| 摘要: | 東南亞地區生質燃燒活動發生的季節主要在每年的3到5月，這些開放式燃燒產生的氣膠和氣體會影響大氣輻射收支，並影響到下風地區的空氣品質。台灣正好位於氣團傳輸的下風處，是觀測東南亞生質燃燒的最佳地點。為了避免受到平地污染物的干擾，本文從2006年6月至2007年4月在海拔2,862公尺高的鹿林站進行8次大氣氣膠觀測，以期瞭解受生質燃燒氣團傳輸影的氣膠特性。 本文使用安裝與未安裝活性碳管的採樣器來推估使用氣膠碳成份，未安裝活性碳管但在濾紙組合內安裝三張石英濾紙，估算的生質燃燒和非生質燃燒事件期間氣膠碳成分分別為8.5 ± 3.89 μg-C m-3和1.78 ± 1.07 μg-C m-3，空氣中揮發性有機物(VOCs)的OC等似平均濃度為0.54 ± 0.24 μg m-3，從濾紙上微粒揮發的VOCs是可忽略的；但安裝活性碳管採樣器的微粒揮發VOCs是明顯的。在鹿林站使用鐵氟龍和石英兩種濾紙材質採集氣膠，分析其水溶性離子發現除了氯離子以外，都是以石英濾紙分析得到較高的濃度，顯示出有些成分不易從鐵氟龍濾紙萃取出來。 鹿林站於生質燃燒事件日細氣膠濃度為非生質燃燒期間濃度的5倍，銨根離子、硝酸根離子和硫酸根離子平均濃度分別為1.37μg m-3、1.58μg m-3和3.30μg m-3。生質燃燒污染物指標之ㄧ的鉀離子濃度為0.59μg m-3，是非生質燃燒期間的4倍。OC各成份濃度在生質燃燒事件日觀測期間都明顯增加，但元素碳(EC)只有EC1-OP濃度增加。左旋葡萄糖在生質燃燒事件日濃度為非生質燃燒期間的9倍，低分子量二元酸以oxalic acid為優勢物種，且與硫酸鹽有很好的相關性，顯示兩者有相同的來源。 鹿林站採集雲霧間隙氣膠的結果顯示氣膠成分中以二次污染物銨根離子、硝酸根離子和硫酸根離子為主。碳成分中以低溫揮發的OC1和OC2比例增加最多，推測這些低飽和蒸汽壓的VOCs於傳輸的過程中會凝結在細氣膠表面，導致OC1和OC2濃度增加。 逆溯軌跡線分類方面，海洋傳輸(NBB-O)由於不受污染，因此所有成分濃度都是最低的；大陸傳輸(NBB-C)發現粗粒徑氣膠濃度明顯上升，推測可能有受到大陸沙塵的影響；比較源區(source)與源區經中國南方(source region via southern China)的結果發現後者在粗細粒徑氣膠、硫酸鹽以及oxalic aicd濃度都有明顯的增加。 為了比較新生和傳輸氣膠成分上的差異，本文進行稻草燃燒實驗，結果顯示燃燒後的煙團主要是以氯化鉀的形式存在，經過短程傳輸後氯離子會快速損失，但鉀離子仍為主要的物種。硝酸鹽於新生和短程傳輸過程中都不是主要的物種，顯示硝酸鹽不會在生質燃燒過程中產生。 Biomass burning (BB) in Southeast Asia frequently occurs from March to May every year. The large-scale open burning produces tremendous amount of aerosol and gases to influence atmospheric radiation budget and the air quality in the downwind area. Taiwan is located in the downwind area of the air masses transported from Southeast Asia. This makes it one of the best places to observe the modification on atmospheric aerosol from BB plume. In order to avoid the interference from ground-level pollution, this study observed atmospheric aerosols at the Lulin Mountain site (2,862 m a.s.l.) for eight times from June 2006 to April 2007. The objective of this study is to investigate aerosol properties modified by BB plume. The estimates of aerosol carbons were compared between sampling devices with and without a preceeding activated carbon denuder. The estimates of aerosol carbons from the sampling device without a preceeding activated carbon denuder but with three quartz filters in series during BB event and non-event period are 8.5 ± 3.89 μg-C m-3 and 1.78 ± 1.07 μg-C m-3, respectively. Meanwhile, the average of volatile organic carbons (VOCs) was estimated at 0.54 ± 0.24 μg-C m-3 in terms of equivalent organic carbon (OC). The VOCs evaporated from deposited particles were found negligible. However, the VOCs evaporated from deposited particles from sampling device with a preceeding activated carbon denuder were obvious. The aerosol water-soluble ions resolved from quartz filters were more abundant than those from Teflon filters except for chloride ion. This indicates some species might be retained by the extracted Teflon filters. In the BB event, fine particle concentration was five times as much as that in the non-event period. Ammonium, nitrate, and sulfate ions are 1.37μg m-3, 1.58μg m-3, and 3.30μg m-3, respectively, during the event period. One of the BB tracers, potassium ion, is at 0.59μg m-3 during the event period, which is four times as high as that in the non-event period. The OC fractions increased significantly during the event period; however, only EC1-OP of EC fractions increased significantly. Meanwhile, aerosol levoglucosan was nine times higher in the event than that in the non-event period. In addition, aerosol oxalic acid was the dominant species of low-molecular-weight dicarboxylic acids; it correlated well with sulfate ion. This suggests both were from the same source origin. The analyses of cloud interstitial aerosol collected at the Lulin site show secondary pollutants such as ammonium, nitrate and sulfate ions are the three major water-soluble ions. Among aerosol OC fractions, low-temperature evolved OC1 and OC2 increased more than the others, it suggests that low-vapor-pressure VOCs condensed on the surface of fine aerosol during transport. In the classification of back-trajectory pathways, because of the pathway from the ocean during the background period belong to unpolluted, the concentrations of all of the components from there are lowest; the coarse mode particle concentrateion from China pathway during the background period increase significant, this suggest that the aerosol form China may be affected by dust storm; the result of comparison between source region and source region via southern China show that the latter concentrateion of coarse and fine aerosol, sulfate and oxalic acid enhance significant. In order to compare the difference between fresh and aged aerosol, this study conducted an experiment of rice straw burning in the field. The results show that potassium chloride is significant in newly burned smoke. Part of chloride ion was lost soon after a short distance transport, but potassium ion remained abundant in aerosol water-soluble ions. In contrast, nitrate ion was not significant in both fresh and slightly aged aerosols. This reveals that nitrate ion is not produced in the BB process. |
