Terrestrial biogenic sulfur emissions

The relative contribution that each reduced sulfur compound makes to the total sulfur flux is often of interest because the various compounds behave differently once they enter the atmosphere. Terrestrial biogenic sulfur emissions are dominated by COS (38%), DMS (35%) and H2S (21%). Emissions of CS2 and DMDS together represent about 6% of the total. DMS emissions dominate during the summer season with 41% of the total. 

To review the extant data base of biogenic sulfur emissions for terrestrial and oceanic environments and to summarize direct estimates of emissions where possible. 

Future studies of biogenic emissions should be designed to include sufficient data for uncertainty analyses of flux estimates. It is also important to conduct intercomparisons ot different sampling and measurement methods, as well as the methods used for estimating emissions, i.e. the dynamic chamber vs the micrometerological methods. Additional data are required to confirm emission estimates for those environments which have been characterized, and to extend the emission estimates to environments which have not been studied. Studies in ecosystems such as tropical rain forests should include surveys designed to identify potential terrestrial "hot spots of volatile sulfur emissions. 

Aneja, V. P., J. H. Overton, and A. P. Aneja (1981). Emission survey of biogenic sulfur flux from terrestrial surfaces. J. Air Pollut. Control Assoc. 31, 256-258. 

Carbonyl sulfide is also the most abundant reduced sulfur gas in Earth s troposphere, but for completely different reasons. Volcanic sources of OCS are negligible by comparison with biogenic emissions, which are important sources of several reduced sulfur gases (e.g., OCS, H2S, (CH3)2S, (CH3)2S2, and CH3SH) in the terrestrial troposphere. Many of these gases are ultimately converted into sulfate aerosols in the troposphere, but OCS is mainly lost by transport into the stratosphere, where it is photochemically oxidized to SO2 and then to sulfuric acid aerosols, which form the Junge layer at —20 km in Earth s stratosphere. 

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