| 摘要: | 生質燃燒活動會產生大量溫室氣體及氣膠，造成地區性的空氣污染及酸雨，也會影響雲的特性、雲量等，間接影響大氣輻射平衡及全球氣候的變化。 每年春季是亞洲中南半島生質燃燒活動頻繁的時間，在適當的天氣系統傳輸下會將當地的污染物帶到台灣。本研究選擇在台灣中部海拔2,862公尺的鹿林山天文觀測站做為大氣氣膠觀測地點，在2004年秋末及2004年12月中旬進行背景觀測，在2005年4月進行生質燃燒事件日觀測；另外，以實驗模擬近生質燃燒源的活動。分析項目包括氣膠質量濃度、氣膠水溶性離子、碳成分、左旋葡萄糖與二元酸。 本研究發現在受到生質燃燒影響時，細粒徑氣膠質量濃度明顯較背景觀測期間高出3倍之多，生質燃燒事件期間PM2.5濃度平均為15.4 μg m-3。在氣膠水溶性離子組成，背景觀測及生質燃燒事件中，顯著離子物種都是銨根離子、硫酸根離子，另外，鉀離子濃度在生質燃燒事件比背景高出3倍。在氣膠碳成分方面，生質燃燒事件發現揮發裂解碳(OCpy)有明顯增加的情形，元素碳則以低溫元素碳(EC1-OP)為顯著物種。氣膠左旋葡萄糖在生質燃燒事件有較大的濃度值，平均為46.5 ng m-3。在少數雲霧氣膠的觀測，硫酸根離子和元素碳都有增加的情形。 本研究進行的稻草及華山松的燃燒氣膠採樣，顯示近生質燃燒源所產生的氣膠多是以細粒徑氣膠為主，且水溶性離子組成多是以氯離子與鉀離子為主；碳成分分布物種則以高溫揮發有機碳(OC3)所佔比例較多，元素碳為EC1-OP所佔比例較顯著。另外，針對不同燃燒狀態下採集分析的結果，悶燒狀態比燃燒狀態產生較多的細粒徑氣膠，水溶性離子組成多是以燃燒狀態有較高的濃度值；在碳成分方面，分別計算OC各物種佔OC與EC各物種佔EC的比例，發現燃燒狀態在高溫揮發有機碳(OC4)和OCpy所佔比例較悶燒狀態高，而悶燒狀態則是在低溫揮發有機碳(OC2)和OC3佔有較大的比例。 在物種指標方面，生質燃燒氣膠主要的物種有碳成分及鉀離子，利用這些物種進行比值的探討。生質燃燒長程傳輸及近污染源K+/EC的比值分別為0.25、0.36，EC/TC在長程傳輸與近污染源比值分別為0.20、0.09，OC/EC對長程傳輸及近污染源的比值為4.58、9.13。另外，計算總二元酸與左旋葡萄糖的比值，計算得值為4.55。利用左旋葡萄糖與鉀離子的比值判斷不同燃燒狀態，獲得燃燒狀態為0.023，悶燒狀態為0.044。本研究顯示了生質燃燒氣膠近污染源觀測和長程傳輸的對比。 Biomass burning produces a great amount of greenhouse gases and aerosols, which cause not only local air pollution and regional acid rain but also affect the formation of clouds and thus regional radiation balance as well as global climate change. Every spring season, biomass burning is frequently occurred in the Southeast Asia. Under the transport of an appropriate weather system, the air mass can carry the produced pollutants. This study chose Lu-lin Mountain (2,862 m a.s.l.) situated in central Taiwan for observation on aerosols from long-range transport. The observations include background periods in Autumn and December in 2004 and event period in April 2005. In addition, the experiment was conducted to sample aerosols near the burning source of rice straw and pine. The analyzed aerosol properties include mass concentration, water-soluble ion, carbonaceous content, monosacchride anhydrides, and dicarboxylic acids. The results show that PM2.5 average in the period of long-range transport biomass burning was 15.4 μg m-3, which was clearly three times than that of the background observation. For water-soluble ions, the dominant species were ammonium and sulfate both in the background observation and in the the period of biomass burning. However, potassium ion observed in the biomass burning was three times more than that of the background. For carbonaceous content, volatility-corrected OC (OCpy) was increased significantly during the biomass burning event. The low temperature (EC1-OP) was dominant in elemental carbon (EC). Aerosol levoglucosan, which is considered as a cellulose burning tracer, was observed higher at an average of 46.5 ng m-3 during the biomass burning event. From the collection of cloud and fog aerosol, both sulfate ion and EC were found higher than background samples. In the study of near source biomass burning, the results showed that the aerosol produced was predominant in the fine mode. Water-soluble ions were dominated by chloride and potassium ions. In terms of carbon fractions, high-temperature voltilized OC3 was the most important species and EC1-OP was the major species in EC. In addition, the results of different combustion phases showed that smoldering phase emitted more fine aerosols than flaming phase. However, the water-soluble ions were in greater amount for flaming phase than smoldering phase. As for carbonaceous fractions, the ratios of high-temperature voltilized OC4 and OCpy in OC for flaming phase were greater than those of smoldering phase. In contrast, smoldering phase had greater ratios of low-temperature voltilized OC2 and OC3 in OC than those of flaming phase. For aerosol tracer study, potassium ion and carbons were found useful in comparing aerosols from near source and long-range transport. The K+/EC values for long-range transport and near source of biomass burning were 0.25 and 0.36, respectively. Meanwhile, the values of EC/TC for long-range transport and near source of biomass burning were 0.18 and 0.09, respectively. For OC/EC, the values were 4.58 and 9.13, respectively, for long-range transport and near source of biomass burning. Furthermore, the ratio of total dicarboxylic acids to levoglucosan was calculated at around 4.55. In using the ratio of levoglucosan to potassium ion as a reference for assessing different phases of biomass burning, the value was 0.023 for flaming phase and 0.044 for smoldering phase. In summary, this study demonstrates a contrast of aerosol properties from biomass burning between near source and long-range transport. |
