Incorrect. The condensation you are seeing in the air is a product of combustion. If no water was added to the air, then compressing it and decompressing it would not create a cloud or vapor trail.
Yes, the lower pressure can create a very temporary contrail, and in rare situations where the engine exhaust also cools down below freezing before it reaches ambient pressure, ice crystals can form and create a longer more visible contrails. Realistically, what you are seeing in a contrail is water vapor from combustion. Seriously, H2O and water are the largest products of combustion, and it’s like 99% of what you are seeing behind aircraft.
The longetivity of a contrail is determined by the atmospheric conditions. In sufficiently dry air no contrail is formed as the water introduced by the combustion isn’t enough to raise the frost point to the ambient temperature. More humidity means that the contrail may form and even persist for a while without sublimating away (Cirrus homogenitus). If the air is even more humid, the contrail may even start to grow and change shape (turning into Cirrus homomutatus). This last case is what I suspect gets the foil hats most riled up about “chemtrails”.
Incorrect. The condensation you are seeing in the air is a product of combustion. If no water was added to the air, then compressing it and decompressing it would not create a cloud or vapor trail.
Edit: Fine. It’s mostly incorrect.
https://en.wikipedia.org/wiki/Contrail
Yes, the lower pressure can create a very temporary contrail, and in rare situations where the engine exhaust also cools down below freezing before it reaches ambient pressure, ice crystals can form and create a longer more visible contrails. Realistically, what you are seeing in a contrail is water vapor from combustion. Seriously, H2O and water are the largest products of combustion, and it’s like 99% of what you are seeing behind aircraft.
The longetivity of a contrail is determined by the atmospheric conditions. In sufficiently dry air no contrail is formed as the water introduced by the combustion isn’t enough to raise the frost point to the ambient temperature. More humidity means that the contrail may form and even persist for a while without sublimating away (Cirrus homogenitus). If the air is even more humid, the contrail may even start to grow and change shape (turning into Cirrus homomutatus). This last case is what I suspect gets the foil hats most riled up about “chemtrails”.
https://cloudatlas.wmo.int/en/explanatory-remarks-and-special-clouds-cirrus.html