Long-Term Temporal Variability in Hydrogen Peroxide Concentrations in Wilmington, North Carolina USA Rainwater

Measurements of hydrogen peroxide (H2O2), pH, dissolved organic carbon (DOC), and inorganic anions (chloride, nitrate, and sulfate) in rainwater were conducted on an event basis at a single site in Wilmington, NC for the past decade in a study that included over 600 individual rain events. Annual volume weighted average (VWA) H2O2 concentrations were negatively correlated (p < 0.001) with annual VWA nonseasalt sulfate (NSS) concentrations in low pH (<5) rainwater. Under these conditions H2O2 is the primary aqueous-phase oxidant of SO2 in the atmosphere. We attribute the increase of H2O2 to decreasing SO2 emissions which has had the effect of reducing a major tropospheric sink for H2O2. Annual VWA H2O2 concentrations in low pH (<5) rains showed a significant increase over the time scale of this study, which represents the only long-term continuous data set of H2O2 concentrations in wet deposition at a single location. This compositional change has important implications because H2O2 is a source of highly reactive free radicals so its increase reflects a higher overall oxidation capacity of atmospheric waters. Also, because rainwater is an important mechanism by which H2O2 is transported from the atmosphere to surface waters, greater wet deposition of H2O2 could influence the redox chemistry of receiving watersheds which typically have concentrations 2-3 orders of magnitude lower than rainwater.