Posted on 05/22/2025 7:28:59 AM PDT by Red Badger
Scientists had never detected these strange particles in plane exhaust before. (santi lumubol/Shutterstock)
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In a nutshell
* Scientists have discovered previously unknown “onion-like” nanoparticles in jet engine exhaust that could pose new health concerns, especially for people living near airports.
* These tiny particles, measuring just 10-20 nanometers, appear downstream from aircraft engines and may originate from the breakdown of lubrication oil, not fuel combustion.
* Unlike traditional soot, these particles remain even when using sustainable aviation fuels, posing a potential challenge for clean aviation initiatives.
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TSUKUBA, Japan — Living near an airport might be more complicated than just dealing with noisy takeoffs. Scientists have just discovered mysterious “onion-like” particles in aircraft exhaust that have never been seen before. These tiny structures could change how we think about air travel’s impact on our lungs and might explain why communities near airports report higher rates of respiratory issues.
A team of international researchers found these unusual particles while examining commercial aircraft engines at a testing facility in Switzerland. Unlike the soot particles we’ve known about for decades, these newly discovered particles have unique internal structures with concentric circular layers, resembling the layers of an onion, that could potentially affect how they interact with our lungs when we breathe them in.
New Aircraft Exhaust Particles The study, published in the journal ACS ES&T Air, examined particles from two types of commercial jet engines, the CFM56 and PW4000 series, both commonly used in airliners like the Boeing 737 and Airbus A330. These engines power thousands of commercial flights globally every day, making their emissions a significant concern for air quality around major airports.
By capturing these tiny particles and examining them under high-resolution transmission electron microscopy, the researchers identified four distinct types of particles. Only one of these, the “turbostratic” soot particles with disorganized carbon layers, was previously known to exist in aircraft exhaust. The other three types, including the onion-like particles, had never been documented before in aircraft emissions.
Southwest Airlines jet
Researchers tested engines used in Boeing 737 planes, commonly used by commercial airlines. (Photo by Nick Morales on Unsplash)
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The composition of the particles changed as the exhaust moved further from the engine. Close to the engine, traditional soot particles dominated, making up about 68% of particles in one engine type. But just 15 meters downstream, a distance that better represents what people near airports might actually breathe, these newly identified particles made up over 99% of all particles, while soot nearly disappeared.
Communities Near Airports
This spatial difference likely explains why these particles have eluded detection until now. Most previous studies have only sampled exhaust directly at the engine exit, not downstream where human exposure would typically occur.
Prior research has already linked ultrafine particles from aircraft to health problems. A 2018 study published in Environmental International found that people exposed to ultrafine particles near airports showed reduced lung function and increased inflammation, particularly those with asthma.
Where do these unusual particles come from? The research team hypothesizes they’re formed when jet engine lubrication oil is released through the engine’s “breather vent,” then undergoes evaporation, nucleation, and partial pyrolysis (decomposition due to heat) in the hot exhaust stream. This would explain why the particles appear further downstream, as they need time to form in the cooling exhaust plume.
Different engine models showed different proportions of these particles. The PW4000 engines produced more onion-like particles than the CFM56 engines, possibly because of differences in the location of their oil breather vents. In PW4000 engines, the vent is located farther upstream at the bottom of the engines in the cold bypass flow, while in CFM56 engines, it’s at the center of the engine core nozzle, surrounded by hot gases exiting the turbine.
Sustainable Aviation Challenges
The size of these newly identified particles also raises concerns. Most measured between 10 and 20 nanometers in diameter, tiny enough to penetrate deep into lung tissue and potentially enter the bloodstream. Their unique physical structure might influence how they interact with human respiratory systems in ways we don’t yet understand.
The industry has been working toward more sustainable aviation fuels (SAFs) that produce less soot, but these efforts might not address these particles. While SAFs can significantly reduce soot particles due to their lower aromatic content, their findings suggest that these onion-like particles would likely still be present even when using cleaner fuels.
Airplane exhaust particles
(a) Turbostratic (soot) particles (diameter 67 nm). (b) Onion-like particles (diameter 17 nm). (c) Amorphous particles (diameter 26 nm). (d) Trace amorphous particles (diameter 17 nm). The four particle types were divided into single and agglomerated particles, and their fractions are shown. Click to expand. (Credit: NIES/ZHAW/TMU)
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With global air travel continuing to grow and many major airports located near densely populated areas, understanding the full spectrum of aircraft emissions is critical for public health policy and airport management strategies.
The mystery of these onion-like particles raises urgent questions about what we’re really breathing when planes take off and land. Even with advances in sustainable fuels, we may still be facing invisible health challenges that affect millions living in flight paths around the world.
Paper Summary
Methodology
Researchers conducted their study at an engine test facility at SR Technics in Zurich Airport, examining commercial CFM56 and PW4000 series turbofan jet engines under various thrust conditions. They collected samples both at the engine exit and 15 meters downstream using specialized equipment. The team measured particle size distributions using scanning mobility particle sizers and engine exhaust particle sizers. For detailed particle analysis, they collected samples on copper grids and examined them using high-resolution transmission electron microscopy (HRTEM) to visualize the internal structures of individual particles.
Results
The researchers identified four distinct types of particles: turbostratic (soot), onion-like, amorphous, and trace amorphous. At the engine exit, turbostratic particles dominated (up to 68%), mostly as agglomerates. However, at 15 meters downstream, these newly identified particles (onion-like, amorphous, and trace amorphous) made up over 99% of all particles examined. The particles had sizes generally between 10-20 nanometers. The team hypothesized that the onion-like particles form when jet engine lubrication oil is released through the breather vent, then undergoes evaporation, nucleation, and partial pyrolysis in the exhaust.
Limitations
The HRTEM samples from the engine exit and 15 meters downstream were not collected simultaneously, so individual engines and thrust settings weren’t completely identical between the two collection points. The samples of CFM56 engine exhaust were only available at the engine exit, limiting direct comparisons with downstream samples from the same engine. Additionally, particle loss inside sampling lines and instruments wasn’t corrected for all measurements, which could affect the absolute concentrations measured.
Funding/Disclosures
The study was supported by the Environment Research and Technology Development Fund of Japan’s Ministry of the Environment, Research Funding from the National Institute for Environmental Studies, a Scientific Exchanges grant from the Swiss National Science Foundation, and Swiss Federal Office of Civil Aviation projects. The authors declared no competing interests.
Publication Information
The study titled “Unique Microphysical Structures of Ultrafine Particles Emitted from Turbofan Jet Engines” was authored by Akihiro Fushimi and colleagues from the National Institute for Environmental Studies in Japan, Zurich University of Applied Sciences in Switzerland, National Institute of Advanced Industrial Science and Technology in Japan, Environmental Science Analysis and Research Laboratory in Japan, and Tokyo Metropolitan University. It was published in the journal ACS ES&T Air in 2025.
What was chemtrails are now onion trails.
I live in the flight path of a civilian airport that used to be an Air Force Base, and I like being in the flight path.
I lay in my hammock with binoculars and my FlightRadar24 application which lets me look at the planes and track them. I love it.
But that is me. Having spent years around military runways, I have found that military aircraft have a distinctly different sound, and I can tell the difference instantly between a private jet and an F-15 or an A-10 (which is not hard to do...)
But I can imagine having a Boeing 777 taking off at a thousand feet is quite a different thing.
My wife’s grandparents lived in East Boston...they had the planes from Logan taking off right over their house, and the Blue Line less than 100 feet from the back of their house.
The first time I went there with my wife to visit them, I was astonished when the train went by, and the whole house would shake and vibrate, and then, a minute later, a plane would take off and go right over the house, which was deafening and made the whole house vibrate and shake...
And while this was happening, except for me, nobody even as much blinked an eye! The were totally inured to the noise and shaking!!!! (both of her grandparents were nearly deaf anyway...)
The CFM56-7B20 burns 2 pounds of fuel per SECOND (7,200 pounds per hour). That engine consumes lubricating oil at a rate of 0.6 pounds per HOUR.
In other words, 0.000083 pounds of lubricating oil are burned for every pound of fuel burned.
They are worried about emissions coming from the lubricating oil?
Conclusions:
1. Pointy-headed people have too much time on their hands and too much grant money.
2. Too many PhD candidates are looking for troubles to “research.”
3. The university systems are churning out too many PhDs and Post-Docs.
My adolescent years we lived in a house a couple hundred feet from a railroad track.
After the first month you don’t even notice them, even at night.....................
Has any studies been done on aircraft exhausts at all altitudes? Also testing aircraft fuels should be useful.
My grandparents lived right next to very very busy train tracks in Central California - at night, the train light would shine right into the house, I was scared to death as a little kid b/c I thought the trains were coming through house.
Now, I live about 1/4 mile from a major train line, freight, metrolink and AmTrak. I can tell the difference between all three and love the sound of the train horn and bell - brings me right back to my childhood.
They built DFW Airport in the middle of no where Texas. Then a bunch of rich foreigners built homes to be near the airport and instantly started filing law suits because of the noise and smell. Like they didn’t know there was an airport there before they built.
I’ve often wondered if somebody isn’t getting rid of certain types of petroleum waste by putting it in jet fuel to be burned up at 39k feet................
Are they onion-like in smell or in taste?
I dunno, jet engines are too hot to taste.................
Yep. Same thing around LAX in Los Angeles - people moved in AFTER the airport was built - and then tried to sue b/c of noise and pollution. They didn’t get very far...
I lived for a few months across the street from a busy freight yard. No sleep at all for the first week (or so it seemed), but after that no problem. Almost missed the noise after I moved.
Sounds like another “travel is dangerous, so everybody but me should stay home” screed from the Democrat party.
Sounds like another “travel is dangerous, so everybody but me should stay home” screed from the Democrat party.
I see business opportunities for testing aviation fuels and aircraft exhausts. I’m to old for that now but somebody honest could make some bucks with that idea. Perhaps a chemist with a good lab and an airplane.
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