Dimethyl global natural emission

Tropospheric chemistry models have to take into account a significant number of chemical reactions required to simulate correctly tropospheric chemistry. In the global background marine troposphere, it seems reasonable to consider a simplified chemistry scheme based on O3/ NOx/ CH, and CO photochemical reactions. However, natural emissions of organic compounds from oceans (mainly alkenes and dimethyl sulphide-DMS) might significantly affect the marine boundary layer chemistry and in particular OH concentrations. Over continental areas both under clean and polluted conditions,... 

Particle precursor gases are emitted into the atmosphere either directly by natural and anthropogenic sources or by oxidation processes in the atmosphere. The most prominent precursor gas is probably sulfur dioxide (SO2). It is the precursor for particulate sulfates, such as sulfuric acid (H2SO4) or ammonium sulfate [(NH4)2S04]. Sulfur dioxide is directly emitted by natural sources (e.g., volcano emptions). Anthropogenic sources in industrial regions are mostly associated with combustion processes (e.g., coal combustion). Additional SO2 is derived from oxidation processes of dimethyl sulfide (DMS) over the oceans. Estimations of the global sulfur emissions from these sources are listed in Table 3. 

Dimethyl sulphide (DMS) is produced in sea-water as a consequence of enzymatic action in phytoplankton and zooplankton grazing. Measurements of DMS indicate an average global sea-to-air flux of 40 Tg of sulphur per year (1.3). Instantaneous emission rates to the atmosphere, however, can vary considerably, and depend on the nature and concentration of the phytoplankton, the time of year and the prevailing meteorology. For example, nigh concentrations of Phaeocystis, a prolific producer of DMS, have been found in the North Sea and when it blooms, emissions of DMS may increase by a factor of 40-60 over those in the absence of blooms (4). The sea-to-air flux is also dependent on the depth at which the phytoplankton is found since DMS is slightly soluble in water and can be oxidized in aqueous solution. 

Bopp L, Boucher O, Aumont O, Belviso S, Dufresne JL, Pham M, Monfray P (2004) Will marine dimethylsulfide emissions amplify or alleviate global warming A model study. Can J Fish Aquat Sci 61 826-835 Bouillon RC, Miller WL (2004) Determination of apparent quantum yield spectra of DMS photo-degradation in an in situ iron-induced Northeast Pacific Ocean bloom. Geophys. Res. Lett. 31 Article no. L06310 Bouillon RC, Miller WL (2005) Photodegradation of dimethyl sulfide (DMS) in natural waters Laboratory assessment of the nitrate-photolysis-induced DMS oxidation. Environ Sci Technol 39 9471-9477... 

Dimethyl sulphide (CH3SCH3, DMS) is the dominant natural sulphur eompound emitted from the world s oeeans (Berresheim et ai, 1995, Urbanski and Wine, 1999), accounting for about one quarter of global sulphur gas emissions. Oceanic DMS, through its oxidation products, is proposed to play a key role in climate regulation, especially in the remote marine atmosphere (Charlson et al, 1987). 

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