Polarized radiative transfer in heterogeneous black carbon aerosol particles

Abstract

Research on the polarized radiative transfer of black carbon (BC) aerosol particles in the atmosphere is of great help for real-time monitoring of climate change. Existing studies generally have not considered the effects of complex morphology and heterogeneity of BC aerosol particles on the polarized radiative transfer. BC aggregates with different coating shapes are established in accordance with the heterogeneous particle superposition model. The vector Monte Carlo method (VMCM) combined with Discrete dipole approximation (DDA) method proposed in this work offers a general method for calculating the polarized radiative transfer of heterogeneous BC aerosol particles with arbitrary coating shapes. The effects of sulfate coating volumes and shapes, and wavelengths on the Stokes parameters, the degree of polarization P, transmissivity T, and reflectivity R of atmosphere containing heterogeneous BC aerosol particles are discussed. The results show that the simplification of coating shape underestimates the Stokes parameter I and the degree of polarization P of the top of atmosphere and overestimates the I of the bottom of atmosphere. The simplification models of coating shape result in a maximum underestimation of the peak I by ∼26% at the bottom of atmosphere and a maximum overestimation of the peak I by ∼8% at the top of atmosphere, relative to that of the irregular coating models. Moreover, coating volumes and wavelengths also significantly affect the polarized radiative transfer characteristics. Thus, the influence of these factors should be considered for the calculation of polarized radiative transfer of heterogeneous BC aerosol particles in the atmosphere.