Contributions of aircraft emissions to the atmospheric NOx content

The relative contribution of aircraft emissions to the total atmospheric NOx content is studied by means of the atmosphere general circulation model ECHAM, which was extended by a simplified (linear) NOx chemistry module with NOx and HNO3 as prognostic variables. NOx originates from fossil fuel combustion, biomass burning, soil microbial activity, lightning, degradation of N2O in the stratosphere, and aircraft emissions. NOx and HNO3 are removed by dry deposition, HNO3 additionally by wet deposition. A simulation in seasonal cycle mode was performed. Both the resulting January and July mean distributions of NOx and the relative contributions of the different sources to the total atmospheric NOx burden are analysed, including their uncertainty ranges. NOx emissions from aircraft cause a significant change to the background NOx concentration. During January more than 60% of the NOx emissions found in the region between 30 and 60°N, and 175–325 hPa arise from aircraft. The maximum value in the North Atlantic flight corridor is found to be larger than 85%. During July, aircraft emissions contribute only about 20% to the NOx burden in this region. In January and July the uncertainty ranges of these contributions are 42–80% and 10–37%, respectively.