NONSPHERICITY OF DUST-LIKE TROPOSPHERIC AEROSOLS - IMPLICATIONS FOR AEROSOL REMOTE-SENSING AND CLIMATE MODELING

The nonsphericity of dust-like tropospheric aerosols causes us to ques tion the applicability of using conventional Mie theory to compute the ir radiative properties. In this paper we compare T-matrix computation s of light scattering by polydispersions of randomly oriented nonspher ical aerosols and Mie computations for equivalent spheres. We demonstr ate that even moderate nonsphericity results in substantial errors in the retrieved aerosol optical thickness if satellite reflectance measu rements are analyzed using Mie theory. On the other hand, the use of M ie theory for nonspherical aerosols produces negligible errors in the computation of albedo and flux related quantities, provided that the a erosol size distribution and optical thickness are known beforehand. T he first result can be explained by large nonspherical-spherical diffe rences in scattering phase function, while the second result follows f rom small nonspherical-spherical differences in single-scattering albe do and asymmetry parameter. Our results demonstrate that no cancellati on of errors occurs if one consistently uses Mie theory in the retriev al algorithm and then in computing the albedo for the retrieved aeroso l optical thickness.