RAINFALL DILUTION OF ANTHROPOGENIC PARTICULATES

A total of 136 rainwater (or snow during the Winter season) samples collected from February 2009 to February 2013 were analyzed. In particular, 33 samples out of 136 were collected during or just after the Asian dust storm (ADS) events, with a hope to directly compare the properties of particulate matter (PM) before and after the ADS events. According to compositional analysis of rainwater with and without ADS, the enrichment of Fe content is most eye-catching. Such enhancement of Fe matches well with the magnetic observation. Therefore, it is likely that Fe content in air dust during ADS event increased than normal days. Anthropogenic process induces enrichment of hazardous elements in air, including Fe-enrichment from the Fe-smelting plant, Cu-Ni enrichment from vehicle traffic, and Pb-Zn enrichment from various anthropogenic sources. On the basis of dust density variation with rainfall, it is possible that the wash-out effect of rainfall is most prominent for rainfalls about 15-20 mm/day. However, it does not necessarily indicate that rainfall over 15-20 mm/day was less effective in diluting dust density in air. Instead, it is more likely to suggest that dust was diluted well enough during the early period of high rainfalls.