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| Titel |
Modelling the cloud condensation nucleus activity of organic acids on the basis of surface tension and osmolality measurements |
| VerfasserIn |
Z. Varga, G. Kiss, H.-C. Hansson |
| 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. 17 ; Nr. 7, no. 17 (2007-09-07), S.4601-4611 |
| Datensatznummer |
250005186
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| Publikation (Nr.) |
 copernicus.org/acp-7-4601-2007.pdf |
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| Zusammenfassung |
| In this study vapour pressure osmometry was used to determine water activity
in the solutions of organic acids. The surface tension of the solutions was
also monitored in parallel and then Köhler curves were calculated for
nine organic acids (oxalic, malonic, succinic, glutaric, adipic, maleic,
malic, citric and cis-pinonic). Surface tension depression is negligible for
most of the organic acids in dilute (≤1 w/w%) solutions. Therefore,
these compounds affect equilibrium vapour pressure only in the beginning
phase of droplet formation when the droplet solution is more concentrated
but not necessarily at the critical size. An exception is cis-pinonic acid
which remarkably depress surface tension also in dilute (0.1 w/w%)
solution and hence at the critical point. The surface tension of organic
acid solutions is influenced by the solubility of the compound, the length
of the carbon chain and also by the polar functional groups present in the
molecule. Similarly to surface tension solubility plays an important role
also in water activity: compounds with higher solubility (e.g. malonic,
maleic and glutaric acid) reduce water activity significantly in the early
phase of droplet formation while less soluble acids (e.g. succinic and
adipic acid) are saturated in small droplets and the solution starts
diluting only in bigger droplets. As a consequence, compounds with lower
solubility have a minor effect on water activity in the early phase of
droplet formation. To deduce the total effect Köhler curves were
calculated and critical supersaturations (Sc) were determined for the
organic acids using measured surface tension and water activity. It was
found that critical supersaturation grew with growing carbon number. Oxalic
acid had the lowest critical supersaturation in the size range studied and
it was comparable to the activation of ammonium sulphate. The Sc values
obtained in this study were compared to data from CCNC experiments. In most
cases good agreement was found. For modelling purposes Sc vs. ddry
plots are given and the dependence of water activity and surface tension on
concentration are also formulated. |
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