Volumetric scattering and absorption by aerosols: parametric sensitivity in Mie modeling and comparisons to observations.

Aerosol complex indices for soot, ammonium sulfate, methylene blue, ambient, Arizona road dust, and combinations were employed in Mie calculations to determine the volume scattering and absorption coefficients beta(s) and beta(a), respectively. Parametric aerosol properties (i.e., number density, particle size distribution, optical complex index of refraction, and particle shapes) were used in the first principles of Mie calculations to derive beta(s) and beta(a), which were then compared to corresponding measurements. The result of the beta(s) and beta(a) calculation was found to depend very sensitively on the number density and size distribution of the aerosols and less strongly on the optical complex index of refraction. The refractive and absorptive portions of the index affect the wavelength dependence of beta(s) and beta(a). When particles are of irregular shapes or when they agglomerate, the effect is to produce increased scattering, the amount depending on the sizes and numbers of the asperities or constituents of the agglomerates.