The positive radiative forcing by the substantial SO<sub>2</sub> emission reductions is counteracted by decreased BC concentrations in China over the recent decade

Abstract

Abstract. Anthropogenic emissions in China play an important role in altering global radiation budget. Over the recent decade, the clean-air options in China result in substantial reductions in anthropogenic emissions, especially sulfur dioxide (SO2), and improved air quality. However, the associated changes in aerosol climate effects are poorly understood. In this study, we use an advanced global climate model integrated with latest anthropogenic emission inventory to estimate the changes in the aerosol radiative forcings by the emission variation in China between 2008 and 2016. First, our simulations exhibit decreases of 46 % and 25 % for the annual mean surface-level sulfate and black carbon (BC) mass concentrations in East China, respectively, which is the key region subject to stringent emission control options. The decreasing tendency of aerosol optical depth and aerosol absorption optical depth retrieved by satellites is also captured by the model for the period. We find that the resultant net radiative forcing by the changes in the BC and SO2 emissions is −0.04 W m−2 in East China. The substantial reductions in SO2 emissions diminish the scattering effects of sulfate and lead to an overall change of +0.17 W m−2 for the annual mean all-sky shortwave aerosol direct radiative forcing at the top of the atmosphere and +0.13 W m−2 for aerosol-induced cloud radiative forcing. In the meantime, the reduction in BC emissions induces a negative BC radiative forcing of −0.34 W m−2. By accounting for the joint effect of BC and SO2 emissions, our results demonstrate that the positive radiative forcing by the SO2 emission reductions is counteracted by the decrease of BC in China over the recent decade. While the local radiative forcing is small due to the counteracted effects of SO2 and BC emissions, it is relatively larger (+0.16 W m−2) over the north Pacific remote regions for this period, primarily contributed by the reductions in sulfate particles and their effects on cloud properties. With a comprehensive future emission scenario for 2030 and 2050 developed by the recent study, we predict that the strictest environmental policies will induce the change of aerosol radiative forcings of +0.55 and +1.23 W m−2 over East China between 2016–2030 and 2016–2050, respectively. Targeted emission control policies are desirable to improve air quality and mitigate climate change in the future.