Both non-uniform mixing states and coating structures are important for the absorption enhancement and radiative effect of black carbon

Black carbon absorption is a major contributor to global warming, with considerable uncertainty due to complex microscopic properties. Previous studies have mainly attributed the complex absorption enhancement (E_abs) to the non-uniform mixing states, while the effects of the non-uniform coating structure have usually been ignored. In this paper, a modeling framework was proposed to simultaneously investigate the effects of complex coating structures and mixing states. At the particle scale, the effects of non-uniform coating structure can generally be reflected by three levels, and we show that modeling the non-uniform coating structure is important to explain the small E_abs observed in laboratory measurements, which are difficult to explain with a Mie-based model and a model of uniform coating structure. On a population scale, the simultaneous consideration of heterogeneous mixing states and coating structures can significantly improve the model performance in reproducing the field measurements. Although both non-uniform mixing states and coating structures have an important impact on the global aerosol optical absorption depth (AAOD) and direct radiative forcing (DRF), they may attenuate each other's effects. Therefore, previous studies may overestimate the effects of mixing states based on Mie theory by assuming a uniform coating structure. This work clearly demonstrates the importance of both non-uniform mixing conditions and coating structure on aerosol absorption and DRF.