The kinetics of the gas phase reaction of nitrous acid with ozone

The kinetics of the gas phase reaction between ozone and nitrous acid have been investigated under conditions applicable to the middle stratosphere. The decay of nitrous acid (-0.005 Torr) in the presence of excess ozone (0.4-14 Torr) has been measured at 226 and 300 K using a mass spectrometer detector. At both temperatures, the observed decay rate is independent of ozone concentration and apparently arises from heterogeneous reactions, rather than from the homogeneous bimolecular reaction, HNO2 + O3 yields HNO3 + O2. Conservative upper limits to the value of Reaction coefficient, calculated by assuming that the entire HNO2 decay results from this reaction, are from 1 to 5 times 10 to the -19 power cu.cm molecule/sec at 300 and 226 K respectively. Calculations based on a simplified mechanism for stratospheric NOx chemistry indicate that reaction, with a rate constant of the magnitude reported above, is unlikely to be important in the chemistry of the stratosphere.