| Summary: | Natural perchlorate (ClO4-) is widespread in the environment and is hypothesized to be produced through atmospheric processes. Limited studies have investigated its production mechanisms, historic deposition trends, and co-occurrence with chlorate (ClO3-), a contaminant that is currently believed to be present in the environment solely due to anthropogenic activities. The purpose of this study is to determine the comparative yields and rates of ClO4- and ClO3- from the O3 and UV mediated oxidation of chlorine (cl) and oxy-chlorine (HxClOyz-) species. Additionally, discrete ice core samples obtained from ice cores in the non-polar regions of North America were analyzed to evaluate the temporal changes in the ClO4- depositional flux. We also show the development of a new ion chromatography electrospray tandem mass spectrometry (IC-ESI/MS/MS) method for quantification and confirmation of chlorate (ClO3-) in environmental samples. Chlorate was not an effective reactant as neither O3 nor photolysis produced ClO4- under the experimental conditions studied. Ozone oxidation of ClO2- and ClO2 produced the highest molar yields of ClO4- (0.6 to 2.7 %) compared to other reactants evaluated. Perchlorate yields (0.0003 to 0.02 %) were much lower for both ozonation and photolysis of HOCl/OCl-. Ozonation but not photolysis of Cl- solutions produced ClO4-. Based on our results, we propose a potential formation pathway for natural ClO4- with emphasis on the role of ClO2 and higher oxy-chlorine radicals/intermediates (e.g., Cl2O6) in its formation. Our preliminary study indicate that the presence of ClO4- in the ice cores corresponds to an intermittent source such as volcanic eruptions and/or any anthropogenic forcing that may directly or indirectly aid in atmospheric ClO4- formation. Further, analysis of environmental samples using the developed analytical technique indicate that ClO3-, like ClO4-, may be atmospherically produced and deposited, then concentrated in dry soils, and are both a minor component in the biogeochemical ...
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