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| Titel |
Sulfur isotope fractionation during oxidation of sulfur dioxide: gas-phase oxidation by OH radicals and aqueous oxidation by H2O2, O3 and iron catalysis |
| VerfasserIn |
E. Harris, B. Sinha, P. Hoppe, J. N. Crowley, S. Ono, S. Foley |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 1 ; Nr. 12, no. 1 (2012-01-06), S.407-423 |
| Datensatznummer |
250010442
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| Publikation (Nr.) |
 copernicus.org/acp-12-407-2012.pdf |
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| Zusammenfassung |
| The oxidation of SO2 to sulfate is a key reaction in determining the role
of sulfate in the environment through its effect on aerosol size distribution
and composition. Sulfur isotope analysis has been used to investigate sources
and chemical processes of sulfur dioxide and sulfate in the atmosphere,
however interpretation of measured sulfur isotope ratios is challenging due
to a lack of reliable information on the isotopic fractionation involved in
major transformation pathways. This paper presents laboratory measurements of
the fractionation factors for the major atmospheric oxidation reactions for
SO2: Gas-phase oxidation by OH radicals, and aqueous oxidation by
H2O2, O3 and a radical chain reaction initiated by iron. The
measured fractionation factor for 34S/32S during the gas-phase
reaction is αOH = (1.0089±0.0007)−((4±5)×10−5) T(°C). The
measured fractionation factor for 34S/32S during aqueous oxidation
by H2O2 or O3 is αaq = (1.0167±0.0019)−((8.7±3.5) ×10−5)T(°C). The observed
fractionation during oxidation by H2O2 and O3 appeared to be
controlled primarily by protonation and acid-base equilibria of S(IV) in
solution, which is the reason that there is no significant difference
between the fractionation produced by the two oxidants within the
experimental error. The isotopic fractionation factor from a radical chain
reaction in solution catalysed by iron is αFe =
(0.9894±0.0043) at 19 °C for 34S/32S. Fractionation
was mass-dependent with regards to 33S/32S for all the reactions
investigated. The radical chain reaction mechanism was the only measured
reaction that had a faster rate for the light isotopes. The results presented
in this study will be particularly useful to determine the importance of the
transition metal-catalysed oxidation pathway compared to other oxidation
pathways, but other main oxidation pathways can not be distinguished based on
stable sulfur isotope measurements alone. |
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