Spontaneous Production of HO at the Liquid-Ice Interface: A Potential Source of Atmospheric Oxidants.

We present experimental evidence for the spontaneous production of hydrogen peroxide (HO) at the liquid-ice interface during the freezing of dilute salt solutions. Specifically, sample solutions containing NaCl, NaBr, NHCl, and NaI at concentrations between 10 and 10 M were subjected to freezing-melting cycles and then analyzed for HO content. The relationship between the production rate of HO and the salt concentration follows that of the Workman-Reynolds freezing potential (WRFP) values as a function of the salt concentration. Our results suggest that HO is formed at the liquid-ice interface from the self-recombination of hydroxyl radicals (OH·), produced from the oxidation of hydroxide anions due to the high electric field generated at the aqueous-ice interface under the WRFP effect. Furthermore, the involvement of O likely acting as an electron capturer could promote to produce more OH radicals and hydroperoxyl radicals (HO·), thus enhancing the production of HO at the liquid-ice interface. Overall, this study suggests a novel mechanism of HO formation in ice via its spontaneous production at the liquid-ice interface, induced by the Workman-Reynolds effect.