Abstract: This study comparatively analyzes PM_2.5 mass concentration and surface meteorological conditions between an urban site (Nanjiao Station) and a suburban site (Shangdianzi Station) during an aerosol pollution episode in Beijing from January 21 to 24,2022.The causes of this episode were investigated using vertical extinction coefficients,radiosonde meteorological data,and backward trajectories.Results show that the average PM_2.5 mass concentration at the urban station during the pollution period was 118.5 μg·m^-3,with significantly higher concentration levels and longer duration than that at the suburban station.Aerosol transport was observed above the urban station,with high aerosol extinction coefficient areas subsiding toward the surface,resulting in increased ground-level aerosol concentrations.The pollution episode began under southerly winds,transporting aerosol pollutants from southern Beijing toward Nanjiao Station.The pollution was exacerbated by a combination of meteorological conditions including decreased near-surface wind speed,increased relative humidity,and the formation and downward movement of temperature inversion layers.During the pollution episode,wind speeds at the urban station were notably lower than those at the suburban station,resulting in poorer dispersion conditions.Under relatively stable emission sources,variations in meteorological conditions during the pollution period served as good indicators of pollution.

Key words: Aerosol extinction coefficient, Radiosonde meteorological elements, Backward trajectory, Temperature inversion