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| Titel |
The link between organic aerosol mass loading and degree of oxygenation: an α-pinene photooxidation study |
| VerfasserIn |
L. Pfaffenberger, P. Barmet, J. G. Slowik, A. P. Praplan, J. Dommen, A. S. H. Prévôt, U. Baltensperger |
| 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 ; 13, no. 13 ; Nr. 13, no. 13 (2013-07-08), S.6493-6506 |
| Datensatznummer |
250018748
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| Publikation (Nr.) |
 copernicus.org/acp-13-6493-2013.pdf |
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| Zusammenfassung |
| A series of smog chamber (SC) experiments was conducted to identify factors
responsible for the discrepancy between ambient and SC aerosol degree of
oxygenation. An Aerodyne high-resolution time-of-flight aerosol mass
spectrometer is used to compare mass spectra from α-pinene
photooxidation with ambient aerosol. Composition is compared in terms of the
fraction of particulate CO2+, a surrogate for carboxylic acids,
vs. the fraction of C2H3O+, a surrogate for aldehydes,
alcohols and ketones, as well as in the Van Krevelen space, where the
evolution of the atomic hydrogen-to-carbon ratio (H : C) vs. the atomic
oxygen-to-carbon ratio (O : C) is investigated. Low (near-ambient) organic
mass concentrations were found to be necessary to obtain oxygenation levels
similar to those of low-volatility oxygenated organic aerosol (LV-OOA)
commonly identified in ambient measurements. The effects of organic mass
loading and OH (hydroxyl radical) exposure were decoupled by
inter-experiment comparisons at the same integrated OH concentration. An OH
exposure between 3 and 25 × 107 cm−3 h is
needed to increase O : C by 0.05 during aerosol aging. For the first time,
LV-OOA-like aerosol from the abundant biogenic precursor α-pinene
was produced in a smog chamber by oxidation at typical atmospheric OH
concentrations. Significant correlation between measured secondary organic
aerosol (SOA) and reference LV-OOA mass spectra is shown by Pearson's
R2 values larger than 0.90 for experiments with low organic
mass concentrations between 1.2 and 18 μg m−3 at an
OH exposure of 4 × 107 cm−3 h, corresponding
to about two days of oxidation time in the atmosphere, based on a global
mean OH concentration of ~ 1 × 106 cm−3.
α-Pinene SOA is more oxygenated at low organic mass loadings.
Because the degree of oxygenation influences the chemical, volatility and
hygroscopic properties of ambient aerosol, smog chamber studies must be
performed at near-ambient concentrations to accurately simulate ambient
aerosol properties. |
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