Model calculations of the contribution of tropospheric SO2 to the stratospheric aerosol layer

Abstract:

Despite its importance, many processes forming the stratospheric aerosol layer are not well understood, including the magnitude of the contribution of tropospheric SO₂ to the non-volcanic background of the aerosol layer. We examine the tropospheric chemistry of SO₂ and its transport to the stratosphere by running a chemical box model along trajectories ascending from the boundary layer to the tropopause. Numerous sensitivity runs are used to assess the range of uncertainty in the global SO₂ flux through the tropopause introduced by the limited knowledge of the involved process parameters. The trajectory model is based on the ATLAS model and is driven by ECMWF ERA Interim data and includes a parametrization for unresolved convection based on a statistival approach. The chemistry model includes the gas phase reactions SO₂+OH and DMS+OH and the liquid phase reactions SO₂+H₂O₂ and SO₂+O₃ and uses background fields of OH, O₃ and H₂O₂ obtained from a GEOS-Chem CTM run. The model results are compared with measurements from the StratoClim aircraft campaign in the Asian Summer Monsoon 2017. Moreover estimates of the global input of sulfur to the stratosphere will be provided.