Ask Marilyn

By Marilyn vos Savant

I think the white trails left behind by jets are fuel ex­haust. But my friends believe they are chemicals purposely ejected from the plane. What's the truth?

-Donna Zubowicz,

Lake Havasu City, Ariz.

The trails in the wake of jets are mostly condensation, caused by the engine emitting hot, humid air into a cold atmosphere. That's why they are called "contrails," short for "condensation trails." Think of this as similar to seeing your breath on a cold winter's day. But the trails also do con­tain exhaust, comparable to the way automobiles emit exhaust. Ugh. Yet as far as pollution and climate change are concerned, contrails are considered a minor component.

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marilyn@parade.com