From road traffic

Study: Microplastics can affect the climate

(Bild: galileo120 - stock.adobe.com)

The abrasion of car tires, brake pads and roads promotes the formation of ice in clouds and can therefore have an impact on the climate. Like desert dust, the tiny plastic particles act as ice cores on which water droplets and vapor freeze.

In some regions of the world, up to 40 percent of ice cores could consist of microplastics, reports Viennese meteorologist Andreas Stohl in the Journal of Geophysical Research. It should therefore be taken into account in climate models. "On its own, water in the atmosphere would only freeze near minus 40 degrees Celsius," explains the researcher. On an ice core made of desert dust, the freezing process would already occur at around 18 degrees below zero, while plastic particles would require temperatures of around minus 20 degrees Celsius. "Microplastics are therefore only slightly less efficient as ice cores than desert dust," he explained.

Hardly any data on released microplastics
With his research team, he wanted to investigate the extent of the influence of microplastics on ice cloud formation. "Unfortunately, there is hardly any reliable data available on how much of it is released into the atmosphere from various sources," says Stohl. For example, there are no reliable measurements or calculations of how much is emitted by the abrasion of synthetic clothing or how much rises from the "Pacific Garbage Patch", an accumulation of thousands of tons of plastic waste in the northern Pacific Ocean.

Microplastics could account for up to 40 percent of the ice cores in so-called mixed-phase clouds in the tropics.

(Bild: stock.adobe.com, Krone KREATIV)

"The best data is still available on microplastic emissions from road traffic," he explained. These are mainly caused by abrasion from tires, brake pads, road markings and asphalt. In the latter, the bitumen component is often provided with plastic polymers to make it less brittle at low temperatures, more resistant to deformation and longer-lasting.

The researchers used computer models to calculate how much such road traffic microplastics end up in the air: less than one to 40 percent of tire abrasion ends up in the atmosphere, one third to all of it from brake pads, one to four percent from markings, and ten percent to one third from polymers from road surfaces.

Microplastics remain in the atmosphere much longer than desert sand
"These microplastics remain in the atmosphere up to seven times longer than desert sand, for example," says Stohl. This is because it is lighter and its irregular shape compared to round grains of sand also contributes to its longer stay in the air. "This makes microplastics relatively important for cloud formation, especially in areas where there are hardly any natural ice cores from desert dust or spores," the meteorologist is convinced.

Microplastics could account for up to 40 percent of the ice cores in so-called mixed-phase clouds in the tropics, and up to 20 percent in cirrus clouds (feather clouds) over the Antarctic. "The difference between these two types of clouds is that in mixed-phase clouds, water droplets containing ice nuclei freeze, whereas in cirrus clouds, ice forms directly from water vapor," he explained.

The additional ice nuclei from microplastics can therefore make the clouds in some regions significantly richer in ice. As a result, they reflect more light. Because the plastic particles float in the air longer than desert dust, for example, this probably also extends their lifespan. This should be taken into account in future climate models, says the expert.