Pressure and Temperature Dependencies of Rate Coefficients for the Reaction OH + NO + M → Products.

The OH + NO reaction is a critically important process for radical chain termination in the atmosphere with a major impact on the ozone budgets of the troposphere and stratosphere. Rate constants for the reaction of OH + NO + M → products have been measured under conditions relevant to the upper troposphere/lower stratosphere with a laser photolysis-laser-induced fluorescence (LP-LIF) technique augmented by in situ optical spectroscopy for quantification of [NO]. The experiments are carried out over the temperature range of 230-293 K and the pressure range 50-750 Torr of N and air and as a function of [O]. The observed rate coefficients in N agree with the newest experimental literature data sets and are within experimental uncertainty of current recommended literature values at 293 K but are systematically higher by up to 22% at 700 Torr and 230 K. The efficacy of different falloff parametrizations has been examined and compared to those in literature sources. The collisional quenching efficiency of O was found to be in excellent agreement with current literature sources, and rate coefficients determined in air at 293 and 245 K were observed to be within uncertainty of the rate coefficients measured in N bath gas. This work has improved confidence in the literature rate coefficients under conditions of the lower troposphere (∼760 Torr, 280-310 K) toward the stratosphere (10-100 Torr, 220-250 K).