IMPACT OF AIRCRAFT AND SURFACE EMISSIONS OF NITROGEN-OXIDES ON TROPOSPHERIC OZONE AND GLOBAL WARMING

ACTUAL and potential increases in aircraft traffic are causing concern about the effects of aircraft exhaust emission on atmospheric chemistry. Model results 1-3 and measurements 4-6 in the Northern Hemisphere have shown that growth in surface emissions of nitrogen oxides and hydrocarbons leads to increases in concentration of tropospheric ozone. Tropospheric ozone is toxic to plants, humans and other organisms, and it is a greenhouse gas 7-9. The radiative forcing of surface temperature is most sensitive to changes in tropospheric ozone at a height of approximately 12 km (ref. 8), where aircraft emissions of nitrogen oxides are at a maximum and where the model sensitivity of ozone to nitrogen oxide emissions is enhanced. Our model results show that the radiative forcing of surface temperature is about thirty times more sensitive to aircraft emissions of nitrogen oxides than to surface emissions. We also find that the impact on global warming of increases in tropospheric ozone caused by increases in surface emissions of nitrogen oxides has previously been overestimated by a factor of five 1,10, owing to an error in the calculation of the ozone budget.