Experimental setup. (a) Optical table with upper cameras (TX and TY) and lower cameras (BX and BY) named after the indicated coordinate system (Z is the direction of gravity g), the settling chamber (SC), l Synchronized pulsed LED unit, controlled with a waveform generator (WG) and oscilloscope (OSC). (b) Snapshots of a settling prolate spheroid were recorded at 2932 fps. The tilt angle (the angle between the particles’ axis of symmetry and gravity) is reported in 5.1 ms intervals in degree units. Credit: Physical Examination Letters (2024). DOI: 10.1103/PhysRevLett.132.034101
The atmosphere contains many small solid particles. Scientists from the Max Planck Institute for Dynamics and Self-Organization (MPI-DS) and the University of Göttingen, in collaboration with the Center National de la Recherche Scientifique (CNRS) in France and the University of Gothenburg, Sweden, studied how such non-spherical particles are deposited in the air.
To do this, they used a new precision device equipped with high-speed cameras and a new particle injection mechanism. Using a 3D printer, they created particles of different shapes resembling disks as thin as 50 micrometers and rods as long as 880 micrometers. Using this device, they were able to observe that the particles tend to oscillate when they settle in still air.
“So far, most studies on the behavior of such small particles have been carried out with models in liquids, because experiments in air are extremely difficult,” Mohsen Bagheri, group leader at MPI-DS, describes previous approaches.
“However, the true dynamics of sedimentation could not be explored in this way. It has now been revealed in our experimental setting, by directly measuring the movement of full-size particles, which are much heavier than the environment” , he continues.
The observed oscillation could have an impact on the collision of individual particles, their travel distance in the atmosphere and their interaction with solar radiation.
Predicting particle dynamics
Typically, atmospheric particles are not perfectly spherical structures but rather flattened or elongated. Scientists developed and tested a model to describe and predict the movement of these particles, which very accurately captures the experimental results.
The new model can be used to study the dynamics and formation of particle clusters and the resulting effects in everyday life. “Our results can in particular help to better predict how long pollutants remain in the atmosphere or how precipitation is triggered in the clouds,” explains Alain Pumir. The CNRS researcher developed this model with his colleagues Bernhard Mehlig and Kristian Gustavsson.
Overall, this new knowledge contributes to a more precise understanding of atmospheric particles and how they affect our environment and our climate.
The study is published in the journal Physical Examination Letters.
More information:
T. Bhowmick et al, Inertia induces strong fluctuations in the orientation of non-spherical atmospheric particles, Physical Examination Letters (2024). DOI: 10.1103/PhysRevLett.132.034101
Provided by the Max Planck Society
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