SUBSONIC AIRCRAFT AND OZONE TRENDS

Growth in subsonic air traffic over the past 20 years has been dramati c, with an annual increase of similar to 6.1% over the decade between 1978 and 1988. Furthermore, aircraft activities in the year 2000 are p redicted to be double those of 1990, with a shift towards more high-fl ying, long-haul subsonics. Aircraft exhaust gases increase the amount of nitrogen oxides (NOx) in the upper troposphere/lower stratosphere t hrough injection at cruise altitudes. Given that NOx is instrumental i n tropospheric ozone production and stratospheric ozone destruction, i t is important to determine the influence of subsonic aircraft NOx emi ssions on levels of atmospheric ozone. This paper describes calculatio ns designed to investigate the impact that subsonic aircraft may alrea dy have had on the atmosphere during the 1980s, run in a 2-D chemical- radiative-transport model. The results indicate a significant increase in upper tropospheric ozone over the decade arising from aircraft emi ssions. However, when comparing model results with observational data, certain discrepancies appear. Lower stratospheric ozone loss over the 1980s does not appear to be greatly altered by the inclusion of aircr aft emissions in the model. However, given the trend in greater number s of long-haul subsonic aircraft, this factor must be considered in an y further calculations.