Visualization and Characterization of Aged Organic-Inorganic Aerosols with Vapor-Phase Transmission Electron Microscopy
MARTIN AHN, Yuhang Wang, Liza-Anastasia DiCecco, Jennifer Gray, Amy Chen, Akua Asa-Awuku, Taylor J. Woehl, University of Maryland, College Park
Abstract Number: 59
Working Group: Instrumentation and Methods
Abstract
Using hermetically sealed microfluidic chambers, vapor-phase transmission electron microscopy (VPTEM) offers a novel method for in-situ single particle observation of aging of organic-inorganic aerosol particles. This previously established method can be further expanded by performing spatial, elemental and crystallographic characterization on these particles using TEM techniques such as diffraction pattern (DP), high-resolution TEM (HRTEM), energy dispersive spectroscopy (EDS), and electron tomography. For visualization, we utilized a MEMS-based in situ TEM sample cell, where relative humidity (RH) control was achieved by mixing humidified and dry air streams at various volumetric flow rate ratios. The dry mixed particles were impinged on silicon nitride sample chips and assembled into the in situ TEM sample cell and observed under controlled RH using in situ scanning TEM (STEM). Here we apply VPTEM on a phthalic acid (PTA)/sodium chloride (NaCl) system to observe aging of single organic acid/inorganic salt aerosol particles and characterize the effects of aging. Organic-inorganic aerosol mixtures exhibit non-ideal mixing behaviors and internal morphologies resulting in complex water-uptake and drying mechanisms. Results show non-prompt and step-like dissolution mechanisms of PTA/NaCl particles when exposed to relatively constant RH (~60%). This RH-independent, transient dissolution may be the result of increasing pH in the aerosol droplet due to chloride depletion. This hypothesis is tested and quantified via crystallographic and elemental analysis of the particles before and after aging using traditional TEM techniques. This work aids in demonstrating the potential of VPTEM as a novel method for multiphase aerosol and droplet studies.