Controls on the Redox Potential of Rainwater

Abstract

Hydrogen peroxide acting as a reductant affects the redox potential of rainwater collected at the Bermuda Atlantic Time Series Station, the South Island of New Zealand, the contiguous USA, and the primary study site in Wilmington, NC. Analytical measurements of both halves of redox couples for dissolved iron, mercury, and the nitrate-nitrite-ammonium system can predict the rainwater redox potential measured directly by a platinum electrode. Measurements of these redox couples along with the pH in rain yields pe⁻ between 8 and 11; the half reaction for hydrogen peroxide acting as a reductant using typical rainwater conditions of 15 μM H₂O₂ at pH 4.7 gives pe⁻ = 9.12, where pe⁻ = negative log of the activity of hydrated electrons. Of the six rainwater redox systems investigated, only manganese speciation appeared to be controlled by molecular oxygen (pe⁻ = 15.90). Copper redox speciation was consistent with superoxide acting as a reductant (pe⁻ = 2.7). The concentration of H₂O₂ in precipitation has more than doubled over the preceding decade due to a decrease in SO₂ emissions, which suggests the redox chemistry of rainwater is dynamic and changing, potentially altering the speciation of many organic compounds and trace metals in atmospheric waters.

Copper Redox Transformation and Complexation by Reduced and Oxidized Soil Humic Acid. 2. Potentiometric Titrations and Dialysis Cell Experiments

“…28,29 Binding of Cu(I) by natural organic ligands has been extensively studied in marine systems 23,26,30−34 as well as in fogand rainwater. 25,35 In these systems, very low levels of Cu(I) were shown to be complexed mainly by ligands containing reduced sulfur, as can be expected due to the softer character of Cu(I) in comparison to Cu(II). 36−38 For conditions in soils, where available ligands and Cu-to-C ratios differ from marine systems, studies addressing both binding and coordination of Cu(I) to humic substances are lacking.…”

Characterization of CHOS compounds in rainwater from continental and coastal storms by ultrahigh resolution mass spectrometry

“…Elucidating the composition of rainwater dissolved organic matter (DOM) has remained at the forefront of atmospheric research principally because of its central role in a host of fundamentally important atmospheric processes (Mullaugh et al, 2011;Willey et al, 2012). Rainwater DOM is a complex heterogeneous mixture of organic compounds, the composition of which remains to a large extent unknown (Altieri et al, 2012;Mitra et al, 2013).…”

Studi Keadaan Oksidasi Besi pada Air Hujan

“…Selain mengandung besi, air hujan juga memiliki kandungan hidrogen peroksida (H2O2). Konsentrasi hidrogen peroksida dalam air hujan yaitu 15 µM [8] dan berada antara 20 sampai 30 µM [9]. Hidrogen peroksida dapat bertindak sebagai oksidator maupun reduktor dalam atmosfer [9].…”

“…Air hujan selain mengandung besi total, besi(II) dan besi(III) mengandung juga hidrogen peroksida (H2O2). Hidrogen peroksida bertindak sebagai oksidator [9] maupun reduktor yang mempengaruhi potensi redoks dalam air hujan [8].…”