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Article Dans Une Revue Atmospheric Chemistry and Physics Année : 2022

The climate impact of hydrogen-powered hypersonic transport

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Hypersonic aircraft flying at Mach 5 to 8 are a means for traveling very long distances in extremely short times and are even significantly faster than supersonic transport (Mach 1.5 to 2.5). Fueled with liquid hydrogen (LH2), their emissions consist of water vapor (H 2 O), nitrogen oxides (NO x), and unburned hydrogen. If LH2 is produced in a climate-and carbon-neutral manner, carbon dioxide does not have to be included when calculating the climate footprint. H 2 O that is emitted near the surface has a very short residence time (hours) and thereby no considerable climate impact. Super-and hypersonic aviation emit at very high altitudes (15 to 35 km), and H 2 O residence times increase with altitude from months to several years, with large latitudinal variations. Therefore, emitted H 2 O has a substantial impact on climate via high altitude H 2 O changes. Since the (photo-)chemical lifetime of H 2 O largely decreases at altitudes above 30 km via the reaction with O(1 D) and via photolysis, the question is whether the H 2 O climate impact from hypersonics flying above 30 km becomes smaller with higher cruise altitude. Here, we use two state-of-the-art chemistry-climate models and a climate response model to investigate atmospheric changes and respective climate impacts as a result of two potential hypersonic fleets flying at 26 and 35 km, respectively. We show, for the first time, that the (photo-)chemical H 2 O depletion of H 2 O emissions at these altitudes is overcompensated by a recombination of hydroxyl radicals to H 2 O and an enhanced methane and nitric acid depletion. These processes lead to an increase in H 2 O concentrations compared to a case with no emissions from hypersonic aircraft. This results in a steady increase with altitude of the H 2 O perturbation lifetime of up to 4.4 ± 0.2 years at 35 km. We find a 18.2 ± 2.8 and 36.9 ± 3.4 mW m −2 increase in stratosphere-adjusted radiative forcing due to the two hypersonic fleets flying at 26 and 35 km, respectively. On average, ozone changes contribute 8 %-22 %, and water vapor changes contribute 78 %-92 % to the warming. Our calculations show that the climate impact, i.e., mean surface temperature change derived from the stratosphere-adjusted radiative forcing, of hypersonic transport is estimated to be roughly 8-20 times larger than a subsonic reference aircraft with the same transport volume (revenue passenger kilometers) and that the main contribution stems from H 2 O.
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hal-03866895 , version 1 (23-11-2022)

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Johannes Pletzer, Didier Hauglustaine, Yann Cohen, Patrick Jöckel, Volker Grewe. The climate impact of hydrogen-powered hypersonic transport. Atmospheric Chemistry and Physics, 2022, 22 (21), pp.14323 - 14354. ⟨10.5194/acp-22-14323-2022⟩. ⟨hal-03866895⟩
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