| Summary: | 碩士 === 國立中興大學 === 環境工程學系 === 91 === 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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