- 期刊
- OpenAccess
Evolution of Key Chemical Components in PM_(2.5) and Potential Formation Mechanisms of Serious Haze Events in Handan, China
摘要
Handan has been one of the most polluted cities in China since 2013 and became the top city for PM_(2.5) in 2017. In this research, we observed coarse particulate matter (PM_(10)), fine particulate matter (PM_(2.5)), submicron particulate matter (PM_1), and the chemical composition of PM_(2.5) from November 16, 2015, till March 14, 2016, in Handan. During the observation period, hourly concentrations of PM_(10), PM_(2.5), and PM_1 peaked at 1070.1, 864.4, and 519.5 μg m^(-3), respectively. Severe pollution occurred on a large fraction of days in the heating season, which was characterized by frequent and long-lasting pollution episodes. A large fraction of the transport trajectories during nine typical episodes during that period in Handan were from the northwest. Water-soluble ions (sulfate, nitrate, and ammonium) in PM_(2.5) accounted for the largest proportion at all pollution levels. The highest proportion of SIA occurred in a heavily polluted episode, during which it was as high as 50.0% (sulfate: 18.8%, nitrate: 18.7%, and ammonium: 12.5%). The sulfate and ammonium in PM_(2.5) increased gradually while the nitrate decreased as the level of pollution rose from clean to heavily polluted. The fraction of SOA and OM to PM_(2.5) decreased as the pollution level increased, indicating a weakening of photochemical reactions. The POA in PM_(2.5) increased with the aggravation of haze, and the heterogeneous chemistry was enhanced by the aggravation of pollution. Liquid reactions were important in the formation of sulfate during pollution and non-pollution stages. Liquid reactions of NO_2 are enhanced in the pollution stage during the heating season in Handan.