Technical note: 12 km resolution capability for the global GEOS-Chem model of atmospheric composition

Abstract. We present a new 12 km nested resolution capability in the GEOS-Chem global model of atmospheric composition. This capability can be applied to simulations for any user-selected domain worldwide from March 2021 onward by accessing a new hourly cubed-sphere C720 (approximately 12 × 12 km2 resolution) global wind archive from the NASA GEOS-FP meteorological data assimilation system. We regridded the archive to support rectilinear GEOS-Chem Classic nested grid simulations worldwide at 0.125° × 0.15625° resolution and denote this as the 12 km GEOS-Chem capability. We evaluate this 12 km configuration of GEOS-Chem by comparison with the standard 25 km (0.25° × 0.3125° resolution) nested configuration in simulations of transport tracers, oxidant-aerosol chemistry, and inversions of satellite data using the Integrated Methane Inversion (IMI). The 12 km simulation features stronger vertical transport (up to 20 % lower surface 222Rn concentrations) because it better captures horizontal convergence both spatially and temporally. Aerosol lifetimes against deposition are shorter by a few percent. The 12 km oxidant-aerosol chemistry can better simulate urban observations of NO2, and shows stronger ozone urban titration together with slightly higher surface ozone background due to enhanced vertical transport. 12 km and 25 km inversions using the IMI show highly consistent results on the regional scale, but the 12 km inversion provides greater information and improved spatial detail to resolve emissions from different sectors.