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| Titel |
Real-time, controlled OH-initiated oxidation of biogenic secondary organic aerosol |
| VerfasserIn |
J. G. Slowik, J. P. S. Wong, 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 ; 12, no. 20 ; Nr. 12, no. 20 (2012-10-29), S.9775-9790 |
| Datensatznummer |
250011535
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| Publikation (Nr.) |
 copernicus.org/acp-12-9775-2012.pdf |
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| Zusammenfassung |
| The chemical complexity of atmospheric organic aerosol (OA) requires novel
methods for characterization of its components and description of its
atmospheric processing-induced transformations. We present the first field
deployment of the Toronto Photooxidation Tube (TPOT), a field-deployable flow
reactor for the controlled exposure of ambient aerosol to OH radicals. The
system alternates between sampling of (1) (unreacted) ambient aerosol, (2)
aerosol exposed to UV light and subjected to a ~4 to 10 °C
temperature increase, and (3) aerosol that is oxidized by OH (in addition to
the aforementioned UV exposure/temperature increase). This allows both
characterization of the aging process and classification of aerosol in terms
of its volatility and reaction-based properties. Summertime measurements by
an aerosol mass spectrometer coupled to the TPOT were performed in the remote
forest of western Canada, resulting in aerosol dominated by biogenic
secondary organic aerosol. Volatilization/UV exposure resulted in an
approximately 10 to 25% decrease in organic mass and resulted in a slight
increase in oxygenation. OH oxidation resulted in a further organic mass
decrease (additional ~25%) and yielded an aerosol with O:C values
comparable to those characteristic of low volatility, highly oxygenated OA.
Most OH-induced changes occurred within ~3 day-equivalents of
atmospheric processing, with further reactions generally proceeding at a
greatly reduced rate. Positive matrix factorization (PMF) analysis of the
TPOT data yielded five factors. One factor is related to primary biomass
burning organic aerosol, while the others describe oxygenated organic aerosol
(OOA) components in terms of reactivity and volatility: (1) volatile and
reactive; (2) non-volatile and reactive; (3) non-volatile and reactive
early-generation product; (4) non-volatile and non-reactive product. This PMF
classification of aerosol components directly in terms of reactivity and
volatility is enabled by the TPOT-modulated perturbation of aerosol
composition, and is not otherwise accessible. The particle-phase reaction end
products have mass spectra similar to the low-volatility oxygenated organic
aerosol (LV-OOA) factors widely reported in the literature, providing
supporting evidence for aged organic aerosol formation from OH-driven
oxidation processes. |
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