| 摘要: | 東亞是全球人為大氣汞排放量最高的區域，不同國際團隊的模式模擬結果都顯示東亞大陸下風區域是高大氣汞濃度與沈降區域，而濕沉降已知是地表環境與生態系統重要污染來源，然而目前仍缺乏東亞下風區域大氣汞濕沈降研究成果發表，尤其是長時間資料分析。因此，本研究分析2010至2015年我國環保署大氣汞濕沈降監測網北部三測站每週雨水汞樣本之資料，包含都會區的台北、離島的彭佳嶼以及山區的鞍部測站，探討北台灣雨水汞濃度及濕沈降量之時空分布與影響機制。
台北、彭佳嶼及鞍部測站雨水汞濃度的 六年權重平均值分別為 10.60、7.77及9.97 ng/L，與北美及歐洲測站之結果相近。而年平均汞濕沈降量分別為 ，與北美及歐洲測站之結果相近。而年平均汞濕沈降量分別為 25.12、12.92及45.36 µg m-2 yr-1，北台灣位於亞熱帶雨量明顯比歐美較多而各測站之樣本汞濕沉 ，北台灣位於亞熱帶雨量明顯比歐美較多而各測站之樣本汞濕沉 降量與樣本雨呈正相關，顯示影響北台灣之汞濕沉。因此結果比美及歐洲之測站較高，尤其在鞍部。
彭佳嶼及鞍部站之雨水汞濃度季節變化不明顯，而台北則在夏最高，顯示 三測站於夏季有另外的雨水汞來源。在夏季西南季風應帶來較乾淨空氣，但雨水汞濃度與冬季相若甚至更高，可能是因為夏天容易產生較強對流，氣團與自由大氣層之高濃度二價汞混合，成為夏季汞濕沈降的來源。後將樣本濃度及雨量作相關性分析，台北及鞍部站西南季風季之雨水汞濃度沒有隨雨量的增加而明顯下降，顯示降雨期間台北雨水汞有持續來源。再將各樣本依據降雨事件型態作天氣事件分類，發現三個測站於代表局地強對流的午後雷陣雨型態中，雨水汞濃度都比其他降雨形態高，進一步說明高層大氣含有高濃度氣態反應汞，並持續地補充至雨水中。
雨水汞濃度及濕沉降總量都有明顯的年際變化，最高值與最低值有約兩倍差距，推測兩者與大尺度氣候系統變化有關，本研究把兩者與南方震盪指數(SOI)作相關性的探討。然而由資料年期太短，需要更長期的資料才能得出結論。
;East Asia is the highest atmospheric mercury emission region in the world, various studies have shown that downwind area in East Asia has high atmospheric mercury concentration and deposition by using model simulations. Atmospheric wet deposition is the important source of mercury pollution to the ecosystem. However, there was lack of studies about mercury wet deposition in the downwind area in East Asia, especially long-term data analysis. Therefore, the mercury wet deposition weekly data from Taiwan EPA during 2010-2015 used at three stations in North Taiwan, include Taipei (urban), Pengjia islet (remote island) and Anbu (mountain) station, to discuss the temporal and spatial variation of the mercury wet deposition in Northern Taiwan.
VWM Hg concentration in Taipei, Pengjia islet and Anbu station were 10.60, 7.77 and 9.97 ng L-1 respectively, which were similar to other stations in Europe and North America. Mercury wet deposition flux were 25.12, 12.92 and 45.36 µg m-2 yr-1 in three stations respectively, North Taiwan is located in the subtropical region, which had higher rainfall compare with Europe and North America, also sample mercury deposition flux was positively correlated with sample rainfall amount. Therefore, mercury deposition flux was higher than Europe and North America, especially in Anbu station.
However, the seasonal variation of rainwater mercury concentration was not clear at Pengjia islet and Anbu station, while it was the highest in Summer at Taipei. In summer, the dominated wind is southwest monsoon in North Taiwan, which took clearer air mass to Taiwan, the source of mercury might relate to high convection rain is more frequently in summer, air mass may mix with a global pool of RGM in the free troposphere, which provides the source of the mercury.
Correlation analysis performed with Hg concentration of each sample and rainfall amount, results showed that the washout effect in Taipei and Anbu station was weak, there should have continuous source beside local emission. Different events were separated according to weather systems causing rain, we found that Hg VWM concentration was the highest in the type of afternoon thunderstorm at both three stations, which show there was high reactive gaseous mercury in the free troposphere and provide a continuous source to rainwater.
Both VWM concentration and wet deposition flux had obvious yearly variation, 2 times difference between the maximum and minimum value, it might relate to the large-scale climate system. Correlation analysis performed between South Oscillation Index and above two parameters. However, the length of data was too short to compare with long-term climate index, longer data was needed to get a conclusion. |
