According to NASA, the ice crystals in the contrails have the same structure as naturally occurring clouds, so they can remain trapped in the atmosphere for up to several hours, affecting the surface temperature, again in a similar way to classical clouds. Condensation trails can cause local temperature increases, which in turn affect climate change.
Richard Moore, a NASA researcher, says they are aware that contrails from jet engine exhaust have an immediate negative impact on the climate, which is faster than carbon dioxide emissions. But our research has shown a loophole that offers the potential to to reduce this impact by using alternative fuels, thereby improving the state of the planet.
The composition of aircraft combustion products is, very simply, just water vapour and soot, which immediately starts to cool and condense (hence the name contrail) as it exits the engine. Condensation, or precipitation, also requires the presence of some kind of microscopic particles to trap the water molecules – soot particles, which are also present, are perfect for this purpose. Plus there are other substances circulating in the atmosphere which can also be the basis for condensation. However, alternative fuels release less soot during combustion, so fewer ice crystals are formed, which in turn swell more as the amount of water does not change. But these larger crystals also fall out of the cold air layer more quickly and melt.
It is interesting that experts have already described this process several times using computer modelling, but their practical experience has been lacking for a long time. Until 2018, to be precise, when experiments were carried out at the US airbase in Ramstein, Germany: an A320 research aircraft was refuelled with alternative biofuels and, after take-off, a DC-8 , a so-called “flying laboratory”, was sent to take samples of the air and analyse them. This experiment was the final stage of a years-long project in which several aircraft types and fuels were tested, but it was the latter tests that provided the researchers with the information they needed.
From the results obtained, the researchers concluded that alternative fuels are both less harmful to the environment and significantly reduce the amount of contrails. All that remains is to put it into practice, and then we can say that the collaboration between the two space agencies has resulted in a more sustainable air traffic.