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| Titel |
Surface tensions of multi-component mixed inorganic/organic aqueous systems of atmospheric significance: measurements, model predictions and importance for cloud activation predictions |
| VerfasserIn |
D. O. Topping, G. B. McFiggans, G. Kiss, Z. Varga, M. C. Facchini, S. Decesari, M. Mircea |
| 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 ; 7, no. 9 ; Nr. 7, no. 9 (2007-05-10), S.2371-2398 |
| Datensatznummer |
250004955
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| Publikation (Nr.) |
 copernicus.org/acp-7-2371-2007.pdf |
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| Zusammenfassung |
| In order to predict the physical properties of aerosol particles, it is
necessary to adequately capture the behaviour of the ubiquitous complex
organic components. One of the key properties which may affect this
behaviour is the contribution of the organic components to the surface
tension of aqueous particles in the moist atmosphere. Whilst the qualitative
effect of organic compounds on solution surface tensions has been widely
reported, our quantitative understanding on mixed organic and mixed
inorganic/organic systems is limited. Furthermore, it is unclear whether
models that exist in the literature can reproduce the surface tension
variability for binary and higher order multi-component organic and mixed
inorganic/organic systems of atmospheric significance. The current study
aims to resolve both issues to some extent. Surface tensions of single and
multiple solute aqueous solutions were measured and compared with
predictions from a number of model treatments. On comparison with binary
organic systems, two predictive models found in the literature provided a
range of values resulting from sensitivity to calculations of pure component
surface tensions. Results indicate that a fitted model can capture the
variability of the measured data very well, producing the lowest average
percentage deviation for all compounds studied. The performance of the
other models varies with compound and choice of model parameters. The
behaviour of ternary mixed inorganic/organic systems was unreliably captured
by using a predictive scheme and this was dependent on the composition of
the solutes present. For more atmospherically representative higher order
systems, entirely predictive schemes performed poorly. It was found that use
of the binary data in a relatively simple mixing rule, or modification of an
existing thermodynamic model with parameters derived from binary data, was
able to accurately capture the surface tension variation with concentration.
Thus, it would appear that in order to model multi-component surface
tensions involving compounds used in this study one requires the use of
appropriate binary data. However, results indicate that the use of
theoretical frameworks which contain parameters derived from binary data may
predict unphysical behaviour when taken beyond the concentration ranges used
to fit such parameters. The effect of deviations between predicted and
measured surface tensions on predicted critical saturation ratios was
quantified, by incorporating the surface tension models into an existing
thermodynamic framework whilst firstly neglecting bulk to surface
partitioning. Critical saturation ratios as a function of dry size for all
of the multi-component systems were computed and it was found that
deviations between predictions increased with decreasing particle dry size.
As expected, use of the surface tension of pure water, rather than calculate
the influence of the solutes explicitly, led to a consistently higher value
of the critical saturation ratio indicating that neglect of the
compositional effects will lead to significant differences in predicted
activation behaviour even at large particle dry sizes. Following this two
case studies were used to study the possible effect of bulk to surface
partitioning on critical saturation ratios. By employing various assumptions
it was possible to perform calculations not only for a binary system but
also for a mixed organic system. In both cases this effect lead to a
significant increase in the predicted critical supersaturation ratio
compared to the above treatment. Further analysis of this effect will form
the focus of future work. |
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