Linear depolarization ratios of nitrate-coated mineral dust particles in haze episodes.

Abstract

This study reports an internal mixed particle model of dust and nitrate aerosols using the actual haze condition. We performed accurate calculations of linear depolarization ratios (LDR) of nitrate-coated mineral dust particles at three wavelengths (0.35, 0.53, and 1.06 µm) using the T-matrix method. The LDRs of the mono-disperse aerosol particles evolve differently as expressions in the Rayleigh and Mie domains. In the Rayleigh domain, the LDRs increase with the core-shell ratio and the aspect ratio and decrease when the wavelength increases. The forward and backward LDRs depend more on aspect ratio than on the core-shell ratio. In the Mie domain, the LDRs overall increase with the core-shell ratio and the aspect ratio, but there is no significant regular change. When the wavelength increases, the gradual change can be explained by the size parameter of the particles in the vicinity of the Rayleigh domain. For poly-disperse particles, the core-shell ratio mainly affects the position of the side-scattering peak, whereas aspect ratio affects the LDRs. The backscattering LDRs depend more on the variation of aspect ratio, and the core-shell ratio only affects LDRs in a small range. Furthermore, our results on the LDRs are highly promising for remote sensing of the non-spherical and inhomogeneous properties of fine aerosols compared with AERONET measurements. Our results provide a comprehensive understanding of the LDR evolution for coated non-spherical particles in a haze atmosphere. The LDRs can be used as an empirical reference for remote sensing to distinguish coated non-spherical particles.