Factors influencing ozone chemistry in subsonic aircraft plumes

Abstract

This study investigates several factors that could influence ozone chemistry occurring in subsonic aircraft plumes in the upper troposphere. The study focuses on uncertainties in gas-phase rate parameters, but also examines the influence of selected heterogeneous reactions, the rate of expansion of the plume, ambient and initial plume concentrations, and the time of emissions. Monte Carlo analysis with Latin hypercube sampling was applied to an expanding box model of an aircraft plume, in order to estimate the sensitivities of O 3 perturbations (ΔO 3) to uncertainties in rate constants in the RADM2 chemical mechanism. The resulting coefficient of variation in ΔO 3 at the end of a 36 h simulation was about 50%. Influential uncertainties in gas-phase rate parameters include those for photolysis of NO 2 and HCHO, O 3+NO, HO 2+NO, and formation of PAN and HNO 3. With high background concentrations of non-methane hydrocarbons, uncertainties in rate parameters of reactions involving peroxy radicals from ethene and propene oxidation were also influential. The coefficient of variation for ΔO 3 due to uncertainties in emission indices of NO x , CO, and organic compounds was less than 15%. The effects of the heterogeneous reaction of N 2O 5 leading to HNO 3 formation, and hypothesized reactions of HNO 3 and NO 2 on soot, were also investigated. The results suggest that the latter two reactions could be influential for ΔO 3 if published estimates of reaction probabilities and high estimates of soot concentrations in plumes are realistic.