Heterogeneous Production of Perchlorate and Chlorate by Ozone Oxidation of Chloride: Implications on the Source of (Per)Chlorate in the Solar System

The occurrence of chlorate (ClO3–) and perchlorate (ClO4–) in the terrestrial and extraterrestrial environments has been partly attributed to ozone (O3)-mediated oxidation of chlorine-bearing compounds. This is based on varying elevated Δ17O values in all measured terrestrial natural ClO4– as well as the nearly universal co-equal occurrence of ClO3– and ClO4–, which has only been reported to occur for dry oxidation of Cl–, a process for which little information is available. In this study, we examine possible factors influencing ClO4– and ClO3– formation by O3 oxidation of sodium chloride (NaCl) salt and hydrochloric acid (HCl) gas in glass reactor vessels. We show that longer reaction times increase production of ClO4– and ClO3–, with ClO3– production generally being lower than ClO4– by 1–2 orders of magnitude. For 1 day oxidation periods, ClO4–/ClO3– ratios were relatively constant (∼50) for low Cl– masses and decreased over 3 orders of magnitude for higher (∼100×) Cl– masses. Perchlorate mass increased...