Evaporation of ternary inorganic/organic aqueous droplets: Sodium chloride, succinic acid and water

We studied the evaporation of submicrometer-sized, aqueous solution aerosol particles containing different mixing ratios of succinic acid, sodium chloride, and water. A modified tandem differential mobility analyzer (TDMA) including a laminar flow-tube was deployed to measure the evaporation rates of the particles at ambient atmospheric pressure and temperature, and at different relative humidities. A phase equilibrium model (extended aerosol inorganic model, E-AIM) was applied to predict the concentration, activity coefficients, and partitioning of the evaporating species. We also investigated the particles evaporation by combining an evaporation model with the phase equilibrium model. The observed evaporation could be predicted with reasonable accuracy at large relative amounts of succinic acid. At low relative amounts, the overpredicted evaporation suggests that inorganic salts might enhance the particle phase partitioning of organic acids more than expected based on present aerosol thermodynamic models.