Description and evaluation of the Emission and atmospheric Processes Integrated and Coupled Community (EPICC) Model version 1.0

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 (i) grid configuration, (ii) transport dynamics, (iii) chemical mechanisms, (iv) aerosol processes, (v) wet/dry deposition parameterizations, and (vi) 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 (O3) and aerosol optical depth. The EPICC model generally demonstrates robust performance in simulating regional concentrations of O3 and PM2.5 (and its components) in China. It successfully captures vertical profiles of both global and regional O3. 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 PM2.5 and O3 concentrations in China. Improved sulfate mechanisms result in an increase of approximately 32.4% (2.8 μg/m3) in simulated winter sulfate concentrations when observations exceed 10 μg/m3. Enhanced HONO elevates winter O3 and PM2.5 by ≤20 and ≤10 μg/m3, respectively. Overall, CPIs dominate over APIs in improving O3 and PM2.5 simulations across China. Locally, APIs mitigate PM2.5 and O3 discrepancies in the Sichuan Basin. Seasonal cloud–chemistry coupling explains the weaker impact of PM2.5 in summer.