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

摘要

We present a novel kinetic multi-layer modeludfor gas-particle interactions in aerosols and clouds (KMGAP)udthat treats explicitly all steps of mass transport andudchemical reaction of semi-volatile species partitioning betweenudgas phase, particle surface and particle bulk. KMGAPudis based on the PRA model framework (P¨oschl-Rudich-udAmmann, 2007), and it includes gas phase diffusion, reversibleudadsorption, surface reactions, bulk diffusion and reaction,udas well as condensation, evaporation and heat transfer.udThe size change of atmospheric particles and the temporaludevolution and spatial profile of the concentration of individualudchemical species can be modeled along with gas uptakeudand accommodation coefficients. Depending on the complexityudof the investigated system and the computational constraints,udunlimited numbers of semi-volatile species, chemicaludreactions, and physical processes can be treated, and theudmodel shall help to bridge gaps in the understanding andudquantification of multiphase chemistry and microphysics inudatmospheric aerosols and clouds.udIn this study we demonstrate how KM-GAP can be usedudto analyze, interpret and design experimental investigationsudof changes in particle size and chemical composition in responseudto condensation, evaporation, and chemical reaction.udFor the condensational growth of water droplets, our kineticudmodel results provide a direct link between laboratory observationsudand molecular dynamic simulations, confirmingudthat the accommodation coefficient of water at 270K isudclose to unity (Winkler et al., 2006). Literature data on theudevaporation of dioctyl phthalate as a function of particle sizeudand time can be reproduced, and the model results suggestudthat changes in the experimental conditions like aerosol particleudconcentration and chamber geometry may influence theudevaporation kinetics and can be optimized for efficient probingudof specific physical effects and parameters. With regardudto oxidative aging of organic aerosol particles, we illustrateudhow the formation and evaporation of volatile reaction productsudlike nonanal can cause a decrease in the size of oleic acidudparticles exposed to ozone.