Potential Impacts of Supersonic Aircraft Emissions on Ozone and Resulting Forcing on Climate

Abstract:

Commercial aircraft flying at supersonic speeds in the lower stratosphere are being discussed once again after a hiatus of almost 20 years. Potential environmental effects from fleets of such aircraft need to be understood for their possible impacts on stratospheric ozone and on climate. Levels of stratospheric ozone determine the amount of biologically-harmful ultraviolet radiation from the Sun reaching the Earth’s surface. Changes in the distribution and concentrations of ozone also have implications on climate in addition to the climate forcing effects from the aviation emissions. To provide a baseline, this study first compares new analyses with previous assessments using emission inventories from 20 years ago. We then conducts a series of sensitivity studies of possible future cruise altitudes (which correspond to Mach numbers) to evaluate the potential atmospheric response for a fleet of supersonic aircraft, assumed to be fully operational by 2050. Even with the greatly enhanced understanding of atmospheric processes, the historical supersonic fleet analyses are quite similar to those found 20 years ago. We show that the effect on total column ozone strongly depends on the cruise altitude and the assumed emissions of nitrogen oxides and water vapor. Total column ozone is found to increase for cruise altitudes below ~17 km, and ozone effects transitions from production to depletion for emissions above 17 km. The ozone response is more sensitivity to nitrogen oxides than water vapor emissions. Although the actual impacts will depend on the specific aircraft design and fleet size, the sensitivity analyses done here provide insights for the technological development and optimization of future supersonic aircraft.