Comparison study between nitrate and sulfate aerosols and their coating effect on the scattering properties of...

The existing numerical models generally employ sulfate instead of nitrate to simulate the scattering properties of aerosol, the corresponding radiative deviation needs to be evaluated urgently. Moreover, the sophisticated mixture of nitrate, sulfate, and mineral particles is formed through a series of chemical reactions, which makes it extremely challenging to understand the scattering properties of atmospheric aerosols. In this study, the core-shell ellipsoid model is used to flexibly characterize the morphology and mixed structures of nitrate, sulfate, and mineral in the fine mode radius range. The T-matrix method is used to compare the scattering properties of nitrate, sulfate, and mineral within different morphologies and mixing states at four selected wavelengths (0.44, 0.675, 0.87, and 1.02 μm). The results show that the difference of mean extinction efficiency factor (< Q_e >) and mean single scattering albedo (< ω >) between nitrate and sulfate-containing particles is very small, mainly within 2%. However, their mean scattering phase function P₁₁(θ) is quite different. The difference of forward scattering phase function P₁₁(0) is up to 7%, while the difference of backward scattering phase function P₁₁(π) can reach more than 25%. Overall, particle morphology and incident wavelength regulate the value of the optical parameters, whereas the coatings on the mineral play a more important role in drifting, but the differences between nitrate- and sulfate-containing particles are still very pronounced.