Evaluation of the Characteristics of Acid Precipitation in Taipei, Taiwan Using Cluster Analysis

This work investigated the characteristics of acid precipitation collected in Taipei, Taiwan during 1991–1995 by performing cluster analysis. The extent to which meteorological conditions influence precipitation chemistry was also elucidated. Three potential sources of water-soluble ions in rainwater were identified: seasalt aerosols (Na+, Cl- and Mg2+), anthropogenic pollutants (H+ and NO3-), and mixing sources associated with sulfate (nss-SO42-, NH4+ and Ca2+). As the northeast flow prevailed during the northeast monsoon season, the concentrations of seasalt and sulfate ions in rainwater were significantly high. During that season, a typically high ratio of nss-SO42-/NO3- was also observed, indicating that Taipei might receive foreign pollutants via a long-range transport. In contrast, when the Pacific high dominated the region, nitrate concentration in rainwater was significantly elevated. Also during that period, the ratio of nss-SO42-/NO3- was substantially lower, indicating the prominence of acidic substances contributed by local sources.