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| Titel |
Sulfur isotope fractionation during heterogeneous oxidation of SO2 on mineral dust |
| VerfasserIn |
E. Harris, B. Sinha, S. Foley, J. N. Crowley, S. Borrmann, P. Hoppe |
| 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. 11 ; Nr. 12, no. 11 (2012-06-04), S.4867-4884 |
| Datensatznummer |
250011216
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| Publikation (Nr.) |
 copernicus.org/acp-12-4867-2012.pdf |
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| Zusammenfassung |
Mineral dust is a major fraction of global atmospheric aerosol, and
the oxidation of SO2 on mineral dust has implications for
cloud formation, climate and the sulfur cycle. Stable sulfur isotopes
can be used to understand the different oxidation processes occurring
on mineral dust. This study presents measurements of the
34S/32S fractionation factor α34 for
oxidation of SO2 on mineral dust surfaces and in the aqueous
phase in mineral dust leachate. Sahara dust, which accounts for
~60% of global dust emissions and loading, was used for the
experiments.
The fractionation factor for aqueous oxidation in dust leachate is
αleachate = 0.9917±0.0046, which is in agreement
with previous measurements of aqueous SO2 oxidation by iron solutions.
This fractionation factor is representative of a radical chain reaction
oxidation pathway initiated by transition metal ions. Oxidation on the dust
surface at subsaturated relative humidity (RH) had an overall fractionation
factor of αhet = 1.0096±0.0036 and was found to be
almost an order of magnitude faster when the dust was simultaneously exposed
to ozone, light and RH of ~40%. However, the presence of ozone,
light and humidity did not influence isotope fractionation during oxidation
on dust surfaces at subsaturated relative humidity. All the investigated
reactions showed mass-dependent fractionation of 33S relative to
34S.
A positive matrix factorization model was used to investigate surface
oxidation on the different components of dust. Ilmenite, rutile and
iron oxide were found to be the most reactive components, accounting
for 85% of sulfate production with a fractionation factor of
α34 = 1.012±0.010. This overlaps within the analytical
uncertainty with the fractionation of other major atmospheric
oxidation pathways such as the oxidation of SO2 by
H2O2 and O3 in the aqueous phase and OH in the gas
phase. Clay minerals accounted for roughly 12% of the sulfate
production, and oxidation on clay minerals resulted in a very distinct
fractionation factor of α34 = 1.085±0.013. The
fractionation factors measured in this study will be particularly
useful in combination with field and modelling studies to understand
the role of surface oxidation on clay minerals and aqueous oxidation
by mineral dust and its leachate in global and regional sulfur cycles. |
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