Amorphous phase state diagrams of secondary organic aerosols
Authors
Sarah S Petters — Colorado State University
Nicholas Rothfuss — NCSU
Markus D Petters — North Carolina State University
Paul J Ziemann — University of Colorado
Sonia Kreidenweis — Colorado State University
Category
Secondary organic aerosol
Description
Amorphous phase state diagram of sucrose.
Atmospheric aerosols can exist in amorphous semi-solid or glassy phase states whose viscosity varies with atmospheric temperature and relative humidity. New measurements of viscosity for semi-solid 100 nm sucrose particles as a function of temperature and RH are reported. Viscosity is measured by inducing coagulation between two particles and probing the thermodynamic states that induce the particle to relax into a sphere. We show that for sucrose aerosol the glass transition temperature can be obtained by extrapolation to 10^12 Pa s from the measured temperature-dependent viscosity in the 10^6 to 10^7 Pa s range. Using the same method, viscosity and glass transition temperatures for four secondary organic aerosol systems were also determined. Ranked from most to least viscous, the systems are (glass transition temperature in degrees C): Limonene + O3 (8.4) > a-pinene + O3 (-4.1) > myrcene + O3 (-9.1) > toluene + OH (-13.8). The temperature-dependent viscosity data are used in conjunction with RH relaxation data, aerosol hygroscopicity, Vogel-Fulcher-Tammann temperature dependence, and the Gordon-Taylor mixing rule to construct a phase state model for amorphous organic aerosols. This phase state model is sufficiently simple that it can be used in global models to delineate glassy and liquid phase states and predict organic aerosol viscosity over the full range of atmospheric temperature and RH.
