Size distribution and dry deposition of road dust PAHs

The size distribution of polycyclic aromatic hydrocarbons (PAHs) for road d ust and for the engine exhaust of both gasoline-powered cars and motorcycle s was investigated. In addition, by using the measured size distribution da ta, monitoring and modeling the PAH dry deposition, the contribution fracti on of road dust on the dry deposition materials was also studied. Twenty-on e PAHs were analyzed primarily by using a gas chromatograph/mass spectromet er (GC/MS). The mass median diameters (MMDs) of 21 individual PAHs for resu spendable road dust (cut size <100 mu m) ranged between 63.4 mu m and 65.5 mu m. However, the MMDs of total-PAM size distributions for the engine exha ust of both gasoline-powered cars and four-stroke motorcycles averaged 0.45 mu m and 0.35 mu m, respectively, which were near the MMDs of PAHs (averag e 0.50 mu m) in the ambient air of traffic intersections. Suspended particl e-phase total PAHs in the ambient air of traffic intersections were found t o be more than 90% of the result of the automobile exhaust; that is, less t han 10% of the amount was contributed by the road dust. However, the modele d MMDs of 21 individual PAHs on the dry deposition material were between 22 .1 mu m and 44.6 mu m, and the contribution fraction of road dust on the PA H dry deposition was found to be more than 95%, even though the suspendable ambient-air PAHs were mainly from the mobile exhaust. (C) 1999 Elsevier Sc ience Ltd.