Abstract:

Reactive oxygen species (ROS) play a central role in aqueous-phase processing and health effects of atmospheric aerosols. Respiratory deposition of secondary organic aerosols (SOA) and transition metals may lead to the generation of ROS to cause oxidative stress, but the underlying mechanism and formation kinetics are not well understood. This dissertation highlights our work using electron paramagnetic resonance (EPR) spectroscopy to characterize ROS formation from aqueous reactions of SOA involving transition metals, lung antioxidants, and reaction media with different pH. and photochemical aging. With the help of kinetic modeling, we provide plausible mechanisms for superoxide and organic radical formation: decomposition of organic peroxides followed by a cascade of aqueous reactions. Meanwhile, we elucidate the interesting role of lung antioxidants in defending against highly reactive ROS while amplifying organic radical formation, whereas acidity significantly affects ROS formation from physiological pH to highly acidic conditions due to several acid-catalyzed reactions. Photochemical aging of SOA can induce substantial formation of organic radicals. These findings and mechanistic understanding have important implications on the atmospheric fate of SOA and particle-phase reactions of highly oxygenated organic molecules as well as oxidative stress upon respiratory deposition.