Multi-model assessment of the atmospheric and radiative effects of supersonic transport aircraft

Abstract. Commercial supersonic aircraft may return in the near future, offering reduced travel time while flying higher in the atmosphere than subsonic aircraft, thus displacing part of the passenger traffic and associated emissions to higher altitudes. For the first time since 2007, we present a comprehensive multi-model assessment of the atmospheric and radiative effect of this displacement. We use four models (EMAC, GEOS-Chem, LMDz–INCA, and MOZART-3) to evaluate three scenarios in which subsonic aviation is partially replaced with supersonic aircraft. Replacing 4 % of subsonic traffic with Mach 2 aircraft that have a NOx emissions index of 13.8 g (NO2) kg−1 leads to ozone column loss of −0.3 % (−0.9 DU; model range from −0.4 % to −0.1 %), and it increases radiative forcing by 19.1 mW m−2 (model range from 16.7 to 28.1). This forcing is driven by water vapor (18.2 mW m−2), ozone (11.4 mW m−2), and aerosol emissions (−10.5 mW m−2). The use of a Mach 2 concept with low-NOx emissions (4.6 g (NO2) kg−1) reduces the effect on forcing and ozone to 13.4 mW m−2 (model range from 2.4 to 23.4) and −0.1 % (−0.3 DU; model range from −0.2 % to +0.0 %), respectively. If a Mach 1.6 aircraft with a lower cruise altitude and NOx emissions of 4.6 g (NO2) kg−1 is used instead, we find a near-net-zero effect on the ozone column and an increase in the radiative forcing of 3.7 mW m−2 (model range from 0.5 to 7.1). The supersonic concepts have up to 185 % greater radiative effect per passenger kilometer from non-CO2 emissions compared to subsonic aviation (excluding contrail impacts).