The Climate Impact of Hypersonic Transport

Pletzer, Johannes Friedrich; Hauglustaine, Didier; Cohen, Yann; Jöckel, Patrick; Grewe, Volker

doi:https://doi.org/10.5194/egusphere-2022-285

Preprints

https://doi.org/10.5194/egusphere-2022-285

Preprints

19 May 2022

| 19 May 2022

The Climate Impact of Hypersonic Transport

Johannes Friedrich Pletzer, Didier Hauglustaine, Yann Cohen, Patrick Jöckel, and Volker Grewe

Abstract. Hypersonic aircraft ﬂying at Mach 5 to 8 are a means for travelling very long distances in extremely short times and even signiﬁcantly faster than supersonic transport (Mach 1.5 to 2.5). Fueled with liquid hydrogen (LH2) their emissions consist of water vapour (H₂O), nitrogen oxides (NO_x) and unburnt 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. While H₂O 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 km to 35 km), with residence times of months to several years, and therefore the emitted H₂O has a substantial impact on climate via high altitude H₂O changes. Since the (photo-)chemical lifetime of H₂O is largely decreasing at altitudes above 30 km via the reaction with O(¹D) and via photolysis, one could speculate that H₂O 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 due to two potential hypersonic ﬂeets ﬂying at 26 km and 35 km, respectively. We show for the ﬁrst time that the (photo-)chemical H₂O depletion at high altitudes is overcompensated by a recombination of hydroxyl radicals to H₂O and an enhanced methane depletion, leading to an increase in H₂O concentrations. This results in a steady increase of the H₂O perturbation lifetime of up to 4.41 ± 0.20 years at 35 km. We ﬁnd a 0.083 ± 0.014 % and 0.16 ± 0.015 % depletion of the ozone layer and a 43.0 ± 4.8 Tg and 94.0 ± 4.5 Tg increase in stratospheric H₂O due to the two hypersonic ﬂeets ﬂying at 26 km and 35 km respectively. Our calculations show that the climate impact 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 H₂O.

Received: 05 May 2022 – Discussion started: 19 May 2022

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Journal article(s) based on this preprint

08 Nov 2022

| Highlight paper

The climate impact of hydrogen-powered hypersonic transport

Johannes Pletzer, Didier Hauglustaine, Yann Cohen, Patrick Jöckel, and Volker Grewe

Atmos. Chem. Phys., 22, 14323–14354, https://doi.org/10.5194/acp-22-14323-2022,https://doi.org/10.5194/acp-22-14323-2022, 2022

Short summary Executive editor

Johannes Friedrich Pletzer, Didier Hauglustaine, Yann Cohen, Patrick Jöckel, and Volker Grewe

Interactive discussion

Status: closed

RC1: 'Comment on egusphere-2022-285', Anonymous Referee #1, 16 Jun 2022

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-285/egusphere-2022-285-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2022-285-RC1
RC2: 'Comment on egusphere-2022-285', Anonymous Referee #2, 26 Jun 2022

authors have presentd a comprehensive study about the climatic impacts of air pollution from hypersonic aircrafts. Authors have covereddetailed explanation about the two set of emissions, two numerical models and the climatic impact. The reviewer 1 made very specifc and accurate observations and I agree that this manuscript may needs minor modification. In particular:

On line 131, authors states: "A comparison with satellite data shows that over the annual cycle ozone volume mixing ratios are well reproduced in the stratosphere, apart from southern polar regions and with larger differences at tropospheric altitud". Can you comment about these differences?

Include color legend for figure 1 and 2.

Suggestion: It is better to communicate the results with bar plots and not pie charts.

Lines 419-421. Is EMAC better? I believe the author plays with the ideia without explicitly stating.

Line 486: The author mention WACCM used by another author without define it.

There are some paragraphs consisting in less than 2 phrases. Each paragrah should have at least thee phrases, intro, body and conclusion.

The manucrsipt has an excessive number of tables and figures. Consider moving some into supplementary material

Citation: https://doi.org/10.5194/egusphere-2022-285-RC2
RC3: 'Comment on egusphere-2022-285', Anonymous Referee #3, 01 Jul 2022

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-285/egusphere-2022-285-RC3-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2022-285-RC3
AC1:
'Comment on egusphere-2022-285', Johannes Pletzer, 08 Aug 2022

Dear Reviewers,
we post a combined author comment on the three reviews that were submitted. We would like to thank each of the reviewers for their time and their contribution to the manuscript. Each review is addressed in an own supplement pdf, which are combined as a zip-file.
Yours sincerely,
Johannes Pletzer

Citation: https://doi.org/10.5194/egusphere-2022-285-AC1
- AC2: 'Reply on AC1', Johannes Pletzer, 15 Sep 2022
  
  Please refer to the supplement, which contains a pdf in regard to the technical comments and a pdf in regard to the reviewer's comments.
  
  Citation: https://doi.org/10.5194/egusphere-2022-285-AC2

Interactive discussion

Status: closed

RC1: 'Comment on egusphere-2022-285', Anonymous Referee #1, 16 Jun 2022

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-285/egusphere-2022-285-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2022-285-RC1
RC2: 'Comment on egusphere-2022-285', Anonymous Referee #2, 26 Jun 2022

authors have presentd a comprehensive study about the climatic impacts of air pollution from hypersonic aircrafts. Authors have covereddetailed explanation about the two set of emissions, two numerical models and the climatic impact. The reviewer 1 made very specifc and accurate observations and I agree that this manuscript may needs minor modification. In particular:

On line 131, authors states: "A comparison with satellite data shows that over the annual cycle ozone volume mixing ratios are well reproduced in the stratosphere, apart from southern polar regions and with larger differences at tropospheric altitud". Can you comment about these differences?

Include color legend for figure 1 and 2.

Suggestion: It is better to communicate the results with bar plots and not pie charts.

Lines 419-421. Is EMAC better? I believe the author plays with the ideia without explicitly stating.

Line 486: The author mention WACCM used by another author without define it.

There are some paragraphs consisting in less than 2 phrases. Each paragrah should have at least thee phrases, intro, body and conclusion.

The manucrsipt has an excessive number of tables and figures. Consider moving some into supplementary material

Citation: https://doi.org/10.5194/egusphere-2022-285-RC2
RC3: 'Comment on egusphere-2022-285', Anonymous Referee #3, 01 Jul 2022

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-285/egusphere-2022-285-RC3-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2022-285-RC3
AC1:
'Comment on egusphere-2022-285', Johannes Pletzer, 08 Aug 2022

Dear Reviewers,
we post a combined author comment on the three reviews that were submitted. We would like to thank each of the reviewers for their time and their contribution to the manuscript. Each review is addressed in an own supplement pdf, which are combined as a zip-file.
Yours sincerely,
Johannes Pletzer

Citation: https://doi.org/10.5194/egusphere-2022-285-AC1
- AC2: 'Reply on AC1', Johannes Pletzer, 15 Sep 2022
  
  Please refer to the supplement, which contains a pdf in regard to the technical comments and a pdf in regard to the reviewer's comments.
  
  Citation: https://doi.org/10.5194/egusphere-2022-285-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Johannes Pletzer on behalf of the Authors (09 Aug 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (10 Aug 2022) by Farahnaz Khosrawi

RR by Anonymous Referee #3 (25 Aug 2022)

Suggestions for revision or reasons for rejection

General comments

I see that the authors have invested substantial effort in improving
the papers taking into account the comments received from all three
referees.

I still have a few wording clarification suggestions (see below).
Should these minor points be adressed I recommend publication of the
paper.

================================================
P. 1, l. 13:

"leading to an increase in H2O concentrations." --> increase compared to what?

I suggest two sentences here:

...methane and nitric acid depletion. These processes lead to an
increase in H2O concentrations compared to a case with no emissions
from hypersonic aircraft.

P. 1 l. 14: increase --> increase with altitude (correct?)

p.1: l 16: suggest: 8-22%

p.1: l 17: suggest: 78-92%

*******************************************
The paper now contains the following text:

New: “The photochemical depletion of H2O and shift to H2
concentrations (e.g. Fig. 5.23, p. 312, Brasseur, 2005) clearly has no
large effect at these emission altitudes. So instead to the expected
removal of emitted H2O by photochemical depletion, we found a before
unknown importance of the reaction rates of the net-recombination of
H2O based on HOx recombination and an increased methane and nitric
acid oxidation. Both models show an increase in H2O perturbation
lifetime and H2O perturbation at the higher altitude, which is further
increased by the net-recombination, i.e. overcompensation of
photochemical depletion. Our finding is robust with good agreement
between the two models.”

First: do you want to be explicit about the mechanisms of H2O by
photochemical depletion? You could add the main chmeical processes or
provide a citation.

Second, I am not sure what "net-recombination of H2O based on HOx
recombination" means. I could imagine that what is meant net
production of water vaour based on the (radical recombination)
reaction HO2 + OH and an increased methane (CH4+OH) and nitric
acid oxidation (HNO3+OH) ...

as it stands the text is confusing and I think that adding the actual
reactions that are most relevant here helps.
(I think the issue is actually better described and discussed in the abstract)

*********************************************
The following text was added to the paper:

"The middle atmospheric balance of water vapour is determined by
methane oxidation, photochemical lifetimes of HOx compounds and
tropical upward transport, which is limited by the coldpoint
temperature (LeTexier et al, 1998; Brasseur, 2005; Frank et al,
2018). Polar dehydration by polar stratospheric clouds and the
sedimentation of the particles contribute to the balance."

First, it is good that the current papers are cited (Frank et al.,
2018; Winterstein & Jöckel, 2021). But I do not understand why/how
tropical upward transport is limited by the coldpoint
temperature. Isn't it the temperature in the lower stratosphere which
is relevant here rather than the temperature at one particular point?
Alternatively, do you mean that stratospheric water vapour is
influenced strongly by the entry value of water vapour? This enty
value is indeed influenced by the cold point temperature. But then
another wording/explanation is required (see also the cited papers).

References

Brasseur and Solomon, 2005.
-- you cite two editions of this book in the paper
but I think you nedd only one citation

Frank, F., Jöckel, P., Gromov, S., & Dameris, M.: Investigating the
yield of H2O and H2 from methane oxidation in the stratosphere,
Atmospheric Chemistry and Physics, 18, 9955–9973, doi:
10.5194/acp-18-9955-2018, URL
https://www.atmos-chem-phys.net/18/9955/2018/ (2018)

Winterstein, F. & Jöckel, P.: Methane chemistry in a nutshell – the
new submodels CH4 (v1.0) and TRSYNC (v1.0) in MESSy (v2.54.0),
Geoscientific Model Development, 14, 661–674, doi:
10.5194/gmd-14-661-2021, URL
https://gmd.copernicus.org/articles/14/661/2021/ (2021)

Hide

ED: Publish subject to minor revisions (review by editor) (25 Aug 2022) by Farahnaz Khosrawi

AR by Johannes Pletzer on behalf of the Authors (15 Sep 2022) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (16 Sep 2022) by Farahnaz Khosrawi

AR by Johannes Pletzer on behalf of the Authors (03 Oct 2022) Author's response Manuscript

Journal article(s) based on this preprint

08 Nov 2022

| Highlight paper

The climate impact of hydrogen-powered hypersonic transport

Johannes Pletzer, Didier Hauglustaine, Yann Cohen, Patrick Jöckel, and Volker Grewe

Atmos. Chem. Phys., 22, 14323–14354, https://doi.org/10.5194/acp-22-14323-2022,https://doi.org/10.5194/acp-22-14323-2022, 2022

Short summary Executive editor

Johannes Friedrich Pletzer, Didier Hauglustaine, Yann Cohen, Patrick Jöckel, and Volker Grewe

Supplement

https://doi.org/10.5194/egusphere-2022-285-supplement

Johannes Friedrich Pletzer, Didier Hauglustaine, Yann Cohen, Patrick Jöckel, and Volker Grewe

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Emissions from conventional aircraft contribute to climate change by forming contrails and by increasing atmospheric CO2 concentrations. To fly faster and reduce the climate impact, super- or hypersonic aircraft fuelled by liquid hydrogen or natural gas are being considered. Hypersonic aircraft would fly at more than Mach 4 in the stratosphere, up to 35 km altitude, where the peak of the ozone layer resides. The paper by Pletzer et al. presents a thorough study of the chemical and radiative impacts of such high-speed aircraft using two chemistry-climate models. The study shows that hypersonic aircraft fuelled by liquid hydrogen and cruising at such altitudes would contribute to a significant global warming although they do not emit CO2. The main radiative effect comes from additional water vapour, with only a small effect from depletion of the ozone layer. Importantly, the authors discovered that although water vapour is destroyed in the stratosphere, perturbation of local photochemistry also creates water vapour. The authors estimate that the mean surface temperature change caused by a hypersonic transport fleet would be roughly 8-20 times larger than for a subsonic reference aircraft with the same transport volume. This comprehensive study provides convincing calculations for a large climatic effect of any future hydrogen-fuelled hypersonic aircraft fleet.

Short summary

Very fast aircraft can travel very long distances in extremely short times and fly at high altitudes (15 km to 35 km). These aircraft emit water vapour, nitrogen oxides and hydrogen. Water vapour emissions remain months to several years at these altitudes and have an important impact on temperature on Earth. We investigate two aircraft fleets flying at 26 km and 35 km. Ozone is depleted more and the water vapour perturbation and temperature change are larger for the aircraft flying at 35 km.


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The Climate Impact of Hypersonic Transport

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