New research from the National Institute for Environmental Studies in Japan has found particles in aircraft engine exhaust which they believe have never been identified before.
The microscopic particles emitted from aircraft engines – particularly from turbofan jet engines which are widely used in commercial aviation – contain a complex mix of particles that may pose risks to both climate and human health.
While it’s known that volatile compounds dominate the particle emissions from aircraft exhaust plumes, the precise mechanisms behind their formation remain poorly understood. To better understand these emissions, researchers from the National Institute for Environmental Studies in Japan have analysed exhaust particles collected both directly at the engine exit and farther downstream in the aircraft plume.
While plenty of soot particles were found directly at the engine exit, their presence sharply declined further away. 15m downstream, soot made up less than 1% of the total particles observed. Instead, the area was dominated by three newly identified types of particle.
The first consisted of particles made of concentric spherical layers, like an onion. The other two were amorphous and trace amorphous particles (ie: non-crystalline particles, lacking an orderly internal structure. The former being fully formed and clearly visible, the latter much thinner or fainter than regular amorphous particles.
These particles are mostly spherical and extremely small (10–20 nanometers in diameter) and are thought to have been created through nucleation and partial pyrolysis processes, with chemical evidence indicating that they are made largely of organic compounds that originate from the engine’s lubricating oil, not from the fuel itself.
The novelty of the particles discovered raises a number of questions regarding the broader implications of these particle types for air quality around airports, and what might they mean for long-term exposure risks to people and the environment?
The researchers conclude: ‘There are many questions regarding the physicochemical characteristics, origin, and formation mechanism of onion-like particles, and whether they are similar in nature to soot or volatile organic particles, such as oil mist. The onion-like particles may have different dynamics in the atmosphere and in the body compared with other particles; therefore, further research is needed to understand their climate and health implications.’
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