Issue Date: July 7, 2008
Another Way To Form Atmospheric Chlorine
National Oceanic & Atmospheric Administration scientists report a new mechanism for the formation of molecular chlorine in the atmosphere: N2O5 can oxidize Cl– to Cl2 on acidic aerosols, the researchers say (Science, DOI: 10.1126/science.1158777). Molecular chlorine is a highly reactive species that affects atmospheric aerosol formation, ozone abundance, and the fate of trace gases such as mercury. Various mechanisms have been proposed to describe the conversion of Cl– to Cl2 in the atmosphere over the oceans. Researchers know that N2O5, which forms at night, interacts with sea salt to form nitryl chloride (ClNO2). They also know that the hydrated surfaces of some aerosols behave more like concentrated solutions than solids. Using mass spectrometry in the lab, James M. Roberts and colleagues tested the reactivity of N2O5 with oxalic acid and ammonium sulfate aerosols that contained various halide ions. They also observed that at low atmospheric pH and low Cl??? concentrations, both N2O5 and ClNO2 efficiently produced Cl2 in an oxalic acid/sodium chloride solution. The researchers note that understanding the implications of this chemistry in the troposphere and stratosphere will require further study.
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