Abstract View
Measurements and Modeling of the Temperature and Humidity Dependent Viscosity Between -30 and 30 Degree Celsius
SABIN KASPAROGLU, Markus Petters, Ying Li, Manabu Shiraiwa, North Carolina State University
Abstract Number: 314
Working Group: Carbonaceous Aerosol
Abstract
Atmospheric aerosols can assume amorphous semi-solid or glassy phase states whose viscosity depends on atmospheric temperature and relative humidity. New measurements characterizing viscosity of sub-100 nm particles from the dimer relaxation method are provided to construct the phase state diagram of citric acid between -30 and 30 degrees Celsius. These measurements of citric acid particles extend the available data of temperature and humidity dependent viscosity to -30 degrees Celsius. The measurements are also tested against the model which predicts the viscosity of the compound applying the water-organic binary mixing rule as a function of the glass transition temperature, a glass transition temperature scaled viscosity fragility, and water uptake parameterization. The proposed function is also compiled from literature data and able to use the fragility parameterization to predict the viscosity. Predicted relationships agree well with observations and with measured isopleths of constant viscosity at ~10^7 Pa s even at cold temperatures. In addition, simulations of the kinetic multi-layer model of gas-particle interactions (KM-GAP) are performed to explore the isopleths of equilibrium time scales, at different temperature and relative humidity values. KM-GAP model simulations showed that the equilibrium limitations of citric acid are below the coalescence time of this study’s experiments at all studied temperature ranges. However, there are some discrepancies for sucrose at colder temperatures, which can be attributed to kinetic limitations of water uptake at the time scales of the dimer relaxation experiments.