TY - JOUR
T1 - Perchlorate production by ozone oxidation of chloride in aqueous and dry systems
AU - Kang, Namgoo
AU - Jackson, W. Andrew
AU - Dasgupta, Purnendu K.
AU - Anderson, Todd A.
N1 - Funding Information:
This study was performed through funding from the Strategic Environmental Research and Development Program (SERDP) under Contract EP-1435.
PY - 2008/11/1
Y1 - 2008/11/1
N2 - 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.
AB - 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.
KW - Chemical oxidation
KW - Chlorate
KW - Chlorine oxyanions
KW - Chlorite
KW - NaCl
KW - Ozonation
UR - http://www.scopus.com/inward/record.url?scp=52949096516&partnerID=8YFLogxK
U2 - 10.1016/j.scitotenv.2008.07.010
DO - 10.1016/j.scitotenv.2008.07.010
M3 - Article
C2 - 18722000
AN - SCOPUS:52949096516
VL - 405
SP - 301
EP - 309
JO - Science of the Total Environment
JF - Science of the Total Environment
SN - 0048-9697
IS - 1-3
ER -