Water-soluble ions of aerosols in Taipei in spring 2002

Dust originating from and and semiarid areas in Central Asia can reach Taiwan during springtime. However, aerosols in a metropolitan region, such as Taipei city, also have significant local sources. In this work, the influence of long-range transport and local pollution, on various water-soluble ions in fine and coarse modes, was investigated for several dust events. Concentration differences between dust-event and non-dust-event days were assessed. Field measurements were conducted in Taipei from February to May 2002. Twelve-hour samples of PM2.5 and PM10 were taken. Ion chromatography was used to analyze water-soluble ions (Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3-, and SO42-). The mean concentrations of Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3-, SO42-, and PM in the fine mode during the entire sampling campaign were 0.29, 2.87, 0.29, 0.029, 0.13, 0.57, 0.92, 2.68, and 28.2 mu g m(-3), respectively. The corresponding mean concentrations in the coarse mode (PM2.5-10) were 0.75, 0.30, 0.096, 0.14, 0.63, 0.84, 2.33, 1.60, and 34.0 mu g m(-3), respectively. Results of Principle Component Analysis showed that elevated concentrations of fine Na+, K+, Mg2+, Ca2+, and Cl- and coarse Na+, Mg2+, Ca2+, NO3-, and SO42- on dust-event days were a result of long-rnge transport. A prolonged influence of long-range transport on concentrations of fine and coarse ions, after dust peaked, was also observed. K+, Mg2+, and Ca2+ increased by about 1.7 to 3.8 fold and Na+ and Cl- increased by45 - 210% on dust-event days. Fine modes of NH4+, NO3-, and SO42- were derived from local pollution, while most coarse NO3- and some coarse SO42- were derived from long-range transport. On average, coarse NO3- and SO42- increased by 67% and 97%, respectively, during dust events.