Dry deposition velocities of polycyclic aromatic hydrocarbons in the ambient air of traffic intersections

Abstract

Abstract Dry deposition and air sampling were undertaken simultaneously at two traffic intersections (TA and TB sites) with several dry deposition plates and PS‐1 samplers from August to December 1995 in southern Taiwan. In addition, samples in a lane (L) and a residence (R) sites were also determined and compared. Twenty‐one individual polycyclic aromatic hydrocarbons (PAHs) were analyzed primarily with a gas chromatographyVmass spectrometer (GC/MS). At the traffic intersections, the dry deposition velocities of total‐PAHs averaged 0.38 and 0.23 cm sec‐1 in the day‐time and at night‐time, respectively. This result shows that, in the ambient of traffic intersections, significant fraction of PAH dry deposition are contributed by the road dust resuspension caused by traveling vehicles. In general, the lower molecular weight (LMW) PAHs, being primarily in the gas phase, have lower dry deposition velocities; while the higher molecular weight (HMW) PAHs, which are mainly associated with particulates, have higher dry deposition velocities. The mean dry deposition velocities for LMW PAHs ‐ Nap, AcPy and Acp ‐ are 0.011, 0.034 and 0.043 cm sec‐1, respectively. However, the dry deposition velocities of10 HMW PAHs, including BbF, BkF, BeP, BaP, PER, IND, DBA, BbC, BghiP and COR, are all at the same level but up to 2 orders of magnitude higher than those of LMW PAHs. Because of the “synergism”; of higher fraction in particle‐phase and higher deposition velocity, more than 94% of the HMW PAH mass in the dry deposition flux is contributed by the particle phase.