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| Titel |
Phase partitioning and volatility of secondary organic aerosol components formed from α-pinene ozonolysis and OH oxidation: the importance of accretion products and other low volatility compounds |
| VerfasserIn |
F. D. Lopez-Hilfiker, C. Mohr, M. Ehn, F. Rubach, E. Kleist, J. Wildt, Th. F. Mentel, A. J. Carrasquillo, K. E. Daumit, J. F. Hunter, J. H. Kroll, D. R. Worsnop, J. A. Thornton |
| 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 ; 15, no. 14 ; Nr. 15, no. 14 (2015-07-16), S.7765-7776 |
| Datensatznummer |
250119900
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| Publikation (Nr.) |
 copernicus.org/acp-15-7765-2015.pdf |
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| Zusammenfassung |
| We measured a large suite of gas- and particle-phase
multi-functional organic compounds with a Filter Inlet for Gases and
AEROsols (FIGAERO) coupled to a high-resolution time-of-flight chemical
ionization mass spectrometer (HR-ToF-CIMS) developed at the University of
Washington. The instrument was deployed on environmental simulation chambers
to study monoterpene oxidation as a secondary organic aerosol (SOA) source.
We focus here on results from experiments utilizing an ionization method
most selective towards acids (acetate negative ion proton transfer), but our
conclusions are based on more general physical and chemical properties of
the SOA. Hundreds of compounds were observed in both gas and particle
phases, the latter being detected by temperature-programmed thermal
desorption of collected particles. Particulate organic compounds detected by
the FIGAERO–HR-ToF-CIMS are highly correlated with, and explain at least 25–50 % of, the organic aerosol mass measured by an Aerodyne aerosol mass
spectrometer (AMS). Reproducible multi-modal structures in the thermograms
for individual compounds of a given elemental composition reveal a
significant SOA mass contribution from high molecular weight organics and/or
oligomers (i.e., multi-phase accretion reaction products). Approximately
50 % of the HR-ToF-CIMS particle-phase mass is associated with compounds
having effective vapor pressures 4 or more orders of magnitude lower than
commonly measured monoterpene oxidation products. The relative importance of
these accretion-type and other extremely low volatility products appears to
vary with photochemical conditions. We present a desorption-temperature-based framework for apportionment of thermogram signals into volatility
bins. The volatility-based apportionment greatly improves agreement between
measured and modeled gas-particle partitioning for select major and minor
components of the SOA, consistent with thermal decomposition during
desorption causing the conversion of lower volatility components into the
detected higher volatility compounds. |
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