Dimethyl sulfide, DMS

Another interesting applieation of MDGC is in the rapid determination of isoprene (the most reaetive hydroearbon speeies) and dimethyl sulfide (DMS) (the major souree of sulfur in the marine troposphere and a preeursor to eloud formation) in the atmosphere (16). The deteetion limits were 5 and 25 ng 1 respeetively. 

Figure 4-13 shows an example from a three-dimensional model simulation of the global atmospheric sulfur balance (Feichter et al, 1996). The model had a grid resolution of about 500 km in the horizontal and on average 1 km in the vertical. The chemical scheme of the model included emissions of dimethyl sulfide (DMS) from the oceans and SO2 from industrial processes and volcanoes. Atmospheric DMS is oxidized by the hydroxyl radical to form SO2, which, in turn, is further oxidized to sulfuric acid and sulfates by reaction with either hydroxyl radical in the gas phase or with hydrogen peroxide or ozone in cloud droplets. Both SO2 and aerosol sulfate are removed from the atmosphere by dry and wet deposition processes. The reasonable agreement between the simulated and observed wet deposition of sulfate indicates that the most important processes affecting the atmospheric sulfur balance have been adequately treated in the model. 

Compare this step to the mechanisms we saw in the previous section syn dihydroxy-lation), and you should see striking similarities. The initial product (shown above) is called a molozonide, and it subsequently undergoes further rearrangements, before ultimately giving the product upon treatment with dimethyl sulfide (DMS). The structure of DMS is ... 

Since antiquity, animal milks have been converted by empirical processes to a wide variety of cheeses. With the development of microbiology as a scientific discipline, the critical role of microorganisms - bacteria, fungi, yeasts - in cheese began to be understood. Today, more than 650 cheese types are recognized and the flavor(s) of cheese has (have) now been investigated for more than a century.33 Typically, the situation is complex and the literature is enormous. For instance, more than 200 volatiles occur in Cheddar cheese. In a listing of 58 of these volatiles, 7 are sulfur compounds dimethyl sulfide (DMS),... 

Dimethyl sulfide (DM) and dimethyl disulfide have been measured in seawater and in the atmosphere by gas chromatography [309] and by GC-MS [310]. Some variety of cryogenic trapping is often used. 

While investigating the potential for an instrument to measure atmospheric dimethyl sulfide (DMS) [69], discussed below, Hills et al. investigated the possibility of adding H2 to the reaction cell to provide chemical amplification of the chemiluminescence signal via the catalytic chain reaction ... 

Br-atom initiated oxidation of dimethyl sulfide (DMS) in a large-volume reaction chamber gave SO2, CHsSBr, and DMSOJ A rapid addition of Br atoms to DMS takes place, forming an adduct that mainly reforms reactants but also decomposes unimolecularly to form CHsSBr and CH3 radicals. DMSO is formed from the reaction of BrO radicals with DMS. The reaction CH3O2 + Br CH3O + BrO is postulated as the source of BrO radicals. 

Gas-phase chemistry in remote areas is, in most cases, analogous to that in more polluted regions. The major difference is in lower NOx emissions and hence concentrations. In addition, in continental regions, there are substantial emissions of biogenic organics, many of which are highly reactive toward OH, 03, N03, and Cl atoms and in oceanic regions, dimethyl sulfide (DMS), which reacts with OH, N03, and Cl atoms. 

Table 8.17 summarizes the rate constants and estimated tropospheric lifetimes of some of these sulfur compounds with respect to reaction with OH or NO-,. The assumed concentrations of these oxidants chosen for the calculations are those characteristic of more remote regions, which are major sources of reduced sulfur compounds such as dimethyl sulfide (DMS). It is seen that OH is expected to be the most important sink for these compounds and that NO, may also be important, for example, for DMS oxidation (see also Chapter 6.J). 

The oxidation of dimethyl sulfide (DMS) to dimethyl sulfoxide (DMSO) and the subsequent oxidation of the latter to methanesulfonic acid (MSA) have been observed in field studies. For example, one study in Antarctica which focused on the chemistry of dimethyl sulfide (Berresheim and Eisele, 1998) measured not only DMS but also a variety of its oxidation products, including DMSO, MSA, and dimethyl sulfone (Berresheim et al., 1998). The measured concentrations of DMSO were in agreement with model results if 80-100% of the OH + DMS reaction gave DMSO as discussed earlier, the addition channel that leads to DMSO becomes relatively more important at the lower temperatures found in Antarctica. Furthermore, the... 

Dimethyl Sulfoxide, Dimethyl sulfoxide is manufactured from dimethyl sulfide (DMS), which is obtained either by processing spent liquors from the kraft pulping process or by the reaction of methanol or dimethyl ether with hydrogen sulfide,... 

The atmospheric oxidation of dimethyl sulfide (DMS) and DMSO has been reviewed. Kinetics of oxidation of DMS and DMSO with OH and NO3 radicals and with halogen and halogen oxides have been described and the mechanistic aspects have been discussed.244 A review of recent studies of the mechanism and kinetics of the gas-phase oxidation of dimethyl ether has mentioned the pressure dependence of the... 

Instrumental accuracy is further highlighted by Figure 4.3, which shows the PTR-MS determination (in both counts-per-second and ppbv) of the output from a dimethyl sulfide (DMS) permeation device with and without an in-line charcoal filter. The device was gravimetrically found to produce a concentration of 2.60 ppbv... 

Figure 4.3 Measured concentrations and raw counts per second (cps) of a gaseous dimethyl sulfide (DMS) standard produced using a permeation device and calibration oven (Hayward et a ., 2002).

Some plants are also known to emit dimethyl sulfide, DMS, (13.371. carbonyl sulfide, COS, (291. and carbon disulfide, CS (13.37-411. and possibly ethyl mercaptan (40.411. A study conducted in a tropical rain forest which focused on Stryphnodendron excelsum is trteated in more detail in a following chapter (411. It is quite possible that additional studies as described in Chapter 5 (411 will lead to die discovery of other terrestrial "hot spots which may be important in biogenic sulfur cycling. 

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. 

The distribution of dimethyl sulfide (DMS) in surface oceans and the principle source of DMS, dimethylsulfoniopropionate (DMSP) in phytoplankton, are reviewed. The distribution of DMSP in marine phytoplankton is widespread and shows considerable variation in concentration from species to species. 

Dimethylsulfoniopropionate (DMSP) is an organic sulfur compound that occurs at high concentrations in many marine algae and plants, wnere it fulfills an osmotic function (1.21. DMSP is a principal form of organic sulfur in productive marine environments and its microbial catabolism entails either enzymatic cleavage to dimethyl sulfide (DMS) and aciylate (3.41 ... 

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