Are “chemtrails” for real?

Dear Tom,
Are “chemtrails” for real?
— Albert O’Mell, Deerfield

Dear Albert,
There is no such thing as “chemtrails,” and the rumors about chemicals intentionally being sprayed into the atmosphere from the exhaust of high-flying jet aircraft are persistent but false. Water vapor is one of the byproduct gases resulting from the combustion of jet fuel in aircraft engines. Temperatures at jet flight levels (about 30,000-40,000 feet aloft) are usually in the range of 30 below to 70 below zero, even in the summer. Water vapor injected at high temperatures into such a cold environment condenses practically instantaneously into ice crystals that, when viewed from a distance, appear as the fleecy white trails that we see. Contrails will not form or will evaporate in a few seconds if the air at flight level is dry, or, if the air is moist, they can persist for hours and expand to cover the entire sky.