Large‐scale enhancements in NO/NOy from subsonic aircraft emissions: Comparisons with observations

Abstract

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 photochemical trajectory model to help interpret observed NO/NOy ratios from the stratospheric portions of this flight. The model is run with and without an additional in situ NOx source from the 1992 Boeing‐McDonnell Douglas (BMD) emissions climatology. During the northern section of this flight, the inclusion of this additional NOx source resulted in a significant improvement with observed large‐scale NO/NOy ratios. This comparison suggests that air traffic over the eastern United States 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 using 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 observed NO/NOy ratios with the model‐predicted enhancements of this ratio arising from aircraft emissions.