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| Titel |
Effect of humidity on the composition of isoprene photooxidation secondary organic aerosol |
| VerfasserIn |
T. B. Nguyen, P. J. Roach, J. Laskin, A. Laskin, S. A. Nizkorodov |
| 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. 14 ; Nr. 11, no. 14 (2011-07-18), S.6931-6944 |
| Datensatznummer |
250009924
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| Publikation (Nr.) |
 copernicus.org/acp-11-6931-2011.pdf |
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| Zusammenfassung |
| The effect of relative humidity (RH) on the composition and concentrations
of gas-phase products and secondary organic aerosol (SOA) generated from the
photooxidation of isoprene under high-NOx conditions was investigated.
Experiments were performed with hydrogen peroxide as the OH precursor and in
the absence of seed aerosol. The relative yields of most gas-phase products
were the same regardless of initial water vapor concentration with exception
of hydroxyacetone and glycolaldehyde, which were considerably affected by
RH. A significant change was observed in the SOA composition, with many
unique condensed-phase products formed under humid (90 % RH) vs. dry
(<2 % RH) conditions, without any detectable effect on the rate and
extent of the SOA mass growth. There is a 40 % reduction in the number and
relative abundance of distinct particle-phase nitrogen-containing organic
compounds (NOC) detected by high resolution mass spectrometry. The
suppression of condensation reactions, which produce water as a product, is
the most important chemical effect of the increased RH. For example, the
total signal from oligomeric esters of 2-methylglyceric acid was reduced by
about 60 % under humid conditions and the maximum oligomer chain lengths
were reduced by 7–11 carbons. Oligomers formed by addition mechanisms,
without direct involvement of water, also decreased at elevated RH but to a
much smaller extent. The observed reduction in the extent of
condensation-type oligomerization at high RH may have substantial impact on
the phase characteristics and hygroscopicity of the isoprene aerosol. The
reduction in the amount of organic nitrates in the particle phase has
implications for understanding the budget of NOC compounds. |
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