Impact of H2O emissions from cryoplanes and kerosene aircraft on the atmosphere -: art. no. 4304

[1] Perturbations in H2O caused by aircraft in the year 2015 are calculated with a chemical transport model (CTM) and used as input for radiative forcing calculations. The focus is on a hypothetical fleet of cryoplanes, i.e., liquid-hydrogen-powered aircraft. For comparison, the effects of subsonic and supersonic kerosene aircraft are assessed. The CTM applies the accurate second-order moment scheme for advective transport and is run in T42 resolution (2.8degrees x 2.8degrees) with 40 layers between the surface and 10 hPa. Aircraft emissions are taken from NASA inventories for the year 2015. In the cryoplane experiments the projected subsonic kerosene fleet is replaced completely by cryoplanes, which emit 2.55 times as much H2O. Longwave and shortwave components of radiative forcing due to the modeled H2O increases are calculated for different seasons. In northern midlatitudes near the tropopause, the fleet of cryoplanes is calculated to increase zonal-mean H2O by more than 250 ppbv on an annual average. The resulting radiative forcing at the tropopause strongly depends on season, ranging from 0.0027 W/m(2) in October to 0.0135 W/m(2) in April on a global average. Subsonic kerosene aircraft are found to have a rather small impact on H2O levels and lead to an annually averaged global-mean radiative forcing of 0.0026 W/m(2). Supersonic kerosene-powered aircraft have a more pronounced impact on H2O concentrations than subsonic cryoplanes and cause a radiative forcing of nearly 0.05 W/m(2). Several sensitivity studies are performed for cryoplanes, dealing with cruising altitude, tropopause height, tropospheric lifetime, and stratospheric sinks of aircraft-emitted water vapor.