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No fumes, just wingtip vortices ! Here is some explanation to that physical phenomenon : as air is crossed by fast moving wingtip, a wingtip vortex is generated. The cores of those vortices spin at very high speed and are regions of very low pressure. That's an approximation, but these low-pressure regions form with little exchange of heat with the neighboring regions (i.e. adiabatically), so the local temperature in the low-pressure regions drops. If it drops below the local dew point, there results a condensation of the water vapor present in the cores of wingtip vortices ...which makes them visible and gives you nice pictures ! The temperature may even drop below the local freezing point, in which case ice crystals will form inside the cores.

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