Dissimilar Roles of Aerosols, Nitrogen Deposition and Ozone on the Terrestrial Carbon Sink in China during 2010–2020

Abstract. China's Clean Air Action (CAA) plan implemented since 2013 has significantly altered atmospheric composition, and yet its impact on the terrestrial carbon sink remains unclear. This study employed the Regional Earth System Model (RegESM), an online-coupled climate–chemistry–ecosystem modeling framework, to quantify the impacts of aerosols, surface ozone (O₃), and nitrogen deposition on China’s net ecosystem productivity (NEP) from 2010 to 2020. The results show that aerosols enhanced China’s NEP by 17.93 TgC yr^-1 (4.49 % of the total NEP), primarily by increasing diffuse radiation, with the most pronounced effects in Southern and Eastern China. Nitrogen deposition further increased NEP by 37.98 TgC yr^-1 (9.52 %), concentrated in Central and Southern regions. In contrast, O₃ pollution reduced NEP by 51.33 TgC yr^-1 (12.9 %), particularly in the forest-dominated Southeast. The positive impacts of aerosols and nitrogen deposition on the carbon sink weakened over time, whereas the negative influence of O₃ was increasing. The combined effects indicate that CAA-induced atmospheric chemistry changes reversed the dominant atmospheric drivers of China’s terrestrial carbon sink, from enhancement by aerosols and nitrogen deposition to suppression by ozone. Our findings highlight the need for stronger O₃ pollution control to achieve co-benefits between air-quality improvement and carbon neutrality.