Ternary solution of sodium chloride, succinic acid and water – surface tension and its influence on cloud droplet activation

Surface tension of ternary solution of sodium chloride, succinic acid and water was measured as a function of both composition and temperature by using the capillary rise technique. Both sodium chloride and succinic acid are found in atmospheric aerosols, the former being main constituent of marine aerosol. Succinic acid was found to de-5 crease the surface tension of water already at very low concentrations. Sodium chloride increased the surface tension linearly as a function of the concentration. Surface tensions of both binary solutions agreed well with the previous measurements. Suc-cinic acid was found to lower the surface tension even if sodium chloride is present, indicating that succinic acid as a surface active compound tends to concentrate to the 10 surface. An equation based on thermodynamical relations was fitted to the data. As a result, a surface tension parameterization of ternary solution was obtained over the whole concentration range. The parameterization can safely be used at temperatures from 10 to 30 • C. These kinds of parameterizations are important for example in atmospheric nucleation models. To investigate the influence of surface tension on cloud 15 droplet activation, the surface tension parameterization was included in an adiabatic air parcel model. Usually in cloud models the surface tension of pure water is used. Simulations were done for characteristic marine aerosol size distributions consisting of the considered ternary mixture. We found that by using the surface tension of pure water, the amount of activated particles is underestimated up to 8% if particles contain 20 succinic acid and overestimated it up to 8% if particles contain only sodium chloride. The surface tension effect was found to increase with increasing updraft velocity.