Yes, jet engines (and car engines, and boat engines, and rear ends) emit exhaust products. If you want to call them "chemtrails" be my guest. If you drove your car where it was cold and humid enough, it would produce contrails. Just ask someone from Canada about ice fog.
In high northern or southern latitudes, especially around urban areas Ice fog can form. Ice fog is any type of fog where the droplets freeze into very tiny crystals in midair. This type of fog forms when the air temperature is well below freezing, generally below zero, so that any vapor present almost immediately condenses. Vapor is added to the air by automobile exhaust, furnaces and industrial plant exhaust. Ice fog can be extremely dense, posing driving hazards and the fog can last all through the day and night.
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