Multiphase Oxidation of Organic Aerosols under Various Environmental Conditions

With support from the Environmental Chemical Sciences (ECS) and the Chemical Structure and Dynamics (CSD) Programs in the Division of Chemistry, Professor Haofei Zhang at the University of California, Riverside is investigating the roles of gas-phase OH and HO2 radicals in organic aerosols (OA) multiphase oxidation under atmospherically relevant conditions. OA are ubiquitous in the Earth’s atmosphere, significantly impacting air quality and human health. Questions regarding the OH-initiated heterogeneous OA oxidation remain elusive because of the large differences between laboratory and atmospheric conditions and analytical limitations. Professor Zhang and his students will conduct laboratory multiphase oxidation experiments of various OA systems under a range of conditions using a custom-designed flow reactor. They will investigate bimolecular and unimolecular peroxy radical autoxidation processes in the condensed phase in the presence of inorganic species and aerosol liquid water. They will utilize isomer-informed techniques to identify the oxidation products and elucidate the oxidation mechanisms. Their studies could provide critical knowledge for understanding aerosol aging chemistry, with potential implications for improving air quality, ultimately contributing to broader societal goals of environmental protection and public health. This project will also provide training opportunities for graduate and undergraduate students through institutional programs to enhance STEM education. This project will focus on studying the mechanism of organic aerosols (OA) multiphase oxidation under diverse conditions, including the interplay of gas-phase OH and HO2 radicals, the effects of core-shell structured binary OA particles, and the differences in OH oxidation under light and dark conditions. Furthermore, this research will assess the impacts of inorganic aerosol components on OA multiphase oxidation, including the effects of relative humidity, particle phase separation, and aerosol acidity. The multiphase oxidation kinetics and molecular-level chemical composition of key oxidation products will be analyzed using state-of-the-art mass spectrometry techniques, such as the thermal desorption chemical ionization mass spectrometry (TD-CIMS) and ion mobility spectrometry time of flight mass spectrometry (IMS-TOF). Additionally, a multiphase reaction-diffusion kinetic model will be developed to interpret experimental results and represent new oxidation mechanisms. Novel aspects of this project include realistic oxidation conditions with lower OH and higher HO2/OH ratios compared to prior studies, systematic aerosol acidity investigations, mechanistic impacts of binary aerosol systems, isomer-informed compositional measurements, and integrated kinetic modeling. This comprehensive approach may reveal accelerated OA multiphase oxidation with enhanced atmospheric impacts, potentially reconciling observational-laboratory discrepancies in OA chemical evolution studies. 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.