Connecting the Hygroscopicity, Viscosity and Water Diffusivity of Internally Mixed Organic-Inorganic Aerosol

JAMES F. DAVIES, Craig Sheldon, Jack Choczynski, Chelsea Price, Katie Morton, Ryan Davis, University of California, Riverside

     Abstract Number: 20
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
Internally mixed aerosol particles containing organic molecules and inorganic salts are prevalent in the atmosphere, arising from direct emission (e.g. from the ocean) or indirect production by condensation of organic vapors onto existing inorganic particle seeds. Aerosol particles co-exist with water vapor and, under humid conditions, will exist as dilute aqueous solution particles. As the humidity decreases, water is lost and the solute concentration increases, leading to significant changes in particle properties and morphology.

In this work we explore model aerosol particles containing inorganic salts, such as ammonium sulphate, mixed with oxygenated organic molecules. Using single particle levitation, we measure the hygroscopicity, viscosity, and rate of water transport in particles across a range of RH conditions and organic mass fractions. These properties are responsible for controlling many important physical and chemical aerosol processes in the atmosphere and are connected by their dependence on RH. We report the RH-dependence of these properties and explore the applicability of commonly used methods that connect them together, such as volume-additivity relations, the Stokes-Einstein relationship, and thermodynamic modelling methods.