Atmospheric aerosols play critical roles in air quality and the Earth-atmospheric energy balance. However, the simulation of atmospheric aerosols in Earth system models is often sensitive to model resolutions due to the use of parameterizations to represent aerosol-related processes. Using the Energy Exascale Earth System Model (E3SM) version 1, this study investigates the impact of horizontal grid spacing on the simulated aerosol mass budget, aerosol-cloud interactions, and the effective radiative forcing of anthropogenic aerosols (ERF_aer) over the contiguous United States. We examine the resolution sensitivity by comparing the nudged simulation results for 2016 from the low-resolution model (LR) and the regional refinement model (RRM). Significant differences are found in natural dust, sea salt, and marine organic matter emissions and the wet scavenging of aerosols by large-scale and convective precipitation between the RRM and LR simulations. In addition, RRM simulates stronger aqueous-phase production of sulfate, but its gas-phase chemical production is slightly suppressed.

Regarding aerosol effects on clouds, RRM enhances aerosol activation in large-scale clouds and boosts water vapor condensation. Consequently, the RRM simulation produces more cloud droplets, a larger cloud droplet radius, a higher liquid water path, and a larger cloud optical depth than the LR simulation. A comparison of the present-day and pre-industrial simulations indicates that ERF_aer at the top of the model is intensified by about 12% under regional refinement, which is mainly attributed to the strengthened indirect effect associated with aerosol-cloud interactions.