Kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB): the influence of interfacial transport and bulk diffusion on the oxidation of oleic acid by ozone

摘要

We present a novel kinetic multi-layer model that explicitly resolves masstransport and chemical reaction at the surface and in the bulk of aerosolparticles (KM-SUB). The model is based on the PRA framework ofgas-particle interactions (P?schl-Rudich-Ammann, 2007), and itincludes reversible adsorption, surface reactions and surface-bulk exchangeas well as bulk diffusion and reaction. Unlike earlier models, KM-SUB doesnot require simplifying assumptions about steady-state conditions and radialmixing. The temporal evolution and concentration profiles of volatile andnon-volatile species at the gas-particle interface and in the particle bulkcan be modeled along with surface concentrations and gas uptakecoefficients.In this study we explore and exemplify the effects of bulk diffusion on therate of reactive gas uptake for a simple reference system, the ozonolysis ofoleic acid particles, in comparison to experimental data and earlier modelstudies. We demonstrate how KM-SUB can be used to interpret and analyzeexperimental data from laboratory studies, and how the results can beextrapolated to atmospheric conditions. In particular, we show howinterfacial and bulk transport, i.e., surface accommodation, bulkaccommodation and bulk diffusion, influence the kinetics of the chemicalreaction. Sensitivity studies suggest that in fine air particulate matteroleic acid and compounds with similar reactivity against ozone(carbon-carbon double bonds) can reach chemical lifetimes of many hours onlyif they are embedded in a (semi-)solid matrix with very low diffusioncoefficients (≤10−10 cm2 s−1).Depending on the complexity of the investigated system, unlimited numbers ofvolatile and non-volatile species and chemical reactions can be flexiblyadded and treated with KM-SUB. We propose and intend to pursue theapplication of KM-SUB as a basis for the development of a detailed mastermechanism of aerosol chemistry as well as for the derivation of simplifiedbut realistic parameterizations for large-scale atmospheric and climatemodels.