Elucidating Nitrogen and Chlorine Recycling Mechanisms from Multiphase Photochemistry of Oxidized Nitrogen

With support from the Environmental Chemical Sciences Program in the Division of Chemistry, Jonathan Raff at Indiana University will study how the pollutant nitrate and other oxidized forms of nitrogen found on environmental surfaces (e.g., atmospheric particles, soil minerals, and sea salt) influence air pollution, which is a leading cause of premature death globally. There is significant evidence that interactions of nitrate with sunlight can change the composition of the atmosphere in ways that can lead to poor air quality or influence cloud formation. The chemical mechanisms involved are still not well understood. Laboratory experiments will be carried out on well-characterized models of soil, sea salt and aerosols using sensitive instrumentation that follows chemical reactions in real time and under real environmental conditions. This research will help clarify how pollutants in the atmosphere are formed and destroyed, with potential long terms scientific relevance to the causes of air pollution, particularly, to the nature of oxidized nitrogen species that might obtain in the atmosphere from nitrate chemistry. Graduate and undergraduate students will be involved in this research. The latter will include entering first-year students from underrepresented groups who will carry out summer research projects designed to increase their interest in pursuing science, technology, engineering and mathematics (STEM) majors. In addition, the outcomes of this project will be used in outreach activities to enhance science education at a local high school. Under this award, the research team led by Jonathan Ruff at Indiana University will study the photochemical reactivity of nitric acid, nitrate, and organic nitrates on environmental surfaces with a focus on elucidating chemical mechanisms leading to the release and recycling of nitrogen oxides and chlorine atom precursors that contribute to the oxidizing capacity of the atmosphere. Experimental approaches will involve UV-visible and infrared diffuse reflection spectroscopy, and photochemical flow reactors with gas phase product detection by chemical ionization mass spectrometry and chemiluminescence analysis. In addition to revealing mechanisms of nitrogen oxide and chlorine recycling, the project will provide the kinetics and photochemical data needed to advance the ability to model and predict multiphase photochemistry of oxidized nitrogen. The long term broader scientific impacts of this research include providing a more complete reaction tree emanating from atmospheric nitrates with a particular focus on the constellation of oxidized nitrogen species that is produced photochemically upon interaction with UV/vis light from the sun. 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.