LARGE-SCALE ENHANCEMENTS IN NO NOY FROM SUBSONIC AIRCRAFT EMISSIONS -COMPARISONS WITH OBSERVATIONS/

One of the DC-8 flights from the 1992 AASE 2 campaign flew south from Maine over the Atlantic Ocean, sampling air downstream of areas in the eastern United States associated with heavy air traffic. We use a pho tochemical trajectory model to help interpret observed NO/NOy ratios f rom the stratospheric portions of this flight. The model is run with a nd without an additional in situ NOx source from the 1992 Boeing-McDon nell Douglas (BMD) emissions climatology. During the northern section of this flight, the inclusion of this additional NOx source resulted i n a significant improvement with observed large-scale NO/NOy ratios. T his comparison suggests that air traffic over the eastern United State s is sufficiently dense to enhance NO/NOy ratios on a regional scale, even when the characteristic NO spikes from exhaust plumes are absent. During the southern portion of the flight, in which the DC-8 flew at a higher altitude, observed NO/NOy ratios agreed much better with the no-emissions scenario. This may be a reflection of the difficulty of u sing a climatological NOx emissions database to infer instantaneous NO /NOy ratios. It would be desirable to have a larger database of lower stratospheric NO and NOy measurements downstream of the eastern United States. This would enable more stringent statistical comparisons of o bserved NO/NOy ratios with the model-predicted enhancements of this ra tio arising from aircraft emissions.