AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Kinetic Process Models for Growth, Evaporation and Multiphase Chemistry of Organic Aerosols
THOMAS BERKEMEIER, Masayuki Takeuchi, Gamze Eris, Ulrich Pöschl, Manabu Shiraiwa, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 422 Working Group: Aerosol Chemistry
Abstract Heterogeneous reactions, gas-particle partitioning and other multiphase processes are important pathways in the formation and processing of atmospheric organic aerosols, but the effects of particle phase state on reaction and condensation kinetics are still not fully elucidated and can often not be described by classical models assuming a homogeneous condensed phase. This presentation outlines how kinetic modelling can be used to gain insight into the coupling of mass transport, phase changes, and chemical reactions in complex multiphase reaction systems.
We apply the kinetic multi-layer model KM-GAP, which explicitly resolves gas adsorption, evaporation, condensed-phase diffusion and condensed-phase chemistry and the Monte-Carlo Genetic Algorithm (MCGA), a novel method that enables automated and unbiased global optimization of model parameters such as reaction rate coefficients, diffusion coefficients and Henry's law solubility. We show how moisture-induced phase changes can affect the gas uptake and chemical transformation of organic matter by applying the kinetic multi-layer model to a comprehensive experimental data set of ozone uptake by shikimic acid. We find that slow diffusion and ozone destruction can effectively shield reactive organic molecules in the particle bulk from degradation.
Online coupling of kinetic multi-layer models to mechanisms of gas-phase chemistry such as the Master Chemical Mechanism (MCM) allows for depth-resolved tracking of concentrations during formation and growth of secondary organic aerosol (SOA) particles. In this work, formation, condensation and evaporation of SOA upon change in temperature were investigated in an environmental chamber for several different SOA precursors, leading to an estimation of diffusion coefficients in secondary organic matter.