Isotopic fractionation of carbonyl sulfide in the atmosphere: Implications for the source of background stratospheric sulfate aerosol

Abstract

In order to assess the contribution of carbonyl sulfide to stratospheric sulfate aerosol (SSA), we examined the stratospheric OC34S and OC32S concentration profiles in the infrared limb- transmittance spectra acquired by the JPL MkIV instrument. We found that OC34S is preferentially depleted by solar photolysis. The derived 34S enrichment factor: ε=+73.8±8.6‰, in conjunction with literature values of δ34S ∼ +11‰ for tropospheric OCS, and a ∼ 10% net processing of the OCS transported upwardly into the stratosphere, suggests that aerosol sulfate proceeding from OCS should be highly enriched in δ34S ∼ 80‰, comparing our prediction with previous reports of δ34S ∼ +2.6‰ for background SSA, we infer either that OCS is a minor contributor to SSA or that current views about its 34S-abundance and atmospheric circulation are seriously flawed.