Characteristics and meteorological conditions analysis of severe haze events over Beijing-Tianjin-Hebei area

Eastern China has suffered severe and continual haze pollution. The meteorological condition which is very important to influence the formation and depletion of the air pollution has been investigated based on the data from European Centre form Medium-Range Weather Forecasts (ECMWF), Meteorological Information Comprehensive Analysis and Process System (MICAPS) and Chinese Network of Environmental Monitor Center (CNEMC) in this study. Besides, the Nested Air Quality Prediction Model System (NAQPMS) was used to simulate the severe haze events occurred in January 2013. The results showed a significant seasonal change of diurnal concentration of PM_2.5 in summer and autumn. The maximum and minimum monthly averaged concentrations were observed in January and July, respectively. Westerly flow in 500 hPa and weakly warm advection stabilized the atmospheric stratification and impaired the diffusivity of pollutants on the surface, especially when Beijing-Tianjin-Hebei Area was in the back or bottom of weak anticyclone on the surface. Furthermore, NAQPMS quantified this effect that when temperature increased by 0~5℃, relative humidity increased by 30%~50% and wind decreased by 2~3 m·s^-1, PM_2.5 concentration increased by 300 μg·m^-3.