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| Titel |
Elemental composition and oxidation of chamber organic aerosol |
| VerfasserIn |
P. S. Chhabra, N. L. Ng, M. R. Canagaratna, A. L. Corrigan, L. M. Russell, D. R. Worsnop, R. C. Flagan, J. H. Seinfeld |
| 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. 17 ; Nr. 11, no. 17 (2011-09-01), S.8827-8845 |
| Datensatznummer |
250010040
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| Publikation (Nr.) |
 copernicus.org/acp-11-8827-2011.pdf |
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| Zusammenfassung |
| Recently, graphical representations of aerosol mass spectrometer (AMS)
spectra and elemental composition have been developed to explain the
oxidative and aging processes of secondary organic aerosol (SOA). It has been
shown previously that oxygenated organic aerosol (OOA) components from
ambient and laboratory data fall within a triangular region in the
f44 vs. f43 space, where f44 and
f43 are the ratios of the organic signal at m/z 44 and
43 to the total organic signal in AMS spectra, respectively; we refer to this
graphical representation as the "triangle plot." Alternatively, the Van
Krevelen diagram has been used to describe the evolution of functional groups
in SOA. In this study we investigate the variability of SOA formed in chamber
experiments from twelve different precursors in both "triangle plot" and
Van Krevelen domains. Spectral and elemental data from the high-resolution
Aerodyne aerosol mass spectrometer are compared to offline species
identification analysis and FTIR filter analysis to better understand the
changes in functional and elemental composition inherent in SOA formation and
aging. We find that SOA formed under high- and low-NOx conditions
occupy similar areas in the "triangle plot" and Van Krevelen diagram and
that SOA generated from already oxidized precursors allows for the
exploration of areas higher on the "triangle plot" not easily accessible with
non-oxidized precursors. As SOA ages, it migrates toward the top of the
triangle along a path largely dependent on the precursor identity, which
suggests increasing organic acid content and decreasing mass spectral
variability. The most oxidized SOA come from the photooxidation of
methoxyphenol precursors which yielded SOA O/C ratios near unity.
α-pinene ozonolysis and naphthalene photooxidation SOA systems have
had the highest degree of mass closure in previous chemical characterization
studies and also show the best agreement between AMS elemental composition
measurements and elemental composition of identified species within the
uncertainty of the AMS elemental analysis. In general, compared to their
respective unsaturated SOA precursors, the elemental composition of chamber
SOA follows a slope shallower than −1 on the Van Krevelen diagram, which is
indicative of oxidation of the precursor without substantial losss of
hydrogen, likely due to the unsaturated nature of the precursors. From the
spectra of SOA studied here, we are able to reproduce the triangular region
originally constructed with ambient OOA compents with chamber aerosol showing
that SOA becomes more chemically similar as it ages. Ambient data in the
middle of the triangle represent the ensemble average of many different SOA
precursors, ages, and oxidative processes. |
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