Why do planes leave white lines (contrails) in the sky?
About This Video
Why do planes leave white lines (contrails) in the sky? Burning jet fuel produces hot water vapor. At cruise altitude the air is usually colder than -40 degrees, so the vapor freezes almost instantly into tiny ice crystals: a line-shaped cloud. In dry air the ice evaporates within seconds; in humid air the trail can last for hours and spread like a natural cirrus cloud. So it isn't smoke: it's water, frozen by the cold, and kept alive by humid air.
Sources:
– FAA / EPA Aircraft Contrails Factsheet:
– NASA Langley (P. Minnis), contrails overview:
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