Atmospheric sulfur cycle, importance

Phytoplankton DMS producers <20 Phaeocystis and small autotrophic flagellates Produce dimethylsulfoniopro-pionate (DMSP) and convert it into DMS using an extracellular enzyme (DMSPIyase). Thus, they affect the atmospheric sulfur cycle. Have high P requirement Particularly abundant in coastal areas, where they are often observed in colonies. Calcifiers are also important for the DMS cycle... 

Obviously our understanding of the involvement of DMSO and DMSO2 in the atmospheric sulfur cycle is at present veiy limited. The results from laboratory and field measurements as briefly discussed here imply that DMSO and DMS02 are important products of the pnotooxidation of DMS which is the major source of reduced sulfur to the marine atmosphere. Further kinetic studies are needed, however, to elucidate the role of DMSO and DMSO2 in the atmospheric sulfur cycle. 

R8, and R12 should dominate in the troposphere as a whole. The sulfur photochemistry is summarized in Figure 1. The possible importance of Me2S to the atmospheric sulfur cycle should be considered, and more experimental data are needed. 

The most important pathway of sulfur through the atmosphere involves injection as a low oxidation state gas and the removal as oxidation state VI sulfate in rainwater (see Fig. 13-2, paths 1,4,5,6, 7, 8,9,10, 12, and 13). Since this pathway involves a change in chemical oxidation state and physical phase, the lifetime of sulfur in the atmosphere is governed by both the kinetics of the oxidation reactions and the frequency of clouds and rain. We will argue below that the overall process is fast - on the order of days -meaning that the atmospheric sulfur cycle is a regional phenomenon and that the distribution of nearly all sulfur species in the atmosphere is necessarily "patchy" over the globe. 

We have seen that, except for OCS, sulfur species in the atmosphere have residence times that are short (days) such that their geographical distribution is patchy. This perspective on the atmospheric sulfur cycle has important implications. While human... 

The study of the atmospheric sulfur cycle is a rapidly expanding field because human activity provides an important sulfur dioxide source. In the atmosphere S02 is converted to sulfate containing aerosol particles which can modify the radiation balance of the Earth-atmosphere system, the optical properties and the precipitation forming ability24 of the air. 

One of the things that environmental scientists do is to keep track of important elements in the biosphere—in what form do these elements normally occur, to what are they transformed, and how are they returned to their normal state Careful studies have given clear, although complicated, pictures of the "nitrogen cycle," the "sulfur cycle," and the "phosphorus cycle," for example. The "carbon cycle," begins and ends with atmospheric carbon dioxide. It can be represented in an abbreviated form as ... 

Comparison of Figs 13-6a and 13-6b clearly demonstrates the degree to which human activity has modified the cycle of sulfur, largely via an atmospheric pathway. The influence of this perturbation can be inferred, and in some cases measured, in reservoirs that are very distant from industrial activity. Ivanov (1983) estimates that the flux of sulfur down the Earth s rivers to the ocean has roughly doubled due to human activity. Included in Table 13-2 and Fig. 13-6 are fluxes to the hydrosphere and lithosphere, which leads us to these other important parts of the sulfur cycle. 

On a global scale, natural emissions of reduced sulfur compounds account for about 50% of the total sulfur flux into the atmosphere (1-3). Hence, it is important to understand the natural sulfur cycle in order to establish a "base line" for assessing the significance of anthropogenic perturbations (primarily SO2 emissions). Dimethylsul-fide (DMS) is the predominant reduced sulfur compound entering the atmosphere from the oceans (4-9), and DMS oxidation represents a major global source of S(VI). The atmospheric oxidation of DMS can be initiated by reaction with either OH or NO3. In marine environments, however, NO3 levels are typically very low and DMS is destroyed primarily by OH ... 

The discovery of substantial amounts of volatile organosulfides in the oceans was one of the major additions to the sulfur cycle in the second half of the twentieth century. The largest flux of reduced sulfur to the atmosphere from the oceans is as DMS. The importance of this compound that was largely unknown in nature until the 1970s was revealed by Lovelock et al. (1972) as a potential explanation for the imbalance in the sulfur cycle. Over time it has become clear that this process has important implications to the atmosphere and offers a source of sulfate to form cloud condensation nuclei. 

In the early 1970s there was some concern that the sulfur cycle did not balance and that there needed to be additional global sources. When James Lovelock discovered DMS in the atmosphere of remote Ireland, this seemed a fine candidate to balance the sulfur cycle. The production of DMS in the oceans and its subsequent oxidation have been extensively investigated, particularly because of its role in producing sulfuric acid droplets that can act as an important cloud condensation nuclei in the remote marine atmosphere. 

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