Direct radiative forcing of light-absorbing carbonaceous aerosol and the influencing factors over China

Abstract. Black carbon (BC) and brown carbon (BrC) are the dominant light-absorbing carbonaceous aerosols (LACs) that contribute significantly to climate change through absorbing and scattering radiation. This study used the GEOS-Chem integrated with the Rapid Radiative Transfer Model for GCMs to estimate LACs properties and direct radiative forcings (DRFs) in China. Primary BrC (Pri-BrC) and secondary BrC (Sec-BrC) were separated from the organic carbon and modeled as independent tracers. The Chinese anthropogenic emissions of LACs emissions and the refractive indexes were updated. Additionally, we investigated the impacts of LACs properties and atmospheric variables on LACs DRFs based on principal component analysis. The results showed that the atmospheric annual mean clear-sky net DRFs of BC, Pri-BrC, and Sec-BrC in China were 1.848 ± 1.098, 0.146 ± 0.079, and 0.022 ± 0.008 W m^-2, respectively. The atmospheric shortwave DRFs of BC and Pri-BrC were proportional to their corresponding concentrations, aerosol optical depth (AOD), and absorption aerosol optical depth (AAOD), and inversely proportional to single scattering albedo, surface albedo, and ozone concentration in most regions. The surface longwave DRFs for the LACs showed negative correlations with water vapor in most areas. The highest atmospheric warming effect of LACs was observed in Central China, followed by East China, owing to the high LACs concentrations, AOD, and AAOD and low surface albedo and ozone concentration. Based on the net DRFs, we found that BC exerts a warming effect at the top of the atmosphere, while Pri-BrC and Sec-BrC induce a cooling effect. Within the atmosphere, they all can contribute to atmospheric heating, whereas at the surface, they collectively lead to surface cooling. This study enhances our understanding of the climatic impacts of LACs.