On-Road Emissions of Particulate Polycyclic Aromatic Hydrocarbons and Black Carbon from Gasoline and Diesel Vehicles

Motor vehicles are a significant source of fine carbonaceous particle emissions. Fuels have been reformulated and vehicle technologies have advanced, so an updated assessment of vehicular emissions is needed. Gas- and particle-phase pollutant concentrations were measured in the Caldecott Tunnel in the San Francisco Bay Area during the summer of 1996. Separate samples were collected for uphill traffic in two tunnel bores: one bore was influenced by heavy-duty diesel truck emissions; a second bore was reserved for light-duty vehicles. Fine particle black carbon and PAH concentrations were normalized to fuel consumption to compute emission factors. Light-duty vehicles and heavy-duty diesel trucks emitted, respectively, 30 ± 2 and 1440 ± 160 mg of fine black carbon particles per kg of fuel burned. Diesel trucks were the major source of lighter PAH, whereas light-duty gasoline vehicles were the dominant source of higher molecular weight PAH such as benzo[a]pyrene and dibenz[a,h]anthracene. Size-resolved measurements of particulate PAH showed significant fractions of diesel-derived PAH to be present in both the ultrafine size mode (<0.12 μm) and the ac cumulation mode (0.12−2 μm). In contrast, gasoline engine-derived PAH emissions were found almost entirely in the ultrafine mode.