concentrations that are a fraction of the present PM10 NAAQSs. This has lead some to postulate that the acute mortality is actually a “harvesting" effect. That is, individuals who are terminally ill die somewhat prematurely due to the additional stress caused by PM or overall air pollution. While this may explain some or most of the acute deaths, it can not explain the apparent long-term, chronic deaths attributed to annual PM concentrations in the prospective cohort studies. These prospective cohort studies suggest that the acute mortality only accounts for about a third to a half of the total deaths attributed to PM. However, all or most of this discrepancy vanishes when additional potentially confounding variables are included in the cohort studies and historical or cumulative rather than concurrent air pollution exposures are considered.

The exposure misclassification concern revolves around the validity of the assumption made in all of the acute studies that daily ambient PM data collected from a centrally located air monitoring site is representative of personal exposure to PM. Results from studies which examined this assumption are ambiguous. The shape of the dose-response function is also a concern. Because of measurement errors, the present statistical methodologies are incapable of detecting the existence of a possible threshold concentration below which acute mortality would not occur. Finally, there is some concern because the statistical models used in the various geographical areas are different. At different sites, different combinations of variables, averaging times, methods for accounting for seasonality and meteorology, and lag times have been used to produce the reported PM-mortality relationships.

The lack of consensus on many of these issues can be partially attributed to the accelerated review schedule. The deadlines did not allow adequate time to analyze, integrate, interpret, and debate the available data on this very complex issue. Nor did the court-ordered schedule recognize that achieving the goal of a scientifically defensible NAAQS for PM may require iterative steps to be taken in which new data are acquired to fill obvious and critical voids in our knowledge. The previous PM NAAQS review took eight years to complete.

The Panel was unanimous, however, in its desire to avoid a similar situation when the next PM NAAQS review cycle is under way by a future CASAC Panel. CASAC strongly recommended that EPA immediately implement a targeted research program to address these unanswered questions and uncertainties. It is also essential that long-term PM2.5 measurements are obtained. CASAC volunteered to assist EPA in the development of a comprehensive research plan that will address the questions which need answers before the next PM review cycle is completed.

PERSPECTIVE

Since PM10 measurements became widespread in 1988, significant and continuous declines in ambient PM10 concentrations have been observed throughout the U.S. Nationwide PM10 concentrations have declined 22% from 1988 to 1995.17 The reason for this decline is because of the implementation of existing control programs required by the 1990 Clean Air Act Amendments that target PM2.5 precursors (VOCs, NOx, and SO2), diesel PM emissions and other primary emission sources. This trend will continue for the foreseeable future as additional measures required by the Amendments are phased in. Consequently, there is time to conduct the research recommended by CASAC which targets the concerns discussed above. Then appropriate PM2.5 NAAQSs could be established.

REFERENCES

1 Yosie, T.F. "The EPA Science Advisory Board," Environ. Sci. Technol. 1993, 27, 1476-1481. 2U.S. EPA Science Advisory Board. "Science Advisory Board FY1995 Annual Staff Report," EPA-SAB-96-001, U.S. EPA, Washington, DC, April 1996.

9 Lippmann, M. "Role of science advisory groups in establishing standards for ambient air pollutants," Aerosol Sci. Technol. 1987, 6, 93-114.

4 Public Health Service. "Air Quality Criteria for Photochemical Oxidants," U.S. Dept. Health, Education, and Welfare, Washington, DC, March 1970.

5 U.S. EPA Office of Research and Development. "Air Quality Criteria for Ozone and Related Photochemical Oxidants," EPA/600/AP-93/004a-c, U.S. EPA, Washington, DC, February 1995. 6U.S. EPA Office of Air Quality Planning and Standards. "Review of National Ambient Air Quality Standards for Ozone Assessment of Scientific and Technical Information OAQPS Staff Paper," U.S. EPA, Durham, NC, June 1996.

Wolff, G.T. "CASAC Closure on the Air Quality Criteria for Ozone and Related Photochemical Oxidants," EPA-SAB-CASAC-LTR-96-001, U.S. EPA, Washington, DC, November 1995. 8 Wolff, G.T. "CASAC Closure on the Primary Portion of the Staff Paper for Ozone," EPA-SABCASAC-LTR-96-002, U.S. EPA, Washington, DC, November 1995.

U.S. EPA Office of Research and Development. “Air Quality Criteria for Particulate Matter," EPA/600/P-95/001aF-cF, U.S. EPA, Washington, DC, April 1996.

10 Public Health Service. "Air Quality Criteria for Particulate Matter," U.S. Dept. Health, Education, and Welfare, Washington, DC, January 1969.

11 U.S. EPA Office of Air Quality Planning and Standards. "Review of National Ambient Air Quality Standards for Particulate Matter, Policy Assessment of Scientific and Technical Information, OAQPS Staff Paper," EPA-452/R-96-013, U.S. EPA, Research Triangle Park, NC, July

1996.

12 American Lung Ass'n v. Browner, 884 F. Supp. 345 (D. Ariz. 1994).

13 Wolff, G.T. "Clean Air Scientific Advisory Committee (CASAC) Comments on the April 1995 draft Air Quality Criteria for Particulate Matter," EPA-SAB-CASAC-LTR-95-005, U.S. EPA, Washington, DC, August 31, 1995.

14 Wolff, G.T. "Clean Air Scientific Advisory Committee (CASAC) Comments on the November 1995 Drafts of the Air Quality Criteria for Particulate Matter and the Review of National Ambient Air Quality Standards for Particulate Matter: Policy Assessment of Scientific and Technical Information (ÓAQPS Staff Paper)," EPA-SAB-CASAC-LTR-96-003, U.S. EPA, Washington, DC, January 5, 1996.

15 Wolff, G.T. "Closure by the Clean Air Scientific Advisory Committee (CASAC) on the Draft Air Quality Criteria for Particulate Matter," EPA-SAB-CASAC-LTR-96-005, U.S. EPA, Washington, DC, March 15, 1996.

16 Wolff, G.T. "Closure by the Clean Air Scientific Advisory Committee (CASAC) on the Staff Paper for Particulate Matter," EPA-SAB-CASAC-LTR-96-008, U.S. EPA, Washington, DC, June 13, 1996. 17 U.S. EPA Office of Air Quality Planning and Standards. "Air Quality Trends," EPA-454/F95-003, U.S. EPA, Research Triangle Park, NC, September, 1995.

1 to 5 exceedances allowed within a year averaged over a 3-year period

Table 4: Estimated Hospital Admissions for Asthmatics in the New York City Area

a - excess asthma admissions attributed to ozone levels exceeding a background concentration of 0.04 ppm; the values with ranges (90% confidence intervals) are from Table V-20 in the Staff Paper; single value estimates are from Figure V-17 in the Staff Paper

b - asthma admissions included in (a) plus those due to background ozone concentrations; admissions due to background = 1065 - 388

= 677