Light absorption properties of inhomogeneous spherical particles, each consisting of absorbing core and nonabsorbing shell, were investigated using the theory of light scattering from a coated sphere. The absorbing core was assumed to be made of either carbon soot or hematite (Fe2O3), both of which are considered to be important substances in determining the absorptivity in the visible region of atmospheric aerosols. The absorption properties of polydisperse systems in which these inhomogeneous particles are distributed by the power law size distribution were also investigated.
The absorption cross section of spherical soot and hematite particles can increase by a factor of about two when they become coated with concentric spherical shells of nonabsorbing substances having real refractive indices 1.33-1.53. This enhancement of absorption occurs for soot particles of any size. For hematite particles, however, in some cases the nonabsorbing coating acts to reduce the absorption cross section in the region where the particle size is comparable to the wavelength of light. It is shown that the imaginary part of the effective refractive index for polydisperse systems composed of absorbing and nonabsorbing substances becomes somewhat larger when the absorbing component occurs as mixed particles coated with nonabsorbing substances.