NG002-0025
Development and application of a tropospheric-stratospheric adjoint to identify the ozone-neutral aircraft cruise altitude

Monday, 14 December 2020
Poster
Thibaud Fritz1, Irene Constantina Dedoussi2,3, Sebastian David Eastham4 and Steven R H Barrett4, (1)Massachusetts Institute of Technology, Cambridge, MA, United States, (2)Massachusetts Institute of Technology, Aeronautics and Astronautics, Cambridge, MA, United States, (3)Delft University of Technology, Faculty of Aerospace Engineering, Delft, Netherlands, (4)Massachusetts Institute of Technology, Laboratory for Aviation and the Environment, Cambridge, MA, United States
Abstract:
Previous assessments of supersonic transport have suggested the existence of a column ozone neutral cruise altitude, but have not quantified it or its sensitivity to emission indices. Adjoint methods would be a natural option for this, but no suitable adjoint models of global tropospheric-stratospheric chemistry exist. Due to the long transport lifetimes and lack of removal processes in the stratosphere, stratospheric adjoint models demand stability, significant data storage, and long integrations. As such, global three dimensions chemistry-transport models (CTMs) which have thus far been adjointed have mostly been limited to the troposphere.

We develop an adjoint of the GEOS-Chem CTM which includes unified tropospheric-stratospheric chemistry-capable of capturing stratospheric chemistry and physics. This enables, for instance, the evaluation of adjoint sensitivities during the Antarctic polar winter, including the influence of polar stratospheric clouds.

We apply this model to produce multi-year sensitivities of global column ozone with respect to potential changes in the cruising altitude and emissions profile of commercial aviation, including the possibility of the reintroduction of supersonic commercial flight. We find that the “ozone-neutral cruise” altitude is around 15 km, but varies with fuel sulfur content (FSC) and nitrogen oxide (NOx) emissions. Chemical sensitivity data shows that, at this altitude, NOx-driven ozone production is offset by ozone depletion from sulfur emissions. However, if the FSC were reduced to zero, the altitude of this band would increase to 16 km.

Using adjoint modeling, we find that the desulfurization of aviation jet fuel could arise as an outcome to greatly reduce aviation-attributable ozone impacts, at the cost of suppressed sulfur-induced cooling. The GEOS-Chem UCX Adjoint opens up new opportunities for both sensitivity evaluation and inverse modeling, including with regards to stratospheric column observations.

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