Formation of hydrogen peroxide from illuminated polar snows and frozen solutions of model compounds

Abstract Hydrogen peroxide (HOOH) is an important trace constituent in snow and ice, including in Arctic and Antarctic ice cores. To better understand the budget of snowpack HOOH, here we examine its production in illuminated snow and ice. To evaluate what types of compounds might be important photochemical sources of HOOH, we first illuminated laboratory ice samples containing 10 different model organic compounds: guaiacol, phenol, syringol, benzoate, formate, octanal, octanoic acid, octanedioic acid, phenylalanine, and mixtures of oxalate with iron (III). Half of these compounds produced little or no HOOH during illumination, but two classes of compounds were very reactive: phenolic compounds (with rates of HOOH of 6–62 nM-HOOH h −1  μM −1 -phenolic) and mixtures of Fe(III) with a stoichiometric excess of oxalate (with rates of HOOH production as high as 2,000,000 nM h −1 per μM iron). To quantify rates of HOOH production in the environment we also illuminated snow samples collected from the Arctic and Antarctic. The average (±1 σ ) HOOH production rate in these samples was low, 5.3 ± 5.0 nM h −1 and replicate measurements showed high variability. In some natural samples there was an initial burst of HOOH production (with a rate approximately 10 times higher than the average production rate), followed by reduced rates at subsequent time points. Although our laboratory ice samples reveal that illuminated organics and metal-organic complexes can form HOOH, the low rates of HOOH formation in the Arctic and Antarctic snow samples suggest this process has only a modest impact on the HOOH budget in the snowpack.