Aero Blog

Contrails or vapour trails are visible trails of condensed water vapour made by the exhaust of aircraft engines. As the hot exhaust gases cool in the surrounding air they may precipitate a cloud of microscopic water droplets. If the air is cold enough, this trail will comprise tiny ice crystals.

The main products of hydrocarbon fuel combustion are carbon dioxide and water vapour. At high altitudes this water vapour emerges into a cold environment, and the local increase in water vapour can push the water content of the air past saturation point. The vapour then condenses into tiny water droplets and/or deposits into ice. These millions of tiny water droplets and/or ice crystals form the vapour trail or contrails.

The grounding of aircrafts for three days in the United States after September 11, 2001 provided a rare opportunity for scientists to study the effects of contrails on climate forcing. Measurements showed that without contrails, the local diurnal temperature range (difference of day and night temperatures) was about 1 degree Celsius higher than immediately before; however, it has also been suggested that this was due to unusually clear weather during the period.

Vapour trails or contrails, by affecting the Earth’s radiation balance, act as a radiative forcing. Studies have found that vapour trails or contrails trap outgoing longwave radiation emitted by the Earth and atmosphere (positive radiative forcing) at a greater rate than they reflect incoming solar radiation (negative radiative forcing).

Dissipation of contrails with a powerful microwave beam aligned behind aircraft engines is being touted as a possible solution to help address air transport’s effects on the climate.

It is believed that ice particles could be prevented from forming, or be evaporated once formed, by remotely heating them, together with condensation nuclei such as soot in the exhaust plume.

The remote heating of condensation nuclei could be achieved by applying electromagnetic radiation, such as microwaves. Depending on assumptions made, calculation shows that the power required for such a device could be as little as 0.1% of the aircraft engine power.

With theoretically low energy requirements and associated weight penalty, existing aircraft could possibly be retrofitted and new aircraft equipped with this technology.

Could this be the end of blue skies, full of aircraft contrails? What do you think?