Report to EPA September 2007 1 Accomplishments of the Particulate Matter (PM) Centers (1999-2005) Elinor Fanning a , John Froines a , Mark Utell b , Morton Lippmann c , Gunter Oberdorster b , John Godleski d , Tim Larson e a University of California, Los Angeles, California b University of Rochester, Rochester, New York c New York University School of Medicine, Tuxedo, New York d Harvard School of Public Health, Boston, Massachusetts e University of Washington, Seattle, Washington The US Environmental Protection Agency (EPA) funded five academic Centers in 1999 to address the uncertainties in exposure, toxicity and health effects of airborne particulate matter (PM) that were identified in the National Research Council’s (NRC) “Research Priorities for Airborne Particulate Matter” (1998). Research Centers were established at Harvard University, New York University, the University of Rochester, the University of Washington, and a consortium of three universities in Southern California. A midterm report of PM Center findings was published previously (Lippmann et al., 2003). This current report highlights in brief major findings of the PM Centers from the first six years. The PM Centers were structured to bring interdisciplinary research approaches to tackle key knowledge gaps, and this approach promised success in advancing PM science. The collective efforts of the five PM Centers led to significant accomplishments in all the priority research areas identified by the NRC Committee that guided the research program and resulted in a wealth of peer reviewed publications. Substantial supplemental material that provides technical summaries of the data from which the overall accomplishments of the Centers derive can be accessed online at http://es.epa.gov/ncer/science/pm/2008sab/index.html. The supplemental material is organized into chapters on: PM characterization and exposure; health effects including epidemiology and toxicology; and mechanisms of PM toxicity, and contains extensive references to previously published findings. 1. Selected Advances in PM Exposure Research Characterization of Ambient PM The PM Centers have significantly advanced the science on characterization of ambient PM and demonstrated that the physical and chemical characteristics of PM vary greatly with region, location, seasonal and diurnal patterns, and size fraction. Selected examples are given here for illustration; for more detail consult the supplemental material to this report. Coarse particles collected in Southern California derive largely from road dust and soil and contain significant quantities of metals, whereas fine particles (PM 2.5 , i.e., PM with aerodynamic diameters <2.5 μm) from the same locations contain primarily nitrates and elemental and organic carbon. Ultrafine PM (UFP) is especially high in organic