Report in Brief
Air QuAlity MAnAgeMent
in the united StAteS
T
he Clean Air Act (CAA)
provides the legal
framework for promoting
public health and public welfare
by pursuing five major air quality
goals (see Box 1). Individual states
must develop state implementation
plans (SIPs) that show how, with
the assistance of national control
programs, they will meet National
Ambient Air Quality Standards
(NAAQA) for six criteria pollutants.
Such efforts, as well as those in pursuit
of other CAA goals, seek to regulate emissions from
a variety of stationary and mobile sources through
the nation’s AQM system (see Figure 1, p. 2). Since
passage of the CAA Amendments of 1970, the
nation has devoted signiicant efforts and resources
to AQM and substantial progress has been made.
Air Quality Management in the United States,
a National Academies report, examines the role of
science and technology in the implementation of the
CAA and recommends ways in which the scientiic
and technical foundations for AQM in the United
States can be enhanced. Over a 2-year period, the
committee that authored the report heard brieings
from experts and stakeholders and examined the
operation, successes, and limitations of the many
components of the nation’s AQM system.
Progress To Date
Implementation of the Clean Air
Act has contributed to substantial
decreases in emissions of several
pollutants. Regulations for lightduty vehicles, light-duty trucks, and
fuel properties have greatly reduced
emissions per mile traveled. Programs
for stationary sources, such as power
plants and large factories, have also
achieved substantial reductions of
pollutant emissions. However, most
of the reductions have been accomplished through
regulations on new facilities, while many older,
often higher-emitting facilities can be a substantial
source of emissions.
Emission “cap and trade” has also provided
a mechanism for achieving emission reductions at
reduced costs. Air quality monitoring networks have
conirmed that ambient pollutant concentrations,
especially in urban areas, have decreased over the
past three decades, and monitoring has documented
a reduction in sulfate deposition in the eastern
United States. Economic assessments of the overall
costs and beneits of AQM in the United States
indicate, despite uncertainties, that implementation
of the CAA has had and will probably continue to
have substantial net economic beneits.
Goals of the Clean Air Act
Mitigate potentially harmful ambient concentrations of six “criteria” pollutants: carbon
monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), particulate matter
(PM), and lead (Pb).
Limit sources of exposure to hazardous air pollutants (HAPs).
Protect and improve visibility in wilderness areas and national parks.
Reduce emissions of substances that cause acid deposition, speciically sulfur dioxide and
nitrogen oxides (NOx).
Curb use of chemicals that have the potential to deplete the stratospheric ozone layer.
Challenges Ahead
Despite the progress, the report identiies scientiic
and technical limitations in the current AQM system
that will hinder future progress, especially as the nation
attempts to meet the following key challenges in the
coming decade:
Meeting new standards for ozone, particulate
matter, and regional haze.
Understanding and addressing the human
health risks from exposure to air toxics.
Responding to the evidence that, for some
pollutants, there may be no identifiable
threshold exposure below which harmful
effects cease to occur.
Mitigating pollution effects that might
disproportionately occur in minority and lowincome communities in densely populated
urban areas.
Enhancing understanding and protection of
ecosystems affected by air pollution.
Understanding and addressing multistate and
international transport of pollutants.
Adapting the AQM system to a changing (and
most likely warmer) climate.
Long-Term Objectives
To meet these challenges and remedy current
limitations, the report identiies a set of overarching
Figure 1. Idealized schematic showing the iterative nature of air quality management. Bullets
under each heading provide examples.
long-term objectives that should guide future
improvement of the AQM system. AQM should work
toward the following goals for the long term:
Strive to identify and assess more clearly
the most significant exposures, risks, and
uncertainties.
Strive to take an integrated multipollutant
approach to controlling emissions of pollutants
posing the most signiicant risks.
Strive to take an airshed-based approach
by assessing and controlling emissions of
important pollutants arising from local,
multistate, national, and international
sources.
Strive to emphasize results over process, create
accountability for the results, and dynamically
adjust and correct the system as data on
progress are assessed.
Recommend Near Term Actions
Immediate attainment of these objectives is
unrealistic. It would require a level of scientific
understanding that has yet to be developed, a commitment
of new resources that would be dificult to obtain in the
short term, and a rapid transformation of the AQM
system that is undesirable in light of the system’s past
successes. The report proposes, therefore, that the AQM
system be enhanced so that it steadily evolves toward
meeting these objectives. In that spirit, the report makes
ive interrelated recommendations to be implemented
through speciic actions:
1. (Highest Priority) Strengthen the scientiic and
technical capacity of the AQM system to assess risk
and track progress.
Critical actions include: enhancing or improving
emissions tracking, air pollution monitoring,
modeling, and exposure assessments; developing
and implementing a system to assess and monitor
human health and welfare effects; continuing to track
implementation costs; and invest in research and human
and technical resources.
2. Expand national and multistate performanceoriented control strategies to support local, state,
and tribal efforts.
Critical actions include: expanding federal emissioncontrol measures, especially for nonroad mobile
sources, area sources, and building and consumer
EPA should strive to take an airshed-based approach
to air quality management by assessing and controlling pollutants arising from local, multistate, national
and international sources. Photo courtesy NASA.
products; emphasizing technology-neutral standards
for emission control; using market-based approaches
such as the SO2 emissions cap-and-trade program
whenever practical and effective; reducing emissions
from existing facilities and vehicles; and addressing
multistate transport problems.
3. Transform the SIP process into a more dynamic and
collaborative performance-oriented, multipollutant
air quality management plan (AQMP) process.
Each state should be required to prepare an AQMP
that integrates all relevant air quality measures, replacing
all single pollutant SIPs with one comprehensive,
multipollutant AQMP. Because these actions would
require signiicant changes in standard procedure at the
federal, state, and local level, it is recommended that
they occur in stages, over a deined transition period,
and possibly with incentives.
Substantial reforms are needed to focus on
tracking results using periodic reviews, encouraging
innovative strategies, retaining conformity with
regional transportation plants, and retaining federal
oversight (see box, p. 4)
4. Develop an integrated program for criteria
pollutants and hazardous air pollutants (HAPs).
Critical actions include: developing a system to set
priorities for those pollutants; instituting a dynamic
review of pollutant classiication; listing potentially
dangerous but unregulated air pollutants for regulatory
attention; addressing multiple pollutants in the NAAQS
review and standard-setting process; and enhancing
assessment of residual risk.
5. Enhance protection of ecosystems and other
aspects of public welfare.
Critical actions include: completing a comprehensive
review of standards to protect public welfare;
implementing networks for comprehensive ecosystem
monitoring; establishing acceptable exposure levels for
natural and managed ecosystems by evaluating data on
the effects of air pollutants on ecosystems at least every
10 years; and promulgating secondary standards and
tracking progress towards them, as well as considering
regionally distinct standards.
Implementing these recommendations will
require substantial resources, but they should not
be overwhelming, especially compared with current
expenditures for CAA compliance and costs resulting
from harmful effects of air pollution on human health
and welfare. Implementing these recommendations
will also require a commitment by all parties to adjust
and change; it may also require new legislation from
Congress. As the transition occurs, it is imperative that
ongoing programs to reduce emissions continue so that
progress toward cleaner air is maintained.
Enhancing Agency Accountability and Performance
The overall goal of these recommendations is to foster a more collaborative and dynamic performanceoriented system, but experience has shown that not all states have equally addressed their air quality
problems. Public accountability and performance could be enhanced through the following:
The Clean Air Act should continue to specify deadlines for attaining NAAQS milestones and to
assess progress along the way; EPA should retain its authority to impose sanctions on states that
fail to submit and implement adequate implementation plans.
States should not be sanctioned for failure of EPA to institute necessary regulations for multistate
or national control programs that are beyond the states control.
Incentives should be created for states that meet or beat deadlines and for those that develop
creative and effective multipollutant reduction strategies.
Existing programs could be enforced with economic mechanisms such as additional emission fees
when states or regions fail to achieve rates of progress set forth in their plans.
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 Saroim,
University of Utah, Salt Lake City, Sverre Vedal, National Jewish Medical and Research Center, Denver, CO,
Lauren Zeise, California Environmental Protection Agency, Oakland, Raymond Wassel (Study Director), Board
on Environmental Studies and Toxicology.
This report brief was prepared by the National Research Council based on the committee’s
report. For more information, contact the Board on Environmental Studies and Toxicology
at (202) 334-3060. Air Quality Management in the United States is available from the National
Academies Press, 500 Fifth Street, NW, Washington, DC 20001; 800-624-6242 or 202-334-3313
(in the Washington area); www.nap.edu.
Permission granted to reproduce this brief in its entirety with no additions or alterations.
Copyright 2004 The National Academies
in the united StAteS
T
he Clean Air Act (CAA)
provides the legal
framework for promoting
public health and public welfare
by pursuing five major air quality
goals (see Box 1). Individual states
must develop state implementation
plans (SIPs) that show how, with
the assistance of national control
programs, they will meet National
Ambient Air Quality Standards
(NAAQA) for six criteria pollutants.
Such efforts, as well as those in pursuit
of other CAA goals, seek to regulate emissions from
a variety of stationary and mobile sources through
the nation’s AQM system (see Figure 1, p. 2). Since
passage of the CAA Amendments of 1970, the
nation has devoted signiicant efforts and resources
to AQM and substantial progress has been made.
Air Quality Management in the United States,
a National Academies report, examines the role of
science and technology in the implementation of the
CAA and recommends ways in which the scientiic
and technical foundations for AQM in the United
States can be enhanced. Over a 2-year period, the
committee that authored the report heard brieings
from experts and stakeholders and examined the
operation, successes, and limitations of the many
components of the nation’s AQM system.
Progress To Date
Implementation of the Clean Air
Act has contributed to substantial
decreases in emissions of several
pollutants. Regulations for lightduty vehicles, light-duty trucks, and
fuel properties have greatly reduced
emissions per mile traveled. Programs
for stationary sources, such as power
plants and large factories, have also
achieved substantial reductions of
pollutant emissions. However, most
of the reductions have been accomplished through
regulations on new facilities, while many older,
often higher-emitting facilities can be a substantial
source of emissions.
Emission “cap and trade” has also provided
a mechanism for achieving emission reductions at
reduced costs. Air quality monitoring networks have
conirmed that ambient pollutant concentrations,
especially in urban areas, have decreased over the
past three decades, and monitoring has documented
a reduction in sulfate deposition in the eastern
United States. Economic assessments of the overall
costs and beneits of AQM in the United States
indicate, despite uncertainties, that implementation
of the CAA has had and will probably continue to
have substantial net economic beneits.
Goals of the Clean Air Act
Mitigate potentially harmful ambient concentrations of six “criteria” pollutants: carbon
monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), particulate matter
(PM), and lead (Pb).
Limit sources of exposure to hazardous air pollutants (HAPs).
Protect and improve visibility in wilderness areas and national parks.
Reduce emissions of substances that cause acid deposition, speciically sulfur dioxide and
nitrogen oxides (NOx).
Curb use of chemicals that have the potential to deplete the stratospheric ozone layer.
Challenges Ahead
Despite the progress, the report identiies scientiic
and technical limitations in the current AQM system
that will hinder future progress, especially as the nation
attempts to meet the following key challenges in the
coming decade:
Meeting new standards for ozone, particulate
matter, and regional haze.
Understanding and addressing the human
health risks from exposure to air toxics.
Responding to the evidence that, for some
pollutants, there may be no identifiable
threshold exposure below which harmful
effects cease to occur.
Mitigating pollution effects that might
disproportionately occur in minority and lowincome communities in densely populated
urban areas.
Enhancing understanding and protection of
ecosystems affected by air pollution.
Understanding and addressing multistate and
international transport of pollutants.
Adapting the AQM system to a changing (and
most likely warmer) climate.
Long-Term Objectives
To meet these challenges and remedy current
limitations, the report identiies a set of overarching
Figure 1. Idealized schematic showing the iterative nature of air quality management. Bullets
under each heading provide examples.
long-term objectives that should guide future
improvement of the AQM system. AQM should work
toward the following goals for the long term:
Strive to identify and assess more clearly
the most significant exposures, risks, and
uncertainties.
Strive to take an integrated multipollutant
approach to controlling emissions of pollutants
posing the most signiicant risks.
Strive to take an airshed-based approach
by assessing and controlling emissions of
important pollutants arising from local,
multistate, national, and international
sources.
Strive to emphasize results over process, create
accountability for the results, and dynamically
adjust and correct the system as data on
progress are assessed.
Recommend Near Term Actions
Immediate attainment of these objectives is
unrealistic. It would require a level of scientific
understanding that has yet to be developed, a commitment
of new resources that would be dificult to obtain in the
short term, and a rapid transformation of the AQM
system that is undesirable in light of the system’s past
successes. The report proposes, therefore, that the AQM
system be enhanced so that it steadily evolves toward
meeting these objectives. In that spirit, the report makes
ive interrelated recommendations to be implemented
through speciic actions:
1. (Highest Priority) Strengthen the scientiic and
technical capacity of the AQM system to assess risk
and track progress.
Critical actions include: enhancing or improving
emissions tracking, air pollution monitoring,
modeling, and exposure assessments; developing
and implementing a system to assess and monitor
human health and welfare effects; continuing to track
implementation costs; and invest in research and human
and technical resources.
2. Expand national and multistate performanceoriented control strategies to support local, state,
and tribal efforts.
Critical actions include: expanding federal emissioncontrol measures, especially for nonroad mobile
sources, area sources, and building and consumer
EPA should strive to take an airshed-based approach
to air quality management by assessing and controlling pollutants arising from local, multistate, national
and international sources. Photo courtesy NASA.
products; emphasizing technology-neutral standards
for emission control; using market-based approaches
such as the SO2 emissions cap-and-trade program
whenever practical and effective; reducing emissions
from existing facilities and vehicles; and addressing
multistate transport problems.
3. Transform the SIP process into a more dynamic and
collaborative performance-oriented, multipollutant
air quality management plan (AQMP) process.
Each state should be required to prepare an AQMP
that integrates all relevant air quality measures, replacing
all single pollutant SIPs with one comprehensive,
multipollutant AQMP. Because these actions would
require signiicant changes in standard procedure at the
federal, state, and local level, it is recommended that
they occur in stages, over a deined transition period,
and possibly with incentives.
Substantial reforms are needed to focus on
tracking results using periodic reviews, encouraging
innovative strategies, retaining conformity with
regional transportation plants, and retaining federal
oversight (see box, p. 4)
4. Develop an integrated program for criteria
pollutants and hazardous air pollutants (HAPs).
Critical actions include: developing a system to set
priorities for those pollutants; instituting a dynamic
review of pollutant classiication; listing potentially
dangerous but unregulated air pollutants for regulatory
attention; addressing multiple pollutants in the NAAQS
review and standard-setting process; and enhancing
assessment of residual risk.
5. Enhance protection of ecosystems and other
aspects of public welfare.
Critical actions include: completing a comprehensive
review of standards to protect public welfare;
implementing networks for comprehensive ecosystem
monitoring; establishing acceptable exposure levels for
natural and managed ecosystems by evaluating data on
the effects of air pollutants on ecosystems at least every
10 years; and promulgating secondary standards and
tracking progress towards them, as well as considering
regionally distinct standards.
Implementing these recommendations will
require substantial resources, but they should not
be overwhelming, especially compared with current
expenditures for CAA compliance and costs resulting
from harmful effects of air pollution on human health
and welfare. Implementing these recommendations
will also require a commitment by all parties to adjust
and change; it may also require new legislation from
Congress. As the transition occurs, it is imperative that
ongoing programs to reduce emissions continue so that
progress toward cleaner air is maintained.
Enhancing Agency Accountability and Performance
The overall goal of these recommendations is to foster a more collaborative and dynamic performanceoriented system, but experience has shown that not all states have equally addressed their air quality
problems. Public accountability and performance could be enhanced through the following:
The Clean Air Act should continue to specify deadlines for attaining NAAQS milestones and to
assess progress along the way; EPA should retain its authority to impose sanctions on states that
fail to submit and implement adequate implementation plans.
States should not be sanctioned for failure of EPA to institute necessary regulations for multistate
or national control programs that are beyond the states control.
Incentives should be created for states that meet or beat deadlines and for those that develop
creative and effective multipollutant reduction strategies.
Existing programs could be enforced with economic mechanisms such as additional emission fees
when states or regions fail to achieve rates of progress set forth in their plans.
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 Saroim,
University of Utah, Salt Lake City, Sverre Vedal, National Jewish Medical and Research Center, Denver, CO,
Lauren Zeise, California Environmental Protection Agency, Oakland, Raymond Wassel (Study Director), Board
on Environmental Studies and Toxicology.
This report brief was prepared by the National Research Council based on the committee’s
report. For more information, contact the Board on Environmental Studies and Toxicology
at (202) 334-3060. Air Quality Management in the United States is available from the National
Academies Press, 500 Fifth Street, NW, Washington, DC 20001; 800-624-6242 or 202-334-3313
(in the Washington area); www.nap.edu.
Permission granted to reproduce this brief in its entirety with no additions or alterations.
Copyright 2004 The National Academies