Emission Survey of Biogenic Sulfur Flux from Terrestrial Surfaces

Abstract

The most critical gap in knowledge important for delineating the global atmospheric cycle of sulfur is uncertainty about the magnitude, distribution, source, and form of biogenic emissions to the atmosphere. All global sulfur budget estimates which have appeared recently in the literature require a substantial biogenic sulfur emission to balance the budget; however, the estimated magnitude of the global natural source strengths vary widely—from ∼35 to ∼280 TgS/yr.

Direct measurements of sulfur emission rates were made by sampling various terrestial surfaces (water surfaces, soil, and selected vegetation) during 1978. An emission flux reactor (chamber) technique was used to determine the emission rates of sulfur compounds into the atmosphere. The sulfur gases were identified and their concentrations in the flux reactor measured with a gas chromatograph equipped with a flame photometric detector specific for S. H₂S (average flux ∼0.5 gS/m²/yr), (CH₃)₂S (average flux ∼0.4 gS/m²/yr), COS (average flux ∼0.03 gS/m²/yr), CS₂ (average flux ∼0.15 gS/m²/yr) were measured. In general, the emission rates of these gases varied over a wide range of concentrations under varying conditions of soils, soil moisture, and temperature. These results are compared with previously measured sulfur emission fluxes. Comparison is also made with global sulfur budgets, sulfur emission rates expressed as fluxes, and from calculations based on a simple mass transfer model in an abiotic environment. The mass transfer model calculations suggest that the emission rates for H₂S are considerably reduced in natural blotic environments, while the reverse is the case for DMS and CS₂.