Phase and Size Distribution of Polycyclic Aromatic Hydrocarbons in Diesel and Gasoline Vehicle Emissions

Emission measurements were obtained for a variety of military vehicles at Hill Air Force Base (Ogden, UT) in November 2000 as part of a Strategic Environmental Research and Development Program. Aircraft ground support equipment vehicles using  gasoline ,  diesel , and JP8 fuels were tested using chassis dynamometers under predetermined load. The exhaust from the tested  vehicle  was passed to a dilution tunnel where it was diluted 30−40 times and collected using Micro-Orifice Uniform Deposit Impactor (MOUDI) fitted with aluminum substrates, an XAD-coated annular denuder, and a filter followed by a solid adsorbent. All MOUDI substrates were analyzed for mass and for organic and elemental (EC) carbon by the thermal/optical reflectance method and for  polycyclic   aromatic   hydrocarbons  (PAHs) by GC/MS. Black carbon was measured with a photoacoustic instrument. The denuder and filter/solid adsorbent samples were analyzed for semivolatile PAH. Overall, there is more mass and higher EC contribution when the  vehicle  is run under higher load in comparison with the low load. However, older vehicles generally show more mass and EC  emissions  than newer vehicles, and there is a shift toward smaller particle sizes for the low load, which is most pronounced for newer vehicles. The particle-associated semivolatile PAHs and nonvolatile four- through six-ring PAHs are present predominantly on the submicron particles collected on MOUDI stages 0.1−0.18, 0.18−0.32, and 0.32−0.56 μm. For the low-load runs, the  distribution  of PAHs seems to be shifted toward smaller  size  particles. The gas-particle  phase   distribution  of semivolatile PAHs depends also on the engine loading. For idle, not only are the more volatile two- and three-ring PAHs, from naphthalene to dimethylphenanthrenes, retained on the denuder portion, but also less volatile four-ring PAHs, such as fluoranthene and pyrene, are retained by the denuder at the 80−90% range, which implies that they are present predominantly in the gas  phase . In contrast, for engines under high loads, a much larger portion of three- and four-ring PAHs are partitioned to the particle  phase .