Equilibrium ternary diagrams of aqueous mixtures of malonic acid and sulfate/ammonium salts.

Tropospheric aerosols are usually complex mixtures organic and inorganic components. Several recent studies have focused on the phase transitions and equilibrium water vapor pressure of mixtures of dicarboxylic acids and ammonium sulfate, because these are often found in ambient particles. On the other hand, ambient particles with non neutralized sulfate have been observed in urban environments. Equilibrium ternary diagrams of mixtures of malonic acid/ammonium sulfate/water and malonic acid/ammonium bisulfate/water will be presented. Solubility of the solid mixtures in water has been determined over the complete range of compositions in the ternary diagram and equilibrium water activity of the aqueous solutions has been measured with an AquaLab water activity equipment. For the malonic acid/ammonium sulfate/water, good agreement with previous studies was found. Differences between this system and the malonic acid/ammonium bisulfate/water system will be described and the effect of acidity in the thermodynamic properties of the mixtures will be discussed.