Sensitivity of dynamic aging on the climate effects of black carbon aerosols over East Asia in summer

Abstract. The climate effects of black carbon (BC) remain highly uncertain, and one critical process that requires accurate representation in climate models is BC aging. This study implements a dynamic aging scheme, which accounts for both condensation and coagulation processes, into the regional climate and chemistry coupled model RegCM-Chem to evaluate the BC climate effects over East Asia in summer. Results indicate that in heavily polluted regions such as the North China Plain and the Sichuan Basin, the BC aging timescale is shorter than 10 hours, promoting the formation and wet deposition of hydrophilic BC, which reduces the BC column burden over East Asia by an average of 0.12 mg m⁻². Conversely, BC surface concentrations and optical depth exhibit an increase over eastern China due to the compensation of reduced dry deposition. The strengthened BC direct effects favor the development of the East Asian summer monsoon and enhance moisture convergence and cloud fraction in southern China. Additionally, accelerated aging also promotes increases in cloud droplet number concentrations and cloud optical depth. Under the dynamic aging scheme, the effective radiative forcing at the top of the atmosphere over East Asia due to BC–radiation interactions, BC–cloud interactions and BC–radiation–cloud interactions are +3.60, −0.58 and +0.90 W m⁻², respectively. The climate effects of BC exhibit pronounced nonlinearity driven by adjustments in circulation and cloud. Overall, BC induces a much drier and warmer surface in northern China, whereas southern China experiences the opposite effect.