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為了瞭解台中都會區酸性空氣污染物之季節性變化，本研究於2002年1月至12月於台中市以環形擴散採樣器採集酸性空氣污染物，數據涵蓋四季，共採集了122組日夜樣本。氣狀污染物HNO2、HNO3及NH3整年平均濃度依序為3.1、1.8及8.3 μg/m3。在粒狀物方面PM2.5、SO4＝、NO3-及NH4+其整年平均濃度依序為42.2、7.6、5.6及4.3 μg/m3，PM2.5水溶性離子中以SO4＝，NO3-及NH4+為主要組成，三者年平均濃度佔PM2.5質量濃度的41.5％。
PM2.5，NO3-，SO4＝及 NH4+中， PM2.5和NO3-有相同的季節性變化，其濃度以春季最高，依序為冬秋及夏季。尤其NO3-季節性變化及差距最為明顯，夏季溫度高，硝酸銨易揮發，因此不利硝酸銨微粒生成，相對的硝酸和氨氣體濃度均以夏季最高，而SO4＝及 NH4+濃度有相同的季節性變化，仍然是以春季最高而夏季最低，而二者在PM2.5中的百分比以夏季最高，顯示夏季光化作用易產生（NH4）2SO4，細粒中SO4＝及 NH4+的百分比分別高達21.6％及11.4％。酸性氣體的季節性變化與微粒不同，從HNO2易光解和NH4 NO3於白天高溫易揮發的特性觀點，可見HNO2濃度以冬季最高，夏季最低，而HNO3則正好相反。
In order to understand the seasonal variations of acidic air pollutants, in Taichung city, Taiwan, an annular denuder system (ADS) was used to collect air samples during day-time and night-time from January to December, 2002. The results showed average concentrations of HNO2, HNO3 and NH3 were 3.1, 1.8, and 8.3μg/m3, respectively. The annual mean concentrations of mass, SO4＝, NO3- and NH4+ in PM2.5 were 42.2, 7.6, 5.6 and 4.3 μg/m3, respectively. The SO4＝, NO3- and NH4+ were the dominant ionic species, which accounted for 41.5% in PM2.5.
The concentrations of PM2.5 and NO3- in spring were higher than those obtained in winter and summer. The concentrations of HNO3 and NH3 were higher in summer because of the volatility under the higher temperature. The percentage of SO4＝and NH4+ in PM2.5 were 21.6% and 11.4% during the summer, respectively, which might result from the photochemical reactions. In particular, the concentrations of HNO2 were lowest in summer, which resulted from the photolysis reactions of HNO2. In contrast to HNO2, the concentrations of HNO3 were highest in summer due to the volatility of particulate ammonium nitrate.
The analyses of the correlation between the air pollutants, which suggesting that the major source of NO3- and PM2.5 were the traffic emissions during the fall and winter. NO significant correlation between SO4＝ and SO2 were observed. However SO4＝ and O3max appeared well correlation in spring, summer and winter, which might indicate the regional SO4＝ were the products by photochemical reactions.
The ratio of [NO3-]/[SO4＝] varied from 0.2 to 2.6 during the whole sampling period. The ratios were mostly higher than 1 during the spring and winter, which showed the strong effect of nitrate on PM2.5 in these seasons. However, good correlations were found among NO3-, NOx and CO during the winter. These results showed the effect of traffic emissions on particulate nitrate.
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