PNNL

Abstract

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 (ERFaer) over the contiguous United States (CONUS). 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). The simulated emissions of natural dust, sea salt, and marine organic matter are remarkably larger in the RRM than in the LR. In addition, RRM simulates stronger aqueous-phase production of sulfate through the enhanced oxidation of sulfur dioxide by hydrogen peroxide due to increased cloud liquid water content. In contrast, the gas-phase chemical production of sulfate is slightly suppressed. The RRM resolves more large-scale precipitation and produces less convective precipitation than the LR, leading to increased (decreased) aerosol wet scavenging by large-scale (convective) precipitation. Regarding aerosol effects on clouds, RRM facilitates more aerosol activation in large-scale clouds (due to the larger temporal variability of large-scale liquid cloud fractions) 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 ERFaer 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.