A 3D chemistry transport model study of changes in atmospheric ozone due to aircraft NOx emissions

The effect of present day aircraft emissions of nitrogen oxides (NOx = NO + NO2) on atmospheric NOx and ozone concentrations is investigated with the global three-dimensional chemistry transport model CTMK. This model uses 12-hourly meteorological data from the ECMWF analysis and includes parameterizations for subgrid scale processes such as convection. CTMK includes an ozone chemistry module containing the methane and carbon monoxide oxidation chain for the troposphere and lower stratosphere. It is found by using the ANCAT aircraft NOx emission invertory that aviation contributes to 20–100 pptv of the NOx at cruise altitudes in northern mid-latitudes, which corresponds to 30–80 and 20–50% of the background mixing ratios for January and July, respectively. This perturbation in NOx occurs mainly in the North Atlantic Flight Corridor and is transported eastwards. The resulting increase in upper tropospheric ozone is 2–3 ppbv (2%) in January and 5–10 ppbv (3%) in July. The ozone perturbation is almost zonally symmetric and attains maximum values at northern mid-latitudes in January and in the polar region in July. The calculated effect of aircraft emissions is found to be small (i.e. less than 5 pptv for NOx and less than 1 ppbv for 03) in the southern hemisphere. The perturbation of NOx by the aircraft emissions at cruise altitudes in northern mid-latitudes is large compared to the standard deviation. Therefore, it is expected that the effect of aviation on NOx is distinguishable from the contribution from other NOx sources. As the modelled natural variability of ozone is already about 30%, it will not be easy to detect the ozone perturbation due to aircraft NOx emissions.