Kinetics, products, and optical property changes during the heterogeneous oxidation of organic aerosols
Renbaum, Lindsay Hall
MetadataShow full item record
A series of laboratory measurements have been developed to study the kinetics and product formation of organic aerosol oxidation and the consequences of oxidation on the optical properties of organic aerosol. The rate of reactive uptake of radical species and the resulting product distributions from the radical initiated oxidation of model solid and liquid organic aerosols exhibited a clear particle phase dependence. In NOx-free experiments, although small differences in the reactive uptake of radical species on solid versus liquid particles were observed, higher degrees of oxidative turnover of condensed phase species occurred in solid particles compared to liquid particles of the same chemical composition. In NOx-containing experiments, organic nitrate formation was observed in the reactions of solid, but not liquid particles. These experiments have many implications for the optical and water-uptake properties organic aerosol will exhibit in the atmosphere. In order to study the changes in light scattering and absorption cross sections of organic aerosols as a function of oxidative age, a UV cavity ring-down spectrometer was constructed. Clear increases in light extinction due to UV absorption were observed for oxidatively aged aerosol in comparison to “fresh” organic aerosol. Lastly, a new technique for studying gas phase and heterogeneous oxidation kinetics has been developed and this “virtual injector” has been used to explore the effect of radical and radical precursor concentrations on the reactive uptake of these radicals and evidence of Langmuir-type adsorption of precursor species was observed. These experiments have important consequences for studying heterogeneous reaction kinetics in a laboratory setting where high concentrations of radicals, and thus high concentrations of radical precursors, must be used to access atmospherically relevant radical exposures on a short timescale.