Three‐dimensional model studies of the effect of NOx emissions from aircraft on ozone in the upper troposphere over Europe and the North Atlantic

A mesoscale chemistry transport model is coupled to a numerical weather prediction model (NWP) for Europe and the North Atlantic. It is applied to show that air traffic emissions significantly increase the concentrations of NO x as well as the net chemical formation rate of ozone over both the Atlantic Ocean and over central Europe. The time period studied was July 1–10, 1991, a period characterized by a high‐pressure ridge over North Europe. In convection the vertical gradient of NO x is strongly reduced because the midtropospheric concentrations increase. In the updraft region of convective plumes, chemical ozone formation up to 1.8 ppbv/h is calculated in the upper troposphere, and this is about a factor 50 higher than the average for 10.5 km over continental Europe during the 10‐day period. The high production rates are not sustained for more than a few hours, and it would be difficult to identify the effect of the process in a local measurement of the ozone concentration. The calculations indicate that 10–25 molecules of O 3 (0.03–0.05 ppb/h) are generated on the average per NO x molecule emitted from aircraft (2–3 ppt/h). On convective days over regions with significant surface sources of NO x , ozone formation in the upper troposphere due to NO x brought there by convection, outweighs the role of aircraft NO x emissions. The net chemical formation rate of ozone across the model domain depends on the boundary concentrations of NO x and O 3 , but the change in the upper troposphere in the net chemical formation rate of ozone induced by aircraft NO x emissions is quite independent of the concentrations of NO x or O 3 .