Electronic Spectra of Carbonyl Sulfide Sulfur Isotopologues

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Abstract

Environmental Context.Sulfate aerosols have been linked with ozone-depleting reactions, and their influence on cirrus cloud formation may affect climate. One source of sulfate aerosols is sulfur-containing gases such as carbonyl sulfide, which can rise up to the statosphere and become transformed into sulfate under the prevailing sunlight, but the importance and details of the phenomena involved are poorly understood. With a view to providing the fundamental information required to analyze the atmospheric processing of carbonyl sulfide, this paper reports the sulfur isotope effects on its ultraviolet absorption spectrum. Abstract.Carbonyl sulfide (OCS), a relatively inert tropospheric species that photolyzes into CO + S upon reaching the stratosphere, is deemed a significant contributor to background sulfate aerosol. A recent analysis of atmospheric infrared transmittance data has revealed that OC34S is preferentially depleted above ~10 km. We now report that the OC34S absorption band between 200 ≤ λ [nm] ≤ 260 at 298 K is broader and more intense than its OC32S counterpart. This finding is consistent with the faster photolysis of OC34S, and with a time-dependent formulation of electronic spectra. Since OCS photolysis in the lower stratosphere occurs in a spectral range in which its absorption cross-section is unaffected by temperature, we are able to estimate a 34S-enrichment factor <34ϵ> ~ (67 ± 7)‰ for this process that is commensurate with the value previously inferred from OC34S/OC32S ratio versus altitude profiles.

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