Exploring the Temperature- and Humidity-Dependent Viscous Properties of Organic and Mixed Organic-Inorganic Aerosol Particles: Impacts on Water Diffusion and Interpreting Chamber Studies

RYAN D. DAVIS, Kyle McMillan, Christian Pattyn, Teresa Palacios Diaz, Katie Morton, Craig Sheldon, Samantha Kruse, Kyuhaeng Lee, Nicole Riemer, Matthew West, Cara Waters, Ali Alotbi, Katherine Kolozsvari, Andrew Ault, Jake Zenker, Lekha Patel, James F. Davies, Sandia National Laboratories

     Abstract Number: 449
     Working Group: Aerosol Chemistry

Abstract
Aerosol particles can exhibit chemical and physical properties that are not observed in bulk. One reason for the unique properties of aqueous aerosol particles is that they can achieve extremely high solute concentrations not replicable under bulk conditions. For example, when aqueous aerosol particles are exposed to low relative humidity, solute concentrations can become higher than the water content, blurring the distinction between solute and solvent. This low water content can promote ultra-viscous or gelatinous phase states. Such viscous phase states are important because they can impact heterogeneous reactivity, hygroscopicity, mass transport of solutes, and the shape factor of coagulated particles. Aerosol viscosity is thus an important property to understand to predict the physico-chemical evolution of aerosol particles in the atmosphere and within controlled chamber studies. However, the viscosity of complex, multi-component aerosol systems is not fully understood.

Here, we discuss experimental and computational efforts to study the viscosity of supersaturated aerosol particles and its effects. To characterize aerosol viscosity, we use a temperature and humidity controlled electrodynamic balance. We explore the viscosity of organic and mixed organic-inorganic aerosol, with a particular focus on organic-inorganic systems where supramolecular interactions can lead to ultra-viscous and gelatinous phase states. The implications of aerosol viscosity on water diffusion and experimental observations of coagulation in chamber studies will be discussed. We show that viscosity and diffusion do not have a straightforward relationship for gelatinous particle phase states. Further, we compare the coagulation of vitreous and liquid aerosol particles to examine the impact that viscosity can have on processing data from chamber studies where coagulation is expected to influence the particle number and size distribution. Combined, these studies explore the impact of aerosol viscosity from the molecular level to aerosol population scales.

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