Association of fine particulate matter from different sources with daily mortality in six US cities

Previously we reported that fine particle mass (particulate matter less tha n or equal to 2.5 mum; PM2.5), which is primarily from combustion sources, but not coarse particle mass, which is primarily from crustal sources, was associated with daily mortality in six eastern U.S. cities (1). In this stu dy, we used the elemental composition of size-fractionated particles to ide ntify several distinct source-related fractions of fine particles and exami ned the association of these fractions with daily mortality in each of the six cities. Using specific rotation factor analysis for each city, we ident ified a silicon factor classified as soil and crustal material, a lead fact or classified as motor vehicle exhaust, a selenium factor representing coal combustion, and up to two additional factors. We extracted daily counts of deaths from National Center for Health Statistics records and estimated ci ty-specific associations of mortality with each source factor by Poisson re gression, adjusting for time trends, weather, and the other source factors. Combined effect estimates were calculated as the inverse variance weighted mean of the city-specific estimates. In the combined analysis, a 10 mug/m( 3) increase in PM2.5 from mobile sources accounted for a 3.4% increase in d aily mortality [95% confidence interval (CI), 1.7-5.2%], and the equivalent increase in fine particles from coal combustion sources accounted for a 1. 1% increase [CI, 0.3-2.0%). PM2.5 crustal particles were not associated wit h daily mortality. These results indicate that combustion particles in che fine fraction from mobile and coal combustion sources, but not fine crustal particles, are associated with increased mortality.