Roger Clague writes in suggestions:
Contrails, does the water vapour come from the burnt fuel or the air?
According to Nasa 99.9% is from the air 0.01% from the burnt fuel.
“Nearly all of the contrail is created from the moisture in the atmosphere. “
Justified by R.G.Knollenberg(1972) paid by Nasa
“There are at least four orders of magnitude more ice present in the contrail core than the Sabreliner originally exhausted!”
A later Nasa paper says
Atlas, Wang and Duda ( 2006)
“The average ice water per meter along the length of the contrail is 1.6 104 g m 1 , some three to four orders of magnitude greater than the water vapor released by typical jet aircraft, also similar to previously reported values.”