Surface Tension of Atmospheric Inorganic Electrolyte Solutions at Low Temperatures and High Concentrations

CARI S. DUTCHER (1), Anthony S. Wexler (1), Simon L. Clegg (1,2)

(1) University of California, Davis, (2) University of East Anglia, UK

     Abstract Number: 760
     Last modified: May 14, 2010

Abstract
Knowledge of surface tension is central to accurate predictions of cloud droplet activation and nucleation by sub-micron sized soluble aerosol particles which typically contain ammonium, sulphate, and components of seasalt and windblown dust. However, surface tension data are limited for inorganic electrolyte solutions at temperatures and concentrations typical of many atmospheric conditions, for which instances of supersaturation or supercooling are common. In this work, a semi-empirical model has been developed to calculate surface tensions of 27 aqueous inorganic electrolyte solutions and their mixtures, for concentrations ranging from infinitely dilute solution to molten salt. The model extrapolates smoothly to temperatures as low at 150 K. The average absolute percentage error between calculated and experimental surface tensions is < 1% (for over 2000 data points). The model can also successfully predict surface tensions of ternary aqueous mixtures, and the effect of salt-salt interactions in these calculations was explored. Additionally, theoretical molten surface tension properties extrapolated to low temperatures for salts with no experimental molten data have been estimated by relating known molten salt surface tension properties to properties such as ion valency and radius, melting temperature, and salt molar volume. The resultant surface tension model for the inorganic electrolytes will be incorporated into the Extended Aerosol Inorganics Model and made available on the web (http://www.aim.env.uea.ac.uk/aim/aim.php).