A team of international researchers has made a surprising discovery in aircraft engine exhaust: tiny particles with an unusual “onion-like” structure.
These nanoparticles, found during emission tests at Zurich Airport in Switzerland, were identified through high-resolution transmission electron microscopy (HRTEM).
The research was led by scientists from the National Institute for Environmental Studies in Japan, Zurich University of Applied Sciences in Switzerland, and Tokyo Metropolitan University, among other institutions.
Their findings were recently published in ACS ES&T Air.
For years, studies have shown that aircraft engines release nanoparticles—tiny particles less than 50 nanometers in diameter—into the atmosphere.
These emissions come from the ground all the way up to the upper levels of the troposphere, creating concerns about air quality and health effects, particularly near busy airports.
Aircraft exhaust is known to produce soot particles, which are primarily non-volatile and made of carbon. However, the new study found that not all particles fit the typical profile of soot.
Using advanced imaging techniques, the researchers observed four distinct types of particles coming from commercial turbofan jet engines. Type (a) consisted of typical soot particles with layered graphene-like structures.
But what surprised scientists were three additional types: type (b), which had an “onion-like” structure with multiple spherical layers of graphene; type (c), which were amorphous and lacked any clear crystal structure; and type (d), which were trace amorphous particles, appearing thin and non-crystalline.
The onion-like nanoparticles are particularly intriguing because this is the first time they have been detected in aircraft exhaust or the atmosphere.
In nanomaterial science, similar onion-like structures are typically created by applying high energy to soot. Their presence in aircraft emissions raises new questions about how they form and what role they might play in atmospheric chemistry and health.
The researchers examined the particles at two different points: right at the engine exit and 15 meters downstream. Interestingly, soot particles dominated near the engine but dropped to less than 1% just 15 meters away.
Farther from the engine, onion-like, amorphous, and trace amorphous particles became the most common. These particles were small—only about 10 to 20 nanometers in diameter—and appeared to be mostly single and spherical.
Further analysis suggests that these unique particles are volatile, forming through nucleation and condensation as the exhaust cools down. They seem to be made mostly of organic compounds that likely originate from the aircraft’s lubrication oil. Their unusual structures may affect how they interact with the environment and even how they impact human health, particularly in the respiratory system.
The discovery of onion-like particles in aircraft exhaust opens up many new questions for scientists.
Are they chemically similar to soot, or do they behave more like oil-based particles? How do they interact with other atmospheric particles, and what happens when they are inhaled? Researchers are calling for more studies to understand their effects on both climate and health.
This breakthrough not only changes what scientists know about aircraft emissions but also sparks curiosity about new ways nanoparticles can form. Understanding these particles better could lead to improvements in air travel emissions and help address environmental and health concerns associated with aviation.
Source: KSR.
