(81f) Using Droplet Microfluidics to Study Chemical Thermodynamics of Aqueous Atmospheric Aerosol Particles

Accurate predictions of gas-liquid-solid equilibrium partitioning of atmospheric aerosols by thermodynamic modeling and measurements is critical for determination of atmospheric particle properties and processes at temperatures and relative humidities relevant to the atmosphere. Organic compounds like dicarboxylic acids that originate from biomass burning, and direct biogenic emission make up a significant fraction of the organic mass in atmospheric aerosol particles. In addition, inorganic compounds like ammonium sulfate and sea salt also exist in atmospheric aerosols, that results in a mixture of single, double or triple charged ions and non-dissociated organic acids. In this work, atmospheric aerosol droplet chemical mimics are generated in microfluidic channels and stored in passive traps until dehydration to study the influence of relative humidity and water loss on phase behavior. The solution volume of the droplet trapped changes with respect to time, and is calculated by image analysis and correlated with the concentration of the solution to determine water activities at each time interval. The research will help determine mixture efflorescence of droplets that include presence of other dissolved components and tend to decrease the water activity. The measurements will also be used to parameterize statistical thermodynamic modeling for predictions of thermodynamic properties of aqueous aerosols as a function of relative humidity.