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| Titel |
Loading-dependent elemental composition of α-pinene SOA particles |
| VerfasserIn |
J. E. Shilling, Q. Chen, S. M. King, T. Rosenoern, J. H. Kroll, D. R. Worsnop, P. F. DeCarlo, A. C. Aiken, D. Sueper, J. L. Jimenez, S. T. Martin |
| 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 ; 9, no. 3 ; Nr. 9, no. 3 (2009-02-02), S.771-782 |
| Datensatznummer |
250006809
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| Publikation (Nr.) |
 copernicus.org/acp-9-771-2009.pdf |
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| Zusammenfassung |
| The chemical composition of secondary organic aerosol (SOA) particles,
formed by the dark ozonolysis of α-pinene, was characterized by a
high-resolution time-of-flight aerosol mass spectrometer. The experiments
were conducted using a continuous-flow chamber, allowing the particle mass
loading and chemical composition to be maintained for several days. The
organic portion of the particle mass loading was varied from 0.5 to >140 μg/m3
by adjusting the concentration of reacted α-pinene
from 0.9 to 91.1 ppbv. The mass spectra of the organic material changed with
loading. For loadings below 5 μg/m3 the unit-mass-resolution
m/z 44 (CO2+) signal intensity exceeded that of m/z 43 (predominantly
C2H3O+), suggesting more oxygenated organic material at lower
loadings. The composition varied more for lower loadings (0.5 to 15 μg/m3)
compared to higher loadings (15 to >140 μg/m3). The
high-resolution mass spectra showed that from >140 to 0.5 μg/m3
the mass percentage of fragments containing carbon and oxygen
(CxHyOz+) monotonically increased from 48% to 54%.
Correspondingly, the mass percentage of fragments representing
CxHy+ decreased from 52% to 46%, and the atomic
oxygen-to-carbon ratio increased from 0.29 to 0.45. The atomic ratios were
accurately parameterized by a four-product basis set of decadal volatility
(viz. 0.1, 1.0, 10, 100 μg/m3) employing products having empirical
formulas of C1H1.32O0.48, C1H1.36O0.39,
C1H1.57O0.24, and C1H1.76O0.14. These findings
suggest considerable caution is warranted in the extrapolation of laboratory
results that were obtained under conditions of relatively high loading
(i.e., >15 μg/m3) to modeling applications relevant to the
atmosphere, for which loadings of 0.1 to 20 μg/m3 are typical. For
the lowest loadings, the particle mass spectra resembled observations
reported in the literature for some atmospheric particles. |
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