A global chemistry-transport model simulation of tropospheric sulfur cycle

The global tropospheric sulfur cycle, including SO₂, SO^2-₄, MSA, and DMS, has been simulated by a global three-dimensional chemistry-transport model (CTM). The model includes emissions, gas and aqueous chemistry, transport, turbulent mixing in the PBL, and wet/dry deposition, and can use meteorological fields provided by GCM outputs, or output from a numerical weather prediction model run in forecast mode. We demonstrate the use of the model to represent accurately the global sulfur cycle, including comparison of model data with surface time series, deposition fluxes, MSA/nss-SO^2-₄ molar ratios, and prior estimates of the global sulfur budget. We compare results from a simplified sulfur oxidation scheme using stored oxidant fields (OH, O₃, H₂O₂, NO₃) to results using a more detailed CH₄-CO-NO_x-SO_x photochemical model for gas-phase chemistry. These tests show the good and bad points of the global CTM simulation of the sulfur sycle.