Aerosol optical depths and direct radiative perturbations by species and source type

We have used the Laboratoire de Meteorologie Dynamique General Circulation Model (LMDZT GCM) to estimate the relative contributions of different aerosol source types (i.e., fossil fuels, biomass burning, and natural) and aerosol species to the aerosol optical depth (AOD) and direct aerosol radiative perturbation (DARP) at the top-of-atmosphere. The largest estimated contribution to the global annual average AOD (0.12 at 550 nm) is from natural (58%), followed by fossil fuel (26%), and biomass burning (16%) sources. The global annual mean all-sky DARP in the shortwave (SW) spectrum by sulfate, black carbon (BC), organic matter (OM), dust, and sea salt are -0.62, +0.55, -0.33, -0.28, and -0.30 Wm(-2), respectively. The all-sky DARP in the longwave spectrum (LW) is not negligible and is a bit less than half of the SW DARP. The net (i.e., SW+LW) DARP distribution is predominantly negative with patches of positive values over the dust source regions, and off the west coasts of Southern Africa and South and North America. For dust aerosols the SW effect is partially offset by LW greenhouse effect.