heric chemical and radiative processes (1). Programs are underway in the United States and other countries to evaluate the effects of increasing the number of high-speed civil transport aircraft that operate in the stratosphere. Apart from the technical challenges, significant environmental issues related to the role of exhaust emissions on climate and global change must be considered. Emission requirements imposed on new engines will depend on the environmental impact of their emissions. High-speed aircraft emit reactive nitrogen in the form of [NO.sub.x] at altitudes in the lower stratosphere between 16 and 23 kilometers while operating at speeds of Mach 1.6 to Mach 3.2, respectively. The [NO.sub.x] participates directly and indirectly in catalytic cycles that destroy [0.sub.3] in the lower stratosphere. However, the sensitivity of the ozone ([0.sub.3]) loss to [NO.sub.x] emissions is reduced in atmospheric models when heterogeneous reactions on background sulfate aerosol particles are included because the [NO.sub.x] is reduced through more effective conversion to [HNO.sub.3].
One current estimate is that the emission from a fleet of 500 supersonic aircraft operating at Mach 2.4 would change ozone by less than one percent between 40o and 50o if the emission index for [NO.sub.x] is 15 g of [NO.sub.x] per kilogram of fuel or less. Losses would increase if either the emission index for [NO.sub.x] or the flight altitude increased. However, these calculations did not include the effects of the emission of sulfate particles. Most particle emission parameters are not well characterized for supersonic aircraft operating in the stratosphere because ground-based tests do not fully simulate the growth and coagulation processes in the plume that change particle number, size, and composition after the engine exhaust enters the surrounding atmosphere.
Fahey et al (1) measured emission indices of reactive gases and particles in the ...