[Analysis of PM_2.5 and O₃ Pollution Causes in Hangzhou Based on High-resolution Enhanced Observation During the Asian Games].

Based on the high-resolution enhanced observation data of PM_2.5 organic molecular tracers, aldehydes and ketone OVOC components, long-chain alkane IVOC components, and key species of atmospheric oxidation during September 1 to October 27, 2023, the causes of PM_2.5 and O₃ pollution in Hangzhou were analyzed. Seven pollution processes were selected with the average daily concentration of PM_2.5 exceeding 35 μg·m^-3 or the maximum 8-hour concentration of O₃ exceeding 160 μg·m^-3. Then, these pollution processes were divided into four types： north-northeast transmission type （T1）, east-southeast transmission type （T2）, north-northwest transmission type （T3）, and statically stable type （T4） by airflow trajectory. The research results indicated that the T2 pollution process exhibited strong PM_2.5 and O₃ composite pollution characteristics and the photochemical oxidation reaction of active VOC components, such as long-chain alkanes and terpenes in the atmospheric environment was the major pollution cause of this type. In the process of T1 and T3 pollution, the overall reactivity of VOCs was low, resulting in relatively weak O₃ generation. However, the causes of PM_2.5 in these two types of pollution processes were different. T1 pollution was affected by low temperature and high humidity meteorological conditions and the enhanced liquid-phase oxidation process led to a significant increase in nitrate concentration. T3 pollution was significantly affected by emissions from coal combustion, biomass combustion, and other sources, with a relatively high proportion of primary components in PM_2.5. The T4 pollution process was significantly affected by local primary anthropogenic emissions, thus the control of local catering source and mobile source emissions must be strengthened.