The real part of the mean complex refractive index and the mean density of samples of atmospheric aerosol particles

Abstract

The computation and the physical explanation of the spectral extinction of light in the atmosphere are mainly influenced by some specific prerequisites such as the number and the size of the atmospheric aerosol particles as well as their complex refractive index. Both size and complex refractive index are functions of the relative humidity. During the last years quite a number of investigations into the size distribution of the atmospheric aerosol particles have been carried out. Their refractive index, however is hardly known. An attempt has been made to overcome this deficiency with a new quantitative method for the simultaneous measurement of the real part of the mean complex refractive index and the mean density of samples of atmospheric aerosol particles. This measuring method and the first preliminary results of measurements are presented in this paper. The arithmetical means of nine measurements are 1.57 for the real part of the mean complex refractive index and 2.7 g cm⁻³ for the mean density. Both these values are valid for a relative humidity of 0.40 ± 0.05. These measurements have been used for computing the dependency of both these quantities on the relative humidity. Formulae for these computations are deduced and the computational results for two samples of aerosol particles are presented: While the relative humidity varied between 0 and 1, for both samples the real part of the complex refractive index varied between 1.33 and about 1.7 and the mean density between 1 g cm⁻³ and about 4 g cm⁻³.