Stratosphere sulfur compounds

Sulfur Compounds Ammonium sulfate Sulfuric acid 0.1 pm Mostly stratospheric 50% globally... 

Biogenic Sulfur Emissions from the Ocean. The ocean is a source of many reduced sulfur compounds to the atmosphere. These include dimethylsulfide (DMS) (2.4.51. carbon disulfide (CS2) (28). hydrogen sulfide (H2S) (291. carbonyl sulfide (OCS) (30.311. and methyl mercaptan (CH3SH) ( ). The oxidation of DMS leads to sulfate formation. CS2 and OCS are relatively unreactive in the troposphere and are transported to the stratosphere where they undergo photochemical oxidation (22). Marine H2S and CH3SH probably contribute to sulfate formation over the remote oceans, yet the sea-air transfer of these compounds is only a few percent that of DMS (2). 

The DVI does not take into account the detailed nature of the process and is based on a fair amount of estimation it can be argued, for instance, that it is not the total amount of dust that matters, but rather the fraction that reaches the stratosphere, particularly as a sulfur compound, and how that content evolves in time also, it is not just the change in direct radiation that has an effect, but the redistribution, in the entire spectrum, of the direct and diffuse radiation, etc. The DVI is an approach to identify and relate the rdevant and measurable parameters it gives a useful insight by associating volcanic and climatic chronologies. In the words of the author this is about as far as one can go towards objectivity in the assessment of past eruptions . In this respect it reflects the state of knowledge on the problem in 1970. 

Cadle R. D. (1975) Volcanic emissions of halides and sulfur compounds to the troposphere and stratosphere. J. Geophys. Res. 80, 1650-1652. 

Castleman, A.W., Jr., Munkelwitz, H.R. and Manowitz, B., 1973. Contribution of volcanic sulfur compounds to the stratospheric aerosol layer. Nature, 244 345—346. 

An interesting exception to the patchiness of atmospheric sulfur compounds is carbonyl sulfide (OCS). This compound, which may be emitted directly or produced by the oxidation of CS2, is highly stable against further oxidation (until it reaches the stratosphere) and so is unavailable for... 

Sulfur compounds are very important atmospheric constituents, since in clean tropospheric air as well as in the stratosphere the majority of aerosol particles are composed of ammonium sulfate or sulfuric acid (see Chapter 4). This finding is particularly interesting since with the exception of sea salt sulfur, a predominant portion of sulfur emission is in gaseous form. 

We can conclude that the origin of stratospheric particles is not well established. It is proposed, however, that volcanic activity is at least one of the most important factors governing the aerosol cycle in the stratosphere. It is obvious that much work remains to be done in measuring not only particulate, but also gaseous sulfur compounds in the stratosphere (see Georgii, 1978). 

Carbonyl sulfide is the most abundant sulfur gas in the global background atmosphere because of its low reactivity in the troposphere and its correspondingly long residence time. It is the only sulfur compound that survives to enter the stratosphere. (An exception is the direct injection of S02 into the stratosphere in volcanic eruptions.) In fact, the input of OCS into the stratosphere is considered to be responsible for the maintenance of the normal stratospheric sulfate aerosol layer. 

Carbonyl sulfide COS is a sulfur compound present in the troposphere at ca. 0.5 ppbv. It is emitted from volcanic activities and also formed in the atmospheric reaction of CS2 and OH as mentioned above. Among the global emissitm of COS, the ratio of the secondary formation from CS2 is estimated to be ca. 30 % (Chin and Davis 1993). The rate constant of the reaction of COS an OH is very small as seen in Table 5.2 (2 x 10 cm molecule s at 298 K), and the atmospheric lifetime calculated from the average concentration of OH assumed to be 8 x 10 molecules cm is about 20 years. Therefore, most of COS emitted and formed in the troposphere is transported to the stratosphere, where it is photolyzed to yield H2SO4, which causes the stratospheric aerosols (see Chap. 8, Sect. 8.5). 

Fig. 8.11 Vertical profiles of sulfur compounds in the stratosphere by model calculation (Adapted from Turco et al. 1979)...

Most of the research to date has focused on aerosols and PSCs containing inorganic species such as nitric and sulfuric acids. While CH4 is the only hydrocarbon that is sufficiently unreactive in the troposphere to reach the stratosphere, it is oxidized to compounds such as HCHO that can be taken up into sulfuric acid particles (Tolbert et al., 1993). The effects of such uptake and subsequent chemistry are not well established. 

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