Flying is one of the fastest-growing sources of greenhouse gas emissions, according to the European Commission. And while road transport emits more carbon over, flying is energy-intensive per person. Flying from Lisbon to New York and back produces roughly the same emissions as an average European Union citizen heating their home for a year.
The aviation industry has adopted several measures to cut its emissions. But data on the impact of these measures has been limited.
Researchers from the German Aerospace Center provide some new insights in a study in the journal Science Advances. The researchers estimated the effects of sustainable aviation fuels and modern efficient engines on aircraft pollution.
“Our findings demonstrate that a substantial reduction of particle emissions requires a synergistic approach, combining the use of alternative fuels with modern engine technologies,” the team writes. “The results may support the optimization of future engine technologies for lower particle emissions…and thereby help to reduce the impact of aviation on climate and public health.”
In addition to carbon dioxide, jet engines emit ultrafine particle pollution, composed mainly of tiny soot and sulfate particles. These emissions impact human health on the ground. Under the right atmospheric conditions, the particles also lead to contrails. That’s because hot water vapor in engine exhaust condenses on the tiny solid particles and freezes. Contrails can persist for hours and trap heat in the atmosphere.
Reducing aviation’s non-carbon dioxide emissions will be key to meet the Paris Agreement’s goal of limiting global warming to 1.5°C, past studies have shown. Sustainable aviation fuels and modern lean-burn engines, which use a higher air-to-fuel ratio, should both reduce particulate emissions.
But “the influence of the fuel composition…on particle emissions in rich-burn and lean-burn combustor conditions has hardly been explored in flight experiments,” Rebecca Dischl and colleagues write in the paper.
So the team analyzed measurements of in-flight particulate emissions from two Airbus airplanes. Both planes flew on lean-burn engines, but one used conventional fuel while the other used sustainable aviation fuel.
As the airplanes cruised, a smaller test aircraft equipped with inlets on the fuselage followed. The test craft had various instruments for measuring aerosol particles and trace gases. Two instruments mounted under the wings detected ice particle number and size. The test flights were conducted in November 2021 and March 2023.
Earlier this year, the research team reported that aircraft made contrails even when they produced less soot. Liquid particles such as engine oil droplets, it turns out, led to contrail formation.
Their new analysis shows that the advanced engines reduce soot particle emissions by three orders of magnitude compared with conventional engines. Further, under the rich-burn conditions, soot particle emissions depended exponentially on the hydrogen content of the fuel burned.
Meanwhile, volatile particle emissions from sustainable fuels increased with the sulfur content of the fuel. And the emissions varied considerably even between engines of the same type, the authors found.
By comparing particle emissions from different aviation fuels and aircraft engines, the findings enhance the understanding of aircraft emissions in the low-soot regime. This data should serve as valuable input for advancing jet engine model development, the researchers write. Optimizing fuel composition and engine technology would reduce particle emissions, improve airport air quality, and mitigate contrails.
Source: Rebecca Dischl et al. Mitigating aviation’s environmental impact through alternative fuels and cleaner engines. Science Advances, 2026.
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