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Abstract:
The chemical processing of organic aerosol particles is important for atmospheric chemistry, climate, and public health. The heterogeneous oxidation of oleic acid particles by ozone is one of the most frequently investigated model systems. The available kinetic data span a wide range of particle size and ozone concentration and are obtained with different experimental techniques including electrodynamic balance (EDB), optical tweezers, environmental chamber, and aerosol flow tube reactors using mass spectrometry and Raman spectroscopy as detection methods. Existing kinetic and mechanistic analyses, however, reveal systematic differences and inconsistencies that are a matter of ongoing debate. We developed and applied an inverse modeling approach using a kinetic multilayer model (KM-SUB) and Monte Carlo-based global optimization algorithms to 11 literature data sets and an additional new set of EDB data. We were able to reconcile most experimental data with consistent sets of multiphase chemical kinetic parameters. For a unique determination of these parameters, however, further experiments with simultaneous measurement of multiple observables at specific, insightful reaction conditions are required. We tested three different reaction mechanisms and conclude that secondary chemistry involving Criegee intermediates appears crucial to resolve the discrepancies found in earlier studies. Primary ozone chemistry occurs close to the particle surface and secondary reactions seem to dominate in the particle bulk, involving OH formation and radical chain reactions.
