THE WASHINGTON POST – Microplastics have popped up in rivers, oceans, soil, food, tea and even Antarctic snow – and now these tiny plastic particles are showing up in clouds.
A group of researchers from Waseda University in Tokyo recently found microplastics in the clouds above Mount Fuji.
In a paper published in Environmental Chemistry Letters, the researchers wrote that these airborne microplastics could influence cloud formation – and in turn the climate.
Plastic is ubiquitous – humans have produced more than eight billion tonnes of it – and less than 10 per cent of it is recycled.
Because plastic waste doesn’t break down easily, it can exist in the environment for hundreds of years, becoming smaller and smaller, and ending up in our food, our bodies and the environment.
It’s still unclear exactly how harmful these tiny particles are to humans, but some of the chemicals in plastics are believed to interfere with reproduction, stress responses, immune response and development.
Microplastics in oceans threaten marine life and birds, and while there’s been less research on mammals, the studies that have been done point to serious harms.
The authors of the new study warn that the presence of microplastics in clouds may present a whole new set of problems, though.
FINDING PLASTIC IN THE SKY
One of the authors of the study, said Hiroshi Okochi said he wasn’t surprised to find airborne microplastics in the clouds above Mount Fuji.
“Early studies of airborne microplastics (AMPs) had found microplastics in atmospheric fallout, including rainwater,” Okochi said in an email.
He and his colleagues hypothesised that, if the tiny particles were in rain water, they must be in cloud water, too.
Studying this wasn’t easy. The Mount Fuji Research Station is located at the highest of the eight peaks of Mount Fuji, next to an unobstructed cliff where the researchers could collect samples of cloud water without interference from climbers or mountain huts.
They collected samples only during the summer months on Mount Fuji, at altitudes of about 3,800 meters, or 12,400 feet. A researcher would collect samples every few hours based on cloud density.
The team analysed cloud water for the presence of plastics. Researchers found material that’s used in many plastic products, such as clear food wrap, shopping bags and detergent bottles.
Then, using a technique known as backward trajectory analysis, they attempted to figure out where the plastic particles came from, and how they ended up in clouds in the first place.
“The backward trajectory analysis showed that the AMPs in cloud water sampled at the top of Mt. Fuji were mainly transported from [the] ocean,” Okochi wrote.
The researchers believe fine marine microplastics were dispersed into the atmosphere from waves splashing into the air.
SHAPE MATTERS
Shape matters with plastic particles, and according to a new paper in the journal Nature Geoscience this week, that shape plays a key role in how far they can travel in the atmosphere.
Scientists have long assumed these particles are basically spheres based on past models. Physicists even joke about how they are quick to make that assumption.
“We want to assume spherical everything,” said professor of atmospheric science at Cornell Natalie Mahowald, one of the authors of the study.
But that did not square with the fact that spherical particles are known to fall to the ground more quickly.
A group of researchers at Cornell University noticed that many of these particles might be shaped less like a ball and more like a ribbon.
This flatter shape would explain why they’re able to travel vast distances and end up in all of these remote places.
Through modelling, the researchers confirmed that a ribbon-shaped particle could travel much farther than a spherical one because they can stay in the atmosphere more than 450 per cent longer.
The researchers also found that the majority of microplastic particles they observed were flat. “This paper really shows using kind of elegant theory why these microplastic fibers can be transported just much farther than you would have thought if you thought they were a sphere,” Mahowald said.
THE CLIMATE
The mechanism by which microplastics in clouds could affect the climate still isn’t well understood, but Okochi explained that when plastic is degraded, it can provide a surface for water to adhere to.
That means clouds could form differently or disperse more quickly, potentially affecting temperature and rainfall.
Another paper published last year in the journal Nature Geoscience explored the potential impacts of airborne microplastics on the climate in greater depth.
“These particles are so small and light that they get transported to high altitudes… Here, they could get involved in cloud formation,” said one of the authors of the study Zamin Kanji.
If there are plastic particles in a cloud, water could condense around them, forming droplets and potentially ice crystals in the atmosphere, Kanji said. This could change how quickly clouds convert into rain, and the life cycle of a cloud, which has an important role in reflecting sunlight from the Earth.
Okochi also pointed out that strong ultraviolet radiation in the upper atmosphere could accelerate the degradation of the floating plastic particles, releasing greenhouse gases like methane and carbon dioxide.
Both Okochi and Kanji noted that the concentration of microplastics in clouds is too low to affect temperature or rainfall significantly – for now. – Maggie Penman
