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Abstract

Atmospheric aerosol particles influence the earth's radiation field by scattering and absorption of solar radiation either in cloudfree parts of the atmosphere or inside clouds. They determine via the cloud condensation nuclei spectrum the number and size of cloud droplets which will be formed under certain conditions of the general circulation. The main result for the cloudfree areas is: Depending on surface albedo and the imaginary part of the refractive index a particle increase can lead to albedo increase or decrease with the crossing point nearly independent on particle size and optical depth. Within cloudy areas one has to distinguish three albedo changing effects. The combination of all three effects enhances cloud albedo for thin clouds and decreases cloud albedo for thick clouds. An estimate for planetary albedo change is nearly impossible at present because of the lack of data on the imaginary part of the refractive index of aerosol particles and on the mean optical depth of clouds.