Optical Properties of Black Carbon Aerosols with Different Coating Models

Abstract

Research on the optical properties of black carbon (BC) aerosols is highly important for investigating global climate change. A general inhomogeneous particle superposition model is developed. Inhomogeneous particles with arbitrary shapes can be constructed by this model. BC aerosols with core-shell, spherical, ellipsoid, and irregular coating models are established to explore the impact of coating shape on their optical properties. The optical properties are studied employing the discrete dipole approximation method (DDA). The influences of the morphology of BC aerosols, the coating volume fractions, and the shape of coatings on the optical properties are analyzed. The irregular coating shape causes a higher forward scattering intensity and a lower extinction cross-section. The forward scattering intensity of the core-shell model is lower than other models. The effect of the coating shape on forward scattering intensity becomes smaller as coating volume and fractal dimension increase. Consequently, assuming irregular coating as spherical coating models considered in most studies leads to inaccuracy in the optical properties of BC aerosols. It is necessary to comprehensively consider the effects of aerosol morphology and coating volume for investigating the optical properties of black carbon aerosols.

Keywords

• inhomogeneous particle superposition model
• black carbon aerosols
• optical properties
• discrete dipole approximation method