Comparisons between Hygroscopic Measurements and UNIFAC Model Predictions for Dicarboxylic Organic Aerosol Mixtures

Hygroscopic behavior was measured at 12 degrees C over aqueous bulk solutions containing dicarboxylic acids, using a Baratron pressure transducer. Our experimental measurements of water activity for malonic acid solutions (0-10 mol/kg water) and glutaric acid solutions (0-5 mol/kg water) agreed to within 0.6% and 0.8% of the predictions using Peng's modified UNIFAC model, respectively (except for the 10 mol/kg water value, which differed by 2%). However, for solutions containing mixtures of malonic/glutaric acids, malonic/succinic acids, and glutaric/succinic acids, the disagreements between the measurements and predictions using the ZSR model or Peng's modified UNIFAC model are higher than those for the single-component cases. Measurements of the overall water vapor pressure for 50 : 50 molar mixtures of malonic/glutaric acids closely followed that for malonic acid alone. For mixtures of malonic/succinic acids and glutaric/succinic acids, the influence of a constant concentration of succinic acid on water uptake became more significant as the concentration of malonic acid or glutaric acid was increased.