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

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-recognised climate benefits via reduction in ozone and contrail warming through this concept. The NOx 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 NOx 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 NOx threshold levels were estimated by STOCHEM-CRI global chemical transport model and IAGOS measurement data and found that northern midlatitudes of the atmosphere are the most favourable region existing with the smallest NOx 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 NOx compensation point, i.e., increased photochemical ozone production. Thus, a simple one-dimensional 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.