| 摘要: | 每年春季3-4月為東南亞生質燃燒活動頻繁的時間，此時當地為春耕時期會大規模燃燒農廢物與森林，進而產生大量的氣體與氣膠污染物。此時假使受到天氣系統的抬升，如鋒面前緣抬升與深對流作用，會將地面污染物抬升至2-5公里的高度。本研究選擇台灣中部海拔2862公尺的鹿林山上進行氣膠採樣，以瞭解東南亞生質燃燒在低自由對流層(2-5公里)的傳輸特性。採樣時間為2003年4月與2004年3月進行兩次生質燃燒事件採樣，以及2003年12月的背景大氣氣膠採樣。利用人工採樣器與連續監測儀器，探討在生質燃燒與背景期間鹿林山高山氣膠特性的變化，並利用後推氣流軌跡線與天氣資料對氣膠的來源進行研判。除此之外，為了瞭解近生質燃燒源的氣膠特性，以開放式燃燒的方法燃燒稻草、木屑等生質，以人工採樣器收集氣膠。將實驗結果與在鹿林山採樣的結果相互比較，瞭解生質燃燒剛產生的氣膠與經過長程傳輸後的氣膠之間有何不同。 結果顯示：在非生質燃燒季節，鹿林山背景氣膠中PM2.5與PM10平均濃度為2μgm-3與4μgm-3。在氣膠體積濃度粒徑分佈在0.1-0.3μm， PM2.5中其化學成分主要以硫酸鹽、銨鹽、硝酸鹽與碳成分為主。在生質燃燒影響下，氣膠質量濃度較高，PM2.5中的硫酸鹽、銨鹽、硝酸鹽與氣膠碳濃度明顯上升，且發現有較高濃度的鉀離子在細氣膠中，而在PM2.5-10中有較高濃度的塵土與海鹽成分。另外，發現在生質燃燒期間PM2.5中的左旋葡萄糖(levoglucosan)成分有明顯濃度較高的趨勢，平均濃度為48ngm-3，比背景大氣時高出幾十倍。另外從氣膠不同溫度揮發有機碳成分的解析中，發現在非生質燃燒期間以低溫揮發的OC1佔百分比為最高，在生質燃燒影響期間則變為高溫揮發的OC3佔百分比最高。 藉由後推氣流軌跡分類的結果，發現只要是經過生質燃燒源區的軌跡線，且有生質燃燒事件產生，此時所收集的濾紙樣本中，有明顯生質燃燒的特徵，像是在PM2.5中有較高濃度的微粒碳、鉀離子與左旋葡萄糖成分。並以氯離子損失與海水加強因子推論鹿林山氣膠水溶性離子來源，發現受到海水氣膠的影響較低。在細氣膠中主要以二次硫酸鹽、二次硝酸鹽與燃燒貢獻為主。粗氣膠中則是有部分海鹽與塵土貢獻。另外從生質燃燒產生源的實驗中發現，生質燃燒剛產生的氣膠主要是以PM2.5為主，其中氣膠碳成分佔絕大部分，將近佔總質量的70~80%，且有較高比例的鉀離子、氯離子。但在經過長程傳輸後的生質燃燒PM2.5中，則是以硫酸鹽、銨鹽、硝酸鹽與鉀離子的比例較高。推斷生質燃燒氣膠在經由長程傳輸之後，仍保有部分生質燃燒氣膠的特性，但會在傳輸過程中加入硫酸根離子、銨根離子。 Every spring from March to April, it is the time period for active biomass burning in East Asia. The aerosols produced from biomass burning were lifted 2 to 5 Km above the ground by the rise of a frontal system and a strong convective air mass. They were then transported to the other areas by the air mass in the high altitude. This study chose Lu-Lin Mountain, as the study site for aerosol collection, which situated in the middle Taiwan 2,862 m above sea level. The goal of this study is to observe the aerosol characteristics from biomass burning in East Asia via long range transport in lower free troposphere. The observations included two biomass burning events in April 2003 and March 2004 and a background observation in December 2003. This study used manual sampler and continuous measuring instrument to obtain the information of aerosol from the two biomass burning events and bacdground. Besides, in order to infer the characteristic of the fresh aerosol near biomass source, we burned wood and hay and used manual sampler to correct fresh aerosol. Comparing the aerosol of fresh-burning biomass and Lu-Lin Mountain, we can tell the differences of long-range transport. The results showed that PM2.5 and PM10 concentrations are 2 and 4 μgm-3 for background observations, respectively. The peak diameter is in the range between 0.1-0.3 μm and major chemical species are sulfate, ammonium ions, nitrate, and carbonaceous materials. For biomass burning events, aerosol mass was increased and specises like sulfate, ammonium ions, nitrate, and carbonaceous materials were all enhanced. In addition, potassium ion was found significantly increased in aerosol fine fraction. Moreover levoglucosan in aerosol was detected high during biomass burning period with an average of 48 ngm-3. In TOR analysis, OC1 is in majority in background observation and OC3 is predominant in biomass burning events. By using Hysplit backward air trajectory model, we find that aerosol are high in potassium ion, carbonaceous materials, and levoglucosan as the air mass passed biomass-burning sources. Besides, using Marine Enrichment Factor(MEF) and Chlorine Loss Method(CLM), we find that the water-solube ions in fine fraction are contributed from secondary sulfate, secondary nitrate and biomass burning. In contrast, the coarse particles included soil materials and seat-salts. Finally, aerosols from long range transport contain high fraction of sulfate, nitrate, and ammonium ions as compared to high carbonaceous material, potassium, and chloride ions. |
