Ocean global sulfur emission

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. 

DMS emission fluxes from Antarctic inshore waters may be important for the tropospheric sulfur budget of Antarctica during summer. The contribution of the Southern Ocean to the global atmospheric sulfur budget (ca. 0.2 Tmol yr1) is consistent with present estimates of the total global DMS emission from the world s oceans (0.5-1.2 Tmol yr1). 

The DMS emissions from the ocean represent a significant part of the global sulfur flux to the atmosphere. It might be of particular interest to find new reaction routes which couple biogenic emissions from the sea to the chemistry of tropospheric photooxidants by which important properties of the atmosphere are regulated. 

The effect of volcanic gas on global sulfur cycle is important. S concentration of volcanic gas from island arc is smaller than CO2 concentration. CO2 concentration of hot spot volcanic gas is similar to that of island arc volcanic gas, but amount of volcanic gas emission from hot spot volcanic activity (e.g., Hawaii) is small (Table 5.3). S concentration of volcanic gas from mid-oceanic ridges is similar to C concentration. Emission of S and C by volcanic gas from mid-oceanic ridge is small because solubility of gas into magma is high under high pressure condition at deep sea depth (3,000-4,000 m). Sulfur in basalt transfers to hydrothermal solution... 

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. 

Little snlfnr is re-emitted from wetlands into the atmosphere. Table 8.7 gives estimates of global emissions of volatile sulfur compounds from different sources. Total emissions are in the range 98 to 120 Tg (S) year 75 % is anthropogenic, mainly from fossil fnel combustion in the northern hemisphere. The main natural sources are the oceans and volcanoes. Wetlands and soils contribnte less than 3 % of the total emission. 

Lovelock et al. (2) made the first quantitative measurement of DMS in the surface ocean and suggested that it, rather than H S, made up the principle oceanic sulfur source. Since that time, a number of measurements have been made of both water column and atmospheric DMS and flux calculations support the view that the emissions of this organic sulfur compound constitute a major global flux. However, the relative importance of the fluxes of DMS and H2S as... 

The global natural flux of sulfur compounds to the atmosphere has recently been estimated to be about 2.5 Tmol yr1 (1) which is comparable to the emissions of sulfur dioxide (SO2) from anthropogenic sources (2). A substantial amount of the natural sulfur contribution (0.5-1.2 Tmol yr1) is attributed to the emission of dimethylsulfide (DMS) from the world s oceans to the atmosphere (3.4). One of the major uncertainties in this estimate is due to a scarcity of DMS and other sulfur data from the Southern Hemisphere, particularly the Southern Ocean region between about 40°S and the Antarctic continent, which represents about one fifth of the total world ocean area. 

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 ... 

Natural and anthropogenic sulfur aerosols play a major role in atmospheric chemistry and potentially in modulating global climate. One theory holds that a negative feedback links the emission of volatile organic sulfur (mostly as DMS) from the ocean with the formation of cloud condensation nuclei, thereby... 

Dimethyl sulfide is emitted mainly from the ocean where it is released from phytoplankton. Estimates of emission rates range from 30 to 68 Tg yr . Soils and vegetation contribute comparatively little to the global emission rate. The rate of DMS emissions evidently exceeds that of all other reduced sulfur compounds. Although this makes DMS the most important reduced sulfur compound globally, its impact is essentially confined to the marine atmosphere. The removal of DMS occurs primarily by reaction with OH radicals. 

---