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| Titel |
AMS and LC/MS analyses of SOA from the photooxidation of benzene and 1,3,5-trimethylbenzene in the presence of NOx: effects of chemical structure on SOA aging |
| VerfasserIn |
K. Sato, A. Takami, Y. Kato, T. Seta, Y. Fujitani, T. Hikida, A. Shimono, T. Imamura |
| 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. 10 ; Nr. 12, no. 10 (2012-05-25), S.4667-4682 |
| Datensatznummer |
250011174
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| Publikation (Nr.) |
 copernicus.org/acp-12-4667-2012.pdf |
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| Zusammenfassung |
| Oxygenated organic aerosol (OOA) observed in remote areas is believed to
comprise aged secondary organic aerosol (SOA); however, the reaction
processes relevant to SOA chemical aging have hitherto been unclear. We
recently measured the mass spectra of SOA formed from the photooxidation of
aromatic hydrocarbons using an Aerodyne aerosol mass spectrometer (AMS) and
reported that SOA aging is slowed with increasing number of alkyl groups in
the precursor molecule. In this study, we selected benzene and
1,3,5-trimethylbenzene (TMB) as precursors to analyze SOA formed from the
photooxidation of aromatic hydrocarbons in the presence of NOx using
high-resolution time-of-flight AMS (H-ToF-AMS) and liquid
chromatography/time-of-flight mass spectrometry (LC/TOF-MS). A van Krevelen
diagram was studied using the O/C and H/C ratios obtained by H-ToF-AMS for
organics present in SOA. The results showed these organics to be rich in
carboxylic acids or hydroxycarbonyls and the O/C ratio of SOA formed by the
reaction of 1,3,5-TMB to be lower than that for benzene. Analytical results
from LC/TOF-MS showed the particulate products formed by the reaction of
1,3,5-TMB to be richer in ketocarboxylic acids than for benzene. These
results indicate that SOA aging proceeds mainly by formation of carboxylic
acids and that the rate of SOA aging in laboratory chambers is limited by
the oxidation of ketone groups. SOA formed in laboratory chamber experiments
is less oxidized than for ambient OOA, not only because the experimental
duration is insufficient or the SOA mass loading in the chamber is higher
than that of the atmosphere. The laboratory chamber experiments under dry
conditions are not able to simulate ketocarboxylic acid photochemical
oxidation in the aqueous phase. The fractions of organic peroxides to the
total SOA mass were determined by iodometric spectrophotometry to be 12 ± 8%
(1,3,5-TMB) and <39% (benzene). Further, it was newly found
that, unlike the reaction of benzene, only very small amounts of
nitrophenols are produced by the reaction of 1,3,5-TMB. |
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