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.
Highlights
Indirect effect of aerosol particles to the atmosphere is currently the most uncertain piece in the climate change puzzle (IPCC, 2007)
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
Measurements of chemical composition of aerosol particles have shown that, in addition of inorganic salts, an extensive number of both water-soluble and water-insoluble organic acids are present in the aerosol phase (Legrand et al, 2007)
Summary
Indirect effect of aerosol particles to the atmosphere (the cloud albedo effect) is currently the most uncertain piece in the climate change puzzle (IPCC, 2007). Measurements of chemical composition of aerosol particles have shown that, in addition of inorganic salts, an extensive number of both water-soluble and water-insoluble organic acids are present in the aerosol phase (Legrand et al, 2007). They are formed for example via gas to particle conversion that results from the oxidation of volatile organic compounds (Kroll and Seinfeld, 2008). Succinic acid is a typical dicarboxylic acid found in aerosol phase (Legrand et al, 2007), and sodium chloride is a hygroscopic compound found in sea salt aerosols (Heintzenberg et al, 2000) This ternary solution can be considered as an atmospherically relevant mixture.
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