RUI: Hydrogen Peroxide Variability in Coastal Rainwater

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9320971 Willey This research will investigate the chemical composition of rainwater in coastal North Carolina. This location is ideal for rainwater research because it receives precipitation of both continental and maritime origins. Previous work has shown that these two general source types are compositionally very different with respect to inorganic ions as well as formic and acetic acids. The specific objective of this study is to define patterns of variation in the rainwater concentrations of the strong oxidant hydrogen peroxide (H2O2). At this time the factors controlling the concentration of H2O2 in maritime and continental storms are poorly defined and unpredictable. The question addressed in this research project is whether H2O2 concentrations are greater in rain of marine or continental origin. It could be argued that H2O2 levels would be lower in continental rain because it can oxidize sulfur dioxide to sulfuric acid and nitrogen oxides to nitric acid, thereby resulting in a net loss of H2O2. Hydrogen peroxide is, however, photochemically produced along with other pollutant atmospheric oxidants, which would increase its concentration in rain of continental origin. The relative concentrations of H2O2 in continental versus maritime rain must be defined to allow global modeling of many important atmospheric oxidants. Hydrogen peroxide is involved in cycles of other stronger atmospheric oxidants including the formation of hydroperoxyl radical and the destruction of hydroxyl radical. Model calculations suggest that concentrations of strong atmospheric oxidants may increase dramatically during the next decade because of stratospheric ozone losses at temperate latitudes. Hence, this is a particularly timely project. Rainwater and atmospheric condensate are appropriate media for the study of H2O2 due to its large water solubility. For example, hydrogen peroxide is often present in rainwater at micromolar concentrations. It is st able in rain for time periods of hours, which makes this laboratory well suited for the project because of the proximity of the collection sites and the analytical laboratory. There is approximately a decade of rainwater composition data for one of the North Carolina sites. This relatively long term data record will be useful in interpretation of new measurement data and will also facilitate comparisons with other sampling locations. ***