Shining light on the sources, sinks and concentrations of singlet oxygen in the atmosphere

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The Earth's atmosphere is exclusively oxidizing, and consequently oxidation reactions govern the fate of most organic molecules in the gas and particle phases. The concentration, speciation and reactivity of atmospheric oxidants are necessary to predict the fate of atmospheric pollutants. My long-term research program centers on studying atmospheric oxidants as well as their oxidation mechanisms, with a short-term focus on an understudied and arguably underappreciated oxidant in the context of atmospheric chemistry: singlet oxygen (1O2) the first excited state of ground state triplet molecular oxygen. 1O2 is a well-known excited state molecule: in biology for photodynamic therapy for cancer treatment, in organic chemistry for enhanced reactivity in oxidation and cylcoaddition reactions, and in surface waters as a key oxidant in determining the fate of pollutants. The key ingredients necessary for the production of 1O2 in surface waters include a sensitizer, oxygen and light - all are indeed present in the atmosphere, yet only a handful of reports have described atmospheric 1O2. My proposed research program builds on recent work from my group demonstrating the efficacy of aqueous organic aerosols to act as sensitizers for 1O2 production under sunlit conditions. My team will elucidate the sources (Task 1) and sinks (Task 2) of 1O2 in organic aerosols in indoor and outdoor air, and will undertake groundbreaking studies on 1O2's gas phase chemistry (Task 3). Task 1 addresses two outdoor air projects (MSc1, MSc2) and an indoor air program (PhD1), kick-starting a burgeoning field of indoor air photochemistry. Task 2 will elucidate the sinks of 1O2 in atmospherically-relevant aqueous organic aerosol conditions (PhD2). Furthermore, Task 3 will demonstrate that 1O2 can partition to the gas phase and have unprecedented impact on gas-phase chemical reactions (Postdoc). These three tasks contribute to three impact goals: (A) predict 1O2 steady-state concentrations and quantum yields within organic aerosols; (B) compare the importance of 1O2 reactivity with other oxidants; and (C) demonstrate the presence and impact of 1O2 in the gas phase for the first time. Overall, this research program will train 1 postdoc, 2 PhDs, 2 MSc, and 10 undergraduates and is designed for high training value. Indeed, it is challenging, innovative, and impactful, yet feasible and designed with risk mitigation and EDI strategies. HQP will lead projects, use state-of-the-art photochemistry techniques and participate in multidisciplinary collaborations as part of a unique HQP training program under my leadership. The original scientific research output generated will provide quantitative data including concentrations, rate constants, product distributions and chemical mechanisms to improve fate modelling of key air quality components. This output will support the development of regulatory guidelines by government agencies, Environment and Climate Change Canada and Health Canada.