摘要 本研究利用桃園地區5個酸雨採樣站1993-2004年的密集酸雨觀測資料，統計解析其降水化學特性、時空分布以及不同降雨強度下對硫化物的清除能力。吾人於研究中比對雨水分析結果與年際和季節性的變化，以探討其時空特性。 5採樣站十年雨水平均pH值為4.63，酸雨(即pH<5.0)發生率為80%。春冬兩季為致酸因子SO42-明顯貢獻季節，反應出伴隨東北季風及春季鋒面雨之長程輸送在此季節的重要性。NO3-年變化則顯示自2000年開始各站有成長趨勢，反應出本區內交通源貢獻之氮氧化物的持續成長。研究中亦發現， SO42-及海鹽離子濃度分布趨勢和離海岸距離呈負相關，NO3-的濃度高值並非位於局部污染嚴重地區，可能因傳送過程造成高值出現在鄰近下風處。NH4+及Ca2+的空間分布則與農業活動區有一致性的分布。 此外，由於清除係數k (s-1)為影響溼沈降量的重要參數，故本研究更進一步選取夏季午後降雨個案來探討降水對本地排放之硫化物的影響，利用估算降雨前大氣混合層中硫化物的濃度與降雨後雨水中硫的濃度來求得清除係數，平均值為7.91×10-5，並利用迴歸分析獲得k與降雨強度P的關係式k =2.48×10-5 P。 Abstract The purpose of this study is to characterize the rainwater chemistry, analyze the temporal and spatial distribution, and estimate the scavenging coefficient of sulfates by precipitation using the rain water data collected from 1993 to 2004 at the five acid rain monitoring sites in Taoyuan County. The average pH value at five sites over ten years is 4.63 and the overall frequency of acid rain events (defined as the pH < 5.0) is about 80%. Sulfate ions were dominant composition for winter and spring samples, associated with the long range transport of air pollutants through winter monsoon flows and frontal systems. The concentration of NO3- was observed to increase from 2000. The SO42- and sea salt ions decreased with the distance from the coast. In contrast, the highest NO3- was not located at the source region but at the remote mountain area, possibly due to the transport of pollutants from upstream source region. The location of higher NH4+ and Ca2+ was consistent with the agricultural area. In addition, the scavenging coefficient k was also estimated. The cases of summer showers were selected to study the scavenging of the sulfate in air by precipitation. As a result, the average scavenging coefficient k is 7.91×10-5, and the regression relationship for k and precipitation rate P is k=2.48×10-5P.
