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| Titel |
Sulfur isotope analyses of individual aerosol particles in the urban aerosol at a central European site (Mainz, Germany) |
| VerfasserIn |
B. W. Sinha, P. Hoppe, J. Huth, S. Foley, M. O. Andreae |
| 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 ; 8, no. 23 ; Nr. 8, no. 23 (2008-12-10), S.7217-7238 |
| Datensatznummer |
250006492
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| Publikation (Nr.) |
 copernicus.org/acp-8-7217-2008.pdf |
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| Zusammenfassung |
Sulfur isotope analysis of atmospheric aerosols is a well established tool
for identifying sources of sulfur in the atmosphere, estimating emission
factors, and tracing the spread of sulfur from anthropogenic sources through
ecosystems. Conventional gas mass spectrometry averages the isotopic
compositions of several different types of sulfur aerosol particles, and
therefore masks the individual isotopic signatures. In contrast, the new
single particle technique presented here determines the isotopic signature
of the individual particles.
Primary aerosol particles retain the original isotopic signature of their
source. The isotopic composition of secondary sulfates depends on the
isotopic composition of precursor SO2 and the oxidation process. The
fractionation with respect to the source SO2 is poorly characterized.
In the absence of conclusive laboratory experiments, we consider the kinetic
fractionation of −9‰ during the gas phase oxidation of SO2 by OH as
suggested by Saltzman et al. (1983) and Tanaka et al. (1994) to be the most
reasonable estimate for the isotope fractionation during gas phase oxidation
of SO2 (αhom=0.991) and the equilibrium fractionation
for the uptake of SO2 (g) into the aqueous phase and the dissociation
to HSO3- of +16.5‰ measured by Eriksen (1972a) to be the best
approximation for the fractionation during oxidation in the aqueous phase
(αhet=1.0165). The sulfur isotope ratio of secondary sulfate
particles can therefore be used to identify the oxidation pathway by which
this sulfate was formed. However, the fraction of heterogeneous and
homogeneous oxidation pathway calculated is very sensitive to the isotope
fractionation assumed for both pathways. With the new single particle
technique, different types of primary and secondary sulfates were first
identified based on their chemical composition, and then their individual
isotopic signature was measured separately. Our samples were collected in
Mainz, Germany, in an urban environment. Secondary sulfates (ammonium
sulfate, gypsum, mixed sulfates) and coatings on silicates or organic
aerosol dominated sulfate loadings in our samples. Comparison of the
chemical and isotopic composition of secondary sulfates showed that the
isotopic composition was homogeneous, independent of the chemical
composition. This is typical for particles that derive from in-cloud
processing. The isotopic composition of the source SO2 of secondary
sulfates was calculated based on the isotopic composition of particles with
known oxidation pathway and showed a strong dependence on wind direction.
The contribution of heterogeneous oxidation to the formation of secondary
sulfate was highly variable (35%–75%) on day-to-day basis and depended
on meteorological conditions. |
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