A study of the meteorological causes of a prolonged and severe haze episode in January 2013 over central-eastern China

This paper employs meteorological observation data from surface and high-balloon stations, China Meteorological Administration (CMA) model T639 output data, NCEP reanalysis data, PM2.5 observations and modeled HYSPLIT4 trajectory results to study the meteorological causes, including large-scale circulation and planetary boundary layer features, which led to the extended haze episode on January 6–16, 2013 in central-eastern China. It discusses the possible impact of pollutants transported from southern Hebei Province on Beijing. The study's results show that: (1) the re-adjustment of atmospheric circulation from a longitudinal to a latitudinal model provides a valuable interpretation of the large-scale circulation background to the haze episode experienced in the metropolitan regions of Beijing, Tianjin, Hebei and their surrounding regions; (2) the regional atmospheric stratification of the planetary boundary layer is stable and the mixing height is low, suppressing air turbulence in the planetary boundary layer and providing favorable meteorological conditions for the formation of haze; and (3) the southwesterly jet stream with wind speeds of 6–11 m/s at a height of 850–950 hPa and the below-700 m air mass trajectory tracking established using the HYSPLIT4 model interdependently suggest a transport of pollutants from southern Hebei Province to Beijing at 850–950 hPa. •Large-scale latitudinal atmospheric circulation is beneficial for the haze forming.•Local stable stratification and weak turbulent is favorable for the haze formation.•Pollutants transportation from south Hebei on 850–925 hPa favors Beijing's pollution.