Characteristics of Aerosol Scattering Hygroscopic Growth Factor under Different Haze Intensities

Based on the hourly observation data from nephelometer and aethalometer, as well as the simultaneous data of visibility (V), relative humidity (H_R), nitrogen dioxide (NO₂) and fine particulate matter (PM_2.5) concentrations from October to December 2017 in Chengdu, aerosol scattering hygroscopic growth factors were calculated by optical synthesis method and the influence of haze intensity (slight, mild, moderate and severe) on the aerosol scattering hygroscopic growth factor was analyzed. The results show that: (1) the aerosol scattering hygroscopic growth factors all obeyed Lognormal distribution under different haze intensities, whose mathematic expectation and variance increased with the growing haze intensity. (2) The hygroscopicity of aerosol increased with the growing haze intensity, and proportion of strong hygroscopicity mode were 6.2%, 11.4%, 50.8% and 84.5% for slight, mild, moderate and severe haze. (3) The determination coefficients (R²) of the simulated and measured values of all the samples corresponding to scattering hygroscopic growth model of quadratic polynomial under slight, mild, moderate and severe haze intensities were 0.684, 0.627, 0.729 and 0.786, respectively. The model of aerosol scattering hygroscopic growth was very sensitive to sample selection and its generalization performance increased with the growing of haze intensity.