Seasonal partitioning characteristics on PM2.5 particle and acidic aerosols in Douliu, Yunlin

• Main Authors: Zhe-Wei Lee, 李哲瑋
• Other Authors: James J.Lee
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/57248972821367045108

碩士 === 國立雲林科技大學 === 環境與安全衛生工程系 === 104 === Atmospheric PM2.5 aerosols in Douliou city assigned as top three air pollution areas in Taiwan. This study attempts to examine on seasonal characteristics as well on daytime/nighttime of PM2.5 aerosols during the past two years (2013 ~ 2015) in Douliou. Ambient experiment was conducted by utilizing annular denuder sampler (ADS) to discuss fine particles (PM2.5), water-soluble ions, anhydrosugar levoglucosan (Levo.), and gaseous pollutants. The results showed that PM2.5 average concentration of spring, fall, and winter (45.7±20.2, 49.7±12.8 and 53.1±15.6μg/m3) were significantly two times higher than the concentration of summer (25.5±9.1μg/m3). Except of northeast monsoon effect in fall and winter, it is also possibly influenced the profile of PM2.5 by upwind biomass burning based on burning marker (Levo. 299~413ng/m3). Large variation of PM2.5 in spring may be due to the highest relative humidity of season (such as the morning fog), which would generate large number of PM2.5 aerosols (NH4NO3). Decreased PM2.5 concentration in summer may cause by the strong wet deposition of seasonal airstream. Major species of ions in four-season aerosols were SO4 2-, NO3-, and NH4+ (account for 50% in PM2.5). Wherein the concentration of NO3- exhibited significant seasonal variation in spring and winter (9.5μg/m3 and 10.2μg/m3, respectively), since the spring has a high humidity environment and the winter season has a sunny daytime with a high humidity at night, and those could be favor of nitrate formation. Higher level of SO42-, accounted for 9μg/m3, was observed in four seasons. On the other hand, average concentrations of NH3, HONO, SO2 (H2SO4) and HNO3 were 13.9, 2.9, 7.0 and 1.8μg/m3, respectively. The higher annual concentrations of NH3 and SO2 presented in the areas, and the source of NH3 gas probably resulted from emissions of pig farms (about 1.4 million pigs raise in the area) and/or biomass burning. A high concentration of H2SO4 (SO2) was possibly derived from upwind of pollutants and/or direct emissions of biomass burning. A rich concentrations of gaseous HONO were found in fall and winter seasons (average ~3.5μg/m3), but lower concentration demonstrated in summer. The source of HONO might release from nearby and upwind of biomass burning, as well from heterogeneous formation of HONO at night. Furthermore, the study evaluated seasonal oxidation index of SOR, NOR, and results showed that the ratio of SOR and NOR in spring, fall, winter seasons higher than in summer. The day/night ratio of SOR and NOR presented a high ratio (>1) in summer, which probably cause by a strong photochemical reaction during the daytime of summer. And, the photo-reaction of daytime with a high humidity of night may lead to the lower day/night ratios (<1) in autumn and winter (i.e. a high oxidation ration during the night). Meanwhile, the study showed that the concentration of levoglucosan (marker of biomass burning) had a correlation with HONO concentrations in Douliou area. This result is similar as the data from reported research. Therefore, this study concludes that a high gaseous HONO emission derived from biomass burning may lead to a chain-reaction process on photochemistry, especially for enhancing the formation of secondary aerosol of PM2.5. Continuous study is worth to explore the formation mechanism on secondary aerosol of PM2.5 in the future. Key words: Secondary aerosol, biomass burning, nitrous acid, and atmospheric oxidation