On radiative effects of anthropogenic aerosol components in Arctic haze and snow

Abstract

The Arctic aerosol is strongly enriched by anthropogenic pollution which may cause significant modifications of the Arctic climate. A radiation model with an optically interactive snow surface layer is developed to investigate the effect of anthropogenic elemental carbon (EC) and sulphuric acid in the Arctic atmosphere. The model, based on the delta-Eddington method, has 490 wavelength intervals covering solar and terrestrial radiation domains. Computations were made for aerosols-containing natural components and cases contaminated by anthropogenic EC and sulphuric acid, both categories with dry and moist conditions. Comparisons of model results with measurements in the Arctic of direct and total irradiance agree well. During mid-spring averaged conditions, the increase in the daily mean solar warming is found to be 2 or 3 times lower than earlier estimates. The previously expected surface cooling can be offset by direct to diffuse conversion in the haze and by snow contamination. In the infrared, the haze located in a temperature inversion can increase the upwelling irradiance by about 1%. This earth-atmosphere column cooling is caused by deliquescent aerosol material. In contrast, hygroscopic but non-deliquescent compounds like sulphuric acid result in internal exchange of radiative energy. In haze layers, the local cooling rate nearly offsets the daily averaged mid-spring local solar heating rate. More significant net warming due to EC particles takes place in dry and optically thin aerosol layers typically found above the Arctic boundary layer during pollution episodes.