Oscillating Particles in the Sky

Tiny particles like ice crystals or ashes tend to oscillate as they settle in the atmosphere. By combining theory and experiments, scientists have constructed a model that can help refine predictions about the wind transport of atmospheric pollutants and weather forecasts.


The atmosphere contains a vast amount of tiny solid particles, ice crystals, soot, ashes, aeolian sands, and silts, microplastics, and various pollutants, which have a significant environmental impact and even significantly influence the physics of the climate (by altering, for instance, the albedo of clouds). Due to their size, these particles are very easily carried by the wind, although their natural tendency is to sediment, meaning to settle slowly because of gravity. Therefore, studying the dynamic behavior of these microparticles is a delicate but necessary task if one wishes to predict their transport distances and deposition areas when their emission location is known.

In recent work, a French-German-Swedish collaboration involving the physics laboratory of the ENS (École Normale Supérieure) of Lyon (LPENSL, CNRS / ENS Lyon) studied both theoretically and experimentally the sedimentation of non-spherical model particles in the air.

With the help of high-speed cameras and a new particle injection mechanism for particles of a few tens of microns and controlled shapes through their printing via a very precise 3D printer (see figure), the researchers observed that these non-spherical particles tend to oscillate as they settle in calm air. Since atmospheric particles in general are not perfectly spherical but have flattened or elongated structures, the researchers suspect that this dynamic feature could significantly affect their properties, for example, the distance they are capable of traveling, their collision rate and thus their ability to aggregate, or even their interaction with solar radiation.

The scientists developed and tested a model to describe and predict the movement of these particles that very accurately reflects the experimental results obtained. This new model can be used to study the dynamics and formation of particle clusters and the resulting effects at a larger scale. These results, which will help to better predict the duration of pollutants in the atmosphere or the initiation of precipitation in clouds, are published in the Physical Review Letters.

References:
Inertia Induces Strong Orientation Fluctuations of Nonspherical Atmospheric Particles,
T. Bhowmick, J. Seesing, K. Gustavsson, J. Guettler, Y. Wang, A. Pumir, B. Mehlig, and G. Bagheri, Physical Review Letters,
published on January 19, 2024.
Doi: 10.1103/PhysRevLett.132.034101
Open Archive: arXiv