Abstract View
Temperature Dependent Phase Separation and Ice Nucleation Studies of Model Aerosols Using Droplet Microfluidics
PRIYATANU ROY, Cari Dutcher, University of Minnesota
Abstract Number: 284
Working Group: Instrumentation and Methods
Abstract
Phase transitions in ambient aerosols are significant in prediction of their primary and secondary effects including optical properties and cloud formation in global climate models. In situ studies of the phase state is expensive and requires complex instrumentation. We present droplet microfluidic platforms for experiments on phase transitions at low temperatures liquid-liquid phase separation (LLPS) in statically trapped aerosol droplets and high-throughput temperature detection of model ice-nucleating particles. LLPS studies at temperature down to -20°C showed that for ternary aqueous droplets containing ammonium sulfate, 3-methylglutaric acid (3MGA) and water, the initial phase transition happens at a lower solute concentration at lower temperatures. Thermodynamic models for activity coefficients E-AIM and AIOMFAC were used to convert solute concentration to separation relative humidity (SRH) showing the SRH for this system was slightly higher for lower temperatures. Similar studies were performed for NaCl and 3MGA system which again showed a slight temperature dependence of the RH at which crystal growth initiated. Other organics studied did not show any significant temperature dependence of LLPS. Ice nucleation study was conducted on a platform with a controllable temperature gradient and a flow-through microfluidic channel. Snomax was used as a model ice nucleating particle (INP) freezing at <-10°C. Rapid detection of ice nucleation was attempted with polarized optics utilizing birefringence of droplets with ice crystals vs. liquid droplets, and a deep neural network using supervised learning to classify frozen vs. liquid droplets with an accuracy >99.8%. Future work would include incorporation of on-chip platinum thin film temperature sensors and investigating INPs from varied sources such as mineral dust, sea spray aerosol, agricultural emissions. These measurements will be used to predict the cloud and ice formation activity of land-based and sea spray aerosols.