AIR QUALITY MANAGEMENT IN THE UNITED STATES
THE NATIONAL ACADEMIES PRESS
Washington, D.C.
www.nap.edu
THE NATIONAL ACADEMIES PRESS
500 Fifth Street, NW Washington, DC 20001
NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.
This project was supported by Grant No. X-82822101-0 between the National Academy of Sciences and the U.S. Environmental Protection Agency. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the organizations or agencies that provided support for this project.
Library of Congress Cataloging-in-Publication Data
Air quality management in the United States / Committee on Air Quality Management in the United States, Board on Environmental Studies and Toxicology, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies.
p. cm.
Includes bibliographical references and index.
ISBN 0-309-08932-8 (hardback)—ISBN 0-309-51142-9 (pdf)
1. Air quality management—United States. I. National Research Council (U.S.). Committee on Air Quality Management in the United States.
TD883.2.A64325 2004
363.739′25′0973—dc22
2004014594
Additional copies of this report are available from: The
National Academies Press
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Copyright 2004 by the National Academy of Sciences. All rights reserved.
Printed in the United States of America
THE NATIONAL ACADEMIES
Advisers to the Nation on Science, Engineering, and Medicine
The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences.
The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Wm. A. Wulf is president of the National Academy of Engineering.
The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine.
The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. Wm. A. Wulf are chair and vice chair, respectively, of the National Research Council.
COMMITTEE ON AIR QUALITY MANAGEMENT IN THE UNITED STATES
WILLIAM CHAMEIDES (Chair),
Georgia Institute of Technology, Atlanta
DANIEL GREENBAUM (Vice-Chair),
Health Effects Institute, Boston, MA
CARMEN BENKOVITZ,
Brookhaven National Laboratory, Upton, NY
EULA BINGHAM,
University of Cincinnati, Cincinnati, OH
MICHAEL BRADLEY,
M.J. Bradley & Associates, Concord, MA
RICHARD BURNETT,
Health Canada, Ottawa, Ontario
DALLAS BURTRAW,
Resources for the Future, Washington, DC
LAURENCE CARETTO,
California State University, Northridge
COSTEL DENSON,
University of Delaware, Newark
CHARLES DRISCOLL,
Syracuse University, Syracuse, NY
JANE HALL,
California State University, Fullerton
PHILIP HOPKE,
Clarkson University, Potsdam, NY
ARNOLD HOWITT,
Harvard University, Cambridge, MA
C.S. KIANG,
Peking University, Beijing, China
BEVERLY LAW,
Oregon State University, Corvallis
JAMES LENTS,
University of California, Riverside
DENISE MAUZERALL,
Princeton University, Princeton, NJ
THOMAS MCGARITY,
University of Texas School of Law, Austin
JANA MILFORD,
University of Colorado, Boulder
MICHAEL MORRIS,
North Central Texas Council of Governments, Arlington
SPYROS PANDIS,
Carnegie Mellon University, Pittsburgh, PA
P. BARRY RYAN,
Emory University, Atlanta, GA
ADEL SAROFIM,
University of Utah, Salt Lake City
SVERRE VEDAL,
National Jewish Medical and Research Center, Denver, CO
LAUREN ZEISE,
California Environmental Protection Agency, Oakland
Project Staff
RAYMOND A. WASSEL, Project Director
LAURIE S. GELLER, Senior Program Officer
K. JOHN HOLMES, Senior Program Officer
AMANDA C. STAUDT, Senior Program Officer
KARL E. GUSTAVSON, Program Officer
CHAD A. TOLMAN, Staff Officer
RUTH E. CROSSGROVE, Editor
RAMYA CHARI, Research Assistant
MIRSADA KARALIC-LONCAREVIC, Research Assistant
EMILY L. BRADY, Senior Program Assistant
DOMINIC A. BROSE, Program Assistant
Sponsor: U.S. Environmental Protection Agency
BOARD ON ENVIRONMENTAL STUDIES AND TOXICOLOGY
Members
JONATHAN M. SAMET (Chair),
Johns Hopkins University, Baltimore, MD
DAVID ALLEN,
University of Texas, Austin
THOMAS BURKE,
Johns Hopkins University, Baltimore, MD
JUDITH C. CHOW,
Desert Research Institute, Reno, NV
COSTEL D. DENSON,
University of Delaware, Newark
E. DONALD ELLIOTT,
Willkie, Farr & Gallagher, LLP, Washington, DC
CHRISTOPHER B. FIELD,
Carnegie Institute of Washington, Stanford, CA
WILLIAM H. GLAZE,
Oregon Health and Science University, Beaverton
SHERRI W. GOODMAN,
Center for Naval Analyses, Alexandria, VA
DANIEL S. GREENBAUM,
Health Effects Institute, Cambridge, MA
ROGENE HENDERSON,
Lovelace Respiratory Research Institute, Albuquerque, NM
CAROL HENRY,
American Chemistry Council, Arlington, VA
ROBERT HUGGETT,
Michigan State University, East Lansing
BARRY L. JOHNSON
Emory University, Atlanta, GA
JAMES H. JOHNSON,
Howard University, Washington, DC
JUDITH L. MEYER,
University of Georgia, Athens
PATRICK Y. O’BRIEN,
ChevronTexaco Energy Technology Company, Richmond, CA
DOROTHY E. PATTON,
International Life Sciences Institute, Washington, DC
STEWARD T.A. PICKETT,
Institute of Ecosystem Studies, Millbrook, NY
ARMISTEAD G. RUSSELL,
Georgia Institute of Technology, Atlanta
LOUISE M. RYAN,
Harvard University, Boston, MA
KIRK SMITH,
University of California, Berkeley
LISA SPEER,
Natural Resources Defense Council, New York, NY
G. DAVID TILMAN,
University of Minnesota, St. Paul
CHRIS G. WHIPPLE,
Environ Incorporated, Emeryville, CA
LAUREN A. ZEISE,
California Environmental Protection Agency, Oakland
Senior Staff
JAMES J. REISA, Director
DAVID J. POLICANSKY, Scholar
RAYMOND A. WASSEL, Senior Program Officer for Environmental Sciences and Engineering
KULBIR BAKSHI, Senior Program Officer for Toxicology
ROBERTA M. WEDGE, Senior Program Officer for Risk Analysis
K. JOHN HOLMES, Senior Program Officer
SUSAN N.J. MARTEL, Senior Program Officer
SUZANNE VAN DRUNICK, Senior Program Officer
EILEEN N. ABT, Senior Program Officer
ELLEN K. MANTUS, Senior Program Officer
RUTH E. CROSSGROVE, Senior Editor
BOARD ON ATMOSPHERIC SCIENCES AND CLIMATE
Members
ERIC J. BARRON (Chair),
Pennsylvania State University, University Park
RAYMOND J. BAN,
The Weather Channel, Inc., Atlanta, GA
ROBERT C. BEARDSLEY,
Woods Hole Oceanographic Institution, Woods Hole, MA
ROSINA M. BIERBAUM,
University of Michigan, Ann Arbor
RAFAEL L. BRAS,
Massachusetts Institute of Technology, Cambridge
CASSANDRA G. FESEN,
Dartmouth College, Hanover, NH
MARGARET A. LEMONE,
National Center for Atmospheric Research, Boulder, CO
MARIO J. MOLINA,
Massachusetts Institute of Technology, Cambridge
WILLIAM J. RANDEL,
National Center for Atmospheric Research, Boulder, CO
RICHARD D. ROSEN,
Atmospheric & Environmental Research, Inc., Lexington, MA
JOHN C. WYNGAARD,
Pennsylvania State University, University Park
Ex Officio Members
EUGENE M. RASMUSSON,
University of Maryland, College Park
ERIC F. WOOD,
Princeton University, Princeton, NJ
Staff
CHRIS ELFRING, Director
JULIE DEMUTH, Program Officer
SHELDON DROBOT, Program Officer
AMANDA STAUDT, Senior Program Officer
ELIZABETH A. GALINIS, Senior Program Assistant
ROB GREENWAY, Senior Program Assistant
DIANE L. GUSTAFSON, Administrative Coordinator
ROBIN A. MORRIS, Financial Associate
OTHER REPORTS OF THE BOARD ON ENVIRONMENTAL STUDIES AND TOXICOLOGY
Endangered and Threatened Fishes in the Klamath River Basin: Causes of Decline and Strategies for Recovery (2004)
Cumulative Environmental Effects of Alaska North Slope Oil and Gas Development (2003)
Estimating the Public Health Benefits of Proposed Air Pollution Regulations (2002)
Biosolids Applied to Land: Advancing Standards and Practices (2002)
Ecological Dynamics on Yellowstone’s Northern Range (2002)
The Airliner Cabin Environment and Health of Passengers and Crew (2002)
Arsenic in Drinking Water: 2001 Update (2001)
Evaluating Vehicle Emissions Inspection and Maintenance Programs (2001)
Compensating for Wetland Losses Under the Clean Water Act (2001)
A Risk-Management Strategy for PCB-Contaminated Sediments (2001)
Acute Exposure Guideline Levels for Selected Airborne Chemicals (3 volumes, 2000–2003)
Toxicological Effects of Methylmercury (2000)
Strengthening Science at the U.S. Environmental Protection Agency (2000)
Scientific Frontiers in Developmental Toxicology and Risk Assessment (2000)
Ecological Indicators for the Nation (2000)
Modeling Mobile-Source Emissions (2000)
Waste Incineration and Public Health (1999)
Hormonally Active Agents in the Environment (1999)
Research Priorities for Airborne Particulate Matter (4 volumes, 1998–2003)
Ozone-Forming Potential of Reformulated Gasoline (1999)
Arsenic in Drinking Water (1999)
The National Research Council’s Committee on Toxicology: The First 50 Years (1997)
Carcinogens and Anticarcinogens in the Human Diet (1996)
Upstream: Salmon and Society in the Pacific Northwest (1996)
Science and the Endangered Species Act (1995)
Wetlands: Characteristics and Boundaries (1995)
Biologic Markers (5 volumes, 1989–1995)
Review of EPA’s Environmental Monitoring and Assessment Program (3 volumes, 1994–1995)
Science and Judgment in Risk Assessment (1994)
Pesticides in the Diets of Infants and Children (1993)
Dolphins and the Tuna Industry (1992)
Science and the National Parks (1992)
Human Exposure Assessment for Airborne Pollutants (1991)
Rethinking the Ozone Problem in Urban and Regional Air Pollution (1991)
Decline of the Sea Turtles (1990)
Copies of these reports may be ordered from The National Academies Press (800) 624-6242 or (202) 334-3313
Preface
Recognizing the central role that science and engineering plays in air quality management and anticipating the next congressional reauthorization of the Clean Air Act and its amendments, the United States Congress directed the U.S. Environmental Protection Agency (EPA) to arrange for a study by the National Academy of Sciences (1) to evaluate from a scientific and technical perspective the effectiveness of the major air quality provisions of the Clean Air Act and their implementation by federal, state, tribal, and local government agencies; and (2) to develop scientific and technical recommendations for strengthening the nation’s air quality management system with respect to the way it identifies and incorporates important sources of exposure to humans and ecosystems and integrates new understandings of human and ecosystem risks. In response, the National Research Council established the Committee on Air Quality Management in the United States, which prepared this report. Biosketches of the committee members are presented in Appendix A.
In the course of preparing this report, the committee met in public sessions in Washington, D.C.; Denver, Colorado; Los Angeles, California; and Atlanta, Georgia, where local, state, and federal officials and representatives from the private sector and nongovernmental organizations, including regulated industries and advocacy groups, were invited to meet with the committee and present their views on air quality management. Interested members of the public at large were also given an opportunity to speak on these occasions. The committee received oral and written presentations from the following individuals:
Daniel Albritton, National Oceanic and Atmospheric Administration Aeronomy Laboratory; William Becker, Association of Local Air Pollution Control Officials; Robert Brenner, EPA; Cynthia Burbank, Federal Highway Administration; Tim Carmichael, Coalition for Clean Air; Michael Chang and Rodney Weber, Georgia Institute of Technology; Patrick Cummins, Western Governors’ Association; Gregory Dana, Alliance of Automobile Manufacturers; Frank Danchetz, Georgia Department of Transportation; Joan Denton, California Office of Environmental Health Hazard Assessment; Howard Feldman, American Petroleum Institute; John Froines, University of California at Los Angeles; Mike Kenny, California Air Resources Board; Eric Fujita, Desert Research Institute; Norma Glover and Barry Wallerstein, South Coast Air Quality Management District; Charles Goodman, Southern Company; Richard Jackson, Centers for Disease Control and Prevention; Kip Lipper, California State Senator Sher’s office; Patricia Mariella, Gila River Indian Community; Barry McNutt, U.S. Department of Energy; Christopher Miller, Environment and Public Works Committee, U.S. Senate; Frank O’Donnell, Clean Air Trust; Harold Reheis, Georgia Department of Natural Resources; Catherine Ross, Georgia Regional Transportation Authority; Chet Tisdale, King and Spaulding; Paige Tolbert, Emory University; Cindy Tuck, California Council for Environmental and Economic Balance; Andrew Wheeler, Clean Air, Wetlands, Private Property, and Nuclear Safety Subcommittee, U.S. Senate; and Robert Yuhnke, Robert Yuhnke and Associates.
In addition to the information from those presentations, the committee made use of the peer-reviewed scientific literature, government agency reports, and unpublished databases, as well as related statistics and data directly obtained from EPA.
This report consists of seven chapters. The first chapter provides an overview of the committee’s charge, the issues related to this charge, and the approach the committee took in completing its task. Chapters 2–6 review the current air quality management system in the United States and assess how well this system is operating. Chapter 7 looks to the future; it identifies the major air quality challenges the nation is likely to face in the coming decade and advances a set of five interrelated recommendations for enhancing the nation’s air quality management system to meet these challenges. The Executive Summary provides a brief overview of the committee’s findings and recommendations. The more-detailed Summary is presented immediately after the Executive Summary. Readers who are well versed in the current operation of air quality management in the United States or who do not need to become well versed may wish to move directly from the Executive Summary or Summary to Chapter 7. The recommendations in
Chapter 7 relate to Chapters 2–6, where the detailed background information and justification for the recommendations are provided.
We wish to thank James Mahoney for his valuable service as a member of the committee during the early stages of this study. He resigned appropriately from the committee upon becoming assistant secretary of commerce for oceans and atmosphere and deputy administrator of the National Oceanic and Atmospheric Administration. The committee’s work was assisted by staff of the NRC’s Board on Environmental Studies and Toxicology (BEST) and its Board on Atmospheric Science and Climate. We wish to thank Raymond Wassel, project director, and James Reisa, director of BEST. Scientific and technical information was provided by Laurie Geller, K. John Holmes, Karl Gustavson, Amanda Staudt, Chad Tolman, Jhumoor Biswas, Ramya Chari, Mirsada Karalic-Loncarevic, and Rachel Hoffman. Craig Hicks assisted with science writing. Invaluable logistical support was provided by Emily Brady and Dominic Brose. The report was ably edited by Ruth Crossgrove.
William L. Chameides, Chair
Daniel S. Greenbaum, Vice Chair
Acknowledgment of Review Participants
This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by NRC’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report:
William Agnew, General Motors (retired); Thomas Burke, Johns Hopkins University; Paul Crutzen, Max Planck Institute for Chemistry; Gregory Dana, Alliance of Automobile Manufacturers; E. Donald Elliott, Willkie, Farr & Gallagher, LLP; David Hawkins, Natural Resources Defense Council; Walter Heck, North Carolina State University; Timothy Larson, University of Washington; Leonard Levin, Electric Power Research Institute; Arthur Marin, Northeast States for Coordinated Air Use Management; Michael Myer, Georgia Institute of Technology; Joseph Norbeck, University of California, Riverside; John Seitz, Sonnenschein, Nath & Rosenthal, LLP; Thomas Tietenberg, Colby College; John Watson, Desert Research Institute; Catherine Witherspoon, California Air Resources Board; Terry Yosie, American Chemistry Council.
Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by Robert Frosch, Harvard University, and Edwin Clark II, Clean Sites. Appointed by the NRC, they were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.
Figures and Tables
FIGURES
ES-1 |
Idealized schematic showing the iterative nature of air quality management, |
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S-1 |
Comparison of growth areas and emission trends, |
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S-2 |
To meet the major challenges that will face air quality management (AQM) in the coming decade, the committee identified a set of overarching long-term objectives, |
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S-3 |
Plot of the estimated relative trends in emissions versus ambient concentrations of various primary pollutants (PM10, NOx, SO2, Pb, and CO), |
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1-1 |
Schematic of the factors influencing the pollutant mix in the atmosphere and the resultant impacts of pollution, |
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1-2 |
National average emission categories for carbon monoxide (CO), sulfur dioxide (SO2), nitric oxide and nitrogen dioxide (NOx), volatile organic compounds (VOCs), particulate matter less than 10 micrometers in diameter (PM10), and particulate matter less than 2.5 micrometers in diameter (PM2.5) for 2001, |
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1-3 |
Idealized schematic showing three of the four sequential activities carried out by the nation’s air quality management system, |
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1-4 |
Comparison of growth areas and emission trends, |
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1-5 |
Electricity generation by fuel in billion kilowatt hours, 1949–1999, and projections for the Reference Case, 2000–2020, |
1-6 |
Counties in the continental United States where any NAAQS were violated in 1999, |
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1-7 |
High cancer risk counties for urban air toxics in 1996 by county, |
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1-8 |
Potential violations of the PM2.5 (1999–2000 data) and 8-hr O3 (1997–1999 data) NAAQS by county, |
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2-1 |
Flow diagram illustrating the process by which the EPA administrator reviews and sets a new NAAQS, |
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2-2 |
Timeline illustrating historical sequence of the periodic NAAQS reviews and final decisions carried out by EPA since the passage of the 1970 CAA Amendments, |
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2-3 |
Foliar injury to cotton induced by chronic exposure to ozone, |
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2-4 |
The impact of haze on visibility, |
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2-5 |
Anthropogenic sources and natural sources contribute emissions that result in the deposition of acidic compounds, |
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2-6 |
Trends in nationwide SO2 and NO2 emissions by year since 1940, |
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2-7 |
Schematic illustrating dose-response relationships between pollutant exposure and (A) human health effects and (B) crop or vegetation effects, |
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2-8 |
Exercising volunteer being exposed to ultrafine particles and monitored for health response, |
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2-9 |
Evidence of health impact of ozone on human respiratory system based on an experimental study involving human subjects, |
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2-10 |
Volunteer wearing a personal exposure monitor to measure actual exposures to PM and gases during daily activities, |
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2-11 |
Four-chamber greenhouse-based exposure system constructed to study effects of elevated CO2 on plants, |
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2-12 |
Studies in open-top field chambers have shown the response of plants to ambient levels of O3, |
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2-13 |
Free air CO2 experiment (FACE) is used to elucidate forest ecosystem responses to elevated CO2, |
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2-14 |
Concentration-response estimation from the reanalysis of the Pope/ American Cancer Society Study on cardiopulmonary disease mortality (excluding Boise, Idaho), |
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2-15 |
Schematic diagram illustrating the source of human exposure to indoor PM pollution, |
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3-1 |
Emission-inventory development, evaluation, and improvement, |
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3-2 |
Appendix J curve, |
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3-3 |
Empirical kinetic modeling approach (EKMA) diagram, |
4-1 |
The evolution of California and federal tailpipe standards on passenger car exhaust emissions since the 1960s, |
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4-2 |
Percentages of U.S. trucks within selected model years (MY) used for various primary daily driving ranges: (1) up to 50 miles, (2) 51 to 100 miles, (3) 101 to 200 miles, (4) 201 to 500 miles, and (5) more than 500 miles, |
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4-3 |
Blood lead concentrations in the U.S. population from 1976 to 1999, |
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5-1 |
SO2 emissions from electric utilities in the United States from 1980 to 2001, |
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5-2 |
Regional SO2 emission from electric utilities, |
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6-1 |
Scatterplot of estimated trends in pollutant emissions derived from emission inventories and changes in average pollutant concentrations derived from air quality monitoring networks, |
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6-2 |
Locations of surface O3 monitoring sites and ozonesonde sites in North America, |
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6-3 |
The PAMS network, |
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6-4 |
Locations of the National Atmospheric Deposition Program and National Trends Network (NADP/NTN) monitoring sites in the contiguous 48 United States, |
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6-5 |
National trend in annual benzene concentrations in metropolitan areas, 1994–1999, |
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6-6 |
Trends in wet sulfate deposition in the United States using data from the Clean Air Status and Trends Network (CASTNet) and the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) (1989–1991 vs. 1997–1999), |
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6-7 |
(A) Total estimated U.S. lead emissions by major source category from 1970 to 1994, |
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7-1 |
To meet the major challenges that will face air quality management (AQM) in the coming decade, the committee identified a set of overarching long-term objectives, |
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7-2 |
Contribution to the sulfate column burden for July 15, 1997, at 00UT (vertical integral of the concentration) from different source regions showing intercontinental transport, |
TABLES
3-1 |
Classification of Nonattainment Areas for O3 and CO Mandated in the CAA Amendments of 1990, |
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3-2 |
Federal, State, and Local VOC Emission-Reduction Measures in Four Illustrative SIPs, |
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3-3 |
Federal, Multistate, State, and Local NOx Emission-Reduction Measures in Four Illustrative SIPs, |
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3-4 |
Classifications and Number of Nonattainment Areas in 1992 Remaining in Nonattainment As of February 6, 2003, |
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4-1 |
Types of Vehicles and Engines Regulated by AQM in the United States, |
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4-2 |
Contribution of Nonroad Emissions to Mobile-Source Total and to Manmade Total, |
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4-3A |
Average PM2.5 Emissions by Vehicle Model Years for Medium- and Heavy-Duty Trucks, |
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4-3B |
Average NOx Emissions by Vehicle Model Years for Medium- and Heavy-Duty Trucks, |
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4-4 |
Timeline of Significant Federal and State Regulations for Motor Vehicle Fuels, |
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4-5 |
Part 1: California and Federal Reformulated Gasoline Programs, |
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Part 2: Future Reformulated Gasoline Program, |
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5-1 |
Allowable Concentration Increments (micrograms per cubic meter) for Prevention of Significant Deterioration (PSD), |
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5-2 |
NOx Emissions from Coal-Fired Boilers in 1999 by Vintage, |
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5-3 |
Open-Market and Other Noncapped Forms of Trading, |
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6-1 |
Summary of EPA’s Trends in Estimated Nationwide Pollutant Emissions and Average Measured Concentrations, |
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6-2 |
Summary of Major U.S. Monitoring Networks, |
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6-3 |
Locations of Initial PM2.5 Supersites, |
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6-4 |
Ozone Monitoring Sites in the United States, |