| 摘要: | 鹿林山標高2,862公尺，是一個評估東亞大陸污染傳輸和西太平洋背景的適當地點。本研究於2008年9月~2009年4月在鹿林山採集大氣氣膠樣本，並將採集樣本歸類為生質燃燒期間與非生質燃燒期間。兩個期間氣膠水溶性離子優勢物種均為硫酸根離子與銨根離子，但在生質燃燒期間，硝酸根離子與鉀離子濃度會顯著增加。生質燃燒期間，氣膠碳成分分別以OC3和EC1-OP為有機碳(OC)及元素碳(EC)主要物種；非生質燃燒期間，氣膠有機碳的OC1及元素碳的EC2是兩個優勢氣膠碳成分物種。生質燃燒期間與非生質燃燒期間左旋葡萄糖是氣膠無水單醣化合物唯一優勢物種，但以生質燃燒期間濃度增加顯著。生質燃燒期間與非生質燃燒期間氣膠二元酸優勢物種均為oxalic acid，表示oxalic acid是二元酸前驅有機物或是其他二元酸的最終產物，在生質燃燒期間oxalic acid濃度也是增加的。 本研究於觀測期間特別觀測氣膠水可溶有機碳(WSOCp)，發現WSOCp主要由低揮發性的OC2、OC3構成，WSOCp在生質燃燒期間與生質燃燒指標有較好的相關性，顯示WSOCp也可作為評估生質燃燒事件的指標。大氣溫度與WSOCp有良好相關性，降雨會顯著降低WSOCp濃度，但不會影響氣相水可溶有機碳(WSOCg)濃度。去除掉降雨事件後，當相對濕度大於70%時，WSOCp佔(WSOCp+WSOCg)比例會顯著上升。鹿林山氣膠中，硫酸根離子主要與銨根離子(線性相關R2=0.90)結合，少部分與鈣離子、鈉離子結合，硫酸根離子與銨根離子結合型態為(NH4)3(H)(SO4)2。 採樣期間氨氣對硫酸氣和硝酸氣有中和不足現象，雖然生質燃燒期間有較多硝酸鹽產生，但硝酸氣並非中和氨氣的主要氣體。2007~2009年鹿林山氣膠量測和中和所需的銨根離子莫耳比(NH4+?meas/NH4+?calc)平均值為0.79，與歐洲瑞士少女峰1999~2005年觀測的0.8差異不大，顯示中歐及東亞地區氨氣均不足以完全中和硫酸氣和硝酸氣。從2009年春季鹿林山受生質燃燒影響時間較長且?NH4+?meas/?NH4+?calc與硫酸鹽、硝酸鹽相關性(線性相關R2=0.53、0.32)較前兩年為佳；顯示氨氣中和硫酸氣和硝酸氣，可能需要較長的反應時間以形成足夠的氣膠硫酸鹽和硝酸鹽。 本研究總計進行五次雲霧事件的前、中、後氣膠採樣觀測，有四次事件雲霧氣流有挾帶氣膠過來；在雲霧事件中，未中和的銨根離子多，硝酸根離子被活化形成雲滴的效率最好，其次為硫酸根離子，銨根離子的效率最低。氣膠碳成分中，OC的滌除率在不同期間相近。雲霧事件過後，可能有乾淨氣團過來使PM1氣膠濃度下降。 Mt. Lulin (2,862m a.s.l.) is a suitable site to assess pollution transport from East Asian continent and West Pacific background. This study observed atmospheric aerosol at Mt. Lulin from September 2008 to April 2009 and split the collected samples into from biomass-burning (BB) and non-biomass-burning (NBB) periods. Aerosol water-soluble ions are dominated by sulfate and ammonium ions during both BB and NBB periods. However, aerosol nitrate and potassium ion levels were noticeably increased during BB period. For aerosol carbons during BB period, OC3 and EC1-OP were the major fractions in organic carbon (OC) and elemental carbon (EC), respectively. In contrast, OC1 in OC and EC2 in EC were the two dominant carbon fractions during NBB period. Aerosol levoglucosan was the only dominant species in aerosol anhydrous monosaccharide during both BB and NBB periods. The level of aerosol levoglucosan was significantly increased during BB period. Oxalic acid was the dominant dicarboxylic acids during both BB and NBB periods. This implies that oxalic acid is the precursor species or the end product of other dicarboxylic acids. The concentration of aerosol oxalic acid was also increased during BB period. Aerosol water-soluble organic carbon (WSOCp) was specifically observed during observation period. The analysis reveals that low-temperature volatiled OC2 and OC3 are the major fractions of WSOCp. The concentration of WSOCp had a better correlation with BB tracers during BB period. It indicates that the WSOCp can be a good tracer for BB event. Atmospheric temperature is found having a good correlation with WSOCp. Rain fall may significantly reduce WSOCp concentration but not for gaseous water-soluble organic carbon (WSOCg). By excluding raining events, the fraction of WSOCp in (WSOCp+WSOCg) is increased when the relative humidity is above 70%. In Mt. Lulin aerosol, sulfate ion is mainly combined with ammonium ion (R2=0.90) and less with calcium and sodium ions. The compound form of sulfate and ammonium ions is (NH4)3(H)(SO4)2. During the study period, ammonia gas was found insufficient in neutralizing sulfuric and nitric gases. Although more aerosol nitrate was observed during BB period, nitric gas is not a major acidic gas in neutralizing ammonia gas. The mole ratio of measured over calculated aerosol ammonium ions (?NH4+?meas/?NH4+?calc) is averaged at 0.79 for the period of 2007－2009. This value is not deviated too much from 0.8 at Jungfracjoch in European Swiss Alps observed during 1999－2005. It indicates that the ammonia gas in middle Europe and East Asia is insufficient in neutralizing sulfuric and nitric gases. By considering longer BB period and higher linear correlation for ?NH4+?meas/?NH4+?calc with aerosol sulfate and nitrate (R2=0.53 and 0.32, respectively) in 2009 spring, this study infers that ammonia gas probably needs more time in neutralizing sulfuric and nitric gases to form sufficient aerosol sulfate and nitrate. Five cloud events were observed to collect aerosols at pre-cloud, in-cloud, and post-cloud periods in this study, respectively. Four cloud events transported aerosols to the collection site. Excess ammonium ion not neutralized is found in cloud event. The activation efficiency of water-soluble ions in the cloud event is the best for nitrate ion, followed by sulfate and ammonium ions. For aerosol carbon fractions, the scavenging ratio of OC is similar in different time periods. PM1 concentration is observed to drop after cloud event, which is probably due to cleaner air masses transported to the site. |
