title: Perchlorate production by ozone oxidation of chloride in aqueous and dry systems.
abstract: Overwhelming evidence now exists that perchlorate is produced through natural processes and can be ubiquitously found at environmentally relevant concentrations in arid and semi-arid locations. A number of potential production mechanisms have been hypothesized and ClO(4)(-) production by ozone oxidation of surface bound Cl(-) was demonstrated. However, no information concerning the impact of concentration, final reaction products distribution, impact of reaction phase, or oxidation of important oxychlorine intermediates has been reported. Using IC-MS-MS analysis and replicate oxidation experiments, we show that exposing aqueous solutions or Cl(-) coated sand or glass surfaces to O(3) (0.96%) generated ClO(4)(-) with molar yields of 0.007 and 0.01% for aqueous Cl(-) solutions and 0.025 and 0.42% for Cl(-) coated sand and glass, respectively. Aqueous solutions of Cl(-) produced less ClO(4)(-) than Cl(-) coated sand or glass as well as a higher ratio of ClO(3)(-) to ClO(4)(-). Reduction of the initial Cl(-) mass resulted in substantially higher molar yields of ClO(4)(-) and ClO(3)(-). In addition, alkaline absorbers that captured gaseous products contained substantial quantities of Cl(-), ClO(3)(-), and ClO(4)(-). Solutions of possible oxychlorine intermediates (OCl(-) and ClO(3)(-)) exposed to O(3) produced only scant amounts of ClO(4)(-) while a ClO(2)(-) solution exposed to O(3) produced substantial molar yields of ClO(4)(-) (4% molar yield). Scanning electron microscopy coupled with energy energy-dispersive X-ray analysis demonstrated a significant loss of Cl(-) and an increase in oxygen on the Cl(-) coated silica sand exposed to O(3). While the experimental conditions are not reflective of natural conditions this work clearly demonstrates the relative potential of Cl(-) precursors in perchlorate production and the likely importance of dry aerosol oxidation over solution phase reactions. It also suggests that ClO(2)(-) may be a key intermediate while ClO(3)(-) and OCl(-) are unlikely to play a significant role.
authors: Department of Civil and Environmental Engineering, Texas Tech University, Lubbock, Texas 79409-1023, USA. nkang@kriss.re.kr
authors: Namgoo
authors: N
authors: Kang
authors: W Andrew
authors: WA
authors: Jackson
authors: Purnendu K
authors: PK
authors: Dasgupta
authors: Todd A
authors: TA
authors: Anderson
mesh_terms: D002712:Chlorides / Q000737:chemistry*; D005898:Glass; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry*; D010472:Perchlorates / Q000138:chemical synthesis*; D012822:Silicon Dioxide
chemical_list: D002712:Chlorides; D010472:Perchlorates; D010126:Ozone; D012822:Silicon Dioxide; C494474:perchlorate