| 摘要: | 本研究以台南郊區中秋節時期、秋季一般空氣品質時期及高污染時期與代表低海拔偏遠地區的曾文水庫之大氣氣膠無機鹽類及二元有機酸，並以阿里山之背景資料，探討不同時空之大氣氣膠化學成份特性、生成來源及粒徑分佈。
曾文水庫偏遠地區及郊區秋季一般空氣品質時期大氣氣狀物之全日平均濃度高低為NH3＞SO2＞HNO3＞HNO2＞HCl＞oxalic acid，但在中秋節時期HCl濃度高於HNO3。中秋節時期及秋季一般空氣品質氣狀oxalic acid日間濃度較大，高污染時期則日夜濃度相當，顯示大氣中在日間有較多氣態oxalic acid來源。曾文水庫大氣PM2.5氣膠無機鹽類之全日平均濃度高低為SO42-＞NH4+＞NO3-；中秋節時期，無機鹽類夜間濃度多高於日間，濃度高低為SO42-＞NO3-＞Na+，Na+在此時期在日、夜間濃度皆比秋季一般空氣品質時期高，除了部份的海鹽粒子外，另一部份可能來自烤肉燃燒之貢獻，另外，中秋節期間Cl-和K+之相關係數為0.76，顯示此時期之大氣環境除了燃放煙火所造成的污染外，亦存在烤肉之生物性燃燒排放的貢獻。
曾文水庫、郊區秋季一般空氣品質時期及高污染時期之PM2.5二元有機酸濃度高低依序為oxalic acid＞succinic acid＞glutaric acid，日間濃度皆高於夜間，但中秋節時期之glutaric acid濃度高於succinic acid，在日間之濃度為秋季一般空氣品質時期之1.4倍，夜間則為1.8倍，顯示夜間有較多之glutaric acid之生成來源，且中秋節時期Na+與glutaric acid之相關性為0.72，顯示中秋節時期的氣膠glutaric acid來自此時期特殊之人為活動所排放。曾文水庫之glutaric acid與succinic acid之相關性為0.70，而succinic acid與oxalic acid之間的相關性及malonic acid與oxalic acid之相關性皆很小，分別僅有0.49及0.27，顯示此偏遠的林地區域之oxalic acid來自當地生物排放。
曾文水庫偏遠地區之無機鹽類濃度粒徑主要分佈在0.54-2.5 μm的液滴峰(droplet mode)，並在10 nm之成核峰(nuclei mode)有初始氣膠微粒之生成，曾文水庫及阿里山之NO3-微粒分佈主要呈單峰分佈，在coarse mode之形成與Na+及succinic acid趨勢一致，顯示二地均有海洋飛沫所貢獻。然而台南郊區之中秋節時期Na+及Cl-濃度於各粒徑波峰皆比曾文水庫高，而二物種在coarse mode之中秋節時期/曾文水庫比值分別為8.63、5.46，顯示在中秋節時期的台南郊區有更明顯的海洋飛沫貢獻，中秋節期間氣膠glutaric acid、succinic acid及malonic acid在coarse mode為曾文水庫之36.09、10.41及14.49，也顯示特殊人為活動對大氣環境所造成的污染。Oxalic acid於台南郊區中秋節時期之質量中位數粒徑(Mass median aerodynamic diameter, MMAD)為0.63 μm，較秋季一般空氣品質時期的0.78 μm小，顯示特殊燃燒產生之oxalic acid分佈於較小尺寸；阿里山oxalic acid氣膠之MMAD為0.83 μm，比曾文水庫的0.73 μm大，而阿里山之平均相對濕度為88.5%較曾文水庫之74.5%高，雖然其MMAD均在雲霧凝結之液滴峰，但顯示氣膠吸濕增大之特性在阿里山背景地區較為明顯。
The spatial and temporal chemical compositions, characteristics, formation, sources, and particle distribution of aerosols in suburban Tainan in southern Taiwan during the Mid-Autumn Festival period, the fall moderate air quality period, and a high pollution loading (PM episode) period, and in the atmosphere of the remote Tseng-Wen Reservoir region are compared with the background information obtained in Alishan region.
The order of magnitude for gaseous pollutants in the atmosphere of the remote Tseng-Wen Reservoir region and of the fall moderate air quality period in the Tainan suburban region is NH3>SO2>HNO3>HNO2>HCl>oxalic acid. Meanwhile, during the Mid-Autumn Festival period, HCl concentration is higher than HNO3 concentration; during both the Mid-Autumn Festival period and the moderate air quality period, the daytime oxalic acid concentration is relatively higher. During the PM episode, both daytime and nighttime oxalic concentrations are high, indicating that there are more sources of oxalic acid during these periods. In Tseng-Wen Reservoir region, however, the order of magnitude for the daily average concentrations in PM2.5 is SO42->NH4+>NO3. During the Mid-Autumn Festival period, concentrations of inorganic salts in PM2.5 are higher during nighttime than daytime; the order of magnitude is SO42->NO3->Na+. Moreover, during the same period, the daytime and nighttime Na+ concentrations are higher than those for the moderate air quality period. Thus, in addition to sea salts, barbecuing activities also contribute to air pollution. Additionally, during the Mid-Autumn Festival period, the correlation coefficient between Cl- and K+ is 0.76 indicating that in additional to firecrackers, barbecuing also contributes to atmospheric pollution.
The order of magnitude for PM2.5 dicarboxylic acid concentrations in the atmosphere in the remote Tseng-Wen Reservoir and those during both the moderate air quality period and the PM episode in the Tainan suburban region is oxalic acid>succinic acid>glutaric acid; the daytime concentrations are higher than the nighttime concentrations. During the Mid-Autumn Festival period, the glutaric acid concentration is higher than the succinic acid concentration; the daytime concentration is 1.4 times whereas the nighttime concentration is 1.8 times those during the moderate air quality period, indicating that there are more sources of glutaric acid precursors during the nighttime period. The correlation coefficient between Na+ and glutaric acid is 0.72 revealing that glutaric acid originates from human activities during the Mid-Autumn Festival period. Additionally, the correlation coefficient between glutaric acid and succinic is 0.72 whereas both the correlations between succinic acid and oxalic acid, and between malonic acid and oxalic acid are low being only 0.49 and 0.27, respectively. This proves that the oxalic acid in the remote region originates from the local bio-emission.
The concentration distribution of inorganic salt concentration in the atmosphere of the Tseng-Wen Reservoir region is a droplet mode between 0.54 and 2.5 μm, and the nuclei mode is at 10 nm at which the primary aerosol forms. The NO3- particulate shows a single-peak distribution whereas tendencies of coarse mode formation for Na+ and succinic acid are the same, indicating that sea spray contributes to the pollution at both locations. However, the Na+ and Cl- concentrations at the peak of the concentration distribution are higher for Tainan suburban region than Tseng-Wen Reservoir region. During the Mid-Autumn Festival period, ratios of Na+ and Cl- concentrations in Tainan suburban region to those in Tseng-Wen Reservoir region are 8.63 and 5.46, respectively. Thus, there are more contributions from sea spray in Tainan suburban region during the Mid-Autumn Festival period than in Tseng-Wen Reservoir region. During the same period, the coarse mode aerosol glutaric acid, succinic acid and malonic acid in Tainan suburban region are 36.09, 10.41 and 14.49 times, respectively, those in Tseng-Wen Reservoir region. This also indicates the consequences of human activities on atmospheric pollution. The mass median aerodynamic diameter (MMAD) of oxalic acid in Tainan suburban region during the Mid-Autumn Festival period is 0.63 μm, which is smaller than 0.78 μm for oxalic acid during the fall moderate air quality period. Thus, the oxalic acid originating from special burning activities is distributed in the relative smaller particle size. The MMAD of oxalic in Alisan region is 0.83 μm, which is greater than 0.73 μm for that in Tseng-Wen Reservoir region. The average relative humidity in Alisan region is 88.5% that is higher than 74.5% in Tseng-Wen Reservoir region. Although the MMAD of oxalic acid in the Alisan region exists in the droplet mode of the cloud condensation similar to that in Tseng-Wen Reservoir region, the above observation shows that the increasing hydroscopic characteristics is more obvious for aerosols in the background Alishan region. |
