In situ measurements of nitrogen oxides and other trace chemicals were performed aboard the DLR Falcon in September and October 1997 during POLINAT 2 over the eastern North Atlantic in areas with predicted high impact of aircraft emissions to search for flight corridor effects. During survey flights in the upper troposphere from the center of the flight corridor to regions south of or below the major transatlantic aircraft routes, large-scale enhancements in mixing ratios of NO of about 50 to 150 pptv were observed in corridor areas compared to the NO abundance measured outside the corridor. Using simultaneous tracer measurements, back trajectory analyses for the air masses sampled, the actual distribution of the North Atlantic air traffic, and comparisons of observed and predicted NO distributions from a regional model of simulations including or excluding aircraft emissions, these enhancements were attributed mainly to aircraft NOx. ¿ 1999 American Geophysical Union