Dry deposition of pahs in the ambient air of central Taiwan

Abstract

The atmospheric polycyclic aromatic hydrocarbons (PAHs) in ambient air of central Taiwan at Wu‐Chi, Sha‐Lu, Ta‐Duh, and the Expressway Interchange of Taichung city were studied. Dry deposition and air sampling were undertaken simultaneously with several dry deposition plates and PS‐1 samplers from May 1995 to March 1996. Twenty‐one individual PAHs were analyzed primarily with a gas chromatography/mass spectrometer (GC/MS). 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 0.054, 0.040 and 0.15 cm sec‐1, respectively. However, the dry deposition velocities of 10 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, less than 0.8% of the HMW PAH mass in the dry deposition flux is contributed by the gas phase.