Effect of Reduced Sulfur Dioxide Emissions on Hydrogen Peroxide Concentrations in Wilmington, NC, USA Rainwater

Measurements of hydrogen peroxide (H₂O₂), pH, dissolved organic carbon and nonseasalt sulfate (NSS) in rainwater were conducted on an event basis at a single site in Wilmington, N.C. for the past decade in a study that included over 600 individual rain events. Annual volume weight average (VWA) H₂O₂ concentrations were negatively correlated (p < 0.001) with annual VWA NSS concentrations in low pH (<5) rainwater. Under these conditions H₂O₂ is the primary aqueous-phase oxidant of SO₂ in the atmosphere. Annual volume weighted average 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. We attribute the increase of H₂O₂ to decreasing SO₂ emissions which has had the effect of reducing a major tropospheric sink for H₂O₂. This compositional change has important implications because H₂O₂ is a major oxidant in both the atmosphere and surface waters. Greater wet deposition of H₂O₂ could influence the redox chemistry of receiving watersheds which typically have H₂O₂ concentrations two to three orders of magnitude lower than rainwater.