Meteorological and Pollution Characteristics of PM2.5 under Atmosphric Circulation Types in Autumn and Winter in Shijiazhuang

According to the ground and vertical meteorological characteristics of atmospheric circulation types during the autumns and winters (Nov.-Feb.) of 2013-2018 in Shijiazhuang, 11 types of atmospheric circulation were classified into five categories. The correlation between each category and PM2.5 pollution was discussed by combining the transport trajectories and the air quality data. Among those categories, Category I (type NW and type N, accounting for 16% of days) was the best condition for air pollution diffusion, characterized by the dominant west or northwest winds near surface with steady direction and high speed, as well as high planetary boundary layer (PBL) height. Category II (type NE, accounting for 9%) and Category III (type E and type SE, accounting for 12%) were the second-best conditions, characterized by high wind speed. Category II was dominated by north wind and medium PBL height, while Category III was dominated by northeast wind and low PBL height. Category IV (type A, 37%) was unfavorable for air pollution diffusion, which was characterized by low-speed, near-surface winds and low PBL height. Category V (type UM, type C, type S, type SW, type W, 26%) was the worst condition, characterized by near-surface winds with low speed and variable directions, as well as low PBL height and intensive temperature inversion in lower atmosphere. The potential areas of sources contributing to PM2.5 pollution in Shijiazhuang under different circulation types varied with different transport trajectories. Concerning the correlation between the PM2.5 pollution in Shijiazhuang during the autumns and winters and the diffusive conditions of different circulative types, the PM2.5 pollution tended to occur (the frequency of pollution was from 78% to 96%, and the frequency of heavy pollution and above was more than 55%) when the region was controlled by Category V; the condition of the PM2.5 pollution tended to change slowly under Category IV, but the PM2.5 concentration was more likely to increase under the continuous Category IV days; the frequency of PM2.5 pollution was lowest under Category I. © 2021 Peking University.