Quantifying the Influence of Supersonic Aviation Emissions on Global Surface Air Quality

Studies of supersonic aviation to date have focused on the potential for stratospheric ozone depletion and climate change, due to the high altitude release of both nitrogen oxides (NOx) and water vapor. However, the impact of these high-altitude emissions on surface air quality is underexplored. We quantify the effects of emissions from a total of 35 compartments, dividing the altitude range from 8 to 22 km into 2 km intervals across nine compartments, and segmenting latitude into five compartments without differentiating by longitude. Using global atmospheric chemistry-transport modeling, 1 Tg of NOx emitted at 20-22 km, a typical cruising altitude for a supersonic aircraft, and 30-60 N results in an addition 0.39 Gg of surface PM2.5. This is 8.4 times greater than the change in surface PM2.5 resulting from 1 Tg of NOx emitted at subsonic altitudes (8-10 km). We also find that NOx emitted at typical supersonic cruise altitudes results in a decrease in surface ozone, compared to an increase when NOx is emitted at subsonic cruise altitudes. Emissions of sulfur oxides (SOx) also cause qualitatively different impacts on surface air quality, again magnified when emitted at higher altitudes. We also assess the mechanism of why these changes occur, providing a comprehensive understanding of the high-altitude emissions impact on surface air quality. This research is not only applicable to policy-making decisions regarding supersonic aviation but also indicates the need for additional research into the global air quality impacts of other high altitude emissions such as those from launch vehicles.