Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 4 3 2004 10.5194/acp-4-589-2004 http://www.atmos-chem-phys.net/4/589/2004/ http://www.atmos-chem-phys.net/4/589/2004/acp-4-589-2004.html http://www.atmos-chem-phys.net/4/589/2004/acp-4-589-2004.pdf 589 608 2004-04-14 Model study of multiphase DMS oxidation with a focus on halogens R. von Glasow P. J. Crutzen Institute for Environmental Physics, Universität Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany Center for Atmospheric Sciences, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, 92093-0221, USA Atmospheric Chemistry Division, Max-Planck-Institut für Chemie, PO Box 3060, 55020 Mainz, Germany We studied the oxidation of dimethylsulfide (DMS) in the marine boundary layer (MBL) with a one-dimensional numerical model and focused on the influence of halogens. Our model runs show that there is still significant uncertainty about the end products of the DMS addition pathway, which is especially caused by uncertainty in the product yield of the reaction of the intermediate product methyl sulfinic acid (MSIA) with OH. BrO strongly increases the importance of the addition branch in the oxidation of DMS even when present at mixing ratios smaller than 0.5pmol mol^-1. The inclusion of halogen chemistry leads to higher DMS oxidation rates and smaller DMS to SO₂ conversion efficiencies. The DMS to SO₂ conversion efficiency is also drastically reduced under cloudy conditions. In cloud-free model runs between 5 and 15% of the oxidized DMS reacts further to particulate sulfur, in cloudy runs this fraction is almost 100%. Sulfate production by HOCl_aq and HOBr_aq is important in cloud droplets even for small Br^- deficits and related small gas phase halogen concentrations. In general, more particulate sulfur is formed when halogen chemistry is included. A possible enrichment of HCO₃^- in fresh sea salt aerosol would increase pH values enough to make the reaction of S(IV)^* (=SO_2,aq+HSO₃^-+SO₃^2-) with O₃ dominant for sulfate production. It leads to a shift from methyl sulfonic acid (MSA) to non-sea salt sulfate (nss-SO₄^2-) production but increases the total nss-SO₄^2- only somewhat because almost all available sulfur is already oxidized to particulate sulfur in the base scenario. We discuss how realistic this is for the MBL. We found the reaction MSA_aq+OH to contribute about 10% to the production of nss-SO₄^2- in clouds. It is unimportant for cloud-free model runs. Overall we find that the presence of halogens leads to processes that decrease the albedo of stratiform clouds in the MBL.