| Summary: | 碩士 === 中興大學 === 環境工程學系所 === 94 === In this study, the dichotomous samplers were used 7 days per month in 2005 to collect daytime and nighttime PM2.5 and PM2.5-10 aerosols. The samples were further analyzed to obtain the concentrations of water-soluble ions. Totally 142 samples were collected. In addition, MOUDI was used to collect the size-segregated aerosols every 24 hours. Seventy-two samples were collected. Particularly only the size-segregated aerosol samples collected during agricultural waste burning and Asian dust storm periods in November were analyzed to obtain the size distributions of ionic species. These results and those measured during the year from 2002 to 2004 were studied, in order to understand the characteristics of urban ambient particulate in Taichung. The characteristics of the aerosol particles measured during the agricultural waste burning and follwed by Asian dust storm were investigated as well.
The annual mean concentrations of PM10 and PM2.5 were 71.7 μg/m3 and 46.3 μg/m3, respectively. The annual mean ratio of PM2.5/PM10 was 0.65. During the year from 2002 to 2005, Asian dust storm, agricultural waste burning and poor dispersion were the major causes of the PM10 episodes.
The mean concentrations of PM10 and PM2.5 of Asian dust storm were 98.4 μg/m3 and 48.2 μg/m3 at Taichung urban city during 2002 to 2005, and the mean ratio of PM2.5/PM10 was 0.47. The concentrations of sea-salt species Na+, Mg2+, Cl- and the crustal component Ca2+ were 2.6, 2.4, 3.4, 2.6 times higher than those measured during the non-Asian dust storm period. Other additional species varied for each dust storm event. And the mean concentrations of PM10 and PM2.5 of agricultural waste burning were 153.4 μg/m3 and 125.5 μg/m3, respectively. The mean ratio of PM2.5/PM10 was significantly increased to 0.81. The major components Cl-, K+, SO42-, OC, and EC were 10.9, 5.7, 5.2, 3.9, and 3.5 times higher than those obtained during the non-burning days. During the agricultural burning, NOx, CO, SO2, and O3 increased, but temperature and relative humidity were almost the same as those during the non-burning days. However the mean wind speed during the burning period was 0.6 times lower than the non-burning days. The low wind speed was one of the major factors causing the PM10 episodes.
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