Kinetics of the OH + NO2 reaction: Rate coefficients (217-333 K, 16-1200 mbar) and fall-off parameters for N2 and O2 bath gases

Abstract

The radical terminating, termolecular reaction between OH and NO2 exerts great influence on the NOy=NOx ratio and O3 formation in the atmosphere. Evaluation panels (IUPAC and NASA) recommend rate coefficients for this reaction that disagree by as much as a factor of 1.6 at low temperature and pressure. In this work, the title reaction was studied by pulsed laser photolysis and laser-induced fluorescence over the pressure range 16-1200 mbar and temperature range 217-333 K in N2 bath gas, with experiments at 295 K (67-333 mbar) for O2. In situ measurement of NO2 using two optical absorption set-ups enabled generation of highly precise, accurate rate coefficients in the fall-off pressure range, appropriate for atmospheric conditions. We found, in agreement with previous work, that O2 bath gas has a lower collision efficiency than N2 with a relative collision efficiency to N2 of 0.74. Using the Troe-type formulation for termolecular reactions we present a new set of parameters with k0(N2) D 2:6 × 10-30 cm6 molecule-2 s-1, k0(O2) D 2:0 × 10-30 cm6 molecule-2 s-1, m D 3:6, k1 D 6:3×10-11 cm3 molecule-1 s-1, and Fc D 0:39 and compare our results to previous studies in N2 and O2 bath gases.