UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C. 20460 

 

 OFFICE OF THE ADMINISTRATOR 

 SCIENCE ADVISORY BOARD 

December 6, 2004 

EPA-COUNCIL-LTR-05-001 

The Honorable Michael O. Leavitt 

Administrator 

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 PM2.5. 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 μm in aerodynamic diameter, i.e. PM2.5. 

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 

issue. 

Our previous comments on this issue noted that because some fraction of the mortality 

risk associated with PM2.5 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

attachment.) 

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. 

 Sincerely,

 /s/ /s/

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

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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: 

1210-1214. 

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 full 

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 “InterventionType” Studies in Health Risk Assessment. Abstract presented at the 16th Conference of 

the International Society for Environmental Epidemiology, 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. 

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NOTICE 

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 

COUNCIL 

CHAIR 

Dr. Trudy Ann Cameron, University of Oregon, Eugene, OR 

Also Member: Science Advisory Board 

MEMBERS 

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 

SCIENCE ADVISORY BOARD STAFF 

Dr. Holly Stallworth, Washington, DC 

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U.S. Environmental Protection Agency 

Advisory Council on Clean Air Compliance Analysis 

Health Effects Subcommittee 

CHAIR 

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

MEMBERS 

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

Kingdom

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 

SCIENCE ADVISORY BOARD STAFF 

Dr. Holly Stallworth, Washington, DC 

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