Radiative Forcing of Smoke Aerosol Taking into Account the Photochemical Evolution of Its Organic Component: Impact of Illumination Conditions and Surface Albedo

We consider the results of simulating the smoke aerosol radiative forcing (ARF) at the top and bottom of the atmosphere depending on the photochemical evolution of its organic component, illumination conditions, and underlying surface types (water, mixed forest, and snow/ice). At the top of the atmosphere, an increase in the surface albedo and a decrease in the aerosol optical depth can lead to the transformation of the cooling into a heating effect. An increase in absorptance of aerosol particles may cause the ARF to increase at the top of the atmosphere, which is manifested most significantly over snow/ice surfaces; while at the bottom of the atmosphere, ARF decreases. As the solar zenith angle grows, the ARF decreases in absolute value when the smoke plume propagates over weakly reflecting surfaces; however, with growing surface albedo, this dependence becomes nonmonotonic. It is shown that, when the transformations of the optical characteristics of organic aerosol are neglected, the aerosol radiative forcing at the top of the atmosphere can be overestimated or underestimated severalfold (by a few tens of W/m 2 ), and this can also cause an error of determining the ARF sign.