Lightning NOx emissions and the impact on the effect of aircraft emissions - Results from the EU-Project TRADEOFF

The intercomparison of upper troposphere and lower stratosphere NOx measured on board of commercial aircraft with results of the chemistry-climate model E39/C revealed an underestimation of summertime simulated NOx concentrations. A further investigation of the causes within the EU-project TRADEOFF, using new satellite data, indicated a deficiency in the lightning parameterisation. A new parameterisation has been developed, which is based on t he convective massflux. The effect of individual emissions on the NOx and ozone concentration is shown. Tropical lightning emissions have the potential to enhance the mid-latitude NOx concentration via transport through the lowermost stratosphere. This transport process enhances ozone at mid - latitudes to the same magnitude as mid-latitude lightning. Compared to the previous formulation of lightning the impact of air traffic is reduced when applying the new lightning parameterisation, although the absolute amount of emitted NOx by lightning was not affected, but the horizontal and vertical location of the emitted NOx. The contribution of air traffic to the NOx budget in the northern upper troposphere is reduced from 30%-40% to 20%-30% and the contribution to ozone is reduced from 3%-4% to 2.5%.