Microplastics are everywhere. From the highest parts of Mount Everest to the depths of the Mariana Trench, and even inside our own bodies, these tiny pieces of plastic seem to pervade every corner of the Earth. A recent study has shown that microplastics even exist within clouds, where water droplets cling to particles, such as microplastics, and freeze into ice crystals, changing precipitation patterns.
Cloud formation occurs when water vapor clings to particles like dust and becomes liquid water or ice. They can contain only liquid droplets, ice crystals, or both. Ice in clouds floating higher in the atmosphere is usually formed by nucleating around particles such as dust or pollen.
Precipitation generally begins as ice particles. Once these ice particles form, they absorb water vapor from the surrounding liquid droplets until the crystals are heavy enough to plummet down to the ground. When ice doesn’t form, clouds simply evaporate.
Microplastics are under 5 millimeters wide, which is smaller than the width of your index finger. They can be far smaller than that, however—in fact, they can even be microscopic. This allows them to be transported in the air. In a study, published in the journal Environmental Science and Technology: Air, researchers found that microplastics can be ice nucleating particles. These are microscopic aerosols that allow ice crystals to form inside clouds. Thus, microplastics may influence precipitation, weather forecasting, climate modeling and aviation safety.
Although water typically freezes at 32 degrees Fahrenheit, this isn’t always the case. Water can reach temperatures as low as negative -36 F (-38 C) before freezing if there are no particles to nucleate onto. Microplastics do not dissolve in water, and can therefore create ice particles at warmer temperatures. The researchers observed the freezing activity of four variations of microplastics. These variations were low density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). The plastics were suspended in water droplets, which were slowly cooled to form ice.
They found out that the droplets froze at an average temperature five to ten degrees Celsius warmer compared to those containing no plastic. This is equivalent to nine to nineteen degrees Fahrenheit. Half of the droplets with microplastics in the study were frozen by -22 °C, or -8 °F. This discovery demonstrates that microplastics may be having an impact on weather and climate already, though what exactly that impact is remains uncertain.
Clouds, including the cumulus, stratus, and nimbus have both liquid water as well as ice. Polluted environments have water distributed among more aerosol particles, creating smaller droplets around them. It only rains when droplets are large enough to fall, so the rain that eventually comes will be heavier. Therefore, there might be periods of little rain followed by heavier downpours.
Clouds usually cool the planet as they shield it from solar radiation. However, some can trap the energy the Earth emits and cause warming instead. The proportion of liquid water compared to ice is a key factor in deciding if a cloud will warm or cool the Earth. Because of this, microplastics probably affect climate, but it’s hard to tell what this effect may be. The researchers learned additionally that environmental aging can alter particles’ interaction with atmospheric gasses and vapors. The group of researchers exposed microplastics to light, ozone and acid to replicate the process and determine if it altered their ice-forming capability. All of the tested plastics were still able to freeze water, but aging diminished the ability of LDPE, PP and PET to do so. Conversely, it increased how well PVC could form ice.
Clearly, microplastics’ existence in the atmosphere is something important. However, in order to fully grasp microplastics’ effect on climate, researchers must pinpoint their concentrations at the altitudes where clouds float, as well as the concentrations of microplastics relative to other ice-nucleating particles.
