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

Abstract

Abstract. We present a novel kinetic multi-layer model that explicitly resolves mass transport and chemical reaction at the surface and in the bulk of aerosol particles (KM-SUB). The model is based on the PRA framework of gas-particle interactions (Pöschl-Rudich-Ammann, 2007), and it includes reversible adsorption, surface reactions and surface-bulk exchange as well as bulk diffusion and reaction. Unlike earlier models, KM-SUB does not require simplifying assumptions about steady-state conditions and radial mixing. The temporal evolution and concentration profiles of volatile and nonvolatile species at the gas-particle interface and in the particle bulk can be modeled along with surface concentrations and gas uptake coefficients.In this study we explore and exemplify the effects of bulk diffusion on the rate of reactive gas uptake for a simple reference system, the ozonolysis of oleic acid particles, in comparison to experimental data and earlier model studies. We demonstrate how KM-SUB can be used to interpret and analyze experimental data from laboratory studies, and how the results can be extrapolated to atmospheric conditions. In particular, we show how interfacial and bulk transport, i.e., surface accommodation, bulk accommodation and bulk diffusion, influence the kinetics of the chemical reaction. Sensitivity studies suggest that in fine air particulate matter oleic acid and compounds with similar reactivity against ozone (carbon-carbon double bonds) can reach chemical lifetimes of many hours only if they are embedded in a (semi-)solid matrix with very low diffusion coefficients (≤10 −10 cm 2 s −1 ).Correspondence to: U. Pöschl (u.poschl@mpic.de) Depending on the complexity of the investigated system, unlimited numbers of volatile and non-volatile species and chemical reactions can be flexibly added and treated with KM-SUB. We propose and intend to pursue the application of KM-SUB as a basis for the development of a detailed master mechanism of aerosol chemistry as well as for the derivation of simplified but realistic parameterizations for largescale atmospheric and climate models.

Protein Cross-Linking and Oligomerization through Dityrosine Formation upon Exposure to Ozone

“…Here, we model the formation of oligomers using the kinetic multilayer model for aerosol surface and bulk chemistry (KM-SUB). 53 KM-SUB explicitly resolves surface-bulk exchange, bulk diffusion and chemical reactions from the gas-particle interface to the particle core, resolving concentration gradients and diffusion throughout the particle bulk. The model fitting to the experimental data for different RH and in aqueous solution was performed using the MCGA method.…”

Heterogeneous chemistry and reaction dynamics of the atmospheric oxidants, O3, NO3, and OH, on organic surfaces

“…To more completely describe the reactive uptake coefficient of NO 3 at substrates investigated by Knopf et al, 103 Shiraiwa et al used computational kinetic flux models to quantify the relative role of surface and bulk reactions for highly functionalized organic molecules relevant to biomass burning. 107,108 More specifically, by relating uptake coefficients to bulk accommodation coefficients (i.e., the probability of a gas molecule colliding with the surface to enter the bulk of the particle), the contribution of surface reaction to the overall reaction was revealed to be dependent on the mechanism of reaction. For example, surface contributions were minor for levoglucosan, which reacts with NO 3 via an initial hydrogen-abstraction step-a relatively slow process.…”

Measurements of uptake coefficients for heterogeneous loss of HO2 onto submicron inorganic salt aerosols

“…The KM-SUB (Kinetic multi-layer model of aerosol surface and bulk chemistry) model 47 is currently being adapted to enable the uptake of reactive radicals onto an aerosol surface to be studied. We plan to use the model to further explore the observed time dependences in our data.…”