Using a Bottom-Up Approach to Understand Dissolved Organic Matter Photoreactivity

This award from the Environmental Chemical Sciences Program in the Division of Chemistry supports Professors Leanne Powers, Nicholas Pflug, Theodore Dibble and their team at the State University of New York - College of Environmental Science and Forestry. The project addresses knowledge gaps in the role of sunlight-driven reactions of natural dissolved organic matter (DOM). DOM is the dominant absorber of solar ultraviolet radiation in most aquatic systems, and this absorption of light generates a suite of reactive intermediates (RI). RI, such as radicals and reactive oxygen species, are highly important because they can react with and degrade contaminants, toxins, and other compounds of concern. However, the nature of the RI formed is highly variable, making it difficult to predict the fate and transport of pollutants in aquatic environments. Because uncertainties are largely due to our lack of understanding of DOM composition and how DOM composition affects production of RI, the goal of this project is to gain a mechanistic understanding of DOM photochemical reactions and thus, better predict these reactions in aquatic environments. This project will use model compounds representative of DOM classes to investigate the dependence of RI production on the nature and concentration of DOM and the nature of the aqueous environment (pH, salt content, ion composition). As aquatic systems act as bridges between terrestrial and marine systems, understanding the transport and fate of pollutants across the land-ocean continuum will shed light on processes relevant to coastal waters. In addition to training of graduate and undergraduate students, the research team will engage in several activities that will promote awareness of research outcomes including, for example, the incorporation of outcomes into the classroom and a water research workshop for high school students in the City of Syracuse. This study will determine apparent quantum yields (AQYs) for triplet excited-state DOM, singlet oxygen, superoxide, hydrogen peroxide, and hydroxyl radical for DOM obtained from the field plus model compounds from the following classes of terrestrial DOM: lignin, tannins, material derived from linear terpenoids, polycyclic aromatic hydrocarbons, coumarins, chalconoids, flavonoids, and chlorophylls. In addition to determining AQYs of RI along gradients of DOM and compound concentration, they will systematically adjust solution pH and matrix composition by adding major ions found in seawater. Once AQY data are obtained, they will determine which model compounds and inorganic constituents best explain DOM photoreactivity, which in turn will allow them to better predict rates of RI photoproduction and pollutant degradation in natural waters. 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.