Description and Evaluation of the Emission and Atmospheric Processes Integrated and Coupled Community (EPICC) Model Version 1.0

Abstract We present a comprehensive description and benchmark evaluation of the global–regional chemical transport model called the Emission and Atmospheric Processes Integrated and Coupled Community (EPICC) model. The framework incorporates (1) grid configuration, (2) transport dynamics, (3) chemical mechanisms, (4) aerosol processes, (5) wet/dry deposition parameterizations, and (6) heterogeneous chemistry treatments associated with sulfate, nitrous acid (HONO) chemistry, and aerosol/cloud–photolysis interactions (APIs/CPIs). Openly shared with the atmospheric research community, the model facilitates integration of advanced physicochemical schemes to enhance simulation accuracy. Globally, the model demonstrates realistic representations of ozone (O 3 ) and aerosol optical depth. The EPICC model generally demonstrates robust performance in simulating regional concentrations of O 3 and PM 2.5 (and its components) in China. It successfully captures vertical profiles of both global and regional O 3 . Notably, the model mitigates frequently reported sulfate underestimations in highly industrialized regions of China. The model accurately captures two regional severe pollution episodes observed in eastern China (January/June 2021). Sensitivity experiments highlight the critical roles of heterogeneous chemical mechanisms associated with sulfate, HONO chemistry, APIs, and CPIs in capturing PM 2.5 and O 3 concentrations in China. Improved sulfate mechanisms result in an increase of approximately 32.4% (2.8 µg m −3 ) in simulated winter sulfate concentrations when observations exceed 10 µg m −3 . Enhanced HONO elevates winter O 3 and PM 2.5 by ⩽20 and ⩽10 µg m −3 , respectively. Overall, CPIs dominate over APIs in improving O 3 and PM 2.5 simulations across China. Locally, APIs mitigate PM 2.5 and O 3 discrepancies in the Sichuan Basin. Seasonal cloud–chemistry coupling explains the weaker impact of PM 2.5 in summer.