Study suggests rain transports microplastics into the atmosphere

Plastics end up in the air due to evaporation from rain splashes and the impact with which they travel

Up to 100 trillion microplastic particles could be reaching the atmosphere each year on a global scale as a result of the rains.

It is an initial estimate, which is still fraught with uncertainty in several respects, that researchers from the Bayreuth University have published in “Microplastics and Nanoplastics”.

Oceans, lakes, and rivers often contain a large amount of microplastic particles in its surface. Shocking raindrops make many drops with an almost equally high concentration of microplastics are thrown into the air. When they evaporate into the air, the particles enter the atmosphere.

The research show that when a raindrop hits the surface of the water, droplets are thrown into the air from a small ring-shaped area around the impact site. They originate at a depth of a few millimeters below the surface of the water. The particles from microplastic contained in the droplets have almost the same concentration as in this narrow layer of water.

Scientists from Bayreuth they also calculated their trajectories in the air and the duration of their flight. This provided a surprising idea: the water from the raindrops, which is free from microplastics, ends up in the oceans, while water containing plastics from the oceans ends up in the air. When the droplets fly into the air until they evaporate, they release the particles microplastics to the atmosphere. This occurs particularly often over the surface of the oceans, where wind conditions and temperatures favor a comparatively long flight duration and a evaporation fast. Most microplastic particles return to the water due to their short flight times.

“It was a great challenge to determine how many drops a single shocking raindrop throws up, how big and fast these drops are, and how many microplastic particles they could contain. The experiments alone would have provided very little information. That is why we have devised a completely new coding for the simulations of these processes and developed a model information technology that allows us to answer these questions with high precision and with an unprecedented level of detail, “said the coordinator of the study, the doctor Stephan Gekle, Professor of Biofluid Simulation and Modeling.

“How realistic our simulations are becomes apparent when compared to technically demanding experiments. High-speed recordings of shocking raindrops confirm calculations based on our model, ”commented first author. Moritz lehmann, PhD student in physics.

To find out how many microplastic particles eventually end up in the atmosphere as a result of these processes, researchers from Bayreuth They collected a large amount of empirically available data and included it in their calculations.

These data refer, among other things, to the concentrations of microplastics on the sea surface, the amounts of annual precipitation, the size of the raindrops, which depends on the intensity of the rain, and the temporal distribution of the intensity of the rain.

An initial estimate leads to the conclusion that the impact of raindrops on water surfaces around the world could release up to 100 trillion microplastic particles to the atmosphere by year.

The authors emphasize that this estimate is still subject to numerous uncertainties and inaccuracies. For example, turbulence in the wind, which can influence on the impact force of raindrops, it has not yet been included in the calculations. Furthermore, the Earth’s marine surfaces do not have the same high concentration of microplastic particles everywhere; on the contrary, the differences are very great.

However, satellite measurements in conjunction with weather models could soon provide more accurate information on the “points hotFrom which particularly large amounts of microplastic particles are transported from the ocean to the atmosphere.