本研究比較東亞五個測站，包括韓國濟州島Gosan站 (126.27°E, 33.48°N, 72 m asl)、日本沖繩Cape Hedo站 (128.2°E, 26.8°N, 60 m asl)、台灣Pengjia Islet站 (彭佳嶼，122.07°E, 25.63°N, 101.7 m asl)、Matsu站 (馬祖，119.92°E, 26.17°N, 97.842 m asl)及Kinmen站 (金門，118.29°E, 24.41°N, 47.88m asl)之降水化學特性。Gosan、Cape Hedo及Pengjia Islet三站屬背景測站，Matsu及Kinmen鄰近中國沿海，屬非背景站。本研究藉由五站不同的特性，探討其降水化學受地理位置分布與氣象條件之影響。其中也利用後推軌跡群集分析分類不同的氣流來源，結果亦顯示各群集的降水中有不同化學組成。三個背景站之雨水中，主要離子為海鹽離子，如Cl-和Na+，佔總離子濃度的50%以上，其次為nss-SO42-。兩個非背景站中，Matsu站雨水最主要的離子為海鹽離子，其次為nss-SO42-及H+，各佔總離子濃度之8%，Kinmen站主要離子仍為海鹽離子，但其nss-SO42-及H+ 所佔總離子濃度比例較高，分別為13%及12%，兩站酸性離子之比例如SO42-及NO3-明顯高於Cape Hedo及Pengjia Islet站。五個測站在東北季風及有春季高壓系統時期，有較高的nss-SO42-濃度，而背景站因無本地的排放源，顯示長程傳輸在該時期對背景站雨水化學影響顯著。五個測站中，Pengjia Islet站有最低之pH平均值，僅4.52，且nss-SO42-濃度亦相對較高(34 μeq l-1)。pH平均值最高的測站為Cape Hedo站，為4.93，且該站之nss-SO42-濃度最低(18 μeq l-1)。nss-SO42- / NO3-之比值可反映何種致酸因子之相對重要性，Gosan站比值為1.63，Cape Hedo為1.88，Pengjia Islet站為1.44，Matsu站為1.58，其中以Kinmen站最高，為1.97。其他更細節的分析亦將於本研究中呈現。

The precipitation chemistry observed at five island stations in East Asia, including Gosan (126.27°E, 33.48°N, 72 m asl), Cheju Island, Korea; Cape Hedo (128.2°E, 26.8°N, 60 m asl), Okinawa, Japan; Pengjia Islet (122.07°E, 25.63°N, 101.7 m asl), Matsu Island (119.92°E, 26.17°N, 97.842 m asl), and Kinmen Island (118.29°E, 24.41°N, 47.88m asl), Taiwan, are compared. Gosan, Cape Hedo and Pengjia Islet are considered as remote and background stations, while, the other two stations are very close to China and considered as non-background stations. This work will elucidate the geographical distribution of chemical composition of rainwater in East Asian oceanic region, and further to assess wet deposition fluxes of sulfate and nitrate in these stations.
Cluster analysis will be used for the backward trajectories to classify the different source of five stations, and it was also shown the different chemical composition of rainwater in each cluster. The daily sampling period at background stations were from January 2003 to December 2008; for non-background stations, it was from April 2005 to December 2008. Principal ions of background stations in rainwater were sea salt ions, such as Cl- and Na+, accounting for more than 50%, and followed by nss-SO42-. In non-background stations, sea salt ions are still the principal ions in Matsu Island, followed by nss-SO42- (8%) and H+ (8%), while in Kinmen Island, the principal ions were still sea salt ions, but the contributions of nss-SO42- (13%) and H+ (12%) were higher.
For all five island stations, rain events containing higher SO42- were found to be associated with northeast monsoon and continental high pressure systems, which are capable of transporting atmospheric pollutants to the sites via long-range transport. The background stations and non-background stations have various chemical compositions with respect to different source regions. It was also shown the influences of long-range transport on background stations, in which have very limited local emissions. Among five stations, Pengjia Islet had the lowest average pH of 4.52 and the relatively higher nss-SO42- of 34 μeq l-1. The highest average pH of 4.93 was found at Cape Hedo, which had the lowest nss-SO42- of 18 μeq l-1. The ratio of nss-SO42- / NO3-, reflecting the relative importance of these two anions, was of 1.63 at Gosan, 1.88 at Cape Hedo, 1.44 at Pengjia Islet, 1.58 at Matsu Island, and 1.97, the highest ratio at Kinmen, respectively. More detailed statistic analyses will be also presented in this study.

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