Effect of nitrate coatings on the optical properties of mineral dust particles during the haze aging process

The frequent occurrence of haze episodes in China poses a severe threat to human health. During the haze period, nitrate and mineral dust form a complex mixing state through heterogeneous reactions. The existing numerical models usually assume sulfate instead of nitrate in simulating the optical properties of aerosol, and the radiation difference between sulfate and nitrate needs to be evaluated. Therefore, it is significant to study the influence mechanism of nitrate coating on the optical properties of mineral particles during the haze aging process. In this study, the effects of nitrate coating on the scattering and polarization properties of mineral dust under multi-spectral conditions are investigated by core-shell spheroid models using the T-matrix method. The results show that the optical properties of mineral dust are wavelength dependent, whereas the coating ratio plays a governing role in the overall floating. The coating ratio changes with the haze aging process, which leads to a dramatic variation in the scattering and polarization properties at short wavelengths. For different coating ratios, the scattering phase function in the backward direction P-11(pi) can be approximately enhanced by a factor of 1.55, while the maximum value of P-12(theta), P-11(0) and the linear backscattering depolarization ratio are weakened by nearly 25%, 10%, 14% at 0.35 mu m, respectively. However, these effects are not obvious in the longer waveband. Overall, various coating structures are characterized by a reasonable number of limit tunable parameters, which is of great significance to understand the mixing structure and optical properties of mineral dust during the haze aging process. (C) 2021 Published by Elsevier Ltd.