Impact of aircraft emissions on NO sub(x) in the lowermost stratosphere at northern midlatitudes

Airborne measurements of NO sub(x) , total reactive nitrogen (NO sub(y) ), O sub(3) , and condensation nuclei (CN) were made within air traffic corridors over the U.S. and North Atlantic regions (35-60 degrees N) in the fall of 1997. NO sub(x) and NO sub(y) data obtained in the lowermost stratosphere (LS) were examined using the calculated increase in NO sub(y) ( Delta NO sub(y) ) along five-day back trajectories as a parameter to identify possible effects of aircraft on reactive nitrogen. It is very likely that aircraft emissions had a significant impact on the NO sub(x) levels in the LS inasmuch as the NO sub(x) mixing ratios at 8.5-12 km were significantly correlated with the independent parameters of aircraft emissions, i.e., Delta NO sub(y) levels and CN values. In order to estimate quantitatively the impact of aircraft emissions on NO sub(x) and CN, the background levels of CN and NO sub(x) at O sub(3) = 100-200 ppbv were derived from the correlations of these quantities with Delta NO sub(y) . On average, the aircraft emissions are estimated to have increased the NO sub(x) and CN values by 130 pptv and 400 STP cm super(-) super(3) , respectively, which corresponds to 70 plus or minus 30% and 30 plus or minus 20% of the observed median values.