In some ways, direct CO2 capture combined with carbon monoxide fuel (if burned super cleanly) might actually be better than either kerosene or hydrogen for supe

In 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.