Estimates of the Contribution of Below-cloud Scavenging to the Pollutant Loadings of Rain in Taipei, Taiwan

In this study, we use a simple and semi-quantitative scheme to estimate the contribution (denoted as/) of below-cloud scavenging of pollutants by raindrops, based on the precipitation chemistry collected in Taipei City and the cloud chemistry observed at the peak of the Mt. Bamboo (around 1100 m MSL) in the winters of 1996-1998. The magnitudes of/ (nss (non sea salt)-SO/"),flN03') and/(NH/) were estimated to range between 0.31-0.88, 0.25-0.88 and 0.54-96, respectively. For instance, 54-96% of the NH/ ions in rainwater arose by below-cloud scavenging, reflecting their origins from local sources. For most of the cases, at least 75% of the N03-was accounted for by the same scavenging mechanism, whereas more than 25 % of nss-SO 42 resulted from in-cloud scavenging. In comparison with NH/ and NO;, relatively higher amounts of nss-SO/" obviously derived from long-range transport.