| 摘要: | 中國大陸沿海廣大的工業區以及西北方沙漠區在春季經常發生沙塵暴，使得中國大陸成為東亞氣膠的主要產生地。台灣位於來自大陸氣流下風，每當發生冷高壓和沙塵暴，大陸工業污染物和黃沙會伴隨著適當的天氣系統南下，往往影響到台灣的空氣品質。 本研究選定台北縣石門鄉進行氣膠觀測，石門鄉地處台灣最北端，當台灣受大陸冷高壓影響時，石門成為台灣本島最先接觸大陸氣流的地方。從2003年5月開始至2004年4月，本研究每月在固定時段進行大氣氣膠監測，監測項目包含PM10、PM2.5氣膠及氣膠質量濃度粒徑分布，共完成了201個PM10及PM2.5有效樣本，並將所採集的樣本進行氣膠質量濃度、氣膠元素成分、氣膠水溶性離子成分及氣膠碳成分分析。 為探討大氣氣流傳輸的影響，本研究先將觀測時段分成受冷高壓與不受冷高壓影響時期，然後利用HYSPLIT後推氣流軌跡線將氣流細分成七種類別，以探討各種氣流來源氣膠化學組成變化及增益，最後再以今年抵台的三波沙塵作一解析。 研究結果顯示，不受大陸冷高壓影響的PM10平均氣膠質量濃度值大約為30 μg m-3，當受到大陸冷高壓影響時上升到60 μg m-3。PM10氣膠水溶性離子Na+和Cl-受冷高壓影響的濃度增加比例是不受冷高壓影響的4~10倍。PM10中NH4+與SO42-在受冷高壓影響時增加70 %與74 %，PM2.5中NH4+與SO42-在受冷高壓影響時增加66 %與70 %，在冷高壓影響期間NO3-於PM10和PM2.5中多出2倍左右。在氣膠碳成分方面，受到冷高壓影響的PM2.5 OC濃度增加12 %，但是EC受影響程度不大。PM10氣膠元素Al、Fe和Ca於冷高壓影響時增加60 %~80 %之間。 從後推氣流軌跡線的歸類，發現北台灣在不受長程傳輸氣膠影響時，以本地來源氣膠的質量濃度最低，其主要組成是以硫酸鹽為主，海鹽氣膠成分並沒有很大份量。當受到黃沙海洋傳輸氣流影響時，海鹽氣膠濃度會比非黃沙時期海洋傳輸高出33 %，非黃沙海洋傳輸則又比本地來源多出2.8~8倍海鹽氣膠，因此，黃沙時期海洋傳輸的海鹽氣膠濃度會比本地來源高出4~11倍。當氣流為黃沙大陸沿岸傳輸時，長程傳輸的氣膠比本地來源氣膠在質量濃度上會高出1.5~2倍，硫酸鹽為2倍，塵土元素中Al、Fe和Ca高出3倍而燃燒排放則會高達6倍並夾帶一些海鹽氣膠。非黃沙高壓迴流氣膠組成以硫酸鹽類、硝酸鹽類、和碳成分為主，其濃度均比本地來源氣膠高出15~135 %，但在黃沙高壓迴流傳輸類型中硝酸鹽類會比本地來源高出2~3倍，碳成分則約多出25~40 %。 以2004年沙塵與非沙塵事件比較，顯示沙塵影響期間粗粒徑(PM2.5-10)質量濃度比非沙塵期間高出0.9~1.5倍，並以第三波沙塵影響最嚴重。沙塵影響期間PM2.5水溶性離子濃度增加不顯著，PM2.5-10氣膠中的Cl-、Na+、Mg2+及Ca2+在沙塵期間濃度明顯增加0.9~7.5倍之間，NH4+反而是在PM2.5及PM2.5-10氣膠中濃度均減少的物種。碳成分在沙塵期間OC濃度有增加的趨勢，但EC在沙塵期間增加不明顯。氣膠元素顯示沙塵影響期間PM2.5-10中的Al、Ca和Fe等塵土元素比非沙塵期間多出9~15倍。 The contributions of industrial aerosols from vast coastal areas in the East China and the outbreaks of dust storms frequently occurred in northwestern desert areas in springtime make China a major source region of aerosols in the East Asia. Taiwan is situated in the lee side of air masses transported from China through cold high-pressure system (cold-high). The aerosols transported from industrial emissions and yellow dusts through a right weather system will affect the air quality in Taiwan. This study chose Shi-Men in Taipei County as the site for aerosol observation. Shi-Men is the first place in the whole island to encounter air masses from China due to its location in northern tip of Taiwan. This study collected atmospheric aerosols in the fixed time interval of each month from May 2003 to April 2004. In total, 201 samples of PM10 and PM2.5 were collected to resolve mass concentration, elemental contents, water-soluble ions, and carbonaceous contents. To investigate the effects of transported air masses, this study divided the study periods into periods under the influence of cold-high and non-cold-high. The air masses were further classified into 7 types of air masses using HYSPLIT back trajectory model from NOAA. This classification of air masses was adopted to differentiate variations and the enhancements of aerosol compositions of the individual air mass. The effects of yellow dusts on aerosol properties in this year will also be discussed. The results show that the average PM10 for the periods of non-cold-high and cold-high were 30 μgm-3 and 60 μgm-3, respectively. Water-soluble Na+ and Cl- of PM10 under the influence of cold-high were 4-10 folds more than that of non-cold-high. PM10 NH4+ and SO42- in cold-high periods were increased 70 and 74 %, respectively. Similarly, PM2.5 NH4+ and SO42- under the influence of cold-high increased 66 and 70 %, respectively. Meanwhile, NO3- both in PM10 and PM2.5 enhanced 2 times for the periods of cold-high. In contrast, aerosol organic carbon only increased 12 % under the influence of cold-high and even without a significant effect for aerosol elemental carbon. The Al, Fe, and Ca were enhanced 60-80 % under the influence of cold-high. Among the seven types of aerosol masses, aerosol mass concentrations were the lowest for local source contributions. Sulfate ion was predominant and with only a small contribution from sea-salts in local source type. The sea-salt aerosols increased 33 % for oceanic transport in yellow-dust periods as compared with that of non-yellow-dust periods. In addition, the sea-salt aerosols were 2.8-8 times higher for oceanic transport in non-yellow-dust periods and 4-11 folds higher in yellow-dust periods than that in local source contributions. Notably, the enhancement of aerosol mass was 1.5-2 folds for the air masses from coastal areas during yellow-dust periods to that of local source contributions. Moreover, sulfate ion was 2 times higher, elemental Al, Fe, and Ca were more than 3 times, and potassium ions was 6 times higher for the comparison between the air masses from coastal areas during yellow-dust periods and that of local source contributions. For the aerosols in non-yellow-dust high-pressure recapitulation periods, sulfate ion, nitrate ion, and carbonaceous materials were major components with concentrations 15-135 % higher than that from local source contributions. Nitrate ion was 2-3 times higher and aerosol carbon was 25-40 % higher in yellow-dust high-pressure recapitulation periods than that from local source contributions. The coarse particles (PM2.5-10) in yellow-dust events were 0.9-1.5 times higher than that in non-yellow-dust periods in 2004. The third yellow-dust event was noted the most severe one in 2004. The water-soluble ions of PM2.5 aerosols in yellow-dust events were only slightly enhanced. However, Cl-, Na+, Mg2+ and Ca2+ in PM2.5-10 were significantly increased 0.9-7.5 times during yellow-dust events. It is noted that NH4+ was the species decreased both in PM2.5 and PM10 aerosols in yellow-dust events. Aerosol organic carbon tended to increase but the increase of elemental carbon was insignificant in yellow-dust events. For the crustal materials in PM2.5-10 like Al, Ca, and Fe, they were 9-15 times greater in yellow-dust events. |
