Flash Freeze Flow Tube to Vitrify Aerosol Particles at Fixed Relative Humidity Values

Abstract

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 (SRH) 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.

Fluorescence Aerosol Flow Tube Spectroscopy to Detect Liquid–Liquid Phase Separation

“…The difference in SRH between the two sets of studies appears greater than can be explained by experimental uncertainty, including RH calibration, for the different techniques. Results from cryo-TEM of submicron particles likewise indicated lower SRH values than previously observed for deposited supermicron particles by optical microscopy …”

“…This transition occurred between 30 and 200 nm for different particle systems. The cryo-TEM technique was further extended by coupling to an RH-adjusted flow tube to flash-freeze particles, and these particles were collected, preserved, and imaged in the cryo-TEM . Differences across a series of images allowed a determination of SRH.…”

“…The cryo-TEM technique was further extended by coupling to an RH-adjusted flow tube to flash-freeze particles, and these particles were collected, preserved, and imaged in the cryo-TEM. 49 Differences across a series of images allowed a determination of SRH. For some mixed organic/inorganic particles, the SRH of the submicron particles was lower by up to 15% RH than their supermicron counterparts.…”

Influence of Ions on the Size Dependent Morphology of Aerosol Particles

“…35 By vitrifying aqueous particles, the size dependence in liquid particles and the separation relative humidity have been studied. 36,37 Our previous studies on LLPS in submicron aerosol particles have all used ammonium sulfate as the inorganic component of the aerosol particles.…”

“…Particle morphology is important for particle properties including the fact that it can influence the ability of particles to act as cloud condensation nuclei . By vitrifying aqueous particles, the size dependence in liquid particles and the separation relative humidity have been studied. , Our previous studies on LLPS in submicron aerosol particles have all used ammonium sulfate as the inorganic component of the aerosol particles.…”