|摘要: ||本研究於2004年9月19日至10月20日及2004年11月26日至11月30日，分別代表非高污染時期及高污染時期進行日夜PM2.5及PM10之無機鹽類與二元有機酸之組成變異探討，並以5-100 nm奈米微粒之粒徑分佈，探討氣膠無機鹽類及二元酸之組成粒徑分佈研究，研究發現如下:
大氣氣膠之樣品進行採集時，先以圓環型固氣分離器(Annular Denuder Systems, ADS)，收集氣狀污染物，以避免人為污染(artifacts)產生，再者利用三層濾紙匣收集微粒，結果發現在Teflon濾紙(第一層)所採集之NO3-會有下降之趨勢，NO3-會沿著收集氣流進入接續於後之Nylon濾紙(第二層)，被Nylon濾紙捕集，最後再接續一層經coating調理之Quartz濾紙(第三層)，若未使用Nylon及Quartz濾紙捕集逸散出的NO3-微粒，則總量會有約10－13 % 的NO3-微粒流失，產生誤差。此外，在各種二元有機酸之成分表現上，未使用Nylon及Quartz濾紙捕集，亦有4.8－22.9 %不等的物種濃度流失。
PM2.5各主要無機鹽類成分，包含Na+、NH4+、K+、Mg2+、Ca2+、Cl-、NO3-和SO42-濃度，在白天的氣膠組成濃度趨勢高於晚上，SO42->NO3-或SO42->NH4+之趨勢一直是南台灣氣膠組成之特性。然而在高污染時期，代表交通排放之NO3-污染源顯著貢獻在氣膠濃度的增量。PM2.5或PM10中之二元有機酸總量平均約佔大氣微粒質量濃度0.8－1%的含量。其中氣膠二元有機酸含量以oxalic acid為最大量，succinic acid次之，再其次為malonic acid。當NH4+處於較偏鹼性之條件下，合成烯類之產物如malic acid和maleic acid會較為穩定。在高污染時期，在PM2.5或PM10氣膠二元酸主要轉化成oxalic acid，其所佔總分析之二元酸的比例，從非高污染時期的69 %，上升至73－80 %，顯示高碳數的二元有機酸在大氣中裂解，最後轉化為二個碳鍵(C2)之oxalic acid的最終產物。
在非高污染時期之各種無機鹽類濃度波峰分佈多出現在0.56－2.5 m的droplet mode及3.1－6.2 m的coarse mode兩部份，僅ammonium和sulfate於5－100 nm 的nuclei mode有微量濃度之分佈。而在高污染時期的氣膠各種無機鹽類，其物種在nuclei mode均有明顯濃度波峰分佈。在氣膠低分子量二元有機酸的濃度分佈，於非高污染時期之粒徑分佈，於droplet mode及nuclei mode已經有明顯的濃度波峰存在，且在高污染時期，氣膠低分子量二元有機酸在nuclei mode之濃度波峰，則多有更明顯增加之趨勢。此外，濃度波峰分佈則偏移至5－18 nm更細之氣膠初始成核粒徑，顯示氣膠低分子量二元酸在高污染時期有更多之奈米微粒的生成貢獻。
The water-soluble inorganic composition and low-molecular-weight dicarboxylic acids of PM2.5 (fine particle) and PM2.5-10 (coarse particle) in both daytime and nighttime were evaluated during both non-episodic period of 19 September to 20 October, 2004 and episode of 26-30 November, 2004. During both non-episodic and episodic periods, the size distribution of the water-soluble inorganic salts / dicarboxylic acids was studied, including those in the nanoaerosols of 5-100 nm.
To avoid the artifacts during each sampling period, the PM2.5 aerosol sampling was carried out after the gaseous pollutants were absorbed by annular denuder system (ADS). PM2.5 Aerosols collected on the Teflon filter (the first plate), but a part of PM2.5 NO3- was lost on the first filter. The lost NO3- species in PM2.5 aerosol was captured on the Nylon filter (the second plate) and was complete collected on the quartz filter of coating absorbent (the third plate). The percentage of PM2.5 NO3-on both Nylon and quartz filters displayed 10-13 % pf total aerosol NO3-. The percentage of total dicarboxylic acids in aerosol on both Nylon and quartz filters displayed 4.8-22.9 % of total dicarboxylic acids in aerosol.
During both episodic and non-episodic periods, the concentration of SO42- in both daytime and nighttime always exceeded contents of NO3- and NH4+ within both fine and coarse fractions. However, the increase of NO3-, presenting the traffic emission, was significant during the period of episode. The percentage contribution of dicarboxylic acids in both PM2.5 and PM10 was 0.8-1.0 % by mass. Oxalic acid was the biggest single dicarboxylic acids. It was followed by succinic acids and malonic acid. When the alkaline situation occurred, the existence of NH4+ induced the alkenes (malic acid and maleic acid) to be more stable. During the episode, the transformation percentage of dicarboxylic acids in both PM2.5 and PM10 increased significantly. The percent of oxalic acid in measured dicarboxylic acids raised from 69 % during non-episode to be 73-80 % during episode, indicating the more carbon-bonding dicarboxylic acids decomposed to be 2 carbon-bonding products, oxalic acid during the period of episode.
The dominant particle sizes of various inorganic salts including Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3- and SO42- in aerosol appeared in both the droplet mode at 0.56-2.5 m and the coarse mode at 3.1-6.2 m, respectively, during the non-episodic period. A small concentration peak of Aerosol NH4+ and SO42- appeared in the nuclei mode at 5-100 nm. Meanwhile, during the episode a significant concentration peak of various inorganic salts in aerosol increased in the nuclei mode at 5-100 nm. On the other hand, the concentration peak of low-molecular-weight dicarboxylic acids in aerosol appeared in both the droplet mode and the nuclei mode during the non-episodic period, but the significant concentration peak of dicarboxylic acids in aerosol existed in the nuclei mode, even at 5-18 nm, during the episode, indicating the concentration of primary dicarboxylic acids in aerosol has formatted more during the episode.