December 8, 2022     

DATA DIVE: Emission Reductions You Can Actually See

Contrails-banner.jpgNASA's "flying laboratory" follows behind a German airplane using alternative fuels

You know those cloudy trails you see behind an airplane as it flies overhead? Those are called contrails. They’re essentially ice crystals made from vapor released by the airplane’s engine exhaust. While ice crystals might not be something you associate with greenhouse gas emissions, they in fact have even worse climate impacts than carbon dioxide.

Researchers have suggested that sustainable aviation fuel (SAF) can help cut airplanes’ ice crystal contrails. Recently, NASA and the German Aerospace Center (DLR) set out to quantify these emission reductions and arrived at some very impressive results. According to the latest tests, SAF can reduce airplanes’ contrails by 50 to 70 percent.

“We know that contrail formation from jet exhaust has a larger, more immediate impact on climate than carbon dioxide emissions,” said Richard Moore, a NASA scientist at Langley Research Center in Virginia. “This research shows we have an opportunity using alternative fuels to make immediate changes that could help the planet.”

So, how does all this work?

Planes running on conventional jet fuel emit water vapor along with plenty of soot. The water vapor interacts with the soot or other particles in the air, forming ice crystals. These crystals stick around, causing what’s known as “light extinction,” essentially scattering sunrays in the atmosphere. However, planes that run SAF emit much less soot. This results in fewer ice crystals, which means fewer contrails.

In other words, you may actually be able to see with your naked eyes how SAF reduces emissions.

Scientists from NASA and DLR observed emission reductions during joint research flights staged over Ramstein Air Base in Germany. During these flights, the DLR Advanced Technology Research Aircraft A320 ran three different blends of alternative fuels. NASA’s DC-8 “flying laboratory” flew behind the German aircraft, collecting and testing the gases and particles it emitted. 

Results of the study, published in a recent issue of Nature, stated that “lower ice numbers as measured in the contrails from sustainable aviation fuel blends directly translate into reduced contrail extinction, reduced energy deposition in the atmosphere and reduced warming.”

Researchers even went a step further, writing, “the development of sustainable, bio-based fuels for reducing soot emissions should contribute to lessening the regional and global climate impact of aviation.”

Still, being able to see emission reductions and being able to commercialize them are two very different things. As reported last issue, SAF currently represents less than 0.1 percent of all jet fuel consumed (see “Is SAF Ready for Takeoff?”). Will the new study help fuel further investments?

We’ll have to see…