A Study of scattering properties of fly ash aerosols: comparison of laboratory and Lorenz-Mie results

This paper compared the results of laboratory measurements of the Stokes scattering matrix of non-spherical fly ash aerosols at a visible wavelength with the results of Lorenz-Mie computations for projected area equivalent spheres. Bidirectional reflectance functions (BRDFs) were calculated and analyzed by DISORT with scattering phase function calculated using Lorenz-Mie theory and measured in an experiment. The results show poor agreement between experimental scattering matrix of non-spherical fly ash aerosol particles and that of Lorenz-Mie calculation for most scattering angles. However, their asymmetry factors are similar. The variation trend of BRDF of spherical particles is basically consistent with that of non-spherical particles, but the BRDF curve of spherical particles is more variable. With the increasing of aerosol optical depth, the curves of BRDF of spherical particles and non-spherical particles go to a steady and similar value. Assumption of spherical particles will result in a certain error under thin optical depth, the relative error of BRDF will grow up to 60%, therefore the influence of non-spherical characteristics must be taken into consideration. However, when the optical depth is larger, the relative error of BRDF is usually lower than 10%, spherical particle assumption has certain applicability.