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Not as helpful for reducing effective emissions as you might think. High altitude water vapor is just as big of a problem as CO2 as the lifetime of water vapor
by Robotbeat 6y ago
Not as helpful for reducing effective emissions as you might think.
High altitude water vapor is just as big of a problem as CO2 as the lifetime of water vapor in the stratosphere is measured in years, not days or hours like it is in the lower troposphere. Water vapor is, after all, a much stronger greenhouse gas than CO2, it's just that normally its lifetime in the atmosphere is so short so as not to matter.
So unless we can be certain these planes will fly solely in the lower troposphere (unlikely, considering the aircraft presented), then hydrogen is not actually necessarily a silver bullet and in some situations (i.e. very high altitude flight, ala Concorde) could actually be worse than kerosene.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2002JD002623 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200...
- skykooler 6y agoKeep in mind however that all hydrocarbon fuels, kerosene included, turn into both CO2 and water.
- Robotbeat 6y agoIn some ways, direct CO2 capture combined with carbon monoxide fuel (if burned super cleanly) might actually be better than either kerosene or hydrogen for super high altitude flight. The years-long lifetime of air in the stratosphere is small compared to the normal lifetime of CO2 in the atmosphere, so on net would be much better than hydrogen fuel.
- ncmncm 6y agoHow do you imagine capturing the CO2 coming out of a turbojet?
- Hypx 6y ago> High altitude water vapor is just as big of a problem as CO2 as the lifetime of water vapor in the stratosphere is measured in years, not days or hours like it is in the lower troposphere. On Table 1 of your study, it’s measuring residence time of stratospheric water vapor in days. How are you getting years from that?
- JAlexoid 6y agoThe article doesn't mention the water vapor lifetime in stratosphere... But they do mention that cryoplanes should not fly close to tropopause, for the fear of water vapor escaping to stratosphere.
- Hypx 6y agoIt states: > f Residence time = accumulated H2O divided by emitted H2O (days). Corresponding values for the stratosphere only are given in parenthesis. That seems like it is in days. Unless there's something that I missed, I'm not seeing the part that claims water vapor lasts for years in the stratosphere.
- ncmncm 6y agoCO2 delivered to the stratosphere certainly stays there a long time; nothing there uses it.
- neuronic 6y agoThe obvious solution is to plant rainforests in the stratosphere.
- benhurmarcel 6y agoIf that’s such a problem we could store onboard the water produced by the fuel cell.