Joint effect of organic acids and inorganic salts on cloud droplet activation

M. Frosch, N. L. Prisle, M. Bilde, Z. Varga, G. Kiss

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)3895-3911
Number of pages17
JournalAtmospheric Chemistry and Physics
Volume11
Issue number8
DOIs
Publication statusPublished - 2011

Fingerprint

inorganic salt
cloud droplet
surface tension
organic acid
supersaturation
sodium chloride
fulvic acid
partitioning
aqueous solution
oxalic acid
acid
ammonium sulfate
surfactant
water
tensiometer
cloud condensation nucleus
citric acid
organic compound
solubility
chemical composition

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

Joint effect of organic acids and inorganic salts on cloud droplet activation. / Frosch, M.; Prisle, N. L.; Bilde, M.; Varga, Z.; Kiss, G.

In: Atmospheric Chemistry and Physics, Vol. 11, No. 8, 2011, p. 3895-3911.

Research output: Contribution to journalArticle

Frosch, M. ; Prisle, N. L. ; Bilde, M. ; Varga, Z. ; Kiss, G. / Joint effect of organic acids and inorganic salts on cloud droplet activation. In: Atmospheric Chemistry and Physics. 2011 ; Vol. 11, No. 8. pp. 3895-3911.
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