Vapor-Phase Transmission Electron Microscopy for Submicron Visualization of NaCl Aerosols and Droplets

MARTIN AHN, Yuhang Wang, Dewansh Rastogi, Kotiba A. Malek, Jiayue Sun, Taylor J. Woehl, Akua Asa-Awuku, University of Maryland, College Park

     Abstract Number: 682
     Working Group: Instrumentation and Methods

Abstract
Single particle measurement techniques, such as electrodynamic balance (EDB) and atomic force microscopy (AFM), provide valuable insights regarding morphology and phase on supermicron-scale systems. Following this trend, we developed a novel application of electron microscopy to image submicron-scale aerosol particles. Using hermetically sealed microfluidic chambers, vapor-phase transmission electron microscopy (VPTEM) allows for in-situ observation of droplet formation from aerosol particles. This novel application of electron microscopy provides submicron and nanoscale visualization of aerosols under relevant atmospheric conditions. Furthermore, the ability to introduce water vapor into the sample holder enables deliquescence and efflorescence studies of these aerosol particles. In this work, the humidification and dehumidification processes are visualized under the VPTEM, and the deliquescence (DRH) and efflorescence (ERH) of the visualized aerosol particles can be obtained. Studies show that sodium chloride particles exhibit small amount of growth prior to the sudden increase due to deliquescence. Additionally, the DRH found using this novel method is significantly lower than that found in the published literature and those determined from bulk-aerosol measurements like the HTDMA measurements. Using the foundational knowledge provided by the simple NaCl/water vapor system, future work will investigate more complex aerosol mixtures under water and organic vapors.