Re: A real explanation from a professional

I want to correct one part of the explanation given above. Water is one of the chemical byproducts of combustion, along with carbon dioxide and other compounds. The ice that allows you to see the contrail is the water vapor in the jet exhaust condensing and then freezing in the very, very cold upper atmosphere. There's not much water in the atmosphere up there (hence no clouds either). The water comes from the jet fuel itself.
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As far as government conspiracies, kudos to our governments (federal and state) for caring about the air we breathe. If you look, you can see the efforts and results everywhere. Southern California (LA) has far fewer pollution alert days than it did 30 years ago. Cars run far cleaner than they did in times past because of government mandates and available technologies. Despite the vast increase in the number of cars on the road, the air is cleaner overall. Because of the EPA, the level of some ozone depleting chemicals such as CFCs (used in air conditioning and refrigeration) is now decreasing.
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Aircraft exhaust is a concern because of the many trace compounds created in the furnace of a jet engine's combustion chamber, and because there are many thousands of aircraft in the air at any time. But it's not easy to put a catalytic converter on a jet engine.

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