GC-MS analysis of trace organic species in motor vehicle emissions for ultrafine particle source apportionment

Measurements are reported that describe the size distribution of particle-phase trace organic species emitted from light duty gasoline-powered vehicles and heavy duty diesel-powered vehicles. The smallest characterized size fraction falls into the "ultrafine" range (Dp < 100 nm) that may be relevant for health effects studies. Emphasis is placed on polycyclic aromatic hydrocarbons (PAHs), hopanes, and steranes because these compounds have direct environmental toxicity and/or these compounds can be used to quantify source contributions to ambient particulate matter concentrations. Size distributions of hopanes and steranes emitted from gasoline- and diesel-powered vehicles that pass quality assurance checks have very similar shape that changes as a function of vehicle type, emissions control technology, and driving cycle. Likewise, size distributions of PAHs that pass quality assurance checks also have similar shape, but the PAH profile may be different than the hopane+sterane profile. These results suggest that hopanes+steranes and PAHs are produced by separate processes within the vehicle's combustion and emissions systems, and that these compounds may therefore act as separate tracers for oil and fuel contributions to emitted carbonaceous particles. Hopane+sterane and PAH size distributions measured next to a busy freeway have the same general shape as the analogous size distributions measured during emissions source tests. Source apportionment calculations predict that the majority of the ultrafine elemental carbon in the freeway environment originates from gasoline and diesel fuel with relatively minor contributions from motor oil. Similarly, the majority of the ultrafine organic carbon in freeway environment is predicted to originate from gasoline and diesel fuel, with smaller amounts attributed to motor oil. A set of large PAHs with molecular weight greater than 302 daltons are identified in gasoline-vehicle exhaust and in ambient particulate matter standards from the National Institute of Standards (NIST). These compounds may further help to differentiate contributions from diesel fuel and gasoline in fine and ultrafine ambient airborne particulate matter.