Dimethyl sulfide natural emissions

Natural emissions of sulfur compounds to the atmosphere occur from a variety of sources, including volcanic eruptions, sea spray, and a host of biogenic processes (e.g., Aneja, 1990). Most of the volcanic sulfur is emitted as S02, with smaller and highly variable amounts of hydrogen sulfide and dimethyl sulfide (CH3SCH3). Sea spray contains sulfate, some of which is carried over land masses. 

A U. S. national biogenic sulfur emissions inventory with county spatial and monthly temporal scales has been developed using temperature dependent emission algorithms and available biomass, land use and climatic data. Emissions of dimethyl sulfide (DMS), carbonyl sulfide (COS), hydrogen sulfide (H2S), carbon disulfide (CS2), and dimethyl disulfide (DMDS) were estimated for natural sources which include water and soil surfaces, deciduous and coniferous leaf biomass, and agricultural crops. The best estimate of 16100 MT of sulfur per year was predicted with emission algorithms developed from emission rate data reported by Lamb et al. (1) and is a factor of 22 lower than an upper bound estimate based on data reported by Adams et al. 

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... 

In the last 150 years the anthropogenic emission of sulfur has increased dramatically, primarily due to combustion processes [1]. In the 1950s anthropogenic emission surpassed natural emission and the atmospheric sulfur cycle is one of the most perturbed biogeochemical cycles [1,2]. The oceans are the largest natural source of atmospheric sulfur emissions, where sulfur is emitted in a reduced form, predominantly as dimethyl sulfide (DMS) and to a much lesser extent carbonyl sulfide (OCS) and carbon disulfide (CS2) [3]. Ocean emitted DMS and CS2 are initially oxidised to OCS, which diffuses through the troposphere into the stratosphere where further oxidation to sulfur dioxide (SO2), sulfur trioxide (SO3) and finally sulfuric acid (H2SO4) occurs [1-4]. 

The biological and atmospheric redox chemistry of sulfur is also complex. The main natural inputs to the atmosphere come from biological decay (mostly FI ) and emissions of dimethyl sulfide... 

Fig. 6.4 Schematic illustration of the key pathways in the atmospheric cycle of S involving (7) the natural emissions of reduced S compounds such as H2S frran terrestrial biota and dimethyl sulfide (CH3SCH3) from oceanic biota (2) anthropogenic emissions of S compounds, principally SO2 (3) the oxidation of reduced S compounds by OH and other photochemical oxidants leading to the production of intermediate oxidation state S compotmds such as SO2 and methane sulfonic acid (MSA) (4) the oxidation of these mtermediate oxidation state compounds within the gas phase by OH-producing H2SO4 vapor (5) the conversion of intermediate oxidation state compounds within liquid could droplets, which upon evaporation yield sulfate-containing particles (6) the conversion of H2SO4 to sulfate-containing particles and (7) the ultimate removal of S fiom the atmosphere by wet and dry deposition (Chameides and Perdue 1997)...

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. 

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