AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Main Parameters Controlling Equilibration Time Scales of Atmospheric Semi-Volatile Aerosols
ANDREY KHLYSTOV, Desert Research Institute
Abstract Number: 253 Working Group: Aerosol Chemistry
Abstract Air quality models assume semi-volatile organic compounds (SVOC) in atmospheric aerosol to be in thermodynamic equilibrium with the gas phase. Recent experimental data suggested a possibility of very slow thermodynamic equilibration due to mass transfer limitations in solid or highly viscous particles. Thus, time scales of gas-particle equilibration need to be studied to verify assumptions made by the current air quality models. Understanding kinetics of gas-particle partitioning is also of great importance for interpretation of laboratory and ambient studies of aerosol volatility using thermodenuders.
In this presentation, I will revisit main parameters that control kinetics of aerosol equilibration to demonstrate that aerosol equilibration depends only on the aerosol size distribution characteristics and, if one accounts for particle size changes due to condensation/evaporation, on the ratio of the initial aerosol mass concentration to the saturation vapor concentration of the condensing species. I will also provide an estimate of the relative influence of this ratio on the equilibration time. Equilibration of the total mass of a multi-component aerosol and the effect of chemical reactions will also be discussed. Finally, the effect of intra-particle transport will be considered. I will use this analysis to provide estimates of the equilibration time scales for ambient aerosols to delineate the region of applicability of the thermodynamic equilibrium assumption. Contribution of different parameters to the overall uncertainty in estimating aerosol characteristic times will also be discussed.