本研究旨在探討2002-2004年亞洲沙塵好發期間，陽明山區竹子山雲水化學之特性，並進一步就氣流來源歸類雲水個案，進行多變量統計，以了解不同氣流來源影響下雲水化學組成及特性。最後，利用一雲水個案來估算沙塵中水溶性氣膠微粒受到雲內清除作用之比例。 2002-2004年亞洲沙塵好發期間，Ca2+離子濃度在非沙塵及沙塵事件時雲水中之比例分別為3%及6%，兩者相差將近一倍，顯示沙塵對雲水化學造成明顯影響。進一步區分沙塵期間不同氣流來源影響下雲水化學結果則顯示，沙塵期間受到來自中國中部與北方一帶氣流影響時，雲水中SO42-、NO3-與Ca2+離子濃度及雲內負荷量皆有最高值；SO42-、NO3-離子濃度及雲內負荷量部分為非沙塵時之1.3倍，Ca2+離子甚至可達四倍之多，顯示在此氣流來源下，雲水受到人為排放污染物及沙塵影響甚鉅。 此外，估算沙塵中水溶性氣膠微粒受到雲內清除作用之比例結果可得知，在2004/2/5-8日受沙塵影響雲水事件中，當沙塵伴隨雲系移入台灣時，沙塵中主要致酸SO42-、NO3-及致鹼NH4+、Ca2+的水溶性氣膠微粒分別有41%、52%及41%、55%會受到雲內清除作用之影響而從大氣中移除。 The purpose of this study is to characterize the cloud chemistry observed during the prevailing seasons of Asian dust in 2002-2004. Based on backward trajectory analysis, cloud events were categorized to study the relationship between dust source regions and cloud chemistry. Furthermore, one cloud event was studied to estimate the scavenging efficiency of water-soluble aerosol particles by clouds. The contribution of Ca2+ to total ions in cloud water is 3% and 6% for non-dust and dust events, respectively. For dust events, highest SO42-,NO3- and Ca2+ ion concentrations and their cloud loadings were associated with the air mass originated from northern and central China. The SO42-, NO3- ion concentrations and their dust loadings for dust events were 30% greater than those for non-dust events, even more than four times for Ca2+. In one case study, the in-cloud scavenging of water-soluble aerosol particles was estimated. The result showed that 41, 52, 41 and 55% of SO42-, NO3-, NH4+ and Ca2+ were scavenged by cloud droplets, respectively.
