کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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4432031 | 1619912 | 2008 | 9 صفحه PDF | دانلود رایگان |
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 ClO4− 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 O3 (0.96%) generated ClO4− 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 ClO4− than Cl− coated sand or glass as well as a higher ratio of ClO3− to ClO4−. Reduction of the initial Cl− mass resulted in substantially higher molar yields of ClO4− and ClO3−. In addition, alkaline absorbers that captured gaseous products contained substantial quantities of Cl−, ClO3−, and ClO4−. Solutions of possible oxychlorine intermediates (OCl− and ClO3−) exposed to O3 produced only scant amounts of ClO4− while a ClO2− solution exposed to O3 produced substantial molar yields of ClO4− (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 O3. 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 ClO2− may be a key intermediate while ClO3− and OCl− are unlikely to play a significant role.
Journal: Science of The Total Environment - Volume 405, Issues 1–3, 1 November 2008, Pages 301–309