Information on Contrails from Aircraft

The U.S. Environmental Protection Agency (EPA) is not aware of any deliberate actions to release chemical or biological agents from jet aircraft into the atmosphere.

• Jet aircraft do form contrails under certain atmospheric conditions – for the same reason that we can see our breath on a cold day.
• Contrails are line-shaped clouds or "condensation trails" composed of ice that can be visibly seen behind jet aircraft engines, under certain atmospheric conditions.
• Jet aircraft engines operating at high altitudes produce combustion-related emissions as part of the exhaust emissions from the engine. These aircraft emissions are no different from/like the types of emissions from diesel car or truck emissions.
• At high-altitude, however, water vapor present in the surrounding ambient atmosphere reacts with these emissions to form contrails. These contrails then spread due to atmospheric turbulence and sometimes join with other contrails and expand into large, natural-looking clouds with cirrus characteristics that can cover large areas of the sky.
• For a contrail to form there must be enough moisture in the air and the temperature must be cold enough to form ice crystals at the altitude at which the aircraft jet is flying. If the temperature is too warm or the air is too dry, contrails will not form.