Lagrangian tracking of particles settling through the atmosphere: influence of particle shape on its dispersion

All solid particles in the atmosphere – such as ash, dust, ice crystals, pollen and microplastics – are non-spherical, which affects their atmospheric transport. However, studies of their dispersion are often based on models derived from measurements in stationary fluids or on field data distorted by atmospheric fluctuations. To address these limitations, the IMPACT (In-situ Measurement of Particles, Atmosphere, Cloud, and Turbulence) field campaign was conducted in northern Finland during May and June 2024. As part of this initiative, we launched an innovative experiment to track the dispersion of small, non-spherical particles released at altitudes between 2 and 7 km. Their trajectories were monitored until they reached the ground.

 

The experiment used particles of consistent mass (8.5 grams) and volume but varying shapes, including icosahedrons (representing near-spherical forms), as well as circular and elliptical discs, some with perforations. Up to 20 paperboard particles equipped with miniaturized, battery-powered electronics were placed inside a biodegradable helium balloon for each launch. At the target altitude, the balloon burst, releasing the particles from a single point. Throughout the particles' ascent within the balloon and their descent after release, GPS data on their position and altitude were transmitted via radio to ground stations. Over the course of the campaign, we tracked up to 150 particles across six distinct shapes. In addition, particle-resolved direct numerical simulations are carried out to determine the settling behavior in still air as a function of particle shape. In this presentation, we will share preliminary findings on particle dispersion patterns and explore the influence of atmospheric turbulence on the behavior of non-spherical particles.