Reconciling multiphase reactivity of oleic acid with ozone using a kinetic flux model

The ozonolysis of oleic acid on aerosol particles has been extensively studied in the past and is often used as a benchmark reaction for the study of organic particle oxidation. However, to date, no single kinetic model has reconciled the vastly differing reactive uptake coefficients reported in the literature that were obtained at different oxidant concentrations, particle sizes and with various commonly used laboratory setups (single-particle trap, aerosol flow tube, and environmental chamber). We combine the kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB, Shiraiwa et al. 2012) with the Monte Carlo Genetic Algorithm (MCGA, Berkemeier et al. 2017) to simultaneously describe nine experimental data sets with a single set of kinetic parameters. The KM-SUB model treats chemistry and mass transport of reactants and products in the gas and particle phases explicitly, based on molecular-level chemical and physical properties. The MCGA algorithm is a global optimization routine that aids in unbiased determination of these model parameters and can be used to assess parameter uncertainty. This methodology enables us to derive information from laboratory experiments using a “big data approach” by accounting for a large amount of data at the same time.

We show that a simple reaction mechanism including the surface and bulk ozonolysis of oleic acid only allows for the reconciliation of some of the data sets. An accurate description of the entire reaction system can only be accomplished if secondary chemistry is considered and present an extended reaction mechanism including reactive oxygen intermediates. The presence of reactive oxygen species on surfaces of particulate matter might play an important role in understanding aerosol surface phenomena, organic aerosol evolution, and their health effects.

 

References

Berkemeier, T. et al.: Technical note: Monte Carlo genetic algorithm (MCGA) for model analysis of multiphase chemical kinetics to determine transport and reaction rate coefficients using multiple experimental data sets, Atmos. Chem. Phys., 17, 8021-8029, 2017.

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.