The fuel is released as a fine spray
When an aircraft designed for fuel jettison needs to lose weight quickly, pumps send fuel through dedicated outlets, usually near the wings. The outlets and the rush of air break the stream into small droplets. This spreads the fuel through a much larger volume of air than a single falling stream would occupy.
That matters because the droplets are exposed to air as they fall. Some evaporate, and the resulting vapor mixes and dilutes in the atmosphere. The fuel does not vanish at the moment it leaves the airplane: what remains can continue downward, with how much reaches the ground depending on conditions such as altitude, wind, temperature, and droplet size.
Why the release is managed
Crews generally jettison fuel only when an emergency makes it important to reduce the airplane’s weight—for example, so it can land sooner at a weight below its maximum landing limit. They follow procedures intended to release it at altitude and over an appropriate area, rather than over a built-up place. Not every airplane has a jettison system; many can instead burn fuel while holding, if circumstances allow.
Jet fuel can harm people, animals, and plants in concentrated amounts, but dispersal and dilution reduce the chance that a jettison creates a dangerous concentration at the surface. The practical aim is to trade a controlled release into open air for a safer landing—not to make the fuel harmless, but to keep it from arriving as a concentrated spill.
