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| Titel |
Effect of relative humidity on SOA formation from isoprene/NO photooxidation: enhancement of 2-methylglyceric acid and its corresponding oligoesters under dry conditions |
| VerfasserIn |
H. Zhang, J. D. Surratt, Y. H. Lin, J. Bapat, R. M. Kamens |
| 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. 13 ; Nr. 11, no. 13 (2011-07-06), S.6411-6424 |
| Datensatznummer |
250009894
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| Publikation (Nr.) |
 copernicus.org/acp-11-6411-2011.pdf |
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| Zusammenfassung |
| The effect of relative humidity (RH) on secondary organic aerosol (SOA)
formation from the photooxidation of isoprene under initially high nitric
oxide (NO) conditions (i.e., isoprene/NO ~3) was investigated in a
dual outdoor smog chamber. Based upon particle volume concentration
measurements and the detailed chemical characterization of isoprene SOA using
gas chromatography/mass spectrometry (GC/MS) and ultra performance liquid
chromatography/electrospray ionization high-resolution quadrupole
time-of-flight mass spectrometry (UPLC/ESI-HR-Q-TOFMS), enhanced SOA
formation was observed under lower RH conditions (15–40 %) compared to
higher RH conditions (40–90 %). 2-methylglyceric acid (2-MG) and its
corresponding oligoesters, which have been previously shown to form from
further oxidation of methacryloylperoxynitrate (MPAN), were enhanced in the
particle-phase under lower RH conditions. In addition, an abundant unknown
SOA tracer likely derived from the further oxidation of MPAN was detected and
enhanced under lower RH conditions. In contrast, the 2-methyltetrols, which
are known to mainly form from the reactive uptake of isoprene epoxydiols
(IEPOX) under low-NO conditions in the presence of acidified aerosol, did not
substantially vary under different RH conditions; however, isoprene-derived
organosulfates were found to be enhanced under high-RH conditions, indicating
the likely importance of the aqueous aerosol phase in their formation. Based
upon the detailed chemical characterization results, particle-phase organic
esterification is tentatively proposed to explain the observed enhancements
of isoprene SOA mass under lower RH conditions. Alternative mechanisms
explaining the enhancement of 2-MG and its corresponding oligoesters cannot
be completely ruled out. This is one of only a few chamber studies that have
examined the effect of RH on isoprene SOA formation. In comparison to our
recent results obtained from aromatic SOA formation, the effect of RH on
isoprene SOA formation is reversed. The results of this study highlight the
importance of elucidating the key reactive intermediates that lead to SOA
formation, especially since RH likely affects their ability in forming SOA.
Furthermore, ignoring the effects of RH may significantly affect the accuracy
of both regional and global SOA models. |
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