Why Do Planes Make White Lines?

The white lines planes make are called contrails, and they are essentially clouds formed from airplane exhaust.

What are Contrails?

Contrails are short for condensation trails. They are visible cloud formations that often appear behind aircraft, particularly jet airplanes, flying at high altitudes. These lines are not smoke but are primarily composed of water vapor that has condensed and frozen into ice crystals.

How Contrails Form

The formation of contrails involves several factors:

• Jet Engine Exhaust: Jet engines burn fuel, producing water vapor as a byproduct.
• Cold Temperatures: At high altitudes, temperatures are very low, often below -40 degrees Celsius.
• Water Vapor Condensation: The water vapor from the jet exhaust condenses and freezes into ice crystals due to the cold temperatures. According to the provided reference, "Water vapor is one of the byproducts of jet fuel combustion and will turn into ice crystals in the cold air at the high elevations where jet airplanes fly."
• Particle Nuclei: Tiny particles in the exhaust act as nuclei around which water vapor can condense and freeze.

Are Contrails Dangerous?

According to the reference, contrails "do not pose any public health risk."

Types of Contrails

Contrails can vary in appearance and duration depending on atmospheric conditions:

• Short-Lived Contrails: These disappear quickly if the air is not humid.
• Persistent Contrails: In humid air, contrails can spread out and last for hours, sometimes merging with natural cirrus clouds.

Summary of Contrail Formation