Ambient Atmospheric Aerosol Extinction Coefficient Reconstruction from PM2.5 Mass Concentrations and Application to Haze Identification in China

ABSTRACT Based on hourly observations of the fine-particle (PM2.5) mass concentration, relative humidity (RH), and visibility at 9 stations in China from 2014-2015, an aerosol extinction coefficient reconstruction method is introduced in this study. The fine aerosol number concentration distribution of wet aerosol particles under ambient conditions can be obtained from the PM2.5 mass concentration by the κ-Kӧhler theory. Then, the aerosol extinction coefficient can be obtained through the Mie theory. The reconstruction model was set up and relevant parameters were recommended. Sensitive tests with different parameters and combinations indicate that good correlations exist between the extinction coefficient calculated with these different parameters and that calculated with the recommended or “reference” parameters. So, a linear regression is adopted to reduce the bias between the calculations and observations. Based on the extinction closure study, the threshold of the extinction ratio (β/βObs) is determined and in order to identify haze and fog weather phenomena at the stations. The bias of haze hour identified by combinations of different values of parameters against that identified by the “reference” parameters are calculated at 61 stations in China. Results indicate that about 99.8% of all stations have a relative bias smaller than 15%, which suggest that the method is feasible for haze identification.