March 15, 1996


Honorable Carol M. Browner
U.S. Environmental Protection Agency
401 M. Street SW
Washington, DC 20460

            Re    Closure by the Clean Air Scientific Advisory Committee (CASAC)
                  on the draft Air Quality Criteria for Particulate Matter

Dear Ms. Browner:

      The Clean Air Scientific Advisory Committee (CASAC) of EPA's Science
Advisory Board (SAB) has held a series of public meetings during its peer review of the
Agency's draft documents which will form part of the basis for your decision regarding
the National Ambient Air Quality Standards (NAAQS) for Particulate Matter (PM). The
Committee  has held public meetings on December 12-13, 1994 (planning and
introductory issues); August 3-4, 1995 (review of the initial draft Criteria Document);
December 14-15, 1995 (review of the  revised draft Criteria Document and the first draft
of the Staff  Paper);  and February 29, 1996 (review of the revised draft Criteria
Document - specified chapters only).  A review of the revised draft Staff Paper is
planned for May 16-17, 1996.  The primary Agency draft documents that we have
reviewed are the: a) Air Quality Criteria for Particulate  Matter (the Criteria Document
prepared by the National Center for Environmental Assessment - Research Triangle
Park, NC - ORD), and b) Review of the National Ambient Air Quality Standards for
Particulate Matter: Policy Assessment of Scientific and Technical Information (the Staff
Paper prepared by the Office of Air Quality Planning and Standards - Research
Triangle Park, NC - OAR).

      As part of our review process, we have kept you informed of our findings through
two letter reports: a) Clean Air Scientific Advisory Committee (CASAC) Comments on
the April 1995 draft Air Quality Criteria for Particulate Matter (EPA-SAB-CASAC-
LTR-95-005; August 30, 1995); and b) Clean Air Scientific Advisory Committee
(CASAC) Comments on the November, 1995 Drafts of the Air Quality Criteria for
Particulate Matter and the Review of the National Ambient Air Quality Standards for

F'articulate Matter: Policy Assessment of Scientific and Technical Information (OAQPS
Staff Paper), (EPA-SAB-CASAC-LTR-96-003, Januarys, 1996).

      The Clean Air Scientific Advisory Committee, supplemented by a number of
expert Consultants (hereinafter referred to as the Panel) reviewed a revised draft of
the PM Criteria Document and a first draft of the Staff Paper for Particulate Matter at a
meeting on December 14-15, 1995 in Chapel Hill,  NC. At that meeting and in
subsequent written comments by individual members which were provided to
EPA Staff, the Panel made numerous recommendations for improving the draft
document.  The Panel was impressed with the breadth and scope of the latest revision
of the draft Criteria Document and agreed that, except for Chapters 1 (Executive
Summary),  5 (Sources and Emissions), 6 (Air Quality), and 13 (Integrative Synthesis),
only minor revisions would be necessary to make the remainder of the draft Criteria
Document satisfactory for  providing an adequate scientific basis for regulatory
decisions on PM based on available information. However, the Panel felt that Chapters
1, 5, 6, and 13 required major revisions which the  Panel would need to review again.

      On February 29, 1996, the Panel again met in Chapel Hill, NC to review revised
drafts of Chapters 1, 5, 6,  and 13 of the Criteria Document.  While Chapter 13 can be
improved, as suggested below, I want to take this  opportunity, on behalf of the entire
Panel, to commend Dr. Lester Grant and his staff in the National Center for
Environmental Assessment (NCEA) for producing  its best ever example of a true
integrative summary of the state of knowledge about the health effects of airborne PM
and the associations between the effects and the various available indices of PM
exposure.  NCEA has outlined some of the options for your subsequent choice of
available PM indicators for a NAAQS by examining the degrees of association between
various health indices and PM indicators including total suspended particulate (TSP),
thoracic particulate (PM10), fine particulate (PM25), sulfate particulate (S04=), acid
particulate (H+) and carbonaceous particulate (BS and CoH), with available knowledge
from dosimetry,  results of controlled human exposure studies in humans and laboratory
animals, and mechanistic understandings. This thorough review and evaluation also
provides an important starting point for focussing the future PM research program on
studies that can better identify the compositional and particle size characteristics of the
most biologically active agents within the PM10.  We were especially impressed that this
integrative summary could be produced in the short time period since our review of the
initial  rough draft in December 1995.

      This  letter is a summary of our findings and conclusions from the February 29th
meeting.  Our comments reflect our satisfaction with the improvements made in the
scientific quality and completeness of these chapters. The changes made in these
chapters are consistent with  our earlier recommendations.  However, the Panel
provided additional comments to your staff at the meeting and subsequently in writing.
Although we feel that it is essential to have these additional comments considered for

incorporation in the Criteria Document, we did not feel that it was essential to review
another revised version and, thus, we came to closure on the entire Criteria Document
anticipating incorporation of our suggested changes. It was our consensus that
although our understanding of the health effects of PM is far from complete, a revised
Criteria Document which incorporates the Panel's latest comments will provide an
adequate review of the available scientific data and relevant studies of PM. With the
incorporation of our suggested changes, the revised Criteria Document will be very
comprehensive and will provide an adequate scientific basis for regulatory decisions on
particulate matter based on available information. However, a number of members
have expressed concern that since we are closing on the Criteria Document before we
will be able to see the revised version, we have no assurance that our comments will
be incorporated. I will  return to this concern later.

       I would like to summarize for you the Panel's major comments on Chapters 1, 6,
and 13. There were no major comments on Chapter 5.  In Chapter 6, Panel members
raised issues concerning the definition and level of background  PM concentrations.
The Panel has provided the Agency with guidance in the written comments to resolve
these concerns.  This is an important issue because some studies suggest effects at
levels which approach background concentrations.

       Of the 17 members of the Panel present, five were satisfied with Chapter 13 as
is, four had no substantive comments because their expertise was outside of Chapter
13, and eight had some substantive comments on one or more aspects of the chapter
which I summarize below. The members who were satisfied with the chapter praised
the Agency for making a compelling case for PM25 being the best available surrogate
index for the causal agent.  They thought  EPA presented a large body of consistent
and coherent studies and that they were appropriately presented as an integrative
synthesis. The issues raised by the other Panel members regarding Chapter 13 fell
into three categories. First, several Panel members felt that additional discussions of
the inherent errors associated with air sampling, estimating human exposure from
central monitoring data, and relating these data to excess mortality and morbidity were
necessary so that the uncertainties of the relative risk estimates would  be better

       Second, about half of the Panel members expressed concern that the case
made  in the Criteria Document for PM2 5 being the best available surrogate for the
principal causative agent in PM10 may be overstated, and that EPA has not adequately
justified its rejection of other alternative explanations discussed  next.  In addition, it
needs to be acknowledged that large particles (e.g., d=4.0 //m) may be responsible for
acute respiratory effects, especially in susceptible groups such as asthmatics.

       Third, several Panelists pointed out that a number of recently published (or
in-press) studies (including the Health Effects Institute study), which were conducted to

critically evaluate some of the epidemiological studies using alternative models or
including additional gaseous pollutant data, present a different perspective of the
PM/mortality issue than the one presented in this chapter.  Collectively, these
reanalyses have confirmed the reproducibility of the earlier studies, but they also
present a more complicated relationship in which causality does not appear to be
unambiguously attributed to any single pollutant let alone a specific portion of the PM.
EPA on the other hand emphasized a PM causal conclusion based on the pattern of

associations across multiple sites having different pollutant mixtures. These results
need to be discussed adequately in Chapter 13.

      Our only comments on Chapter 1, the Executive Summary, were that it reflect
the revisions that have been recommended for Chapters 6 and 13.

      As mentioned above, Panel members have expressed concern that the Agency
may not be responsive to some of our comments or may misinterpret them since we will
not have another opportunity to review the final document. This concern  is another
unfortunate consequence of the court- mandated "accelerated" time schedule, but
nevertheless, it is a real concern.  We anticipate being advised of text changes made in
response to our concerns prior to or at the May 16-17, 1996 meeting, and we can
advise you afterward about whether our concerns have been adequately addressed by
the Agency.

      On behalf of the Panel, I would like to thank EPA staff for their considerable
efforts in preparing the Criteria Document on the accelerated schedule. We look
forward to seeing the revised final version once it is completed.  The Panel also looks
forward to reviewing the revised Staff Paper during the public meeting presently
scheduled for May 16-17,  1996.
                                          Dr. George T. Wolff, Cha
                                          Clean Air Scientific
                                           Advisory Committee


      This report has been written as part of the activities of the 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.

                     U.S. Environmental Protection Agency
                           Science Advisory Board
                    Clean Air Scientific Advisory Committee
                        Particulate Matter Review Panel
Dr. George T. Wolff
General Motors
Environmental & Energy Staff
Detroit, Ml

Dr. Stephen M. Ayres
Office of International Programs
Virginia  Commonwealth University
 /Medical College of Virginia
Richmond, VA

Dr. Phil  Hopke
Department of Chemistry
Clarkson University
Pottsdam, NY

Dr. Jay S. Jacobson
Boyce Thompson Institute
Cornell University
Ithaca, NY

Dr. Joe L. Mauderly
Inhalation Toxicology Research
Lovelace Biomedical & Environmental
 Research Institute
Albuquerque,  NM

Dr. Paulette Middleton
Science and Policy Associates
Boulder, CO

Dr. James H. Price, Jr.
Texas Natural Resource Conservation
Austin, TX

Dr. Petros Koutrakis
Harvard School of Public Health
Boston, MA

Dr. Morton Lippmann
Institute of Environmental Medicine
New York University
Tuxedo, NY

Dr. Kinley Larntz
Department of Applied Statistics
University of Minnesota
St. Paul, MN

Dr. Allan Legge
Biosphere Solutions
Calgary, Alberta,  Canada

Dr. Roger 0. McClellan
Chemical Industry Institute of
Research Triangle Park, NC

Dr. Daniel Menzel
Department of Community
 and Environmental Medicine
University of California, Irvine
Irvine, CA

Dr. William R. Pierson
Energy & Environmental Engineering
Desert Research  Institute
Reno, NV

Dr. Carl M. Shy
Department of Epidemiology
School of Public Health
University of North Carolina
Chapel Hill, NC

Dr. John Samet
School of Hygiene & Public Health
Johns Hopkins University
Baltimore, MD

Dr. Christian Siegneur
AER, Inc
San Ramon, CA

Dr. Frank Speizer
Harvard Medical School
Channing Lab
Boston, MA

Dr. Jan Stolwijk
Yale University
New Haven, CT
Dr. Mark Utell
Pulmonary Disease Unit
University of Rochester Medical Center
Rochester, NY

Dr. Warren White
Washington University
St. Louis, MO

Science Advisory Board Staff
Mr. A. Robert Flaak
Designated Federal Official
Science Advisory Board
Washington, DC

Ms. Connie Valentine
Staff Secretary
Science Advisory Board
Washington, DC

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