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| Titel |
Aqueous-phase photooxidation of levoglucosan – a mechanistic study using aerosol time-of-flight chemical ionization mass spectrometry (Aerosol ToF-CIMS) |
| VerfasserIn |
R. Zhao, E. L. Mungall, A. K. Y. Lee, D. Aljawhary, J. P. D. Abbatt |
| 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 ; 14, no. 18 ; Nr. 14, no. 18 (2014-09-16), S.9695-9706 |
| Datensatznummer |
250119036
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| Publikation (Nr.) |
 copernicus.org/acp-14-9695-2014.pdf |
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| Zusammenfassung |
| Levoglucosan (LG) is a widely employed tracer for biomass burning (BB).
Recent studies have shown that LG can react rapidly with hydroxyl (OH)
radicals in the aqueous phase despite many mass balance receptor models
assuming it to be inert during atmospheric transport. In the current study,
aqueous-phase photooxidation of LG by OH radicals was performed in the
laboratory. The reaction kinetics and products were monitored by aerosol time-of-flight chemical ionization mass spectrometry (Aerosol ToF-CIMS).
Approximately 50 reaction products were detected by the Aerosol ToF-CIMS
during the photooxidation experiments, representing one of the most detailed
product studies yet performed. By following the evolution of mass defects of
product peaks, unique trends of adding oxygen (+O) and removing hydrogen
(−2H) were observed among the products detected, providing useful
information for determining potential reaction mechanisms and sequences. Additionally, bond-scission reactions take place, leading to reaction intermediates
with lower carbon numbers. We introduce a data analysis framework where the
average oxidation state (OSc) is plotted against a novel molecular
property: double-bond-equivalence-to-carbon ratio
(DBE/#C). The trajectory of LG photooxidation on this plot
suggests formation of polycarbonyl intermediates and their subsequent
conversion to carboxylic acids as a general reaction trend. We also
determined the rate constant of LG with OH radicals at room temperature to be
1.08 ± 0.16 × 109 M−1 s−1. By coupling an
aerosol mass spectrometer (AMS) to the system, we observed a rapid decay of
the mass fraction of organic signals at mass-to-charge ratio 60 (f60),
corresponding closely to the LG decay monitored by the Aerosol ToF-CIMS. The
trajectory of LG photooxidation on a f44–f60 correlation plot matched
closely to literature field measurement data. This implies that aqueous-phase
photooxidation might be partially contributing to aging of BB particles in
the ambient atmosphere. |
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