Effect of emissions inventory versus climate model resolution on radiative forcing and precipitation over the continental United States

We evaluate the impact of anthropogenic emission inventory and climate model grid resolution on aerosol concentrations and black direct aerosol top of atmosphere forcing. Anthropogenic aerosol concentrations of sulfate, black carbon (BC), and organic carbon (OC) are simulated using a high‐resolution (25 km) regional climate model (RegCM) with (1) the 2000 1° × 1° EDGAR inventory and (2) the 1999 4 km U.S. Environmental Protection Agency (EPA) National Emissions Inventory. A third 60 km EPA simulation tests the effect of climate model resolution. Simulated SO2 and SO42− concentrations from the 25 km simulations agree with observations in DJF, but JJA modeled SO2 is high and SO42− is low by a factor of 2–3 suggesting incomplete sulfate conversion in the model. Simulated BC and OC concentrations are lower than observations, and sensitivity tests suggest the inventories are missing carbonaceous sources. Total aerosol optical depth (AOD) is greater than observations in DJF and lower in JJA, confirming an underestimation of aerosols during summertime. Derived top of atmosphere radiative forcing has a maximum JJA decrease of 7, 8, and 10 W/m2 in the EDGAR, EPA 25 km, and EPA 60 km simulations, respectively. Generally, the 60 km simulations improve measured‐modeled aerosol agreement due to reduced precipitation and wet deposition in the 60 km simulation. Comparisons with observations indicate that total precipitation in the 60 km simulation is closer to observations. Thus, aerosol forcings from a regional model may be equally sensitive to resolution and emissions inventory due to the parameterization of large‐scale precipitation and wet removal processes. Key Points Choice of emission source and resolution equally important Choice of model resolution relatively important Model resolution affects precipitation, which changes removal