Impact of aircraft emissions on NOx in the lowermost stratosphere at northern midlatitudes

Airborne measurements of NOx, total reactive nitrogen (NOy), O-3, and conde nsation nuclei (CN) were made within air traffic corridors over the U.S. an d North Atlantic regions (35-60 degrees N) in the fall of 1997. NOx and NOy data obtained in the lowermost stratosphere (LS) were examined using the c alculated increase in NOy (Delta NOy) along five-day back trajectories as a parameter to identify possible effects of aircraft on reactive nitrogen. I t is very likely that aircraft emissions had a significant impact on the NO x levels in the LS inasmuch as the NOx mixing ratios at 8.5-12 km were sign ificantly correlated with the independent parameters of aircraft emissions, i.e., Delta NOy levels and CN values. In order to estimate quantitatively the impact of aircraft emissions on NOx and CN, the background levels of CN and NOx at O-3 = 100-200 ppbv were derived from the correlations of these quantities with Delta NOy. On average, the aircraft emissions are estimated to have increased the NOx and CN values by 130 pptv and 400 STP cm(-3), re spectively, which corresponds to 70+/-30 % and 30+/-20 % of the observed me dian values.