Optical properties of mineral dust aerosols with non-absorptive coating: A numerical investigation

Abstract

Mineral particles form complex mixed states with other anthropogenic species through a series of chemical reactions during the long-range transport and aging process, which modifies their optical properties. Traditional homogeneous particle models do not effectively describe the variability of particle size distribution, morphology and mixing structure, and the discrepancy between the simulations and experimental results is still apparent. In this paper, the impact of non-absorptive coating material on the optical properties of mineral dust particles with varying particle size distribution, morphology, and inhomogeneous characteristics is investigated by the core-shell spheroid model. The results reveal that the real part of the complex refractive index (RRI) of non-absorptive coating material has a more prominent effect on the scattering matrix elements than the particle size distribution, morphology, and inhomogeneity. The P11(π)/P11(30°) generally increases with the square of RRI, for any mean effective radius(r0), coating ratio(fcoating), and aspect ratio(α). However, the variation of -P12(θ)/P11(θ) with the r0, fcoating, and α is more complicated and depends on the RRI. The particle inhomogeneity promotes positive values of -P12(θ)/P11(θ) for lower RRI, and negative values for higher RRI in general. The maximum value of -P12(θ)/P11(θ) (Pmax) and the minimum value of -P12(θ)/P11(θ) (Pmin) are strongly depends on the RRI, r0, fcoating, and α. Moreover, the Pmax has an excellent Gaussian distribution relationship with RRI, r0, fcoating, and α. Furthermore, the parameterization scheme of the P11(π)/ P11(30°) and the Pmax as a function of RRI, r0, fcoating, and α are systematically studied. Considering further research, our study may be of great significance for the study of aerosol composition retrieval and remote sensing applications.