The plastic is falling from the sky. But where does it come from?

These microplastics are not dry cleaned and stacked on beaches. When the waves crash and the wind sweeps the ocean, they drop drops of sea into the air. These, of course, contain salt, but also organic matter and microplastics. “Then the water evaporates, and you’re left with aerosols,” or small floating parts of a moving particle, says Cornell University researcher Natalie Mahowald, who co-directed the work with Brahney. “Classically, atmospheric scientists have always known that sea salts come this way,” he continues. But last year, another team of researchers he demonstrated this phenomenon with microplastics, showing that they appear in the sea winds.

This time around, Mahowalde and Brahney thought bigger, using atmospheric models to show how far marine microplastics can travel after taking off into the air. Other sources of microplastic emissions were also examined, such as roads, cities, and agricultural areas. They knew, for example, how much dust is created from the fields and how much microplastics can be in that dust.

The researchers then combined this atmospheric modeling with real-world data. Brahney used air samples scattered in remote places throughout the American West, so at one point he said how many plastic particles fell from the sky. Mahowalde’s modeling could also tell us what the atmospheric and climatic conditions were like at the time, to explain to researchers where the particles probably exploded.

Agricultural dust was found to provide only 5 percent of atmospheric microplastics in the West. And, surprisingly, cities supplied only 0.4 percent. “If you were to ask how plastics get into the atmosphere, they would say it from urban areas,” says Brahney. “I like to think that there are more roads leaves the most important cities. ‘

When a car pulls off a road, small sticks protrude above the tires as part of normal wear. This material is not pure rubber; contains a variety of synthetic rubbers and other chemicals. The tire particles are therefore technically microplastic and are everywhere. A study conducted in 2019 calculated this 7 trillion microplastics cleaned up in San Francisco Bay every year, mostly with tires.

Cities have been producing an astonishing amount of microplastics in road traffic and since garbage is distributed, but it doesn’t seem to get into the atmosphere. Therefore, Brahney and Mahowalde believe for two reasons: buildings block the wind from cleaning the surfaces of a city and moving away from those parts, and people drive cars more slowly on the subway, so there is less disturbance of tire particles that end up on the road. But get off the national highways and there are wider places where the wind can blow away the debris. In addition, says Mahowalde, “cars are moving at 60 miles per hour. That’s a lot of energy. And with that energy, tiny particles can enter the atmosphere. “