Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 3 1 2003 10.5194/acp-3-49-2003 http://www.atmos-chem-phys.net/3/49/2003/ http://www.atmos-chem-phys.net/3/49/2003/acp-3-49-2003.html http://www.atmos-chem-phys.net/3/49/2003/acp-3-49-2003.pdf 49 65 2003-01-28 DMS atmospheric concentrations and sulphate aerosol indirect radiative forcing: a sensitivity study to the DMS source representation and oxidation O. Boucher C. Moulin S. Belviso O. Aumont L. Bopp E. Cosme R. von Kuhlmann M. G. Lawrence M. Pham M. S. Reddy J. Sciare C. Venkataraman Laboratoire d’Optique Atmosphérique, CNRS UMR 8518, USTL, Villeneuve d’Ascq, France Laboratoire des Sciences du Climat et de l’Environnement, CEA/CNRS, Gif sur Yvette, France Laboratoire d’Océanographie Dynamique et de Climatologie, CNRS/UPMC/IRD, Paris, France Laboratoire de Glaciologie et Géophysique de l’Environnement, CNRS, Saint-Martin-d’Hères, France Max Planck Institute for Chemistry, Air Chemistry Department, Mainz, Germany Service d’Aéronomie, CNRS/UPMC/UVSQ, Paris, France Centre for Environmental Science and Engineering, Indian Institute of Technology, Bombay, India The global sulphur cycle has been simulated using a general circulation model with a focus on the source and oxidation of atmospheric dimethylsulphide (DMS). The sensitivity of atmospheric DMS to the oceanic DMS climatology, the parameterisation of the sea-air transfer and to the oxidant fields have been studied. The importance of additional oxidation pathways (by O₃ in the gas- and aqueous-phases and by BrO in the gas phase) not incorporated in global models has also been evaluated. While three different climatologies of the oceanic DMS concentration produce rather similar global DMS fluxes to the atmosphere at 24-27 Tg S yr ^-1, there are large differences in the spatial and seasonal distribution. The relative contributions of OH and NO₃ radicals to DMS oxidation depends critically on which oxidant fields are prescribed in the model. Oxidation by O₃ appears to be significant at high latitudes in both hemispheres. Oxidation by BrO could be significant even for BrO concentrations at sub-pptv levels in the marine boundary layer. The impact of such refinements on the DMS chemistry onto the indirect radiative forcing by anthropogenic sulphate aerosols is also discussed.