Abstract
This paper presents a discussion of the effective complex refractive index of aerosols composed of particles having large and small absorption coefficients in the visible region. Based on Mie theory, the effective complex refractive indices at the wavelength of 0.55μm which give correct values of both the extinction coefficient and the single-scattering albedo were calculated for the following two kinds of aerosol models: one is composed of carbon soot and ammonium sulfate particles and the other is composed of hematite and ammonium sulfate particles in varied proportion. The power law was assumed for the size distribution of the particles, with the exponent being varied from 2.5 to 3.5. The phase functions and the volume backscattering coefficients were also calculated in order to check the validity of using the effective refractive indices.
The imaginary part of the effective refractive index increases with increase of carbon soot or hematite content and it also depends on the size distribution of these substances. The imaginary part of the refractive index obtained for a possible range of the soot content is consistent with that so far reported for atmospheric aerosols by several authors. It rarely exceeds 0.05 in this study. Based on these results, the possible effect of aerosol on the heat balance of the earth-atmosphere system is briefly discussed.
