Hydrogen sulfide, hydroxyl radical reaction

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. 

The measured radical concentrations in the reaction zone were often found to be very high. The concentration of atomic hydrogen in rarefield hydrogen flames can be ten percent of the molecular hydrogen concentration. The measured hydroxyl concentrations in the same flames were also found to be high [229], just as those of atomic oxygen and of SO radicals in a carbon sulfide flame [233, 234]. These concentrations exceed the equilibrium concentrations by factors of thousands and tens of thousands which is evidence of their chemical rather than thermal origin. 

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