A study of the global distribution of sulfate aerosols with a 2D model including microphysics
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The global distribution of sulfate aerosols in the troposphere and lower stratosphere has been calculated using a two-dimensional model. The chemistry includes the main families (NO x , NO y , HO x ) plus the sulfur compounds, while the heterogeneous processes are modelled with a microphysics code which takes into account nucleation, condensation and coagulation. The results are compared with experimental data wherever available. A too low concentration of sulfuric acid is predicted by the model in the troposphere and this is explained by too large a flux of condensation nuclei and partly by the absence of sulfate production from methane sulfuric acid (MSA) in our scheme. Aerosol concentration and size distribution are comparable to observations; however the calculations show a more complex meridional structure than observed, while the size distribution is somewhat shifted toward smaller sizes. This fact is also attributed to the presence of a large number of nuclei and to the absence of any mechanism for evaporation of aerosol particles back to the core. We have also perturbed the anthropogenic fluxes of SO2, CS2 and the OCS ground mixing ratios to asses the sensitivity of the aerosol concentration: we have found very little changes in the aerosol distribution because H2SO4 chemistry is dominated by heterogeneous processes.
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