>>Jet engines also emit the usual things engines emit: carbon dioxide, smoke, and small amounts of unburnt hydrocarbons, oxides of nitrogen, carbon monoxide and small amounts of other things.
Contrail Science - Chemtrail Pseudoscience » Chemical Analysis of Contrails
Having said that, the jet engine PRODUCES the water vapor itself. The cold of the air freezes it. What you need to do is describe why they wouldn't persist for long periods. The present view is that the surrounding air needs to be quite humid. You claim contrails have come about in none humid areas. Proof?