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Physical and Chemical Characteristics of Ambient Particulate During PM10 Episodes in Taichung Urban Area
|關鍵字:||suspended particulate;懸浮微粒;dust storm;biomass burning;PM10 episode;沙塵事件;農廢燃燒;冬季高污染;PM10事件日||出版社:||環境工程學系||摘要:||
台中都會區2004年空氣品質較過去兩年明顯惡化，PM2.5年平均質量濃度為54.8 ± 37.6 μg/m3，PM2.5-10則為22.1 ± 14.9 μg/m3，PM2.5季節性變化以冬季最高( 73.7 ± 44.9 μg/m3 )，夏季最低( 40.1 ± 28.7 μg/m3 )，PM2.5-10以冬季最高( 29.1 ± 19.8 μg/m3 )，春季最低( 15.6 ± 9.8 μg/m3 )，化學組成亦大致呈相同趨勢。採樣期間發現3波高污染事件日，採樣日期分別為2/9 - 2/19、6/23 - 7/1及11/26 - 12/2。
2/15 - 2/16為沙塵事件日，PM2.5平均質量濃度為80.3 ± 30.3 μg/m3，PM2.5-10則為56.9 ± 8.6 μg/m3，粗粒比例較非沙塵事件增加1.9倍。此時風速及相對溼度降低，溫度升高，PM2.5-10以Cl- (4.7倍)、Na+ (2.8倍) 、Mg2+ (2.5倍)及Ca2+ (2.0倍)增加較明顯，結合氣流逆軌跡圖分析推論沙塵事件日沙塵微粒會藉由長程傳輸為台灣帶來塵土礦物以及海鹽微粒等，沙塵事件日過後之2/17 - 18因大氣擴散不良而引起PM10事件日。
6/29 - 6/30農廢燃燒事件日PM2.5平均濃度上升至126.6 ± 31.9 μg/m3，PM2.5-10濃度為15.2 ± 6.4 μg/m3，期間NOx、CO、SO2及O3濃度上升1.2至1.9倍，風速降低至非事件日之0.8倍。農廢燃燒對PM2.5影響較大，PM2.5/PM10＝0.89，為非事件日之1.3倍。水溶性離子濃度於細粒中NH4+、NO3-、SO42-、K+、Cl-及OC較非事件日增加3.0至4.9倍，推測此波農廢燃燒帶來K+、Cl-細微粒，期間亦可能受強烈光化反應之影響。
12/1 - 12/2為冬季高污染事件日，期間PM2.5平均濃度上升至155.2 ± 38.7 μg/m3，PM2.5-10濃度增至38.3 ± 12.9 μg/m3，事件日期間PM2.5/PM10增加1.1倍，以細粒PM2.5為主。期間溫度、相對溼度、SO2、NOx、CO及O3濃度增加，為非事件日之1.0至2.0倍，風速降低至非事件日之0.7倍。水溶性陰陽離子濃度於細粒PM2.5中NO3- (5.5倍)、OC (3.2倍)、NH4+ (2.9倍)較非事件日明顯增加，粗粒PM2.5-10則以Na+ (2.9倍)及Cl- (3.6倍)增加較顯著，推測此波高污染主要受到光化反應、交通污染及海鹽微粒之影響。
The study used dichotomous samplers to collect PM2.5 and PM2.5-10 aerosols about one week every month during the year 2004. Throughout the sampling periods, 125 samples were gathered to analyze the mass concentration, water-soluble ions and carbonaceous composition. Furthermore, we combined the analyzed data with weather and air quality information to discuss the physical and chemical characteristics of the ambient particulate during air pollution episodes.
The air quality of Taichung urban area in 2004 was worse than the last two years, the annual mean concentration of PM2.5 and PM2.5-10 were 54.8 ± 37.6 and 22.1 ± 14.9 μg/m3, respectively. Seasonal variation of PM2.5 concentration was highest in winter ( 73.7 ± 44.9 μg/m3 ), lowest in summer ( 40.1 ± 28.7 μg/m3 ), PM2.5-10 was highest in winter ( 29.1 ± 19.8 μg/m3 ), lowest in spring ( 15.6 ± 9.8 μg/m3 ). Moreover, the chemical composition was approximately showing the similar trend. There were three spans of PM episodes during the sampling duration, and the sampling dates were 2/9 - 2/19, 6/23 - 7/1 and 11/26 - 12/2.
2/15 - 2/16 was a dust storm event, the mean concentration of PM2.5 and PM2.5-10 were respectively 80.3 ± 30.3 and 56.9 ± 8.6 μg/m3, and the proportion of coarse particles was 1.9 times higher than the non-dust days. At the time, the wind speed and the relative humidity decreased while the temperature increased. Concentrations of Cl-(4.7 times), Na+(2.8 times), Mg2+(2.5 times) and Ca2+(2.0 times) distributed in PM2.5-10 raised significantly. By way of combining HYSPLIT Model with the analyzed data, we supposed when dust storm occurs, the soil and sea-salt components might be brought to Taiwan by long-range transportation. Besides, 2/17 - 2/18, after the dust storm, two PM episodes took place due to the poor diffusion of the atmosphere.
6/29 - 6/30 was a biomass burning event, the mean concentration of PM2.5 and PM2.5-10 increased to 126.6 ± 31.9 and 15.2 ± 6.4 μg/m3, respectively. During the event, NOx, CO, SO2 and O3 concentrations were all increased 1.2 to 1.9 times compared to the non-biomass burning days, but the wind speed decreased. PM2.5/PM10 = 0.89, and was 1.3 times higher than other sampling data. NH4+, NO3-, SO42-, K+, Cl- and OC concentrations increased from 3.0 to 4.9 times. We suggested the biomass burning episode brought K+ and Cl- fine particles, and might also influenced by strong photochemical reactions.
12/1 - 12/2 was a winter high pollution event, the mean concentration of PM2.5 increased to 155.2 ± 38.7 μg/m3, and PM2.5-10 was 38.3 ± 12.9 μg/m3. Temperature, relative humidity, SO2, NOx, CO and O3 concentrations were 1.0 to 2.0 times higher than non-episode days, but the wind speed was relatively lower. NO3-(5.5 times),OC(3.2 times) and NH4+(2.9 times) in PM2.5, Na+(2.9 times) and Cl-(3.6 times) in PM2.5-10 raised significantly. This presumed that the winter pollution was effected by photochemical reactions, traffic pollution and sea-salt components.
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