Scientists investigate contrail formation to reduce climate impact

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From the development of new materials that make airplanes lighter to the exploration of alternative fuels, the aviation industry is making strides toward reducing its carbon footprint.

One aspect of flights that is surprisingly bad for the environment is contrails, the long, thin clouds that form behind jet aircraft as they fly through the sky.

Contrail formation is a complex process involving the mixing of hot exhaust gases with cold air. Under certain atmospheric conditions, these wispy trails of condensed water vapor can spread out to form contrail cirrus clouds, which trap heat that would otherwise be released into space. This warming effect is estimated to account for more than half of aviation's total climate impact.

Fangqun Yu, a senior researcher at the University at Albany's Atmospheric Sciences Research Center, has released a paper in Environmental Science & Technology that examines the contrail formation process, specifically exploring the role of non-volatile (soot) particles and volatile particles.

Their findings may offer new clues into how to mitigate contrail climate impacts and build more sustainable aviation.

"Soot particles, formed during fuel combustion inside aircraft engines, are known to dominate the formation of contrail ice particles," Yu said. "As the aviation industry moves toward sustainable fuels and new engine technologies, soot emissions are being significantly reduced and volatile particles formed in engine exhaust plumes (after emission) become important to analyze."

"This research aims to improve our understanding of the processes controlling the number of contrail ice particles formed during flights, focusing on both soot particle sizes and volatile particles."

The science of contrails

To arrive at their findings, the research team, which also included Bruce Anderson of the NASA Langley Research Center and Bernd Kärcher of the German Aerospace Center, conducted flight simulations using data from the recent ECLIF (Emission and CLimate Impact of alternative Fuels) field campaigns.

While previous research has found that volatile particles only matter after soot emissions are significantly reduced during flights, the new findings suggest that might actually not be the case.

Yu says their results underscore the need for a deeper understanding of the contrail formation process.

"Our research indicates that volatile particles can contribute to the number of ice particles in a contrail at medium levels of soot emissions and average temperatures in the air, extending the ranges of conditions when these particles become a factor," Yu said. "This is important as we assess the climate impact of contrails, both during current flights and for future more sustainable ones."

Focus on sustainable aviation

Yu's research is focused on size-resolved particle microphysics and aerosol-cloud interactions that affect climate change. He has studied the microphysics of particles in the atmosphere (including contrail formation) and their impact on the environment for more than two decades.

In his prior work, Yu developed an advanced model for simulating particle and contrail formation and has published a number of scientific papers on the topic.

He's currently partnering with a team at GE Research to help better understand the impact of clean aviation fuels and new engine technologies on contrail formation. Over the last year, the research team has conducted experiments inside the altitude simulation chamber at NASA's Glenn Research Center in Cleveland.

More information: Fangqun Yu et al, Revisiting Contrail Ice Formation: Impact of Primary Soot Particle Sizes and Contribution of Volatile Particles, Environmental Science & Technology (2024). DOI: 10.1021/acs.est.4c04340

Journal information: Environmental Science & Technology

Provided by University at Albany