As part of its last review, EPA's Office of Air Quality Planning and Standards (OAQPS) sponsored a risk assessment for two urban areas, Philadelphia County and Los Angeles County, to assess the risks associated with then-current PM levels and the effects of alternative PM standards on reducing estimated health risks attributable to PM (Abt Associates Inc., 1996; and Abt Associates Inc., 1997a,b. See also Deck et al., 2001 and Post et al., 2001 for published articles describing the risk assessment methodology used in the 1996-1997 analyses). Results were presented and discussed as part of the OAQPS Staff Paper (U.S. EPA, 1996b), that presented factors relevant to the evaluation of the then-current primary (health-based) NAAQS, as well as staff conclusions and recommendations of alternative standards for the EPA Administrator to consider. The risk assessment described in this report focuses on the two PM indicators for which EPA now anticipates making decisions - PM(sub 2.5) and PM(sub 10-2.5). The report provides a description of the methodology used, taking into account comments received from the CASAC (Hopke, 2004; Henderson, May 2005) and the public on the August 2003 and January 2005 draft reports. The report also presents the assessments of the health risks associated with 'as is' concentrations of PM(sub 2.5) and PM(sub 10-2.5) in excess of their PRB levels and various specified cutpoints, as well as an assessment of the reduced health risks associated with just meeting the current and alternative standards for PM(sub 2.5), and alternative standards for PM(sub 10-2.5). In addition, in an appendix, we present an assessment of the health risks associated with 'as is' concentrations of PM(sub 10) in excess of PRB levels. The risk assessment is based on the health effects evidence assessed in the 2004 PM CD, which includes the re-analyzed studies presented in the HEI special report (HEI, 2003). The goals of the PM risk assessment are: (1) to provide estimates of the potential magnitude of mortality and morbidity associated with current PM(sub 2.5) and PM(sub 10-2.5) levels and with attaining the current suite of PM(sub 2.5) NAAQS (as well as the reduced effects associated with attaining alternative PM(sub 2.5) and PM(sub 10-2.5) standards identified as part of this review) in specific urban areas, (2) to develop a better understanding of the influence of various inputs and assumptions on the risk estimates (e.g., choice of PRB levels, and consideration of various cutpoints below which effects are assumed not to occur), and (3) to gain insights into the nature of the risks associated with exposures to ambient PM (e.g., patterns of reduced risks associated with meeting alternative annual and daily standards).

Project officer: Nancy Riley. Work assignment manager: Harvey Richmond. "December 2005." "Abt. Associates, Inc." "EPA 452/R-05-007A." PB2006-102407. "Some of the preliminary work for this report was completed under Contract No. 68-D-98-001, Work Assignments 1-36, 2-46, 3-51, and 4-65 and Contract No. 68-D-03-002, Work Assignment No. 0-04"--p.i. Includes bibliographical references (156-161). Contract No. 68-D-03-002