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4244502 
Journal Article 
Heterogeneous Production of Perchlorate and Chlorate by Ozone Oxidation of Chloride: Implications on the Source of (Per)Chlorate in the Solar System 
Jackson, WA; Wang, S; Rao, B; Anderson, T; Estrada, N 
2018 
1 
ACS Earth & Space Chemistry
EISSN: 2472-3452 
Amer Chemical Soc 
WASHINGTON 
2 
2 
87-94 
English 
WOS:000425569600002 
The occurrence of chlorate (ClO3-) and perchlorate (ClO4-) in the terrestrial and extraterrestrial environments has been partly attributed to ozone (O-3)-mediated oxidation of chlorine-bearing compounds. This is based on varying elevated Delta O-17 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 O-3 oxidation of sodium chloride (NaCI) salt and hydrochloric acid (HCI) 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 (similar to 50) for low Cl- masses and decreased over 3 orders of magnitude for higher (100X) CI- masses. Perchlorate mass increased with increasing glass reactor surface areas but not the salt surface area. Increasing the relative humidity (RH) from 2 to 67% increased ClO3- production but did not affect the amount of ClO4 produced, confirming previous reports that free water will promote additional ClO3- but not ClO4 production pathways. Additionally, oxidation of HCI (g) produced CIO4- at higher yields than oxidation of NaCI but produced less ClO3-. Our findings suggest that sufficient O-3 saturation and availability of active sites are essential for heterogeneous formation of ClO4- and ClO3-. While glass surfaces per se are not relevant to environmental production, catalytic surfaces (silicate or others) abound in terrestrial and extraterrestrial environments. The Cl- form oxidized and amount of water vapor present will also significantly impact the ClO4-/ClO3- ratio, which could be helpful in evaluating the sources of ClO4- and ClO3- in extraterrestrial material, with important implications on the availability of water during formation. 
heterogeneous oxidation; oxychlorine; Mars; perchlorate; chlorate 
ACS EARTH AND SPACE CHEMISTRY