|摘要: ||摘要本研究探討恆春沿海地區大氣微粒(Particulate matter, PM)化學組成及數目粒徑濃度，藉以瞭解偏遠無特定近污染源之臺灣最南端沿海氣膠化學及微粒數目特性，氣膠化學特性項目包括無機鹽類、醣類、醣醇類、脫水醣類及有機酸類的組成，微粒數目特性包括數目濃度及數目粒徑分布。恆春沿海地區PM平均質量濃度為25.59 12.27 g/m3，其物種濃度由高至低依序為SO42- >Cl- >Na+ >NO3- >NH4+，此五種物種濃度分別為3.46 2.18 g/m3、2.15 0.98 g/m3、2.14 1.37 g/m3、1.50 0.77 g/m3、1.27 1.15 g/m3，其物種分布的主要粒徑在原生的Coarse mode和衍生的Submicron-Droplet mode，顯示偏遠沿海氣膠受至海洋飛沫所貢獻，亦有光化產物之貢獻影響。一般K+與levoglucosan被視為生質燃燒氣膠的指標物種，然而K+的分布粒徑波峰主要在6.2 m、1.8 m及0.54 m之三峰分布，而levoglucosan雖在Submicron-Droplet mode有粒徑濃度呈現，但未與K+有一致性的濃度峰值高低，顯示研究期間沿海大氣環境存有生質燃燒產物，但非明顯近距離燃燒，而Coarse mode的K+亦顯示沿海地區的K+來自於海洋飛沫或塵土物質的貢獻。大氣氣膠有機酸以二次衍生氣膠之oxalate濃度最高，此oxalate為二元有機酸最終產物，佔總有機酸的35.4 26.7 %，次者為acetate，佔總有機酸的28.9 21.9 %，為最主要的單元酸，而非海鹽硫酸鹽(non-sea salt SO42-, nss-SO42-)佔PM質量濃度的11.58 7.62 %，oxalate與nss-SO42-相關係數(correlation coefficient, r)更高達0.919，且兩者粒徑主要生成在Submicron-Droplet mode的0.54 m，但0.32-1.0 m的粒徑範圍oxalate/nss-SO42-平均比值達到15.7 %，遠高於台灣南部郊區的5.88 %，顯示Submicron-Droplet mode的二元有機酸的光化生成潛勢高於無機鹽類的硫酸鹽。此外，早上和下午各有一氣膠數目濃度的高峰值，分別在早上7時和下午4時，其總數目濃度各為2,571 1,440 #/cm3和2,399 262 #/cm3，白天因海風的吹拂引進新鮮海洋大氣及發展出較高混合層高度，於中午至下午1時降至一天中最低濃度，其總數目濃度為951 453 #/cm3，當日最高數目濃度為最低數目濃度的2.70倍，而下午4時的眾數粒徑為75.7 nm與早上7時相近，但其眾數粒徑濃度較高，顯示數目濃度貢獻來源相似，均與鄰近小規模交通排放飄散有關。綜觀氣膠化學組成及微粒數目特性探討，恆春沿海地區大氣微粒之貢獻來源主要為海洋飛沫及光化產物與少量的遠距離生質燃燒。|
AbstractThis study is focused on the chemical composition and the particle number size concentration of atmospheric particulate matter (PM) in the coastal region of Hengchun Peninsula to understand the aerosol chemistry and particle number characteristics in the remote region of the southernmost tip of Taiwan, which is far away from any specific pollution sources. The aerosol chemical characteristics include the composition of inorganic salts, carbohydrates, sugar alcohols, anhydrosugars, and organic acids. The particle number characteristics include the number concentrations and the particle number size distribution.The average mass concentration of PM in Hengchun coastal area is 25.59±12.27 μg/m3. The concentration of species in PM is in the following order: SO42- > Cl- > Na+ > NO3- > NH4+; the corresponding concentrations of these five species are 3.46 ± 2.18 μg/m3, 2.15 ± 0.98 μg/m3, 2.14 ± 1.37 μg/m3, 1.50 ± 0.77 μg/m3 and 1.27 ± 1.15 μg/m3 respectively. The main distributions of the species are the primary coarse mode and the photochemical submicron-droplet mode. This indicates sea spray and photochemical products significantly contribute to remote coastal aerosol.Generally, K+ and levoglucosan are regarded as molecular indicators of biomass burning aerosol, however the particle size peaks of K+ concentration are mainly at 6.2 μm, 1.8 μm, and 0.54 μm, whereas although levoglucosan showed up in the particle size peaks of submicron droplet mode, its concentration peaks differed from those of K+. This indicated that despite the slightly presence of long-range transport of biomass burning aerosols in the coast atmosphere environment during the period of study, there is no prominent burning in close range. Moreover, coarse mode K+ also indicated that K+ in the coastal region came from sea spray and crustal matters.Among the organic acids of remote coastal aerosol, oxalate appeared the highest concentration. Oxalate is the final product of dicarboxylates; it constitutes 35.4 ± 26.7% of the total carboxylates, followed by acetate, the most important monoacid, which accounts for 28.9 ± 21.9% of the total carboxylates. Non-sea salt sulfate (nss-SO42-) accounted for 11.58 ± 7.62% of the PM mass concentration. The correlation coefficient, r, between oxalate and nss-SO42- was as high as 0.919 and the peak concentration of both was generated in the submicron droplet size mode at 0.54 μm. However, in the 0.32 ~ 1.0 μm particle size range, the average oxalate/nss-SO42- ratio is as high as 15.7%, far exceeding the average 5.88% of suburban southern Taiwan. This indicated that the photo-generation potential of carboxylates in the submicron droplet size mode was higher than that of inorganic sulfate.In addition, a peak in aerosol number concentration was observed at dawn and at dusk, occurring respectively at 7 AM and 4 PM. The total number concentrations were 2,571 ±1,440 # cm-3 and 2,399 ±262 # cm-3 respectively. During the day, the ocean breeze brings in fresh ocean air and a higher mixed layer is resulted in, especially at noon. The total number concentration dropped to the daily low of 951 ±453 # cm-3 from noon to 1 PM. The highest number concentration of the day was 2.7 times of the lowest number concentration of the day. The mode diameter of 75.7 nm at 4 PM was close to that at 7 AM, but the corresponding mode concentration was higher. This showed that the contributing sources of the particle number concentration were similar and both were related to the small scale local traffic exhaust transport.An overview of the aerosol chemistry composition and particle number characteristics showed that the main contributing sources of the remote atmospheric particulates in Hengchun area were sea spray and photochemical products, as well as long-range transport of biomass burning.