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| Titel |
Photochemical processing of aqueous atmospheric brown carbon |
| VerfasserIn |
R. Zhao, A. K. Y. Lee, L. Huang, X. Li, F. Yang, 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 ; 15, no. 11 ; Nr. 15, no. 11 (2015-06-04), S.6087-6100 |
| Datensatznummer |
250119786
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| Publikation (Nr.) |
 copernicus.org/acp-15-6087-2015.pdf |
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| Zusammenfassung |
| Atmospheric brown carbon (BrC) is a collective term for light
absorbing organic compounds in the atmosphere. While the
identification of BrC and its formation mechanisms is currently
a central effort in the community, little is known about the
atmospheric removal processes of aerosol BrC. As a result, we report
on a series of laboratory studies of photochemical processing of BrC in
the aqueous phase, by direct photolysis and OH oxidation. Solutions
of ammonium sulfate mixed with glyoxal (GLYAS) or methylglyoxal
(MGAS) are used as surrogates for a class of secondary BrC mediated
by imine intermediates. Three nitrophenol species, namely
4-nitrophenol, 5-nitroguaiacol and 4-nitrocatechol, were
investigated as a class of water-soluble BrC originating from
biomass burning. Photochemical processing induced significant
changes in the absorptive properties of BrC. The imine-mediated BrC
solutions exhibited rapid photo-bleaching with both direct
photolysis and OH oxidation, with atmospheric half-lives of minutes
to a few hours. The nitrophenol species exhibited photo-enhancement
in the visible range during direct photolysis and the onset of OH
oxidation, but rapid photo-bleaching was induced by further OH
exposure on an atmospheric timescale of an hour or less. To
illustrate the atmospheric relevance of this work, we also performed
direct photolysis experiments on water-soluble organic carbon
extracted from biofuel combustion samples and observed rapid changes
in the optical properties of these samples as well. Overall, these
experiments indicate that atmospheric models need to incorporate
representations of atmospheric processing of BrC species to
accurately model their radiative impacts. |
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