to be reduced at a ratio equal to or greater than the anticipated new emissions before the construction of the new source of air contaminants. The allowable amounts were established using dispersion modeling as a planning tool. The concept of lowest achievable emission rate (LAER) was established for emission units in stationary sources. LAER is the degree of emissions control that is considered to be most stringent for a source in a nonattainment area and that applies to new or modified major sources. The definition of major source or major modification depends on the contaminant. LAER is based on the most stringent rate contained in any state implementation plan or the level of control achieved in practice by similar sources. For those sources, in areas attaining the ambient air quality standard another level of control technology is established. This is best available control technology (BACT). BACT is determined on a case-by-case basis for new sources in PSD areas and takes into account energy and economic, as well as environmental, effects. Although it is more flexible than LAER, BACT always has to be sufficient to meet new source performance standards. Emergency Episodes In addition to those regulations at the federal level dealing with ambient air quality, the federal government was given the authority to deal with air quality episodes similar to those seen in London, United Kingdom, following the winter of 1952. These include stringent limitations on operations, emissions, fuel use, and so on in the event of federal air quality emergency levels (Chapter 3) being exceeded. Areawide shut-downs of industrial and commercial operations are also allowed under federal emergencies.


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Hazardous Air Pollutants In addition to concerns for criteria pollutants, the federal government established national emission standards for hazardous air pollutants (NESHAPs). The NESHAP regulations established nationwide standards for existing, modified, or new sources that emit listed hazardous air pollutants (HAPs). These air contaminant emissions were limited to certain specific industries that emitted those NESHAPs. The NESHAP concept was expanded on in the Clean Air Act Amendments (CAAA). Global Concerns The EPA was given the authority to regulate stratospheric ozone-depleting chemicals in earlier versions of the Clean Air Act. This was the first attempt at dealing with emissions of a global nature. The focus was protection of the stratospheric ozone layer, based on early research indicating a link between potential ozone destruction and the emissions of certain CFCs. The power to regulate these emissions was significantly expanded on in the latest Clean Air Act Amendments. Federal Environmental Statutes The federal government has the authority to regulate air emissions under a variety of different federal laws in addition to the CAA. These include other laws dealing with operations or activities that may generate air emissions. These are typically fugitive emissions such as volatile organic compounds or hazardous air pollutants, as well as criteria contaminants such as particulates and NOx. Toxic Substances Control Act The Toxic Substances Control Act was the first statute (1976) to deal with air contaminant emissions of a hazardous nature, by its regulation of emissions of polychlorinated biphenyls (PCBs). Incinerators discharging air contaminants while burning PCB and PCB-containing waste materials were required to meet a strict level of control efficiency. The destruction and removal efficiency (DRE) for PCBs in the exhaust gases had to be equal to or greater than 99.9999%. This was based on the total PCB mass input to the incinerator. Resource Conservation and Recovery Act The Resource Conservation and Recovery Act (RCRA) deals with ongoing waste management facilities that have an air emissions component or that deal with waste fuels. The emissions from facilities handling waste materials may be fugitive as well as direct or combustion-oriented for their air component. RCRA established specific standards for incinerators disposing of hazardous waste by requiring, under the provisions of a trial burn (for the operating permit), that the DRE be equal to or greater than 99.99% for the principle organic hazardous compounds (POHC) identified in the waste materials. In addition, a limitation on the emissions of hydrochloric acid, particulates, and CO were established for the operating permits for those RCRA incinerators.



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Whenever any “corrective action” is required at a RCRA facility, the owner or operator of that facility must deal with all air emissions occurring as a result of that corrective action. Such corrective action may include the decontamination of soil or groundwater during a clean-up activity at the ongoing waste facility. RCRA also provides for injunctive relief in court to force former owners and operators to remediate or take measures to reduce pollution. RCRA regulations also deal with air emissions from hazardous waste burned in boilers and industrial furnaces (BIFs). For these rules, the facility must obtain a permit under RCRA to burn such waste fuels. With respect to organic emissions, the boilers and industrial furnaces must meet the DRE standards of 99.99% for all listed waste materials and their fuels, and a 99.9999% DRE for those wastes that contain dioxin. These boilers and industrial furnaces are also subject to emission limits for certain heavy metals, HCl and chlorine gas, particulates (0.08 grains per standard dry cubic foot at 7% oxygen), and carbon monoxide. Although the majority of the focus is on the air quality side, these are regulations under RCRA. There is the potential for multiple federal laws to be applicable in certain situations, such as with regard to waste oils from refrigeration compressors in old household appliances. Because the compressor oil may contain CFCs or halogens, it may be subject to both RCRA and the Clean Air Act. Comprehensive Emergency Response, Compensation, and Liability Act Hazardous waste site clean-ups (where no current operator or owner exists) are regulated under the Comprehensive Emergency Response, Compensation, and Liability Act (CERCLA), commonly known as Superfund. The Amendments of 1986, termed the Superfund Amendments and Reauthorization Act (SARA), further clarified the requirements for such clean-up activity. Under CERCLA/SARA, all existing federal regulations for either NSPS or NESHAPs must be met for any clean-up activity. In addition, concerns for fugitive emissions, monitoring of the air at the perimeter of the facility during clean-up activities, emissions testing of sources during remediation, and public input must be provided for during the implementation of site restoration. For a CERCLA/SARA clean-up action, federal authority preempts all local and state regulations for air quality management; however, remedial actions must take into account all local applicable, relevant, and appropriate regulations during cleanup activities. No permit is required for clean up of a federal “superfund” site, as the remediation is carried out under the authority of the federal government. The rationale is that because of the immediate health risk of hazardous waste, specific regulations requiring long periods of time (such as permitting) are preempted by federal authority. Considerable CERCLA litigation has been generated among the many Superfund sites, for which many current and former owners and operators are being sued for reimbursement by the EPA and by others for contribution. CERCLA litigation includes insurance coverage actions, due diligence actions, and prior owner, lessee, and successors-in-interest liability lawsuits, all of which are intended to bring about the cleanup of contaminated sites.


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THE CLEAN AIR ACT The Clean Air Act and its amendments introduced sweeping changes in the federal approach to air quality management. These amendments redirected the entire scope of federal regulations with respect to criteria pollutants, hazardous air pollutants, and global issues. There are 11 major titles to the CAAA. The significant provisions are seen in Table 9.1. These provisions deal with ambient air quality standards, changes in mobile source regulations, hazardous air pollutants, acid deposition, federal permits, stratospheric ozone protection, enforcement, and a number of miscellaneous provisions. In addition, the CAAA outlined a 20-year time frame for regulations to be adopted to implement the act’s specifics. These regulations are reviewed in the following sections. Key among these is the emphasis on attainment of ambient air quality standards and the protection of public health and welfare. For each of the relevant titles, a synopsis of the significant major provisions is provided below. These synopses follow the specific titles of the amendments and the major focus of each.

TABLE 9.1 Significant Provisions of the Clean Air Act Title I

II

III

Provisions/Focus Attainment and Maintenance of the NAAQS Classification and attainment dates SIP revision NOx requirements Multistate areas and sanctions Mobile Source Provisions Vehicle emission standards Emissions control and compliance Fuel requirements Nonroad engines Reformulated and oxygenated gasoline Clean fuels Hazardous Air Pollutants Pollutant lists and source categories Emission standards and compliance schedules State programs Shoreline deposition Special studies Prevention of accidental releases Risk assessment and management commission Solid waste combustion



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TABLE 9.1 (continued) Significant Provisions of the Clean Air Act Title IV

V

VI

VII

VIII

TITLE I — ATTAINMENT

Provisions/Focus Acid Deposition Program SO2 provisions NOx provisions Emissions documentation Clean coal technologies Permits EPA/state program interface Program requirements Permitting process Special provisions Stratospheric Ozone Protection Chemical lists and ozone-depletion potentials Reporting Reduction and schedules Use, recycling, and disposal of chemicals Products made with ozone-depleting chemicals Enforcement Provisions Administrative, civil, and criminal provisions Judicial review Citizen suits Miscellaneous Outer continental shelf emissions sources Contaminated oil-ship fuel Visibility and source/receptor concepts Interstate commission Fuel cell research

AND

MAINTENANCE

OF THE

NAAQS

The EPA in 1997 reviewed the NAAQS to account for new technology and standards. This review resulted in the EPA issuing two new standards, the Eight-Hour Ozone Standard, which will replace the One-Hour Ozone Standard when areas demonstrate compliance with the One-Hour standard, and a new standard, on fine particulate matter, known as PM2.5. The final designation of attainment and nonattainment areas was announced by the EPA on December 14, 2004. Seen earlier in Figure 3.3 are the ozone nonattainment areas as of that date. A recognition that the ambient air quality standards were not being met in a timely fashion led to the major provisions of Title I. In particular, these provisions concerned ozone air quality, ozone formation, oxides of nitrogen and hydrocarbon emissions, and the relationship of fuels and combustion to CO emissions.


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Title I classifies and assigns attainment dates for ozone, carbon monoxide, and PM10 for different areas of the country. For each classification, specific measures for implementation and sanctions are outlined. Using the statistical metropolitan area Census Bureau tabulations, as well as the air quality control regions, the EPA organized five classifications for those areas in the United States that were not attaining the ozone standard, and two classifications of nonattainment for both carbon monoxide and for PM10. The designations of classes range from “marginal” through “extreme” nonattainment areas. These classifications are based on the design value, which is the fourth-highest contaminant concentration (usually ozone hourly average) monitored anywhere within any one of those regions in a period of three consecutive years. On the basis of the design value, areas were classified and specific requirements were listed in Title I for each of those areas. For each area, there are periods from 3 to 20 years from the date of enactment by which the implementation of specific air quality management strategies and regulations must be implemented and by which date the ambient air quality standard must be obtained. Marginal areas for ozone included metropolitan areas that were to have achieved attainment within 3 years of the applicable regulation. As seen earlier, these marginal areas are only slightly above the ambient air quality standard. Moderate through extreme classification areas were far enough above the ambient air quality standard that significant air quality management strategies had to be implemented. Ozone Nonattainment Requirements SIPs must be submitted to the EPA to demonstrate how each state will attain the ozone standard by the deadline. Nonattainment areas must achieve compliance with the NAAQS by dates ranging from 2007 to 2021, depending on the severity of the nonattainment air quality designation. States will be adopting new regulations to control ozone precursors and to extend controls into areas not previously designated as ozone nonattainment. Deadlines for attainment of the 8-hour standard would be based on the amount of time specified in the Clean Air Act. Therefore, marginal areas would have 3 years for attainment, moderate areas would have 6 years, serious areas would have 9 years, severe-15 areas would have 15 years, severe-17 areas would have 17 years, and extreme areas would have 20 years. However, the Eight-Hour Ozone Standard will come into effect only following compliance with the One-Hour Ozone Standard. For the moderate, serious, and severe areas of nonattainment for ozone, there will be an increasing gradation of severity of measures required to meet the ambient air quality standard. The Los Angeles basin, as the single “extreme” area, is in a class by itself. For each of these areas, a series of mandatory changes to the State Implementation Plans is required, depending on the degree of nonattainment. In each case, in moving from the moderate to the extreme cases, additional measures are required.



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Marginal Areas For the marginal areas, accurate emissions inventories must be completed, new source review requirements will be required on major NOx sources, and automotive inspection and maintenance of mobile source control systems will be required. Major stationary sources of VOCs and NOx must submit inventories of emissions every year. An offset ratio for new stationary source emissions of at least 1.1 is required (110% reduction). For each increase in VOC emissions, there must be an equivalent 115% decrease of emissions elsewhere under new source review regulations. Moderate Areas In addition to the requirements for marginal areas, the moderate areas of nonattainment must revise the state implementation plans to include, for mobile sources, requirements for additional air pollution control, inspection and maintenance programs, and stage II vapor recovery systems during refueling (vacuum-assisted vapor recovery at the nozzle). Contingency measures are to be included in the event that these requirements fail to attain the required ambient air quality within the 6-year time frame. Reasonable further progress requirements for the moderate ozone areas will include up to a 15% total VOC reduction in the entire area affected. For stationary sources of VOCs and NOx, the emission threshold for inclusion in SIP revisions is defined as 100 tons per year for new and existing plants; 40 tons per year is the emission threshold for increases during a modification of an existing facility. For control systems on the major sources, the reasonably available control technology (RACT) is required for the existing major sources of VOCs and NOx. For new major sources or modifications of an existing major source, the LAER level of control will be required. For new source reviews, internal offset ratios of at least 1.0 are required. External offsets (those found outside the plant boundaries) are 115% of the VOC increases at the new facility. Serious Areas For the serious ozone nonattainment areas, mobile sources receive much greater scrutiny. These requirements include clean fuel programs for fleet vehicle owners, transportation and congestion management plans or control measures for all mobile sources, vapor recovery requirements for fleet owners during vehicle refueling, and significantly enhanced inspection and maintenance procedures. The latter procedures require annual auto emissions testing, repair, and maintenance; provisions for denial of registration for vehicles failing the test; and decentralized testing and certification of onboard emissions control diagnostics systems and computerized emission analyzers. Reasonable further progress requirements include NOx and VOC reductions. The threshold levels (existing emissions) for VOC and NOx stationary sources are 50 tons per year for new or existing facilities and 25 tons per year for existing sources. Control levels required for those major new or modified stationary sources are at the LAER, whereas for existing sources either RACT or BACT may be used. BACT applies in those cases in which a modified facility has no offsets for its emission increases and when the total emission is less than 100 tons per year of


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VOCs. The VOC offset ratios under new source review will be 120% for those sources outside plant boundaries, but they will be 130% (or 1.3 to 1) for internal sources of VOCs. Severe Areas In addition to all of the preceding requirements on mobile and stationary sources, those areas classified as severe nonattainment areas will see requirements for mobile sources to include total vehicle miles traveled reductions by the imposition of transportation control measures. As an additional measure of reducing mobile source emissions, Section 182(d)(1)(B) of the CAA allows the implementation of employerbased trip reduction programs that are aimed at improving the average vehicle occupancy rates. As an alternative to trip reduction programs, Section 182(d)(1)(B) also allows the substitution of these programs with alternative programs that achieve equivalent emission reductions. The VOC or NOx new source review threshold for all facilities becomes 25 tons per year, and the control level becomes LAER for major new or modified sources. The VOC offset ratios under new source review are 1.3 to 1 for both internal and external reductions of emissions. Extreme Areas Los Angeles, including the entire South Coast Air Basin in California, continues to be the only extreme ozone nonattainment area. As such, it is required to implement further controls on all sources. For mobile sources, in addition to all of the preceding requirements, there will be demands for new technologies, additional traffic control measures during heavy traffic hours, and enhancement of all of the lower-level requirements. Further contingency measures are required in the event that those actions fail. These measures are to be included in the state implementation plan as mandatory requirements. The VOC and NOx threshold for the definition of a major source is 10 tons per year for a new or existing facility, or any increase during modification of an existing source. Additional controls are imposed on all combustion systems for boilers, and “clean fuel” combustion or new and additional NOx emission controls are specifically required. The VOC offset ratios for new source review are 1.5 for external sources or 1.3 for internal sources controlled at a given facility. Additional Ozone Strategies Title I provides for a number of additional strategies to be implemented in all ozone nonattainment areas. The first of these is the requirement that all of the plan provisions for stationary VOC sources also apply to major stationary sources of NOx, unless the EPA determines that additional NOx controls would not create a net benefit, or for areas that are not a part of an ozone transport region. Milestones Milestones are required under Title I for serious, severe, and extreme nonattainment areas to demonstrate that the applicable emission reductions have been met within stated time periods. In addition, for the areas that fail to demonstrate compliance



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with those milestones, there are additional requirements that the EPA adopt, or force the adoption, of an “economic incentive program” for those areas that fail to meet those compliance demonstration requirements. In addition, those areas may be reclassified up to the next higher classification or be required to implement control measures adequate to meet the next milestone in emission reductions. Interstate Transport Recognizing that certain geographic areas are specific sources of precursor contaminants leading to ozone nonattainment and that other areas may be merely the receptor, Title I allows for the inclusion of a multistate area to be set up in which the included states must coordinate SIP revisions. A specific ozone transport region and a commission for one region has been specifically required in the law. Originally, 11 states and the District of Columbia (the number has since expanded) had to assess the degree of interstate transport and recommend measures to the EPA necessary to ensure that the relevant SIPs meet the plan requirements. Additional requirements for these states include enhanced vehicle inspection in metropolitan areas of greater than 100,000 population, RACT levels of control in all sources of VOCs, and stage II vapor recovery controls during vehicle refueling. Stationary sources emitting at least 50 tons per year of VOCs are considered major by this provision of Title I and are subject to all plan requirements applicable to at least a moderate nonattainment area. The EPA retains the right to oversee all activities of the interstate transport region. Clean Air Interstate Transport In 2005, the EPA announced a final rule to states in the area from North Carolina northward along the eastern Atlantic seaboard to Maine. These 28 states and the District of Columbia were found to contribute significantly to nonattainment of the NAAQS for fine particles or 8-hour ozone in downwind states. The EPA is now requiring these upwind states to revise their SIPs to include control measures to reduce emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx). The states have 2 years to revise their SIPs to include the required measures. Control Guidelines The EPA has established Control Technique Guidelines (CTGs) for additional categories of stationary-source VOC emissions. CTGs are used by state and local governments to identify requirements for VOC reductions. These guidelines give priority to those categories that make the most significant contributions to ozone nonattainment. Best available control measures are required in these CTGs. Specific source categories addressed in the EPA’s CTGs pertaining to VOCs include surface coating of fabrics, cans, large appliances, metal coils, metal furniture, flat wood paneling, paper, and magnet wire; solvent metal cleaning; and surface coating of automobiles and light-duty trucks. Consumer Products Consumer or commercial products are required to be addressed by the EPA. The EPA must list categories of consumer or commercial products that account for at


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least 80% of the VOC emissions from such products in ozone nonattainment areas and must require best available controls. The EPA may control or prohibit by regulation the manufacture, sale, or introduction to commerce of any product that is a source of VOC emissions. In addition, the EPA may impose fees or charges or collect funds associated with the regulations of these products in addition to requiring labeling, self-monitoring and reporting, prohibitions, and limitations on these materials. Marine and Harbor Emissions VOC emissions and any other pollutants from the loading and unloading of marine tank vessels in harbors in ozone nonattainment areas are the focus of additional standards that will require RACT for such emissions. Stationary Source Fees In addition to all of the above, stationary sources in those areas classified as severe or extreme that fail to achieve attainment by their respective deadlines will be required to pay an annual fee to the state, beginning the year after the attainment date. The baseline amount (“federal penalty”) begins at $5000 per ton of VOCs emitted during a calendar year. If the state fee provisions are not adequate in the SIP, the EPA may collect the unpaid fees. Some states have enacted additional “emission fees” to be imposed by local districts for each ton of VOC emitted in addition to the federal penalty. These fee provisions do not apply if the population is less than 200,000 persons and the nonattainment area is a receptor of ozone transport. Additional sanctions against ozone nonattainment areas include prohibitions on highway funding, withholding of air pollution planning or control grants, and a requirement that all emissions be offset by at least 2 to 1 for any increases under new source review. Carbon Monoxide Nonattainment Provisions The mandatory Title I provisions for CO nonattainment areas closely parallel many of the provisions for ozone nonattainment. The focus is combustion sources of emissions, primarily from vehicular sources. These provisions include restrictions on vehicle miles traveled, submissions of accurate current inventories of CO emissions, inspection and maintenance programs of mobile source control systems, clean fuel fleet programs, and transportation control measures as required in the severe ozone nonattainment areas, except that the program applies to CO. Enhancements of each of the mandatory mobile source control requirements are required for the serious nonattainment areas. For both the moderate and serious areas of nonattainment, oxygenated fuels (reformulated gasoline) are required in all motor vehicle fuels during those times of the year that are considered to have high CO conditions. The Reformulated Gasoline Regulations program took effect in 1997. The 2.7% oxygen weight minimum for oxygenated fuels’ control periods was not affected by the rule, and it did not change the applicable oxygen standards under state oxygenated fuels programs.



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If it is determined that stationary sources in serious areas contribute significantly to CO levels, a major stationary source is defined as one that has the potential to emit 50 tons per year. This source will be subject to major source requirements for CO similar to those for ozone. In addition, an economic incentive and transportation control program will be required for each state it fails to meet its milestone demonstration on time. The economic incentive program, when combined with other revisions in the SIP, must reduce total CO emissions in the area by 5% each year until attainment. Within the three serious CO nonattainment areas, the oxygenated fuel requirement is a minimum of 3.1% by weight, as required under this provision. Oxygenated Fuels — The Rise and Fall of Methyl-Tertiary-Butyl-Ether The 1990 Clean Air Act required that those metropolitan areas with high CO concentrations use oxygenated fuels during the winter months. Oil companies had known since at least the early 1980s that methyl-tertiary-butyl-ether (MTBE) was the best available additive for oxygenating fuels. However, following MTBE’s widespread use as a fuel additive, in addition to its positive use in oxygenating fuels, the compound was found to have several undesirable characteristics, which have since led to its replacement. The additive, if spilled or leaked, tends to travel through soil and groundwater much more quickly than water. It is also known to possess a foul odor and taste when small amounts are present in groundwater. Because of the widespread problem of leaking underground storage tanks, MTBE was released into groundwater in the areas where it was used as a gasoline additive. This is an example of how an additive used to help solve air pollution problems is now considered a groundwater pollutant. This contamination has generated litigation across the United States. Plaintiffs allege that MTBE-mixed gasoline is a defective product and that the oil companies failed to warn their customers of the negative aspects of MTBE. This situation placed oil companies in the difficult position of complying with the federal Clean Air Act in using oxygenates, and yet potentially violating state laws. California, which is required to use oxygenated gasoline in all of its motor vehicles, banned the use of MTBE as an additive in gasoline in 2004. To fulfill legal requirements, therefore, gasoline producers switched to ethanol, which satisfies the oxygenated fuel requirement, as the only remaining approved additive for its gasoline. There is a move, however, to lobby Congress to amend the CAA to eliminate the oxygenated fuel requirement and replace it with a flexible national renewable fuels program. It should be noted that because ethanol is a byproduct of corn, certain states and their political representation that are heavily dependent on agricultural concerns would likely oppose any change in the oxygenated fuel requirements. PM10 Nonattainment Areas Airborne particles less than 10 µm in diameter (PM10) are known to pose a health risk because they can be inhaled into and can accumulate in the respiratory system. Initially, all areas considered nonattainment for PM10 were classified as moderate. Upgrades to serious areas of nonattainment are provided for in Title I.


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For those stationary area sources in the moderate areas, states must implement a construction and operating permit program (if it does not already exist) for new and modified major stationary PM10 sources. Remaining moderate areas for stationary PM10 standards have been granted extensions to remain in compliance with the CAA, and many have since been determined by the EPA to have attained the PM10 NAAQS in 2001. If a serious area does not reach PM10 attainment by the deadline, SIP revisions must be submitted that allow for an additional annual 5% emission reduction of PM10 or PM10 precursor emissions in the area, as reported in the most recent inventory. In addition, PM10 control measures for stationary sources also apply to major stationary sources of PM10 precursors. The EPA has issued technical guidance on what constitutes RACM and best available control measures for urban fugitive dust sources, residential wood combustion, and prescribed agriculture and forestry-clearing burning operations. PM2.5 Nonattainment Areas In 1997, the EPA established annual and 24-hour NAAQS for PM2.5 for the first time. Particles less than 2.5 µm in diameter (PM2.5) are referred to as fine particles and are believed to pose a large health risk because of their small size. These fine particles can lodge deeply into the lungs. The EPA issued official designations for the PM2.5 standard in 2004 and made modifications in 2005. States must submit their SIPs to EPA within 3 years after the agency makes final designations in 2007.

TITLE II — MOBILE SOURCE PROVISIONS As seen in Chapter 4, transportation emissions by light-duty and heavy-duty vehicles and trucks are among the most significant contributors to air pollutants. In Title II, the CAAA details requirements for all aspects of new regulation over mobile source emissions. These requirements relate to emission standards as well as to the fuels used in those programs and vehicles. The first of these requirements takes the form of tailpipe emission standards, whereas the latter standards take the form of requirements for fuel and fuel compositions. Light-Duty Vehicle Standards Increasing percentages of light-duty vehicles must meet the standards as a function of model year. A significant new addition to the EPA requirement is that these standards be met for the initial 50,000 miles of travel and then, additionally, only a slightly higher level of emissions is permitted at the 100,000-mile mark. Heavier weight trucks have different requirements. Taken together, these new tailpipe standards are estimated to reduce hydrocarbons about 40% and NOx by about 60% from transportation sources. Nonroad vehicle fuels and engines will be the focus of additional standards to achieve the greatest degree of emission reductions achievable. Separate standards for new locomotives and the engines powering them have been in effect since 1995.



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Again, the greatest degree of emissions reduction achievable, using available technology, is required. California is expressly authorized to regulate nonroad engines and vehicles that are at least as protective as federal standards, whereas other states are not allowed that waiver of federal preemption. However, any state with an approved SIP may adopt the California approach as long as it is equivalent. The Urban Buses Standard (Title II, §219) originally required a 50% reduction in particulate matter. However, the section was revised to allow the administrator of the EPA to increase the level of emissions of particulate matter allowed if it is determined that the 50% reduction is not technologically achievable, taking into account durability, costs, lead time, safety, and other relevant factors. In addition to tailpipe emissions, evaporative emissions controls are required from gasoline vehicles operating in summer high-ozone conditions during operation and following 2 or more days of no usage. These regulations must include the greatest degree of emission reduction achievable considering volatility, cost, energy, and safety factors. Tailpipe Toxics With respect to mobile source air toxics control, the EPA requires that refiners maintain their average 1998–2000 toxic emission performance levels. These toxic air pollutant performance levels pertain to benzene, formaldehyde, acetaldehyde, 1,3-butadiene, and POM. As a result, the EPA reports that benzene levels in urban areas have decreased nationwide by almost 40% in the last 10 years. Emissions Control Two key issues regarding nontailpipe standards revolve around emissions during refueling and computerized diagnostic systems. These latter standards evaluate the ability of existing air pollution control systems on vehicles to function properly. The first requirement is that new light-duty vehicles will require onboard vapor recovery systems with a minimum capture efficiency of 95%. One hundred percent of all vehicles must have onboard vapor recovery systems. For serious, severe, or extreme ozone nonattainment areas, the EPA may require these in addition to current stage II vapor-recovery requirements during vehicle refueling. In addition to standards on sale, vehicles are required to have their own onboard computerized diagnostic systems, which will evaluate and alert drivers as to whether these onboard control systems are still effective. All light-duty vehicles and trucks now have these onboard emission control diagnostics. States must include in their SIPs that their inspection and maintenance programs include evaluation and testing of such onboard systems. These requirements will ensure that control systems will remain effective on each individual vehicle, rather than a general average being computed for all vehicles in the system. Automobile warranties must cover these diagnostic systems as well as catalytic convertors and emission control systems for at least 8 years or 80,000 miles. Penalties


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at the federal level for tampering with emission-control devices vary from $2500 to $25,000 for tampering with, defeating, or rendering inoperative such control systems. Reformulated Gasoline Fuel Requirements Specific fuel compositions have direct effects on air emissions resulting from the combustion of such fuels. Therefore, Title II specifically looks at fuels and fuel composition to help attain ambient air quality standards. Specific items that come under the heading of fuel requirements relate to prohibitions for misfueling of leaded gasoline in vehicles intended only for unleaded gas. Another requirement is that the Reid vapor pressure not exceed 9.0 pounds per square inch (psi) unless the fuel blend is for gasoline with 10% ethanol, in which case the Reid vapor pressure requirement is 10.0 psi. With respect to diesel fuels, the federal sulfur content may not exceed 0.05% (500 ppm). In addition, all motor vehicle gasolines containing lead or lead-based additives are totally prohibited nationwide. Additional fuel requirements are in place for the nine worst ozone nonattainment areas. These requirements include reformulated and oxygenated fuels. A reformulated fuel must meet certain general requirements for NOx, oxygen, benzene, and heavy metal content and must also achieve reductions in ozone-forming VOCs and toxic air pollutants. Phase II Reformulated Gasoline Performance Standards Phase II reformulated gasoline standards are now required to be sold in states participating in the Reformulated Gasoline Regulations program. This reformulated gasoline reduces VOCs by 25%, NOx by 6%, and toxic emissions by 32%. The minimum composition requirements of reformulated fuels have undergone some transition since the implementing regulations were established. However, the requirements of the CAA include a minimum 2.0% by weight oxygen content, a benzene level of 1.0% or less by volume, and a prohibition on any heavy metals, including lead or manganese. The aggregate limit of aromatic hydrocarbons is 25% by volume, and a use of additives is required as needed to meet VOC and toxic emission standards. In addition, the emission of ground-level ozone-forming compounds (ozone VOCs) and toxic air pollutants must be reduced by 25% and 20%, respectively, from the aggregated baseline levels. The CO nonattainment areas must use oxygenated fuels that have a minimum content of 2.7% oxygen by weight. These are required to be sold during the highCO portion of the year (typically wintertime conditions). Since the combustion of these reformulated gasolines can cause increased emissions of NOx, the law also prohibits vehicles that are using reformulated gasoline from increasing NOx emissions beyond the levels associated with vehicles burning conventional fuels. In addition to varying the percentages of standard gasolines, Title II lays out a requirement for fleet vehicles (10 or more) to use “clean fuels” in the serious, severe, or extreme ozone nonattainment areas. These clean fuels include methyl alcohol, ethanol, blends of other alcohols of 85% with gasoline, reformulated gasolines or



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diesels, natural gas, liquefied petroleum gas, hydrogen, or other power sources. Thirty percent of all new fleet vehicle purchases must use “clean fuels.” California enjoys the only exemption from federal law for mobile sources. Because of the extreme severity of the air pollution problem, California is allowed to have mobile source emissions standards more stringent than the federal standards; that is, fuel sulfur content cannot exceed 30 ppm, as opposed to the higher 500 ppm federal standard. California Low-Emission Vehicle II Regulations The California Low-Emission Vehicle (LEV) standards refer to clean fuel-emission vehicles that are sold in California. By using the clean fuel vehicle approach, including ultralow-emission vehicles (ULEVs) and zero-emission vehicles (ZEVs), fleet operators can obtain credits for those fleet vehicles that do not meet the clean fuel requirements. LEV II regulations, which run through 2010, are intended to represent the continuing progress in emission reductions. Because California’s passenger vehicle fleet continues to grow as its population swells, new, more stringent LEV II standards are used for California to meet federally mandated clean air goals outlined in the SIP. The new LEV II regulations provide for the super-ultra-low emission vehicle (SULEV) category for light-duty vehicles. The SULEV’s are designed to emit 1 pound of hydrocarbons over driving 100,000 miles. These regulations also provide for partial zero-emission vehicle credits for vehicles that achieve near-zero emissions. The credits include 0.2 for a gasoline-fueled SULEV, 0.4 for a compressed natural gas SULEV, 0.7 for methanol reformer fuel cell vehicles, and full zeroemission vehicle credit for a stored hydrogen fuel cell vehicle.

TITLE III — HAZARDOUS AIR POLLUTANT PROGRAM A major expansion of the Clean Air Act Amendments was in dealing with HAPs. Among the major provisions of Title III were • • • •

The listing of 189 original hazardous air pollutants with source categories New levels of control technology (MACT) for HAPs Provisions for area sources calculations of residual health risks after implementation of controls, and Provisions for accidental releases of hazardous air pollutants.

The definition of a major source of hazardous air pollutants is “a stationary source or group of stationary sources under common control which emit or have the potential to emit a total of 10 tons or more per year of any single hazardous air pollutants or 25 tons or more per year of any combination of HAPs.” For a single listed contaminant such as perchlorethylene, this might amount to as little as six and a half gallons per day being lost through fugitive emissions. Some of the substances listed by the EPA in Title III are seen in Table 9.2. Substances may be deleted from or added to this list by the EPA on the basis of


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TABLE 9.2 Selected Title III Hazardous Air Pollutants Antimony Arsenic Beryllium Cadmium

Metal Compounds Chromium Cobalt Lead Manganese

Organics+ Benzene Formaldehyde Biphenyl Hexane Carbon disulfide Methanol Dioxins Nitrobenzene Halogenated organics (TCA, TCE, etc.) Pesticides (2,4 D; DDE; Parathion, etc.)

Mercury Nickel Selenium

Phenol PCBs Toluene Xylenes

Acids, Oxidizers, and Physical Agents Asbestos HCl Phosphorus Chlorine Phosgene HF Fine mineral fibers Radionuclides (includes Radon) +

Some common representative substances.

additional scientific evidence regarding adverse human health effects. Specifically excluded from this list are the six criteria pollutants, including elemental lead. Lead compounds, however, are included on the list of hazardous air pollutants. Toxic Release Inventory Program The Emergency Planning and Community Right-to-Know Act (EPCRA) was enacted in 1986 to inform communities and citizens of chemical hazards in their areas. According to the EPCRA §311, §312, businesses are required to report the locations and quantities of chemicals stored on site to state and local governments. In addition, §313 of the EPCRA requires the EPA and states to collect data on releases and transfers of certain toxic chemicals from industrial facilities, and to make the data available through the Toxic Release Inventory Program (TRI). Other requirements include waste management and source reduction activities to be reported under the TRI. The TRI is a source of HAP data, and has been very effective as a pollution reduction measure, due largely to the potential public outcry following any toxic releases. HAP Sources The source categories are those industry groups that emit HAP substances. Industrial source categories include cooling towers, electroplating operations, synthetic organic chemical manufacturing operations, decreasing operations, commercial sterilization facilities, dry cleaners, pulp and paper mills, petroleum refineries, polymer and resin



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operations, surface coatings, magnetic tape manufacturing, secondary metal operations, waste treatment storage and disposal facilities, and coke ovens. Area sources such as gasoline stations, dry cleaners, manufacturers of furniture, printing presses, and small boilers are also included.

STANDARDS Emission standards for HAPs are classified into two categories: technology based and health based. Emission standards must achieve the maximum degree of emissions reduction deemed achievable by the EPA for new or existing sources in the applicable category, considering cost, health, environmental effect, and energy requirements. Technology-Based Standards The maximum achievable control technology (MACT) standards may include process changes, material substitutions, collection, capture and treatment of emissions, control technology, design equipment and work practice operational changes, and so on. MACT is defined according to the amount of emissions from the HAP source. For new major sources, MACT is at least as stringent as the emissions level achieved in practice at a best-controlled similar source. For existing major sources, MACT may be less stringent than that for new sources but must be at least as stringent as either the average emissions limitation achieved by the best performing 12% of similar sources, (excluding those that have recently achieved the LAER for that category) or the average emission limitation achieved by the best performing five sources, if the specific category has fewer than 30 units. From smaller-area sources, the EPA may require either MACT or a less stringent generally available control technology. Each source category has a deadline for attainment of the technology-based emission standards. However, the new law does create an incentive for facilities to achieve early reductions. In this case, if all listed toxics are reduced at a facility (by 90% or more for organics and 95% or more for particulates), the facility may receive a 6-year extension in the deadline to comply with MACT standards. This is to provide an incentive for early HAP reductions by whatever means. Health-Based Standards Title III requires investigation of the health-based emission standards as applied to major sources. Area sources may also be included in the industry-related source category. These health-based standards must provide an ample margin of safety to protect public health and to prevent adverse environmental effects after implementation of MACT for major sources. These health-based standards must also include the calculations of potential residual risk from carcinogenic air pollutants if the applicable technology-based standards are not reduced to a lifetime excess cancer risk to less than 1 in a million (individual risk) for the “maximum exposed individual.” If any single source shows a residual health risk greater than 1 × 106 (one chance in a million), the EPA must promulgate additional standards.


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Area Sources: Urban Air Toxics Strategy The EPA has developed a specific strategy for air toxics in urban areas. The three goals for their Air Toxics Strategy include attaining a 75% reduction in incidence of cancer attributable to exposure to HAPs emitted by large and small stationary sources nationwide; attaining a substantial reduction in public health risks (such as birth defects and reproductive effects) posed by HAP emissions from small industrial sources; and addressing disproportionate effects of air toxics hazards across urban areas, including predominantly minority and low-income communities. The EPA has issued 79 air toxic standards for many of the major industrial and commercial sources, including chemical plants, steel mills, and smaller sources such as dry cleaners. The Air Toxics Strategy is the EPA’s framework for addressing air toxics in urban areas by looking at stationary-, mobile-, and indoor-source emissions. When fully implemented, the regulations are intended to reduce air toxic emissions by almost one million tons per year. SIP Revisions Again, under EPA authority, states must revise their implementation plans to set up HAP standards that are no less stringent than the federal requirements. In addition, states must review their statutes for regulation of potential high-risk point sources or toxic hot spots. Such programs also evaluate those facilities that produce, process, handle, or store substances listed under the accidental release provisions of Title III in quantities greater than threshold amounts. These revised state implementation plans are subject to review by the EPA. HAP Permits In addition to those permits required for major new or modified sources within a nonattainment area, permits are also required for air toxics sources. Title III hazardous air pollutant permits must specify emission limits based on control technologies, require monitoring of emissions, and require compliance with baseline health-based emission limits. All major HAP sources must have permits. Special Studies A number of special studies are required by Title III. These include a study of the emissions of hazardous air pollutants from electric utility steam-generating units. Alternative control strategies and potential regulations necessary to control emissions of HAPs from those sources are also studied. Clean Air Mercury Rule In March 2005, the EPA issued the Clean Air Mercury Rule to permanently cap and reduce mercury emissions from coal-fired power plants for the first time. This rule, combined with the EPA’s Clean Air Interstate Rule, will significantly reduce emissions from the nation’s largest remaining source of human-caused mercury emissions.



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The Clean Air Mercury Rule establishes “standards of performance” limiting mercury emissions from new and existing utilities and creates a market-based capand-trade program that will reduce nationwide utility emissions of mercury in two distinct phases. In the first phase, due by 2010, emissions will be reduced by taking advantage of “cobenefit” reductions; that is, mercury reductions achieved while reducing sulfur dioxide (SO2)and nitrogen oxides (NOx) under the Clean Air Interstate Rule. In the second phase, due in 2018, utilities will be subject to a second cap, which will reduce emissions to 15 tons per year of total mercury on full implementation. Prevention of Accidental Releases Title III set up an accident prevention program similar to those in other federal statutes such as EPCRA. The provisions of Title III for accidental releases apply to the 100 extremely hazardous substances originally listed under EPCRA. The following common substances are included on the list that triggers the provisions of this section of Title III: • • • • • • • • • • • • • •

Chlorine Hydrogen sulfide Anhydrous ammonia Toluene diisocyanate Methyl chloride Phosgene Ethylene oxide Bromine Vinyl chloride Hydrous hydrogen fluoride Methyl-isocyanate Anhydrous sulfur dioxide Hydrogen cyanide Sulfur trioxide

The EPA has established threshold release quantities of those HAPs eligible for regulation at affected facilities. For those facilities handling more than the threshold quantities of the initial 100 chemicals, risk-management plans were required for dealing with accidental releases. These plans included mitigation of the potential adverse human health or environmental effects from the release of more than the threshold amounts of HAPs. These plans included a hazardous assessment, a program for preventing accidental releases, and a response program in the event of an accidental release. The risk management plan had to be in accordance with guidelines issued by the EPA for those stationary sources and to be registered with the EPA. Regulations for the prevention and detection of accidental releases from these stationary sources had to include use, operation, repair, replacement, and maintenance of the equipment used to monitor, detect, inspect, and control releases of


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HAPs. The regulations also included provisions for personnel training in proper equipment operation to prevent releases. Under 29 CFR 1910, the Department of Labor’s Occupational Safety & Health Administraton maintains the “Process Safety Management List of Highly Hazardous Chemicals” to protect employees from hazards associated with accidental releases of highly hazardous chemicals. The standard included a listing of highly hazardous chemicals including toxic, flammable, highly reactive, and explosive substances. Solid Waste Combustion As a result of the concerns for emissions of hazardous air pollutants expressed in the recent past, such as dioxins from combustion of solid waste, Title III established a requirement for NSPS for solid-waste incineration units. Both existing and new or proposed solid-waste units come under the provisions of Title III. Emission standards must reflect the maximum degree of emissions reduction, considering cost and non–air quality health and environmental effects. In addition, Title III set up specific requirements to monitor emissions and report findings, provide operator training, and have a permit as issued under Title IV. Acid gas scrubbers are required to be reviewed as a control technology for small new or existing facilities before promulgation of new source performance standards. Provisions are also made for handling ash from solid-waste incineration.

TITLE IV — ACID DEPOSITION PROGRAM The stated purpose of Title IV was to reduce the annual emissions of SO2 by 10 million tons per year and of oxides of nitrogen by approximately 2 million tons per year from the 1980 levels. The provisions of this title applied to fossil fuel–fired electric utilities’ boilers in specified states. Title IV implemented SO2 reductions by using a market allowance system, an imposition of excess emission fees on those exceeding an allowance, and a deadline extension for additional control technologies to reduce SO2 emissions. SO2 Provisions — Clean Air Interstate Rule 2005 Effect The SO2 reductions targeted emissions from large, higher-emitting utility power plants. Over a 10-year period, starting in 2005, states must devise and implement rules to achieve a 73% reduction in sulfur dioxide (SO2) emissions and a 61% reduction in nitrogen oxides (NOx) emissions. To meet these targets, states have the option of participating in a federally managed cap-and-trade program, or they may meet individual state caps through measures of their own choosing. The key to the SO2 reductions is a system of marketable emission allowances. In essence, an allowance provides an affected source with the authority to emit 1 ton of SO2. The affected sources must not emit more sulfur dioxide than they hold allowances for. This market-based system is intended to allow the most efficient use of resources and emission credits. Both spot auctions and advance auctions are provided for on a sliding scale. These allowances can be purchased, sold, or banked for use in a later year. All new



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sources are required to buy into the allowance system. New sources will not be allocated allowances but will have to purchase them. Market-Based Allowance Program As noted, allowances will be issued annually to affected utility sources on the basis of their baseline fuel use and the emission rate required by the legislation. Once allocated, an allowance is fully marketable. The fundamental allowance rule is that an affected source must hold enough allowances to cover its emissions. Sources can comply with this rule through one of two methods: by reducing emissions (through the installation of pollution control equipment, fuel switching, or conservation) to the level of allowances it holds or by obtaining additional allowances to cover its emissions. Sources can also elect to substitute alternative plans, pool emissions reduction requirements across two or more affected units, or craft compliance strategies using limited time extension provisions found in the legislation. As noted above, a source can comply by obtaining additional allowances sufficient to cover its emissions. These allowances can be obtained in a number of ways: 1. A source can obtain allowances through transfers from other units within its utility system. 2. A source can buy additional allowances on the open market from another source. That other source may have spare allowances for a number of reasons — perhaps because it exceeded its control requirements, thus freeing up allowances for sale permanently or for a limited period of time. 3. A source can obtain allowances from an industrial source that has costeffective reductions and elects to opt into the allowance system. 4. Sources will be able to obtain allowances through the EPA allowance auctions and sales. The allowance trading system is expected to provide benefits over the traditional command-and-control type of regulation. First, by not demanding a specific control option, the legislation provides sources with the flexibility to develop the most costeffective control strategy. In addition, the allowance trading system incorporates an incentive for energy conservation and technology innovation, both of which can lower the cost of compliance and yield pollution prevention benefits. However, NSPS requirements may not be ignored — these cap and trade provisions are “over and above” existing standards. NOx Provisions — Budget Training Program Differing from previous NOx provisions, the EPA has set up the NOx Budget Training Program to allow for compliance based on allowances. Facilities can maintain compliance by “banking” allowances for future years. Also, the Clean Air Interstate Rule allows for NOx reduction using cap-and-trade system of reductions. These allowance-based compliance programs represent the future in emissions controls. Popular in European air pollution programs, they are gaining in popularity in all areas of emissions controls in the United States.


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The EPA may approve alternative limits if the facility in question cannot meet the rate limits using low-NOx burner technology. Emissions averaging between two or more units are possible under the EPA permit program. Other Provisions There are provisions for excess SO2 or NOx emissions above the facility “cap,” with a penalty of $2000 per excess ton of emissions, adjusted for inflation. This is in addition to any other liabilities, fees, or forfeitures for noncompliance. In addition, in the case of excess SO2, the facility must offset the excess emissions by reducing the emissions by an equivalent tonnage the following year. The emission standards are accomplished by the promulgation of revised NSPS for NOx from all fossil fuel–fired steam-generating units. In addition to the emission requirements or fee caps and allowances, Title IV requires that emissions be monitored for SO2, NOx, opacity, and volumetric flow rate. In addition, “acid rain” permits are required under this title but are administratively handled under the provisions of Title V (q.v.). In other words, large utility boilers will have an acid rain permit for Title IV as a part of the operating permit under Title V. The initial permits will be issued by the EPA, whereas the later permits will be issued by states with EPA-approved permit programs. Control technologies for coal-fired power-generation facilities that achieve significant reductions of either SO2 or NOx will be deemed “clean coal technologies.” This section of the act allows for a temporary project to demonstrate clean coal technology. Permanent installations of clean coal technologies will be allowed where there are no emission increases.

TITLE V — OPERATING PERMITS The goal of Title V is for states to issue federally enforceable operating permits to major stationary sources of air pollution. These operating permits are designed to enhance the ability of the EPA, the state, and citizens to enforce the requirements of the act. The permitting programs will provide for permit fees to the states to support their programs. Title V is structured to allow states to develop their permitting program with EPA oversight. This program requires that a federal permit be obtained by each major source in every area within every state, regardless of attainment status. Major sources are defined according to the ozone nonattainment status by geographic area within each state. These also include the 10-ton-per-year sources of a single hazardous air pollutant or 25 tons per year of all combined HAPs. Other sources coming under the operating permit program include those regulated under any of the following CAAA categories: • • • • •

NSPS sources NESHAP sources PSD sources New source review sources Acid precipitation sources (Title IV)



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Title V permits PSD sources

Acid rain sources

NSR sources

HAP sources

NSPS sources

FIGURE 9.1 The Clean Air Act permit structure.

There are some possibilities for exemptions or additions by the EPA. An exemption may be found for a category where the permits would be considered impractical, unfeasible, or unnecessarily burdensome. Figure 9.1 illustrates the overlap of the various programs requiring a permit under this title. Permit Program Requirements For each permit to be issued for a facility, it must contain specific provisions that will ensure that the requirements of the permit are being realized. These permit provisions are • • • •

Fixed term, not to exceed 5 years, but renewable Operating and maintenance conditions to ensure compliance Schedules of compliance, including remedial measures Inspection, entry monitoring, compliance certification, and reporting requirements to ensure compliance with terms and conditions

To be approvable, each permit program under state provisions must contain the elements seen in Table 9.3. As seen, the provisions of the state program and the state permit are extensive. It should be noted that the state or local agencies will issue one federal permit for a facility with multiple sources of air-contaminant emissions. Fees Each approved state permit program must require the source of the air contaminants to pay an annual fee to the state sufficient to cover “all reasonable costs” associated with developing and administering the permit program. The fee may be increased each year in accordance with the Consumer Price Index. If the EPA determines that a state’s fee program is not approvable or the state is not adequately administering or enforcing the fee program, the EPA may step in


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TABLE 9.3 Title V (Part 70) Operating Permit Program Requirements Each approved state permit program must contain provisions for 1. Permit applications and criteria for determining completeness 2. Monitoring and reporting requirements 3. A permit fee system 4. Adequate personnel and funding 5. The authority to issue permits and ensure that each permitted source complies with applicable requirements 6. The authority to terminate, modify, or revoke and reissue permits “for cause” and a requirement to reopen permits in certain circumstances 7. Authority to enforce: permits, permit fees, and the requirement to obtain a permit, including civil penalty authority and “appropriate criminal penalties” 8. Authority to assure that no permit will be issued if EPA timely objects 9. Processing applications and public notice, including • Offering an opportunity for public comment • A hearing on applications • Expeditious review of permit actions • State court review of the final permit action 10. Authority and procedures to provide that the permitting authority’s failure to act on a permit or renewal shall be treated as a final permit action solely to allow judicial review 11. Authority and procedures to make available to the public any permit application, compliance plan, permit, emissions, or monitoring report, subject to confidentiality provisions 12. Allowing operational flexibility at the permitted facility

and collect the fees from the permittee. Failure to pay a fee results in a penalty of 50% of the amount due, plus interest. Small stationary sources coming under the provisions of Title V as small businesses may incur reduced fees. Other Provisions A new item required under the operating permits fee program is that the state or local authority is required to notify all contiguous states whose air quality may be affected by the facility receiving the permit. In addition, all states within 50 miles of the application source must be notified. All states contiguous to the state of the permitted source must be given the opportunity to submit written “recommendations” for the permit to the local or state agency. If the permitting authority refuses to accept those recommendations, it must provide written notice of its reasons to the state that submitted the recommendation, as well as to the EPA. The EPA reserves the right to review the local or state agency permit. The EPA also has the authority to reject and require revisions to a proposed operating permit from a local or state agency, and the EPA retains final authority to issue or deny operating permits. The EPA may waive its own and neighboring states’ review of



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permits for any category of sources, except major sources, either when approving an individual program or in a regulation applicable to all programs. Title V also provides for state court review of the permit application initiated by anyone who participated in the public comment process or permitting activity. Any person may petition the EPA to veto a permit if the EPA fails to object during a 45-day EPA review period. Objections to the petition must have been raised during the comment period. The EPA must issue an objection if the petition demonstrates that the permit is not in accordance with the Clean Air Act. Valid Permits If a source complies with its permit conditions, the permit indicates that the source is deemed in compliance with the provisions of the Clean Air Act. However, every three years the permit is subject to reopening and to revision, depending on the promulgation of other relevant provisions of the law. Permits issued by the states may be more stringent in their terms and conditions than federal requirements, provided they are not inconsistent with the national permit requirements of the Clean Air Act.

TITLE VI — STRATOSPHERIC OZONE PROTECTION When addressing concerns for protection of stratospheric ozone, certain compounds containing bromine, chlorine, fluorine, and carbon were implicated. Title VI of the Clean Air Act Amendments set up a series of regulations to phase out all emissions of such substances. The EPA published two classes (I and II) of substances containing chlorine, fluorine, bromine, and carbon (Table 9.4), which have the potential to deplete stratospheric ozone levels. The class I substances are composed of bromofluorocarbons and CFCs; the class II substances contain hydrochlorofluorocarbons. The brominecontaining compounds are termed halons. All chlorine-containing compounds are now banned.

TABLE 9.4 Ozone-Depleting Chemicals Class I Ozone-Depleting Substances CFC isomers 11–13, 111–115, 211–217 Halon isomers 1211, 1301, and 2402 Carbon tetrachloride Methyl chloroform Methyl bromide and derivatives Chlorobromomethane Class II Ozone-Depleting Substances HCFC isomers


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Recapture and Recycling The use of class I substances is to be at the lowest achievable level. Recapture and recycling of class I substances are required. These substances include air conditioning and refrigeration units at any stationary source. Venting of either class I or class II substances is banned, with penalties of $25,000 per event. This section also set up a requirement that persons servicing refrigerant-containing equipment must be certified to perform the recapture and recycling of the refrigerant during motor vehicle air conditioning services. CFC-containing small-quantity items, such as party streamers, noise horns, cleaning fluids for photooptic and electrical equipment, and other nonessential consumer products are banned. Hydrochlorofluorocarbons (class II substances) are banned from aerosol containers or plastic foam products. Labeling On all containers of class I or class II substances, mandatory warning labels are required. In addition, products manufactured with a class I substance must also have a warning label on the final product unless substitutes are not available. Class II substances in products or used in making products must have a warning label indicating that they contain ozone-depleting substances.

TITLE VII — ENFORCEMENT PROVISIONS Title VII modernizes, updates, and increases enforcement provisions of the act. Title VII enforcement provides a much more severe set of penalties for noncompliance with the Clean Air Act. In addition to violations and fines, the Clean Air Act institutes new environmental crimes and raises to the felony level a knowing violation of any provisions of the act, in addition to penalties for failure to comply with the permit requirements of Title V. Administrative penalties include up to $25,000 per day per individual violation (to a maximum of $200,000) and up to $5000 for a field citation for a minor violation of any aspect of the regulations. For civil violations, penalties up to $25,000 per day per violation, with no maximum, are possible. Criminal penalties include up to 15 years in jail and penalties of up to $1 million dollars. Clean Air Crimes By far the most severe penalties follow from the creation of new crimes. People who knowingly release hazardous air pollutants and potentially endanger the life of another person may receive up to 15 years imprisonment and fines up to $250,000. For negligent releases of HAPs that endanger another individual, misdemeanor prosecutions may be pursued. Knowingly violating a record-keeping provision becomes a felony. In addition, convicted persons may make their companies ineligible for any future federal contracts, grants, or loans. The EPA may extend this prohibition to other facilities owned or operated by a convicted person.



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Violations of the provisions of a state implementation plan carry a potential individual fine of up to $250,000 or maximum imprisonment of 5 years. Failure to monitor emissions and certify compliance with specific emission limitations may lead to violations. The amount of civil penalties has been increased, and the definition of an operator of a stationary source is now “any person who is senior management personnel or corporate officer.” Compliance monitoring, as provided in earlier titles, puts the burden on sources of air contaminations to prove compliance once the EPA makes a prima facie showing that the violation is likely to have continued. Successive violations of any provision of the act may lead to doubling of the original penalties imposed. Sources are required to certify their compliance and to report their own violations. No right of appeal is provided from issuance of administrative compliance orders. Citizens were given a “private right of action” in Title VII to sue for civil penalties. Awards up to $100,000 may be applied for “beneficial mitigation projects which are consistent with this Act and enhance the public health or the environment.” If an alleged violation in the past has been repeated, the citizens may sue over these past violations. Monetary awards up to $10,000 are provided to citizens for information leading to penalties on violators. Criminal liability has been substantially expanded. Sources may be held criminally liable for the negligent acts of an employee who faces no liability under the Title VII amendments.

TITLE VIII — MISCELLANEOUS PROVISIONS A number of additional provisions have been included under the miscellaneous sections of the Clean Air Act. Visibility and Source Receptor Concepts The act set up visibility transport regions and corresponding Visibility Transport Commissions. These commissions deal with the interstate transport of air pollutants into class I PSD areas. The purpose of these commissions is to evaluate all information regarding visibility effects and to recommend policies and strategies for addressing regional haze. Recommendations address how air quality is to be protected through clean air corridors — areas in which additional restrictions on emissions may apply — and potential regional regulations for visibility impairment. Programs sponsored by the EPA and the park service, as well as other federal agencies, are conducted to provide a foundation for developing visibility control programs. The effects of all other provisions of the act are to be assessed for their effect on visibility reduction and haze. Grand Canyon Visibility Transport Commission In 1996, the Grand Canyon Visibility Transport Commission made a series of recommendations that were transmitted to the EPA in accordance with the Clean Air Act Amendments. The recommendations included:


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•

• •

• •

Preventing and reducing per capita air pollution through policies based on energy conservation, increased energy efficiency, and promotion of the use of renewable resources for energy production Tracking emissions growth that may affect air quality in clean air corridors, which are key sources of clear air in class I areas Continuing cooperative relationships and creating new ones between local, state, tribal, federal, and private interests to develop new strategies, expand data collection, and improve modeling for reducing or preventing visibility impairment in areas within and adjacent to parks and wilderness areas Endorsing national strategies aimed at further reducing tailpipe emissions, including the so-called 49-state low-emission vehicle Implement programs to reduce emissions and visibility effects from prescribed fires and to educate the public about the continued need for prescribed fires to reduce the spread of dangerous wildfires.

Other provisions of Title VIII required that the EPA, in conjunction with the National Aeronautics and Space Administration and the Department of Energy, conduct a study-and-test program on the development of a hydrogen fuel cell electric vehicle. The study-and-test program determined how to transfer existing National Aeronautics and Space Administration hydrogen fuel cell technology into a massproducible, cost-effective hydrogen fuel cell vehicle. Research and development by the government and the private sector concerning hydrogen fuel cell vehicles is continuing.

INTERNATIONAL TREATIES MONTREAL PROTOCOL A significant environmental treaty, the Montreal Protocol on Substances that Deplete the Ozone Layer, was adopted in 1987 and is the basis for Title VI of the Clean Air Act. The Montreal Protocol’s chief aim was to reduce and eventually eliminate the production and use of man-made ozone-depleting compounds. By ratifying the terms of the Montreal Protocol, signatory nations committed to take actions to protect the ozone layer, hoping in the long term to reverse the damage that had been done by the use of ozone-depleting substances. There have been four amendments to the Montreal Protocol, all dealing with various aspects of emission standards regarding the protection of the ozone layer. [The four amendments to the Montreal Protocol are named according to the city where the amendments were signed, thus: London (1990), Copenhagen (1992), Montreal (1997), and Beijing (1999).] These amendments recognized the need for additional adjustment of standards in response to various political or environmental issues. This program has been an outstanding success, as noted in Chapter 8.

KYOTO ACCORDS At a conference held in 1997, in Kyoto, Japan, the Parties to the UN Framework Convention on Climate Change agreed to a historic protocol to reduce greenhouse



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gas emissions by harnessing the forces of the global marketplace to protect the environment. Key aspects of the Kyoto Protocol included emissions targets, timetables for industrialized nations, and market-based measures for meeting those targets. The protocol was intended, according to the EPA, to make a down payment on the meaningful participation of developing countries. However, the Kyoto Protocol was notable for its lack of regulations of developing countries’ emissions. The United States has stated its desire to secure meaningful developing country participation. The Kyoto Protocol, a treaty, was signed by President Clinton in 1998, with the stated intention of never submitting it to the U.S. Senate for approval. Subsequently, President Bush in 2001 withdrew the signature of the United States, calling the protocol “fatally flawed.” As such, the Kyoto Accords, subject to expiration in 2012, will likely never gain the binding force of law in the United States. Recent data have indicated that all of the present signatories to Kyoto have failed to meet their targeted goals of CO2 reduction.

THE INFLUENCE OF NONREGULATORY GOVERNMENTAL ACTIONS There are two major areas that may significantly affect air quality management strategies and, in particular, compliance. The first of these comprises nonregulatory documents or activities. The second deals with court decisions. The influence of nonregulatory documents or activities cannot be ignored. These include policies, administrative or executive orders, guideline documents, and standard test methods. Policies of a regulatory body set priorities and internal preferred strategies for regulatory action that are not spelled out by regulations. These are discretionary decisions that may have a significant effect on individuals, localities, or sources of emissions. Administrative or executive orders tend to focus on either organization or priorities for resources within an organization. Typically, an air quality management agency has limited resources and, therefore, must prioritize those that are available for dealing with the multitude of laws, regulations, enforcement, and monitoring programs currently in effect. These orders may significantly affect or delay action by regulatory bodies, such as action concerning a permit. Guideline documents are written reports of approaches, favored techniques, or models that, although not legally required to be followed, form the basis of most procedures in determining compliance. Even when incorporated by reference into laws or regulations, these guideline documents may be changed without changes in either the law or the regulations themselves. Thus, they have the force and effect of law without going through the legislative process. Methods of testing and analysis may have a significant effect on compliance or air quality management strategies. Inventories of relative emission rates of different contaminants are highly dependent on the monitoring or test methods used in formulating those inventories. Thus, if a monitoring or test method is in error or does not accurately represent the true day-to-day emissions of various sources of air contaminants, significant errors in the inventories may result. This error would


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lead to an inappropriate emphasis on one strategy, which might be virtually ineffective in actually lowering pollutant concentrations. Thus, appropriate monitoring or test methods may be at the heart of choosing effective strategies to attain the ambient air quality standards. Accuracy of the models (such as the Urban Airshed Model) that are used as tools in evaluating strategies may a have significant effect on the emission reduction regulations being adopted.

COURT DECISIONS The EPA issued revised standards for ozone and particulate matter (smog and soot) in July 1997. These revised standards were the subject of a multiyear appeals process, in which industry groups affected by the change challenged the law on constitutional grounds. In 2001, the U.S. Supreme Court in Whitman v. American Trucking Associations unanimously upheld the constitutionality of the Clean Air Act as the EPA had interpreted it in setting health-protective air quality standards. The Supreme Court also reaffirmed the EPA’s long-standing interpretation that it must set these standards based solely on public health considerations without consideration of costs. This decision represents the most significant Supreme Court precedent regarding air pollution laws in the early 2000s. Decisions by courts function as clarifications for either laws or regulations. Court decisions are typically based on a point of law that is brought to bear on a deficiency in a regulation or law. Or they may clarify apparently conflicting laws as to which law has priority. The air quality management field is replete with lawsuits in which court decisions are used to force either agencies or sources of air-contaminant emissions to address a particular problem that is a focus of the lawsuit. Lawsuits filed by environmental groups in the past have forced the EPA, for instance, to list chemicals for regulation. In general, court decisions tend to clarify or redirect priorities for regulatory bodies. Citizen lawsuits also form a large portion of court decisions, and many cases are “taken on” as representative of the public interest.

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10

Management, Trends, and Indoor Air Quality

There is yet another expedient, which I have here to offer by which the City and environs about it, might be rendred one of the most pleasant and agreeable places in the world … That all low-grounds circumjacent to the City, be cast and contriv’d into square plots, or fields of twenty, thirty and forty akers, … That these be elegantly planted, diligently kept and supply’d, with the most fragrant and odoriferous flowers … roses … lavander … rosemary … But even the whole City, would be sensible of the sweet and ravishing varieties of the perfumes … Fumifugium, 1661

In the field of air quality management and the improvement of our environment, our first task is to come to a true understanding and definition of the problem. This includes understanding trends in air quality from the past to the present, the approaches that have been successful, those trends (and new issues) perceived for the future, and the relative contribution of air quality levels to our personal environment. Each of these is interrelated in the big picture of air quality resources and their management. The scale of the issues in air quality management range from individual health to the potential for vegetation effects at the regional or continental scale. Global issues, such as intercontinental pollutant transport, are worldwide in scope. Other considerations that must be taken into account are the trends in effectiveness that we have seen through previous efforts at managing air quality resources. If we take these into account we will be better able to understand the success or failure of approaches taken in the past. Each approach to air quality management has a cost. And all resources are limited to some degree, and therefore we must find a proper balance among a number of factors, among which are: human health, the naturally occurring background contaminant concentrations, the relative importance of anthropogenic versus natural sources, the costs to provide different levels of control, and even the potential for adaptation to different levels of air quality or to global impacts. One of the areas of recent concern is indoor air quality. There are significantly different pollutant gas concentrations indoors than outdoors. Therefore, the approaches taken for protecting indoor air quality must be of a different kind than those taken for the exterior environment. Likewise, the issues of societal preference versus personal freedom enter the picture.

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ELEMENTS OF AIR QUALITY MANAGEMENT Management as a technical discipline has been described as one in which five distinctive steps are continuously being performed. These include: •

• • • •

Definition — With the management of any operation or resource, the first step must be a full definition of both the objective and the problems that appear to interfere with attainment of the objective. Planning — The next step in management is to plan the approach: how and what is to be accomplished in the management scheme. Implementation — The implementation of the planned approach requires the execution of each of these steps and the enforcement of the steps. Control — Control of the activities involved that lead to the attainment of the defined objective. Evaluation — The final step in the process is an evaluation of the effectiveness of each of the previous steps.

In the chapter opening quote from Fumifugium, John Evelyn touched upon each of these steps from the objective (the city of London becoming one of the most pleasant places in the world), to the evaluation of the effectiveness of the approaches taken. The goal was that the whole city would be sensible of the sweetness of the air. There are strong correlations between general management and the approaches taken in air quality management. Figure 10.1 is the air quality analog of a typical management plan to improving air quality by an iterative process. A definition of the effects of air pollutants on the general population, and an assessment of the objective — minimal levels of air contaminant emissions — is our starting point. With respect to concentrations and effects, we have seen earlier that there is general agreement on human health impacts for criteria air pollutants. These are verified in the setting of air quality standards. Noncriteria air contaminants have much less data available, and therefore the evaluation of effects and acceptable levels is still somewhat unclear (beyond risk reduction approaches). This leads to the second step in the process: an evaluation of strategies that may be most effective in attaining the desired goal. These evaluations consist of analyzing Air pollutant concentrations & effects Control strategies & evaluations Legislation & enforcement Sources & emissions Transportation & transformation

FIGURE 10.1 Elements of air quality management.



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the trends monitored in ambient air and comparing them to the approaches adopted in the past. Ongoing research in atmospheric chemistry, investigations of emissions control improvements, and different approaches to emission reduction are factors included in these evaluations. The next step is to implement the control strategies by legislation and enforcement action. This step impacts sources and their emissions. Implementation of selected control strategies by legislation and enforcement proceed from an understanding of air pollution effects and control strategies. In the United States, the Clean Air Act has set a fairly definitive implementation strategy for the attainment of national ambient air quality standards. The sources of emissions reflect the scale and the sectors of society that are most impacted by the adopted strategies. As seen for stationary sources, a greater emphasis is now being placed upon emission reduction by pollutant prevention, while the emphasis on continual process modifications and more effective control technologies has continued. Indirect approaches have focused on techniques to reduce the number of vehicle miles traveled for automobiles, as well as tighter emission standards for each automobile on the road. Other approaches have taken the form of encouraging mass transit, controlling land use, cap-and-trade emission strategies, supporting car pooling programs, and additional taxes on emissions of undesirable contaminants. Changes in future power plants and fuels for mobile sources will be one area in which air quality management strategies will focus on feasibility and technology research. Transport and transformation of contaminants in the air will lead to the attainment of the desired levels of air quality or to a reevaluation of further control strategies. If the latter are indicated, we again “enter the cycle.” The transportation and transformation of air contaminants in the atmosphere are an ongoing area of research. A better understanding of dispersion and location effects leads to a better understanding of source impacts at local receptor sites, particularly for hazardous air pollutants. As our understanding of air pollutant effects is refined, there will be changes in control strategies and a re-evaluation of existing strategies for attaining acceptable levels of air quality.

NONREGULATORY AIR QUALITY MANAGEMENT APPROACHES A number of other approaches may also help to reduce air contaminants, both in the near- and long-term. These approaches are societywide, and include industrial action and consumer awareness. Source reduction, a strong point in many of the new approaches to hazardous waste minimization, has a corresponding benefit in the air quality management field. In general, activities that reduce the generation of hazardous waste also contribute to decreases in fugitive HAP emissions. On the industrial side, one of the programs voluntarily agreed to by more than 300 major industrial firms was the “33/50” program. In this effort, industrial manufacturing firms agreed to a 33% reduction in hazardous waste by the end of 1992 and a 50% reduction by 1995. Attained decreases were greater for air contaminant emissions, especially of VOC and hazardous organic air pollutants.


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TRENDS The trends we speak of include air quality levels, contaminant emissions, and management strategies to attain those desirable goals. Based on an assessment of the trends and previous strategies used to set those trends, we are better able to forecast improved techniques and approaches.

TRENDS

IN

EMISSIONS

Significant emission reductions have been accomplished in the last 35 years of national air quality management strategies. Figure 10.2 illustrates the reduction in emissions over this period for the criteria pollutants and organic compounds (as a surrogate for ozone). Over 50% reductions in national emissions of CO, VOCs, and SO2 have occurred in this time period. Emissions of PM10 have been reduced by about 80% while lead emissions (not shown) have been reduced from 221,000 tons per year to about 3000 tons per year. Figure 10.3 illustrates the significant reductions of CO emissions over the same 35-year period. A number of new areas have attained the federal ambient CO air quality standards in the last few years, including Los Angeles. Well in excess of 98% of all lead emissions have been eliminated. The majority of these have been in the transportation source category. The lead ambient air quality standard is being attained in all but a few localized monitoring sites in the country. Oxides of nitrogen emission trends (Figure 10.4) have shown about a 20% reduction overall. The reductions occurred primarily because of improvements in transportation emissions. As a result of these efforts, the majority of ambient air quality monitoring stations are reporting attainment status nationwide for NO2.

200 180

Millions of tons

160 140 120 100 80 60 40 20 0 CO

NOx

VOC 1970

PM10

SO2

2004

FIGURE 10.2 Reduction in emissions for criteria pollutants and organic compounds.



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30 250 NOx - millions of tons/year

CO-millions of tons/year

25 200

150

100

50

0

20

15

10

5

1970 Transportation Industrial

2002 Fuel combustion Miscellaneous

FIGURE 10.3 Downward CO emission trends.

0



FIGURE 10.4 Downward NOx emission trends.

Reductions in SO2 emissions (Figure 10.5) over the same period exceed 40% and have been predominantly in the industrial and fuel combustion areas. Ambient air quality for sulfur dioxide shows attainment for the overwhelming majority of air quality monitoring sites. PM10 emissions (Figure 10.6) show a dramatic lowering of emissions by twothirds over the period. This was due primarily to reductions in PM10 from industrial processes and fuel combustion. However, a number of areas are still in nonattainment status for PM10. VOC emissions are seen in Figure 10.7. Over the period, the emissions of VOC have dropped by over 50%. These much lower emissions levels, in the face of population increases of 43% in the period, have contributed to the dramatic improvement in air quality, especially in the nonattainment areas.

TRENDS

IN THE

EXTREME OZONE AREA

With respect to ozone, the most significant trends in the United States are those seen in the single extreme nonattainment area, the Los Angeles basin. It has the longest history of both monitoring ozone and implementing source control strategies. In Figure 10.8 are the monitored reductions in ozone for 45 years in Southern California at three sites that exceeded the federal standard. Significant in this figure are the decreases in the number of days exceeding the federal AAQS as a result of dedicated effort. Central Los Angeles achieved dramatic reductions in going from more than 150 days per year over the 1 hour standard to only 1 day in the last 5 years. Other



35

14

30

12

PM10 - millions of tons/year

SO2 - millions of tons/year

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25 20 15 10 5 0

10 8 6 4 2

1970

0

2002

Transportation Industrial

Fuel combustion Miscellaneous

FIGURE 10.5 SO2 emission trends.


FIGURE 10.6 Downward PM10 emission trends.

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VOCs - millions of tons/year

30

25

20

15

10

5

0




FIGURE 10.7 Downward VOC emission trends.



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Days over O3 standard

200

160

120

80

40 0 1960

1965

1970

1975

1980

1985 Year

1990

West LA

Long Beach

1995

2000

2005

Los Angeles

FIGURE 10.8 Ozone reductions in Southern California.

locations, being closer to the ocean, have exceeded the 1-hour ozone standard only once in the last 15 years. This figure points out the dramatic reductions due to rigorous air quality management approaches in the face of increasing population. Probably the most significant impact has been the reduction in the total number of days, basinwide, of high ozone (federal alert) levels over the last 30 years. In Figure 10.9 are the number of days that federal alert (0.20 ppm) and second stage 160 140

Days Over Alert Level

120 100 80 60 40 20 0

6

7 19

80

19

84

19

>0.35ppm

88

19

92

19

96

19

00

20

04

20

>0.20ppm

FIGURE 10.9 Reduction in ozone alert days in Southern California.


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ozone episodes (0.35 ppm) occurred during any single day. Since 1989 there have been no second stage episodes anywhere in California. Federal alert levels have been reduced from over 120 days per year in 1977 to only 1 day since 2000. These reductions in elevated ozone readings are a result of aggressive implementation of air quality management strategies in Southern California. In this most extreme case of ozone nonattainment, a continuing downward trend has occurred in which significantly fewer hours and days are experiencing even moderate ozone levels. Likewise, fewer nonattainment days of the federal 8-hour average ambient ozone standard are occurring. Thus it appears that within Southern California, some areas will continue to experience days of poor air quality for the foreseeable future, though the trend is for continuous improvement.

TRENDS

IN

STRATEGY

As a result of the emissions and continuing ambient air quality patterns seen to date, a number of future trends may be inferred. The most interesting case, of course, is seen in Southern California, which is the “test case” for many air quality strategies. Seven general categories are seen as the focus of these management trends: • • • • • • •

Fuels and transportation Small sources Governance Hazardous air pollutants Lifestyle impacts Stationary sources Natural sources

Fuels and Transportation Across the board, cleaner fuels will be pushed by all levels of governmental authority. With respect to mobile sources, we may expect to see compressed natural gas as a near-term fuel source. Diesel fuels will be subject to more stringent specifications. The long-term trend is for all transportation in areas of poor ozone air quality to involve some form of electrical powered individual vehicles, coupled with significant attempts to provide mass transit for the commuting work force. Fuel cells burning hydrogen will continue to be pushed as the “power plant” of the future due to the low air emissions from those power plants. True success with fuel cells will be problematic. For heavy-duty vehicles powered by diesel fuel, with its problems of NOx and particulate matter, the emphasis will change to enhancing combustion within the engine (for NOx control), cleaner diesel fuel and more effective particulate filters for PM10/PM2.5 emissions. Railroads, long out of the picture for emissions (apart from visible pollution), are the next target due to the use of diesel engines; ports and harbors will also be added to the list. Agricultural operations, also long exempt from most air quality regulations, are now subject to increased regulations. Permits, at the state or local level, will be required for the first time.



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Small Sources In the more serious nonattainment areas for criteria pollutants, there will be an increasing focus on smaller and smaller sources of air contaminants. With Southern California as an example, increasing regulations on consumer products, such as solvent content of cosmetics, perfumes, paints, barbecue lighter fluid, and windshieldwashing fluids, will be seen. Small combustion sources, such as home hot water heaters, small boilers and pool heaters, will be required to install natural gas burners utilizing high-efficiency, low NOx combustion systems. Continuous pilot light combustion systems will be banned. Small engines will require permits and be subject to emission limits. As the regulatory burden continues to reach out to all segments of society, not only will consumer products be affected, but also smaller businesses. Small businesses will continue to be held to a strict level of air emissions limitations; however, there will be temporary fee breaks or assistance programs to help small businesses survive. Governance As a result of public pressure, greater public input may be expected on all aspects of air pollutant reporting and permitting of stationary sources. As seen in the Clean Air Act, one person’s objection to the issuance of an operating permit may cause the entire permitting process to halt and enter a minimum additional 30-day hearing period before any permit is granted. The concept of stakeholders has entered into the regulatory lexicon, which means that in addition to individuals, more nongovernmental organizations (NGOs) and special interest groups will have a greater input in rule development, approvals for permits to operate, and citizen lawsuits. The concept of environmental justice — where expectations of equal air quality are required — will enter the requirements for planning, permits, and rule making by regulatory agencies. Where development projects may cause a localized increase in air pollutants, Localized Significance Thresholds — emission limitations from a proposed area source project — may be invoked. These thresholds will require greater control of emissions during construction or operation of the area source than would otherwise be required under national or state ambient air quality standards. Local environmental justice councils will become part of NGOs with a stake in local decision making. One of the more interesting emerging concepts is the precautionary principle. It advocates requiring additional governmental and regulatory action when an activity raises potential threats of harm to human health or the environment, even if causeand-effect relationships are not fully established. Enforcement will enter a new stage with the advent of remote sensing devices and digital surveillance cameras. The technology includes remote emissions sensing from tail pipes and point sources coupled with optical recorders to capture the identity of vehicles with high emissions. Computers will be used to log the information and forward it to the enforcement divisions of regulatory agencies.


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To complement enforcement, taxes will be increasingly used as a method of reducing emissions. Heavier penalties will ensue for persons in charge of air pollutant-emitting sources; personal liability for emissions will enter the picture. An increasing federalization of air quality management strategies, regulations, planning, and permitting will be seen with states limited to purely local issues. More federal departments, in addition to the EPA, will find a need to have an air quality element in their regulations. As a result of increasing pressures on budgets for various levels of government, the future will see a greater number of fee-based services as a part of air quality management strategies. Every service or action required as a result of new rules will be reviewed by various arms of government for which specific fees will be assessed for each reviewer. This will include reviews of indirect source plans; performance reviews of risk assessments and dispersion models; reviews and evaluations of selfmonitoring data; and evaluations of the adequacy and attainment of air toxic hot spots regulations. At the local level, as backlogs increase at regulatory agencies because of increasing regulations, there will be attempts to streamline operations. One will be a requirement that standardized equipment, such as hot water heaters, package boilers and certain coating operations, be certified by the manufacturer as meeting stringent air emission standards throughout the life of the equipment with emissions monitoring data submitted for each type of equipment. Use of tax incentives and tax credits to direct technologies and to encourage conservation and greater efficiency will be used in the near term. These will include tax incentives to encourage construction of clean coal facilities; to expand wind, geothermal, and biomass production of energy; to increase production of power from nuclear power plants; and tax credits for alternative powered vehicles. Finally, there will be greater emphasis in dealing with long-range transport of air emissions, within local jurisdictions, between states and, ultimately, from country to country. The Clean Air Interstate Rule (CAIR) — impacting primarily electric power producing facilities — is the first of such regulation and is unlikely to be the last. Hazardous Air Pollutants As a result of concerns over hazardous air pollutants, there will be an increasing focus on all toxic and noncriteria contaminants. They will include both carcinogens (suspected or promoters) and noncarcinogens that may contribute to other detrimental health effects. These will require increasing controls, as these emissions are orders of magnitude lower than the criteria contaminant emissions. Promulgation of mandatory maximum available control technology (MACT) standards for stationary sources of hazardous air pollutants will be completed. The MACT rules for residual risk at major hazardous air pollutant (HAP) sources and rules for area sources will be finalized. Industries will continue to review the possibilities for using the MACT allowable “off-ramp” process to be subject to less stringent controls or escape new HAP controls if the facility can demonstrate that



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its HAP emissions show low risk (i.e., where additional HAP controls would provide little or no public health benefits). As a result of the unknowns involved in noncriteria air contaminant effects, there will be an increasing emphasis on risks to health because of noncriteria air contaminant emissions. Risk assessments will, therefore, continue to occupy a large part of the concern for allowing emission sources to continue to receive permits. The risk assessment process will be streamlined to meet the demand for more risk based decisions. Lifestyle Impacts Increasingly, more aspects of individual lifestyle will be impacted. The focus will be on curbing or restricting individual mobility (i.e, fewer cars driven by IC engines), consumer products with fewer VOCs, and smaller combustion sources. In certain areas, prohibitions on solid fuels, such as wood stoves and wood burners — unless controlled by either high-temperature thermal systems, precipitators, or other particulate control strategies — will be required. There will be a much greater emphasis on indirect sources. In particular, these regulations will focus on vehicle usage and attempts to reduce not only the total number of miles traveled, but also the number of individual trips taken. Attempts to reduce the number of miles traveled focus on the emissions during operation. Limits on the numbers of vehicle registrations allowed, additional parking lot usage fees, mandatory delayed starts of workdays, and bans on single occupant vehicles are proposed as backup measures to control mobile source emissions in extreme nonattainment areas. Stationary Sources Employers will continue to be the enforcers of air quality management regulations. In Southern California, employers have been held responsible for the transportation modes of employees and their willingness to join car pools, van pools, and other methods of reducing indirect source (auto) emissions. In the extreme nonattainment areas, “dirty” liquid fuels will be banned for all stationary sources except for essential public services or emergencies. Solid fuels are already effectively banned. Routine testing of emergency diesel equipment such as standby power generators, once a monthly event for periods of up to an hour, will be severely limited as to time periods and frequency. Diesel fuel will be increasingly refined. There will be increasing attempts to incorporate air pollution “bubbles” on stationary sources. These will set a cap on total emissions for each individual source and a cap on the emissions throughout an entire region. These programs will involve both internal and external trading and the issuance of air pollution certificates or credits, which may be bought and sold. As sources reduce emissions beyond that required by law, those excess emission reduction credits will become available to other sources which may need “offsets” for new source emission increases.


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There will be an increasing emphasis on self-reporting of emissions or alternative process parameters, which may be correlated to emissions. These will include continuous emission monitors (CEM) for large sources and the installation and monitoring of fuel flow, solvents, raw materials and paints for lesser sources. Remote sensing and reporting of emissions will also be applied to stationary sources from outside plant boundaries. Additional management approaches will be required for stationary sources, which will involve certifications of employee training, “clean” operating practices, additional record-keeping and reporting, as well as continued testing of emissions to verify compliance. As the regulatory burden increases, both business and industry will struggle to meet air pollution codes. This will lead to relocations of industries to areas with less severe attainment status. Some businesses, however, will find increasing opportunity. These businesses will be the manufacturers of air pollution control equipment, those providing engineering and consulting services, and those providing measurement and analysis services to affected stationary and mobile sources. Natural Sources Even nature will not be exempt. PM10 emissions from wind erosion are considered sources subject to human control. Control actions will be required from private landowners, particularly during construction activities. Air quality management plans in Southern California have proposed maximum speeds of 15 miles per hour on improved public and private roads to be appropriate for PM10 emissions in arid nonattainment areas. On the other hand, the federal government has allowed the implementation of the Natural Events Policy (NEP) that may be invoked when natural events (hurricanes, high wind events, etc.) deteriorate air quality in spite of applicable regulations. This is important when attainment of national ambient air quality standards, especially PM10/PM2.5, is threatened. When the NEP is invoked, those days of poor air quality may not be used in determining maximum daily or annual average pollutant levels. Whether the NEP will be applied to international sources of air pollution is unknown.

THE OUTLOOK Overall air pollutant concentrations will continue to drop; however, it may be expected that these concentrations will approach some asymptotic level with the implementation of these strategies, particularly with increasing population trends. Highly urbanized areas in locations with low inversions, coupled with existing background concentrations of NOx and high natural sources of reactive hydrocarbons, such as terpines, may find it nearly impossible to reach the new federal ozone standards. At that point, other strategies may be implemented. Upgrading buildings and indoor air quality to counterbalance the time spent in the outdoor environment (where the air quality may not achieve federal standards) could come to the fore. This brings us to the next concern: indoor air quality.



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INDOOR AIR QUALITY At the personal level, there is significant concern for the quality of the air inside residences and public buildings. Figure 10.10 shows the percent of a person's day spent inside buildings, as opposed to that time spent outside or in transit for the average person in the United States. As a result of the emphasis in the United States, even developing countries are now concerned with indoor air. Remaining indoors during high air pollutant episodes is one method that allows a person to breath more easily with a modest amount of lifestyle interruption. Regulatory agencies have been recommending for decades that people remain indoors to avoid serious air pollutant episode levels. However, this advice is increasingly being questioned because of new information on the levels of air contaminants found indoors. Table 10.1 lists common contaminants in the indoor environment in urbanized settings. With respect to reactive gases like sulfur dioxide and ozone, the advice to remain indoors on a smoggy day is well taken. These reactive gases have short half-lives

Outside 8% In transit 6%

Indoors 86%

FIGURE 10.10 The percent of the day the average person in the United States spends inside, outside, and in transit.

TABLE 10.1 Indoor Air Pollutants of Concern Criteria Pollutants Radon Environmental Tobacco Smoke Combustion Emissions: CO, NO2, Particles, Polycyclic Aromatic Hydrocarbons Formaldehyde Volatile Organic Compounds Pesticides Bio-aerosols, e.g., molds, spores, infectious agents


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SO2 concentration (µg/m3)

60 50 40 30 20 10

Site: 1

9

7

4 Outdoor

5

2

3

8

Indoor

FIGURE 10.11 Concentrations of SO2 measured simultaneously indoors and in the outside ambient environment for eight sites in the Kansas City area.

in an indoor environment. Figure 10.11 shows the relative concentrations of SO2 measured simultaneously indoors and in the outside ambient environment for eight different sites in the Kansas City area. Ozone, in the absence of high voltage sources such as photocopiers or electrostatic precipitator equipment, shows reductions in indoor air quality concentrations as opposed to those outdoors. However, other gases, such as NO2, may exhibit appreciably higher concentrations indoors than outdoors due to the mode of generation. Figure 10.12 shows the levels of NO2 at various points in a residence compared to those concentrations simultaneously measured outside of the structure. Depending on location, the indoor NO2 concentration varies from two to three times higher indoors. This residence had a natural gas fired stove and oven combination that was used for cooking. Other measurements of noncriteria pollutants, such as organic gases, show significantly higher concentrations indoors as opposed to outdoors, as well. Table 10.2 lists the results of simultaneous testing of a large number of sources indoors and outdoors for different organic gases. The ratios of personal exposure indoors to those levels found outside range from a factor of three times higher (with styrene) to over twenty times higher for contaminants such as 1-1-1 trichloroethane (TCA). The variety of indoor air contaminants of concern range from the obvious, such as tobacco smoke, to the less obvious, such as bio-aerosols, which include molds, spores, and other infectious agents. Of all of the contaminants to which people may be exposed in the indoor urban environment, the number one risk factor is tobacco smoke and includes lifestyle, occupational, and indoor exposures. With respect to lung cancer and early or premature death, smokers who are exposed to radon experience the synergistic effects of both. Other volatile organic compounds, such



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200 180 160

NO2, µg/m3

140 120 100 80 60 40 20 0 0200 0400 0600 0800 1000 1200 1400 1600 1800 2000 2200 2400 Time, hr Kitchen, 1 m from stove Living room Bedroom Outside of structure

FIGURE 10.12 Diurnal indoor/outdoor pattern for NO2 in a home (composite day based on six days of data).

TABLE 10.2 Indoor-Outdoor Relationships — Organic Gases Arithmetic Mean Compound 1,1,1-Trichloroethane Benzene Carbon Tetrachloride Trichloroethylene Styrene m,p-Dichlorobenzene Xylenes

Ambient Air, µg/m3

Indoors, µg/m3

5.4 8.6 1.2 2.1 0.9 1.5 15.0

110 30 14 7.3 2.7 56 71

as formaldehyde, are also on the list of indoor chemicals found in the indoor urban environment. Table 10.3 summarizes the usual sources of indoor air pollutants, which include combustion, building materials, consumer products, people and, to a lesser degree, infiltration of outdoor air.


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TABLE 10.3 Sources of Indoor Air Pollutants Combustion Sources Tobacco smoke Woodburning stoves Kerosene heaters

Gas stoves Automobiles in attached garages

Building Materials and Furnishings Particleboard Caulks Paints Carpeting Adhesives Consumer Products Pesticides Cleaning materials Waxes, polishes

Cosmetics, personal products Hobby materials

People Outdoor Air Ozone CO

Perceived indoor air quality issues common to office workers in buildings are called building-related occupant complaint (BROC) syndrome, or “sick-building” syndrome. Not the same, but related issues, such as building-related illnesses (BRI) do have clinical symptoms associated with disease such as Pontiac fever or Legionnaires disease. These are more properly biological factors than air pollutant factors.

ENVIRONMENTAL TOBACCO SMOKE That smoking indoors causes indoor air pollutants is a fact. Table 10.4 lists measured concentrations of air contaminants in a variety of smoking environments, as compared to nonsmoking controls in similar indoor structures. Tobacco smoke is a complex mixture of thousands of volatile, semivolatile, and particulate organic and inorganic compounds formed from the smoldering combustion of tobacco leaves. In general terms, mainstream smoke is tobacco smoke that is inhaled directly by the smoker and then exhaled. Sidestream smoke is tobacco smoke that is emitted by the smoldering end of the cigarette between puffs. Environmental tobacco smoke (ETS) is “aged” sidestream tobacco smoke that nonsmokers are exposed to in areas sharing a common air volume. The range of vapor phase constituents from tobacco smoke are listed in Table 10.5 on a mass basis per cigarette. Many of these compounds come under the heading of “tar.” The EPA has estimated that the health effects of environmental tobacco smoke include approximately 3,000 excess lung cancer deaths per year and trigger 8,000 to 26,000 new cases of asthma in previously unaffected children. Symptoms are exacerbated in 400,000 to 1 million asthmatic children per year.



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TABLE 10.4 Tobacco-Related Contaminant Levels in Indoor Spaces Contaminant

Type of Environment

Levels in Smoking Area

CO

Room (18 smokers) 15 restaurants Arena (11,806 people) Bar and grill Bingo hall Fast food restaurant Restaurant Bar Room (18 smokers) Restaurant Arena

50 ppm 4 ppm 9 ppm 589 µg/m3 1140 µg/m3 109 µg/m3 63 ppb 21 ppb 500 µg/m3 5.2 µg/m3 9.9 ng/m3

PM

NO2 Nicotine Benzo-α-pyrene

Nonsmoking Controls 0.0 ppm 2.5 ppm 3.0 ppm 63 µg/m3 63 µg/m3 24 µg/m3 50 ppb 48 ppb — — 0.69 ng/m3

Studies of nonsmoking office workers exposed to ETS have a demonstrated reduction in small airway function, comparable to smokers who consume between one and ten cigarettes per day. Studies conducted in Japan have shown that nonsmoking wives of smoking husbands have a significantly elevated risk of developing lung cancer compared to nonsmoking households. Other risks of environmental tobacco smoke are the production and emission of radioactive decay products of radon acting synergistically. Radon daughters, which are particulate matter, remain suspended in the atmosphere for long periods of time and provide a vehicle for the transport of radon progeny into the lungs. Chemical fertilizers used in growing tobacco are transported through the crop chain due to the use of phosphorus-containing fertilizers. These compounds have been associated with radioactive polonium, found to be a cancer-causing agent highly correlated with tobacco smoke. Analyses of the particle size of cigarette smoke (0.1 to 0.5µ) indicate that the predominant particle sizes are in the aerodynamic range most likely to cause deposition in lungs.

RADON The relationship between high radon levels and lung cancer death in uranium and other mines has been known for decades. Only recently have we become aware of radon’s subtle health risks in homes and other indoor dwellings under normal living conditions. Radon, which emanates from soil, building materials, water, and air, is now understood to have some role in the cause of lung cancer. Radon is produced by the decay of radium, another element which occurs naturally in rocks and soil. It is estimated by the EPA that in the United States, 7,000 to 30,000 lung cancer deaths occur annually because of indoor radon. Radon is the heaviest of all naturally occurring inert or noble gases. In the periodic table, it is element number 86. Since it is an inert gas, it is not prone to


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TABLE 10.5 Some Vapor-Phase Constituents of Sidestream Cigarette Smoke Compound NOx CO HCN NH3 Ethene Propene 1,3-Butadiene Dimethylamine Formaldehyde Acetaldehyde Acrolein Acetone Propenal 2-Butanone Crotonaldehyde Benzaldehyde N-Pentanal Benzene Toluene Styrene N-Nitrosodimethylamine Nicotine Formic Acid Acetic Acid Methyl Chloride Pyridine Phenol Catechol Aniline 2-Toluidine 4-Aminobiphenyl Benz(α)anthracene

µg/Cigarette 750 58,000 100 9,450 2,100 1,550 360 40 2,000 4,700 1,090 1,080 390 720 280 80 60 650 1,260 100 0.9 1,230 525 1,500 940 370 230 170 10.8 3.0 0.14 0.14

chemical reactions and, therefore, as soon as it is produced, it is able to move freely through pores in soil and cracks through walls. Radon is also radioactive, it will decay into another element as soon as it is produced, eventually ending up as a stable element — lead. Outdoors, the risk from radon or radon daughters is very slight. However, inside a building, the release of radon gas to the outside is blocked, and it accumulates in the dwelling. Even in well-ventilated dwellings, the indoor level is higher than



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outside. With well-constructed and well-insulated homes, radon may accumulate to high levels. Radon gas is soluble in cold water; however, its solubility decreases with increases in temperature. Since the gas is constantly being produced naturally from rocks and soil, all homes and buildings contain some radon as natural background. There are 27 known isotopes of radon. The most common radon isotopes are radon 219 (Rn-219, also called actinon), radon 220 (Rn-220, also called thoron), and radon 222 (Rn-222). Most indoor radon is Rn-222. The elements formed from decay are referred to as daughters. The three types of radiation are alpha, beta, and gamma. Alpha particles are helium nuclei. The basic unit of radioactivity, set by the International Radium Standard Commission, is the curie (Ci). One curie equals 37 billion (or 3.7 × 1010) disintegrations per second of radioactivity, which was arbitrarily set for general use. The magnitude of the curie was historically based on the activity of radium and is approximately equal to the rate of decay of one gram of Ra-226 per second. However, as the accuracy of measurements increased, the exact value has changed. Since the radioactivity of radon is very small, it is usually reported in picocuries (pCi), or 10-12 curies. The amount of radioactivity of radon is reported per liter of air. The EPA regards 4 pCi/l as the “action level” for indoor radon and recommends remedial action if the level is higher. Other agencies recommend remedial action at different levels. The EPA standard is a statistical one and is not based on a threshold health effect. The 4 pCi/l level is the rounded off geometric mean value of homes tested in the United States plus one standard deviation.

RADON

IN

BUILDING SOURCES

Soil Radon in soil gas is affected by several factors, including radium content and distribution, the porosity of the soil, moisture content, density and the material types, and the underlying bedrock. The radium content of soils reflects the different types of parent bedrock from which the soils were derived. Rock types with high uranium concentration are granites, metamorphosed igneous rocks, and shales. Soil-gas radon levels vary widely even in small areas, such as within a housing tract, and are not well-correlated with radium content of the soil. Soil porosity has a high correlation with soil-gas radon. High permeability soils in combination with very small pressure differentials in buildings increase indoor radon levels easily. In soils, such as sand and gravel, radon diffusion is high. On the other hand, relatively impermeable soils, such as clays, do not have a high enough porosity to allow a significant amount of soil gas into the structure. Figure 10.13 is an EPA map that shows the average concentration of radon in counties for three zones: counties with soils exhibiting over 4 pCi/l in air (Zone 1), between 2 and 4 pCi/l (Zone 2), and less than 2 pCi/l (Zone 3). It should be remembered that any individual location or even structure may have significantly different radon levels than seen here.


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Legend Zone 1 Zone 2 Zone 3

FIGURE 10.13 Average concentration of radon in U.S. counties.

Fractured bedrock may also be an important contributor to high indoor radon levels. This fractured bedrock is from the sheared and fractured rocks associated with mountain building. Fractures allow transport of radon from great depth, where uranium can be located along the fractures. The major mechanism of radon transport through soil into structures is pressure differential. The stack effect (Figure 10.14) is due to atmosphere, building, and soil gas pressure differentials. The stack effect is a major contributor to air infiltration, especially in winter. Atmospheric pressure differentials of 1% to 2%, due to warm/cold front passage, produce inversely proportional changes in the radon levels. Increased atmospheric pressure forces air into the ground while lower atmospheric pressure draws the air together with radon from the ground. Water In the United States, about half of the population relies on ground water, while the other half relies on surface water, rivers, or lakes for water supplies. Among those who use underground waters, most use public supplies that are treated and distributed. Those who use underground water drawn directly from private wells or from community wells may have the water supply as the major source of indoor radon. When the ground water is exposed to the air, the radon content will be reduced drastically, within days, to a low level, typically around 10 pCi/l. Also when the water is heated or agitated, radon in water is reduced dramatically. Thirty to seventy percent of radon will be released from the water just by running water out of a faucet. Over 90% of the radon will be released from water when a dishwasher or clothes washer is used. This can be a significant indoor radon problem for families that use high radon content ground water directly from the well.



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Indoor radon

Ventilation Domestic water; natural gas

Outdoor Rn

Floorboard joints Ventilation

Crawl space Rn

Rn Loose-fitting pipes

Basement

Floor Diffusion drain

Cracks

Floor-wall joint

In soil: Ra→Rn

Weeping tile sump system

FIGURE 10.14 Building stack effect.

Building Materials Although concrete is one of the strongest emitters of radon, most building materials have relatively low source strengths. The use of phosphate slag in concrete in the United States has been studied, and it has been estimated that there are as many as 74,000 homes built with concrete containing up to 19,980 pCi/l of Ra-226. Bricks tend to have slightly higher Ra-226 concentrations but have significantly lower radon emission rates than concrete. Red bricks are thought to have higher uranium content than lighter-colored bricks. However, since red bricks are mostly used in the exterior of the buildings, they are of less concern. Other building materials, such as granite, marble, sandstone and volcanic rocks, have a wide range of Ra-226 concentrations and radon emanation rates. Overall, most building materials in the majority of homes in the United States do not have significant problems with radon.

MEASUREMENT

AND

ACTION LEVELS

EPA publications contain guidelines for radon and radon progeny sampling procedures, and provide guidance for using seven different types of instruments. For radon measurements, the instruments are charcoal canister, alpha-track detector, grab


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sampling, and continuous radon monitor. For radon daughter measurements, continuous working level monitors, radon progeny integrated sampling units, and grab sampling are available. If the radon level is found to be less than 4 pCi/l, no action is required. However, a follow-up measurement is considered a good idea. Although there may be some risk of lung cancer, reduction from this low level is not easy. If the measured radon level is between 4 and 20 pCi/l, the EPA recommends follow-up tests to determine the average levels for each season of the year. If followup tests indicate a similar level, the EPA recommends the level be reduced to less than 4 pCi/l within a few years. If the level is between 20 to 200 pCi/l, a follow-up test within three months is recommended. If the level is higher than 200 pCi/l, the EPA recommends immediate remedial action. Follow-up measurements are recommended within a week of remediation.

HOUSE CHARACTERISTICS

AND

RADON GAS ENTRY

There are many types of dwelling structures. Some are constructed on grade, while others are either subgrade or above grade. Basements are subgrade, while wood houses are constructed above grade over a foundation. The space between the grade surface and the bottom of the floor is the crawl space. Homes on grade have a cement slab under the floor. Basements are most vulnerable to radon entry. There are usually cracks between the floor and the walls of the basement. Additionally, there are numerous holes and cracks in the walls and spaces around pipes and wiring conduits. Due to the stack effect, radon gases can enter dwellings easily. Houses built over a cement slab are usually built over sand or gravel that may or may not be sealed. Sealants are commonly used to prevent moisture from entering the cement and are also effective in preventing radon entry. However, cracks can form in slabs, around pipes, and other openings that are not sealed tight enough.

MITIGATION In all mitigation techniques, the goal is to reduce the indoor concentration of radon. Depending on the measured concentration of radon, costs range from inexpensive to costly. If mitigation is necessary, homeowners are usually advised to contact state or local agencies for advice in the selection of a mitigation technique. In some states a contractor’s license is required to engage in radon mitigation. If the radon concentration is low, some EPA recommended measures may suffice: avoid areas of higher radon concentration (that is, spend less time in the basement or areas of the house directly above the soil). Also, stairwell doors, fireplace dampers, and laundry chutes that go to the basement may be closed to reduce radon from lower levels. One should also keep in mind that combustible appliances can cause negative pressurization inside the dwelling. The most effective mitigation technique is to replace indoor air with outside air. In moderate climates ventilation is perhaps the least costly method. Increasing the



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Fan

Duct

Sand or gravel

FIGURE 10.15 Schematic diagram of subslab ventilation system.

ventilation of the living spaces by opening windows is usually recommended. Crawl space vents, if so equipped, may be opened to the outside of the structure. Subslab ventilation (Figure 10.15) is the current recommended “mechanical fix.” Here, clean outside air is drawn into the sand/subslab materials that vent the soil gas away from the structure, thus reducing the infiltration rate. Visible holes, including the exposed soil in the basement, are sealed off. The exposed soil in the crawl space is also sealed. Other holes and cracks to look for and seal include uncapped sump pits, floor drains, perimeter drains, utility penetrations, and cracks in walls and floors. Cracks and pores on block walls may not be easily spotted. Airborne particles may be removed by fans, filters, or electrostatic precipitation. Figure 10.16 illustrates the relative effectiveness of each in reducing the gas and particulate phase radioactivity for the polonium, bismuth, and lead isotopes resulting from radon decay. Of course, with any collector, it will eventually become a source following usage. Care must be taken for disposal of the collected media. In extreme climates, where opening windows for ventilation is not feasible, forced air ventilation with heat recovery may be cost effective. The process works best when the indoor–outdoor temperature differentials are large. The indoor air is drawn through a heat-recovery ventilator where the heat of the indoor air is transferred to the cooler outdoor air. Heated outdoor air is then supplied into living areas through ducting, while the stale air is blown out.


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16

A Attached activity Unattached activity

14 B 12 Concentration (pCi/L)

A 10

C

A

A = Ra A(Po-218) B = Ra B(Pb-214) C = Ra C(Bi-214)

A 8

A 6 B

B

C

4

B

C 2

C

B C

0

Baseline

Box fan

Ceiling fan Treatment

ESP

Filter

FIGURE 10.16 Effect of various air treatments on attached and unattached radon decay product levels.

OTHER INDOOR AIR CONTAMINANT CONCERNS Formaldehyde, a listed carcinogen, while it may be much lower on the list of hazards, nevertheless is present in a significant number of residences. Sources of formaldehyde include pressed wood products, such as plywood, particle board, and fiberboard, which are made using urea formaldehyde resins. These compounds are chemically unstable, and in the presence of moisture, they undergo hydrolysis to liberate gaseous formaldehyde. A number of symptoms have been associated with this, such as eye irritation. Emission rates of these components range from 10 to 15 mg/m2 per day for new sources of pressed wood products. In addition, free formaldehyde trapped in the resin may be volatilized as a function of heat and time. It is the release of unreacted formaldehyde that is primarily responsible for the high initial formaldehyde levels associated with these emission sources. Mobile homes, with a significant percentage of these products, represent the largest single category of high indoor formaldehyde buildings.



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Urea formaldehyde insulation products represent the next largest category of sources with a emission rate of 15 mg/m2 per day. Other sources include furnishings, fabrics, paper plates and cups, carpets, and clothing with much lower emission rates of formaldehyde. Other contaminants and their sources that may contribute to indoor air quality relate to poor combustion. The combustion contaminants, carbon monoxide, nitric oxide, PM10, aldehydes, and hydrocarbons, are readily generated from stoves, heaters, gas appliances, and wood-burning equipment or fireplaces operating under conditions of poor combustion. Ozone may build up in confined spaces typically associated with photocopy machines or in locations where attempts are made to clean the air by use of ion generators. The latter, due to their high voltages, will build up concentrations of ozone, particularly if they are in confined spaces. Asbestos, occurring in acoustical ceilings, tiles, and insulation, is the focus of significant regulatory action for school children, as well as some public buildings. The key element in asbestos exposure is whether the material has been disturbed and whether fibers are being released. In many cases, an optimum solution is to ensure that asbestos-containing materials are not disturbed. Clean-out, removal, and remediation of asbestos-containing materials are the subject of an extensive body of regulatory requirements. The known health effects of both lead and mercury are sufficient to warrant concerns for older buildings and structures containing lead and mercury in paints. These materials may represent significant hazards should they be in a poor state of surface condition, causing sloughing of paint fragments into the atmosphere, or where exposure to children may occur where these materials are deteriorating. Again, the removal of these materials or stabilizing them in place represents a significant investment in lowering exposures to these contaminants. (It should be remembered that old paint may not be the only source of exposure of children to lead. An exposé in Southern California in 2004 by a local newspaper revealed that minority children were receiving high doses of lead in flavored candy imported from Mexico!) In general, for most indoor air contaminants, the approaches taken to lessen public exposures and reduce human health effects have been primarily under the category of source reduction. These include elimination of smoking, either by local ordinance or as a building management requirement. Increasing the ventilation rate, or the number of air exchanges per hour in buildings, has provided significant reductions (up to 90%) in indoor air contaminants. Improving or eliminating poor combustion will significantly improve the quality of the indoor air. This will reduce the combustion contaminants as well as eliminate particulates containing toxic compounds. For instance, putting in a gas-fired artificial log in the fireplace rather than using wood will lower air contaminant emissions by orders of magnitude, thus improving ambient air quality as well as preventing the blow-back of combustion contaminants into the structure from a poorly burning woodpile in a fireplace. Replacing gas burning equipment containing pilot lights with equipment having electronic ignition will significantly improve indoor air quality.


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Elimination of certain solvents, paints, and chemicals and/or replacement of products containing formaldehyde may be considered a significant source reduction approach which will eliminate air contaminants. Building “bake-outs” in which the temperature of the building when unoccupied is artificially raised to high temperatures while increasing the air exchange rates to the maximum feasible have not been found to be particularly effective. It should be remembered that there are no known residential air quality standards in the United States. However, many building owners have expressed interest in voluntary cleanups of hazards for buildings to which the public has access.

PUBLIC BUILDINGS There are a variety of indoor building-related occupant complaint syndromes that come under the heading of indoor air pollution or poor indoor air quality. In some cases, the syndromes have been lumped under the term sick building syndrome. There are distinctions, however. Building-related illness (BRI) is a known circumstance where occupants possess clinical disease symptoms. The symptoms have been found to be closely associated with bacterial infections as a result of organisms growing in, or in association with, heat exchangers and condensers used for building air conditioning and ventilation. Building sickness is usually considered an issue that may be more of perception than reality when it comes to common air contaminants. In fact, it is believed that such complaints possess a multifaceted cause. In general, the issue appears to be more occupant comfort than air pollution. In a recent investigation in California where building occupant complaints were registered, 13 office buildings were selected for study. Three had natural ventilation, three had simple mechanical ventilation (fans), and six were air conditioned with sealed windows. Data was collected from 880 occupants along with weeklong measurements of indoor and outdoor concentrations of VOCs, CO2, and carbon monoxide, and short-term measurements of fungi and bacterial counts. In addition, temperature and humidity were monitored to determine the results. The symptoms monitored included runny nose, stuffy nose, throat irritation, sleepiness, difficulty in breathing, chills, and skin irritation. The results from the California Healthy Building Pilot Study are summarized in Table 10.6. In this table, the prevalence of the symptoms is expressed as the ratio of the number of complaints for mechanical (fan) or air-conditioned ventilation systems to a natural (or open-window) structure. These ratios were adjusted in a linear regression model for gender, job, race, education, age, and smoking. The average ratio as well as the range of prevalence/odds ratios for each specific symptom was calculated. Significantly higher ratios for both the air-conditioned and simple mechanical ventilation were found for chills and skin irritation, with lesser prevalence ratios for throat irritation and difficulty in breathing. Findings of this study found that the higher symptoms were associated with: • • •

Higher job stress Use of carbonless copy machines Use of photocopiers



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TABLE 10.6 California Healthy Building Pilot Study, Prevalence Odds Ratios* Ventilation Type Symptoms Runny nose Stuffy nose Throat irritation Sleepiness** Difficulty breathing** Chills** Skin irritation**

Natural

Simple Mechanical

Air Conditioned

1.0 1.0 1.0 1.0 1.0 1.0 1.0

1.7 1.9 2.6 2.0 2.3 4.8 4.1

1.3 1.6 2.5 1.9 2.5 4.9 3.3

* Adjusted in a logistic regression model for gender, job, race, education, age, and smoking. ** Adjusted in a logistic regression model only for gender.

• • •

Female gender New carpets No window within 15 feet of the work station

Other findings of this study indicated that the highest levels of CO2 were found in air-conditioned buildings along with the least thermal discomfort. The lowest levels of airborne fungi were found for air-conditioned buildings. The most significant finding was that there was no relationship between the symptoms reported and total volatile organic compounds measured in the structures. Thus, the issue of perception versus actual contaminant concentrations appears to dominate the issue. Nevertheless, good management practice would require that even perceived symptoms be alleviated. Better training, higher ventilation rates, and more windows could contribute to lessened complaints in addition to better humidity and bio-aerosol control. A number of technologies may be adapted from stationary source approaches to control indoor air pollutants where they do occur. The technologies include electrostatic precipitators, scrubbers, activated carbon adsorption units, and high efficiency filters.

INDOOR AIR POLLUTION IN DEVELOPING COUNTRIES The concerns for indoor air quality have raised the consciousness of many people to the situation in developing countries. The key fact is that half of the world’s population cooks with solid fuels on inefficient stoves. More than a third of the world’s 2.4 billion people use biomass (wood, crop residues, charcoal, and dung) for cooking and heating. Of these, approximately 800 million people depend solely on crop residues and dung. It is a technology that has changed little since the Stone


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Age. If coal is included, a total of 3 billion people — approximately half the world’s population — cook with solid fuel. As a result, smoke in homes from these cook stoves is the fourth greatest risk factor for death and disease in the world’s poorest countries, and, according to the World Health Organization, is linked to 1.6 million deaths per year. The burden tends to fall predominately on women and children due to their greater indoor air exposure and family positions. It is estimated that smoke in the home is one of the world’s leading child killers, claiming nearly 1 million children’s lives each year. Illness caused by smoke is reported to kill more children annually than malaria or HIV/AIDS. The main cause of children’s death from indoor air pollution is acute lower respiratory infections (ALRI). ALRI is the world’s leading killer of children under the age of 5. The solutions to poor indoor air quality are complex and include elevating the overall economic conditions of the people exposed and raising the consciousness of local communities and Third World government leaders to the importance of indoor air, coupled with technology improvements, clean fuels, solar panels, and increased hygiene. If modern society is to truly manage its air quality, it can do no less. While we have come a long way, there is still much to be done, particularly on indoor air quality.


List of Acronyms AAQ ACGIH AEL AQMP ARARs AVOR BACM BACT BIF BOF BOOS BRI BROCS BTU CAA CAIR CEM CERCLA CFC CO COH CONCAWE CTGs DES DRE EKMA EPA EPCRA ESP ETS FIFRA FIP GACT GCM HAP HCFC

ambient air quality American Conference of Governmental Industrial Hygienists acceptable exposure level air quality management plan applicable, relevant, and appropriate regulations average vehicle occupancy rate best available control measure best available control technology boilers and industrial furnaces basic oxygen furnace burners out of service building-related illness building related occupant complaint syndrome British thermal unit Clean Air Act Clean Air Interstate Rule continuous emission monitors Comprehensive Emergency Response, Compensation, and Liability Act chlorofluorocarbon carbon monoxide coefficient of haze Conservation of Clean Air and Water, Western Europe Control Technique Guidelines diethyl stilbestrol destruction and removal efficiency Empirical Kinetic Modeling Approach Environmental Protection Agency Emergency Planning and Community Right to Know Act electrostatic precipitator environmental tobacco smoke Federal Insecticide, Fungicide, and Rodenticide Act Federal Implementation Plan generally available control technology general circulation model hazardous air pollutant hydrochlorofluorocarbon

307


308

HDT HFC ICE ICRP IDLH I/M LAER LDT LEV LFL LPG MACT MMH MSA MW NAAQS NAMS NAPAP NESHAPs NIOSH NOAEL NOEL NSPS NSR OCS OEL OSHA PAN PCB PEL PIC PM POHC POTWs PSD PSI psi P-V RACT RCRA RFP RICE


heavy duty truck hydrofluorocarbon internal combustion engine International Council on Radiation Protection immediately dangerous to life and health inspection and maintenance lowest achievable emission rate light duty truck low emission vehicle lower flammability limit liquefied petroleum gas maximum available control technology maximum mixing height metropolitan statistical area megawatt national ambient air quality standard National Air Monitoring Station National Acid Precipitation Assessment Program National Emission Standards for Hazardous Air Pollutants National Institute for Occupational Safety and Health No Observed Adverse Effect Level No Observed Effect Level New Source Performance Standard New Source Review outer continental shelf occupational exposure level Occupational Safety and Health Administration peroxyacyl nitrate polychlorinated biphenyl permissible exposure level product of incomplete combustion particulate matter principal organic hazardous constituent publicly owned treatment works Prevention of Significant Deterioration pollutant standards index pounds per square inch pressure-volume reasonably available control technology Resource Conservation and Recovery Act reasonable further progress reciprocating internal combustion engine


List of Acronyms

RVP SARA SCR SDCF SI SICs SIP SLAMS SNCR SPM STEL TCA TCE TDI TLV TSCA TSDFs TWA TPY ULEV URF UV VMT WHO ZEV

reid vapor pressure Superfund Amendments and Reauthorization Act selective catalytic reduction standard dry cubic foot spark ignited Standard Industrial Classifications State Implementation Plan state and local air monitoring station selective noncatalytic reduction special purpose monitor short-term exposure level trichloroethane trichloroethylene toluene diisocyanate threshold limit value Toxic Substances Control Act treatment storage and disposal facilities time-weighted average ton per year ultra-low emissions vehicle unit risk factor ultraviolet vehicle miles traveled World Health Organization zero emission vehicle

309



Glossary abatement The reduction in degree or intensity (or elimination) of pollution. acceptable daily intake (ADI) The highest daily amount of a substance that may be consumed over a lifetime without adverse effects. acid deposition A comprehensive term for the various ways acidic compounds precipitate from the atmosphere and deposit onto surfaces. It can include: (1) wet deposition by means of acid rain, fog, and snow; and (2) dry deposition of acidic particles (aerosols). acid rain Rain which is especially acidic (pH

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