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| Titel |
Widening the gap between measurement and modelling of secondary organic aerosol properties? |
| VerfasserIn |
N. Good, D. O. Topping, J. Duplissy, M. Gysel, N. K. Meyer, A. Metzger, S. F. Turner, U. Baltensperger, Z. Ristovski, E. Weingärtner, H. Coe, G. McFiggans |
| 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. 6 ; Nr. 10, no. 6 (2010-03-15), S.2577-2593 |
| Datensatznummer |
250008242
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| Publikation (Nr.) |
 copernicus.org/acp-10-2577-2010.pdf |
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| Zusammenfassung |
The link between measured sub-saturated hygroscopicity and cloud activation
potential of secondary organic aerosol particles produced by the chamber
photo-oxidation of α-pinene in the presence or absence of ammonium
sulphate seed aerosol was investigated using two models of varying
complexity. A simple single hygroscopicity parameter model and a more complex
model (incorporating surface effects) were used to assess the detail required
to predict the cloud condensation nucleus (CCN) activity from the
sub-saturated water uptake. Sub-saturated water uptake measured by three
hygroscopicity tandem differential mobility analyser (HTDMA) instruments was
used to determine the water activity for use in the models. The predicted CCN
activity was compared to the measured CCN activation potential using a
continuous flow CCN counter.
Reconciliation using the more complex model formulation with measured cloud
activation could be achieved widely different assumed surface tension
behavior of the growing droplet; this was entirely determined by the
instrument used as the source of water activity data. This unreliable
derivation of the water activity as a function of solute concentration from
sub-saturated hygroscopicity data indicates a limitation in the use of such
data in predicting cloud condensation nucleus behavior of particles with a
significant organic fraction. Similarly, the ability of the simpler single
parameter model to predict cloud activation behaviour was dependent on the
instrument used to measure sub-saturated hygroscopicity and the relative
humidity used to provide the model input. However, agreement was observed for
inorganic salt solution particles, which were measured by all instruments in
agreement with theory.
The difference in HTDMA data from validated and extensively used instruments
means that it cannot be stated with certainty the detail required to predict
the CCN activity from sub-saturated hygroscopicity. In order to narrow the
gap between measurements of hygroscopic growth and CCN activity the processes
involved must be understood and the instrumentation extensively quality
assured. It is impossible to say from the results presented here due to the
differences in HTDMA data whether: i) Surface tension suppression occurs
ii) Bulk to surface partitioning is important iii) The water activity
coefficient changes significantly as a function of the solute concentration. |
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