043018HuntingtonBeachCaTripMP0029
SHOT 4/27/18 9:09:04 AM - Clouds, sky and a contrail off a commercial jetliner during a flight from Denver International Airport to John Wayne/Orange County Airport. Contrails are line-shaped clouds produced by aircraft engine exhaust or changes in air pressure, typically at aircraft cruise altitudes several miles above the Earth's surface. Contrails are composed primarily of water, in the form of ice crystals. The combination of water vapor in aircraft engine exhaust and the low ambient temperatures that exist at high altitudes allows the formation of the trails. Impurities in the engine exhaust from the fuel, including sulfur compounds (0.05% by weight in jet fuel) provide some of the particles that can serve as sites for water droplet growth in the exhaust and, if water droplets form, they might freeze to form ice particles that compose a contrail. Their formation can also be triggered by changes in air pressure in wingtip vortices or in the air over the entire wing surface. Contrails, and other clouds directly resulting from human activity, are collectively named homogenitus. (Photo by Marc Piscotty / © 2018)
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