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| Titel |
The hygroscopicity parameter (κ) of ambient organic aerosol at a field site subject to biogenic and anthropogenic influences: relationship to degree of aerosol oxidation |
| VerfasserIn |
R. Y.-W. Chang, J. G. Slowik, N. C. Shantz, A. Vlasenko, J. Liggio, S. J. Sjostedt, W. R. Leaitch, 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 ; 10, no. 11 ; Nr. 10, no. 11 (2010-06-01), S.5047-5064 |
| Datensatznummer |
250008513
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| Publikation (Nr.) |
 copernicus.org/acp-10-5047-2010.pdf |
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| Zusammenfassung |
| Cloud condensation nuclei (CCN) concentrations were measured at Egbert, a
rural site in Ontario, Canada during the spring of 2007. The CCN
concentrations were compared to values predicted from the aerosol chemical
composition and size distribution using κ-Köhler theory, with the
specific goal of this work being to determine the hygroscopic parameter
(κ) of the oxygenated organic component of the aerosol, assuming that
oxygenation drives the hygroscopicity for the entire organic fraction of the
aerosol. The hygroscopicity of the oxygenated fraction of the organic
component, as determined by an Aerodyne aerosol mass spectrometer (AMS), was
characterised by two methods. First, positive matrix factorization (PMF) was
used to separate oxygenated and unoxygenated organic aerosol factors. By
assuming that the unoxygenated factor is completely non-hygroscopic and by
varying κ of the oxygenated factor so that the predicted and measured
CCN concentrations are internally consistent and in good agreement, κ
of the oxygenated organic factor was found to be 0.22±0.04 for the
suite of measurements made during this five-week campaign. In a second,
equivalent approach, we continue to assume that the unoxygenated component of
the aerosol, with a mole ratio of atomic oxygen to atomic carbon (O/C)
≈ 0, is completely non-hygroscopic, and we postulate a simple linear
relationship between κorg and O/C. Under these assumptions, the
κ of the entire organic component for bulk aerosols measured by the
AMS can be parameterised as κorg=(0.29±0.05)·(O/C), for the range of O/C observed in
this study (0.3 to 0.6). These results are averaged over our five-week study
at one location using only the AMS for composition analysis. Empirically, our
measurements are consistent with κorg generally increasing with
increasing particle oxygenation, but high uncertainties preclude us from
testing this hypothesis. Lastly, we examine select periods of different
aerosol composition, corresponding to different air mass histories, to
determine the generality of the campaign-wide findings described above. |
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