You Might Be Breathing In Unusual ‘Onion-Like’ Jet Particles If You Live Near An Airport

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.

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.

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.