This award from the Environmental Chemical Sciences Program in the Division of Chemistry and the Atmospheric Chemistry Program in the Division of Atmospheric and Geospace Sciences supports Professor Eleanor Browne and her graduate and undergraduate students. They study the atmospheric degradation processes of the organosilicon compounds known as siloxanes. Siloxanes are high-production compounds manufactured for a variety of uses, including as components of adhesives, coatings, and personal care products. The siloxanes can be detected in environmental samples worldwide including in remote Arctic regions. Due to the environmental persistence of these compounds and concerns over their toxicity to aquatic organisms, the environmental chemistry of siloxanes is an emerging area of interest. In the environment, siloxanes preferentially partition to the atmosphere where they undergo chemical reactions to form new products. These products may have a different fate than the original compound. This project improves the understanding of the timescale and products of the atmospheric degradation of siloxanes and provides the data necessary to evaluate their environmental fate. Through this project, graduate, undergraduate, and high-school students receive training in atmospheric chemistry techniques and analytical instrumentation. Students also develop scientific communication skills by creating videos describing the work. Results are incorporated into undergraduate educational materials.  This project uses laboratory experiments to investigate the multigenerational atmospheric chemistry of siloxanes. The reaction rates of common linear and cyclic siloxanes with the hydroxyl radical and chlorine atom are measured to understand the lifetime of the compounds. The work investigates the mechanism and products of the gas-phase oxidation of siloxanes under conditions approximating urban, rural, and remote atmospheres. Experiments probing the uptake of oxidation products into particles explore the interactions between gas-phase siloxanes and submicron particles. Both reactants and products are measured in real time with chemical ionization mass spectrometry.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.