Kinetic studies of reactions of the nitrate radical (NO3) with peroxy radicals (RO2): an indirect source of OH at night?

Abstract

A discharge–flow system, coupled to cavity-enhanced absorption spectroscopy (CEAS) detection systems for NO₃ at λ = 662 nm and NO₂ at λ = 404 nm, was used to investigate the kinetics of the reactions of NO₃ with eight peroxy radicals at P ∼ 5 Torr and T ∼ 295 K. Values of the rate constants obtained were (k/10⁻¹² cm³ molecule⁻¹ s⁻¹): CH₃O₂ (1.1 ± 0.5), C₂H₅O₂ (2.3 ± 0.7), CH₂FO₂ (1.4 ± 0.9), CH₂ClO₂ (3.8^+1.4_−2.6), c-C₅H₉O₂ (1.2^+1.1_−0.5), c-C₆H₁₁O₂ (1.9 ± 0.7), CF₃O₂ (0.62 ± 0.17) and CF₃CFO₂CF₃ (0.24 ± 0.13). We explore possible relationships between k and the orbital energies of the reactants. We also provide a brief discussion of the potential impact of the reactions of NO₃ with RO₂ on the chemistry of the night-time atmosphere.