| 摘要: | 每年3~5月是東南亞生質燃燒最活躍的季節，在這個地區會有大規模的農廢和森林燃燒，產生大量的氣體與氣膠。這些生質燃燒產生的氣膠經由氣團傳輸會影響到下風地區的空氣品質。台灣位於氣團傳輸的下風地區，是觀測東南亞生質燃燒的適當地點，為了避免周遭環境污染物的干擾，本文從2005年8月至2006年4月在海拔2,862公尺鹿林山進行大氣氣膠觀測，研究期間涵括生質燃燒事件日與平常日，足以比較長程傳輸生質燃燒與背景氣膠氣膠特性的差異。 結果顯示：在非生質燃燒期間，鹿林山的PM2.5質量濃度有明顯的四季變化，夏季濃度最高，平均濃度達7.9 µg m-3，秋季濃度最低，平均濃度為4.1µg m-3。氣膠水溶性離子成分，四季均以硫酸鹽和銨根離子為主；氣膠碳成分則以有機碳為優勢物種；各溫度下有機碳成分是以較低溫度揮發的OC1~OC3為主；元素碳則是以較低溫度揮發的EC2所佔比例較大。氣膠的氣體前驅物，四季均以氨氣為優勢物種；氨氣和銨根離子所佔比例接近。 在生質燃燒期間，鹿林山氣流軌跡源自生質燃燒源區時，氣膠質量濃度明顯較非生質燃燒期間為高。氣膠離子成分以硫酸鹽、硝酸鹽、銨根離子和鉀離子為優勢物種；氣膠碳成分明顯較高，有機碳平均濃度為2.1μg m-3，且以OC3為主，元素碳平均濃度為0.8 μg m-3，且以EC1-OP為優勢物種。氣膠的氣體前驅物同樣以氨氣為優勢物種，二次污染物以硫酸鹽較多，生質燃燒指標物種左旋葡萄糖(levoglucosan)和二元酸平均濃度分別為10.4 ng m-3和244.8 ng m-3均較背景觀測時為高。 為了比較新鮮和傳輸一些距離生質燃燒氣膠成分的差異，本文收集稻草在農田進行焚燒並收集分析氣膠特性。結果發現近污染源以細氣膠為主，氣膠碳成分濃度佔質量濃度超過50%，且有較高濃度的鉀離子和氯離子；污染源下風處的短程傳輸氣膠也是以細氣膠為主，有較高的鉀離子和有機碳成分。新生氣膠離子結合型態為氯化鉀，短程傳輸氣膠結合型態則以硫酸鉀或硝酸鉀為主。 在夏季觀測期間鹿林山常在中午過後，雲霧由山腰逐漸飄上來籠罩在整個地區。本文收集分析雲霧間隙氣膠，發現質量濃度較背景觀測時高，PM2.5平均濃度為15 μg m-3，氣膠水溶性離子成分以硫酸鹽和銨根離子為優勢物種；碳成分則是以元素碳增加較多。 Biomass burning in South East Asia is active from March to May every year. Massive burning of agricultural wastes and deforestation generate a great amount of gaseous and aerosol species. The generated pollutants from biomass burning can influence the air quality in the downwind areas through long-range transport. Taiwan is located in the downwind side of air masses transported from the burning area and is an appropriate place for transported pollutants. To avoid the interference from local pollution sources, this study collects atmospheric aerosol at Lu-Lin mountain (2,862 m a.s.l) site from August 2005 to April 2006. The study period includes biomass burning events and background observations. This will provide an in-depth contrast for transported biomass burning aerosol and background aerosol. The results show that a distinctive variation of PM2.5 in different seasons is observed for non-biomass burning period. An average of PM2.5 at 7.9 µg m-3 in summer is the highest and a value of 4.1µg m-3 in autumn is the lowest. In all seasons, PM2.5 sulfate, PM2.5 ammonium ion, and PM2.5 organic carbon (OC) are the dominant species. For aerosol carbon fractions evolved from different temperatures, OC1, OC2 and OC3 are the predominant OCs; while EC2 is the major component among elemental carbons (ECs). Ammonia is found the dominant precursor gas with mixing ratio closes to ammonium ion. Aerosol mass concentration transported from biomass burning area is observed significantly higher in the burning events than in the non-burning background. Sulfate, nitrate, ammonium ion, and potassium ion are major species in the resolved water-soluble ions. Aerosol carbon is higher in the event with an average OC value of 2.1μg m-3 dominated by OC3. In addition, the average of EC is at 0.8 μg m-3 with EC-OP as the dominant fraction. Ammonia again is the dominant species in aerosol precursor gases and sulfate is the most abundant aerosol species in the biomass burning event. The averages from aerosol levoglucosan and dicarboxylic acids, the known biomass burning tracers, are 10.4 ng m-3 and 244.8 ng m-3, respectively. They both are higher in biomass burning period than background time. For the comparison of aerosol properties from freshly burnt and that transported from the source for some distance, this study conducts rice straw burning in the field and collects aerosol for analysis. The aerosol collected near the source is dominated by PM2.5 with more than 50% of carbon in aerosol mass and is abundant of potassium and chlorine ions. Moreover, the fresh burnt aerosol is rich in the compound form of potassium chloride. In contrast, this compound is converted into potassium sulfate and potassium nitrate after a short distance of transport. Cloud and fog are frequently moved up from lower elevation to cover the site in the summer afternoon. The interstitial aerosol is collected without the mix of fog or cloud droplets. The PM2.5 average from this collection is at 15 μg m-3, which is higher than the value in the background observation. Sulfate and ammonium ions are the dominant water-soluble ions and EC is more enhanced than OC in aerosol carbons. |
