干旱区生态环境知识资源中心

Sandstorms in the desert and loess regions of north-northwestern China and Mongolia, as well as the associated dustfall episodes in the Korean Peninsula, were monitored between January and December 2005. Composite color images were made on the basis of data received directly from the National Oceanic and Atmospheric Administration satellite advanced very high resolution radiometer, and the distribution and transport of dust clouds were analyzed. The ground concentrations of PM10 and PM2.5 and visibility during dustfall episodes (where the PM10 concentration exceeds 190 mu g m(-3) for at least 2 h) were also analyzed at Cheongwon, in central South Korea, which lies in the leeward direction from the origin of sandstorms. Fewer strong sandstorms occurred in the places of origin in 2005, mainly because of the snow cover with moderate high and low pressure systems in the place of dust origin. The weather patterns explain why there were fewer dustfall episodes in Korea in 2005 than in the period between 1997 and 2004. A total of seven dustfall episodes were monitored in Korea in 2005 and they covered a period of 11 days. In the summer of 2005, sandstorms occurred less frequently in the source region due to high humidity and weaker winds; as a result, there were no dustfall episodes in Korea. When the sandstorms at the source headed directly to Korea without passing through any large cities or industrial areas of China, the PM2.5 concentrations were up to 20% of the PM10 concentrations. However, when the sandstorms headed to Korea via the industrial areas of eastern China, where they pick up anthropogenic air pollutants, the PM2.5 concentrations were at least 25% of the PM10 concentrations. In five of the cases that were observed and analyzed in 2005, the PM10 concentrations of the sand dust that originated in the deserts were 190 mu g m(-3) or less, which is below the level of a dustfall episode.