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| Titel |
Dependence of SOA oxidation on organic aerosol mass concentration and OH exposure: experimental PAM chamber studies |
| VerfasserIn |
E. Kang, D. W. Toohey, W. H. Brune |
| 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 ; 11, no. 4 ; Nr. 11, no. 4 (2011-02-28), S.1837-1852 |
| Datensatznummer |
250009380
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| Publikation (Nr.) |
 copernicus.org/acp-11-1837-2011.pdf |
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| Zusammenfassung |
| The oxidation of secondary organic aerosol (SOA) is studied with mass
spectra analysis of SOA formed in a Potential Aerosol Mass (PAM) chamber, a
small flow-through photo-oxidation chamber with extremely high OH and ozone
levels. The OH exposure from a few minutes in the PAM chamber is similar to
that from days to weeks in the atmosphere. The mass spectra were measured
with a Quadrupole Aerosol Mass Spectrometer (Q-AMS) for SOA formed from
oxidation of α-pinene, m-xylene, p-xylene, and a mixture of the
three. The organic mass fractions of m/z 44 (CO2+) and m/z 43
(mainly C2H3O+), named f44 and f43 respectively,
are used as indicators of the degree of organic aerosol (OA) oxidation that
occurs as the OA mass concentration or the OH exposure are varied. The
degree of oxidation is sensitive to both. For a fixed OH exposure, the
degree of oxidation initially decreases rapidly and then more slowly as the
OA mass concentration increases. For fixed initial precursor VOC amounts,
the degree of oxidation increases linearly with OH exposure, with f44
increasing and f43 decreasing. In this study, the degree of SOA
oxidation spans much of the range observed in the atmosphere. These results,
while sensitive to the determination of f44 and f43, provide
evidence that some characteristics of atmospheric OA oxidation can be
generated in a PAM chamber. For all measurements in this study, the sum of
f44 and f43 is 0.25 ± 0.03, so that the slope of a linear
regression is approximately −1 on an f44 vs. f43 plot. This
constancy of the sum suggests that these ions are complete proxies for
organic mass in the OA studied. |
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