Kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP): linking condensation, evaporation and chemical reactions of organics, oxidants and water M. Shiraiwa1, C. Pfrang2, T. Koop3, and U. Pöschl1 1Max Planck Institute for Chemistry, Biogeochemistry Department, P.O. Box 3060, 55128 Mainz, Germany 2University of Reading, Department of Chemistry, P.O. Box 224, Whiteknights, Reading RG6 6AD, UK 3Bielefeld University, Faculty of Chemistry, Universitätsstraße 25, 33615, Bielefeld, Germany
Abstract. We present a novel kinetic multi-layer model for gas-particle interactions
in aerosols and clouds (KM-GAP) that treats explicitly all steps of mass
transport and chemical reaction of semi-volatile species partitioning
between gas phase, particle surface and particle bulk. KM-GAP is based on
the PRA model framework (Pöschl-Rudich-Ammann, 2007), and it includes
gas phase diffusion, reversible adsorption, surface reactions, bulk
diffusion and reaction, as well as condensation, evaporation and heat
transfer. The size change of atmospheric particles and the temporal
evolution and spatial profile of the concentration of individual chemical
species can be modeled along with gas uptake and accommodation coefficients.
Depending on the complexity of the investigated system and the computational
constraints, unlimited numbers of semi-volatile species, chemical reactions,
and physical processes can be treated, and the model shall help to bridge
gaps in the understanding and quantification of multiphase chemistry and
microphysics in atmospheric aerosols and clouds.
In this study we demonstrate how KM-GAP can be used to analyze, interpret
and design experimental investigations of changes in particle size and
chemical composition in response to condensation, evaporation, and chemical
reaction. For the condensational growth of water droplets, our kinetic model
results provide a direct link between laboratory observations and molecular
dynamic simulations, confirming that the accommodation coefficient of water
at ~270 K is close to unity (Winkler et al., 2006). Literature data on
the evaporation of dioctyl phthalate as a function of particle size and time
can be reproduced, and the model results suggest that changes in the
experimental conditions like aerosol particle concentration and chamber
geometry may influence the evaporation kinetics and can be optimized for
efficient probing of specific physical effects and parameters. With regard
to oxidative aging of organic aerosol particles, we illustrate how the
formation and evaporation of volatile reaction products like nonanal can
cause a decrease in the size of oleic acid particles exposed to ozone.
Citation: Shiraiwa, M., Pfrang, C., Koop, T., and Pöschl, U.: Kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP): linking condensation, evaporation and chemical reactions of organics, oxidants and water, Atmos. Chem. Phys., 12, 2777-2794, doi:10.5194/acp-12-2777-2012, 2012.