The reactions of NO3 with OH and H

Abstract

Rate constants for the reaction NO3+ OH → products (1) have been measured in a flow system. NO3 radicals were generated from the reaction of F with HNO3, and OH radicals were generated by the reaction of H with NO2. Concentrations of NO3 were determined by multipass optical absorption in the visible region, while [OH] was measured by resonance fluorescence. Numerical modelling allowed a rate coefficient to be derived for the reaction at room temperature of k1=(2.0 ± 0.6)× 10–11 cm3 molecule–1 s–1. The modelling shows that secondary reactions are of only minor importance.We describe a hitherto-unknown reaction between H and NO3. NO3+ H → OH + NO2. (2) Production of OH was demonstrated explicitly from the resonance fluorescence measurements. The reaction is fast, with a room-temperature rate constant given by k2=(1.1 ± 0.6)× 10–10 cm3 molecule–1 s–1. Reaction (1) follows the formation of OH in reaction (2), so that the time-dependence of [OH] can be used to give further information about k1. The rate constants so obtained were entirely consistent with those obtained in the direct study.The possible influence of steric effects and orbital degeneracy on the relative rates of the H and OH interactions with NO3 are pointed out. Atmospheric involvement of the reactions, in either troposphere or stratosphere, is shown to be improbable, although the new data illustrate that NO3 can be highly reactive towards suitable partners.