WASHINGTON D.C. 20460
                                                              OFFICE OF THE ADMINISTRATOR
                                                               SCIENCE ADVISORY BOARD
                                  December 6,2004

The Honorable Michael O. Leavitt
U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, N.W.
Washington, D.C. 20460

        SUBJECT:  Advisory Council on Clean Air Compliance Analysis Response to Agency
                    Request on Cessation Lag

Dear Administrator Leavitt:

       In a letter of August 11,2004, the Office of Air and Radiation and Office of Policy,
Economics and Innovation jointly asked the Health Effects Subcommittee (HES) of the Advisory
Council on Clean Air Compliance Analysis to comment on an EPA proposal. This proposal,
developed in collaboration with OMB, concerns the cessation lag of PM?.}. The cessation lag is
defined as the time pattern of reductions in risks of mortality that would be expected after a
decrease in ambient particulate matter smaller than 2.5 urn in aerodynamic diameter, i.e. PM2.$.
The letter requested the Council's Subcommittee to consider whether a proposed lag structure is
generally consistent with our recommendations regarding a previous charge question on this

       Our previous comments on this issue noted that because some fraction of the mortality
risk associated with PM2.s is the result of long-term exposures and disease processes such as
chronic respiratory disease and cancer, the reduction in mortality risk that occurs when exposures
are reduced may take several years to be fully realized. The EPA described a proposed lag
structure that would allocate 20% of the benefits in the first year, a further 50% equally divided
in the years-2 through 5, and the final 30% equally divided in the years 6 through 20.  While we
believe this proposal is broadly consistent with our recommendations, and preferable to the 5-
year distributed lag used earlier, we would suggest a slight modification to this proposal. We
have reviewed newly available evidence on this issue and considered several intervention studies
examining reductions in exposure to either air pollution or from direct smoking. (See

       While there is still considerable uncertainty about the cessation lag, the air pollution
evidence is generally suggestive of greater impacts in the first year relative to the proposed lag

structure in question. In fact, some recent abstracts suggest that substantial benefits might occur
in the first year. Therefore, the Advisory Council on Clean Air Compliance Analysis
recommends that EPA use a primary case where 30% of the mortality reductions occur in the
first year, 50% occur equally in years 2 through 5, and the remaining 20% occur equally over
years 6 through 20.

       These proposed changes to the cessation lag (both the EPA proposal and the HES
recommended modification) do not change the estimates of total mortality reductions expected as
a result of reductions in PM2.5, but they both represent changes in the estimated timing of the
expected mortality reductions. The HES recognizes that measures of health benefits in physical
terms are not the final step in benefit-cost analysis, where all benefits need to be valued.  The
time profile assumed for health benefits may have implications for "net present value"
calculations. However, this final step of economic valuation does not lie within the scope of
expertise of the HES. The charge to the HES on this matter specifically concerns the pattern of
health benefits in physical terms, so we limit our comments to this question.

       We also urge EPA to: (1) review and keep abreast of the emerging literature in this area;
(2) provide the best available justification for the lag structure they use; and (3) strongly consider
conducting sensitivity analyses of other possible lag structures.  EPA should also consider using
smoothed distributions.

       With regard to the suggestion to review emerging literature, it should be noted that, in
addition to the literature from PM intervention studies, information from the smoking cessation
literature is considered very relevant to the PM/mortality cessation lag question.  Therefore, we
recommend that EPA conduct a systematic review of the literature on the time course of health
benefits following cessation of active and passive smoking to better account for this potentially
useful information.
Trudy Cameron, Ph.D.                                 Bart Ostro, Ph.D.
Chair                                                Chair
Advisory Council on Clean Air Compliance Analysis      Health Effects Subcommittee
Attachment:  Studies Considered by HES on PM-Mortality Cessation Lag

            Studies Considered by the Health Effects Subcommittee
                                       on the
                           PM-Mortality Cessation Lag
Clancy, L., Goodman, P., Sinclair, H., and Dockery, D.W. (2002). Effect of Air-Pollution
       Control on Death Rates in Dublin, Ireland: An Intervention Study. The Lancet 360:

Fry, C., Hoelscher, B., Cyrys, J., Wjst, M, Wichmann, H. and Heinrich, J. (2003). Association of
       Lung Function with Declining Ambient Air Pollution. Environmental Health
       Perspectives 111: 383-387.

Heinrich, J. Hoelscher, B., Frye, C., Meyer, I. Pitz, M. Cyrys, J., Wjst, M. Neas, L., Wichmann,
       H.E. (July 2002). Improved Air Quality in Reunified Germany and Decreases in
       Respiratory Symptoms. Epidemiology 13: 394-401.

Heinrich, J., Hoelscher, B., and Wichmann, H.E. (2000). Decline of Ambient Air Pollution and
       Respiratory Symptoms in Children. American Journal of Respiratory Critical Care
       Medicine 161: 1930-1936.

Hurley, Fintan. (2004). Does Reducing Air Pollution Really Lead to Improvements in Health?
       Excerpt from a report entitled Evaluation of the Air Quality Strategy prepared for the
       Department for Environment, Food and Rural Affairs in the United Kingdom.  The fill!
       report will be published in the coming months at http://www.defra. gov/uk.

Lan, Q., Chapman, R.S., Schreinemachers, D.M., Tian, L., and He, X. (2002). Household Stove
       Improvement and Risk of Lung Cancer in Xuanwei, China. Journal of the National
       Cancer Institute 94: 826-836.

Leksell, Ingemar and Rabl, Ari. (2001). Air Pollution and Mortality:  Quantification and
       Valuation of Years of Life Lost. Risk Analysis 21: 843-857.

Roosli, M., Kunzli, N. and Braun-Fahrlander, C. (2004).  Use of Air Pollution "Intervention-
       Type" Studies in Health Risk Assessment. Abstract presented at the 16th Conference of
       the International Society for Environmental Epidemiology t August 1  - 4,2004.

Schwartz, Joel and Laden, Francine. (2004). Dose, Time and Death: Association with PM2.5 in
       Cohort Study. Presentation to 16th Conference of the International Society for
       Environmental Epidemiology, August 1-4,2004.

       This report has been written as part of the activities of the EPA Advisory Council on
Clean Air Compliance Analysis (Council), a public advisory  committee providing extramural
scientific information and advice to the Administrator and other officials of the Environmental
Protection Agency.   The  Council 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. Reports of the EPA Council are posted on the
EPA website at: http://www.epa.gov/sab.

                     U.S. Environmental Protection Agency
             Advisory Council on Clean Air Compliance Analysis
Dr. Trudy Ann Cameron, University of Oregon, Eugene, OR
      Also Member: Science Advisory Board

Dr. David T. Allen, University of Texas, Austin, TX

Dr. Dallas Burtraw, Resources for the Future, Washington, DC

Ms. Lauraine Chestnut, Stratus Consulting Inc., Boulder, CO

Dr. Charles T. Driscoll, Jr., Syracuse University, Syracuse, NY

Dr. Wayne Gray, Clark University, Worcester, MA

Dr. James K. Hammitt, Harvard University, Boston, MA

Dr. F. Reed Johnson, Research Triangle Institute, Research Triangle Park, NC

Dr. Katherine Kiel, College of the Holy Cross, Worcester, MA

Dr. Nino Kuenzli, University of Southern California, Los Angeles, CA

Dr. Virginia McConnell, Resources for the Future, Washington, DC

Dr. Bart Ostro, California Office of Environmental Health Hazard Assessment, Oakland, CA

Dr. V. Kerry Smith, North Carolina State University, Raleigh, NC

Dr. Chris Walcek, State University of New York, Albany, NY
Dr. Holly Stallworth, Washington, DC

                    U.S. Environmental Protection Agency
             Advisory Council on Clean Air Compliance Analysis
                        Health Effects Subcommittee
Dr. Bart Ostro, California Office of Environmental Health Hazard Assessment, Oakland, CA

Mr. John Fintan Hurley, Institute of Occupational Medicine (IOM), Edinburgh, United

Dr. Patrick Kinney, Columbia University, New York, NY

Dr. Michael Kleinman, University of California, Irvine, Irvine, CA

Dr. Nino Kuenzli, University of Southern California, Los Angeles, CA

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

Dr. Rebecca Parkin, The George Washington University, Washington, DC
      Member: Science Advisory Board
Dr. Holly Stallworth, Washington, DC