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 OC^(34)S and OC^(32)S concentration profiles in the infrared limb-transmittance spectra acquired by the JPL MkIV instrument. We found that OC^(34)S is preferentially depleted by solar photolysis. The derived ^(34)S enrichment factor: ε = +73.8 ± 8.6‰, in conjunction with literature values of δ^(34)S ∼ +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 δ^(34)S ∼ 80‰, comparing our prediction with previous reports of δ^(34)S ∼ +2.6‰ for background SSA, we infer either that OCS is a minor contributor to SSA or that current views about its ^(34)S-abundance and atmospheric circulation are seriously flawed.

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