Seasonal characteristics of air masses arriving at Gosan, Korea, using fine particle measurements between November 2001 and August 2003

The characteristics of air masses arriving at Gosan, Korea, were investigated on the basis of PM2.5 measurements during six intensive measurement periods (IMPs) in order to delineate the influences of various types of seasonal events in northeast Asia. The air masses arrived from the northwest/west along prevailing westerlies during three IMPs performed in the nonsummer seasons. Three characteristic periods of stagnation, Asian dust, and pollution periods were identified in November 2001, spring 2002, and February 2003, respectively. Another three characteristic periods of typhoon, biomass burning, and marine background periods were identified in the summer seasons: late August to early September 2002, June 2003, and August 2003, respectively. Anthropogenic pollution levels increased significantly not only because of stagnant meteorological conditions but also because of transport from high-emission areas with prevailing westerly winds during heating seasons (winter and/or fall). In spring, there was a good contrast between a weak Asian dust (AD) period with dusts transported from the Gobi desert and a strong AD period with dusts transported from Inner Mongolia. During the weak AD period the levels of anthropogenic pollutants were high, whereas during the strong AD period, anthropogenic ion concentrations were significantly low in spite of high mass concentrations. In summer, marine influences were strong either because of transport from the Pacific Ocean or the effects of typhoons. Influences from biomass burning from China and/or Russia were the strongest in June (biomass burning period) but continued in the marine background period.