Mobile sources are significant contributors to ambient fine particulate matter (PM2.5), accounting for 50% or more of the total observed levels in some locations. One of the important methods for resolving the mobile source contribution is through chemical mass balance (CMB) receptor modelling. CMB requires chemically speciated source profiles with known uncertainty to estimate source contributions to observed pollutant levels. Mobile source particulate matter profiles are available from various sources and are generally in the form of weight fraction by chemical species. This paper examines the similarities and differences in US mobile source PM2.5 profiles that contain data for elements, ions, elemental (EC) and organic carbon (OC), and, in some cases, speciated organics (e.g. polyaromatic hydrocarbons, PAHs). Notable characteristics of the mass fraction data include the variability in the relative contributions of elements and ions among supposedly similar sources, and the wide range of average elemental to organic carbon ratios (0.60 plus or minus 0.53 to 1.42 plus or minus 2.99) for light-duty gasoline vehicles (LDGVs), indicating LDGVs may be significant sources of EC emissions. Different populations of the same class of emitters exhibited considerable variability in the relative emissions of other chemical species as well, suggesting caution be exercised when selecting and using receptor models to apportion the mobile sources contribution to PM2.5. (A)
Abstract