AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
The Importance of Particle History When Exploring Particle Phase, Viscosity, and Structure within Individual Organic-Inorganic Mixed Particles Using Microscopy and Spectroscopy
ANDREW AULT, Amy Bondy, Rebecca Craig, Sydney Niles, Nicole Olson, University of Michigan
Abstract Number: 419 Working Group: Aerosol Chemistry
Abstract Recent work has shown that atmospheric aerosols with secondary components, such as secondary organic aerosol (SOA) and ammonium sulfate, are frequently not in a well-mixed aqueous state at thermodynamic equilibrium. The presence of viscous or glassy aerosol, efflorescence/deliquescence behavior, and liquid-liquid phase separations have been shown experimentally in the atmosphere and through laboratory studies, along with global model simulations. These non-equilibrium states can challenge many assumptions about aerosol behavior, such as limited diffusion impacts on heterogeneous and multiphase reactions. Herein, we focus on the behavior of organic-inorganic mixtures, such as SOA and ammonium sulfate as a function of relative humidity (RH) using both ambient samples and model systems to probe changes to structure and viscosity. This is probed using established methods, such as scanning electron microscopy with energy dispersive X-ray spectroscopy (EDX), and novel methods for studying atmospheric aerosols including atomic force microscopy with infrared spectroscopy (AFM-IR) and Raman microspectroscopy. By varying how aerosols are generated, studying particles formed during different atmospheric conditions, and cycling RH, insights into how particles change in the atmosphere have been obtained. Specifically, these measurements and experiments show that particle history plays an important role in determining phase and structure, and that it is not safe to assume that particle behavior is reversible after changes in RH. This has important implications for processes such as SOA formation, heterogeneous reactions, cloud droplet and ice crystal nucleation. Further measurements are needed to create a framework that can account for these non-equilibrium and non-reversible processes.