Abstract:In recent years, the eastern part of China, especially the Jing Jin Ji (shortly for Beijing Tianjin Hebei Region) has suffered increasingly severe pollution of PM2.5. A case of PM2.5 pollution over the Jing Jin Ji Region during the autumn of 2014 is studied with WRF Chem model in this paper. The results show that the pollution was caused by a stable weak high pressure system with the dominant southerly wind on the surface. The temperature inversion layer further suppressed the diffusion of pollutants in the vertical direction. High concentration of PM2.5 mainly spread in southern Beijing, Tianjin and northern Hebei Province, where the contribution of secondary PM2.5 was higher than that of primary PM2.5 to most of the pollution areas. Vertically, the secondary inorganic particles accumulated around Beijing, then became a high concentration region affixed to the ground surface. On the other hand, there was a zone of high pollutants over 1.2-1.6 km, and primary pollutants only had one high value area near the surface. The vertical distribution height of PM2.5 showed a similar trend with the boundary layer height.