OCS, stratospheric aerosols and climate

Abstract

Carbonyl sulphide (OCS) is found to be the predominant sulphur-bearing compound in our atmosphere^1–3. It contributes to the formation of stratospheric sulphate aerosol particles⁴, which affect the Earth's radiation balance and climate^5–7. Using recently obtained data, we estimate that OCS has a global source of ∼5 tg per year (tg = 10¹² g) and a lifetime of roughly 1 yr. We calculate that increasing anthropogenic emissions of OCS could cause measurable climate alterations within the next century. Numerous sources of OCS have been identified (see Fig. 1). Crutzen et al.⁸ estimate that natural and agricultural fires contribute 0.2–0.3 tg of OCS to the atmosphere each year. Adams et al.⁹ measured average OCS emission rates for a variety of common soils of about 0.004 g m⁻² yr⁻¹, which may be extrapolated to a global OCS source of nearly 0.5 tg yr⁻¹. Adams et al.⁹ also noted OCS emissions several thousand times greater than average above saline marshes. Carbonyl sulphide has been detected near cattle feedlots in concentrations as high as 6,000 p.p.b.v.¹⁰. Volcanoes and fumaroles seem to represent a minor source of OCS (refs 11,12). We estimate that the direct contributions of biospheric processes to the OCS budget may be ∼1 tg yr⁻¹.