Carbon disulphide and carbonyl sulphide from biogenic sources and their contributions to the global sulphur cycle

Abstract

Estimates of the magnitude of biogenic sulphur emissions range from ∼70% of the total atmospheric sulphur burden1–7, and the chemical nature of the emissions has not been clearly established. Conway1 speculated that the principal volatile biogenic component of the sulphur cycle was hydrogen sulphide (H2S) whereas Lovelock et al.8 and Rasmussen9 have suggested that dimethyl sulphide (DMS) contributes to the apparent source deficits. Aneja et al.10 have shown that both H2S and DMS are emitted from saltmarshes. Other volatile sulphur compounds which may contribute to the sulphur burden of the atmosphere include methyl mercaptan (CH3SH)11,12, dimethyl disulphide ((CH3)2S2)11,12, carbonyl sulphide (COS)13 and carbon disulphide (CS2)14,15. We report here the discovery of CS2 and COS emanating from a saltmarsh and estimate their emission rates using emission flux reactor and bag chamber techniques. The species CS2 and COS are relatively inert in the troposphere, so may be assumed to penetrate to the stratosphere, where they may be photolysed to form the sulphur dioxide (SO2) and sulphates (SO42−) known to be present in the stratosphere. Based on the measured fluxes, we show that the emissions from marshes are important to the sulphate aerosol burden (≲19%) of the stratosphere, but not important for the tropospheric sulphur burden (≲0.2%).