- 學位論文
2007-2009年台北都會區大氣汞時序變化：濃度、機制與來源
Temporal Variation of Atmospheric Mercury in Metropolitan Taipei during 2007-2009: Concentrations, Mechanisms, Sources and Implication
摘要
本研究量測2007~2009年台北都會區大氣元素汞(Gaseous elemental mercury, GEM)濃度，並利用大氣汙染物(NOx, HC, CO, SO2, PM2.5, PM10, O3)與氣象資料(地表氣溫、相對濕度、日照強度)進行分析探討大氣汞來源及其控制因子。大氣汞時序變化是由實驗室自製之大氣汞自動分析儀(Automated Gaseous Mercury Analyzer, AGMA)現場量測，2007~2009年大氣汞平均濃度為4.4±1.3 ng m-3 (n=1096)，濃度範圍為1.1~23.7 ng m-3，其結果顯示出獨特季節變化，大氣汞濃度在夏季最高，其次為冬季，濃度最低為春季與秋季，濃度較全球背景值高2~3倍。大氣汞濃度具有明顯日夜變化，呈現日高夜低的趨勢，最高值出現在中午至下午一點，最低值出現在半夜，此現象尤其是在夏季與秋季時特別顯著。利用主成分分析(principal component analysis, PCA)、相關性分析與氣流軌跡方法一同進行分析，顯示出在夏季時大氣汞變化與氣溫、日照強度及光化學產物(O3, PM10 and PM2.5)呈現正相關，白天升高日照強度與高氣溫導致大量汞由地表逸散至大氣，此外也會受到當地人為活動影響。在冬季大氣汞濃度與大氣汙染物(NOx, HC and CO)，且所量測到之GEM與CO比值為0.0059±0.0009 ng m-3ppbv-1，此結果與美國MBO測站、沖繩HSO測站所觀測到中國大陸地區之亞洲長程傳輸的結果相當接近，證實了冬季東北季風吹拂帶來了中國大陸工業源大氣汞至台灣，而春季與秋季介於季節轉換時期，大氣汞境外來源複雜。台北大氣汞濃度亦會受到特殊天氣事件影響，莫拉克及芭瑪颱風期間所帶來之瞬間強降雨、強陣風會降低GEM濃度且無日夜變化現象，沙塵暴事件將內蒙古地區揚起的沙塵隨高空西風帶向東傳送，在傳輸過程會帶來懸浮微粒及高濃度GEM至台灣地區。整體而言，台北都會區大氣中具有高濃度大氣汞，對相鄰周邊海域為大氣汞逸散之來源。
並列摘要
The study of characterizing the source attributions and controlling factors of atmospheric mercury (Hg) in metropolitan Taipei, Taiwan was performed by analyzing gaseous elemental mercury (GEM) with major air pollutants (e.g., NOx, HC, CO, SO2, PM2.5, PM10, O3) and meteorological data (e.g, surface air temperature (SAT), Relative humidity (RH), Wind, solar radiation (Rad)) during 2007-2009. Temporal GEM concentration, measured by a lab-made Automated Gaseous Mercury Analyzer (AGMA), ranged from 1.1 to 23.7 ng m-3 with an average of 4.4±1.3 (n=1096) during 2007-2009. Seasonal variation of GEM was observed in this study, high in summer and winter, and lows in spring and autumn, which concentrations were 2-3 times higher than global background. Diurnal GEM variation was observed with a peak in the early afternoon and a minimum in the mid-night during warm seasons, especially in summer and autumn. Principal component analysis (PCA) and correlation analysis showed GEM concentration was positively correlated to ambient SAT, Rad and photochemical products (O3, PM10 and PM2.5) in summer. High Rad and SAT in daytime caused substantial mercury emission from ground surface to atmosphere, besides emissions from the local human activities. In winter, GEM concentration was positively related to primary air pollutants (NOx, HC and CO). Back trajectory analysis and GEM/CO ratio were used for identifying long-range transport. In winter the measured GEM/CO ratio of 0.0059±0.0009 ng m-3ppbv-1 was similar to the results from Mount Bachelor observatory, USA (MBO) and Hedo Station, Okinawa (HSO). It demonstrated that the prevailed northeast monsoon in winter brought continental- and industrial-derived GEM from the mainland China to Taiwan. Hg sources in spring and autumn were variably influenced by where air masses from during alternation of monsoon. Temporal variation of GEM in Taipei was also affected by episodic weather events. During the summer typhoons of Morakot and Parma, the decline GEM with less diurnal change was observed likely due to heavy rains, clouds and strong winds. During dust storm periods, atmospheric particles were brought with high GEM levels from Mongolia and Siberia region to Taiwan via long-range monsoon transport. Overall, high GEM levels in the metropolitan Taipei could be an atmospheric Hg emission source to adjacent areas.