ATMOSPHERIC IMPACT OF NOX EMISSIONS BY SUBSONIC AIRCRAFT - A 3-DIMENSIONAL MODEL STUDY

Three-dimensional model calculations suggest that the world's fleet of subsonic aircraft has enhanced the abundance of nitrogen oxides in th e upper troposphere by up to 20-35% and has produced a significant inc rease in the ozone concentration in this region of the atmosphere (4% in summer and 1% in winter). In year 2050, on the basis of current sce narios for growth in aviation, the concentration of NOx at 10 km could increase by 30-60% at midlatitudes, and the concentration of ozone co uld be enhanced by 7% and 2% in summer and winter, respectively (relat ive to a situation without aircraft effects). The perturbation is not limited to the flight corridors but affects the entire northern hemisp here. The magnitude (and even the sign) of the ozone change depends on the level of background atmospheric NOx and hence on NOx sources (lig htning, intrusion from the stratosphere, and convective transport from the polluted boundary layer) and sinks which are poorly quantified in this region of the atmosphere. On the basis of our model estimates, 2 0% of the NOx found at 10 km (midlatitudes) is produced by aircraft en gines, 25% originates from the surface (combustion and soils), and app roximately 50% is produced by lightning. For a lightning source enhanc ed in the model by a factor of 2, the increase in NOx and ozone at 10 lan due to aircraft emissions, is reduced by a factor of 2. The magnit ude of aircraft perturbations in NOx is considerably smaller than the uncertainties in other NOx sources.