Originally Posted by
Excargodog
Don’t know that THAT would be a realistic concern. If anything it might increase the albedo a little, reflecting solar energy back up and decreasing global warming. But in any event, it’s difficult to see where a combustion product of water would be worse than a combustion product of water, CO2, oxides of Sulfur, Oxides of Nitrogen, unburned fuel, and soot, which are the products of combustion of Jet A.
Water and CO2 have different absorption spectra... water vapor lets some light through, and absorbs some light which becomes heat. Then the light that got through reaches the ground and heats it. The ground then radiates IR back up, and water vapor absorbs IR pretty well, so that stays in the biosphere as heat.
There's a graph in this article:
https://jpenhall.wordpress.com/2012/...-water-vapour/
Carbon-neutral SAF might actually be better for global warming than H2.
Also considering the stoichiometric process Jet A combustion produces only C02 and water vapor. The other pollutants are the results of impurities or catalytic processes involving atmospheric N2.
An H2 combustion of an equivalent amount of O2 would produce more H2O than Jet A and zero carbon... so while you're reducing the carbon you emit more H2O than before so now that's significant for greenhouse purposes. The other pollutants need to be considered too of course, but there's no equation to compare/contrast C02 vs. smog pollution... that's in the eye of the beholder.