i UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
May 23, 2002
EPA-SAB-CASAC-ADV-02-002
OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD
Honorable Christine Todd Whitman
Administrator
U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, NW
Washington, DC 20460
Subj ect: Revi e w of the Agency' s draft Proposed Me thodologyfor Particulate
Matter Risk Analysis for Selected Urban Areas; an Advisory by the Clean
Air Scientific Advisory Committee
Dear Governor Whitman:
The Clean Air Scientific Advisory Committee (CASAC) Particulate Matter Review Panel
("CASAC PM Review Panel" or the "Panel") met via public teleconference on Wednesday,
February 27, 2002. In this teleconference, the CASAC PM Review Panel reviewed the draft
document Proposed Methodology for Particulate Matter Risk Analysis for Selected Urban Areas
that outlines part of the procedures to be used in preparing the human health risk analysis for
PM2 5 that will accompany the Staff Paper on the National Ambient Air Quality Standards
(NAAQS) for Particulate Matter (PM) that will be released later this year. The CASAC PM
Review Panel consulted with the Agency's Office of Air Quality Planning and Standards
(OAQPS) last summer on the plans for this risk analysis and this document reflects some of the
comments and concerns that were raised at that time. We would like to commend OAQPS and
its contractors for responding to our comments and substantially improving the proposed plans.
OAQPS has asked the CASAC PM Review Panel to comment on the following specific charge
questions:
1. Given the goals set forth above for the planned PM risk analyses, has the draft
methodology appropriately drawn from the existing scientific and technical
information in developing the overall approach? To the extent it does not, what
salient features are missing or require change?
2. Have the appropriate sensitivity analyses been included in the proposed
methodology? If not, which additional sensitivity analyses should be included
and should any of the proposed sensitivity analyses be dropped?
3. The draft methodology report describes the planned approach to adjusting air
quality to simulate just meeting alternative PM25 air quality standards. Is this
approach reasonable? Are there other approaches that should be considered?
4. Have the appropriate health effect studies and concentration-response functions
been identified for use in the planned PM2 5 risk analyses? If not, which
additional studies and/or concentration-response functions should be considered?
Are there any studies and/or concentration-response functions that should be
dropped from the planned analyses?
5. Is the draft report clear and transparent in its description of the proposed
approach? Are the various assumptions and judgments that must be made in
carrying out the planned risk analyses clear and transparent?
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This report will summarize the Panel's consensus findings with respect to the draft
document and these questions. Additionally, some of the CAS AC PM Review Panel Members
have also prepared individual comments on the review document and these are included in
Appendix A to this report.
As a prelude to our comments, the Panel would like to indicate the importance that this
risk assessment analysis has in the primary standard setting process for PM. While prior EPA
policy and the legislative history of the Clean Air Act indicate that assessment of quantitative
risks should not play a determinant role in recommending primary, health-based standards, such
estimates can provide important information to the Administrator in assessing alternative
standard levels. The human health risk assessment analysis helps to provide a quantitative link
between the science described in the Criteria Document and the policy implications and
recommendations in the Staff Paper and thus, we believe that it is critical that the risk assessment
analysis be done at the state of the current science in this field.
In response to charge question 1, the Panel concluded that the general methodology as
described in the report is appropriate. It recognizes the need to use concentration/response
functions to obtain risk estimates in a series of locations. Thus, the general framework of the
approach is the sensible approach to this risk analysis. However, the Panel has a number of
comments that relate to the details of application of the method.
One of the most critical questions is the choice of the locations for which the analyses
will be made. For two reasons, the Panel strongly suggests including analyses of health risks for
PM10, as well as PM2 5. First, the small amount of concentration-response data for PM2 5 led the
proposed methodology to use data from different cities for different health effects. Although
short-term and long-term mortality will be examined in seven of the eight proposed cities, only
two or three cities will be used for the review of hospital admissions or respiratory symptoms.
Recent comparisons of PM10 results from different cities demonstrate spatial variations in
concentration-response relationships that may also exist for PM2 5. Using concentration-response
functions from different cities for different health effects may then lead to inaccurate views of
the relative potency of PM2 5 in causing the different effects. Data for PM10 would help clarify
these differences and resulting uncertainties by permitting estimation of concentration-response
functions for a wider range of health effects such as hospital admissions or respiratory symptoms
in the same cities. In doing this, it is important to include comparisons in cities in which PM10
has relatively greater and lesser effects, not just those cities showing the highest concentration-
response effect. Second, evaluation of PM10 concentration-response relationships would provide
a bounding analysis for the health burden from PM2 5. Although the potency per unit mass could
be greater for PM25 than for PM10, the total public health burden of mortality and morbidity from
PM2 5 must be contained within the health burden from PM10 (i.e., it cannot be greater).
Including PM10 therefore, would provide a valuable perspective for the likely upper bound of the
health impact of PM25 and help provide some measure of the variability of risk across a wider
range of conditions than the eight cities afford. The analysis should include a clear statement of
the rationale for selecting the cities that are included
In response to charge question 2, we want to commend the Agency for starting the
process with the recognition of the need for: 1) sensitivity analyses; and 2) for building them into
the risk analysis process. In general, the sensitivity studies presented are appropriate as part of
the understanding of the uncertainties in the results of the risk analysis. However, there are other
aspects of the problem that may be useful to examine as well. These aspects include: 1) the
seasonality in the baseline rates; and 2) the concentration/response functions for health effects.
It will be useful to provide the results of the multiple analyses in terms of the sensitivity of the
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overall process to locations across the United States and thus, sensitivity to the likely differences
in ambient aerosol compositions that those locations represent. The sensitivity of the risk to the
pollutant when used in a single pollutant model as compared with multi-pollutant models is also
essential. We are always exposed to a mixture of pollutants and it is important to understand the
risk of a single pollutant within the context of the full set of chemical species to which the people
displaying adverse effects are exposed.
The Panel agreed that the proportional rollback approach is the appropriate method.
However, a rationale should be offered for the decision to base the rollback percentage on the
"above background" portion of the "as is" concentration distribution. The "background" portion
of the "as-is" distribution is unknown, and is almost certainly poorly approximated by the
assumption of a constant level equal to the annual average. The annual average "background" is
so small relative to some of the probable individual day values that the analysis results will be
quite insensitive to the estimate of the constant annual average "background". Given this, and
given the difficulty of estimating individual-day "backgrounds", it might be better to calculate
the rollback from total observed concentrations.
The Panel believes that the most critical aspect of the choice of concentration-response
functions for PM2 5 is providing a clear rationale for each choice. It is essential that an
appropriate distribution of concentration-response functions be used that represent the range of
PM2 5 concentrations in various cities across the country. The current review document suggests
that there was an intent to select functions that would show the highest response per unit
concentration. For example, it is stated that the intent is to use lag models that have the highest
corresponding effect estimates. Doing so would present biased estimates of the risk. Therefore,
in cities where studies have presented the results for multiple lags, all of the published results
should be used in the risk analyses to develop the full range of possible risk estimates.
It is important to make the studies in cities chosen for geographical coverage and a range
of PM compositions rather than only looking at cities for which there are PM25 data. To the
extent possible, it will be useful to examine the range of all of the possible health endpoints for
each of the selected cities so that the relative morbidity and mortality effects in each city can be
put into perspective. Again, we recognize that it may be necessary to use PM10 -based estimates
in order to address this issue.
In addition, given the new information provided in the recently published paper by Pope
et al. (J. Amer. Med. Assoc. 287:1132-1141, 2002), it may be appropriate to examine lung
cancer as an endpoint in the risk analysis as well as cardiopulmonary mortality and morbidity
effects.
Finally, the question of the transparency of the process is raised in charge question 5.
The Panel felt that the current review document could be improved by starting the document by
describing the set of assumptions that are necessary to make the analysis to be subsequently
presented. These assumptions include the causality of effects by particulate matter mass,
constancy in levels of individual activity leading to equivalent exposures to the ambient
parti culate matter and equal toxicity of the parti culate matter within the geographical region for
which the analysis is being performed. We understand that these assumptions need to be made
in order to proceed with the data analysis that are available. However, it would be prudent to
present the assumptions explicitly early in the document. This addition in conjunction with more
clear presentation of the rationales for making the variety of choices that are needed will
improve the transparency of the process and help to frame the uncertainties that all such analyses
are typically subject to.
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At all stages in the plan and its execution, it is important that EPA and its contractors
clearly distinguish between and attempt to characterize uncertainty and variability. The present
plan does not always clearly make this distinction. As noted by the NRC Committee on
Hazardous Air Pollutants in Science and Judgement, it is important to make these distinctions as
clear as possible. At this time, there is abundant scientific information to characterize some
aspects of variability, i.e., variations in concentrations/response functions in some communities
as a function of season at least for PM10. At the same time, there are major uncertainties in our
knowledge of PM and these different aspects of the problem should be treated separately and as
completely as possible.
The CASAC PM Panel recognizes that the present review document does not represent
the complete set of risk analyses that are expected to be performed as part of this NAAQS
process. Depending on the extent of data and scientific information presented in the next draft of
the Particulate Matter Criteria Document, there may be a need for risk analyses for PM10_2 5 and
alternative PM25 standards. The Staff Paper to be presented in July will present a discussion of
any alternative PM2 5 and PM10_2 5 standards. It will be essential that there be a clear rationale
for the inclusion or exclusion of specific indicators of PM concentration, the statistical forms of
the standards, and the averaging period. If the decision is then made to perform a risk analysis
on PM10_2 5 or the alternative PM25 standards, it would be helpful to provide an outline of risk
analysis plans for these standards (data sets, endpoints, etc) to the Panel as soon as possible for
comment (via an SAB "Consultation") rather than to present a completed analysis without any
prior commentary. We would not necessarily suggest a full document with review, but
communication of the plans and an opportunity for individual comments back to OAQPS would
potentially help provide a better analysis. This consultation could potentially be done as part of
the Staff Paper review to be held in September.
These are the major issues that the Panel have identified with respect to the risk analysis.
We believe that the basic process is sound and have provided a number of suggestions in this
report and in the appendices to refine the analyses that are to be done. We look forward to
seeing the final results in conjunction with the PM Staff Paper later this year.
The CASAC Particulate Matter Review Panel is composed of the seven statutory
CASAC members along with expert consultants. As such, it represents the full CASAC and no
further advisory committee review is needed prior to submission of this final advisory review
report to the Agency.
Sincerely,
/Signed/
Dr. Philip Hopke, Chair
Clean Air Scientific Advisory
Committee
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U.S. Environmental Protection Agency
EPA Science Advisory Board
Clean Air Scientific Advisory Committee
CHAIR
Dr. Philip Hopke, Bayard D. Clarkson Distinguished Professor, Department of Chemical
Engineering, Clarkson University, Potsdam, NY
Also Member: Research Strategies Advisory Committee
Executive Committee
MEMBERS
Dr. Frederick J. Miller, Vice President for Research, CUT Centers for Health Research,
Research Triangle Park, NC
Mr. Richard Poirot, Environmental Analyst, Air Pollution Control Division, Department of
Environmental Conservation, Vermont Agency of Natural Resources, Waterbury, VT
Dr. Frank Speizer, Edward Kass Professor of Medicine, Channing Laboratory, Harvard
Medical School, Boston, MA
Dr. George E. Taylor, Professor, Honors Program, George Mason University, Fairfax, VA
Dr. Sverre Vedal, Professor of Medicine, National Jewish Medical and Research Center,
Boulder, CO
Dr. Barbara Zielinska, Research Professor, Desert Research Institute, Reno, NV
EPA SCIENCE ADVISORY BOARD STAFF
Mr. A. Robert Flaak, Designated Federal Officer, US EPA, EPA Science Advisory Board,
1200 Pennsylvania Avenue, NW, Washington, DC
Ms. Rhonda Fortson, Management Assistant, US EPA, EPA Science Advisory Board, 1200
Pennsylvania Avenue, NW, Washington, DC
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U.S. Environmental Protection Agency
EPA Science Advisory Board
Clean Air Scientific Advisory Committee
CASAC Particulate Matter Review Panel*
CHAIR
Dr. Philip Hopke, Bayard D. Clarkson Distinguished Professor, Department of Chemical
Engineering, Clarkson University, Potsdam, NY
Also Member: Executive Committee
Research Strategies Advisory Committee
CASAC MEMBERS
Dr. Frederick J. Miller, Vice President for Research, CUT Centers for Health Research,
Research Triangle Park, NC
Mr. Richard L. Poirot, Environmental Analyst, Air Pollution Control Division, Department of
Environmental Conservation, Vermont Agency of Natural Resources, Waterbury, VT
Dr. Frank Speizer, Edward Kass Professor of Medicine, Channing Laboratory, Harvard
Medical School, Boston, MA
Dr. George E. Taylor, Professor and Assistant Dean, School of Computational Sciences,
George Mason University, Fairfax, VA
Dr. Sverre Vedal, Professor of Medicine, National Jewish Medical and Research Center,
Denver, CO
Dr. Barbara Zielinska, Research Professor , Division of Atmospheric Science, Desert Research
Institute, Reno, NV
OTHER SAB MEMBERS
Dr. Paul J. Lioy, Associate Director and Professor, Environmental and Occupational Health
Sciences Institute, UMDNJ - Robert Wood Johnson Medical School, Piscataway, NJ
Member: Advisory Council on Clean Air Compliance Analysis
CONSULTANTS
Dr. Jane Q. Koenig, Professor, Department of Environmental Health, School of Public Health
and Community Medicine, University of Washington, Seattle, WA
Dr. Petros Koutrakis, Professor, Environmental Science and Engineering Program, School of
Public Health, Harvard University, Boston, MA
Dr. Allan Legge, President, Biosphere Solutions, Calgary, Alberta, CANADA
Dr. Morton Lippmann, Professor, Nelson Institute of Environmental Medicine, New York
University School of Medicine, Tuxedo, NY
Dr. Joe Mauderly, Vice President, Senior Scientist, and Director, National Environmental
Respiratory Center, Lovelace Respiratory Research Institute, Albuquerque, NM
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Dr. Roger O. McClellan, Consultant, Albuquerque, NM
Dr. Gunter Oberdorster, Professor of Toxicology, Department of Environmental Medicine,
University of Rochester, Rochester, NY
Dr. Robert D. Rowe, President, Stratus Consulting, Inc., Boulder, CO
Dr. Jonathan M. Samet, Professor and Chair, Department of Epidemiology, Bloomberg School
of Public Health, Johns Hopkins University, Baltimore, MD
Dr. Arthur C. Upton, Clinical Professor, Environmental and Community Medicine, UMDNJ-
Robert Wood Johnson Medical School, New Brunswick, NJ
Mr. Ronald White, Assistant Executive Director, Education, Research and Community Affairs,
National Osteoporosis Foundation, Washington, DC
Dr. Warren H. White, Senior Research Associate , Chemistry Department, Washington
University, St. Louis, MO
Dr. George T. Wolff, Principal Scientist, General Motors Corporation, Detroit, MI
EPA SCIENCE ADVISORY BOARD STAFF
Mr. A. Robert Flaak, Designated Federal Officer, US EPA Science Advisory Board, 1200
Pennsylvania Avenue, NW, Washington, DC
* Members of this SAB Panel consist of
a. SAB Members: Experts appointed by the Administrator to serve on one of the SAB Standing
Committees.
b. SAB Consultants: Experts appointed by the SAB Staff Director to a one-year term to serve on ad hoc
Panels formed to address a particular issue.
in
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NOTICE
This report has been written as part of the activities of the EPA Science Advisory Board,
a public advisory group providing extramural scientific information and advice to the
Administrator and other officials of the Environmental Protection Agency. The Board is
structured to provide balanced, expert assessment of scientific matters related to problems facing
the Agency. This report has not been reviewed for approval by the Agency and, hence, the
contents of this report do not necessarily represent the views and policies of the Environmental
Protection Agency, nor of other agencies in the Executive Branch of the Federal government, nor
does mention of trade names or commercial products constitute a recommendation for use.
Distribution and Availability: This EPA Science Advisory Board report is provided to the EPA
Administrator, senior Agency management, appropriate program staff, interested members of the
public, and is posted on the SAB website (www.epa.gov/sab). Information on its availability is
also provided in the SAB's monthly newsletter (Happenings at the Science Advisory Board).
Additional copies and further information are available from the SAB Staff [US EPA Science
Advisory Board (1400A), 1200 Pennsylvania Avenue, NW, Washington, DC 20460-0001; 202-
564-4533].
IV
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APPENDIX A - INDIVIDUAL PANELIST WRITTEN COMMENTS
Note: These are the written comments provided by a number of individual Panelists as a
result of their review of the draft fProposedMethodology for Paniculate Matter Risk Analysis
for Selected Urban Areas at the February 27, 2002 meeting. These individual comments are
included here to present the full range of opinion and to document all edits suggested by
Panelists. These are individual comments and do not necessarily represent the views of the
Clean Air Scientific Advisory Committee (CASAC) nor the EPA Science Advisory Board
(SAB). The consensus position of the CASAC Parti culate Matter Review Panel is contained in
the preceding report.
Contents:
Dr. Koenig A-2
Dr. Legge A-3
Dr. Miller A-3
Dr. Lippmann A-5
Dr. Mauderly A-6
Dr. McClellan A-7
Dr. Oberdorster A-9
Dr. Rowe A-9
Dr. Taylor A-10
Dr. Vedal A-12
Dr. W. White A-13
Dr. Wolff A-13
Dr. Zielinska A-14
A- 1
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Dr. Koenig
PagelO:
Background levels. What is the definition of background? Non anthropogenic??? If so, why are
we estimating health effects based on changes from background???
Page 20.
2.6 Calculating health effects. Why not skip days with missing data? Are there that many??
2.7 Baseline health effects incidence data. Page 21. It seems to me that the baseline incidence
of health will be based on data from "as is" pollutant levels. Certainly it is not baseline air poll
days—not manmade pollution??? Can not the average health indicators on the days of, say the
25th percentile be used??
2nd para. Incidence varies by air pollution levels?? If that has already been shown, that
could be our report!!!
3rd para. Make it clear that the incidence rates described here are NOT air pollution-free
rates.
4th para, it may introduce serious exposure error to use county wide population and city
wide air monitors. In King County, there are no air monitoring data for the rural sections
of the county. King County is very large and includes populations for which Seattle air
quality data are not representative.
3.2.1.
page 29. first para. Criteria of at least 11 observations per quarter. Surely we can be more
robust than that!
Page 30. 2nd full para. 2nd line. I think that should be morbidity??
4.2
page 33 no effect of the four gaseous pollutants. With what certainty can that be stated.?
5. Baseline health effects. Same issue I have commented on. What is meant by the annual
number of cases in a location before a change in PM air quality? How is that different from
incidence at "as is " air pollution levels???
Page 37. First full para These data Don't hospital discharge records show date of admission??
6. Sources of uncertainty. FYI, Data have been published on S in children with asthma residing
in Seattle. Yu et al, 2000.
Exhibit 6.1. Page 45. Define background and differentiate from'as is"
6.1.1
PM2.5 and PM2.1 How about PM 1.0 (nephelometry data) These can be transformed to PM2.5.
Page 47. Repeat comment. How can we be certain that PM effects are not confounded by other
gaseous criteria pollutants?? And then of course there are all the unmeasured co-pollutants!!
A-2
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6.1.2
page 48 PM is only dominated by windblown particles in areas where there are no mobile
source pollutants. Why is that even mentioned??
6.3.1
Use of nonresidents of a city in data analysis is a problem. That is why we use zip code data.
Dr. Legge
I have only one comment on the draft document entitled 'Proposed Methodology for
Particulate Matter Risk Analyses for Selected Urban Areas' dated January,2002. The comment
is very basic and relates to using PM mass, in any form, as a surrogate for various health
endpoints. PM chemistry is essentially ignored. While I understand that the focus to this point in
the process has been on PM mass, the document as written understates the importance of PM
chemistry (see page 48, para 1). The document should clearly state that PM chemistry is
important eventhough it is recognized at this time that more data are required.This is an
important 'next step' issue. All the best in pulling together all of the CAS AC comments.
Dr. Miller
The Panel was charged with addressing and providing comments on five questions related to the
methodology and proposed course of action by EPA relative to potential risk assessment
activities in conjunction with the reevaluati on/re vision of NAAQS for PM. While comments are
provided below for the five charge questions, some aspects of these comments could be placed
under more than one of the questions.
Of particular concern to this Panel member is the focus on PM2.5 to the exclusion of other
indicators of PM. In that sense, the overall approach being proposed in the document is not as
much at issue as is the scope of the document. The current document presents to critics of EPA
the notion of a pre-bias towards PM2.5. Beyond the wording of sections of the document, the
need to address the broader aspects of the various indicators of PM is scientifically compelling
and prudent for public health protection.
Question 1: Given the goals set forth above for the planned PM risk analyses, has the
draft methodology appropriately drawn from the existing scientific and technical
information in developing the overall approach? To the extent it does not, what salient
features are missing or require change?
EPA has drawn from their previous experience in the 1996 PM risk analyses that they conducted
to refine the methodology and provide some additional types of analyses. I would agree that the
figures on pages 8 and 9 of the document contain the basic elements and components of risk
analyses that could be conducted for short term and long term effects, respectively. Most features
or other approaches that might be incorporated basically fall into implementation methods for
activities within the various major boxes contained in the figures. To this extent, my overall
response to charge question #1 is that the draft methodology is appropriate.
However, there are two major elements of concern. First, while currently complying with the
existing way standards are set, the use of the simple arithmetic mean for averaging quarterly
values from a monitor and then continuing with the arithmetic mean of the four quarters should
be reexamined. Just as there have been significant improvements in statistical methodologies for
the analysis of epidemiological study responses, so have there been advances in the ability to do
bootstrapping or windsorized trimmed means in sampling statistical survey or air quality data.
A-3
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The current simple arithmetic average has significant deficiencies and needs to be reevaluated as
the basis for obtaining the value to use in standard setting.
Second, the current approach has a significant weakness in that analyses based upon seasonal
data are not used to the fullest extent possible. Given the regional heterogeneity of PM
composition and level in conjunction with period of the year, I believe it is critical that seasonal
analyses be used to the greatest extent possible. The aspect of seasonality can be used for
background incidences of response rates, potential rollback strategies, and the list goes on.
Question 2: Have the appropriate sensitivity analyses been included in the proposed
methodology? If not, which additional sensitivity analyses should be included and should
any of the proposed sensitivity analyses be dropped?
There is a discrepancy in the document relative to the listing of types of sensitivity analyses that
are being considered. The Agency should recast the sensitivity analyses identified in Exhibit 6.1
so that they fall into comparable categories as presented earlier in Exhibit 2.5. The Panel brought
up a number of additional sensitivity analyses that should be conducted as part of the broader
category of examining the nature of the concentration response function, the selection of the
distribution of lag times or distributed lags, and the approach to handling rollbacks.
Collectively, the conference call advisory review on February 27, 2002 identified a number of
areas that would benefit from sensitivity analyses from the perspective of either exploring
alternative hypotheses, bounding the level of risk, or assessing the reasonableness of the
preferred approach compared to alternative approaches for handling a specific technical
question. It would behoove EPA to consider all of the proposed sensitive assessments and
provide CASAC with a prioritization for addressing what EPA believes would be the most
critical sensitivity analyses to be performed. Here, the intent would be to ensure that within the
time and resources available, EPA conducts the most critical sensitivity analyses.
Question 3: The draft methodology report describes the planned approach to adjusting
air quality to simulate just meeting alternative PM2.5 air quality standards. Is this
approach reasonable? Are there other approaches that should be considered?
The planned approach for adjusting air quality to simulate just meeting alternative PM 2.5 air
quality standards appears to be reasonable. However, Panel members noted other approaches that
could be considered such as seasonal rollback or peak shaving that might be examined in various
sensitivity analyses. In view of the regional heterogeneity identified in the latest epidemiological
analyses, these alternative methods for adjusting air quality data may be more relevant for one
region compared to another. By examining some of these alternative approaches, EPA scientists
will be in a better position to inform the Administrator on potential courses of action for PM
standards.
Question 4: Have the appropriate health effect studies and concentration-response
functions been identified for use in the planned PM2.5 risk analyses? If not, which
additional studies and/or concentration-response functions should be considered? Are
there any studies and/or concentration-response functions that should be dropped from
the planned analyses?
The current proposed methodology is not very explicit relative to alternative C-R models that
might be used that allow an assessment of the existence of a biologically plausible threshold.
Clearly, the current document heavily emphasizes robust and extensive datasets for a select
number of responses. The Panel discussed the desirability of examining a broader set of health
A-4
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indices with an indicator such as PM10 and an adjustment of inclusion criteria such that a more
expanded analysis may be done with a greater number of cities. I would endorse such an
approach. EPA staff have acknowledged that the next draft of the PM Criteria document may
inform them as to other concentration-response functions or indicators that should be examined.
Question 5: Is the draft report clear and transparent in its description of the proposed
approach? Are the various assumptions and judgments that must be made in carrying out
the planned risk analyses clear and transparent?
There are a number of assumptions that are inherent in the proposed methodology. I would agree
with other Panel members that these assumptions need to be explicitly stated. Currently, the
various sections do not adequately convey the underlying assumptions. In addition, by clearly
stating the underlying assumptions, EPA can provide insights on the validity of some of these
assumptions through sensitivity analyses.
Dr. Lippmann
1. Given the goals set forth above for the planned PM risk analyses, has the draft
methodology appropriately drawn from the existing scientific and technical information in
developing the overall approach? To the extent it does not, what salient features are missing or
require change?
Yes, appropriate use has been made of the existing literature and technical information.
However, the next version should include a risk analysis for lung cancer associated with long-
term PM2 5 exposure. This association can be based on findings in a paper by Pope et al. that is
in press in JAMA and based on a 16-year follow-up of the ACS cohort.
2. Have the appropriate sensitivity analyses been included in the proposed methodology? If
not, which additional sensitivity analyses should be included, and should any of the proposed
sensitivity analyses be dropped?
Yes, the outline provided on planned sensitivity analyses describes a reasonable approach.
3. The draft methodology report describes the planned approach to adjusting air quality to
simulate just meeting alternative PM25 air quality standards. Is this approach reasonable? Are
there other approaches that should be considered?
Yes, this approach is quite reasonable, and I have no other approaches to suggest.
4. Have the appropriate health effect studies and concentration-response functions been
identified for use in the planned PM2 5 risk analyses? If not, which additional studies and/or
concentration-response functions should be considered? Are there any studies and/or
concentration-response functions that should be dropped from the planned analyses?
Yes, appropriate selections have been made. As noted in response to charge Question #1, the
concentration-response function for lung cancer from Pope et al. (2002) should also be included
and used in a risk analysis. Consideration should also be given to the inclusion of the risks
associated with PM2 5 reported for the Childrens Health Study in 12 Southern California
communities.
5. Is the draft report clear and transparent in its description of the proposed approach? Are
the various assumptions and judgments that must be made in carrying out the planned risk
analyses clear and transparent?
A-5
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Yes, the report was quite clear and transparent in its description of the various assumptions and
judgements made.
In summary, the Abt Associates report was very well done, and represents a maturation of
specialized field of risk analysis for air pollution health effects.
Dr. Mauderly
General Comments
For the most part, the approach seems reasonable. However, it seems both a mistake and
misleading to avoid including PM10 in the risk analysis. We know more about PM10 than the
other fractions, and the total health burden of the other fractions must be contained within the
burden from PM10. It seems like that would be the place to start a thorough assessment of PM-
related health risks.
Specific Comments
P 3, para 3: Given that the purpose of the document is to lay out an approach for quantitating
concentration-response relationships, it stretches credibility to imply that quantitation of
risks is not a central purpose, and that quantitative risks will not play a significant role in
recommending standards (and defending them).
P 3, footnote: It is not reasonable that assessment of risks for PM10 will not be a part of the
strategy. We still have more information, and increasingly detailed information (e.g.,
NMMAPS), on associations between health and PM10 than we do for all other PM
indicators combined. PM10 should be included in the assessment. This is especially
important if you are going to propose a standard for PMcoarse (PM10_2 5). Data on PM10_25
vs. health are scarce. Presumably, information on PM10 would provide a background for
estimating the health burden from both the fine and coarse fractions. Because both are
contained within PM10, the sum of the health burdens of PM fine and coarse must be
contained within the health burden of PM10. Of course, the specific toxicity of either
fraction (but not both) could be greater than that of PM10, but the estimated risks and
health burden from PM10 would provide some context for consideration of the other
fractions.
P 16, footnote: Gosh -1 wish you'd define "heteroskedasticity" so I won't have to look it up. I
want to use that one at cocktail parties!
P 29, para 2: I am not very comfortable with dropping monitors that might yield higher than
average concentrations. People might not live there, but they work there, shop there, and
drive through there. Besides, it's been argued for years that PMfme concentrations at
monitors are broadly representative because of dispersal. Of course, tossing out the
higher values will give you an apparently greater concentration-specific PM effect, if the
effect is really due to a combination of the higher and lower exposures. The rationale for
tossing the higher monitors is not convincing.
P 30, para 2: This paragraph indicates that no generalization will be made to national PM-
related health burden, and that national-level "body counts" will not be invoked in setting
or defending the standard. Again, that stretches credibility.
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P 31, Exhibit 3.1: A serious weakness of the proposed strategy is the use of different cities for
mortality and morbidity estimates. The rest of the document repeatedly notes that PM
composition, exposures, populations, and therefore likely risks probably vary among
locations. The proposed strategy purposefully looks at different kinds of morbidity in
different cities, and at morbidity in one city (Seattle) for which mortality data are not to
be used. It is recognized that morbidity data are not as broadly available as mortality
data. Regardless, a strong effort should be made to compare the different types of
morbidity data in the same cities, and in cities for which there are mortality data. This
should be done even if forces the use of data that are a bit weaker than those from another
city. At least you would be comparing "apples to apples".
P 52, para 2: Does this mean that "admissions" data (which you say are really discharge data) do
not include people entering the hospital and dying there? Considering the evidence and
emphasis on mortality, why wouldn't those entering the hospital and dying there also
comprise an important part of the population affected by morbidity (arguably the most
important part)? If they are excluded, the morbidity data are skewed by under-reporting
of both the numbers affected and those who are most seriously affected.
P 53, para 4: Instead of using an annual average baseline incidence rate (i.e., annual divided by
365), couldn't you at least use quarterly rates? It seems unlikely that the incidence rate
would be identical year-round.
Dr. McClellan
I am pleased to offer the following comments to augment my input to the CASAC
Particulate Matter (PM)Panel review of the EPA's Proposed Methodology for Particulate Matter
Risk Analyses For Selected Areas held on February 27, 2002.
As a point of departure I wish to emphasis that I view this document and the analyses to
be performed as an exceptionally important bridge between the science reported in the PM
Criteria Document and the more policy relevant PM Staff Position Paper. These analyses are
critical to helping assess how the science on PM can inform decisions on the four key elements
of the National Ambient Air Quality Standard for PM, namely, the indicator, the averaging time,
the numerical level, and the statistical form.
Because of the importance of the document I am baffled as to why the document is not
authored by EPA staff but rather by contractor personnel with some apparent EPA ghost writing.
I would have strongly preferred that a document of this type impacting very directly on policy
decisions be authored by EPA staff. If this had been done it would have been much easier to
document the linkage between the risk analyses being performed, the Staff Paper(SP), and the
ultimate decisions to be made by EPA on the PM NAAQS. In the absence of clear
documentation the public is left in the dark as to how EPA will make science-based decisions on
the PM NAAQS and especially the core decision of "how low is low enough?" to provide an
adequate margin of safety.
Despite the critical shortcoming noted the document and, most importantly, the proposed
methodology it is improved relative to the earlier version. Unfortunately, the document and
methodology is still not adequate for performing the analyses essential to setting a science-based
NAAQS for PM. IN the following text I will relate the deficiencies of greatest concern.
An over arching deficiency in the document and plan is the failure to clearly distinguish
between uncertainty and variability. The authors and EPA are urged to review the discussion of
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this issue contained in the National Academy of Science/National Research Council report--
Science and Judgement in Risk Assessment. In the present document many times matters of
variability are erroneously presented as uncertainty. The document and the methodology it is
describing must clearly distinguish between uncertainty and variability and then do a better job
of addressing both matters.
The issue of variability is of special concern with regard to regional variability. The
document and methodology is improved by including more cities in the current version.
However, it still falls short. More cities must be included to help understand the range of
variability in PM related health effects across the United States, which appear to range from
clearly substantial impact in some areas to no impacts in other areas. By failing to adequately
cover the United States the document leaves the impression that the authors and EPA are only
interested in documenting health effects rather than providing a complete and balanced
exposition. One approach to illustrating the high degree of variability for cities is to include in
the analyses all the cities include in the analyses performed on PM10 by the Johns Hopkins
team.
Another area that needs to be more adequately analyzed with regard to both variability
and uncertainty is the matter of indicator. It is imperative that the document provide balanced
analyses of PM10, PM10-2.5 and PM2.5. The excessive attention to PM2.5 leads some to
conclude that EPA is only interested in analyses that will support some pre-determined decision
as to the details of the PM NAAQS. Indeed, rigorous analyses based on today's science might
lead to the conclusion that a PM10 indicator might provide equal or even better protection of
public health than a PM2.5 indicator for many regions of the USA or even the entire USA. Of
course, it is not possible to know this if the analyses of multiple indicators are not performed.
The document and methodology will also be improved by directing more attention to
analyses that will inform decisions on the numerical level, averaging time and statistical form of
the NAAQS's for PM. The issue of the statistical form of the NAAQS tends to be left to the end
of the process and does not get the attention it deserves. One way to correct this deficiency is to
make it less of a black box decision by performing the analyses now that will provide science
based results that will stimulate discussion of these critical matters.
And finally, I want to comment on the issue of the extent to which the document and
methodology are quantitative or qualitative. The EPA staff appear to be concerned with showing
their hand as to how the results of the analyses will be used. Obviously, if the results are not
going to be used then the work should not be done. Clearly, the analyses are going to be
quantitative. It is hard to argue otherwise in view of all the planned number crunching.
Perhaps what EPA is trying to relate is that the risk analyses results will be used to
inform decisions on the PM NAAQS but the analyses are not the only input, hence, the use is
qualitative. One solution to this dilemma is for EPA to more clearly articulate how it plans to
establish the four key elements of the NAAQS: the indicator, the averaging time, the numerical
level, and the statistical form.
I argue that public interest would be best served by debating the approaches to how to set
the NAAQS now rather than after the NAAQS for PM is set and the debate about approaches is
complicated by the results on the table. Consideration of the risk analysis document and the
under laying methodology is very difficult in the absence of EPA having laid out for the public
how it intends to make critical decisions on the setting of the PM NAAQS.
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Dr. Oberdorster
I have just a few comments following yesterday's conference call on the PM risk analysis
document. Before the teleconference, I had questions/comments in three areas, all of which
were addressed during the meeting:
One is the issue of lag effects of PM since results of the Epi group of our PM Center
specifically points to such effects for cardiac responses of certain particles. However, data on
lag effects in general are probably too limited at this point.
The other is to consider long-term effects with the endpoint cancer, and I was very
interested in Mort's announcement of the pending publication which will be quite useful.
Thirdly, the issue of background or baseline PM with consideration of anthropogenic
versus natural PM contributions. This requires knowledge about PM chemistry. Increases of
specific PM constituents relative to existing background levels will carry different risks, and
risk estimates for PMx reflect always an integration over very diverse particles. This makes C-
R relationships very complex and, depending on compositions, different for different locations
(as if a toxicologist would attempt to average effects of many particles ranging from highly
cytotoxic crystalline SiO2 to benign TiO2). I think a future need for PM risk analysis is to
identify mechanisms of effects, for which PM compositional data are one requirement. That will
allow a mechanism-based risk analysis as a goal for the future. I don't have additional comments
on the document.
Dr. Rowe
Below are comments on the proposed EPA PM Risk Assessment, as outline in the
methodology report of January, 2002 and discussed at our teleconference earlier today. I am in
agreement with most all of the resolutions of the conference call today, which largely covered
my comments on the methodology.
1. The overall approach is appropriate, subject to revisions and clarifications as
suggested by the panel. I concur with the key recommendations to retain the PM10 component of
the analysis, to do more to try to measure all included health endpoints for each selected
location, to revise the basis for selecting lags for coefficients, and to better address some of the
assumptions outlined in the methodology (e.g., assuming uniform HA/ERV ratios). The
recommendation to include even more cities seems to me to be nice but a lower priority.
2. Appropriate sensitivity analyses are included, but others need to be included, as
identified by the panel on the teleconference.
3. The approach to simulating air quality meeting current PM25 (using linear rollback) is
reasonably, but not by it self sufficient. The report was vague on alternatives, and not
necessarily tied to reality. I believe attention should be given to evaluating reality based
"seasonal" rollbacks (or peak shaving) for locations where that appears merited in terms of the
peak episodes routinely occurring in a specific season and where seasonal shaving could occur
via episodic or seasonal controls (recognizing this will require attention to seasonal C-R
coefficients and seasonal baselines for health events).
4. Generally, the appropriate health effects studies and C-R relationships have been
identified for use in the analyses.
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5. The report is generally clear and transparent. However, more documentation is
particularly required in terms of the decision rules for including PM metrics, cities, and C-R
relationships. Some key assumptions need are missing and can be directly stated (e.g., assumed
causality, lack of detail on constituents resulting in an assumption of constant toxicity, and
uncertainty about the most relevant exact dose metric (hourly, annual, PM2 5).
Additional comments and questions not covered in the meeting follow:
Page 10 discussed the AIRS data and the proposal to use either 2000 data (where it
exists) or 1999 data (where 2000 data does not exist). I am curious why EPA would not use both
1999 and 2000 data where both exist for a city, at least for the health endpoints relating to annual
average values (and reflecting the long-term standard is based on a 3 year average).
The characterization that EPA will not rely on the quantitative results seems misleading
(page 1, and EPA cover memos), and undercuts the motivation for the study. Clearly the risk
assessment is used as a quantitative input for consideration to Staff Paper insights (even the FR
text referenced on page 1 discussed order of magnitude events caused by air pollution). It may be
more appropriate to communicate that EPA does not use the risk assessment to generate specific
definitive quantification of the number of health impacts in a location or nationally, but does use
the results as "an indicator" (rather than "rough sense") of the magnitude of events, and to
understand the potential significance of alternative specifications of components of the standard
(level, statistical form, averaging time).
Minor editorial comments:
The title should be "Proposed Methodology for ... Human Health Risk Analyses..."
After the introductory paragraph of the report, the "human health" text can be dropped.
Page 29, be clear that the Monte Carlo analysis is used to accumulate quantified elements
of the uncertainty.
In Appendix C, an event-days metric value of 9 is used to select mortality studies, even
though some studies are just below 9. No such discussion occurs for morbidity endpoints (where
many studies are selected with values less than 9). The 9 cut-off seems particularly arbitrary.
Future results will likely be presented as absolute numbers of events. However, given the
differing sizes of the locations to be studies, it may be useful to also report numbers across
locations on a consistent metric, such as x/100,000 people.
Comments on January 2002 Draft Report "Proposed Methodology for Particulate Matter Risk
Analyses for Selected Urban Areas"
Dr. Taylor
This correspondence follows the telephone conference earlier today on the "Proposed
Methodology for Particulate Matter Risk Analysis for Selected Urban Areas ". The
correspondence enumerates the concerns that I have relative to the document.
The specific issues are as follows:
1. Risk Analysis versus Risk Assessment. There is some confusion on this issue. The
ecological community uses the term "risk assessment" in a very specific and formal way.
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Conversely, there is no conventional use of the term "risk analysis". I assume the Agency used
the term "analysis" for a reason so there was no misunderstanding that a formal assessment was
being proposed. Assuming my assumptions are correct, I would recommend that the Agency
make this point clear. In my judgment, a great deal of the committee's comments today was
assuming that a more formal assessment was in progress. (Charge No 1)
2. Primary versus Secondary Standard. The document presents the argument that the
proposed methodology is in support of the NAAQS for particulate matter (PM). The charge
document to the committee from the SAB alludes to the NAAQS but does not specifically state
that the focus is solely the primary standard. There is no intent by the Agency to address the
secondary standard in this document (and I concur with that), but my request is that the
document states this boundary condition.
My rationale for requesting this is straightforward. There are many secondary standard issues
that are appropriate for consideration with respect to PM, and these are addressed in the CD
(e.g., visibility, biogeochemistry in terrestrial and aquatic landscapes of PM-deposited
contaminants). None of these issues are addressed in this methodology, and appropriately so.
However, it should be stated that the methodology focuses exclusively on the NAAQS primary
standard.
At the CAS AC meeting last summer I was approach by OAQPS staff who stated their intent to
nest secondary standard issues in a subservient manner to the primary standard, operating under
the assumption that any air quality improvement due to the primary standard would benefit
ecology, natural resources and visibility. I would disagree with that position as a blanket
condition; it also is at odds with the CAA. My more obvious concern is that this could establish
a precedent for all air quality standards so the importance of secondary standard would be even
further eroded.
My recommendation is simple: clearly state that the proposed methodology addresses solely the
primary standard. (Charge No. 1)
3. Southern States. On my list of concerns but voice ardently by others is the omission
of Southern States from the list of cities to be analyzed. I would recommend that the Agency re-
address the issue of the Southern region. If the criteria for selection are sufficient to justify the
inclusion, that would suffice. But that argument has not been made. (Charge No. 5)
4. Rural Areas. My perspective is ecology so I may be uninformed, but it struck me as
odd from a sample perspective that areas without a marked urban signature were not part of the
methodology. The rationale for their inclusion would be the absence of a marked urban
signature in air quality, loss of some difficult confounding factors, introduction of some new
confounding factors, elevation of the importance of geochemical background factors in PM, and
the inclusion of an unrecognized group of the population (rural). The sampling protocol would
be more difficult for sure, but the omission seemed to be an obvious one. There may be a simple
answer to this but there was never any mention of whether rural areas were ever considered.
(Charge No. 5)
5. Scaling Up and Aggregation. This section is missing from the document. I would
prefer to see clearly in one place how the Agency plans to scale the results to represent the cities
as whole or aggregate results by region (e.g., West versus East). While I suspect the Agency is
not intending to do that in a formal sense, it is likely that this will happen anyway. (Charge No.
5).
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The opportunity to participate in the review process is appreciated.
Dr. Vedal
The following is organized by section. I have identified the "charge" to which comments
are relevant when possible. Otherwise, the comments refer to the section only without obvious
relevance to any of the charges.
2.2
1. Is background PM really that low? Yes, for PM2.5, but there must be seasonal variability that
complicates the rollback procedures proposed.
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1. [Charge 1 & 4] No southern city was included. What about Texas? Why San Jose? This
raises a much larger issue which is the likely biased picture we get by just including only cities
that were included in published health studies and had PM2.5 data. NMMAPS has taught us that
not only is there regional heterogeneity in the response to PM, but that likely the published
studies as a whole reflect a publication bias. The resultant risk analysis is therefore also likely to
be biased, or at least not reflective of the heterogeneity that is likely also present for PM2.5.
2.4
1. [Charge 2 & 3] What about also including a "shaving" rollback approach as a sensitivity
analysis? p. 15-16. Add to analysis 2 in exhibit 2.5 (p.25)
2.5
1. [Charge 2] Some argue that looking at only one day of pollution (vs. say a composite of
lags) underestimates the effect of PM (p. 17). OK, p. 18. Sensitivity? Yes, p.25 (exhibit 2.5,
analysis 4)
2. [Charge 5] Notation (p. 16,17): isn't it more standard to use x0 and y0 as baseline?
3. [Charge 5] Motivate use of lowest level observed in any study as the lower PM (p. 18 &
exhibit 2.2) What is the purpose of using it? OK, not counting effects below data used to
estimate it, since there may be a threshold there (p.44, 2nd row).
4. [Charge 5] Given the notation, why is x0 lower than x (background)? p. 19
2.6
1. Point about short-term mortality being included in long-term is interesting. Maybe not, since
short-term estimates of effect do not depend on long-term level. That is, same short term effects
at low concentrations as at high. p.20
2.8
1. What about a Bayesian approach to uncertainty, if such a thing is realistic here?
3 .2.1
1. [Charge 1 & 4] natural log of 9.0, therefore 8103 total deaths over time. Why not use a rate,
i.e., #/day and a given period of follow up, since the proposed could include a long series with
few daily deaths?
2. [Charge 2] Concentration-response functions for the "long-term" mortality studies have been
shown to differ by level of education (Krewski reanalysis of ACP data) (bottom p.29 & exhibit
C.4). The distribution of educational levels in the cities studied will then affect which function
to use. Also, accounting for population mobility (measured ecologically) affected the estimates.
Which model of Krewski's was selected? A sensitivity analysis is appropriate here as well.
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3. Interesting statement about not using risk estimates as principal basis for recommending
standards (p.30). What is the alternative at this time?
4. For respiratory symptoms, do we have any data on regional heterogeneity in estimates of
effect? p.30
4.3
1. Would not use the distributed lag model resulting in the largest RR. Should be based on what
the best model is. p.33
5.1
1. Fixed ratio of hospitalizations to ER visits is probably an untenable assumption (p.37)
2. Why are there no mortality rates for locations by type of mortality? p.38 (exhibit 5.2), etc.
6.1.1
1. Multi-pollutant issue: in NMMAPS, confounding was not addressed at city level, and not
with seasonal stratification (important for ozone) p.47 Therefore not comparable to approaches
used in other individual city studies.
Dr. W. White
I generally accept the proposed assessment as a useful exercise. My main suggestion
would be to emphasize more clearly the much greater order of uncertainty that is introduced
when the short-term (24h) standard is considered.
A rationale should be offered for the decision to base the rollback percentage on the
above-"background" portion of the "as-is" concentration distribution. The "background" portion
of the "as-is" distribution is unknown, and is almost certainly poorly approximated by the
assumption of a constant level equal to the annual average. The annual average "background" is
so small relative to some of the probable individual-day values that the assessment results will be
quite insensitive to the estimate of the annual average "background". Given this, and given the
difficulty of estimating individual-day "backgrounds", I would rather see the rollback calculated
from total observed concentrations. The fact that EPA can't actually roll back all natural
emissions would then just be another consideration to be dealt with under the heading of
implementation, along with such other facts as that rolling back coal-fired power plants and
diesel motor vehicles would have different impacts on the distribution of individual-day
concentrations.
A minor comment on page B-5: The slopes of regression lines such as those in exhibits
B2 and B3 will ALWAYS be statistically significant, regardless of the nature of the change in
concentration distribution. By its very nature, a decile-decile (or percentile-percentile) plot will
ALWAYS show a monotonic relationship, which will always look fairly good statistically. This
finding therefore offers no positive evidence to support a conclusion (middle of page) that "the
change in PM2.5 concentrations ... is consistent with a proportional rollback model."
Dr. Wolff
1. The authors should be explicit in stating the assumptions and caveats necessary to
perform a risk assessment. They should explain that epidemiology studies do not and cannot, by
themselves, demonstrate a cause and effect relationship. However, for the purposes of this
exercise, it is assumed that the statistical relationships indicate cause and effect relationships.
Furthermore, it should be stated that it is also assumed that all ambient fine particle mass is
equally toxic regardless of chemical composition or size in a given city.
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2. Statistical association does not prove causation" is the first statement in exhibit 6.1 on
page 43 of the draft. The fact is that PM2 5 has not been demonstrated to be the cause of
mortality and other health effects reported in the myriad of recent epidemiology studies at
present U.S. ambient concentrations. Thus, there is a chance that the cause of the effects is
something other than PM25mass. Consequently, any risk assessment of the effects of PM25 must
include zero in the range.
3. For the C-R functions that are not statistically significant, the lower risk estimate
should be the value of the 95th percentile limit.
4. For cities with multiple studies, all of the results should be used.
5. Results from single pollutant and multiple pollutant studies should be used where
available.
6. Background is not a constant. It is affected by meteorology and has a distribution,
which will vary, from city to city. Sensitivity runs should be performed with various
distributions for background.
7. All of the above comments also apply to PM10_25 as well.
8. Page 47, lines 5 - 9 - NMMAPS cannot be used as the definitive word that PM is not
confounded by gases because NMMAPS did not treat PM and gases equally and they used 24-
hour averaged ozone which is inappropriate.
9. Why are the EPRI Veterans Study and the AHSMOG study not included in Exhibit
C.4? For balance, these studies need to be included, as they show no statistically significant
effects.
10. The C-R functions derived from Krewski et. al. (2000) should also include the multi-
pollutant relationships.
Dr. Zielinska
In my opinion there is a missing link between ambient PM2 5 concentrations and
the health effect endpoints, namely the exposure estimation. We do not spend 24
hr per day outdoors and an exposure model that includes some activity pattern
would be more realistic. Besides, the indoor PM has different sources (especially
during the time when air exchange rates are low, due to the heating or air
conditioning usage) and may have different composition than outdoor PM.
I'm concerned with the estimation of background PM2 5 concentrations. As stated
on page 10 of the report, the authors propose to use 2.5 |ig/m3 in the Western and
3.5 |ig/m3 in the Eastern U.S. as a background PM25. If the background PM
includes PM from natural sources and transport from outside of North America, it
may vary seasonally and regionally. For example, the atmospheric transformation
of biogenic emissions will be more important in summer than in winter, and will
depend on a geographical location. It has been estimated (Griffin et al., 1999)
that between 13 and 24 TgC yr"1 of secondary biogenic organic aerosol is
produced each year from terpenes and other biogenics. These secondary organic
aerosols contribute to the fine particle mass.
Similarly, the city-specific baseline health effect incidence rates depend on the
season of the year.
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I understand that in order to be consistent with the approach used in the
epidemiological studies, the average daily PM2 5 concentrations are used, but if
the hourly PM2 5 data are available, why not to use them?
I think that if the risk analysis is performed for PM25, it should also be done for
PM10 and possibly for PM10_2 5. This may provide some reality check.
Section 4.3, page 33-34. If the only reason for the use of a particular model is
that it produces the greatest relative risk, this is not a legitimate reason.
Section 6 of the document discusses sources of uncertainty, but it is not clear to
me how these uncertainties will be reflected in the proposed methodology. Will
the final risk estimate for a given area include these uncertainties in some
numerical way?
References:
Griffin Dr. J.; Cocker, D.R.; Sienfeld, J.H.; Estimated of Global Atmospheric Organic Aerosol from
Oxidation of Biogenic Hydrocarbons, Geophys. Res. Let, 26, 2721-2724, 1999.
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