United States Government Accountability Office

GAO Report to Congressional Requesters

CLEAN AIR ACT 

EPA Should Improve 

the Management of Its 

Air Toxics Program 

June 2006 

 

GAO-06-669 
What GAO Found

United States Government Accountability Office

Why GAO Did This Study

Highlights

Accountability Integrity Reliability

June 2006

CLEAN AIR ACT

EPA Should Improve the Management of 

Highlights of GAO-06-669, a report to Its Air Toxics Program 

congressional requesters 

The Environmental Protection 

Agency’s (EPA) most recent data 

indicate that 95 percent of all 

Americans face an increased 

likelihood of developing cancer as 

a result of breathing air toxics—

pollutants such as benzene and

asbestos that may cause cancer or 

other serious health problems. 

Sources of air toxics include large 

industrial facilities, smaller 

facilities such as dry cleaners, and 

cars and trucks. The 1990 Clean

Air Act Amendments required EPA

to regulate 190 pollutants from 

these sources through a 

multifaceted regulatory program. 

While EPA issues federal 

standards, state and local agencies

generally administer these 

standards, and some develop their 

own rules to complement the 

federal standards. In this context, 

GAO was asked to assess (1) EPA’s 

progress and challenges in 

implementing the air toxics

program, (2) available information 

on the program’s costs and 

benefits, and (3) practices of state 

and local air toxics programs. 

What GAO Recommends

GAO recommends that EPA 

develop a plan for improving the 

management of its air toxics

program, including a prioritization

scheme, timelines, and estimates of 

resources needed to meet its 

statutory obligations. EPA agreed, 

in part, with our conclusions and 

recommendations, and provided 

clarifications on three statements 

in the report. 

While EPA has made some progress in implementing its air toxics program 

mandated by the 1990 Clean Air Act Amendments, most of its regulatory 

actions were completed late and major aspects of the program have still not 

been addressed. Most of EPA’s progress relates to issuing emissions 

standards for large stationary sources, although EPA completed these 

standards about 4 years behind schedule. However, many of the unmet 

requirements pertain to limiting emissions from small stationary and mobile 

sources, which collectively account for most emissions of air toxics. The 

agency faces continuing implementation challenges stemming from the 

program’s low priority relative to other programs and related funding 

constraints. To this end, the agency lacks a comprehensive strategy for 

completing the unmet requirements or estimates of resources necessary to 

do so. Senior EPA officials said the program’s agenda is largely set by 

external stakeholders who file litigation when the agency misses deadlines. 

As a result of EPA’s limited progress, the agency has not addressed health 

risks from air toxics to the extent or in the time frames envisioned in the 

Clean Air Act. Senior EPA officials said that issuing standards for large 

stationary sources had addressed the greatest risks from air toxics and that 

other clean air programs also control air toxics as a side benefit. However, 

EPA does not have reliable data on the degree of risk reduction achieved 

through its regulations. Furthermore, the data that are available suggest that

the agency has substantial opportunities to reduce emissions from mobile 

and small stationary sources. 

Available information on EPA’s efforts to control air toxics is not sufficiently 

comprehensive to measure the program’s total costs and benefits. 

Specifically, EPA has not comprehensively estimated the national economic 

costs of all air toxics standards and lacks the data necessary to assess the 

benefits of these standards, such as decreased incidence of cancer. 

Information on these impacts would help the agency assess the overall net 

benefits (total benefits minus total costs) of the air toxics program and 

compare these effects with those generated by higher-priority clean air 

programs, such as those intended to address smog. Data on other indicators 

of the program’s effectiveness, such as changes in emissions, concentrations 

of air toxics in the (ambient) outdoor air, and data on compliance with air 

toxics standards are also limited and inconclusive. 

The state and local programs we reviewed use practices that could 

potentially help EPA enhance the effectiveness of its air toxics program. For 

example, several state programs have systematic approaches for identifying 

and prioritizing new pollutants that could inform EPA’s efforts to meet the 

act’s requirement to review and update the list of regulated pollutants. 

www.gao.gov/cgi-bin/getrpt?GAO-06-669.

To view the full product, including the scope 

and methodology, click on the link above. 

For more information, contact John

Stephenson at (202) 512-3841 or

stephensonj@gao.gov. 
Contents 

Letter 1

Results in Brief 4

Background 8

EPA Has Made Limited Progress in Addressing the Clean Air Act’s 

Requirements for Air Toxics and Faces Significant 

Implementation Challenges 15 

Available Information on Costs and Benefits Is Not Sufficient to

Measure the Program’s Effectiveness 25 

State and Local Programs Employ Practices That Could Potentially 

Help EPA Enhance the Effectiveness of the Federal Air Toxics 

Program 33

Conclusions 41

Recommendations for Executive Action 42 

Agency Comments 43 

Appendix I Status of EPA’s Efforts to Respond to 

Recommendations in the National Academies’ 

Report on Air Quality 47 

Appendix II Objectives, Scope, and Methodology 48 

Appendix III Profiles of State and Local Air Toxics Programs 52 

California 53

New Jersey 53 

Oregon 54

Wisconsin 54

Louisville, Kentucky 55 

Appendix IV Comments from the Environmental Protection 

Agency 56 

GAO comments 63 

Appendix V GAO Contact and Staff Acknowledgments 65 

Page i GAO-06-669 Clean Air Act
Tables 

Table 1: The Five Most Commonly Emitted Air Toxics, 2002 10 

Table 2: Overview of the Risk Assessment Process 12 

Table 3: Number of Air Toxics Actions Required under the 1990 

Clean Air Act Amendments 14 

Table 4: EPA Progress in Meeting Air Toxics Requirements 16 

Table 5: Timeliness of MACT Emission Control Standards for Major 

Source Categories 17 

Table 6: EPA Funding for Air Toxics Program as a Percentage of 

Funding for All Clean Air Programs, Fiscal Years 2000 

through 2005 20 

Table 7: Percentage of Estimated Total Air Toxics Emissions by

Source Type, 1993, 1999, and 2002 22 

Table 8: Issues Rated by Stakeholders as Challenges to a Large or 

Great Extent 24 

Table 9: Summary of Annual Costs Imposed by the 1990 Clean Air 

Act Amendments 26 

Table 10: Key Steps in Estimating the Benefits of Controlling Air 

Toxics 28

Table 11: Results of Inspections at Facilities Regulated by Air 

Toxics Standards, 2003 and 2004 33 

Table 12: Selected State and Local Air Toxics Programs 52 

Figures 

Figure 1: Common Sources of Air Toxics Emissions 9 

Figure 2: EPA Air Toxics Regulatory Framework for Major 

Stationary Sources 13 

Figure 3: Emission Points at an Industrial Facility Emitting Air 

Toxics 38

Page ii GAO-06-669 Clean Air Act
Abbreviations 

CRS Congressional Research Service 

DEP New Jersey Department of Environmental 

 Protection 

DEQ Oregon Department of Environmental Quality 

DNR Wisconsin Department of Natural Resources 

EPA Environmental Protection Agency 

IRIS Integrated Risk Information System 

MACT Maximum Achievable Control Technology 

NATA National Air Toxics Assessment 

NSPS New Source Performance Standards

OAQPS Office of Air Quality Planning and Standards 

OAR Office of Air and Radiation 

OMB Office of Management and Budget 

OPAR Office of Policy Analysis and Review

ORD Office of Research and Development 

SAB Science Advisory Board 

STAPPA/ALAPCO State and Territorial Air Pollution Program 

 Administrators and the Association of Local Air 

 Pollution Control Officials 

STAR Strategic Toxic Air Reduction 

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Page iii GAO-06-669 Clean Air Act
United States Government Accountability Office

Washington, DC 20548 

June 23, 2006 

Congressional Requesters

The Environmental Protection Agency’s (EPA) most recent data indicate

that 95 percent of all Americans face an increased likelihood of developing 

cancer from air toxics—pollutants such as benzene, asbestos, and 

chlorine—by breathing outdoor air.1 Other adverse health effects 

associated with air toxics include damage to reproductive functions and 

birth defects.

2

 Air toxics are emitted into the air in the United States by 

large stationary sources such as industrial facilities, small stationary 

sources such as dry cleaners, and mobile sources such as automobiles. 

According to the most recent data available, EPA estimates that these and 

other sources emitted 4.6 million tons of air toxics in 2002.3

 The Clean Air 

Act of 1970 established a program to reduce emissions of air toxics, and 

the 1990 amendments to the act significantly expanded the program. Prior 

to the amendments, the act had required EPA to identify air toxics that 

posed unacceptable health risks and issue emissions standards for sources 

of these pollutants. In part because of the limited success of this 

approach—EPA established standards for seven air toxics over a 20-year 

period—the amendments identified 190 specific air toxics to be regulated,

required EPA to list categories of sources to be regulated, and established 

implementation timelines. 

Specifically, the 1990 amendments established a range of air toxics 

requirements for EPA to implement that generally fall into four categories: 

(1) establishing emission standards based on existing pollution control 

technologies, called Maximum Achievable Control Technology (MACT), 

 1

Cancer risk data from EPA’s 1999 National-Scale Air Toxics Assessment, released in 

February 2006, estimates that more than 270 million people in the United States are 

exposed at levels of risk that exceed 10 in 1 million due to the combined impacts of all 

sources of air toxics. This risk level implies that more than 10 persons out of a million may 

develop cancer if exposed continuously over their lifetime. Section 112 of the Clean Air Act

identifies a lifetime cancer risk of 1 in 1 million as a threshold above which regulation may

be warranted for individual sources of air toxics, considering feasibility and costs.

2

The Clean Air Act refers to these substances as “hazardous air pollutants,” which EPA 

uses interchangeably with the more common term “air toxics.” In this report, we generally 

use the shorter term, air toxics. 

3

We discuss the limitations of EPA’s emissions data later in this report. 

Page 1 GAO-06-669 Clean Air Act
for an estimated 84,000 major stationary sources within 158 industries;4

 (2) 

examining the remaining health risk (called the “residual risk”) from these 

sources 8 years after implementing each MACT standard and, if warranted, 

issuing additional standards to protect public health or the environment; 

(3) regulating air toxics emissions from small stationary sources,5

 such as 

dry cleaners; and (4) evaluating the need for and feasibility of regulation of 

air toxics emissions from mobile sources, such as cars, and regulating 

these sources based on this evaluation. In addition, the 1990 amendments 

required EPA to periodically assess the costs and benefits of the entire 

Clean Air Act. This included an assessment of the act’s costs and benefits 

prior to 1990 as well as projections of future economic impacts resulting 

from the amendments. Information on impacts, such as the costs to 

regulated industries and the public health benefits resulting from cleaner 

air, is necessary for analyzing whether the benefits of clean air regulations 

exceed the costs. Furthermore, estimating the economic impacts of 

individual regulations and clean air programs can help EPA compare the 

net benefits and cost-effectiveness of its programs under the act. Finally, 

the amendments required EPA to periodically review and revise the list of

regulated air toxics. The agency currently regulates 187 substances.6

Prior GAO work dating to 1991 identified EPA’s difficulties in regulating

air toxics, including missed deadlines and inadequate funding.7

 Most 

recently, a May 2005 GAO report found that EPA had completed MACT 

standards for major stationary sources but issued most of them behind 

 4

Major stationary sources are those that emit 10 or more tons per year of a single hazardous 

air pollutant or 25 or more tons per year of any combination of hazardous air pollutants. 

5

The Clean Air Act refers to small stationary sources as “area sources.”

6

In total, three chemicals and several substances from a listed group of chemicals have 

been removed from the list of air toxics originally provided in the 1990 amendments. By a

joint resolution, Congress corrected the inadvertent addition of hydrogen sulfide to the 

substances originally listed in the 1990 amendments. EPA delisted caprolactam and methyl 

ethyl ketone. The agency also removed the compound ethylene glycol monobutyl ether

(EGBE) and compounds called surfactant alcohol ethoxylates and their derivatives (SAED)

from the listed glycol ethers category. The group glycol ethers is still listed. 

7

See GAO, Air Pollution: EPA’s Strategy and Resources May Be Inadequate to Control Air

Toxics, GAO/RCED-91-143 (Washington, D.C.: June 26, 1991); Air Pollution: Progress and

Problems in Implementing Selected Aspects of the Clean Air Act Amendments of 1990, 

GAO/T-RCED-94-68 (Washington, D.C.: Oct. 29, 1993); Air Pollution: Reductions in EPA’s

1994 Air Quality Program’s Budget, GAO/RCED-95-31BR (Washington, D.C.: Nov. 29, 

1994); and Clean Air Rulemaking: Tracking System Would Help Measure Progress of 

Streamlining Initiatives, GAO/RCED-95-70 (Washington, D.C.: Mar. 2, 1995). 

Page 2 GAO-06-669 Clean Air Act
schedule.8

 In addition, the EPA Inspector General, National Academies, 

Congressional Research Service, and Office of Management and Budget 

(OMB) have identified shortcomings with various aspects of the air toxics

program. 

While responsibility for establishing federal standards under the Clean Air 

Act rests with EPA, state and local air pollution control agencies generally

implement EPA’s emission standards. The act allows these agencies to 

impose more stringent requirements than the federal standards, and some 

state and local agencies have developed innovative air toxics programs 

that go beyond the federal program, thereby enabling them to address air 

toxics concerns that remain unaddressed by EPA’s standards. 

In this context, you asked us to assess (1) EPA’s progress toward 

implementing the air toxics program and any implementation challenges 

the agency faces, (2) available information about the costs and benefits of 

EPA’s efforts to control air toxics, and (3) the program design and 

management practices of state and local air toxics programs that could 

potentially help EPA enhance the effectiveness of the federal program. 

You also asked us to assess EPA’s progress in responding to 

recommendations pertaining to the air toxics program made by the 

National Academies in 2004.9

To respond to the first objective, we updated our previous analysis of the 

agency’s progress in implementing the air toxics requirements under the 

Clean Air Act and reviewed available studies by the National Academies, 

OMB, and the EPA Inspector General to identify potential implementation 

challenges. Based on this information, we conducted structured interviews 

with EPA officials and external stakeholders to identify the most 

important challenges. We met with senior air program officials to discuss 

the priority of the air toxics program relative to other air programs as well 

as priorities within the program. To respond to the second objective, we 

analyzed available information on the economic impacts of the program 

and data on trends in emissions, health risks, and compliance. We also met

with EPA staff responsible for analyzing the economic effects of clean air 

 8

See GAO, Clean Air Act: EPA Has Completed Most of the Actions Required by the 1990 

Amendments, but Many Were Completed Late, GAO-05-613 (Washington, D.C.: May 27, 

2005). 

9

The National Academies, National Research Council, Air Quality Management in the 

United States (Washington, D.C., 2004). 

Page 3 GAO-06-669 Clean Air Act
regulations. To respond to the third objective, we conducted interviews 

with officials from a nonprobability sample of four state and one local air 

toxics programs to identify innovative program designs or management 

practices. Among other criteria, we selected programs identified as 

innovative by EPA and other stakeholders and that used strategies that 

differ from those at the federal level. We focused primarily on practices 

that EPA might find useful in addressing its program implementation 

challenges and did not evaluate the effectiveness of these programs. 

Finally, we obtained information from EPA officials on the agency’s 

progress in responding to the National Academies’ recommendations 

pertaining to air toxics and describe the status of these efforts in 

appendix I. Our work included an assessment of data reliability and 

internal controls. Unless otherwise noted, data are sufficiently reliable for 

the purposes of this report. See appendix II for a more detailed description 

of our scope and methodology. We conducted our work from June 2005 to

June 2006 in accordance with generally accepted government auditing 

standards. 

While EPA has made progress toward implementing the air toxics program 

mandated by the Clean Air Act, most of the completed requirements were 

met late and many requirements and significant challenges remain. EPA 

has completed one of the four categories of requirements—issuing 96 rules 

that set emissions standards for major stationary sources—but did not do 

so until 2004, which was 4 years behind the schedule outlined in the act. 

These delays, in turn, pushed back the evaluation of the residual health

risks from these sources that EPA must complete 8 years after issuing 

each standard. Consequently, EPA will not complete the residual risk 

reviews—which are intended to provide information on any potential 

adverse health effects that may warrant further regulation—until 2012 at

the earliest, rather than in 2008 as the act provided. Further, EPA has 

completed only 16 of 70 emissions standards for small stationary sources 

that cumulatively accounted for about one-third of all air toxic emissions 

in 2002 and has proposed, but not finalized, a required rule making 

covering mobile sources. Finally, EPA has not met the act’s requirement to

review and update, as appropriate, the list of regulated air toxics, despite 

evidence that potentially harmful chemicals remain unregulated. As a 

result of EPA’s limited progress, the agency has not identified and reduced 

health risks from air toxics to the extent and in the time frame envisioned 

in the act. EPA’s limited progress to date stems, in part, from the 

program’s low priority relative to other air programs, such as those 

targeting smog, which the agency believes have a higher potential to 

reduce human health risks. Senior program officials also said that the 

Results in Brief 

Page 4 GAO-06-669 Clean Air Act
agency’s progress in implementing the act’s requirements does not reflect 

all of the agency’s progress in limiting toxic emissions because other EPA 

programs decrease emissions of air toxics as a side benefit. In addition, 

within the air toxics program, senior EPA officials said that the agency’s 

focus on issuing emissions standards for major stationary sources had 

addressed the greatest risks from air toxics. However, EPA does not have

reliable data on the degree to which its programs have reduced risks. 

Furthermore, the data that are available suggest that the agency still has 

substantial opportunities to control emissions from mobile and small 

stationary sources. 

EPA faces significant challenges in implementing the air toxics program, 

many of which stem from its relatively low priority within the agency.

Importantly, the agency lacks a comprehensive strategy for managing its 

implementation of the remaining air toxics requirements. Senior EPA 

officials said that the program’s agenda is largely set by external 

stakeholders who file litigation when the agency misses deadlines. For 

example, EPA currently faces a court order to issue emissions standards 

for small stationary sources. Previous reports by GAO identified 

inadequate funding for the air toxics program as a challenge, and key 

stakeholders—including senior EPA officials, environmental advocates, 

and state and local agency officials—said resource constraints continue to 

pose a major challenge. The percentage of funding for the air toxics 

program relative to all clean air programs ranged from 18 percent to 19

percent between 2000 and 2003 and declined to 15 percent in 2004 and 12

percent in 2005. EPA has not estimated the level of resources necessary to 

comply with the remaining requirements of the 1990 amendments, 

according to a senior program official. We believe that such estimates 

would help inform congressional oversight and appropriations decisions. 

Senior EPA officials and other stakeholders also cited a lack of 

information on the benefits of regulating air toxics as a major challenge, 

which, in turn, reinforces the program’s relative priority because the 

agency cannot demonstrate its effectiveness. The stakeholders identified a 

number of other challenges, but perceptions varied by stakeholder group. 

For example, EPA and industry stakeholders rated the large number of 

statutory requirements as a challenge, while environmental stakeholders 

rated a lack of reliable data on air toxics sources and their emissions as a 

challenge. 

Available information on the costs and benefits of EPA’s efforts to control 

air toxics is not sufficiently comprehensive to measure the total economic 

impacts resulting from the air toxics program. As a result, it is difficult to 

compare the net benefits (total benefits minus total costs) of EPA’s 

Page 5 GAO-06-669 Clean Air Act
investments in the air toxics program with those of other air quality 

programs. The agency’s 1999 report responding to the act’s mandate for a 

comprehensive cost-benefit analysis of all Clean Air Act programs 

contained limited information on the costs of regulating air toxics and no

estimates of the human health benefits, such as likely reductions in cancer 

risk. The analysis estimated that the cost to industry of complying with the 

21 control standards that had been issued by 1999 would total $780 million 

in 2000 and rise to $840 million in 2010. EPA officials said the agency plans 

to issue a revised analysis in 2007 that will estimate the costs of all 

standards issued before September 2005. However, the analysis will only 

provide limited data on the benefits of regulating air toxics because of the 

analytical challenges involved. These challenges include a lack of reliable 

data on changes in emissions attributable to air toxics regulations and 

difficulties in estimating the effects that changes in emissions have on

health outcomes. Specifically, EPA has not monetized the health benefits 

of its air toxics regulations individually or in total because of the analytical 

difficulty of characterizing health outcomes associated with incremental 

reductions in exposure to 187 different chemicals. Instead of using a costbenefit analysis to measure the program’s effectiveness, EPA uses data on

national trends in emissions of all air toxics. However, as EPA’s Inspector 

General reported in 2004, the agency needs to improve its methods for 

estimating emissions before it can accurately gauge the extent to which its 

programs have actually reduced emissions. Other indicators of the 

program’s effectiveness, such as changes in concentrations of air toxics in

the ambient (outdoor) air over time and data on compliance with air 

toxics standards, are also limited and inconclusive. For example, the 

agency’s data on compliance with air toxics standards cannot be 

generalized to describe compliance at the universe of regulated facilities 

because inspectors often target facilities where they suspect 

noncompliance. 

The five state and local air toxics programs we reviewed use several 

program design and management practices that EPA could consider as 

part of efforts to enhance the effectiveness of the federal air toxics 

program. First, the programs we reviewed address gaps in the federal 

program by, for example, regulating more emissions sources than EPA, or 

setting more stringent standards to control emissions. As part of efforts to 

strengthen its program and establish priorities for meeting its remaining 

obligations under the act, EPA could benefit from assessing and 

considering what states perceive as the primary gaps in the federal 

program. Second, these programs use risk-based approaches to prioritize 

efforts to control air toxics. For example, Oregon’s air toxics program is 

designed to monitor emissions in various parts of the state, identify areas 

Page 6 GAO-06-669 Clean Air Act
of elevated risk from air toxics, and then concentrate resources on the 

emissions sources that drive these risks. Third, some of these programs 

base their regulatory decisions on the risk posed by entire facilities, 

whereas, to date, EPA has limited the scope of its residual risk program to 

only those emission points within facilities that must comply with existing 

federal standards. As a result, according to several state and local officials, 

EPA’s decision to exclude some emissions points from risk assessments 

may, in turn, cause it to underestimate the total risk from facilities and 

thereby enable some facilities to avoid further regulation. Fourth, several

of the programs we reviewed have systematic approaches for identifying

and prioritizing new chemicals. In contrast, EPA does not proactively 

consider new chemicals and instead has taken a reactive approach in 

which it considers petitions from external parties to list or delist 

chemicals. Considering the practices used by these programs could inform

future EPA efforts to meet the act’s requirement to periodically review and 

update the list of regulated chemicals. In addition to these practices, all of

the programs we reviewed highlighted the importance of reliable data on

emissions and chemical toxicity. Several require major and small 

stationary sources to submit standardized emissions reports and certify 

their accuracy. In contrast, EPA, to date, generally has not required 

emissions sources or state or local agencies to systematically report these 

data. Such standardized data collection could enhance EPA’s analysis and 

decision making in future air toxics rule makings. In addition, several 

officials said that EPA does not regularly update chemical toxicity values

that inform the work of state and local programs. 

We are recommending that EPA develop an air toxics program 

improvement plan that, among other things, (1) provides a schedule for 

completing its mandated requirements under the act and identifies the 

resources necessary to complete these actions, (2) prioritizes activities 

within the air toxics program, (3) establishes a process and timeline for 

meeting the act’s requirement to review and update the list of air toxics, 

(4) outlines an approach and timelines for improving the agency’s ability 

to measure the program’s costs and benefits, and (5) describes how the 

agency plans to improve its air toxics emissions inventory. In commenting 

on the report, EPA’s Acting Assistant Administrator for Air and Radiation 

said that EPA agrees in part with our conclusions and recommendations. 

The agency did not identify specific aspects of our conclusions or 

recommendations with which it disagreed, but offered clarifications on 

our statements regarding information on the costs and benefits of the 

agency’s efforts to control air toxics, the agency’s progress in completing 

certain air toxics requirements of the Clean Air Act, and EPA’s 

management of the remaining requirements. EPA also provided technical 

Page 7 GAO-06-669 Clean Air Act
comments, which we have incorporated, as appropriate. EPA’s letter, and

our response, are included as appendix IV. 

Under the Clean Air Act, EPA regulates two primary types of air 

pollutants. The first category—the so-called “criteria pollutants” for which 

EPA has established air quality criteria that limit the allowable 

concentrations in the ambient air—includes carbon monoxide, groundlevel ozone (smog), lead, nitrogen oxides, particulate matter, and sulfur 

dioxide. EPA sets these standards at a level it believes protects public 

health and the needs of sensitive populations such as asthmatics, children, 

and the elderly. EPA and the states use air quality monitoring to measure 

compliance with the standards and develop pollution control strategies to

help bring areas with poor air quality into compliance. 

Background 

The second category consists of hazardous air pollutants (or “air toxics”) 

for which no ambient air quality standards exist, and includes 187 

chemicals that cause a variety of adverse health effects, including cancer.

A variety of sources emit one or more of these air toxics (see fig. 1). In 

2002, mobile sources emitted 41 percent of all air toxics, small stationary 

sources emitted 30 percent, major stationary sources emitted 20 percent, 

and other sources, such as fires, emitted 9 percent, according to EPA’s 

most recent data. 

Page 8 GAO-06-669 Clean Air Act
Figure 1: Common Sources of Air Toxics Emissions

Industrial facilities

Automobiles

(large stationary source)

(mobile source) 

Dry cleaner 

(small stationary source) 

Gas station 

(small stationary source) 

Diesel engines 

(mobile source) 

Sources: EPA (data); GAO, Art Explosion (images). 

Table 1 identifies the most widely emitted air toxics, the primary sources 

of these pollutants, and some of the adverse health effects associated with

exposure to these substances. It is important to note that the health risks 

posed by air toxics vary considerably. Thus, small quantities of more 

harmful pollutants can pose greater health threats than large quantities of

less harmful pollutants. 

Page 9 GAO-06-669 Clean Air Act
Table 1: The Five Most Commonly Emitted Air Toxics, 2002 

Pollutant 

Percentage of

total air toxics 

emissions

Primary sources of

emissions Health effects

Toluene 18 Mobile sources Impairment of the nervous system with symptoms including 

tiredness, dizziness, sleepiness, confusion, weakness, 

memory loss, nausea, loss of appetite, and hearing and 

color vision loss; kidney problems; unconsciousness; and 

death. 

Xylenes 13 Mobile sources,

asphalt paving

Irritation of the skin, eyes, nose, and throat; headaches, 

dizziness, memory loss, and changes in sense of balance; 

lung problems; stomach discomfort; possible effects on the 

liver and kidneys; unconsciousness; and death. 

Hydrochloric acid 12 Coal-fired utility and 

industrial boilers 

Eye, nose, and respiratory tract irritation; corrosion of the 

skin, eyes, mucous membranes, esophagus, and stomach; 

severe burns; ulceration; scarring; inflammation of the 

stomach lining; chronic bronchitis; and inflammation of the

skin. 

Benzene 9 Mobile sources, open 

burning, pesticide 

application 

Drowsiness, dizziness, vomiting, irritation of the stomach, 

sleepiness, convulsions, rapid heart rate, headaches, 

tremors, confusion, unconsciousness, anemia, excessive

bleeding, weakened immune system, increased incidence of 

cancer (leukemia), and death. 

Formaldehyde 7 Mobile sources, open 

burning 

Irritation of the eyes, nose, throat, and skin; severe pain; 

vomiting; coma; limited evidence of cancer; and death. 

Sources: EPA and Agency for Toxic Substances and Disease Registry. 

Note: Health effects are dependent upon the concentration of the air toxic and the length of exposure. 

Prior to 1990, the Clean Air Act required EPA to list air toxics it deemed 

hazardous and then promulgate regulations for them. However, by 1990,

EPA had regulated only seven such pollutants. In 1990, Congress 

dramatically changed the program. Instead of requiring EPA to develop

ambient standards for air toxics as it does for the six criteria pollutants, 

the Clean Air Act Amendments of 1990 listed the air toxics to be controlled 

and directed EPA to control them by, among other things, (1) developing

technology-based emissions limits (MACT standards) for major stationary 

sources, such as incinerators and chemical plants; (2) regulating emissions 

from smaller sources, such as dry cleaners and gas stations; and (3) 

evaluating the need for and feasibility of regulations from mobile sources,

such as cars, and regulating these sources based on this evaluation. The 

standards for major stationary sources generally require the use of 

available control technologies to achieve emissions reductions without the 

explicit consideration of a chemical’s toxicity or potential risk. To develop 

MACT standards, the 1990 amendments directed EPA to group emissions 

points at industrial facilities into categories of similar sources and then 

Page 10 GAO-06-669 Clean Air Act
develop regulations for each “source category.” Examples of source 

categories include cement manufacturing, hazardous waste combustion, 

and semiconductor manufacturing.10 The next step consisted of evaluating

the level of emissions control achieved by the best-performing facilities in 

each source category and using this as the minimum level of control 

required throughout the entire source category.11

Additionally, the amendments required EPA to review the MACT 

standards every 8 years to evaluate any remaining, or residual, health risks 

from these sources and identify developments in control technologies. 

EPA has combined the residual risk assessments and technology reviews 

into a concurrent process. Thus, the agency simultaneously evaluates the 

remaining risks from each source category and the availability of new 

pollution control technologies. The risk assessment process seeks to 

estimate the cancer and other health risks faced by individuals exposed to 

toxic emissions. As shown in table 2, the four steps of risk assessment 

include hazard identification, dose-response assessment, exposure 

assessment, and risk characterization. 

 10EPA currently regulates 158 major source categories. Some industrial facilities may 

belong to multiple source categories. 

11MACT standards require all sources within a source category to control emissions to the 

same level. Existing sources generally must meet the average emission level achieved by 

the best performing 12 percent of sources in the source category. New sources must meet a 

more stringent emission level. 

Page 11 GAO-06-669 Clean Air Act
Table 2: Overview of the Risk Assessment Process 

Step Description

Hazard identification Determine the association between pollutants and adverse health 

effects. This involves reviewing studies of illnesses among groups 

of people or laboratory animals exposed to air pollutants. 

Dose-response 

assessment 

Describe the adverse health effects associated with different levels 

of exposure to a particular pollutant. 

Exposure 

assessment 

Estimate the amount of an air toxic a person is likely to inhale in a 

given period of time using data on emissions, meteorological 

conditions, and information on the locations of homes and 

workplaces relative to emissions sources. 

Risk 

characterization

Integrate the information from the three previous steps to describe 

the degree of increased risk faced by individuals. Typical results of 

this step include measures of excess lifetime cancer risk (e.g., a 

risk of 100 in 1 million), the population risk (e.g., the number of 

people that face a cancer risk exceeding 100 in 1 million), or the 

estimated number of additional cancer cases each year. 

Source: GAO analysis of EPA documents. 

Notes: EPA maintains information used in the hazard identification and dose-response assessment

stages of risk assessments in its Integrated Risk Information System (IRIS) database. 

Lifetime excess cancer risk refers to the estimated additional risk of developing cancer that a person 

would have if exposed to a specific concentration of an air toxic 24 hours a day, 7 days a week, for 70

years. 

The risk assessment process is limited by scientific uncertainty about the 

health effects associated with exposure to air toxics. Nonetheless, the 

Clean Air Act’s residual risk program seeks to determine whether the most 

exposed individuals face excess cancer risk of more than 1 in 1 million. In 

cases where estimated risks exceed this threshold, EPA develops a 

residual risk standard that seeks to provide an ample margin of safety for

affected individuals.12 Figure 2 provides an overview of the regulatory 

process for major stationary sources of air toxics, including MACT 

standards and 8-year technology and residual risk reviews. 

 12EPA generally uses a lifetime cancer risk of 1 in 10,000 as the upper boundary of

acceptability. As part of the ample margin of safety decision, EPA considers costs, 

technological feasibility, uncertainties, and other relevant factors. In this step, EPA must 

also assess whether to adopt more stringent standards to prevent adverse effects to 

wildlife, aquatic life, or natural resources considering cost, energy, and other relevant

factors. 

Page 12 GAO-06-669 Clean Air Act
Figure 2: EPA Air Toxics Regulatory Framework for Major Stationary Sources 

Source: GAO. 

Identify and list major 

source categories

that emit air toxics

Develop MACT 

standard based on 

the best performing 

sources within each 

source category 

Develop residual risk 

standards for each 

source category 

Evaluate developments

in control technology 

Study emissions and 

control technologies

for source categories

8 years later 

● Air toxics listed in 

Clean Air Act

● EPA to periodically 

revise and update list

In addition to requirements for major sources, the act required EPA to 

develop a comprehensive strategy to control emissions of air toxics in 

urban areas, including identifying at least 30 small stationary source 

categories that account for 90 percent of the risk from these sources, and 

issue regulations by November 2000. EPA has listed 70 small stationary 

source categories for regulation. The act also required EPA to assess the 

need for and feasibility of air toxics standards for motor vehicles and 

fuels, and, based on that assessment, issue regulations to control air toxics 

from motor vehicles and fuels. 

Table 3 summarizes the 453 actions required of EPA under the air toxics 

provisions of the 1990 amendments. Because these actions range in scope

from developing MACT standards to issuing reports, they vary in their 

potential to reduce emissions. 

Page 13 GAO-06-669 Clean Air Act
Table 3: Number of Air Toxics Actions Required under the 1990 Clean Air Act 

Amendments

Air toxics category 

Number of actions

required

Major stationary sources regulated by MACT standards 158

8-year residual risk reviews for MACT standards 96

8-year technology reviews for MACT standards 96

Standards for small stationary sources 70

Mobile sources 2

Other (reports, studies, etc.) 31

Total 453

Source: GAO analysis of EPA documents. 

Note: The act required EPA to list major and small source categories of the listed hazardous air 

pollutants (currently 187 chemicals). In response, EPA identified 158 major source categories and 

was required to issue a standard for each category. EPA responded by issuing 96 different standards,

some of which apply to multiple source categories. The 8-year residual risk and technology reviews 

apply to the 96 standards, which accounts for the difference between the 158 requirements to 

regulate major sources and the 96 requirements each for residual risk and technology reviews. 

EPA’s Office of Air and Radiation has primary responsibility for 

completing air toxics actions required under the Clean Air Act. Within the 

Office of Air and Radiation, responsibility for implementing the air toxics

requirements of the Act rests primarily with the Office of Air Quality 

Planning and Standards and, to a lesser extent, with the Office of 

Transportation and Air Quality. The responsibility for analyzing the health,

economic, and other effects of individual air toxics programs also rests 

with these offices. The Office of Policy Analysis and Review supplements 

these program-specific analyses by conducting periodic assessments of the 

health, ecological, and economic effects of the overall Clean Air Act, 

including the air toxics provisions, and coordinating these studies as 

appropriate with other EPA offices. In conducting these broader studies, 

the Office of Policy Analysis and Review also works with the Advisory 

Council for Clean Air Act Compliance Analysis, an independent, multidisciplinary panel of outside experts organized under the auspices of 

EPA’s Science Advisory Board. The agency’s Office of Research and 

Development performs scientific research on air toxics to support 

regulatory efforts. The Office of Enforcement and Compliance Assurance 

directs efforts to ensure compliance with air toxics requirements. In most 

cases, state and local air pollution control agencies implement the 

standards developed by EPA. Additionally, the act generally allows these 

agencies to impose more stringent requirements than the federal 

standards, although some states have enacted laws or rules prohibiting air 

Page 14 GAO-06-669 Clean Air Act
pollution control agencies from adopting more stringent requirements. 

Nonetheless, some state and local programs have developed innovative air 

toxics programs. 

EPA has completed issuing emissions standards for major stationary 

sources but issued most of these standards late and has made limited 

progress toward completing the remaining air toxics requirements. In 

particular, EPA has made little progress and is behind schedule in 

completing residual risk and technology reviews and in issuing emissions 

standards for small stationary sources and mobile sources. EPA’s limited 

progress and program implementation challenges have resulted primarily 

from the program’s lower priority relative to other clean air programs. 

Furthermore, the agency lacks a program implementation strategy. 

Stakeholders we interviewed—including EPA, state and local agency

officials, environmental groups, and industry representatives—provided 

additional perspective on EPA’s implementation of the air toxics program 

and highlighted data limitations and inadequate funding as major 

challenges. 

EPA has completed issuing the MACT standards for major stationary 

sources but has made limited progress in addressing requirements related 

to residual risk and technology reviews, and in issuing standards for small 

stationary sources and mobile sources. As a result of the limited progress 

in implementing these requirements, EPA has not reduced human health 

risks from air toxics to the extent and in the time frames envisioned in the 

act. Table 4 summarizes EPA’s overall progress in implementing air toxics 

requirements under the Clean Air Act. 

EPA Has Made 

Limited Progress in 

Addressing the Clean 

Air Act’s 

Requirements for Air 

Toxics and Faces 

Significant 

Implementation 

Challenges 

EPA Issued Most of the 

MACT Standards behind 

Schedule and Has Made 

Limited Progress in 

Completing the Other Air 

Toxics Requirements 

Page 15 GAO-06-669 Clean Air Act
Table 4: EPA Progress in Meeting Air Toxics Requirements 

Requirements met Requirements unmet 

Number of 

requirements Met on timea

Met late 

Unmet—

past due

Unmet—not 

yet due

Issue MACT emission standards for major 

source categories 158 4 154 0 0

Residual risk reviews 96 0 5 16 75

Control technology reviews 96 0 5 16 75

Small stationary sources 70 0 16 54 0

Mobile sources 2 0 1 1 0

Other 31 8 21 2b0

Total 453 12 202 89 150

Source: GAO analysis of EPA documents. 

Notes: This analysis reflects the status of the requirements as of April 2006. 

a

We count requirements met by EPA that did not have deadlines specified in the act as on time. 

b

EPA is required to periodically review the list of air toxics established by the act but has not yet done 

so. This requirement was not accompanied by a deadline. Based on other time frames required by

the act, we list this requirement as unmet/past due instead of unmet/not yet due. 

To meet the act’s requirements for major stationary sources, EPA had to 

identify a list of major source categories and then issue standards 

beginning in 1992, with all standards due by November 2000. In response, 

EPA identified 158 major source categories and issued 96 standards 

covering these categories between 1993 and 2004. Table 5 summarizes the 

timeliness of EPA’s MACT standards relative to the act’s deadlines. While 

the agency missed most of the deadlines, a senior EPA official said that 

issuing the 96 standards represented a major achievement and that the 

agency had never previously issued so many standards for one program in 

such a limited period of time. 

Page 16 GAO-06-669 Clean Air Act
Table 5: Timeliness of MACT Emission Control Standards for Major Source 

Categories

Requirements met according to the schedule 

specified in the Clean Air Act 

Number of 

requirements

On time

or early 

0-1 years 

late 

1-2 years 

late

More than

2 years 

late 

Issue MACT emission 

standards for major 

source categories 158 4 23 68 63

Source: GAO analysis.

Note: This analysis reflects the status of the requirements as of April 2006. 

Because EPA issued most of the MACT standards well behind schedule, 

the residual risk and control technology reviews, which EPA is to 

complete 8 years after issuing each standard, have been pushed back

commensurately, thereby delaying any additional public health protection 

that these reviews may provide. Specifically, instead of completing the 

initial residual risk assessments and technology reviews for all of the 

MACT standards by 2008 as specified by the act, EPA is not required to 

complete all of the initial reviews until 2012 because it issued many MACT 

standards behind schedule. For example, because EPA issued the MACT 

standard for industrial boilers in 2004 rather than 2000, as required, the 

residual risk assessment and technology review for this source category 

become due in 2012, almost 4 years later than the act’s intended timeline. 

Furthermore, EPA is behind schedule on the residual risk assessments and 

technology reviews. As of April 2006, EPA had finalized only five of these 

reviews, and all of these were late. Three additional reviews have courtordered deadlines and will be completed by the end of 2006, according to

EPA. 

The act required EPA to develop regulations for small stationary sources 

by November 2000.13 However, the agency has not met this schedule. In 

July 2000, EPA outlined its plans for issuing standards for small stationary

sources in a report to Congress describing its strategy for reducing threats 

 13EPA was to promulgate regulations for small stationary sources listed under section 

112(k) of the act by November 2000. Small stationary sources not listed under section 

112(k) were subject to a different schedule. 

Page 17 GAO-06-669 Clean Air Act
from air toxics in urban areas.14 This report identified 16 categories of 

small stationary sources that it described as “already subject to regulation” 

or “will be subject to regulation.” The report also identified 13 additional 

categories for which it planned to issue standards by 2004. In 2002, EPA 

expanded the list to include a total of 70 source categories. However, as of

April 2006, EPA has issued standards for only 16 categories of sources, 

leaving standards for 54 source categories past due. Furthermore, the 

agency faces court-ordered deadlines to complete standards for all of the

remaining categories of small stationary sources by June 15, 2009. 

The act also required EPA to study the need and feasibility of air toxics 

standards for motor vehicles and fuels and, based on the study, develop a 

regulation to control air toxics from motor vehicles and fuels by 1995. EPA 

completed the study in 1993 (about 11 months after the deadline) and, 

after missing the 1995 deadline for the regulation, faced a court-ordered 

consent decree to complete the regulation by 2001. To comply, EPA issued 

an initial rule in 2001 that stated that a second and final rule making would 

follow in 2004.15 The agency missed this deadline and eventually proposed 

a second rule in February 2006, with a final rule planned for February 

2007.

16 The proposed rule would limit the benzene content of gasoline and 

reduce toxic emissions from passenger vehicles and gas cans according to

EPA. 

Finally, the act contained 31 requirements that do not fit into the 

categories discussed above, including reports to Congress and guidance 

for state and local programs. As of April 2006, EPA has met 29 of these 

requirements. One of the key areas where EPA has not taken action relates 

to the act’s requirement for the agency to periodically review and update, 

as appropriate, the list of air toxics. Officials responsible for the program 

said the agency does not proactively conduct such reviews and instead has 

 14U.S. Environmental Protection Agency, National Air Toxics Program: The Integrated

Urban Strategy, Report to Congress (Research Triangle Park, North Carolina, 2000). 

15Among other things, the 2001 rule required refiners to maintain current levels of 

compliance with air toxic performance standards and did not require refiners to install new

equipment or use technologies beyond those already in use. EPA did not set additional air 

toxics requirements for vehicles at that time because the agency had already established 

other standards for vehicles and fuels that it believed represented the greatest degree of 

toxics control achievable at that time. See Control of Hazardous Air Pollutants From 

Mobile Sources, 66 Fed. Reg. 17229 (Mar. 29, 2001). 

16Control of Hazardous Air Pollutants from Mobile Sources, 71 Fed. Reg. 15804 (Mar. 29, 

2006). 

Page 18 GAO-06-669 Clean Air Act
adopted a reactive approach, whereby the agency responds to petitions 

filed by external stakeholders seeking to add or delete chemicals. EPA 

officials, citing insufficient resources to develop a more proactive 

approach, said that their efforts have focused on reviewing petitions for 

additions and deletions filed by external stakeholders. 

Since 1990, EPA has received one petition to list a new air toxic (diesel 

exhaust) and seven petitions to delist. The petition to list diesel exhaust is

under review, and of the seven petitions to delist, three have been granted, 

two have been denied, and two are under review, according to EPA. 

Overall, EPA has not added any new chemicals to the list of regulated

pollutants, but three chemicals and several substances from a listed group 

of chemicals have been removed. The agency’s consideration of diesel 

exhaust in response to an environmental group’s petition has taken more 

than 2 years, resulting in a lawsuit when the agency did not complete its 

review within 18 months, as required by the act. EPA and the

environmental group reached an agreement in February 2006 that requires

the agency to decide by June 2006 whether to list diesel exhaust as an air 

toxic. 

A 2004 report by the National Academies highlighted EPA’s lack of a

process for reviewing new pollutants despite the estimated 300 chemicals 

that enter commerce each year. The report recommended that EPA 

“establish a more dynamic process for considering new pollutants.” To 

date, EPA has not addressed this recommendation, according to senior 

agency officials. Furthermore, a 2004 study published in the Journal of the 

Air & Waste Management Association screened 1,086 chemicals for 

potential addition to the list of regulated air toxics and found that 44 

merited further consideration for addition to the list based on available 

toxicity and emissions data. 

Senior EPA air program officials said the agency’s progress in meeting the

act’s air toxics requirements should be viewed within the context of 

limited funding for clean air programs and the agency’s need to focus its 

resources on the areas where it expects the greatest health-risk 

reductions. Scientific information on the health effects of air toxics is less 

comprehensive than that available for higher-priority clean air programs, 

such as those targeting smog and particulate matter. Additionally, several 

Page 19 GAO-06-669 Clean Air Act
officials said that other regulatory and voluntary programs limit emissions 

of air toxics as a side benefit.17

EPA Faces Implementation 

Challenges and Lacks an 

Overall Management 

Strategy 

EPA considers the air toxics program a lower priority than its three other 

major clean air programs—including those to address criteria pollutants,

international environmental issues such as climate change, and indoor air 

quality issues such as exposure to radon gas—because senior officials in 

EPA’s Office of Air and Radiation believe these programs have more 

potential to reduce health risks. As shown in table 6, the percentage of 

funding for air toxics relative to all clean air programs ranged from 18 

percent to 19 percent between 2000 and 2003, but declined to 15 percent in

2004 and 12 percent in 2005. However, the total dollar amounts (in 

inflation-adjusted 2005 dollars) devoted to air toxics increased each year 

between 2000 and 2004, with a decline in 2005. 

Table 6: EPA Funding for Air Toxics Program as a Percentage of Funding for All

Clean Air Programs, Fiscal Years 2000 through 2005 

Thousands of dollars 

Fiscal year 

Funding for air

toxics program

Funding for all 

clean air 

programs 

Funding for air toxics

program as a percentage of

all clean air programs

2000 106,475 605,574 18

2001 118,331 640,056 18

2002 121,668 636,851 19

2003 122,118 641,514 19

2004 143,575 936,286 15

2005 112,986 909,219 12

Source: GAO analysis of EPA data. 

Note: Dollar amounts are in inflation-adjusted 2005 dollars. 

Within the air toxics program, EPA’s initial priority was to complete the 

MACT standards because the agency believed that this aspect of the 

program had the greatest potential to address risks from air toxics. 

Despite EPA placing a priority on issuing the MACT standards, the agency 

 17EPA officials cited the Toxics Release Inventory, various rules affecting motor vehicle 

fuel formulations, Design for the Environment, the Green Suppliers Network, and

community-based initiatives such as Community Action for a Renewed Environment

(CARE). 

Page 20 GAO-06-669 Clean Air Act
still fell behind schedule when it missed deadlines for the first round of 

standards (due in 1992) and has never caught up to the act’s 

implementation schedule. EPA officials said they missed some of the 

MACT deadlines because of technical challenges, including a lack of 

emissions data from affected source categories and the complexity of 

many of the regulated facilities. The missed deadlines led to lawsuits filed 

by external parties seeking compliance with the act’s implementation 

schedule, resulting in court-ordered deadlines for the agency to complete

standards. Furthermore, senior EPA officials said these court-ordered 

deadlines largely drive the program’s agenda. In this way, EPA ceded 

control of the priority-setting process, and this problem is still evident. For 

example, a senior official responsible for the development of regulations 

said that the agency’s highest priority for the remaining requirements is 

addressing residual risk reviews and small stationary source standards 

with court-ordered deadlines. 

The lower priority of the air toxics program in general and the priority 

given to MACT standards within the program, as well as technical 

challenges, have caused delays in completing the residual risk and 

technology reviews, as well as standards for small stationary and mobile 

sources. Further, as shown in table 7, available EPA data indicate that 

small stationary and mobile sources in total have accounted for more 

emissions than major stationary sources in every emissions inventory 

completed since the 1990 amendments. Furthermore, the agency has 

estimated that benzene—a known carcinogen emitted primarily by mobile 

sources—accounts for about 25 percent of the cancer risk posed by air 

toxics across the nation. Benzene is also the only air toxic that, to date,

EPA has determined poses sufficient risks to qualify as a “national cancer 

risk driver.”18

 18EPA applies the term “national cancer risk driver” to any air toxic that poses an estimated 

maximum lifetime cancer risk exceeding 10 in 1 million to more than 25 million people. 

Page 21 GAO-06-669 Clean Air Act
Table 7: Percentage of Estimated Total Air Toxics Emissions by Source Type, 1993, 

1999, and 2002 

Percent

Year 

Estimated total 

emissions

(million tons)

Mobile 

sources

Small 

stationary 

sources 

Major stationary 

sources Other

2002 4.6 41 30 20 9

1999 5.1 43 25 25 6

1993 7.1 46 24 27 3

Source: GAO analysis of EPA data. 

Note: Totals may not add to 100 percent due to rounding. 

EPA developed air toxics emission inventories for 1993, 1996, 1999, and 

2002. A large part of the 1993 baseline inventory is based on data obtained

from 1990. For simplicity, and because EPA has traditionally referred to it 

as such, we refer to this data as the 1993 baseline inventory. EPA said it 

did not provide data for 1996 because the agency has not updated the 

information from that year for consistency with the methodology used for

the 1993, 1999, and 2002 data. 

EPA expects that the proposed mobile source air toxics rule will reduce 

benzene emissions. In addition, a senior EPA air program official said that 

other regulations for mobile sources, including standards that affect 

gasoline formulations as well as programs addressing emissions from 

diesel engines, will also reduce emissions of air toxics as a side benefit.

Nonetheless, mobile sources will continue to represent an area of 

significant opportunity to reduce emissions and related human health 

risks. 

Addressing the remaining requirements for residual risk standards and 

small stationary sources will require overcoming significant technical 

challenges. Regarding residual risk standards, the Clean Air Act’s 

requirement that EPA introduce a risk element into the regulatory 

decision-making process marks a departure from the approach the act 

used with MACT standards, which generally did not require EPA to take 

the inherent toxicity or health risks from pollutants into account. EPA 

officials said that conducting the residual risk assessments requires a large 

amount of data, much of which is difficult to obtain. For example, to 

adequately assess the human health risk posed by a particular source, EPA 

needs data on the health effects associated with each pollutant, the 

Page 22 GAO-06-669 Clean Air Act
location of sources, distances between sources and affected populations, 

and the concentrations of emissions at different distances from facilities. 

Challenges in regulating small stationary sources center on difficulty in 

characterizing the large number of widely dispersed facilities such as 

industrial boilers, paint-stripping operations, and auto-body shops. In 

some cases, data do not exist on the number or location of facilities 

potentially subject to a regulation. Furthermore, unlike the large stationary

sources affected by MACT standards, owners and operators of these 

sources have limited resources to implement regulations and will require 

extensive outreach and compliance assistance. 

EPA’s challenges in meeting the act’s remaining requirements are 

exacerbated by the lack of a management plan that identifies priorities and 

necessary resources. The agency’s overall strategic plan outlines the goals 

and targets for emissions and risk reduction across all clean air programs 

but does not specify priorities or necessary levels of funding for the air 

toxics program. Similarly, the agency’s budget requests provide limited 

information on the agency’s air toxic program activities or priorities. 

Furthermore, a senior EPA official said that the agency has not estimated 

how much funding the air toxics program needs to meet the act’s 

remaining requirements. Such information could assist Congress in 

making its appropriations decisions, enhance the program’s transparency 

to the public, and guide the agency in implementing the program. 

Key Program Stakeholders 

Provided Further Insights 

on EPA’s Implementation 

Challenges 

To better understand the challenges facing EPA’s air toxics program, we 

interviewed various stakeholders, including officials from EPA, industry 

and environmental groups, and state and local air pollution control 

agencies.19 Each respondent rated the extent to which nine specific issues 

posed a challenge to EPA in implementing the air toxics program, and we 

then averaged the responses within each stakeholder group. As shown, in 

table 8, the average response within each group identified at least one of 

seven different issues as a challenge to a large or very great extent.20

Although perceptions varied among the stakeholder groups, three issues 

emerged as primary challenges—the availability of reliable data to assess 

 19See appendix II for information on our methodology for interviewing stakeholders. 

20The two challenges not rated as significant by any stakeholder groups were “complexity 

of required analyses to support regulatory actions” and “rigidity of Clean Air Act 

requirements.” 

Page 23 GAO-06-669 Clean Air Act
the benefits of regulating air toxics, the adequacy of program funding, and

the program’s low priority relative to other clean air programs. As shown 

in the table, respondents from at least three of the four stakeholder groups 

we interviewed identified each of these challenges as significant. 

Table 8: Issues Rated by Stakeholders as Challenges to a Large or Great Extent

Stakeholder groups

Challenges EPA Industry Environmental 

State and

local 

Availability of reliable data to assess benefits of regulating hazardous air 

pollutants 9 9 9

Adequacy of program funding 9 9 9

Priority of program relative to other air programs 9 9 9

Number of Clean Air Act requirements pertaining to hazardous air 

pollutants 9 9

Adequacy of resources at the state, local, and tribal levels to implement 

regulations 9 9

Strain on resources due to litigation 9

Availability of reliable data on sources and their emissions 9

Source: GAO.

Several stakeholders identified linkages among the three primary 

challenges. For example, some stakeholders said that the problems with 

limited resources stemmed from the program’s low priority. In addition, 

some stakeholders said that the lack of information on the benefits of 

regulating air toxics reinforced the program’s low priority because the 

agency cannot demonstrate the results it achieves through investments in 

the program. 

In addition, industry and EPA stakeholders cited the number of air toxics 

requirements as a challenge to a large or very great extent. Respondents 

from both groups stated that the agency has insufficient resources to meet 

such a large number of requirements in the specified time frames. Industry 

officials noted that the number of requirements was unrealistic, and some 

EPA stakeholders said that Congress did not understand the number of 

emissions sources involved or the level of effort required to write 

standards. EPA and state and local stakeholders also cited the adequacy of 

resources at the state, local, and tribal levels to implement regulations as a 

significant challenge. 

Page 24 GAO-06-669 Clean Air Act
The information available on the costs and benefits of EPA’s air toxics 

program is not sufficiently comprehensive to measure the overall 

effectiveness of the program. For example, because of limited data, EPA’s 

major economic assessments of the Clean Air Act have not included 

monetized estimates of the program’s benefits, such as reduced incidence 

of cancer, and have provided only limited information on costs. The 

absence of information on benefits stems from a lack of data on the extent

to which incremental reductions in exposure to air toxics affect an 

average person’s chance of developing adverse health effects. The agency 

also lacks reliable data on the quantities of each pollutant emitted prior to 

the adoption of air toxics regulations or in the years thereafter. 

Furthermore, other potential indicators of the program’s effectiveness, 

such as data on compliance with air toxics regulations, are inconclusive.

As a result, it is difficult to compare the results of investments in the air 

toxics program with those generated by clean air programs on which EPA 

has placed a higher priority. 

Although EPA has conducted two major assessments of the costs and 

benefits of its programs under the Clean Air Act, the agency has not fully 

analyzed the air toxics program primarily because of difficulty in 

characterizing the program’s effects on public health.21 Without a 

comprehensive assessment of costs and benefits, it is difficult to gauge the 

program’s cost effectiveness or net benefits (total benefits minus total 

costs) or compare these effects with those of higher-priority air pollution

control programs. 

Available Information 

on Costs and Benefits 

Is Not Sufficient to 

Measure the 

Program’s 

Effectiveness 

EPA’s Assessments of the 

Clean Air Act Have Not 

Estimated the Economic 

Benefits of the Air Toxics 

Program 

The two assessments of the act’s costs and benefits focused on separate 

time periods. EPA refers to the first assessment, completed in 1997, as the 

“retrospective” analysis because it covered the period 1970 to 1990. It is of 

limited use in understanding the economic effects of the current air toxics 

program because this time period predates the significant expansion of the 

program after the 1990 amendments. 

The second analysis, completed in 1999, is referred to as the “prospective” 

analysis because it covered the period 1990 to 2010. This study attempted 

to forecast the future economic impacts of the 1990 amendments and 

 21U.S. Environmental Protection Agency, The Benefits and Costs of the Clean Air Act,

1970 to 1990 (Washington D.C., 1997); and The Benefits and Costs of the Clean Air Act, 

1990 to 2010 (Washington D.C., 1999). 

Page 25 GAO-06-669 Clean Air Act
estimated that the overall net benefits of clean air regulations from 1990 to

2010 would total $510 billion (1990 dollars), with a benefit-to-cost ratio of 

four to one. Most (over 90 percent) of the monetized benefits included in 

the analysis stemmed from reduced incidence of health effects associated 

with exposure to five of the six criteria pollutants—carbon monoxide, 

ground-level ozone, particulate matter, nitrogen oxides, and sulfur dioxide. 

EPA places the highest priority within its clean air programs on the 

criteria pollutants. 

The prospective analysis is of limited use in understanding the effects of 

the air toxics program because it provided incomplete information on the 

costs of air toxics standards and did not include estimates of the human 

health or other benefits of these standards. Specifically, the cost estimates 

reflect only the 21 standards EPA had issued at the time of the study—a 

number that has since grown to 96. EPA estimated that the cost to industry 

of complying with these 21 MACT standards would total $780 million in 

2000 and rise to $840 million by 2010. According to EPA, these estimates 

primarily reflect the cost of purchasing, operating, and maintaining 

pollution control equipment. As shown in table 9, these costs represent a 

relatively small fraction of the total estimated costs of the 1990

amendments over that time period. 

Table 9: Summary of Annual Costs Imposed by the 1990 Clean Air Act Amendments 

Dollars (in millions) 

Programs Costs in 2000

Percentage of

 total costs Costs in 2010

Percentage of

 total costs 

Title I—Ambient air quality standards $8,600 44 $14,500 54

Title II—Mobile sources 7,400 38 9,050 34

Title III—Air toxics 780 4 840 3

Title IV—Acid rain 2,300 12 2,040 8

Title V—Permitting 300 2 300 1

Total annual costs $19,400 100 $26,800 100

Source: EPA. 

Note: Dollar Amounts are in 1990 dollars. 

An EPA official responsible for the prospective study said that the agency 

did not include estimates for the aspects of the program that it had not yet

implemented—such as the 75 remaining MACT standards—because, at the 

time, the agency did not have information on the number of facilities that

would have to comply with future standards or the level of emissions 

control the standards would require. Without this information, the official 

Page 26 GAO-06-669 Clean Air Act
said it was appropriate to exclude these future standards from the 

analysis. Nonetheless, EPA acknowledged the lack of information on the 

costs of future air toxics standards as a key uncertainty of the analysis.22

EPA plans to update its cost estimates as part of a new prospective 

analysis covering 1990 to 2020. The revised cost estimates will include all

of the completed MACT standards as well as any other air toxics rules 

issued by September 2005 (except the residual risk rule for coke ovens, 

which entails emissions reductions and compliance costs that would have 

a negligible effect on the overall analysis). An EPA official responsible for 

the analysis said the agency expects to have preliminary results of the 

revised cost estimates in late 2006, with a final report expected in 2007. 

EPA Lacks Key Data 

Needed to Estimate the 

Benefits of Air Toxics 

Regulations 

The prospective analysis of the 1990 Clean Air Act amendments did not 

include monetized estimates of the benefits of air toxics regulations, such 

as decreased cancer risks to affected individuals, because the agency did 

not have sufficient data to estimate these effects. As shown in table 10, 

estimating the benefits of EPA’s air toxics program requires a substantial

amount of scientific data. Specifically, this process involves determining 

the extent to which reductions in exposure to air toxics have decreased 

the incidence of adverse health effects, including cancer and noncancer 

illnesses. This, in turn, requires estimating the extent of adverse health 

effects stemming from exposure to air toxics both before (see steps 1 to 3 

below) and after (see steps 4 to 6 below) adopting air toxics regulations.

For example, exposure to air toxics prior to the adoption of a regulation

may have caused 1,000 cases of cancer per year but the presence of a

regulation may have decreased this number to 500 cases per year. The 500 

avoided cases would represent a key health benefit of the regulation. The 

final step of the process (step 7) involves assigning dollar values to these 

health benefits. 

 22EPA identified other key uncertainties with its cost analysis, including that the estimates 

were based on the costs of pollution control technologies that were available at the time

and did not account for potential reductions in future costs due to technological 

innovation. 

Page 27 GAO-06-669 Clean Air Act
Table 10: Key Steps in Estimating the Benefits of Controlling Air Toxics 

Step Task Data requirements

1 Characterize the relationship between pollutants and the 

adverse health effects associated with exposure to these 

pollutants (referred to as “dose-response” relationships). 

Information on cancer and noncancer effects of 187 different

pollutants, as well as on how incremental decreases in 

exposure to these pollutants affect the incidence of each 

adverse health effect. 

2 Determine the baseline level of human exposure to pollutants 

in the absence of air toxics regulations. 

Information on concentrations of each pollutant in the ambient 

air prior to adoption of air toxics regulations, and on human

exposures to these pollutants. This requires information on the 

amount of each pollutant emitted prior to the regulations, as 

well as computer models that calculate human exposures 

based on emissions data and other key variables such as 

meteorological conditions. 

3 Use data from steps 1 and 2 above to determine the number 

of cases of each adverse health effect in the absence of 

regulations. 

No additional data required. 

4 Determine level of human exposure to pollutants after the 

regulation. This involves estimating the extent to which the 

regulation has decreased emissions of each pollutant and 

related human exposures. 

Information on the amount of each pollutant emitted after 

adopting air toxics regulations, and computer models used in 

step 2 to estimate the remaining level of exposure to each 

pollutant. 

5 Calculate the remaining incidence of each health effect after 

implementing the regulation. 

Same as step 3; no additional data required.

6 Determine the number of cases of each health effect avoided 

as a result of the regulation by subtracting the number of 

remaining cases of adverse health effects (identified in 

step 5) from the number of baseline cases prior to the 

regulation (identified in step 3). 

No additional data required. 

7 Assign dollar values to the number of avoided cases 

identified in step 6. 

Economic studies on the value of reducing incidence of cancer 

and noncancer health effects.

Source: GAO analysis of EPA data. 

Two primary factors limit EPA’s ability to estimate the benefits of air 

toxics regulations. First, EPA lacks adequate information on the extent to

which incremental reductions in exposure affect an average person’s 

chance of developing adverse health effects. The limited information on 

these “dose-response” relationships represents the greatest challenge for 

the agency in conducting a benefits assessment for the air toxics program, 

according to a senior EPA official responsible for the retrospective and 

prospective analyses. A senior EPA official responsible for risk analysis 

drew a distinction between the type of data needed for a risk assessment, 

which often involves extrapolation from studies involving laboratory 

animals, and the type of data that economists need for a benefits 

assessment, which generally requires studies of human exposures. The 

official said that EPA currently has sufficient toxicological data, primarily 

from animal studies, to assess risks from 133 of the 187 air toxics. 

Page 28 GAO-06-669 Clean Air Act
However, the official said the agency only has the type of dose-response 

data needed to estimate the economic benefits for a handful of pollutants.23

Second, EPA lacks reliable information on the quantities of each pollutant 

emitted prior to the adoption of air toxics regulations or in the years after 

adopting the regulations. EPA has tracked emissions of air toxics since 

1993 and prepares a National Emissions Inventory every 3 years. In 2006, 

EPA completed its most recent inventory, which has information on 

emissions in 2002. While the inventory represents the best available data

on emissions of air toxics and is useful for identifying the relative 

contribution of emissions from different sources, a 2004 EPA Inspector 

General report identified shortcomings of the inventory that raise 

questions about its reliability and usefulness in measuring the effects of 

the air toxics program.24 For example, the report said that EPA cannot tell

whether apparent reductions or increases in the inventory have resulted 

from changes in the way the agency estimated the inventory or from real 

reductions or increases in emissions. The report also cited problems with

the limited involvement of state agencies in the development and 

validation of the inventory. 

Although the data in the emissions inventory are limited, EPA has used the 

emissions inventory and other available data to estimate human exposures 

to these pollutants. In 1999, EPA released its first National-Scale Air 

Toxics Assessment (NATA), which relied on data from the 1996 emissions 

inventory to estimate the potential health risks posed by air toxics in 

different geographic areas. EPA updated this analysis in 2006 using data 

from the 1999 emissions inventory. While NATA is a useful indicator of 

potential health risks from air toxics at a given point in time, it is not 

useful as a measure of the agency’s effectiveness in implementing the air 

toxics program because, according to EPA, the agency revised the number 

of stationary sources and pollutants included in its analysis. For example, 

the analysis based on the 1996 emissions inventory assessed risks from 33 

pollutants, while the most recent analysis included 177 pollutants. As a 

 23EPA has some dose-response data for benzene and plans to include the results of a case 

study assessing the benefits of reductions in benzene emissions in the Houston area in the

next comprehensive assessment of Clean Air Act programs, which the agency expects to

issue in 2007. 

24U.S. Environmental Protection Agency, Office of Inspector General, EPA’s Method for 

Calculating Air Toxics Emissions for Reporting Results Needs Improvement 

(Washington, D.C., 2004). 

Page 29 GAO-06-669 Clean Air Act
result, EPA believes it is not meaningful to compare the results of the two 

assessments.

Overall, the limited information on health outcomes associated with 

changes in exposure to air toxics hinders EPA’s ability to quantify or 

monetize the economic benefits resulting from the air toxics program. In 

turn, this limits EPA’s ability to develop monetized estimates of the 

program’s net benefits or cost effectiveness. Such information would be 

useful not only for better understanding the economic effects of the air 

toxics program, but also for comparing the cost effectiveness of different 

air quality programs, which would help prioritize funding in addressing 

human health problems caused by air pollution. This information would 

also help EPA prioritize its remaining obligations under the 1990 

amendments. In May 2002, EPA’s Office of Research and Development 

(ORD) released a draft air toxics research strategy that discussed the 

agency’s plans for improving information on dose-response relationships.25

In addition, ORD issued an air toxics plan in April 2003 that identified the

shortcomings of existing dose-response data and plans for improving this 

information.26 In reviewing these documents, the agency’s Science 

Advisory Board identified several concerns, including poor linkages across 

the two documents, inadequate research funding, and the need for a better 

research prioritization scheme.27

Other Indicators of the 

Program’s Effectiveness 

Are Inconclusive 

Without sufficient information to conduct a comprehensive cost-benefit 

analysis, EPA measures the effectiveness of its air toxics program based 

on estimated data from its emissions inventory. Specifically, EPA 

measures the changes in aggregate emissions (measured in tons per year) 

of all air toxics by comparing estimates from the most recent emissions 

inventory with the 1993 baseline inventory. While estimated emissions 

decreased by about 35 percent between 1993 and 2002 according to EPA, 

the data quality problems discussed above limit their usefulness in 

measuring the program’s effectiveness. 

 25U.S. Environmental Protection Agency, Office of Research and Development, Air Toxics 

Research Strategy (external review draft) (Washington, D.C., 2002). 

26U.S. Environmental Protection Agency, Office of Research and Development, Air Toxics 

Multi-Year Plan, (Washington, D.C., 2003). 

27U.S. Environmental Protection Agency, Science Advisory Board, EPA’s Air Toxics 

Research Strategy and Air Toxics Multi-Year Plan (Washington, D.C., 2004). 

Page 30 GAO-06-669 Clean Air Act
Two other problems also limit the usefulness of the emissions data as a 

performance measure. First, because pollutants differ substantially in their 

toxicity—small quantities of some chemicals pose greater risks than large 

quantities of less harmful chemicals—measuring changes in the total tons

of all air toxics emitted does not necessarily provide a strong indication of 

the program’s effectiveness in addressing health risks. The EPA Inspector 

General report discussed above recommended developing performance 

measures that address progress toward reductions in human exposure and 

health risk. Such measures would provide a better indication of changes in

risks from air toxics. In the justification for its proposed fiscal year 2007 

budget, EPA said that it was developing a “toxicity-weighted” emissions 

measure for the program. 

Second, EPA’s practice of measuring the air toxics program’s performance 

using estimated aggregate emissions data may not accurately measure the 

effect that the program has had on changes in emissions. The current 

performance measure attributes all changes in emissions to the federal air 

toxics program, but emissions may change for reasons unrelated to the 

agency’s regulations. Some decreases in emissions may reflect cases 

where state and local air pollution control agencies have issued rules to 

control emissions that go beyond the federal regulations. As discussed in 

the next section of this report, some states set more stringent standards 

than EPA. On the other hand, a senior EPA official responsible for the 

economic analysis of air pollution regulations said that the agency may 

actually underestimate the program’s effect. The official said that because 

of economic growth and related increases in industrial production over 

time, emissions would far exceed the current levels without the existing 

EPA air toxics regulations. 

We also evaluated two other potential indicators of the program’s 

effectiveness—data on levels of air toxics in the ambient air and 

information on the degree of compliance with clean air regulations—to 

determine their usefulness as indicators of the program’s effectiveness. 

While both could eventually serve as useful performance indicators, the 

available data are currently limited and inconclusive. Regarding data on 

ambient levels of air toxics, EPA has a monitoring network that includes 

22 locations nationwide. The monitors generally track ambient levels of 

Page 31 GAO-06-669 Clean Air Act
six priority air toxics that EPA believes pose a concern in all geographic 

areas of the United States.

28

A 2005 EPA Inspector General report found shortcomings of the 

monitoring network, including limited monitoring in areas with the highest 

estimated cancer risks from air toxics as well as inconsistencies in the 

operation of the monitors.29 In responding to the report, EPA said that the 

Inspector General’s concerns generally aligned with the agency’s 

monitoring improvement efforts. It is currently unclear whether the 

existing monitoring data are representative or reliable indicators of the 

program’s effectiveness. Nonetheless, ambient monitoring is a valuable 

component of the air toxics program and could eventually serve as a 

useful performance measure. It is also important to note that, while not 

part of the national monitoring network, a number of state and local 

agencies conduct their own air toxics monitoring. 

Finally, we reviewed available information on the degree of compliance 

with air toxics standards identified through evaluations of regulated 

facilities conducted by federal and state enforcement officials. As shown 

in table 11, inspectors have found most facilities in compliance with air 

toxics standards, with some degree of noncompliance at about one-quarter 

of all facilities. Compliance rates for these facilities may not represent the 

degree of compliance at all facilities because enforcement officials do not 

visit each facility every year and often target facilities where they suspect 

noncompliance.30 EPA enforcement officials said they do not currently 

have comprehensive data explaining the magnitude of the noncompliance 

in cases where inspectors found violations. For example, noncompliance 

could range from record-keeping problems to more serious violations, 

such as exceeding an emissions standard. Furthermore, it is important to 

note that, while EPA has completed issuing all of the MACT standards, 16 

standards have compliance dates after June 2006. Thus, information on 

 28The six priority air toxics include acrolein, arsenic, benzene, hexavalent chromium, 

formaldehyde, and 1,3 butadiene. EPA currently monitors for arsenic, benzene, hexavalent

chromium, formaldehyde, and 1,3 butadiene at all locations, and plans to monitor for

acrolein at all locations beginning January 1, 2007. 

29U.S. Environmental Protection Agency, Office of Inspector General, Progress Made in

Monitoring Ambient Air Toxics, But Further Improvements Can Increase Effectiveness 

(Washington, D.C., 2005). 

30According to EPA, a total of 4,271 facilities were required to comply with MACT 

standards as of 2004. 

Page 32 GAO-06-669 Clean Air Act
compliance with these standards will not become available until after that 

time. 

Table 11: Results of Inspections at Facilities Regulated by Air Toxics Standards, 2003 and 2004 

Year 

Total facilities 

inspected

Facilities in compliance 

(percentage of total)

Facilities in 

noncompliance

(percentage of total) 

Facilities with unknown 

compliance status

(percentage of total)

2004 731 483 (66) 194 (27) 54 (7)

2003 664 432 (65) 174 (26) 58 (9)

Source: GAO analysis of EPA data. 

While the available enforcement data are limited, EPA has identified cases

of significant noncompliance with air toxics regulations. Specifically, the 

agency has initiated a nationwide air toxics enforcement strategy to 

identify and correct noncompliance and achieve emissions reductions in 

targeted industry sectors. According to EPA, in 2005, the agency took 

enforcement actions against facilities that failed to comply with targeted 

MACT standards which resulted in air toxics reductions of more than 160 

tons and fines exceeding $600,000 (2005 dollars). Furthermore, an official 

in EPA’s Office of Enforcement and Compliance Assurance said that the

agency achieved about 190 additional tons of air toxics reductions in 2005 

through enforcement actions that were not associated with the national air 

toxics enforcement strategy. 

State programs we reviewed in California, New Jersey, Oregon, and 

Wisconsin, and the local program we reviewed in Louisville, Kentucky,

have air toxics programs that go beyond the federal program and employ 

practices that might help EPA enhance the effectiveness of its program. 

First, these programs address some public health risks that have not been

addressed by the federal program. EPA could potentially strengthen its 

program by assessing and considering what states perceive as the primary 

gaps in the federal program. Second, the programs generally prioritize air 

toxics activities based on their risk reduction potential, which could serve 

as an example for EPA in prioritizing its remaining obligations under the 

act. Third, some of the programs conduct comprehensive risk assessments 

to identify the risk posed by all emissions from a facility, while EPA’s 

residual risk program assesses risk in a more piecemeal and limited 

fashion. Fourth, several of the programs employ systematic approaches to

identify and prioritize chemicals for addition to their lists of regulated air 

toxics, whereas EPA does not have such a process. Finally, the agencies 

stressed the importance of reliable data on emissions and chemical 

State and Local 

Programs Employ 

Practices That Could 

Potentially Help EPA 

Enhance the 

Effectiveness of the 

Federal Air Toxics 

Program 

Page 33 GAO-06-669 Clean Air Act
toxicity, and several programs have processes to better ensure the 

accuracy of emissions data submitted by regulated facilities. (See app. III 

for information on the key features of the state and local programs we 

reviewed.) 

Several State and Local 

Programs Address Gaps in 

EPA’s Program 

The five programs we reviewed address some public health risks that 

EPA’s program does not. For example, the programs regulate smaller 

sources than EPA, set more stringent technology standards to control 

emissions, and include some large stationary sources that EPA does not 

address.31 In Wisconsin, any facility that emits one of 535 air toxics in 

amounts that exceed certain thresholds may be subject to the state’s air 

toxics program. In some cases, annual emissions of less than 1 pound per 

year from a facility could trigger the state rule, depending upon the 

toxicity of the chemical. Wisconsin officials said that they use lower 

thresholds than the Clean Air Act’s 10- or 25-ton thresholds because even 

small emissions of very toxic chemicals can present risks to the public.

Similarly, New Jersey officials said that their state program addresses 

smaller facilities than EPA because most of the numerous chemical 

facilities in the state are not subject to MACT standards since they do not

emit air toxics at levels that exceed federal thresholds. In contrast, in 

accordance with the Clean Air Act, MACT standards for major sources and 

the corresponding residual risk reviews apply to facilities in 158 industries 

with emissions of 10 tons or more of a single air toxic or 25 tons or more 

of a mixture of the 187 federal air toxics. 

In terms of the stringency of the technology standards used to limit 

emissions of air toxics, California and New Jersey officials said that the 

technology standards in their states were often more stringent than EPA’s 

MACT standards. For example, California officials said that petroleum 

refineries in their state use more stringent control technologies, and they 

noted that EPA chose not to include these technologies as part of its 

survey of controls already in use when it developed the MACT standard 

for this industry. 

Regarding the types of facilities that are regulated by EPA, some state 

officials expressed concern that EPA did not develop MACT standards for 

some major stationary sources of air toxics in their states. For example, 

 31Establishing more stringent pollution control requirements generally involves trade-offs

between regulatory costs and potential public health benefits. 

Page 34 GAO-06-669 Clean Air Act
Oregon officials said that they requested EPA to issue MACT standards for 

several categories of sources, including ceiling tile manufacturing and 

titanium smelting if it found that they were major sources of air toxics. 

Oregon officials expressed concern with EPA’s apparent lack of response 

to their request because these significant emitters of air toxics in Oregon 

do not fall into one of the 158 major source categories that EPA identified

and regulates. Further, the State and Territorial Air Pollution Program 

Administrators and the Association of Local Air Pollution Control Officials 

(STAPPA/ALAPCO) has compiled a list of over 40 major emission source 

categories of air toxics that were not regulated by EPA MACT standards. 

While the five programs we reviewed would generally address such 

sources, similar sources would be unregulated in the states whose 

programs are based entirely on the federal program. Importantly, in a 

number of cases, state law limits the ability of state and local programs to 

go beyond federal requirements. For example, in 2002, STAPPA/ALAPCO 

found that 26 states from every region in the country have precluded their 

state air pollution control agencies from imposing clean air requirements 

beyond those established by EPA. 

State and Local Programs 

Prioritize Their Actions 

Based on Risk Reduction 

Potential 

The approaches some state and local agencies use to develop their air 

toxics programs differ from EPA’s approach in that they direct resources 

to the areas of highest risk, whereas, given the Clean Air Act’s prescribed 

schedule, EPA has primarily focused on regulating emissions from certain 

large stationary sources. In contrast, several state and local programs 

generally rely on monitoring (the measurement of air toxics in the ambient 

air) and modeling (estimating toxics in the air using computer models) to 

identify chemicals, geographic areas, or facilities of concern and develop 

measures to address these risks. 

The Oregon and Louisville, Kentucky, programs illustrate the use of riskbased prioritization. Oregon’s air toxics program seeks to identify 

geographic areas of high risk through modeling and monitoring and to 

then concentrate resources on those areas. While not yet fully 

implemented, the program plans to conduct statewide modeling using its

emissions inventory to identify areas of potential concern and then 

conduct monitoring to delineate geographic areas of high risk. According 

to program staff, the geographic approach is an efficient way to address 

risk because it is targeted and focuses on the greatest risks. Because 

public health risks from air toxics may vary depending on proximity to 

emissions sources and other factors, the practice of identifying areas of 

high risk and taking steps to address these risks shows promise as part of 

an overall risk reduction strategy. 

Page 35 GAO-06-669 Clean Air Act
Similarly, Louisville created a program to address high health risks near an 

industrial complex and in the surrounding community that were identified 

through monitoring of pollutants in the ambient air. According to program 

officials, toxic emissions from a section of Louisville called 

“Rubbertown”—home to a complex of chemical facilities and other 

manufacturers—have been the subject of public concern since the 1940s. 

From 2000 through 2001, program officials worked with the University of 

Louisville, EPA, and other stakeholders to monitor the ambient air near 

Rubbertown and the surrounding community to assess the extent of the 

problem. A risk assessment based on the monitoring data determined that 

18 chemicals posed an unacceptable risk to the public. Consequently, 

Louisville officials designed the program to target large emitters of these 

18 chemicals before targeting smaller emitters of air toxics. 

In addition to some states’ focus on identifying geographic areas or 

chemicals of concern, the state and local programs we reviewed use 

monitoring and modeling data to focus their efforts on specific facilities 

that pose risks to the public. For example, California requires certain large 

and small sources of air toxics to conduct facilitywide risk assessments 

using a standardized risk-screening model. If the modeling results show 

that risks exceed certain thresholds, the facility must conduct a more 

comprehensive risk assessment. This process allows California’s state and

local agencies to identify and focus on the sources that pose high risks to 

the public. In addition, Louisville and Wisconsin require certain sources to 

conduct facilitywide risk assessments as part of the permitting process.32

In contrast, several state and local officials said that EPA’s program has 

not focused on the greatest risks. While EPA may have been driven by 

certain deadlines in the act, some state and local officials said that the 

agency has chosen to focus on certain large stationary sources even 

though EPA’s data suggest that emissions from small stationary sources 

and mobile sources may pose greater risks. Further, EPA is currently 

developing a rule that would exempt MACT-regulated facilities from 

regulation under its residual risk program if, on the basis of risk 

assessments, the facilities demonstrate that the cumulative risks from all 

of their toxic emissions do not exceed certain thresholds. According to 

EPA, this strategy could achieve voluntary risk reductions from facilities 

 32New Jersey may also require some sources to conduct facilitywide risk assessments as 

part of the permitting process, but this is not a routine practice, according to a New Jersey 

program official. 

Page 36 GAO-06-669 Clean Air Act
that would not be required to reduce risks under the current residual risk 

program and will provide high-quality, site-specific emissions data for use 

in future assessments and emission reduction strategies. While this 

approach has the potential to ease the regulatory burden on low-risk 

facilities, EPA may have opportunities to apply its limited resources to 

approaches that have greater potential to reduce risks. 

Several of the Programs 

We Reviewed Conduct 

More Comprehensive 

Facilitywide Risk 

Assessments Than EPA 

Several state and local programs we reviewed generally evaluate the 

emissions from all of the emissions points within a facility in a single risk 

assessment in order to assess the health risks associated with the entire 

facility. In contrast, EPA’s residual risk assessments—aimed at identifying 

and mitigating any remaining health risk from emissions sources subject to 

MACT standards—have only evaluated risk from a portion of the facilities. 

Specifically, to date, EPA has limited the scope of its residual risk 

determinations to emissions points within facilities that must comply with 

the MACT standards at issue, although other emissions points may also 

emit air toxics.33 As a result, according to several state and local officials, 

some facilities with a high impact on public health may avoid additional 

control requirements because EPA’s focus on limited portions of facilities 

may underestimate the risk posed by whole facilities. 

Figure 3 illustrates a facility emitting air toxics from four emission points. 

Of the four emission points within the facility, points 1 and 2 are each 

covered by different MACT standards and, therefore, are subject to 

separate residual risk assessments. Emission points 3 and 4 emit air 

toxics, but are not subject to MACT standards, because emissions from 

these two points do not exceed the MACT threshold. 

 33The preamble to EPA’s first final residual risk rule, the National Emission Standards for 

Coke Oven Batteries, 70 Fed. Reg. 19991, 19998 (Apr. 15, 2005), articulates the agency’s 

approach for evaluating remaining health risks from facilities regulated by MACT 

standards. EPA relied on this approach in its five final residual risk rules to date. 

Page 37 GAO-06-669 Clean Air Act
Figure 3: Emission Points at an Industrial Facility Emitting Air Toxics 

The programs we reviewed in California, Wisconsin, and Louisville would 

generally evaluate the emissions from all of the emissions points in this 

facility in a single risk assessment.34 In contrast, EPA’s approach to date 

would be to conduct a residual risk assessment for emission point 1 that 

would consider the exposure and human health risk attributable to 

emissions from that emission point, and generally would not consider the 

emissions from point 2, which falls under a different MACT standard, or 

the emissions from points 3 and 4. According to EPA, it is not entirely 

precluded from considering emissions from additional emissions points 

not covered by the MACT standards at issue, but the agency, to date, has 

not exercised this discretion in a final rule. 

Several state and local stakeholders said that they were concerned that 

EPA’s risk assessments may show a lower level of risk to the public than if 

the agency considered emissions from all of the emission points at the 

facility. They said that EPA’s residual risk approach may exclude some 

facilities with a high impact on public health from more stringent control 

requirements. Several officials said it would make more sense, from a 

 34According to New Jersey officials, the program in that state does not routinely require 

sources to conduct facilitywide risk assessments. However, New Jersey’s program may 

evaluate emissions from all emission points in a facility in a single risk assessment in 

situations where there is the potential for high risk. 

Page 38 GAO-06-669 Clean Air Act
public health perspective, to consider the impact from all sources at the 

facility at once, as some states do, rather than review each emission point 

individually. Along these lines, several EPA officials said that evaluating all 

of the emissions from a facility simultaneously would enhance the 

efficiency of the program and better protect public health. 

Several of the state programs we reviewed use systematic approaches to 

identify and prioritize chemicals for addition to their air toxics lists. In 

contrast, EPA has not acted on the requirement to periodically review and

revise the list of regulated federal air toxics.35 For example, California 

officials work with the state’s public health agency to determine if a 

substance qualifies as a state air toxic. This process includes assessing (1) 

the potential for human exposure to a substance, (2) the chemical’s 

cancer-causing potential, (3) any noncancer effects such as irritation of 

the lungs or nausea, and (4) the impact on children’s health, among other 

factors. A panel of scientific experts reviews the work for accuracy, 

followed by the formal development of a regulation, including a public

hearing. Similarly, Oregon works with a committee composed of 

toxicology, public health, and technical experts to periodically identify air 

toxics for review and to develop health-based emission benchmarks. The 

committee prioritizes air toxics for review based on Oregon’s emission 

inventory, the pollutant’s toxicity or potency, the number of people at risk, 

and the impact on sensitive populations such as children, among other 

factors spelled out in state regulations. The systematic approaches of 

these programs could inform EPA’s efforts to meet the act’s requirement 

to review and update the federal list of regulated air toxics. 

Several of the state and local programs we reviewed require major and 

small stationary sources to submit standardized annual emissions reports 

and certify their accuracy. These programs, like EPA, rely on emissions 

inventory data to develop regulations and conduct risk assessments. For 

example, Wisconsin requires over 2,000 facilities to report emissions of 

623 air toxics each year if the facility emits more than certain quantities of

each pollutant. Facilities must certify the accuracy of their final 

submissions. The air toxics program in California similarly requires certain

major and small stationary sources to report air toxics emissions of over 

450 chemicals and to certify that the data are correct. New Jersey and 

Several Programs Have 

Systematic Approaches to 

Identify and Prioritize Air 

Toxics 

The Programs We

Reviewed Stressed the 

Importance of Data on 

Emissions and Toxicology 

 35As noted above, about 300 chemicals enter commerce each year. 

Page 39 GAO-06-669 Clean Air Act
Louisville have similar requirements for a smaller subset of air toxics and 

sources. 

In contrast to the programs that require sources to report and certify their

emissions, EPA, to date, generally has not required emissions sources or 

state or local agencies to systematically report these data.36 Such data 

collection could enhance EPA’s analysis and decision making in future air 

toxics rule makings. However, it is not clear how states without air toxics 

emissions inventories would comply with a federal requirement or the 

extent to which the data collected from the states would be comparable. 

For example, in 2002, EPA solicited comments on a rule to require state 

and local agencies to submit standardized air toxics emissions inventory 

data but the agency postponed consideration of the requirements partly 

due to concerns raised by state and local agencies about the lack of detail 

in EPA’s proposal.37 EPA officials also told us that they had concerns over 

whether there is adequate statutory authority to collect these data. 

Officials representing the state and local programs we spoke with 

expressed mixed opinions about a potential EPA requirement to submit 

standardized air toxics emissions inventories. For example, officials in the 

states we reviewed except California supported a federal requirement to 

report air toxics emissions because it would improve the consistency of 

the federal inventory and its usefulness to states in activities such as risk 

assessment modeling. In addition, some state officials said that a federal 

requirement would enable states that are prohibited from having their own 

programs to collect information on emissions of air toxics. However, 

several officials cautioned that some programs would have difficulty 

meeting such a requirement without additional funding. California officials

said that EPA should focus on states that do not currently have an 

inventory. 

 36For fiscal year 2006, EPA Region 4 included a grant commitment for the Louisville Metro 

Air Pollution Control District to submit its air toxics emission inventory as part of an air 

planning agreement to obtain federal funding for the local air program. EPA officials said 

that the agency’s fiscal year 2007 grant guidance for state and local agencies does not 

require the submission of air toxics emissions inventories as a condition to obtain federal 

funding. 

37EPA, in its Consolidated Emissions Reporting Rule, 67 Fed. Reg. 39602, 39604 (June 10,

2002), agreed with commenters and stated that it planned to develop air toxics reporting

measures at a later date. 

Page 40 GAO-06-669 Clean Air Act
In addition, state and local officials said that EPA does not regularly 

update chemical toxicity values that describe the potency of different air

toxics—key information for conducting risk assessments. These officials 

told us that their agencies generally do not have the resources to develop 

quantitative risk estimates for air toxics and must rely on other sources of 

data, such as EPA’s Integrated Risk Information System (IRIS). According 

to several officials, the basic science necessary to develop air toxics 

regulations is lacking in many cases. For example, Oregon officials cited 

limited and out-of-date toxicity values for a number of common chemicals 

in the IRIS database. Officials from other programs expressed similar 

concerns and said that EPA needed to enhance its efforts to provide 

quantitative toxicity information and conduct studies of sufficient quality 

to make determinations about chemical toxicity. A 2004 report by the 

National Academies also identified the need for more timely updates to 

EPA’s IRIS database. In addition, California officials pointed out that EPA 

does not have a cancer toxicity value for diesel particulate matter, so some 

states have developed a patchwork of different toxicity values. Further, 

state and local officials questioned EPA’s use of a formaldehyde risk factor

developed by an industry group instead of its peer-reviewed IRIS value 

when developing a recent MACT standard for plywood and composite 

wood products.38 Several officials were concerned that the deviation from 

IRIS would cause confusion about what toxicology data were most 

accurate for state and local requirements. 

EPA has made some progress in controlling emissions of air toxics, but its 

overall implementation of the air toxics program falls short of the agency’s 

statutory obligations because of the limited progress in (1) addressing 

requirements to limit emissions from small stationary sources and mobile 

sources, (2) evaluating the residual health risks associated with existing 

emissions standards and setting additional standards as appropriate, and 

(3) reviewing and updating the list of regulated pollutants, as appropriate.

While EPA places a lower priority on air toxics than other programs that it 

believes have a greater potential to reduce adverse health effects from air 

pollution, more comprehensive information on the air toxics program’s 

costs and benefits would help the agency compare the cost effectiveness 

of its investments in various clean air programs. Key data issues affecting

the agency’s ability to develop more comprehensive cost and benefit 

Conclusions 

 38National Emission Standards for Hazardous Air Pollutants: Plywood and Composite Wood 

Products, 71 Fed. Reg. 8342 (Feb. 16, 2006). 

Page 41 GAO-06-669 Clean Air Act
estimates include unreliable data on emissions and limited information on 

the extent to which changes in exposure to air toxics affect the incidence 

of adverse health effects. Until EPA supports efforts to address these data 

gaps that hinder its ability to evaluate the health risks of air toxics, the 

agency will not have assurance that its current priorities and programs 

necessarily target the areas of greatest opportunity for reducing health

risks associated with air pollution. 

EPA still has a significant number of remaining requirements under the 

act, including (1) setting 54 emissions standards for small stationary 

sources; (2) conducting more than 90 reviews of the remaining health risks 

associated with emissions sources covered by its existing standards, and 

issuing additional standards as necessary; and (3) reviewing and updating,

as appropriate, the list of regulated air toxics. Over the past 15 years, the 

air toxics program has not met its statutory deadlines, in part, because of 

its low priority relative to other programs and related funding constraints. 

Obtaining sufficient funding will continue to pose a challenge for EPA, 

especially in light of the nation’s current fiscal situation. We believe that 

developing an implementation plan that identifies the remaining tasks, 

data needed to estimate the benefits of reductions in exposure to air 

toxics, timelines, and required funding would improve the management of

the program as well as its transparency and accountability to Congress 

and the public. In addition, EPA could examine state and local approaches 

to air toxics that may have the potential to more effectively address risks 

by focusing resources on sources, communities, and geographic areas that 

face the greatest risks. This would require EPA to evaluate opportunities 

to enhance its efforts to focus on the greatest risks to human health within

the current legislative framework. 

To improve the management of EPA’s air toxics program and enhance its 

ability to reduce risks of cancer and other adverse health effects, we 

recommend that the EPA Administrator require the Assistant 

Administrator for Air and Radiation to develop an air toxics program 

improvement plan that incorporates the following five issues: 

Recommendations for 

Executive Action 

• provides a detailed schedule for completing its mandated air toxics 

activities and identifies the staffing and funding resources needed to meet 

the schedule and address the health risk assessment needs; 

• prioritizes activities within the air toxics program, placing the highest 

priority on those actions that have the greatest potential to address health 

risks, to the extent permitted by the Clean Air Act; 

Page 42 GAO-06-669 Clean Air Act
• establishes a process and timelines for meeting the act’s requirements to 

periodically review and update the list of air toxics; 

• outlines an approach and timelines for improving the agency’s ability to 

measure the program’s costs and benefits; and 

• describes how the agency plans to improve its air toxics emissions 

inventory, including a discussion of the statutory authority for, and the 

merits of, requiring states and emissions sources to submit standardized 

emissions data. 

We provided EPA’s Office of Air and Radiation with a copy of this report 

for review and comment. In commenting on the report, the Acting 

Assistant Administrator for Air and Radiation said that EPA agrees in part

with the conclusions and recommendations in the report. The agency did 

not identify specific aspects of our conclusions or recommendations with 

which it disagreed, but rather provided only clarifications to statements in 

the report regarding the availability of information on the costs and 

benefits of the agency’s efforts to control air toxics, the agency’s progress

in completing certain air toxics requirements of the Clean Air Act, and on 

EPA’s management of the remaining requirements. EPA’s letter and our 

response to their clarifications are included as appendix IV. EPA also 

provided technical comments, which we have incorporated, as 

appropriate.

As agreed with your offices, unless you publicly announce the contents of

this report earlier, we plan no further distribution until 30 days from the 

report date. At that time, we will send copies to the EPA Administrator 

and other interested parties. We will also make copies available to others

upon request. In addition, the report will be available at no charge on the 

GAO Web site at http://www.gao.gov. 

Agency Comments 

Page 43 GAO-06-669 Clean Air Act
If you or your staff have any questions about this report, please contact me 

at (202) 512-3841 or stephensonj@gao.gov. Contact points for our Offices 

of Congressional Relations and Public Affairs may be found on the last 

page of this report. Key contributors to this report are listed in appendix V. 

John B. Stephenson 

Director, Natural Resources and Environment 

Page 44 GAO-06-669 Clean Air Act
List of Congressional Requesters 

The Honorable James M. Jeffords 

Ranking Minority Member 

Committee on Environment and Public Works 

United States Senate 

The Honorable Lincoln Chafee 

Chairman 

Subcommittee on Fisheries, Wildlife and Water 

Committee on Environment and Public Works 

United States Senate 

The Honorable Barbara Boxer 

Ranking Minority Member 

Subcommittee on Superfund and Waste Management 

Committee on Environment and Public Works 

United States Senate 

The Honorable Thomas R. Carper 

Ranking Minority Member 

Subcommittee on Clean Air, Climate Change, and Nuclear Safety 

Committee on Environment and Public Works 

United States Senate 

The Honorable Hillary Rodham Clinton 

United States Senate 

The Honorable Patrick J. Leahy 

United States Senate 

The Honorable Joseph I. Lieberman 

United States Senate 

The Honorably Paul Sarbanes 

United States Senate 

The Honorable Olympia J. Snowe 

United States Senate 

Page 45 GAO-06-669 Clean Air Act
The Honorable John D. Dingell 

Ranking Minority Member 

Committee on Energy and Commerce 

House of Representatives 

The Honorable Tom Allen 

House of Representatives 

The Honorable Lois Capps 

House of Representatives 

The Honorable Edward J. Markey 

House of Representatives 

The Honorable Hilda L. Solis 

House of Representatives 

The Honorable Henry A. Waxman 

House of Representatives 

Page 46 GAO-06-669 Clean Air Act
Appendix I: Status of EPA’s Efforts to 

Respond to Recommendations in the National Appendix I: Status of EP Academies’ Report on Air QAuality

’s Efforts to 

Respond to Recommendations in the 

National Academies’ Report on Air Quality 

This appendix discusses the Environmental Protection Agency’s (EPA) 

response to the findings and recommendations of the National Academies’

(Academies) report on air quality management. The Academies prepared 

this report in response to a congressional request for an independent 

evaluation of the effectiveness and implementation of the Clean Air Act. 

The report examined the roles of science and technology in the 

implementation of the act and recommended ways to improve air quality 

management. One of the report’s key recommendations was for EPA to 

form a work group to evaluate the report and provide a detailed list of 

actions EPA could take to improve its implementation of clean air 

programs. The work group completed this review in December 2004 and

provided the agency’s Clean Air Act Advisory Committee with a list of 38

recommendations. 

EPA’s Office of Policy Analysis and Review has taken the lead in 

responding to the recommendations and provided an initial response in 

April 2005, which was updated in November 2005.1

 The response included 

information about ongoing and proposed activities to address the 

recommendations and estimated time frames for responding to each 

recommendation. The agency has prioritized the recommendations and 

developed a proposed schedule for completing its activities, with some 

actions already under way or completed and others not scheduled for 

completion until fiscal year 2008. Based on our review of available 

documents and discussions with EPA program managers, the agency has 

taken affirmative steps to respond to a number of the recommendations, 

and its proposed actions generally appear responsive to the Academies’ 

findings. A comprehensive evaluation of EPA’s response to the Academies’ 

recommendations will not be possible until the agency has made further 

progress in implementing its proposed response actions. 

 1

Environmental Protection Agency, Compilation of Status Reports on the Implementation

of Recommendations Made to EPA by the CAAAC on Air Quality Management 

(Washington, D.C., November 2005) 

Page 47 GAO-06-669 Clean Air Act
Appendix II: Objectives, Scope, and Appendix II: Objectives, Scope, and Methodology 

Methodology 

We were asked to assess (1) EPA’s progress toward implementing the air 

toxics program and any implementation challenges the agency faces, (2) 

what available information indicates about the costs and benefits of EPA’s 

efforts to control air toxics, and (3) the program design and management 

practices of state and local air toxics programs that could potentially help

EPA enhance the effectiveness of the federal program. In addition, we 

were asked to assess EPA’s progress in responding to recommendations 

pertaining to the air toxics program made by the National Academies in 

2004. 

To respond to the first objective, we updated our previous analysis of the 

agency’s progress in implementing program requirements. We reviewed 

the requirements of the Clean Air Act Amendments of 1990 and EPA’s 

actions to respond to these requirements, including the number of 

regulations the agency promulgated and other requirements to issue 

reports and guidance. Specifically, we considered EPA’s Maximum 

Achievable Control Technology (MACT), small stationary source, mobile 

source, residual risk, and technology review activities, and other activities 

in the act that were specifically related to air toxics. 

We also evaluated the timeliness of EPA’s actions versus the schedule

mandated by the act by comparing the dates specified in the act with the 

dates on which EPA published the rules in the Federal Register. We 

independently developed a list of actions required by EPA and worked 

with agency officials to refine and confirm the list we used. We made 

minor modifications to the list approved by EPA to account for the 

promulgation of residual risk and area source standards, to separately 

count area source standards issued in conjunction with MACT standards, 

and to delete source categories that were delisted. 

To determine the priority of the air toxics program relative to other air 

programs, and the priorities within the air toxics program, we met with 

senior air program officials and analyzed budget data submitted by EPA. 

Specifically, we compared the funding for EPA’s air program as a whole 

with the funding for the air toxics program. 

To identify the implementation challenges EPA faces, we reviewed 

available studies by the National Academies, the Office of Management 

and Budget (OMB), and the EPA Inspector General. We identified nine 

implementation challenges, such as the adequacy of program funding and 

the priority of the program relative to other air programs, and developed a 

structured interview in order to evaluate the magnitude of the challenges

identified by these studies in the opinions of various stakeholders. We 

Page 48 GAO-06-669 Clean Air Act
Appendix II: Objectives, Scope, and

Methodology 

pretested the interview questions and made relevant changes to the 

questions based on the pretest. 

We designed the structured interview so that respondents could rate each 

implementation challenge on a scale from 0 (not a challenge at all) to 4 (a

challenge to a very great extent). When conducting the interviews, we 

asked followup questions if the respondents rated the challenge as a 3 (a 

challenge to a large extent) or 4, such as what they thought could be done 

to address the challenge. We also provided a list of key definitions, an 

explanation of the rating system, and a description of each challenge to 

respondents prior to conducting each interview.

We conducted structured interviews with a nonprobability sample1

 of 22 

officials, including 8 EPA, 5 industry, 4 environmental, and 5 state and 

local officials. Specifically, for EPA, we interviewed senior officials within 

the Office of Air Quality Planning and Standards and the Office of 

Transportation and Air Quality. We identified national-level environmental 

and industry stakeholders through consultation with EPA (and referrals 

from contacts identified through this consultation) and membership on the 

Clean Air Act Advisory Committee. The five industry groups we 

interviewed were the American Forest & Paper Association, the American 

Petroleum Institute, the Council of Industrial Boiler Owners, the American 

Chemistry Council, and the Alliance of Automobile Manufacturers. The 

four environmental groups we interviewed were the Natural Resources 

Defense Council, Environmental Defense, Earth Justice, and an air toxics 

consultant recommended by environmental stakeholders and EPA. We 

interviewed officials from state and local programs in California, New 

Jersey, Oregon, Wisconsin, and Louisville, Kentucky. 

Following the structured interviews, we determined the most significant 

challenges for all of the stakeholders by averaging the ratings from all 22 

respondents for each challenge. However, because ratings of the most 

significant challenges differed for each stakeholder group, we also 

averaged the scores for each challenge for each stakeholder group. We 

identified the greatest challenges identified by each stakeholder group (an 

average rating of 3 or higher, or those rated as challenges to a large or very 

 1

Results from nonprobability samples cannot be used to make inferences about a

population, because in a nonprobability sample, some elements of the population being

studied have no chance or an unknown chance of being selected as part of the sample. 

Page 49 GAO-06-669 Clean Air Act
Appendix II: Objectives, Scope, and

Methodology 

great extent) to assess how perceptions of the challenges differed among

the stakeholder groups. 

To respond to the second objective, we analyzed available information on 

the economic impacts of the program, as well as data on trends in 

emissions, health risks, and compliance. Regarding data on economic 

impacts, we reviewed EPA’s 1997 and 1999 reports to Congress on the 

economic impacts of the Clean Air Act as well as the agency’s guidance for 

analyzing the effects of air pollution regulations. We also met with EPA 

staff in the Office of Air Quality Planning and Standards and Office of 

Policy Analysis and Review responsible for analyzing the economic effects 

of clean air regulations. Regarding emissions and monitoring data, we met 

with EPA staff responsible for maintaining the National Emissions 

Inventory, reviewed the agency’s documentation and plans for improving 

the inventory, and reviewed relevant reports by EPA’s Inspector General.

Regarding data on health and risks, we met with EPA staff responsible for 

risk assessment and the development of the National-Scale Air Toxics 

Assessment. We also reviewed EPA’s methodology for developing the 

assessment and available information on the risk assessment process. We 

obtained compliance data from the Office of Enforcement and Compliance 

Assurance’s Air Facility Subsystem. We reviewed these data for obvious 

completeness and consistency problems, reviewed available 

documentation, and interviewed the system administrator. Unless 

otherwise noted, we determined the data were sufficiently reliable for the 

purposes of this report. 

To respond to the third objective, we reviewed a nonprobability sample of 

air toxics programs from California, New Jersey, Oregon, and Wisconsin 

and from Louisville, Kentucky to identify innovative program designs or 

management practices. We focused on programs that (1) went beyond 

federal standards, (2) were identified by EPA and other stakeholders as 

innovative programs, (3) used strategies to address air toxics that differed 

from those used by EPA, and (4) represented a range of geographic 

locations and experience addressing air toxics. Specifically, we asked EPA 

and the State and Territorial Air Pollution Program Administrators and the 

Association of Local Air Pollution Control Officials (STAPPA/ALAPCO), 

the stakeholders most knowledgeable about state and local air toxics 

programs, whether there were specific programs we should review, and 

used their recommendations as selection criteria. GAO conducted 

independent research to confirm that the selections cited by these 

stakeholders were reasonable, including analyses of the stringency of state 

and local air toxics programs based on current law, policy, and guidance 

Page 50 GAO-06-669 Clean Air Act
Appendix II: Objectives, Scope, and

Methodology 

documents and summary documents developed by EPA and state and 

local agencies. 

We visited each program selected for review and conducted 

semistructured interviews with state and local officials. We developed an 

interview protocol and revised it after limited testing with respondents. 

The semistructured interview included questions about how the programs 

interact with EPA, how the program views EPA’s current and future 

requirements, regulate different chemicals and sources, account for risk, 

collect emissions inventory data, and measure progress, among other 

factors. We focused primarily on practices that EPA might find useful in 

addressing its program implementation challenges and did not evaluate 

the effectiveness of the state and local programs we reviewed. Our 

discussion of the practices employed by these programs should not be 

construed as an endorsement of any particular approach but rather as an 

acknowledgement that alternative strategies exist. 

In addition, we obtained information about EPA’s response to the 

recommendations of the National Academies’ 2004 report entitled Air 

Quality Management in the United States. We reviewed the

recommendations in the report, the associated recommendations of the 

Clean Air Act Advisory Committee, and EPA’s actions to respond to these 

recommendations. We worked with EPA officials to determine whether 

EPA’s actions addressed the recommendations. Our work included an 

assessment of data reliability and internal controls. We conducted our 

work from June 2005 to June 2006 in accordance with generally accepted 

government auditing standards. 

Page 51 GAO-06-669 Clean Air Act
Appendix III: Profiles of State and Local Air Appendix III: Profiles of State and Local Air Toxics Programs

Toxics Programs 

This appendix provides general information on the nonprobability sample 

of four state and one local air toxics programs we reviewed to identify 

innovative program designs or management practices. We focused on 

programs that (1) went beyond federal standards, (2) were identified as 

innovative by EPA and other stakeholders, (3) used strategies to address 

air toxics that differ from EPA’s, and (4) represented a range of geographic 

locations and experience addressing air toxics. Table 12 presents basic 

information about the programs we reviewed, followed by profiles of each

program. 

Table 12: Selected State and Local Air Toxics Programs 

Program 

Date 

created

Number of 

chemicals Strategy Description

State 

California 1983 245 Control

technology 

Requires certain large and small stationary sources to 

apply control technologies to reduce emissions. 

1987 451 Risk

assessment 

Requires certain large and small stationary sources to 

report emissions of air toxics, estimate the public health 

impact of their emissions, and reduce emissions as 

necessary to meet health-based standards. 

New 

Jersey 

1979 237 Control

technology and

risk 

assessment 

Requires certain facilities seeking permits to apply air 

toxics emission control technology, estimate the risk 

posed by the remaining emissions, and take additional 

measures as necessary to meet health-based targets. 

Oregona2003 49bGeographic,

control 

technology, 

and risk 

assessment 

Requires facilities in specific geographic areas of high risk 

to develop, with other stakeholders, a risk reduction plan 

to meet health-based benchmarks. In addition, some 

stationary sources may be required to apply control 

technologies and estimate and mitigate the risk they pose 

to the public. 

Wisconsin 1988 535 Control

technology and

risk 

assessment 

Requires certain facilities that emit specific amounts of 

cancer-causing air toxics to apply control technology to 

reduce emissions. Certain facilities that emit specific 

amounts of other air toxics must estimate the risks posed

by these chemicals and meet health based standards. 

Local 

Louisville, 

Kentucky 

2005 191 Risk

assessment 

Requires certain facilities seeking permits to construct or 

modify processes or equipment to estimate the risk posed 

by their air toxics emissions and to reduce the risk, 

potentially through the application of control technologies, 

to meet certain health-based goals. Certain existing 

facilities must meet similar requirements for 37 chemicals.

Source: GAO analysis of state and local agency data.

a

Oregon’s program is still being developed and has not been fully implemented. This description 

presents the requirements as spelled out in the 2003 state rule that created the program. 

Page 52 GAO-06-669 Clean Air Act
Appendix III: Profiles of State and Local Air 

Toxics Programs

b

The Oregon Department of Environmental Quality proposed to adopt benchmarks for 49 air toxics in 

February 2006. The benchmarks were not final as of the date of this report. 

California’s air toxics program regulates certain new and existing major 

stationary sources, small stationary sources, and mobile sources more 

stringently than EPA. In 1983, the state legislature adopted Assembly Bill 

1807, the Toxic Air Contaminant Identification and Control Act, which 

defined a process for identifying chemicals that qualify as state air toxics 

and developing control standards to reduce emissions from certain 

sources based on the application of pollution control technology. 

California has listed 245 toxic air contaminants as of May 2006. The state 

regulates diesel particulate matter emissions from motor vehicles, such as 

school buses, under its program. 

In 1987, the state legislature passed an additional law, Assembly Bill 2588, 

the Air Toxics “Hot Spots” Information and Assessment Act, which 

required the submission of air toxics emissions inventory data from 

certain facilities and notification of local residents of significant risk from 

nearby sources of air toxics. Under this act, certain sources of air toxics 

must conduct risk assessments to determine their health impact on the 

community. In conducting these risk assessments, regulated facilities must 

consider the risks posed by their emissions of 451 different chemicals.1

 In 

1992, the legislature passed an amendment to the “hot spots” law that 

required facilities that pose a significant health risk to the community to 

develop risk management plans. Policy documents and other information 

are available at the program’s Web site 

http://www.arb.ca.gov/toxics/toxics.htm. 

New Jersey’s air toxics program regulates certain large and small 

stationary sources more stringently than EPA through the state’s 

permitting program. The New Jersey Air Pollution Control Act of 1954 

requires new or modified sources that emit air pollutants, including air 

toxics, to incorporate state-of-the-art air pollution controls to reduce their 

California 

New Jersey 

 1

California requires certain facilities to quantify and report emissions of 451 chemicals as 

part of its risk assessment program. In 2006, the state may consider the addition of several 

hundred chemicals to the list of chemicals reported and used in risk assessments. Some 

facilities are also required to report the use or manufacture of 310 additional chemicals for 

a potential total of 761 chemicals, but these chemicals are not currently considered in risk 

assessments.

Page 53 GAO-06-669 Clean Air Act
Appendix III: Profiles of State and Local Air 

Toxics Programs

emissions. In 1979, the New Jersey Department of Environmental 

Protection (DEP) adopted a regulation that specifically addressed air 

toxics emissions. This rule listed 11 air toxics and required sources 

emitting these chemicals to register with DEP and demonstrate that they 

utilize state-of-the-art controls to limit their emissions. The department 

incorporates control requirements for other air toxics on a case-by-case 

basis as part of the permitting process. In the early 1980s, the DEP 

instituted a risk assessment policy to better ensure that sources with stateof-the-art controls protect public health. The risk assessment policy 

requires certain facilities seeking permits to estimate the risk to the 

community that remains after the application of technology standards and 

to take additional measures as necessary to meet health-based targets 

established for 237 air toxics. General information about New Jersey’s air 

toxics program is available at http://www.state.nj.us/dep/airmon/airtoxics/, 

and policy documents, such as risk assessment policies are available at 

http://www.state.nj.us/dep/aqpp/risk.html. 

Oregon’s air toxics program is authorized to go beyond federal

requirements for some large and small stationary sources. In November 

1998, the Oregon Department of Environmental Quality (DEQ) convened a 

broad-based stakeholder group to outline a program to complement the 

existing federal program and reduce the impact of air toxics in Oregon. 

DEQ worked with stakeholders until the adoption of Oregon’s air toxics 

rule on October 9, 2003. The rule requires sources in specific geographic 

areas of high risk to develop, with other stakeholders, a risk reduction 

plan to meet certain health based goals.2

 In addition, some stationary 

sources may be required to estimate and mitigate the risk they pose to the 

public and apply control technologies. The program is still being 

developed and has not been fully implemented. Policy and guidance 

documents and other information are available at the program’s Web site 

http://www.deq.state.or.us/aq/hap/index.htm. 

Wisconsin’s air toxics program regulates certain new and existing 

stationary sources more stringently than EPA. In 1983, the Wisconsin 

Department of Natural Resources (DNR) formed a group of scientists, 

Oregon 

Wisconsin 

 2

The Oregon Department of Environmental Quality proposed to adopt benchmarks for 49 

air toxics in February 2006. The benchmarks were not final as of the issue date of this

report. 

Page 54 GAO-06-669 Clean Air Act
Appendix III: Profiles of State and Local Air 

Toxics Programs

industry, environmental, and government stakeholders in response to 

public concern about the health effects of air toxics and the lack of policy 

and regulations at the federal level. The group recommended an approach 

for a state air toxics rule in 1985, and DNR developed a rule that became 

effective in 1988. This original rule was rewritten and redeveloped from 

2000 through 2004 using an advisory committee process that included 

government, industry, and environmental stakeholders. The final rule 

became effective in July 2004. The rule lists 535 air toxics and requires 

certain facilities that emit specific amounts of cancer-causing air toxics to 

apply control technology to reduce emissions. In addition, certain facilities 

that emit other air toxics beyond specific thresholds must estimate the 

risks posed by these chemicals and meet health-based standards.3

Guidance documents and other information are available on the program’s 

Web site, http://www.dnr.state.wi.us/org/aw/air/health/airtoxics/. 

In September 2004, the Louisville Metro Air Pollution Control District 

prepared a draft Strategic Toxic Air Reduction (STAR) program in 

response to air monitoring that documented and modeled data that 

suggested that air toxics posed significant risks to the community. 

Adopted by the Louisville Metro Air Pollution Control Board in June 2005,

the STAR program requires certain facilities to estimate the risk posed by 

their air toxics emissions and to reduce the risk, potentially through the 

application of control technologies, to meet certain health-based goals. 

Louisville’s program first focuses on emissions of 18 air toxics that posed 

unacceptable risk to the public based on monitoring studies. In total, the 

STAR program applies to new or modified processes and process 

equipment that will emit any of 191 air toxics, and existing sources that 

emitted any of 37 air toxics in quantities that exceed certain thresholds. 

Policy documents and other information are available on the program’s 

Web site, http://www.apcd.org/star/. 

Louisville, Kentucky 

 3

Wisconsin state law provides that Wisconsin’s air toxics program does not apply to 

emissions that are regulated by federal MACT standards under section 112 of the Clean Air 

Act. 

Page 55 GAO-06-669 Clean Air Act
Appendix IV: Comments from the Appendix IV Environmental Protection Agency : Comments from the 

Environmental Protection Agency 

Note: GAO comments 

supplementing those in 

the report text appear at 

the end of this appendix. 

See comment 1. 

Page 56 GAO-06-669 Clean Air Act
Appendix IV: Comments from the 

Environmental Protection Agency 

See comment 2. 

Page 57 GAO-06-669 Clean Air Act
Appendix IV: Comments from the 

Environmental Protection Agency 

See comment 3. 

Page 58 GAO-06-669 Clean Air Act
Appendix IV: Comments from the 

Environmental Protection Agency 

Page 59 GAO-06-669 Clean Air Act
Appendix IV: Comments from the 

Environmental Protection Agency 

Page 60 GAO-06-669 Clean Air Act
Appendix IV: Comments from the 

Environmental Protection Agency 

Page 61 GAO-06-669 Clean Air Act
Appendix IV: Comments from the 

Environmental Protection Agency 

Page 62 GAO-06-669 Clean Air Act
Appendix IV: Comments from the 

Environmental Protection Agency 

1. Regarding our discussion of the economic effects of air toxics

regulations, EPA stated that the agency finds it appropriate to focus 

risk assessments and benefits analysis on the air toxics that pose the 

most significant risks within the context of the residual risk program. 

EPA’s letter also stated that such an approach would assist the 

rulemaking process to a greater extent than comprehensive 

assessments of the total benefits and costs of all air toxics controls. 

While EPA may hold this view, the Clean Air Act requires the agency

not only to assess residual risks after completing the MACT standards, 

but also to periodically assess the costs and benefits of clean air 

programs. Regarding the first set of requirements, EPA was late in 

issuing almost all of the MACT standards and is already well behind 

schedule in completing the residual risk assessments. With respect to 

the second set of requirements, EPA’s economic assessments of clean

air programs have included limited information on the costs of 

regulating air toxics and have not included monetized estimates of the 

human health or other benefits—either for individual pollutants or for 

all of the pollutants in total. More complete information on costs and 

benefits would help the agency, Congress, and the public understand 

the effects of the air toxics program and enable the agency to compare 

the net benefits of the air toxics program with those achieved under 

other clean air programs on which the agency has placed a higher 

priority. 

GAO comments 

2. In its letter, EPA stated that GAO uses an inappropriately narrow 

measure of progress in regulating air toxics and that the agency has 

issued a number of regulations that control air toxics as a side benefit.

However, as we discuss in the report, data limitations compromise the 

usefulness of other performance measures. EPA has indeed taken 

regulatory actions outside of the air toxics program that control toxic 

emissions as a side benefit. However, the progress—in terms of 

emissions reductions—that EPA cites should be considered in the 

context of the limitations of the emissions data discussed in this 

report. For example, the EPA Inspector General has reported that EPA 

cannot tell whether apparent reductions or increases in emissions have 

resulted from changes in the way the agency estimates emissions or 

from actual reductions. It is also important to note that EPA does not 

expect some of the emissions reductions cited in its letter to occur 

until 2020. Furthermore, EPA’s most recent data on risks from air 

toxics identifies benzene—a known carcinogen emitted primarily by 

mobile sources—as a national risk driver that accounts for 25 percent 

of the cancer risks posed by air toxics across the nation. This suggests 

that EPA has substantial opportunities to further address air toxics 

risks from mobile sources. Finally, the Clean Air Act mandated specific 

Page 63 GAO-06-669 Clean Air Act
Appendix IV: Comments from the 

Environmental Protection Agency 

actions and timelines for evaluating and regulating toxic emissions 

from mobile sources. As discussed in this report, the agency has 

missed its deadlines for completing these actions but has proposed a 

mobile source air toxics rule that it intends to finalize in 2007. 

3. In response to our finding that EPA lacks a strategy for managing its 

implementation of the remaining air toxics requirements, the agency’s 

letter stated that the Clean Air Act provides a road map for air toxics 

and that EPA developed an integrated air toxics strategy in 1999. EPA 

also stated that the agency is developing a strategy to respond to its 

court-ordered deadlines for completing certain air toxics requirements. 

As discussed in the report, EPA has missed most of the act’s deadlines 

related to air toxics and has not fully implemented the actions outlined 

in its integrated strategy. Additionally, EPA’s discussion of its efforts 

to meet court-ordered deadlines underscores the need for more 

proactive management.

Page 64 GAO-06-669 Clean Air Act
Appendix V: 

A

GAO Contact and Staff 

cknowledgments 

Page 65 GAO-06-669

Appendix V: GAO Contact and Staff 

Acknowledgments 

John B. Stephenson, (202) 512-3841 or stephensonj@gao.gov

In addition to the contact named above, Christine Fishkin (Assistant 

Director), Jennifer Dougherty, Cindy Gilbert, Tim Guinane, Michael Hix, 

Andrew Huddleston, Karen Keegan, Alison O’Neill, Judy Pagano, Melissa 

Saddler, and Joseph Thompson made significant contributions to this 

report. 

Clean Air Act

GAO Contact 

Staff 

Acknowledgments 

(360594) 
GAO’s Mission The Government Accountability Office, the audit, evaluation and 

investigative arm of Congress, exists to support Congress in meeting its 

constitutional responsibilities and to help improve the performance and 

accountability of the federal government for the American people. GAO 

examines the use of public funds; evaluates federal programs and policies; 

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