Exploring Uncharted Atmospheric Chemical Space with Direct Peroxy Radical Generation

With support from the Environmental Chemical Sciences (ECS) program in the Division of Chemistry, Professor Victoria Barber of the University of California, Los Angeles is investigating the gas-phase reaction pathways of peroxy radicals (RO2), the central intermediates formed in the oxidation of organic compounds in the Earth’s atmosphere. While some reaction pathways of RO2 are well understood, others—particularly isomerization and self- or cross-reactions—remain poorly characterized, despite their implications for secondary organic aerosol formation.

Professor Barber and her students will use sophisticated, real time analytical techniques to examine how isomerizations and self- and cross- reactions of peroxy radicals work together to shape gas-phase product distributions and produce secondary organic aerosol. Their studies could result in improved understanding of the role of peroxy radical chemistry in determining atmospheric composition, tropospheric ozone production, and the formation of secondary organic aerosol, which would enable future improvements in 3D modeling of atmospheric composition and air quality.

The proposed work will help cultivate the next generation of researchers in atmospheric chemistry at both the graduate and undergraduate level, and results from the work will be integrated into Professor Barber’s undergraduate environmental chemistry course.

Gas-phase non-methane organic compounds are present in air in small concentrations, but exert outsized influence on atmospheric composition via oxidation chemistry. RO2 are central intermediates in oxidation, with four major reaction pathways: reaction with NO, reaction with HO2, isomerization, and self- or cross-reactions. While the first two pathways are well-characterized, isomerizations and self- or cross-reactions remain poorly understood, despite their implications for secondary organic aerosol (SOA) formation.

This project will investigate the interactions between these pathways and their effects on product distributions and SOA formation using controlled environmental chamber experiments. Traditional oxidant-based chamber experiments struggle to isolate these pathways due to concurrent generation of NO and/or HO2. The proposed work circumvents this using alkyl iodide photolysis as a radical source, enabling precise control over RO2 concentrations and reactivity.

Coupled to online chemical ionization mass spectrometry and scanning mobility particle sizing, this approach allows for systematic investigations of these reaction pathways, their interactions, and their role in aerosol formation. Specific project goals include examining how RO2 concentrations influence product distributions and SOA yields, assessing the impacts of low levels of NOx on oxidation outcomes, and systematically exploring the role of RO2 structure in modulating isomerization and self- or cross-reaction pathways.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.