- 學位論文
Temporal and Spatial Distribution of Mercury and Heavy Metals in Wet Deposition in Taiwan
Temporal and Spatial Distribution of Mercury and Heavy Metals in Wet Deposition in Taiwan
摘要
臺灣位於東亞大陸下風處，並因此受到此區域人為排放的污染物，包含汞以及其他重金屬的影響。本研究於臺灣鞍部、中壢和嘉義三測站採樣，收集2009年此三測站每周的溼沉降樣本進行汞與重金屬(砷、鎘、鉛、釩、鋅)的分析，以此分析結果探討溼沉降中汞與重金屬的季節性變化趨勢與長程傳輸的貢獻。 汞的權重平均濃度於鞍部、中壢和嘉義站分別為9.5、10.7、13.5 ng/L，以嘉義站的濃度為最高。鞍部站的汞濃度呈現夏季高於其他季節的情形，此結果可能與夏季的環境有利元素汞的氧化反應有關；另外，夏季旺盛的對流作用也可促使大氣中較高層的二價汞被雨水移除。 而其他重金屬(砷、鎘、鉛、釩、鋅)的權重平均濃度，在鞍部站依序為0.6，0.1，3.8，0.7，31.0 ?g/L，中壢站是0.3，0.1，2.2，0.8，24.2 ?g/L，嘉義站則分別為0.1，0.1，1.0，0.5，14.2 ?g/L，大部分的金屬以鞍部站的濃度為三站中最高，嘉義站最低。而此三測站的重金屬濃度季節性變化，則多以夏季為低值，在非夏季則濃度較高，此季節性變化應與氣團來源有關。夏季氣團多以太平洋、南海之較乾淨的海洋性氣團為主；而自秋季到春季的氣團抵達臺灣之前會先通過東亞大陸，隨著氣團帶來的人為排放污染物，以及此時期溼沉降樣本當中通常有較高的金屬濃度，顯示了長程傳輸的影響對臺灣的重要性。
並列摘要
Taiwan is located downwind of the East Asian continent and thus could be under the influence of anthropogenic air pollutant emission, including mercury (Hg) and the other heavy metals, from East Asia. In 2009, weekly wet deposition samples have been collected at Anbu, Jhongli and Chiayi sites in Taiwan for Hg and heavy metal (As, Cd, Pb, V, and Zn) analyses. These data were used to discuss seasonal trends for Hg and heavy metals in wet deposition and to evaluate the contribution of regional/long-range transport. The volume weight mean (VWM) concentrations of Hg at Anbu, Jhongli, Chiayi were 9.5, 10.7 and 13.5 ng/L, respectively. The concentration of Hg at Chiayi is higher than at the northern sites, Anbu and Jhongli. At Anbu site, the concentrations of Hg in wet deposition were higher in summer than in other seasons, indicating the importance of Hg0 oxidation and/or scavenging of upper-altitude Hg(II) by deep convection. For the other heavy metals, the VWM concentration of As, Cd, Pb, V and Zn at Anbu site were 0.6, 0.1, 3.8, 0.7 and 31.0 ?g/L, respectively. At Jhongli site, the VWM concentration of As, Cd, Pb, V and Zn were 0.3, 0.1, 2.2, 0.8 and 24.2 ?g/L, respectively. The VWM concentration of As, Cd, Pb, V and Zn at Chiayi site were 0.1, 0.1, 1.0, 0.5 and 14.2 ?g/L, respectively. Higher concentrations of these heavy metals were usually observed at Anbu while lower concentrations were observed at Chiayi. Regarding the seasonal distribution of concentrations of theses heavy metals, lower values were usually observed in summer. Seasonal variations in heavy metal concentrations were correlated with air masses origin. In summer, air masses came mainly from the Pacific Ocean and South China Sea, which were relatively clean marine air. Between fall and spring, air masses passed the East Asian continent prior to reaching Taiwan, contributing to the elevated heavy metal concentrations. The air masses in winter monsoon brought large amount of pollutants and caused higher concentrations in wet depositions, indicating the importance of regional/long-range transport to Taiwan.