Abstract
Aerosol particles have a complex index of refraction and therefore contribute to atmospheric emission and radiative cooling rates. In this paper calculations of the longwave flux divergence within the atmosphere at different heights are presented including water vapour and aerosol particles as emitters and absorbers. The spectral region covered is 5 to 100 microns divided into 23 spectral intervals. The relevant properties of the aerosol particles, the single scattering albedo and the extinction coefficient, were first calculated by Mie-theory and later by an approximation formula with a complex index of refraction given by Volz. The particle growth with relative humidity is also incorporated for different aerosol types and size distributions. These values were taken from Hänel. The results show a significant contribution of aerosol particles to longwave flux divergence, although strongly dependent on the imaginary part of the refractive index, the size distribution and relative humidity. The aerosol contribution to radiative cooling becomes very important in layers below temperature inversions, which are barriers for particle diffusion. There exist atmospheric conditions where the aerosol contribution to radiative cooling is as large as cooling by water vapour.
© 1973 Hartmut Grassl, published by Stockholm University Press
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