Seasonal variation of particle size distributions of PAHS at Seoul, Korea

The atmospheric size distributions of particulate polycyclic aromatic hydrocarbons (PAHs) up to 10 μm in diameter were measured at Seoul in the summer and winter of 2003. The concentrations of total PAHs were from 4.32 to 5.48 ng m^-3 in summer and from 25.6 to 35.9 ng m^-3 in winter, respectively. Majority of the PAHs concentrations were found on fine particles (D_p<2.1 μm). The size dis-tributions of individual PAH compounds were bimodal with the peaks in the 0.43-0.65- and 4.7-5.8-μm range in summer. In winter, those were unimodal or weakly bimodal with the peaks in the 0.65-1.1- and 4.7-5.8-μm range. The seasonal variation of the peak size range in the fine mode might be caused by longer residence time in the air in winter. Based on the previously reported source diagnostic ratios of PAHs for the major emission sources, it was suggested that vehicles were the major source of PAH in summer, while coal-related emissions and firewood fire were the major sources in winter for fine particles. The seasonal variation of the peak size ranges in the fine particles had not shown noticeable effect on the dry deposition fluxes. However, it might affect the optical properties of the atmosphere.