Characterization of Compositions and Size Distributions of Inorganic Salts and Dicarboxylic Acids in Background and Suburban Aerosols

• Main Authors: Tzu-hsiang Weng, 翁子翔
• Other Authors: Ying -I Tsai
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/97796619018937713316

碩士 === 嘉南藥理科技大學 === 環境工程與科學系碩士班 === 94 === Abstract In this research, variations of characteristic composition as well as size distributions of the atmospheric inorganic salts and low-molecular-weight dicarboxylic acids (low-Mw DCAs) in aerosol for the background Ali Mountain and Tainan suburban regions during summer season, the autumn non-serious pollution period, the autumn high pollution period and the agricultural burning period were studied. During the high pollution period, Tainan has higher concentrations of daytime and nighttime concentrations of SO2, a precursor to the formation of SO42-, than other periods; the daytime and nighttime SO2 concentrations are 32.8±7.6 ug m-3, 20.3±7.7 ug m-3, respectively. The background Ali Mountain region has the lowest daytime (0.15±0.04 ug m-3) and nighttime (0.12±0.06 ug m-3) SO2 concentrations indicating that the background environment SO2 concentration is much lower than man-made pollution emission in Tainan suburban region. The background daytime concentrations of SO42-, NO3- and NH4+ in PM2.5 aerosols in Ali mountain region are higher than nighttime concentrations. This region is abundant in NH3, which is a precursor of NH4+, leading to relative higher concentrations of NH4+ produced from photochemical reactions. During summer and autumn, Tainan suburban region experiences the maximum quantities of SO42-, NO3- and NH4+ photochemical products while the autumn non-serious polluted season has higher concentrations of SO42-, NO3- and NH4+ than summer with 9.67±2.29 ug m-3 of SO42- being the highest concentration. During the high pollution period, the aerosol has higher NO3- concentration than SO42- that is different from the higher SO42-concentration than NO3- concentration during summer and the autumn non-serious pollution period. The quantity of ratio of NO3- to PM2.5 mass is the highest during high pollution and agricultural waste burning periods; the ratios are 19.6% of the daytime PM2.5 mass during high pollution period and 18.0% of the daytime PM2.5 mass during agricultural waste burning period, respectively. These observations indicate that during the high pollution and the agricultural waste burning periods, the contribution of NO3- to PM2.5 mass apparently increases. Additionally, the NH4+ concentration during the agricultural waste burning period is 0.95 ug m-3 higher than during the high pollution period. Oxalic acid is the most abundant low-Mw DCAs in the Ali Mountain region followed by succinic acid and malonic acid. These low-Mw DCAs are highly correlated with NH4+ demonstrating that the aerosol low-Mw DCAs in Ali Mountain are the photochemical products from natural emissions. In Tainan suburban region during high pollution period, concentrations of the daytime and nighttime low-Mw DCAs are obviously higher. Similarly, oxalic acid during summer is the most abundant followed by succinic acid and maleic acid. Additionally, daytime concentrations of the six observed low-Mw DCAs are 2 to 3 times higher than those during summer while during agricultural waste burning period, the diurnal variation tendency is quite similar to that during high pollution period. The concentration matrix reveals that the correlation coefficients are 0.72 between oxalic acid and NH4+ and 0.69 between oxalic acid and K+. Since during the agricultural burning period, these three chemical species are more correlated than other seasons and periods indicating that the sol from agricultural waste burning contains a large quantity of oxalic acid. As the atmospheric particle size distribution is concerned, the Ali Mountain background inorganic salts show droplet mode (concentration peaks between 0.46-2.4 um), coarse mode (concentration peaks between 5.7-11.3 um) and nuclei mode (concentration peaks between 4-90 nm). The low-Mw DCAs are principally droplet mode with concentration peaks in 0.46-2.4 um; the 4 nm peaks shows the beginning formation of low-Mw DCA primary particles. For Tainan suburban region, the particle size distributions for both aerosol inorganic salts and low-Mw DCAs change from single peak or double peaks in summer to triple or multiple peaks in autumn. During the high pollution period, the maximum concentration peaks for low-Mw DCAs dominant in the condensation mode of 0.19-0.32 um. This reveals that particle coagulation and photochemical products contribute to the observed aerosols during the high pollution period. Additionally, the aerosol succinic (C4) and malonic acids (C3) have different maximum concentration peaks from oxalic acid (C2). During the autumn non-serious pollution period and high pollution period, the maximum concentration peak for oxalic acid shifts toward the nanometer range indicating that the autumn sol oxalic acid is an end photochemical product from C4 and C3 low-Mw DCAs.