Comparing the Heterogeneous Reactivity of Viscous and Gel State Particles

STEPHANIE SALAS, Craig Sheldon, Teresa Palacios Diaz, Katie Morton, Kyle McMillan, Ryan Davis, James F. Davies, University of California, Riverside

     Abstract Number: 241
     Working Group: Aerosol Chemistry

Abstract
The phase state of aerosol particles directly influences the rate of heterogeneous chemistry. In the atmosphere, viscous phase states have been identified that significantly slow the rate of heterogeneous oxidation reactions by impeding the diffusion of oxidants and reactants/products in the particle. Recently, the formation of gel states in particles containing a mix of organic molecules and salts have been identified. In this work, we present an experimental platform to probe the composition of levitated aerosol particles and compare the reactivity of viscous and gel particles towards ozone. We use a linear quadrupole electrodynamic balance (LQ-EDB) to levitate individual particles and Mie resonance spectroscopy to determine the size and refractive index. Particles are ejected individually from the LQ-EDB to an open port sampling interface (OPSI) and aspirated into the electrospray ionization source to be sampled by an Orbitrap Q Exactive mass spectrometer to characterize the evolving chemical composition. Our results demonstrate that the reaction rate of viscous particles becomes slowed, while the reaction rate in gel particles becomes fully arrested after an initial period of rapid reaction. These observations are the first to demonstrate clear reactivity differences between viscous and gel states in aerosol particles, with implications for our understanding of heterogeneous aging in atmospheric aerosol.