Release of oxygen atoms and nitric oxide molecules from the ultraviolet photodissociation of nitrate adsorbed on water ice films at 100 K

Production of O(³P_J, J = 2, 1, 0) atoms from the 295-320 nm photodissociation of NO₃^- adsorbed on water polycrystalline ice films at 100 K was directly confirmed using the resonance-enhanced multiphoton ionization technique. Detection of the O atom signals required an induction period after deposition of HNO₃ onto the ice film held at 130 K due to the slow ionization rate of HNO₃ to H⁺ and NO₃^- with a rate constant of k = (5.3 ± 0.2) × 10^-3 s^-1. Translational energy distributions of the O atoms were represented by a combination of two Maxwell-Boltzmann energy distributions with translational temperatures of 2000 and 100 K. Direct detection of NO from the secondary photodissociation process was also successful. On the atmospheric implications, the influence of the direct release of the oxygen atoms into the air from NO₃^- adsorbed on the natural snowpack was included in an atmospheric model calculation on the mixing ratios of ozone and nitric oxide at the South Pole, and the results compared favorably with the field data.