This project seeks to better understand what chemical species result from the oxidation of non-methane volatile organic compounds. Model-informed chamber studies will be conducted during which the reactivity of organic peroxy radicals will be carefully controlled and monitored. A better understanding of volatile organic compound oxidation in the atmosphere will lead to better predictions of the formation of secondary atmospheric species such as ozone, formaldehyde, and secondary organic aerosol, species that contribute to degraded air quality. The major scientific objectives of the project are: (1) To better understand the formation mechanism and yields of these key secondary species, across the range of organic peroxy radicals (RO2) conditions found in the atmosphere; and (2) To understand the extent to which these secondary species are accurately predicted using state-of-the-art chemical mechanisms or approximated from measurements of extreme RO2 conditions, in which RO2 reacts only with NO or only with HO2, simplifying the product distributions considerably. Chamber experiments will cover a number of model volatile organic compounds (isoprene, monoterpenes, aromatics, and others), across the full range of RO2 conditions found in the global atmosphere, a much wider range than previously studied. The project will support the training of both graduate and undergraduate students. This award reflects NSF's statutory mission and has been deemed worthy of support through