Changes of local planetary albedo by aerosol particles

Abstract

The climate parameter local planetary albedo is affected both in clear and cloudy areas by aerosol particles. In both cases the albedo may increase or decrease if turbidity increases, i.e. there are areas where an additional pollution leads to an energy gain or loss. While the most important parameters in clear areas are surface albedo and the mass absorption coefficient of the particles, aerosol particle concentration via the number of condensation nuclei and again absorption are the dominating factors in clouds. A reappraisal of known bulk formulae for clear areas points to additional parameters determining the crossover from heating to cooling. The most important additional parameter is sun elevation, however, aerosol optical depth also has to be considered. The weakness of former estimates of cloud albedo change with aerosol particle characteristics is demonstrated for broad cloud drop size distributions and for simultaneous changes in particle number, size, and chemical composition. The terrestrial radiation does not compensate for the partly drastic changes in the solar radiation in clear and cloudy areas, again pointing to a strong influence of aerosol particles on local planetary albedo.