7.3. Carbonyl sulphide (COS)

Carbonyl sulphide is the most abundant sulphur compound naturally present in the atmosphere (0.5 ± 0.05 ppb), because it is emitted from oceans, volcanoes and sea vents. COS is a significant compound in the global sulphur cycle. Analysis of ice cores from Antarctica and air trapped in snow above glaciers provided how the COS concentration changed during the past few centuries. These measurements provided an understanding of the relative importance of anthropogenic and natural sources of this gas to the atmosphere. Some carbonyl sulphide that is transported into the stratospheric sulphate layer is oxidized to sulphuric acid. Sulphuric acid forms particulate which affects energy balance due to light scattering. The long atmospheric lifetime of carbonyl sulphide makes it the major source of stratospheric sulphate. COS is also removed from the atmosphere by vegetation by enzymes associated with the uptake of carbon dioxide during photosynthesis and by hydrolysis in ocean waters.

The largest anthropogenic sources of carbonyl sulphide release include its primary use as a chemical intermediate and as a byproduct of carbon disulfide production. However, it is also released from automobiles, coal-fired power plants, biomass combustion, fish processing, combustion of refuse and plastics, petroleum manufacture, and manufacture of synthetic fibers, starch, and rubber. The average total worldwide release of carbonyl sulphide to the atmosphere has been estimated at about 3 million tons/year, of which less than one third was related to human activity.