An assessment of the mobile source contribution to PM10 and PM2.5 in the United States

Mobile sources are significant contributors to ambient particulate matter ( PM) in the United States. As the emphasis shifts from PM10 to PM2.5, it bec omes particularly important to account for the mobile source contribution t o observed particulate levels since these sources may be the major contribu tor to the fine particle fraction. This is due to the fact that most mobile source mass emissions have an aerodynamic diameter less than 2.5 mu m, whi le the particles of geological origin that tend to dominate the PM10 fracti on generally have an aerodynamic diameter greater than 2.5 mu m. A common a pproach to assess the relative contributions of sources to observed particu late mass concentrations is the application of source apportionment methods . These methods include material balance, chemical mass balance (CMB), and multivariate receptor models. This paper describes a number recent source a ttribution studies performed in the United States in order to evaluate the range of the mobile source contribution to observed PM. In addition, a revi ew of the methods used to apportion source contributions to ambient particu late loadings is presented.