Modelling the impact of subsonic aviation on the composition of the atmosphere

Subsonic aircraft increase the ozone concentration in the tropopause region at northern midlatitudes by the emission of nitrogen oxides. Different model calculations indicate that aircraft emissions cause an increase of the NOx concentration in the range of 20-70% in North Atlantic flight corridor: the 8-12 km layer at northern midlatitudes, between the US and the European continents. According to these models, the NOx perturbations induce by photochemical processes an increase of ozone in the range of 2-10%. Assessments of the possible climate impact of these calculated ozone increases cause an estimated radiative forcing of about 0.015-0.05 W/m2 for 1992. However, the calculated increases of the NOx and O3 concentrations stem from different chemistry transport models that are insufficiently validated with observations. Furthermore, the uncertainties involved in chemistry transport modelling are numerous and impose a constraint on the reliability of such calculations. In this thesis the impact of aircraft emissions of NOx was calculated with the three-dimensional global chemistry transport model TM3. These model results were compared to observations of NOx and O3. This comparison aimed to obtain confidence in the earlier performed impact studies, but also to reveal model weaknesses in order to improve the model. Not long ago suitable measurements were not available to test the model with respect to aircraft emission studies, so the work presented in this study forms an important contribution to the reliability of the reported effects of subsonic aviation. Obviously the process of testing and improving of a model is an iterative and ongoing process. This work constitutes also a first step in that process.