Chemical Dynamics of Organic Peroxy Radicals at Aerosol Particle Interface

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This award from the Environmental Chemical Sciences Program in the NSF Division of Chemistry supports Professor Haofei Zhang at the University of California, Riverside to study organic aerosol (OA) particles. Atmospheric OA affect the Earth’s climate in crucial but poorly understood ways. The uncertainty is largely due to the complex chemical processes that constantly change OA compositions during their lifetime of weeks. Professor Zhang and his group study the chemical reactions of organic peroxy radicals (RO2) at the surfaces of the particles. These chemical processes largely determine the chemical composition and physiochemical properties of the particle interface. Better knowledge of the details of these reactions improves our understanding of the evolution and impacts of OA. Other broader impacts of this project include the training and mentoring of undergraduate and graduate students, especially those from the underrepresented groups. In addition, Professor Zhang leads outreach activities with Riverside high schools that serve minority students and participates in a summer academy program aimed at enhancing STEM education for diverse students.The project focuses on the heterogeneous hydroxyl radical oxidation of OA proxies and the subsequent pathways of RO2 at the OA particle interface. This includes the previously under-explored RO2 + hydroperoxyl radical, RO2 + nitric oxide, RO2 dimerization, and RO2 autoxidation reactions. Laboratory oxidation experiments are performed using a hybrid continuous-flow reaction system. This provides information on the relative importance of the various RO2 reaction pathways. The different pathways are impacted by the OA composition, liquid water content, oxidation timescales, and oxidant concentrations. The team uses a suite of advanced mass spectrometry instrumentation to systematically study the oxidation kinetics and the chemical composition of key oxidation products. A multiphase reaction-diffusion kinetic model framework representing the interfacial RO2 processes of interest is being developed. The model is based on experimental results and presents a crucial extension to the current understanding of radical-initiated OA heterogeneous oxidation mechanisms.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.