This study estimates cruising times and related pollutant emissions (NOx, CO, HC) and H2O of today's aircraft fleet within the troposphere and stratosphere performed for the North Atlantic region in between 45 ¿N, 65 ¿N, 10 ¿W, and 50 ¿W for the years 1989, 1990, and 1991. The tropopause surface distribution is determined through analysis of assimilated data. Both conventional lapse rate and potential vorticity criteria are employed to determine the location of the tropopause surface. These data combined with air traffic statistics are used to evaluate cruising times within the troposphere and stratosphere separately. The study shows an average of about 44% of the cruising time of the aircraft above the North Atlantic flown within the stratosphere. Based on emission indices of aircraft engines, the emission rates of NOx (in mass units of NO2) into the stratosphere and troposphere in the given region result in 0.26 and 0.33¿10-12 kg m-2 s-1, respectively. ¿ American Geophysical Union 1993