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Microplastics may float higher in Earth鈥檚 atmosphere than previously thought, posing a risk that they might release chemicals that damage the ozone layer.

Small fragments of plastic can travel long distances on air currents, settling in remote locations, but there isn鈥檛 good data on just how far they can move. Most simulations assume that the microplastics are small spheres, but they can actually take a variety of irregular shapes, from kinked fibres to tangled complexes with other materials.

at the Max Planck Institute for Dynamics and Self-Organization in Germany and his colleagues measured how microplastics of different shapes float through the air in the laboratory, finding that they settle up to 76 per cent more slowly compared with similarly sized microplastic spheres.

鈥淣obody has actually measured these particles settling in the air,鈥� says Bagheri. 鈥淚t鈥檚 so difficult to do these experiments because you have to have such precisely manufactured particles that are very small.鈥�

Bagheri and his team used a custom 3D printer print microplastic fragments that were spherical, semicircular, curved or straight, with a variety of thicknesses. They then recorded the fragments falling through air with two cameras to calculate their speed.

They found that the oddly shaped fibres fell at between a quarter and half of the speed of the spherical fragments. When they used these findings to tweak their atmospheric models, they found that the microplastics could travel much further than predicted by previous models, potentially reaching the stratosphere.

If these far-flung fragments were to degrade due to solar radiation, they might damage the ozone layer, says Bagheri. 鈥淚t involves much more investigation, but it鈥檚 definitely something that we have to look into,鈥� he says.

at Imperial College London says previous studies had shown that fibres of irregular shapes settled more slowly than spherical microplastics, but it could be useful to have detailed data for a range of shapes in a structured way. 鈥淭his is the first study I鈥檝e seen that systematically showed it for representative microplastics,鈥� she says.

However, there is still not enough evidence to say that microplastics in the atmosphere are damaging the ozone layer. Previous studies that have shown damaging compounds being released from microplastics involved very different conditions to those in the stratosphere, says Wright.