The kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB) resolves mass transport and chemical reaction in aerosol particles explicitly in depth. The particle is divided into a sorption layer, a quasi-static surface layer and a user-defined number of bulk layers, between which species are exchanged by molecular diffusion.
The model treats a gas-phase species X (e.g., ozone) taken up by a particle consisting of a condensed-phase species Y (e.g., oleic acid). Processes include adsorption and desorption, surface-bulk exchange, bulk diffusion, and chemical reaction both at the surface (rate coefficient kSLR) and in the bulk (rate coefficient kBR). Gas-phase diffusion is not resolved: the gas phase concentration of X is held constant, so the uptake coefficient is referred to the concentration directly at the particle surface.
The simulation returns the total number of Y molecules in the particle, NY(t), and the uptake coefficient of X, γ(t). Both are shown as time series and can be downloaded as CSV. By default the model is run in spherical geometry, appropriate for particles and aerosol flow tube experiments.
Note to Users: if you use results from the KM-SUB model, please cite the publication listed below and this website giving the URL https://www.multiphasekinetics.org/kmsub.
The model available on this site is a Python implementation of the original MATLAB code of KM-SUB as published in Shiraiwa et al. (2010), offered here with a selected set of model input parameters. The measurements that can be plotted alongside the model are the oleic acid decay data of Ziemann (2005), as they appear in the KM-SUB paper. The calculation of the kinetic regime follows the decision tree presented in Berkemeier et al. (2013). Here is a table of possible kinetic regimes in this example:
| S | Surface reaction – no clear limiting process |
| B | Bulk reaction – no clear limiting process |
| Srx | Surface reaction limited by chemical reaction rate |
| Sbd | Surface reaction limited by bulk diffusion |
| Sα | Surface reaction limited by surface accommodation |
| Brx | Bulk reaction limited by chemical reaction rate |
| Bbd | Bulk reaction limited by bulk diffusion |
| Brd | Bulk reaction limited by reaction and diffusion of X in well-mixed Y |
| Bα | Bulk reaction limited by bulk accommodation |
| SBα | Surface and bulk reaction limited by accommodation |
Please contact us in case of questions or ideas for collaboration.
Shiraiwa, M., Pfrang, C., and Pöschl, U.: 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, Atmos. Chem. Phys. 10, 3673–3691, (2010).