Microplastics may also be affecting the climate

Nov. 7 () –

Scientists at Penn State University have proven that microplastics in the atmosphere could be affecting the weather and climate.

a study, published in the ACS ES&T Air magazineshowed that microplastics act as ice nucleating particles, microscopic aerosols that facilitate the formation of ice crystals in clouds.

Scientists have discovered microplastics, tiny pieces of plastic less than 5 millimeters, in some of the most pristine environments on Earth, from the depths of the Mariana Trench to the snow on Mount Everest and the clouds atop the mountains. mountains of China and Japan. Microplastics have been detected in human brains, sea turtle bellies and plant roots.

Detecting them in the atmosphere means that microplastics could affect precipitation patterns, weather forecasting, climate modeling and even aviation safety by influencing how atmospheric ice crystals form clouds, explained Miriam Freedman, a professor of chemistry at Penn State and lead author of the paper, in a statement.

“Over the last two decades of research into microplastics, scientists have discovered that they are everywhere, so this is another piece of that puzzle“Freedman said. “It is now clear that we need to have a better understanding of how they interact with our climate system, because we have been able to show that the cloud formation process can be triggered by microplastics.”

In the controlled environment of the laboratory, the researchers studied the freezing activity of four different types of microplastics: low-density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). The team suspended the four types of plastics in small droplets of water and slowly cooled the droplets to observe how the microplastics affected ice formation.

They found that the average temperature at which the droplets froze was 5 to 10 degrees warmer than the drops without microplastics. Typically, a defect-free drop of atmospheric water freezes at about -38°C, explained Heidi Busse, a graduate student at Penn State and lead author of the paper.

Any type of defect in the water droplet, be it dust, bacteria or microplastics, can result in ice forming (or nucleating) around it. That small structure is enough for the water drop to freeze at warmer temperatures.

“In the case of our microplastics, 50% of the droplets froze at -22°C in most of the plastics studied,” Busse said. “It turns out that if you introduce something insoluble, you introduce a defect in that droplet and ice can nucleate at warmer temperatures.”

What this discovery means for weather and climate is not entirely clear, Freedman explained, but it suggests that microplastics are likely already having an impact. He added that mixed-phase clouds, such as puffy cumulus clouds, blanket-like stratus and dark, ominous nimbus-type clouds, contain a combination of liquid and frozen water. These clouds can be scattered throughout the atmosphere, including the classic “anvil”-shaped clouds that can form during thunderstorms.

“When air patterns are such that a droplet rises into the atmosphere and cools, that is when microplastics could be affecting weather patterns and forming ice in clouds”said Freedman, who is also affiliated with Penn State’s Department of Meteorology and Atmospheric Sciences.

“In an environment contaminated with many more aerosol particles, such as microplastics, the available water is distributed among many more aerosol particles, forming smaller droplets around each of those particles. When there are more droplets, you get less rain, but since the droplets only rain when they are large enough, more total water is collected in the cloud before the droplets are large enough to fall and, as a result, you get heavier rains when they arrive.”

In general, clouds cool the Earth by reflecting solar radiation, but certain clouds at certain altitudes can have a warming effect by helping to trap energy emitted from the Earth, Freedman explained. The amount of liquid water compared to the amount of ice is important in determining the extent to which clouds will have a warming or cooling effect. If microplastics influence the formation of mixed-phase clouds, Freedman said, they likely also affect the climate, but it is extremely difficult to model their overall effect.

“We know that the fact that microplastics can nucleate ice has far-reaching effects, but we’re still not quite sure what they are,” Busse said. “We can think about this on many different levels, not just in terms of more powerful storms, but also through changes in light dispersion, that could have a much bigger impact on our climate.”

The researchers also found that environmental aging, the natural photochemical processes that aerosol particles undergo over time, can significantly change the way particles interact with gases and vapors in the atmosphere. The team simulated environmental aging by exposing microplastics to light, ozone and acids.