| 摘要: | 研究探討台南市區中秋節前後時期之大氣氣狀物及PM2.5氣膠化學組成中無機鹽類、羧酸、醣醇類、脫水醣類之特性與其生成來源及粒徑分佈，進而瞭解節慶活動是否影響都市地區之空氣品質。
在都市大氣氣狀物之平均濃度高低依序為NH3>SO2>HCl>HNO3>HNO2>oxalic acid，PM2.5無機鹽類的濃度依序為SO42- > NH4+ > NO3- > Na+，此四物種的質量濃度平均佔PM2.5質量的42.8±5.6%，顯示PM2.5濃度受交通排放及光化產物影響，同時因靠近海邊亦受海洋飛沫之影響，此外，氣膠離子組成中最主要物種：SO42-及NH4+ ，其主要粒徑均分布於液滴峰(Droplet mode)之0.54 mm與凝結峰(Condensation mode)之0.19 mm，又以droplet mode之波峰尤為明顯。
PM2.5氣膠羧酸以oxalate之濃度最高，此為羧酸最終產物，其平均濃度佔PM2.5 mass 的0.69±0.19%，而無機鹽類最終產物：非海鹽硫酸鹽(Non-sea salt SO42-, nss-SO42-)佔PM2.5 mass的21.7±5.9%，oxalate卻僅為nss-SO42-的3.18±0.86%，顯示都市環境氣膠無機鹽類遠多於有機物種。秋季各時期之acetate/formate (A/F)的平均比值為1.36±0.39，顯示此時期之大氣PM2.5氣膠處在較原生物種之貢獻，再者malonate/succinate平均比值為0.44±0.22，更顯示台南市區之大氣氣膠主要受自交通排放影響。
代表生質燃燒指標物種的levoglucosan在本研究期間的都市PM2.5氣膠平均佔質量的0.051±0.049%，但在中秋節慶前後期間未有高濃度的上升，其濃度佔PM2.5 mass的0.021±0.009%，然而在中秋節慶之後的一般空氣品質時期levoglucosan卻有較明顯的濃度增加，其濃度佔PM2.5 mass的0.068±0.048%，並與PO43-、erythritol、mannosan的濃度變化有高度相關性，其相關係數介於0.76-0.94 (p value <0.05) 之間，結合氣流逆軌跡發現台南市區受長距離境外農業廢棄物的生質燃燒產物及伴隨燃燒源當地土壤微生物一併被燃燒之產物的影響與貢獻。
This study is to investigate the characteristics of atmospheric gaseous pollutants and chemical composition of PM2.5 aerosol in Tainan city during the Mid-Autumn Festival. The characteristics of PM2.5 aerosol, which consist of inorganic species, carboxylates, sugar alcohols and anhydrosugars are investigated along with probable sources and atmospheric particle size distribution to understand whether festival activities will affect the air quality in Tainan urban area.
The order in the concentration of urban atmospheric gaseous pollutants is NH3> SO2> HCl> HNO3> HNO2> oxalic acid. The PM2.5 concentration of inorganic species is the following order SO42- > NH4+ > NO3- > Na +, the mass concentration of these four species consisted of PM2.5 shows an average mass value of 42.8 � 5.6%, which indicates that PM2.5 concentration is influenced by traffic exhaust and photochemical reactions; furthermore, the investigated area is also subject to be impacted by of marine droplets due to close to seashore. In addition, SO42- and NH4+, the major species of aerosol shows a particle size distribution with concentrtration peaks at 0.19 µm in the droplet mode and 0.54 µm in condensation mode. The concentration peak in the droplet mode is much more obvious than condensation mode .
The concentration of oxalate is the highest of PM2.5 carboxylates, which is the final product of the carboxylates and shows the average concentration with 0.69�0.19 % by PM2.5 mass, while the final product of inorganic species: non-sea salt SO42- (nss-SO42-) accounted 21.7�5.9 % of PM2.5 mass. Oxalate with only 3.18�0.86 % of nss-SO42- concentration indicates that the aerosol inorganic species are more abundant than the organic species within urban environment. The acetate/formate (A/F) ratio with the average value of 1.36�0.39 during the autumn season shows the contribution of PM2.5 aerosol attributes to the primary sources. Furthermore, the average malonate/succinate mass ratio is 0.44�0.22 in Tainan District, indicating that the atmospheric aerosol is mainly affected by primary traffic exhaust.
Levoglucosan is often used as a chemical tracer for biomass burning. Levoglucosan accounted for an average 0.051�0.049 % of the urban PM2.5 mass, but no obvious variation is observed in the period before and after the Mid-Autumn Festival, with 0.021�0.009 % of PM2.5 mass, while levoglucosan in the general air quality after the Mid-Autumn Festival, however, has a more significant concentration percentage increase with 0.068�0.048 % of PM2.5 mass. Additionally, levoglucosan were highly correlated with the concentration of phosphate, erythritol, mannosan, with the good correlation coefficient between 0.76-0.94 (p value <0.05). With the simulation of backward air mass trajectory, we found the urban airborne PM2.5 in the Tainan District during the period of general air quality was influenced and contributed by the agricultural waste biomass combustion products of long-range transportation and the burnt products of the corresponding local soil biota. |
