AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Experimental Determination of the Relationship between Organic Aerosol Viscosity and Deposition Mode Ice Nucleation at Upper Free Tropospheric Conditions
SABIN KASPAROGLU, Russell Perkins, Paul DeMott, Sonia Kreidenweis, Markus Petters, North Carolina State University
Abstract Number: 337 Working Group: Carbonaceous Aerosol
Abstract Atmospheric aerosols can assume amorphous semi-solid or glassy phase states, where particle viscosity exceeds 104 Pa s. Particle viscosity varies with temperature and relative humidity. The viscosity of submicrometer particles can be determined by the preparation of dimer particles using the dual tandem DMA technique, followed by identifying the thermodynamic conditions where dimer particles are relaxing into spheres. Amorphous phase state diagrams that delineate glassy, semisolid and liquid states can be constructed from these data. Below −40 °C some glassy organic particles have been proposed to be able to serve as heterogeneous freezing nuclei in the deposition mode. However, measurements of viscosity in the semi-solid/glassy regime at temperatures less than 0 °C in the aerosol phase are limited. Here we present new experiments using the dual tandem DMA technique that extend the measurement range closer toward upper free tropospheric temperatures. From these data, phase state diagrams over the temperature range −60 °C to 40 °C are constructed. These phase state diagrams are juxtaposed with deposition mode ice nucleation data obtained using a continuous flow diffusion chamber (CFDC). Combined these datasets are used to delineate the conditions where the ice nucleation behavior switches from homogeneous freezing nucleation of haze to deposition freezing nucleation on glassy surfaces.