May 31, 1996 EPA-SAB-CASAC-LTR-96-007 Honorable Carol M. Browner Administrator U.S. Environmental Protection Agency 401 M. Street S.W. Washington, DC 20460 RE: CASAC Comments on Air Quality Modeling for the Section 812 Retrospective Study Dear Ms. Browner: At their December 22, 1992 meeting, the Science Advisory Board's Advisory Council on Clean Air Compliance Analysis (ACCACA, formally known as the Clean Air Act Compliance Analysis Council, CAACAC) decided to refer review of the air quality modeling part of the Retrospective Study of the impacts of the Clean Air Act to the Clean Air Scientific Advisory Committee (CASAC). The request was made to CASAC in a March 22, 1993 memo from Mr. Jim DeMocker of the Office of Policy Analysis and Review (OPAR) in EPA's Office of Air and Radiation. Subsequently, a Panel of CASAC members (the Air Quality Models Subcommittee, AQMS) and SAB consultants was constituted to review the air quality modeling. Three public conference calls on October 1, 21, and December 2, 1993 served to brief the panel members on the charge and air quality methodology and for Panel members to comment on the methodology. The panel members provided EPA with numerous comments during the conference calls and subsequently in writing. These comments were summarized for you in a June 30, 1994 letter report (EPA-SAB-CASAC-LTR-94-009). A major concern at the time was that the uncertainties in the air quality estimates in the "no-Clean Air Act" scenarios would be intolerable. The six member panel conducted a final public conference call on April 26, 1996 to review the completed air quality modeling. During the call and subsequently in writing, the panel members provided comments to the Agency. All the panel members expressed their satisfaction that the Agency followed the Panel's recommendations and ------- that the final product is sound. Our concern over the uncertainties has diminished considerably, but nevertheless, it still exists. We have provided your staff with a number of recommendations to explicitly articulate the uncertainties, to not overstate the precision of the estimates, and to more carefully present the implications of the uncertainties for the overall study results. With the incorporation of these relatively minor changes, the Panel feels that air quality estimates are reasonable and are appropriate to use to estimate the benefits of the Clean Air Act. Please let me know if we can assist you any further. Sincerely, /. Dr. GeoVge T. Wolff, Clean Air Scientific Advisory Committee ------- U.S. ENVIRONMENTAL PROTECTION AGENCY SCIENCE ADVISORY BOARD CLEAN AIR SCIENTIFIC ADVISORY COMMITTEE AIR QUALITY MODELING SUBCOMMITTEE CHAIR Dr. George T. Wolff, General Motors Environmental & Energy Staff, Detroit, MI MEMBERS Dr. Philip Hopke, Clarkson University, Dept. Of Chemistry, Pottsdam, NY Dr. Harvey Jeffries, Dept. of Env. Sciences & Engineering, University of North Carolina, School of Public Health, Chapel Hill, NC Dr. Paulette Middleton, Science Policy Associates, Boudler, CO Dr. Peter K. Mueller, Electric Power Research Institute, Palo Alto, CA Dr. James H. Price, Jr., Texas Natural Resource Conservation Commission, Austin, TX SCIENCE ADVISORY BOARD STAFF Dr. K. Jack Kooyoomjian, Designated Federal Official, USEPA, Science Advisory Board, 401 M Street, SW, Mail Code 1400F, Washington, DC 20460 Ms. Diana Pozun, Staff Secretary, USEPA, Science Advisory Board, 401 M Street, SW, Mail Code 1400F, Washington, DC 20460 ------- NOTICE 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. ------- DISTRIBUTION LIST Administrator Deputy Administrator Assistant Administrators Deputy Assistant Administrator for Science, ORD Director, Office of Science Policy, ORD Director, Office of Air Quality Planning and Standards, OAR Director, National Center for Environmental Assessment, ORD, RTP, NC EPA Regional Administrators EPA Laboratory Directors EPA Headquarters Library EPA Regional Libraries EPA Laboratory Libraries Library of Congress National Technical Information Service Congressional Research Service ------- |