| 摘要: | 中國沙塵暴對於東亞地區輻射的平衡、氣候的改變、能見度的衰竭、人類的健康以及生態系統的平衡有相當顯著的影響（Chung et al., 1996）。本研究於2001年3月到5月之間配合環太平洋主要國家對沙塵暴的監測，在台北縣石門鄉進行密集性的PM2.5及PM10氣膠採樣，並進行氣膠質量濃度、氣膠水溶性離子、碳成分、氣膠元素等氣膠成份的分析。 結果顯示台灣北海岸氣膠化學特性在沙塵暴與平常日有所差異，沙塵暴時期PM2.5、PM10及PM10-2.5氣膠平均質量濃度分別為43.7、124.4及80.8 μg/m3；平常日的PM2.5、PM10及PM10-2.5氣膠平均質量濃度則分別為26.0、50.6及24.5 μg/m3。這個結果展現沙塵暴時期主要是以PM10-2.5粗粒徑氣膠為主，其質量濃度為平常日的3.3倍。此外，沙塵暴時期較平常日凸顯的成分有水溶性離子的 ， 以及Ca、Fe、Si三種元素；沙塵暴時期的OC/EC介於1.5∼2.29低於平常日的3.26∼3.30，而且沙塵暴時期的 佔PM10及PM2.5氣膠質量濃度百分比均較平常時期為低，顯示沙塵暴會影響二次氣膠光化反應的生成。 在確認氣膠化學組成分析的準確性，利用質量重建方法可將PM10及PM2.5分析的化學成分回復到化合物的狀態，使得可解析百分比提升到79.3％及94％。從氯離子損失法的計算，我們發現61.8％ PM2.5氣膠是二次硫酸鹽；至於PM10氣膠則有38.5％的二次硫酸鹽及27.6％的海鹽氣膠。絕對主成份的分析指出，PM2.5氣膠的最主要來源為人類活動、交通污染及二次光化反應混合的污染源，貢獻質量濃度達65.5％；而PM10氣膠的最主要來源則為海水飛沫、塵土來源、農廢燃燒以及部分的二次光化反應的混合污染源，貢獻其質量濃度的61.7％。氯離子損失法與絕對主成份法推估的一致性，確認了本研究對氣膠污染來源推估的結果。 China dust storms play a significant role in the radiation budget, climate change, visibility degradation, health effects, and the equilibrium of ecosystems in East Asia (Chung et al., 1996). In collaboration with the major countries of Pacific Rim on the monitoring of China outflow, this study collects PM2.5 and PM10 at Shi-Men in Taipei County from March to May in 2001. Aerosol mass concentration, water-soluble ions, carbonaceous content, and elemental content were resolved from the collected filters. The results demonstrate a contrast of aerosol chemical properties between dust storm events and normal days in the Taiwan northern coast. During dust storm events, the average mass from PM2.5, PM10, and PM10-2.5 was 43.7, 124.4, and 80.8 μg/m3, respectively. In contrast, that of PM2.5, PM10, and PM10-2.5 was 26.0, 50.6, and 24.5 μg/m3, respectively. It shows that PM10-2.5 dominated PM10 fraction with more than triple fold in the dust events as compared to normal days. In addition, the concentrated species in the dust storm events were Ca2+, Ca, Fe, and Si. For the ratio of organic carbon to elemental carbon (OC/EC), the values in the dust storm events ranged between 1.5~2.29 that were smaller than 3.26~3.30 in the normal days. More, the fraction of SO42- in PM10 and PM2.5 during the events was found smaller than that of normal days. This result implies the hindrance of dust storms on the formation of secondary aerosols. In validating the analytical accuracy on aerosol composition, a method of reconstructed mass was adopted to convert aerosol species into aerosol compounds. The method increased the resolved mass fraction PM2.5 and PM10 to a value of 79.3 and 94%, respectively. From the calculation of chlorine loss, we found 61.8% of PM2.5 is secondary sulfate, whereas 38.5 and 27.6% of PM10 is secondary sulfate and sea-salt aerosol, respectively. Meanwhile, the absolute principal component analysis shows the most significant source of PM2.5 contributed 65.5% of mass concentration, which is a source mixed with anthropogenic activity, vehicle emission, and secondary reactions. In contrast, sea-salt spraying, resuspended dusts, agricultural burning, and part of the secondary reactions contributed 61.7% of PM10. The consistency between chlorine loss and absolute principal component methods confirms the results of aerosol source apportionment in this study. |
