During a twenty-day period in 2005, a nine-stage Andersen cascade impactor was used to determine the seasonal size distribution of atmospheric particles and its inorganic ion species sampled for 24hr in Iksan city, located southwest of the Korean peninsula. Samples were analyzed for major water-soluble ion species using Dionex-100 ion chromatograph. Average fine and coarse mass concentrations of atmospheric particles were, respectively, 31.4 and 82.6 g m3 in spring and 35.8 and 73.4 g m3 in fall-winter during the sampling period of 2005, while measurements of 69.8 and 9.9 were obtained in the sampling period of summer. The size distribution of particulate mass concentration during the non-Asian dust period was generally bimodal, whereas the size distribution of particulate mass concentration during the Asian dust period was unimodal due to the significant increase of coarse particles, which originated from long-range transport of soil dust particles from loess regions of the Asian continent. Among ionic species, SO42, NH4+, and K+ were mainly distributed in fine particles due to their characteristics of emission sources and gas-to-particle conversion, while Na+, Mg2+ and Ca2+ were dominantly in coarse particles. However, NO3 and Cl were distributed in both coarse particles and fine particles. Although SO42 was mainly distributed in fine particles, the size distributions of SO42 in coarse mode were significantly increased during the Asian dust events compared to those during the non-Asian dust period. Ca2+ showed the most abundant species in the atmospheric particles during the Asian dust period. NH4+ was found to mainly exist as (NH4)2SO4 in fine particles.
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