Off-setting climate change through formation flying of aircraft, a feasibility study reliant on high fidelity gas-phase chemical kinetic data

Abstract

Application of formation flights to civil aviation is gaining interest, primarily due to the fuel burn reduction achieved by flying through another aircraft's wake. However, it is emerging that there are additional, less-recognized climate benefits via reduction in ozone and contrail warming through this concept. The NO_x threshold level is defined as when the loss rate for OH by reaction with NO₂ is equal to the loss rates for OH with CO and CH₄, beyond which level, ozone formation will decrease. In this study, The NO_x threshold level was calculated at different altitudes and found that at cruise altitude (∼10 km), the amount of NO₂ required for parity in OH loss with loss due to reaction with CO and CH₄ is around 2 ppb. The spatial and temporal NO_x threshold levels were estimated by STOCHEM-Common Representative Intermediate (CRI) global chemical transport model and In-service Aircraft for Global Observing System (IAGOS) measurement data and found that northern midlatitudes of the atmosphere are the most favorable region existing with the smallest NO_x thresholds (0.5 ppb) needed before reduction in ozone formation is likely to occur at cruise altitude of aircraft. Incorporating the major air traffic corridors into the coarse spatial resolution of the chemical transport model overestimated the NO_x compensation point, that is, increased photochemical ozone production. Thus, a simple one-dimensional (1D) aircraft plume dispersion model was developed with higher spatial and temporal resolution for considering aircraft plumes and its chemistry more accurately. The model run shows that the impact of formation flying aircraft emissions on spatially averaged ozone could be halved if the aircraft could maintain separations inside 4 km relative to well separated flights of 10 km or more.