Spatial variations of the aerosols in river-dust episodes in central Taiwan

Daily and hourly average data of PM(10) from 17 air-quality monitoring stations distributed throughout four counties and along four rivers (the Ta-an River, the Tachia River, the Wu River and the Choshui River) in central Taiwan were collected from November 15 to 21, 2008. During this period, the wind speed and daily PM(10) concentrations increased drastically from the 17th to the 19th, and reached a maximum level on the 19th. Six air-quality monitoring stations (Dajia, Wurih, Siansi, Dungnan, Lunbei and Taisi) in the central Taiwan were selected for sampling fine (PM(2.5)) and coarse (PM(10-2.5)) aerosols samples during and after the river-dust episode. Most of the ratios of [crustal elements (Fe or Al)/reference elements (Cd or Mo)] for the samples obtained during episode are higher than those obtained after episode. The values of Fe(10-2.5)/Cd(10-2.5) and Fe(10-2.5)/Mo(10-2.5) were very high in Lubei, Taisi, and Dungnan stations where heavy aeolian river dust occurred. These data suggest that the ratios of Fe(10-2.5)/Cd(10-2.5) and Fe(10-2.5)/Mo(10-2.5) can be successfully used as indexes to evaluate the comparative degree of effect of aeolian river dust on the atmosphere of multiple stations.