This was on a hot, low-humidity day in San Diego. Those contrails should not have lasted for hours.
There is lots of air traffic in San Diego and I haven't seen large passenger 747s producing the effect. It's these military aircraft dispersing something which lingers in sky and gradually forms a very long and wide haze with an color hue that doesn't seem to suggest water vapor. Days where the RH is 10-20. It only happens every so often with no discernible relation to temperature or moisture. It's not something that I noticed more than 10+ years ago.
You linked a retracted paper full of objectively incorrect data as listed in the retraction.
Military planes and passenger planes fly at different speeds and altitudes.
This may come as a shock, but the temperature and humidity at ground level does not reflect the temperature and humidity experienced by planes during flight.
The author disputed the retraction which seems politically motivated.
The authors site (http://www.nuclearplanet.com/) and his response http://www.nuclearplanet.com/explainretractions.pdf
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