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Clouds form when water vapor, an invisible gas in the atmosphere, sticks to tiny floating particles, like dust, and turns into liquid water droplets or ice crystals. In a recently published study, we show that microplastic particles can have the same effectsproducing ice crystals at temperatures 5 to 10 degrees Celsius (9 to 18 degrees Fahrenheit) warmer than droplets without microplastics.
This suggests that microplastics in the air may affect weather and climate by producing clouds in conditions where they would not otherwise form.
We are atmospheric chemists who study how different types of particles form ice when they come into contact with liquid water. This process, which occurs constantly in the atmosphere, is called nucleation.
Clouds in the atmosphere may consist of liquid water droplets, ice particles or a mixture of both. In the clouds of the middle and upper atmosphere, where temperatures are between 32 and –36 degrees Fahrenheit (0 to –38 degrees Celsius), ice crystals normally form around mineral dust particles from dry soils or biological particles, such as pollen or bacteria.
Microplastics are less than 5 millimeters wide, about the size of a pencil eraser. Some are microscopic. Scientists found them in Deep seas of AntarcticaTHE summit of Mount EverestAnd fresh Antarctic snow. Because these fragments are so small, they can easily be carried in the air.
Clouds are important parts of Earth’s complex weather system, impacting precipitation, temperature, and climate.
Why it matters
Ice in clouds has significant effects on weather and climate, as most precipitation starts as ice particles.
Many cloud tops in nontropical areas of the world extend high enough into the atmosphere that cold air causes some of their moisture to freeze. Then, once the ice has formed, it draws in water vapor liquid droplets surround it, and the crystals become heavy enough to fall. If ice does not form, clouds tend to evaporate rather than causing rain or snowfall.
Although children learn in elementary school that water freezes at 32 degrees Fahrenheit (0 degrees Celsius), this is not always true. Without something to nucleate on, like dust particles, water can be supercooled at temperatures as low as –36 degrees Fahrenheit (–38 degrees Celsius) before freezing.
