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Clouds form when water vapor – an unseen gas found in the atmosphere – sticks to small floating particles such as dust and turns into liquid water droplets or ice crystals. We show this in a newly published study microplastic particles can have the same effectsproducing ice crystals that are 5 to 10 degrees Celsius (9 to 18 degrees Fahrenheit) warmer than droplets without microplastics.
This suggests that microplastics in the air can influence weather and climate, producing clouds in conditions where they would not otherwise form.
We are atmospheric chemists who study how different types of particles form ice when in contact with liquid water. This process, which constantly takes place in the atmosphere, is called nucleation.
Clouds in the atmosphere can fold up liquid water droplets, ice particles or a mixture of two. In clouds in the middle and upper atmosphere, where temperatures range from 0 to -38 degrees Celsius, ice crystals usually form around particles of mineral dust from parched soil or biological particles such as pollen or bacteria.
The microplastic is less than 5 millimeters wide – about the size of a pencil eraser. Some are microscopic. Scientists discovered them in Antarctica’s deep seas, the peak of Mount EverestAND fresh Antarctic snow. Because these fragments are so petite, they can be easily removed transported in the air.
Clouds are an essential part of Earth’s convoluted weather system, influencing rainfall, temperature and climate.
Why it matters
Ice in clouds has a significant impact on weather and climate because most precipitation is typical it starts with ice particles.
Many cloud tops in non-tropical zones around the world reach so high into the atmosphere that chilly air freezes some of their moisture. Then, when ice forms, it absorbs water vapor from the liquid droplets surrounding it, and the crystals become ponderous enough to fall. If ice does not form, clouds tend to evaporate rather than produce rain or snow.
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, such as dust or water particles may be subcooled to temperatures as low as -36 degrees Fahrenheit (-38 degrees Celsius) before it freezes.