For decades, soot—carbonaceous, non-volatile particles—has dominated scientific discussions surrounding aircraft exhaust. These soot particles, often exhibiting a turbostratic structure characterized by disordered graphene-like layers, have been well documented. However, the latest research conducted at a Zurich Airport test facility challenges this narrow view by revealing a spectrum of particle types far more diverse than previously recognized. High-resolution transmission electron microscopy (HRTEM) has enabled scientists to delve beneath the surface, uncovering four distinct categories of nanoparticles varying not only in size but more crucially in their internal architecture.

Among the four particle types identified, the turbostratic soot particles conform to conventional expectations, exhibiting diameters around 67 nanometers. They show layered and disordered graphene-like carbon sheets, typical indicators of soot formed by incomplete combustion. However, what sets the research apart is the discovery of three other particulate morphologies not previously attributed to aircraft exhaust. One of these is the “onion-like” particle, measuring approximately 17 nanometers, boasting well-ordered, spherical multilayered graphene structures reminiscent of concentric carbon shells. This structure is commonly synthesized in nanomaterials science but had not before been observed in the aviation emission context.

Complementing these are amorphous particles, measuring roughly 26 nanometers, lacking a crystalline framework and thus described as non-crystalline or disordered. These particles exhibit a more irregular internal composition, suggesting formation processes distinct from soot. Even smaller, trace amorphous particles measuring about 17 nanometers were also documented. Crucially, these latter three types tend to be single, non-agglomerated spheres rather than clusters, contrasting strikingly with the large, grape-like agglomerates typical of turbostratic soot.

A revealing aspect of the study lies in the spatial distribution of these particles relative to the engine exit. While turbostratic soot dominated in sheer number at the immediate engine exit, their relative abundance declines precipitously within a mere 15 meters downstream. At this juncture, the particle landscape is largely dominated by the onion-like and amorphous types. This shift strongly indicates dynamic chemical and physical transformations occurring almost instantaneously in the wake of the exhaust plume.

The research team proposes that the onion-like and amorphous particles belong predominantly to the volatile fraction of emissions, formed through nucleation and condensation processes rather than direct combustion. These volatile particles likely originate from the thermal and chemical breakdown of jet engine lubricating oils, subsequently aggregating into nanoscale spheres. Their diminutive size and volatile nature suggest they may behave quite differently in the atmosphere compared to traditional soot, affecting both atmospheric chemistry and human respiratory exposure in novel ways.

Exploring their physicochemical properties, the unique internal microstructures are hypothesized to influence particle volatility, surface reactivity, and solubility. The onion-like multilayered graphene shells, for example, may confer surprising chemical stability or distinct interaction potentials with biological tissues and atmospheric constituents. Conversely, the amorphous particles—without ordered carbon frameworks—may readily dissolve or react in pulmonary environments or cloud droplets, altering their environmental fates.

This discovery also propels fundamental questions about particle formation mechanisms in high-temperature combustion environments. Known synthetic methods for producing onion-like carbon nanoparticles, such as applying high-energy conditions to soot or carbon precursors, echo the possible energetic environments within jet engines. Yet the spontaneous formation of such highly ordered spheres in aircraft exhaust is unprecedented and demands comprehensive mechanistic studies. These investigations could unlock insights not only into atmospheric aerosol science but also into advanced nanomaterials synthesis inspired directly by combustion phenomena.

Beyond scientific intrigue, the findings bear significant ramifications for climate science and public health. Ultrafine particles from aircraft can influence atmospheric radiative forcing both directly and indirectly through contrail formation and cloud interactions. An expanded understanding of particle diversity and volatility is essential for improving predictive models of climate impact. Additionally, differential toxicity or deposition patterns within the human respiratory system between soot agglomerates and these newly identified nanoparticle morphologies remain unexplored terrain crucial for risk assessment among populations residing near airports or frequently exposed to aviation pollution.

Despite such advances, this research also lays bare many uncertainties. Questions linger regarding the exact chemical composition of onion-like and amorphous particles, their atmospheric longevity, and the extent to which these particles undergo further transformation or removal by environmental processes. The atmospheric dynamics of these nanostructures, their interactions with other pollutants, and biological membranes are fertile ground for multidisciplinary inquiry.

In conclusion, this meticulous study heralds a paradigm shift in the comprehension of aircraft particulate emissions. By employing sophisticated microscopy techniques and strategically positioned sampling downstream of engine exhausts, researchers have mapped a complex particle population previously unknown. The implications resonate across climate science, nanotechnology, toxicology, and atmospheric chemistry, compelling collaborative efforts to elucidate the life cycle, impacts, and mitigation strategies for these newly characterized ultrafine particles. Such understanding is vital as the world confronts intensifying aviation demands alongside stringent environmental and health standards.

Subject of Research: Not applicable

Article Title: Unique Microphysical Structures of Ultrafine Particles Emitted from Turbofan Jet Engines

News Publication Date: 8-Apr-2025

References:
Fushimi, A.; Saitoh, K.; Fujitani, Y.; Takegawa, N. Identification of jet lubrication oil as a major component of aircraft exhaust nanoparticles. Atmos. Chem. Phys. 2019, 19, 6389−6399.

Image Credits: NIES/ZHAW/TMU

Keywords

Aircraft exhaust particles, ultrafine nanoparticles, turbofan jet engines, turbostratic soot, onion-like carbon particles, amorphous particles, volatile particles, internal microstructure, nanoparticle formation, atmospheric aerosol, jet engine lubrication oil, high-resolution transmission electron microscopy (HRTEM).

Nanomaterials owe their remarkable properties to the precise arrangement of atoms within their structure. However, observing these intricacies has proven challenging, particularly because many materials deteriorate under the intense electron beams required by conventional electron microscopy. Titanium oxyhydroxide nanoparticles, a class of nanomaterials critical to catalytic and energy-related applications, are especially vulnerable. To tackle this obstacle, the team led by Professor Yoshifumi Oshima developed a hybrid technique that synergizes high-resolution transmission electron microscopy (HRTEM) with sophisticated data-driven lattice correlation analysis.

This novel methodology leverages the power of machine learning and advanced image processing algorithms to extract detailed three-dimensional atomic structures while drastically minimizing the electron exposure. By reducing the electron dose by a factor ranging from 20 to 500 compared to traditional methods, the researchers significantly mitigate sample degradation and preserve the native structure of these fragile materials during imaging. Such a low-dose approach not only safeguards the integrity of the particles but also preserves the utility of the captured data for rigorous structural analysis.

The crux of their approach rests on an innovative lattice correlation analysis that processes the subtle contrast variations of HRTEM images. Essentially, this analytical technique identifies and correlates specific lattice patterns within particles through a comprehensive Fast Fourier Transform (FFT) examination and subsequent mapping of crystallographic orientations. This data-centric method transcends conventional image interpretation by uncovering hidden periodicities and lattice symmetries, allowing the extraction of accurate three-dimensional structural information from two-dimensional projections.

Applying this technology to metatitanic acid (H₂TiO₃) nanoparticles, the researchers uncovered a distinctive alternating layered morphology composed of titanium dioxide (TiO₂) and titanium hydroxide (Ti(OH)₄) units. This arrangement bears a striking resemblance to the anatase phase of TiO₂, a naturally occurring mineral renowned for its exceptional optical and electronic properties. Such a discovery is pivotal, as it elucidates the longstanding observation that metatitanic acid serves as a crucial precursor in the synthesis of anatase titanium dioxide, which plays a vital role in photocatalysis and energy conversion devices.

Crucially, the researchers demonstrated that the technique’s efficacy extends beyond mere imaging. The detailed structural insights gleaned from this approach equip scientists with the ability to tailor nanomaterials at the atomic level. By understanding the precise layering and lattice orientation, material scientists can rationally design titanium oxyhydroxide catalysts that maximize surface activity or engineer battery electrodes with superior charge transport characteristics. This opens avenues for optimized materials in domains ranging from environmental catalysis to advanced energy storage.

The implications of this advancement reach further still, as many cutting-edge nanomaterials share the fragility issues of titanium oxyhydroxide. The capacity to conduct high-precision, low-dose imaging preserves the essential structure of a broad spectrum of sensitive materials, enhancing the reliability of atomic-scale analyses previously untenable due to beam damage. This paves the way for accelerated discovery and innovation across nanoscience disciplines, deepening our understanding of complex materials systems under near-native conditions.

Professor Yoshifumi Oshima and his interdisciplinary team combined their expertise in surface physics, electron diffraction, and computational analysis to push the envelope of microscopy and materials characterization. Their study, recently published in Communications Chemistry, underscores a growing trend in materials science toward integrating data-driven computational tools with experimental investigations. Such hybridized research methodologies are critical for navigating the increasing complexity of nanomaterials and for translating microscopic observations into impactful technological advancements.

This work also exemplifies the paradigm shift towards non-destructive characterization techniques in nanoscale research. By emphasizing safer imaging protocols that minimize sample perturbation, the JAIST group has set a new standard for responsible experimentation with beam-sensitive materials. The direct benefits of reduced beam damage are manifold, including preserving elusive transient states and enabling repeated measurements on single particles—capabilities that unlock new dimensions in dynamic studies and real-time monitoring.

Looking ahead, the research group envisions their lattice correlation analysis integrated into broader computational frameworks, forming an indispensable component of next-generation materials design platforms. Such integration would facilitate the rapid screening of candidate materials, guiding synthetic efforts through predictive insights grounded in atomic-scale structural fidelity. Consequently, this approach heralds a future where data-driven discovery accelerates the pathway from basic science to technological application.

Moreover, this development ties into the grander vision of sustainable materials science, where precisely engineered nanomaterials contribute to greener energy solutions. Enhanced catalysts derived from accurate atomic-level understanding are key to boosting efficiency in processes like water splitting, CO₂ reduction, and pollutant degradation. Similarly, optimized nanostructured electrodes could revolutionize energy storage, allowing batteries to retain higher capacities and exhibit longer lifetimes, essential for electrification and decarbonization agendas.

By breaking free from the constraints imposed by traditional electron microscopy, this breakthrough offers a window into the atomic world of nanomaterials without sacrificing their integrity. It champions a convergence of imaging, computation, and materials chemistry that propels not only fundamental understanding but also tangible technological impact. As this powerful technique gains adoption, it is poised to redefine standards in nanomaterials characterization and catalyze innovations that harness the full potential of atomic-scale engineering.

Subject of Research: Titanium oxyhydroxide nanoparticles and their atomic-scale structural characterization using data-driven lattice correlation analysis.

Article Title: Three-dimensional atomic-scale characterization of titanium oxyhydroxide nanoparticles by data-driven lattice correlation analysis

News Publication Date: April 28, 2025

Web References:
https://doi.org/10.1038/s42004-025-01513-2

References:
Kohei Aso, Koichi Higashimine, Masanobu Miyata, Hiroshi Kamio, and Yoshifumi Oshima. "Three-dimensional atomic-scale characterization of titanium oxyhydroxide nanoparticles by data-driven lattice correlation analysis." Communications Chemistry, 2025.

Image Credits: Yoshifumi Oshima from JAIST

Keywords

Nanoparticles, Chemical analysis, Image analysis, Titanium, Crystal structure, Atomic structure