Abstract: This study investigated the diurnal and hourly variations of PM_2.5 mass concentration,together with the evolution characteristics of meteorological parameters,aerosol extinction coefficients,and radiative effects during pollution episodes in different background stations in Beijing.The results show that during winter pollution episodes,PM_2.5 mass concentration at Shangdianzi station were relatively low and exhibited gentle fluctuations,whereas those at the Nanjiao station exhibited substantial variability,indicating typical urban pollution characteristics.During autumn pollution episodes,the fluctuation range of PM_2.5 mass concentration at Shangdianzi station increased slightly,while the "weekend effect" at Nanjiao station weakened.In winter,both Shangdianzi station and Nanjiao station exhibited a decreasing trend in wind speed accompanied by rising temperatures and increasing relative humidity,indicating meteorological conditions favorable for pollutant accumulation.In contrast,increased wind speeds at both stations during autumn indicated that regional transport played a significant role in pollutant dispersion.During winter,aerosol extinction coefficients at Yanqing station were generally low,while a distinct aerosol extinction layer was observed near the surface at Nanjiao station.During autumn,the aerosol extinction coefficients at Nanjiao station exhibited relatively high values at altitudes of 1.1 km.The enhancement of aerosol extinction during pollution episodes represented the primary factor leading to increased heating rates.In winter,aerosol radiative heating rates at Nanjiao station increased significantly near the surface,while those at Yanqing station was relatively low.In autumn,high aerosol radiative heating rates occurred around 1.1 km altitude at Nanjiao station.These results indicate that the Nanjiao station was influenced by both local emission sources and regional transport,whereas the Yanqing station was predominantly affected by seasonal meteorological conditions and regional dispersion.This study provides a scientific foundation for understanding the spatiotemporal distribution characteristics of air pollution and its interaction mechanisms with meteorological conditions at different urban and suburban background stations in Beijing.