Solid/Liquid Phase Diagram of the Ammonium Sulfate/Maleic Acid/Water System

Abstract

We have studied the low temperature phase diagram and water activities of the ammonium sulfate/maleic acid/water system using differential scanning calorimetry and infrared spectroscopy of thin films. Using the results from our experiments, we have mapped the solid/liquid ternary phase diagram, determined the water activities based on the freezing point depression, and determined the ice/maleic acid phase boundary as well as the ternary eutectic composition and temperature. We also compare our results to the predictions of the extended AIM aerosol thermodynamics model and find good agreement for the ice melting points in the ice primary phase field of this system; however significant differences were found with respect to phase boundaries, maleic acid dissolution, and ammonium sulfate dissolution.

Solid/Liquid Phase Diagram of the Ammonium Sulfate/Succinic Acid/Water System

“…We have studied five dicarboxylic acid/(NH 4 ) 2 SO 4 /H 2 O ternary systems in our lab: C 3 H 4 O 4 /(NH 4 ) 2 SO 4 /H 2 O, C 4 H 4 O 4 /(NH 4 ) 2 SO 4 /H 2 O, C 4 H 6 O 5 /(NH 4 ) 2 SO 4 /H 2 O, C 5 H 8 O 4 /(NH 4 ) 2 SO 4 /H 2 O, and C 4 H 6 O 4 /(NH 4 ) 2 SO 4 /H 2 O studied in this paper. Table summarizes some of the key physical properties that we measured in these systems.…”

Isotherm-Based Thermodynamic Models for Solute Activities of Organic Acids with Consideration of Partial Dissociation

“…In a study of growth factor of hygroscopic acids such as malonic acid, citric acid, and malic acid, Peng et al found that these water-soluble organic acids at low concentrations contribute less than inorganics to the hygroscopicity of atmospheric aerosols. Extended to ternary systems, Beyer et al − and Pearson and Beyer studied thermodynamic properties of dicarboxylic acids/ammonium sulfate/water mixtures using differential scanning calorimetry and infrared spectroscopy of thin films. They have reported water activities and solid/liquid ternary phase diagrams for systems having dicarboxylic acids like malonic, glutaric, maleic, and succinic acids below 300 K. Bilde et al have reviewed experimental measurements of equilibrium vapor pressures from evaporation rate of straight-chain dicarboxylic acids with water and inorganics.…”

“…Given the abundance and importance of organic acids in atmospheric aerosols, measurements and models of thermodynamic properties of the organic species in solution are essential for accurate predictions of the gas/particle partitioning and aerosol size distribution and composition . Experimental thermodynamic studies include investigations into vapor pressure measurements and hygroscopic properties. − Soonsin et al reported that organic acids with an even number of carbon molecules (“even acids”, e.g., succinic acid) are less soluble in water and have lower vapor pressures than odd acids. In a study of growth factor of hygroscopic acids such as malonic acid, citric acid, and malic acid, Peng et al found that these water-soluble organic acids at low concentrations contribute less than inorganics to the hygroscopicity of atmospheric aerosols.…”