Question

Why do jets leave a white trail in the sky?

• A. The exhaust gas has ice crystals in it
• B. The trails are formed due to the mixing of water vapour in the jet exhaust with the wet cold air
• C. A mixture of carbon dioxide and carbon monoxide is released from the engines
• D. Because of the water vapours coming out of the catalytic converters of the exhaust system

Answer 1

The correct option is B The trails are formed due to the mixing of water vapour in the jet exhaust with the wet cold air

The white trails what you see when a jet flies in the sky are actually some sort of ice crystals, which may sometimes even persist for hours and span across miles wide! Sometimes these trails are so short-lived that we hardly get to see them. These trails are called contrails (short for “condensation trails”). Temperature and humidity at the altitude at which they're formed decide the span and timelines of these contrails.



But how is it that they're formed?

Jet exhaust usually contains water vapour as one of its constituents. Because the air is cold and wet at such high altitudes, this water vapour mixes with cold air which tends to freeze, forming ice crystals. It is these ice crystals which are spread out that give rise to these white trails.

Some contrails which may last for hours together resemble cirrus clouds. In fact, these are so prevalent that they are of special interest as they are suspected to have an effect on global climate!