CONTRIBUTIONS OF AIRCRAFT EMISSIONS TO THE ATMOSPHERIC NOX CONTENT

The relative contribution of aircraft emissions to the total atmospher ic NOx content is studied by means of the atmosphere general circulati on model ECHAM, which was extended by a simplified (linear) NOx chemis try module with NOx and HNO3 as prognostic variables. NOx originates f rom fossil Fuel combustion, biomass burning, soil microbial activity, lightning, degradation of N2O in the stratosphere, and aircraft emissi ons. NOx and HNO3 are removed by dry deposition, HNO3 additionally by wet deposition. A simulation in seasonal cycle mode was performed. Bot h the resulting January and July mean distributions of NOx and the rel ative contributions of the different sources to the total atmospheric NOx burden are analysed, including their uncertainty ranges. NOx emiss ions from aircraft cause a significant change to the background NOx co ncentration. During January more than 60% of the NOx emissions found i n the region between 30 and 60 degrees N, and 175-325 hPa arise from a ircraft. The maximum value in the North Atlantic flight corridor is fo und to be larger than 85%. During July, aircraft emissions contribute only about 20% to the NOx burden in this region. In January and July t he uncertainty ranges of these contributions are 42-80% and 10-37%, re spectively. (C) 1997 Published by Elsevier Science Ltd.