Radiative impact of ammonium-sulfate-nitrate aerosols in a general circulation model study

We implemented a new ammonium-sulfate-nitrate module into an aerosol global model, SPRINTARS, and calculated global distributions of both ammonium and nitrate components, which have not been evaluated adequately so far, and then estimated their radiative impacts. The ammonium-sulfate-nitrate module in this study is based on a thermal equilibrium theory of ion components with dependence on the meteorological condition such as temperature and relative humidity (RH), taking account for the light computational burden. In terms of radiation, an increase in the scattering components brought an increase in both aerosol optical thickness (AOT) and single scattering albedo (SSA). In the global calculation, the predicted AOT and SSA results are comparable with observed ones by satellite and ground-based measurements, although the predicted AOT was still underestimated. As a result, the global annual mean radiative forcings due to total anthropogenic aerosol direct and indirect effects were estimated to be -0.6 W m-2 (-0.3 W m-2 without ammonium and nitrate components) and -0.8 W m-2 (similar magnitude to one without ammonium and nitrate components), respectively, with both uncertainties of less than 0.1 W m-2 estimated from sensitivity experiments for several ammonium-sulfate-nitrate schemes. By implementing the ammonium and nitrate aerosols, the contributions of the aerosol radiative forcings by aerosol direct effect to that by aerosol total effects increase all over the world and those are estimated to be more than 40 % over the industrial areas.