Simulation of stratospheric sulfate aerosols using a Center for Climate System Research/National Institute for Environmental Studies atmospheric GCM with coupled chemistry 1. Nonvolcanic simulation

A new middle-atmosphere general circulation model (GCM) that includes the photochemistry for O-x-HOx-NOx-ClOx-SOx species has been developed. The dynamical, radiative, and chemical processes of the model are fully interactive. The model is based on the Center for Climate System Research/National Institute for Environmental Studies atmospheric GCM (CCSR/NIES AGCM). The chemical process predicts the concentration of 37 chemically reactive gases and includes 26 photolysis and 71 homogeneous reactions. It also includes four heterogeneous reactions on the surface of sulfate aerosols. Gaseous sulfuric acid is produced by the photolysis of carbonyl sulfide (OCS) and SO2 oxidation, and saturated sulfuric acid is condensed into aerosols. The aerosol size distribution is assumed to be unimodal and lognormal, and the aerosol composition is assumed to be 75% sulfuric acid droplets. The model considers washout, surface deposition, and sedimentation of sulfate aerosols. The parameterized updraft and downdraft of tracers by deep convection is also taken into consideration. In order to investigate the chemical effect of nonvolcanic sulfate aerosols, an 8-year integration has been done. A net flux of gaseous sulfate precursors from the troposphere to the stratosphere is estimated to be 0.067 TgS/yr. The transport of SO2 from the troposphere to the stratosphere contributes about 48% of the net flux.