Aircraft emission mitigation by changing route altitude: A multi-model estimate of aircraft NOx emission impact on O3 photochemistry

The atmospheric impact of aircraft NOx emissions are studied using updated aircraft inventories for the year 2006, in order to estimate the photochemistry-related mitigation potential of shifting cruise altitudes higher or lower by 2000 ft. Applying three chemistry-transport models (CTM) and two climate-chemistry models (CCM) in CTM mode, all including detailed tropospheric and stratospheric chemistry, we estimate the short-lived radiative forcing (RF) from O3 to range between 16.4 and 23.5 mW m−2, with a mean value of 19.5 mW m−2. Including the long-lived RF caused by changes in CH4, the total NOx-related RF is estimated to about 5 mW m−2, ranging 1–8 mW m−2. Cruising at 2000 ft higher altitude increases the total RF due to aircraft NOx emissions by 2 ± 1 mW m−2, while cruising at 2000 ft lower altitude reduces RF by 2 ± 1 mW m−2. This change is mainly controlled by short-lived O3 and show that chemical NOx impact of contrail avoiding measures is likely small.