What is the white smoke from the tail of the plane?

This is not real smoke, but the exhaust gas from the plane is mixed with the surrounding air.

The aircraft consumes a lot of fuel when flying, and the generated water vapor and some heat are discharged from the aircraft with the exhaust gas, enter the atmosphere, and quickly mix with the surrounding air to form a condensation trail. Its formation process is different from dew on the ground, frost and clouds in the air. The exhaust gas from high-altitude aircraft is mixed with ambient air, and the saturation of this mixed gas depends on the net effect of heat and water vapor increment.

The process of aircraft generating aerodynamic wake is that the aircraft is flying in nearly saturated air, and the air near the propeller and the top of the wing is adiabatic cooled and condensed due to dynamic depressurization. But this situation is relatively rare.

Aircraft wake cloud does not exist for a long time and usually disappears quickly, but it can exist for more than 1 hour when conditions are favorable, and can expand into a relatively wide cloud layer. The seasonal variation of aircraft wake height is not obvious. Generally speaking, it appears more frequently in winter than in summer.