NOx can lead to the formation of O3 through a photochemical reaction Aircraft emissions of NOx are more effective at producing ozone in the upper troposphere where ozone is more effective at increasing radiative forcing than at the surface Aircraft water and sulphur emissions in the stratosphere tend to reduce O3 The net impact of aircraft appears to be an increase O3 and a decrease in ultra violet (UV) radiation IPCC estimates that aircraft NOx emissions have increased ozone by up to 6% and this is anticipated to rise to 13% by 2050. The increases are expected on average to have a warming effect |