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

Abstract

Abstract. 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 decrease 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. Succinic 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 surface. An equation based on thermodynamical relations was fitted to the data and extrapolated to the whole concentration range by using estimated surface tensions for pure compounds. As a result, we obtained an estimate of surface tensions beyond solubility limits in addition to a fit to the experimental data. 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 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 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.

Succinic acid in aqueous solution: connecting microscopic surface composition and macroscopic surface tension

“…Surface enrichment factors that result in a best fit to the experimental surface tension data for the model introduced by Sprow and 4 This shows the direct correlation between increased surface concentration of succinic acid on the molecular level and surface tension, which is a macroscopic property of an aqueous solution.…”

“…We are now in a position to compare the surface tension values obtained by using the surface enrichment factors obtained from XPS experiments and MD simulations in the two models with experimentally obtained surface tension values from Vanhanen et al 4 at 10 C, which is the temperature closest to that of the liquid micro-jet used in the XPS experiment where surface tension observations were available in literature. Table S2 in the ESI † .…”

“…Table S2 in the ESI † . The figures show i) the surface tension for pure water; ii) surface tension calculated with enrichment factors from XPS experiments using the conservative estimate for the sensitivity considering 25%, 50% and 75% of the total PE signal coming from the bulk of the solution; iii) surface tension derived with enrichment factors from the XPS experiment and MD simulation results (45% and 67%); and iv) the experimentally obtained surface tension values from Vanhanen et al at 10 C. 4 Note, higher bulk contribution leads to lower modeled surface tensions.…”

Surfactants in cloud droplet activation: mixed organic-inorganic particles

“…Increased organic activity in an aqueous salt solution can decrease the corresponding solubility and lead to precipitation or enhanced surface partitioning. This is often called the "salting-out effect" (Lin et al, 2005;Tuckermann, 2007;Vanhanen et al, 2008). In macroscopic solutions, enhanced surface partitioning may increase surfactant strength.…”

“…, is obtained by linear fitting to data from Vanhanen et al (2008). Szyskowski equation fitting-parameters a and b depend on the relative FAS and NaCl solute mass-fractions, where w FAS + w NaCl = 1, as…”