LAUSR

Development of methods to measure the phase transitions and physical properties of submicron atmospheric aerosol particles is needed to better model these systems. In this paper, we present a method to flash freeze submicron particles to measure phase transitions as a function of relative humidity (RH). Particles are equilibrated at a fixed RH, vitrified in a temperature-controlled flow tube, and imaged with cryogenic transmission electron microscopy (cryo-TEM). We demonstrate the use of the technique for measuring the efflorescence relative humidity (ERH) of potassium sulfate and potassium chloride aerosol as well as the separation RH for a multicomponent organic/inorganic system that undergoes liquid-liquid phase separation (LLPS). The location of phase transitions can shift between the micrometer and nanometer size regimes and particles in a given population may have a range of RH over which a phase transition occurs. This technique addresses these requirements by allowing for characterization of the phase transitions for individual particles in a population on the submicron scale.