Source apportionment of PM2.5 and its optical properties during a regional haze episode over north China plain

Based on the data of air pollutants in a typical regional haze pollution episode over North China Plain (NCP) in November 2018, Positive matrix factorization (PMF), potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models were used to analyze the sources and affecting areas of PM2.5 under different development stages. The whole observation period was divided into 6 segments (clean days, fog process, haze process including three stages of I: accumulation, II: growth, III: explosion, and dry haze process) according to PM2.5 concentration, visibility and relative humidity (RH). The dominant source in clean days was soil dust, with contribution percentage of 30.0%. The contributions of coal combustion and secondary nitrate increased with the development of haze pollution, while those of photochemical product, soil dust and secondary sulfate decreased. Coal combustion contributed the most in stage III (35.8%), indicating that the local coal combustion emission was the main reason for the rapid explosion of pollutants. The contribution of vehicular emission was 16.7%, 30.1% and 12.8% in stage I, II, and III, respectively, which was 2.1, 3.8, and 1.6 times that on clean days, presenting significant regional distribution characteristics. The significant local contribution and short-range transport were the major sources of haze pollution episodes in NCP, and Xianghe will bring pollutants to its northeast and southwest directions in the future. (NH4)2SO4, NH4NO3, and organic matter (OM) were the major components of aerosol extinction coefficient (bext) under all development stages, together accounting for 59.5%–78.6%. With the development of haze process, the contribution of (NH4)2SO4 to bext decreased, while that of NH4NO3 increased.