Surface tension of solutions containing dicarboxylic acids with ammonium sulfate, d-glucose, or humic acid

To examine the effect of organic/inorganic solutes on the properties of cloud condensation nuclei and other atmospheric aerosols, the surface tension of various mixtures including dicarboxylic acids, ammonium sulfate, d-glucose, and humic acid sodium salt (NaHA) was measured at 20 °C using the Wilhelmy plate method. An equimolar mixture of oxalic/malonic acids (0-0.5 mol/kg water) was added to ammonium sulfate (0.1-3 mol/kg water), d-glucose (0.01-2 mol/kg water), and NaHA (0.1-10 g/kg water) solutions. The surface tensions of ammonium sulfate, d-glucose, and NaHA solutions decreased as the concentration of the added oxalic/malonic acid mixture increased. The trend in surface tension for the ammonium sulfate solution is roughly similar with and without the addition of the oxalic/malonic acid mixture. However, the surface tension trend for the d-glucose and NaHA solutions with the oxalic/malonic acid mixtures does not follow that of pure d-glucose and NaHA solutions. With the presence of oxalic/malonic acids in the solution, the surface tension increase by d-glucose becomes larger and the surface tension reduction by NaHA becomes smaller.