Contrasting Impacts of Surface Coating on the Short and Longwave Radiative Effects of Dust Aerosol: A Theoretical Study

In this study, we investigated the effects of the dust surface coating by pollution aerosols, such as sulfate and nitrate aerosol, on the shortwave (SW) and longwave (LW) radiative effects of dust aerosols. Three hypothetical schemes were developed to emulate different pathways and mechanisms of surface coating by pollution aerosols on dust particles. The surface coating of pollution aerosol increases the extinction in comparison with pure dust, and thereby increases the magnitude of both shortwave and longwave DRE of dust. However, this extinction enhancement effect is much more efficient in the LW than in SW. It is because the extinction efficiency (Qe) of dust particles approaches the geometrical limit Qe~2 regardless of size in the SW whereas Qe quickly increases with dust particle size in the LW. As a result of this contrast, surface coating enhances the warming SW DRE of dust more efficiently than it does the LW cooling DRE, leading to a decreased (less cooling) net DRE of dust particles compared to that of pure dust.