鹿林山大氣汞分布與乾濕沉降特徵及來源推估

林達偉(Da-wei Lin)

指導教授 ： 林能暉 ； 許桂榮

國立中央大學/地球科學學院/大氣物理研究所/碩士(2014年)

摘要

台灣位居東亞大陸下風處，冬季季風可將東亞大陸空氣污染物傳送至台灣，而春季高層西風則可將中南半島生質燃燒排放之污染物傳送至台灣山區，影響空氣品質與環境生態。鹿林山大氣背景站位於台灣中部山區，海拔高度2862公尺，是東亞少數具有代表性的的大氣背景測站，有助於了解與特徵化東亞大陸汞排放的長程傳輸，以及對下風區域的影響。
2010年鹿林山觀測到氣態元素汞(gaseous element mercury, GEM)、氣態二價汞(reactive gaseous mercury, RGM) 與顆粒汞(particulate mercury, PHg)平均濃度(±標準差)分別為1.56(±0.42) ng m-3、13.95(±31.32) pg m-3與0.71(±2.65) pg m-3，CO平均濃度為143(±67) ppb，O3平均濃度為33.8(±15.0) ppb。GEM與CO濃度有高度正相關(r = 0.78)，顯示鹿林山大氣汞濃度變化與人為影響有關。同期間雨水汞權重平均濃度為8.8 ng L-1，總降水量為3173.2 mm，濕沉降量為33.7 µg m-2。模式推估的乾沉降量估算為69.5 μg m-2，其中GEM乾沉降量為58.8 μg m-2，RGM乾沉降量為10.6 μg m-2，PHg乾沉降量僅0.1 μg m-2。夏季濕沉降量高於乾沉降量，其它季節則相反，因為中南部山區降雨集中於夏季。文獻資料顯示北美地區(溫帶氣候)大氣汞以乾沉降為主，年乾沉降量(RGM+PHg) 約15 µg m-2，年濕沉降平均為10 µg m-2，台灣(熱帶/亞熱帶)山區雖然也是以乾沉降為主，但濕沉降量約為北美地區的3倍，此差異主要係由於台灣降雨量高於北美所致。
為了進一步探討鹿林山大氣汞之源與受體關係，運用濃度權重後推軌跡法推論可能的大氣汞來源區域。分析結果顯示中國西南及華南地區與中南半島北部為各汞物種的主要來源區；此外，中國東海與黃海沿海地區是GEM的另一個主要來源區，而菲律賓與南海則為RGM的另一個主要源區。使用軌跡聚類分析顯示海洋性氣團的大氣汞與其它污染物濃度較低，大陸性氣團的大氣汞與其它污染物濃度較高，其中以經過中南半島和中國而來的氣團污染物濃度最高。

關鍵字

大氣汞 ； 長程傳輸 ； 生質燃燒 ； 源與受體間關係 ； 沉降 ； 後推氣流軌跡 ； 聚類分析

並列摘要

Taiwan is located to the southeast of the East Asian continent. In winter, the northeast monsoon can transport air pollutants from East Asia to Taiwan. In spring, the prevailing westerlies can transport the biomass burning emitted pollutants from the Indochina Peninsula to the high elevation mountain areas of Taiwan. This long-range transport of pollutants can influence the air quality, environment, and ecosystem of Taiwan. Lulin Atmospheric Background Station (LABS, 2862 m a.s.l.) was established in central Taiwan in 2006 to study the impact of regional and long-range transported air pollutants on the environment and ecosystem in Taiwan. Therefore, the location of LABS is ideal for the study of characterizing the export of mercury(Hg) from the East Asian continent to its downwind region.
In 2010, mean concentrations(±SD) of gaseous element mercury(GEM), reactive gaseous mercury(RGM) and particulate mercury(PHg) measured at LABS were 1.56(±0.42) ng m-3, 13.95(±31.32) pg m-3 and 0.71(±2.65) pg m-3, respectively. Mean concentrations(±SD) of carbon monoxide(CO) and ozone(O3) were 143(±67) and 33.8(±15.0) ppb, respectively. Good positive correlation between GEM and CO(r = 0.78) indicated that the variation in GEM concentrations was related to anthropogenic activities. The volume-weighted mean (VWM) concentration of mercury in rainwater was 8.8 ng L-1. Total precipitation depth was 3173.2 mm. Wet deposition flux was 33.7µg m-2. Total dry deposition flux was 69.5 μg m-2, with 58.8, 10.6 and 0.1 μg m-2 contributed by GEM, RGM, and PHg, respectively. Wet deposition flux was higher than dry deposition flux in summer because of higher rainfall amount. The opposite was observed in the other seasons. It has been suggested that the dry deposition flux was more important in North America (Temperate Zone). Mean dry and wet deposition fluxes in North America were about 15 and 10 µg m-2, respectively. The wet deposition flux in North America is about one-third of Mt. Lulin’s (Subtropical Zone) value because of higher rainfall in Taiwan.

並列關鍵字

atmospheric mercury ； long-range transport ； biomass burning ； source-receptor relationship ； deposition ； backward trajectory ； cluster analysis

參考文獻

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