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 climatechemistry 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 m2, with a mean value of 19.5 mW m2. Including the long-lived RF caused by changes in CH4, the total NOxrelated RF is estimated to about 5 mW m2, ranging 1e8 mW m2. Cruising at 2000 ft higher altitude increases the total RF due to aircraft NOx emissions by 2 ± 1 mW m2, while cruising at 2000 ft lower altitude reduces RF by 2 ± 1 mWm2. This change is mainly controlled by short-lived O3 and show that chemical NOx impact of contrail avoiding measures is likely small.
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