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| Titel |
Joint effect of organic acids and inorganic salts on cloud droplet activation |
| VerfasserIn |
M. Frosch, N. L. Prisle, M. Bilde, Z. Varga, G. Kiss |
| 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 ; 11, no. 8 ; Nr. 11, no. 8 (2011-04-28), S.3895-3911 |
| Datensatznummer |
250009657
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| Publikation (Nr.) |
 copernicus.org/acp-11-3895-2011.pdf |
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| Zusammenfassung |
| We have investigated CCN properties of internally mixed particles composed
of one organic acid (oxalic acid dihydrate, succinic acid, adipic acid,
citric acid, cis-pinonic acid, or Nordic reference fulvic acid) and one
inorganic salt (sodium chloride or ammonium sulphate). Surface tension and
water activity of aqueous model solutions with concentrations relevant for
CCN activation were measured using a tensiometer and osmometry,
respectively. The measurements were used to calculate Köhler curves and
critical supersaturations, which were compared to measured critical
supersaturations of particles with the same chemical compositions,
determined with a cloud condensation nucleus counter. Surfactant surface
partitioning was not accounted for. For the aqueous solutions containing
cis-pinonic acid and fulvic acid, a depression of surface tension was
observed, but for the remaining solutions the effect on surface tension was
negligible at concentrations relevant for cloud droplet activation. The
surface tension depression of aqueous solutions containing both organic acid
and inorganic salt was approximately the same as or smaller than that of
aqueous solutions containing the same mass of the corresponding pure organic
acids. Water activity was found to be highly dependent on the type and
amount of inorganic salt. Sodium chloride was able to decrease water
activity more than ammonium sulphate and both inorganic salts are predicted
to have a smaller Raoult term than the studied organic acids. Increasing the
mass ratio of the inorganic salt led to a decrease in water activity. Water
activity measurements were compared to results from the E-AIM model and
values estimated from both constant and variable van't Hoff factors. The
correspondence between measurements and estimates was overall good, except
for highly concentrated solutions. Critical supersaturations calculated with
Köhler theory based on measured water activity and surface tension, but
not accounting for surface partitioning, compared well with measurements,
except for the solutions containing sodium chloride and oxalic acid or one
of the more surface active organic compounds. In such cases, significantly
lower values were obtained from Köhler theory than the measured critical
supersaturations with deviations above 50% for a 60 nm particle
containing 50% (dry mass) of Nordic reference fulvic acid, suggesting
that surfactant partitioning and/or an effect of sodium chloride on
solubility of the organic component is important. |
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