杭州冬季大气细颗粒物污染特征及形成机制

To investigate the pollution characteristics and formation mechanism of fine particulate matter in Hangzhou in winter, atmospheric PM_2.5 samples were collected on a daily basis from December 2019 to January 2020. According to the weather conditions, the sampling period was classified as dry, rainy and less-rainy periods, and the differences in chemical characteristics and formation mechanisms of dicarboxylic acids and related secondary organic aerosols (SOA) during the three periods were investigated. pH values of PM_2.5 during the rainy periods were 2.2±0.6, which were 1~2 units lower than those in the dry and less-raining periods, mainly due to the effective removal of NH₃(g) by precipitation. Being similar to those in other cities, dicarboxylic acids of PM_2.5 in Hangzhou during winter were dominated by oxalic acid, followed by malonic and succinic acids, but the much higher ratio of methglyoxal to glyoxal observed in the city suggested that SOA in Hangzhou during winter were mostly derived from photochemical oxidation of biogenic emissions. Compound-specific stable carbon isotope composition results further showed that most of the detected diacids and related SOA in Hangzhou were enriched in ¹³C during the rainy days but depleted in ¹³C during the non-rainy and less-rainy periods, which can be ascribed to an enhanced aerosol-phase decomposition of primary organic aerosols (POA) and a decreased gas-phase oxidation of volatile organic compounds (VOCs).