The Impact of Model Horizontal Resolution on Aerosol Modeling Over East Asia Using Variable-Resolution CESM2

Abstract

To quantify uncertainties and reduce biases in aerosol modeling over East Asia, we run the Community Earth System Model version 2 at variable-resolution (VR-CESM) with the highest resolution at ∼0.125° over East Asia and globally quasi-uniform resolution at ∼1° (UN-CESM) to investigate responses of simulated aerosol to model resolution. The subgrid variability of aerosol and precursor gas emissions is better represented at the higher resolution. The budget analysis of aerosols in eastern China shows that wet/dry deposition is not sensitive to the model resolution, but sulfate formation (e.g., sulfuric acid gas condensation and aqueous-phase chemistry) increases and aerosol transport out of the region decreases as the resolution increases, which lead to increased aerosol burden and lifetime. Compared to UN-CESM, VR-CESM simulates stronger descending motion along the mountain edge and blocking effects of mountain peaks, which weakens the dispersion of aerosols over the Taihang Mountains and Sichuan Basin. In comparison to surface observations, VR-CESM simulates higher aerosol concentrations in urban areas than UN-CESM does. Over eastern China, increasing model resolution improves the simulated aerosol optical depth (AOD) in terms of spatial distribution and magnitude. Over northern (southwestern) China, the simulated AOD increases by ∼17% (∼32%) with increasing resolution and becomes more comparable to satellite retrievals. The improvements are more significant in urban areas and regions with complex terrains than in rural and coastal areas. The regional annual-mean aerosol direct radiative effect in eastern China simulated by VR-CESM increases by ∼54% (−1.08 W/m² more cooling) at the top of the atmosphere compared to UN-CESM.