Comparison and validation on global aerosol distribution simulated with two different aerosol models in the Community Atmosphere Model version 5.3

Estimates of atmospheric aerosol in current climate models have a large diversity. In order to investigate the uncertainty in global aerosol simulations, we compare two different aerosol models: Piecewise log-normal approximated Aerosol Model (PAM) and 7-mode version of Modal Aerosol Model (MAM7). Aerosol size distribution and mixing state, parameterizations of chemical and physical processes are essentially different in PAM and MAM7. Both aerosol models are driven with a same atmospheric model, the Community Atmosphere Model version 5.3 (CAM5.3). Meteorological conditions such as wind, clouds and precipitation are forced uniformly to constrain their effects on aerosol source and sink processes. The Coupled Model Intercomparison Project Phase 6 (CMIP6) provides the historical emission data for sulfate, black carbon and organic carbon. While dust and sea salt emission schemes are the default ones used in PAM and MAM7, respectively. The experiments aim to quantify how different aerosol models will influence the simulated global aerosol distribution. Comparing to observations from ground stations, model calculated sulfate aerosol shows a generally good agreement but black carbon and organic carbon still have non-negligible biases. The different aerosol size parameters for each aerosol type in PAM and MAM7 have crucial influences on the simulated particle sizes. We compare PM10 and PM2.5 measurements (aerosol particles with diameter smaller than 10 and 2.5 micrometers, respectively) to examine the modeled aerosol size distributions. In North America and Europe, model estimated PM2.5 and PM10 agree decently to the site observations. However, PM2.5 is underestimated in PAM in some desert regions such as Sahara and Taklamakan. In addition, we compare the aerosol optical depth and number concentration of particles larger than 20 nanometers (CN20) with the relevant data from satellite retrievals and surface measurements. The comprehensive comparison of aerosol distributions in PAM and MAM7 provide a solid base for further exploring the uncertainty in aerosol simulation caused by different aerosol schemes in a climate model.