In Berlin Spandau (Germany)…
Contrails (short for “condensation trails”) or vapour trails are visible trails of condensed water vapour made by the exhaust of aircraft engines. As the hot exhaust gases cool in the surrounding air they may precipitate a cloud of microscopic water droplets. If the air is cold enough, this trail will comprise tiny ice crystals.
The wingtip vortices which trail from the wingtips and wing flaps of aircraft are sometimes partly visible due to condensation in the cores of the vortices. Each vortex is a mass of spinning air and the air pressure at the centre of the vortex is very low. These wingtip vortices are unrelated to the exhaust from the engines.
Depending on atmospheric conditions, contrails may be visible for only a few seconds or minutes, or may persist for many hours.