A GLOBAL 3-DIMENSIONAL MODEL OF THE TROPOSPHERIC SULFUR CYCLE

The tropospheric part of the atmospheric sulfur cycle has been simulated in a global three-dimensional model. The model treats the emission, transport, chemistry, and removal processes for three sulfur components; DMS (dimethyl sulfide), SO2 and SO4(2-) (sulfate). These processes are resolved using an Eulerian transport model, the MOGUNTIA model, with a horizontal resolution of 10-degrees longitude by 10-degrees latitude and with 10 layers in the vertical between the surface and 100 hPa. Advection takes place by climatological monthly mean winds. Transport processes occurring on smaller space and time scales are parameterized as eddy diffusion except for transport in deep convective clouds which is treated separately. The simulations are broadly consistent with observations of concentrations in air and precipitation in and over polluted regions in Europe and North America. Oxidation of DMS by OH radicals together with a global emission of 16 Tg DMS-S yr-1 from the oceans result in DMS concentrations consistent with observations in the marine boundary layer. The average turn-over times were estimated to be 3, 1.2-1.8, and 3.2-6.1 days for DMS, SO2, and SO4(2-) respectively.