Particulate Matter
EPA Needs to Make More Progress in Addressing the National Academies' Recommendations on Estimating Health Benefits Gao ID: GAO-06-992T July 19, 2006Scientific evidence links exposure to particulate matter--a widespread form of air pollution--to serious health problems, including asthma and premature death. Under the Clean Air Act, the Environmental Protection Agency (EPA) periodically reviews the appropriate air quality level at which to set national standards to protect the public against the health effects of six pollutants, including particulate matter. EPA proposed revisions to the particulate matter standards in January 2006 and issued a regulatory impact analysis of the revisions' expected costs and benefits. The estimated benefits of air pollution regulations have been controversial in the past, and a 2002 National Academies report to EPA made recommendations aimed at improving the estimates for particulate matter and other air pollution regulations. This testimony is based on GAO's July 2006 report Particulate Matter: EPA Has Started to Address the National Academies' Recommendations on Estimating Health Benefits, but More Progress Is Needed (GAO-06-780). GAO determined whether and how EPA applied the National Academies' recommendations in its estimates of the health benefits expected from the January 2006 proposed revisions to the particulate matter standards.
While the National Academies' report generally supported EPA's approach to estimating the health benefits of its proposed air pollution regulations, it included 34 recommendations for improvements. EPA has begun to change the way it conducts and presents its analyses of health benefits in response to the National Academies' recommendations. For its particulate matter health benefit analysis, EPA applied, at least in part, about two-thirds of the Academies' recommendations. Specifically, EPA applied 8 and partially applied 14. For example, in response to the Academies' recommendations, EPA evaluated how benefits might change given alternative assumptions and discussed sources of uncertainty not included in the benefit estimates. Although EPA applied an alternative technique for evaluating one key uncertainty--the causal link between exposure to particulate matter and premature death--the health benefit analysis did not assess how the benefit estimates would vary in light of other key uncertainties, as the Academies had recommended. Consequently, EPA's response represents a partial application of the recommendation. Agency officials said that ongoing research and development efforts will allow EPA to gradually make more progress in applying this and other recommendations to future analyses. EPA did not apply the remaining 12 recommendations to the analysis, such as the recommendation to evaluate the impact of using the assumption that the components of particulate matter are equally toxic. EPA officials viewed most of these 12 recommendations as relevant to the health benefit analyses but noted that the agency was not ready to apply specific recommendations because of, among other things, the need to overcome technical challenges stemming from limitations in the state of available science. For example, EPA did not believe that the state of scientific knowledge on the relative toxicity of particulate matter components was sufficiently developed to include it in the January 2006 regulatory impact analysis. The agency is sponsoring research on this issue. We note that continued commitment and dedication of resources will be needed if EPA is to fully implement the improvements recommended by the National Academies. In particular, the agency will need to ensure that it allocates resources to needed research on emerging issues, such as the relative toxicity of particulate matter components, and to assessing which sources of uncertainty have the greatest influence on benefit estimates. While EPA officials said they expect to reduce the uncertainties associated with the health benefit estimates in the final particulate matter analysis, a robust uncertainty analysis of the remaining uncertainties will nonetheless be important for decision makers and the public to understand the likelihood of attaining the estimated health benefits.
GAO-06-992T, Particulate Matter: EPA Needs to Make More Progress in Addressing the National Academies' Recommendations on Estimating Health Benefits
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Testimony:
Before the Committee on Environment and Public Works, U.S. Senate:
United States Government Accountability Office:
GAO:
For Release on Delivery Expected at 9:00 a.m. EDT:
Wednesday, July 19, 2006:
Particulate Matter:
EPA Needs to Make More Progress in Addressing the National Academies'
Recommendations on Estimating Health Benefits:
Statement of John B. Stephenson, Director Natural Resources and
Environment:
GAO-06-992T:
GAO Highlights:
Highlights of GAO-06-992T, a testimony before the Committee on
Environment and Public Works, U.S. Senate
Why GAO Did This Study:
Scientific evidence links exposure to particulate matter”a widespread
form of air pollution”to serious health problems, including asthma and
premature death. Under the Clean Air Act, the Environmental Protection
Agency (EPA) periodically reviews the appropriate air quality level at
which to set national standards to protect the public against the
health effects of six pollutants, including particulate matter. EPA
proposed revisions to the particulate matter standards in January 2006
and issued a regulatory impact analysis of the revisions‘ expected
costs and benefits. The estimated benefits of air pollution regulations
have been controversial in the past, and a 2002 National Academies
report to EPA made recommendations aimed at improving the estimates for
particulate matter and other air pollution regulations.
This testimony is based on GAO‘s July 2006 report Particulate Matter:
EPA Has Started to Address the National Academies‘ Recommendations on
Estimating Health Benefits, but More Progress Is Needed (GAO-06-780).
GAO determined whether and how EPA applied the National Academies‘
recommendations in its estimates of the health benefits expected from
the January 2006 proposed revisions to the particulate matter
standards.
What GAO Found:
While the National Academies‘ report generally supported EPA‘s approach
to estimating the health benefits of its proposed air pollution
regulations, it included 34 recommendations for improvements. EPA has
begun to change the way it conducts and presents its analyses of health
benefits in response to the National Academies‘ recommendations. For
its particulate matter health benefit analysis, EPA applied, at least
in part, about two-thirds of the Academies‘ recommendations.
Specifically, EPA applied 8 and partially applied 14. For example, in
response to the Academies‘ recommendations, EPA evaluated how benefits
might change given alternative assumptions and discussed sources of
uncertainty not included in the benefit estimates. Although EPA applied
an alternative technique for evaluating one key uncertainty”the causal
link between exposure to particulate matter and premature death”the
health benefit analysis did not assess how the benefit estimates would
vary in light of other key uncertainties, as the Academies had
recommended. Consequently, EPA‘s response represents a partial
application of the recommendation. Agency officials said that ongoing
research and development efforts will allow EPA to gradually make more
progress in applying this and other recommendations to future analyses.
EPA did not apply the remaining 12 recommendations to the analysis,
such as the recommendation to evaluate the impact of using the
assumption that the components of particulate matter are equally toxic.
EPA officials viewed most of these 12 recommendations as relevant to
the health benefit analyses but noted that the agency was not ready to
apply specific recommendations because of, among other things, the need
to overcome technical challenges stemming from limitations in the state
of available science. For example, EPA did not believe that the state
of scientific knowledge on the relative toxicity of particulate matter
components was sufficiently developed to include it in the January 2006
regulatory impact analysis. The agency is sponsoring research on this
issue.
We note that continued commitment and dedication of resources will be
needed if EPA is to fully implement the improvements recommended by the
National Academies. In particular, the agency will need to ensure that
it allocates resources to needed research on emerging issues, such as
the relative toxicity of particulate matter components, and to
assessing which sources of uncertainty have the greatest influence on
benefit estimates. While EPA officials said they expect to reduce the
uncertainties associated with the health benefit estimates in the final
particulate matter analysis, a robust uncertainty analysis of the
remaining uncertainties will nonetheless be important for decision
makers and the public to understand the likelihood of attaining the
estimated health benefits.
[Hyperlink, http://www.gao.gov/cgi-bin/getrpt?GAO-06-992T].
To view the full product, including the scope and methodology, click on
the link above. For more information, contact John B. Stephenson at
(202) 512-3841 or stephensonj@gao.gov.
[End of Section]
Mr. Chairman and Members of the Committee:
I am pleased to be here today as the committee considers the science
and risk assessment supporting the Environmental Protection Agency's
(EPA) proposed revisions to the national air quality standards for
particulate matter. A large body of scientific evidence links exposure
to particulate matter--a ubiquitous form of air pollution commonly
referred to as soot--to serious health problems, including asthma,
chronic bronchitis, heart attack, and premature death. Under the Clean
Air Act, EPA periodically reviews the appropriate air quality level at
which to set national standards to protect the public against the
health effects of particulate matter. As you are aware, EPA proposed
revisions to the particulate matter standards in January 2006 and
issued a draft regulatory impact analysis of the revisions' expected
costs and benefits.
EPA's estimates of the expected benefits from its air pollution
regulations have often been controversial, and the methods the agency
has used to prepare these estimates have been questioned. In 2000, at
the direction of the Senate Appropriations Committee, EPA asked the
National Academies (Academies) to evaluate EPA's overall methodology
for estimating the health benefits of proposed air regulations. In
2002, the Academies issued a report that made recommendations focusing
on conducting more rigorous assessments of uncertainty, increasing the
transparency of how EPA estimates benefits, conducting more detailed
analyses of exposure, and estimating the benefits of each regulatory
option under consideration. My testimony summarizes the highlights of
our report being released today on the extent to which EPA applied the
recommendations made by the Academies to its January 2006 proposed
revisions to the particulate matter standards.[Footnote 1] Our report
provides a more detailed discussion of each recommendation, including
whether and how EPA applied it to the regulatory impact analysis on
particulate matter.
Summary:
While the National Academies' report generally supported EPA's overall
approach to estimating benefits, it included 34 recommendations for
improvements. EPA has begun to change the way it conducts and presents
its analyses of health benefits in response to the National Academies'
recommendations. In the case of the January 2006 proposed rule on
particulate matter standards, EPA applied, at least in part, about two-
thirds of the recommendations to its particulate matter health benefit
analysis; it applied 8 and partially applied 14 more. For example, in
applying the recommendations, EPA evaluated how benefits might change
given alternative assumptions and discussed sources of uncertainty not
included in the benefit estimates. In addition, EPA applied an
alternative technique for evaluating one important source of
uncertainty in its analysis--the uncertainty underlying the causal link
between exposure to particulate matter and premature death. Consistent
with the National Academies' recommendation to assess uncertainty by
developing ranges of estimates of benefits and specifying the
likelihood of attaining those levels of benefits, EPA systematically
gathered expert opinions about this link and developed ranges
reflecting the experts' confidence in attaining reductions in premature
death expected from the proposed revisions. However, the health benefit
analysis did not assess how the benefit estimates would vary in light
of other key uncertainties as the Academies recommended. Consequently,
EPA's response represents a partial application of the recommendation.
Agency officials told us that ongoing research and development efforts
will allow EPA to gradually make more progress in applying this and
other recommendations to future analyses.
EPA did not apply the remaining 12 recommendations to the analysis,
such as the recommendation to evaluate the impact of using the
assumption that the components of particulate matter are equally toxic.
EPA officials viewed most of these 12 recommendations as relevant to
its health benefit analyses but noted that the agency was not ready to
apply specific recommendations because of, among other things, the need
to overcome technical challenges stemming from limitations in the state
of available science. For example, EPA did not believe that the state
of scientific knowledge on the relative toxicity of particulate matter
components was sufficiently developed to include it in the January 2006
regulatory impact analysis, but the agency is sponsoring research on
this issue.
Background:
EPA is required by the Clean Air Act to conduct reviews of the National
Ambient Air Quality Standards (NAAQS) for the six criteria pollutants,
including particulate matter, every 5 years to determine whether the
current standards are sufficient to protect public health, with an
adequate margin of safety. If EPA decides to revise the NAAQS, the
agency proposes changes to the standards and estimates the costs and
benefits expected from the revisions in an assessment called a
regulatory impact analysis. In January 2006, EPA prepared a regulatory
impact analysis for one such rule--particulate matter--that presented
limited estimates of the costs and benefits expected to result from the
proposed particulate matter rule. EPA developed the estimates by, for
example, quantifying the changes in the number of deaths and illnesses
in five urban areas that are likely to result from the proposed rule.
The National Academies' 2002 report examined how EPA estimates the
health benefits of its proposed air regulations and emphasized the need
for EPA to account for uncertainties and maintain transparency in the
course of conducting benefit analyses. Identifying and accounting for
uncertainties in these analyses can help decision makers evaluate the
likelihood that certain regulatory decisions will achieve the estimated
benefits. Transparency is important because it enables the public and
relevant decision makers to see clearly how EPA arrived at its
estimates and conclusions. Many of the recommendations include
qualifying language indicating that it is reasonable to expect that
they can be applied in stages, over time; moreover, a number of the
recommendations are interrelated and, in some cases, overlapping. Soon
after the National Academies issued its report, EPA roughly
approximated the time and resource requirements to respond to the
recommendations, identifying those the agency could address within 2 or
3 years and those that would take longer. According to EPA officials,
the agency focused primarily on the numerous recommendations related to
analyzing uncertainty. As is discussed below, EPA applied some of these
recommendations to the particulate matter analysis.
EPA Applied Some, but Not All, of the National Academies'
Recommendations to the Particulate Matter Regulatory Impact Analysis:
EPA applied--either wholly or in part--approximately two-thirds of the
Academies' recommendations in preparing its January 2006 particulate
matter regulatory impact analysis and continues to address the
recommendations through ongoing research and development. According to
EPA, the agency intends to address some of the remaining
recommendations in the final rule and has undertaken research and
development to address others.
Recommendations EPA Applied or Partially Applied to Its Particulate
Matter Health Benefit Analysis:
The January 2006 regulatory impact analysis on particulate matter
represents a snapshot of an ongoing EPA effort to respond to the
National Academies' recommendations on developing estimates of health
benefits for air pollution regulations. Specifically, the agency
applied, at least in part, approximately two-thirds of the
recommendations--8 were applied and 14 were partially applied--by
taking steps toward conducting a more rigorous assessment of
uncertainty by, for example, evaluating the different assumptions about
the link between human exposure to particulate matter and health
effects and discussing sources of uncertainty not included in the
benefit estimates. According to EPA officials, the agency focused much
of its time and resources on the recommendations related to
uncertainty. In particular, one overarching recommendation suggests
that EPA take steps toward conducting a formal, comprehensive
uncertainty analysis--the systematic application of mathematical
techniques, such as Monte Carlo simulation--and include the uncertainty
analysis in the regulatory impact analysis to provide a "more realistic
depiction of the overall uncertainty" in EPA's estimates of the
benefits.[Footnote 2]
Overall, the uncertainty recommendations call for EPA to determine (1)
which sources of uncertainties have the greatest effect on benefit
estimates and (2) the degree to which the uncertainties affect the
estimates by specifying a range of estimates and the likelihood of
attaining them. In response, EPA examined a key source of uncertainty-
-its assumption about the causal link between exposure to particulate
matter and premature death--and presented a range of expected
reductions in death rates. EPA based these ranges on expert opinion
systematically gathered in a multiphased pilot project. The agency did
not, however, incorporate these ranges into its benefit estimates as
the National Academies had recommended.
Moreover, the Academies recommended that EPA's benefit analysis reflect
how the benefit estimates would vary in light of multiple
uncertainties. In addition to the uncertainty underlying the causal
link between exposure and premature death, other key uncertainties can
influence the estimates. For example, there is uncertainty about the
effects of the age and health status of people exposed to particulate
matter, the varying composition of particulate matter, and the
measurements of actual exposure to particulate matter. EPA's health
benefit analysis, however, does not account for these key uncertainties
by specifying a range of estimates and the likelihood of attaining
them. For these reasons, EPA's responses reflect a partial application
of the Academies' recommendation.
In addition, the Academies recommended that EPA both continue to
conduct sensitivity analyses on sources of uncertainty and expand these
analyses. In the particulate matter regulatory impact analysis, EPA
included a new sensitivity analysis regarding assumptions about
thresholds, or levels below which those exposed to particulate matter
are not at risk of experiencing harmful effects. EPA has assumed no
threshold level exists--that is, any exposure poses potential health
risks.[Footnote 3] Some experts have suggested that different
thresholds may exist, and the National Academies recommended that EPA
determine how changing its assumption--that no threshold exists--would
influence the estimates. The sensitivity analysis EPA provided in the
regulatory impact analysis examined how its estimates of expected
health benefits would change assuming varying thresholds.
In response to another recommendation by the National Academies, EPA
identified some of the sources of uncertainty that are not reflected in
its benefit estimates. For example, EPA's regulatory impact analysis
disclosed that its benefit estimates do not reflect the uncertainty
associated with future year projections of particulate matter
emissions. EPA presented a qualitative description about emissions
uncertainty, elaborating on technical reasons--such as the limited
information about the effectiveness of particulate matter control
programs--why the analysis likely underestimates future emissions
levels.
Recommendations EPA Did Not Apply to the Particulate Matter Analysis:
EPA did not apply the remaining 12 recommendations to the analysis for
various reasons. Agency officials viewed most of these recommendations
as relevant to its health benefit analyses and, citing the need for
additional research and development, emphasized the agency's commitment
to continue to respond to the recommendations. EPA has undertaken
research and development to respond to some of these recommendations
but, according to agency officials, did not apply them to the analysis
because the agency had not made sufficient progress.
For example, EPA is in the process of responding to a recommendation
involving the relative toxicity[Footnote 4] of components of
particulate matter, an emerging area of research that has the potential
to influence EPA's regulatory decisions in the future.[Footnote 5]
Hypothetically, the agency could refine national air quality standards
to address the potentially varying health consequences associated with
different components of particulate matter. The National Academies
recommended that EPA strengthen its benefit analyses by evaluating a
range of alternative assumptions regarding relative toxicity and
incorporate these assumptions into sensitivity or uncertainty analyses
as more data become available.[Footnote 6] EPA did not believe the
state of scientific knowledge on relative toxicity was sufficiently
developed at the time it prepared the draft regulatory impact analysis
to include this kind of analysis. In a separate report issued in 2004,
the National Academies noted that technical challenges have impeded
research progress on relative toxicity but nonetheless identified this
issue as a priority research topic. The Clean Air Scientific Advisory
Committee also noted the need for more research and concluded in 2005
that not enough data are available to base the particulate matter
standards on composition. The Office of Management and Budget, however,
encouraged EPA in 2006 to conduct a sensitivity analysis on relative
toxicity and referred the agency to a sensitivity analysis on relative
toxicity funded by the European Commission.
We found that EPA is sponsoring research on the relative toxicity of
particulate matter components. For example, EPA is supporting long-term
research on this issue through its intramural research program and is
also funding research through its five Particulate Matter Research
Centers and the Health Effects Institute. In addition, an EPA
contractor has begun to investigate methods for conducting a formal
analysis that would consider sources of uncertainty, including relative
toxicity. To date, the contractor has created a model to assess whether
and how much these sources of uncertainty may affect benefit estimates
in one urban area. Agency officials told us, however, that this work
was not sufficiently developed to include in the final particulate
matter analysis, which it says will present benefits on a national
scale.
Another recommendation that EPA did not apply to the particulate matter
analysis focused on assessing the uncertainty of particulate matter
emissions. The National Academies recommended that EPA conduct a formal
analysis to characterize the uncertainty of its emissions estimates,
which serve as the basis for its benefit estimates.[Footnote 7] While
the agency is investigating ways to assess or characterize this
uncertainty, EPA did not conduct a formal uncertainty analysis for
particulate matter emissions for the draft regulatory impact analysis
because of data limitations. These limitations stem largely from the
source of emissions data, the National Emissions Inventory[Footnote 8]-
-an amalgamation of data from a variety of entities, including state
and local air agencies, tribes, and industry. According to EPA, these
entities use different methods to collect data, which have different
implications for how to characterize the uncertainty. EPA officials
stated that the agency needs much more time to address this data
limitation and to resolve other technical challenges of such an
analysis. While the final particulate matter analysis will not include
a formal assessment of uncertainty about emissions levels, EPA
officials noted that the final analysis will demonstrate steps toward
this recommendation by presenting emissions data according to the level
emitted by the different kinds of sources, such as utilities, cars, and
trucks.
Finally, EPA did not apply a recommendation concerning the transparency
of its benefit estimation process to the particulate matter analysis.
Specifically, the National Academies recommended that EPA clearly
summarize the key elements of the benefit analysis in an executive
summary that includes a table that lists and briefly describes the
regulatory options for which EPA estimated the benefits, the
assumptions that had a substantial impact on the benefit estimates, and
the health benefits evaluated. EPA did not, however, present a summary
table as called for by the recommendation or summarize the benefits in
the executive summary. EPA stated in the regulatory impact analysis
that the agency decided not to present the benefit estimates in the
executive summary because they were too uncertain. Agency officials
told us that the agency could not resolve some significant data
limitations before issuing the draft regulatory impact analysis in
January 2006 but that EPA has resolved some of these data challenges.
For example, EPA officials said they have obtained more robust data on
anticipated strategies for reducing emissions, which will affect the
estimates of benefits. The officials also said that EPA intends to
include in the executive summary of the regulatory impact analysis
supporting the final rule a summary table that describes key analytical
information.
Concluding Observations:
While EPA officials said that the final regulatory impact analysis on
particulate matter will reflect further responsiveness to the
Academies' recommendations, continued commitment and dedication of
resources will be needed if EPA is to fully implement the improvements
recommended by the National Academies. In particular, the agency will
need to ensure that it allocates resources to needed research on
emerging issues, such as the relative toxicity of particulate matter
components, and to assessing which sources of uncertainty have the
greatest influence on benefit estimates. The uncertainty of the
agency's estimates of health benefits in the draft regulatory impact
analysis for particulate matter underscores the importance of
uncertainty analysis that can enable decision makers and the public to
better evaluate the basis for EPA's air regulations. While EPA
officials said they expect to reduce the uncertainties associated with
the health benefit estimates in the final particulate matter analysis,
a robust uncertainty analysis of the remaining uncertainties will
nonetheless be important for decision makers and the public to
understand the likelihood of attaining the estimated health benefits.
Mr. Chairman, this concludes my prepared statement. I would be happy to
respond to any questions that you or other Members of the Committee may
have.
GAO Contact and Staff Acknowledgments:
For further information about this testimony, 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 statement. Individuals who made key contributions to this
statement include Christine Fishkin, Assistant Director; Kate
Cardamone; Nancy Crothers; Cindy Gilbert; Tim Guinane; Karen Keegan;
Jessica Lemke; and Meaghan K. Marshall.
FOOTNOTES
[1] See GAO, Particulate Matter: EPA Has Started to Address the
National Academies' Recommendations on Estimating Health Benefits, but
More Progress Is Needed, GAO-06-780 (Washington, D.C.: July 14, 2006).
[2] Monte Carlo simulation refers to a computer-based analysis that
uses probability distributions for key variables, selects random values
from each of the distributions simultaneously, and repeats the random
selection over and over. Rather than presenting a single outcome--such
as the mostly likely or average scenario--Monte Carlo simulations
produce a distribution of outcomes that reflect the probability
distributions of modeled uncertain variables.
[3] Recent EPA analyses used the natural background concentrations of
particulate matter, rather than zero, for its assumption of no
threshold level. The National Academies supported the assumption of no
threshold level, but it recommended that EPA conduct a consistent and
transparent sensitivity analysis to consider various threshold levels.
[4] Particulate matter is a highly complex mixture comprising particles
emitted directly from sources and particles formed through atmospheric
chemical reactions. Particles span many sizes and shapes and consist of
hundreds of different chemicals. EPA identifies the major components of
fine particulate matter as carbon, sulfate and nitrate compounds, and
crustal/metallic materials such as soil and ash.
[5] Relative toxicity refers to the premise that different components
of particulate matter have different levels of potency affecting
premature mortality and illness. In the draft particulate matter
regulatory impact analysis, EPA assumed equivalent toxicity, stating
that "while it is reasonable to expect that the potency of components
may vary across the numerous effect categories associated with
particulate matter, EPA's interpretation of scientific information
considered to date is that such information does not yet provide a
basis for quantification beyond using fine particle mass." EPA, Draft
Regulatory Impact Analysis for the PM-2.5 National Ambient Air Quality
Standards (Washington, D.C., 2006), 3-21.
[6] In the context of the National Academies' recommendations, a
sensitivity analysis would assess how changes in one or more variables
affect the outcome, whereas a comprehensive or formal uncertainty
analysis evaluates the probability distributions of multiple variables.
[7] Because the precise levels of total emissions are not knowable but
rather are approximations based on a sample of measurements, there is
uncertainty about the true quantity of emissions.
[8] EPA compiles the National Emissions Inventory, a national database
of air emissions data that includes estimates of annual emissions, by
source, of air pollutants in each area of the country on an annual
basis.
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