Impacts of Non-ideal Mixing and Phase State on Equilibration Timescales of Secondary Organic Aerosol Partitioning

MEREDITH SCHERVISH, Manabu Shiraiwa, University of California, Irvine

     Abstract Number: 84
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
Experimental analysis and numerical modeling that probe equilibration timescales of secondary organic aerosol partitioning usually employs an ideal mixing assumption in the particle phase. Here we apply the kinetic multilayer model of gas-particle partitioning (KM-GAP) to simulate SOA partitioning into a core-shell phase-separated particle. By varying key parameters of a condensing gas-phase species including activity coefficient and bulk diffusivity, we probe the complex interplay of mass transfer kinetics and thermodynamics of partitioning. We found that non-ideality can impact SOA partitioning kinetics: a higher activity coefficient of the condensing species in the shell leads to the transport of species to the core being limited by the total amount of species the shell can hold, whereas a lower activity coefficient will require higher amounts of species to reach equilibrium being limited by gas-particle mass transfer. In addition, we notice that the particle may achieve quasi-equilibrium with the gas phase long before it achieves full equilibrium of the entire particle bulk with low activity coefficient of species in the shell in a semi-solid or amorphous solid state. These results provide useful insights into analysis and interpretation of SOA partitioning experiments as well as description and treatment of SOA in aerosol models.