Identifying PM_2.5 and PM_0.1 sources for epidemiological studies in California

The University of California-Davis-Primary (UCD-P) model was applied to simultaneously track ∼900 source contributions to primary particulate matter (PM) in California for seven continuous years (January 1st, 2000 to December 31st, 2006). Predicted source contributions to primary PM_2.5 mass, PM_1.8 elemental carbon (EC), PM_1.8 organic carbon (OC), PM_0.1 EC, and PM_0.1 OC were in general agreement with the results from previous source apportionment studies using receptor-based techniques. All sources were further subjected to a constraint check based on model performance for PM trace elemental composition. A total of 151 PM _2.5 sources and 71 PM_0.1 sources contained PM elements that were predicted at concentrations in general agreement with measured values at nearby monitoring sites. Significant spatial heterogeneity was predicted among the 151 PM_2.5 and 71 PM_0.1 source concentrations, and significantly different seasonal profiles were predicted for PM _2.5 and PM_0.1 in central California vs southern California. Population-weighted concentrations of PM emitted from various sources calculated using the UCD-P model spatial information differed from the central monitor estimates by up to 77% for primary PM_2.5 mass and 148% for PM_2.5 EC because the central monitor concentration is not representative of exposure for nearby population. The results from the UCD-P model provide enhanced source apportionment information for epidemiological studies to examine the relationship between health effects and concentrations of primary PM from individual sources.