White trails in the sky: why aircraft brands are a concern – 06/17/2023 – Market

On cold days, it is common for planes to leave a white trail in the sky, which can stay there for a few minutes or for several hours. What happens next to that material, however, has yet to be studied by science.

These trails are called “contrail”, short for “condensed trail”. The phenomenon occurs when the gases released by aircraft engines freeze, forming ice crystals that can be seen from afar. Generally, the phenomenon occurs between 8 km and 13 km of altitude.

The contrail has pollutants such as particulate matter, nitrogen oxide and sulfur dioxide. Generally, the trail does not include CO2.

“This condition not only impacts climate, but also air quality and public health,” explains Florian Allroggen, director of climate and aerospace sustainability at MIT.

The researcher spoke on the subject at the general meeting of IATA (International Air Transport Association), in Istanbul. The entity, which represents more than 300 companies in the sector, launched this year a task force to reduce emissions of pollutants other than CO2, which includes studying ways to reduce contrail.

The pressure for companies to adapt comes especially from the European Union. As of 2025, companies operating on the continent will have to map and report their emissions of other pollutants, in addition to CO2.

Airlines have pledged to become carbon-neutral by 2050, but need to flesh out plans further for other waste generated by flights.

“Most contrails last less than ten minutes. However, they can persist when the air humidity exceeds 100% in relation to ice, and form clouds that can last up to a day”, analyzed Roger Teoh, a researcher at Imperial College of London, in a 2020 study on the subject.

These contrail clouds also end up reflecting solar radiation back to Earth, generating a greenhouse effect that contributes to global warming, albeit on a small scale.

“Flight rearrangement strategies in areas supersaturated with ice seem to be the most feasible mitigation solution to be implemented in the short term”, considers Teoh. A study by him found that 2% of flights in Japan generated 80% of the total frozen trails, and that changing the routes of 1.5% of flights would cut the problem by 59%.

The formation of contrail clouds occurs more frequently in areas with a large number of flights, such as on airport approach routes. IATA estimates that less than 10% of flights generate such contrails.

There are also advances in mapping the areas and climatic conditions that favor the formation of ice crystals, so that planes can avoid them. Some companies in Europe already offer this service.

However, if the route deviation is too long, aircraft engines will burn more fuel and, consequently, increase costs and pollute more.

Another possible solution is to adopt less polluting engines and use cleaner fuels. The advancement of SAF (sustainable aviation fuel), however, remains slow. In 2022, 300 million liters were produced, about 0.1% of the total used by aviation. IATA projects that production will reach 69 billion liters in 2028, as new production units come into operation.

The reporter traveled at the invitation of IATA.