Clouds are pictured above residential buildings in the southern suburbs of Beirut, amid ongoing hostilities between Hezbollah and Israeli forces, as seen from Baabda, Lebanon, November 11, 2024. | Photo credit: Reuters

Clouds form when water vapor – an invisible gas in the atmosphere – sticks to tiny floating particles such as 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 airborne microplastics can affect the weather and climate by producing clouds in conditions where they would not otherwise form.

WE atmosphere chemist which studies how different types of particles form ice when they come into contact with liquid water. This process, which takes place constantly in the atmosphere, it’s called nuclear.

Clouds in the atmosphere can be made up of liquid water droplets, ice particles or a mixture between the two. In clouds in the middle to upper atmosphere, where temperatures are between 32 and minus 36 F (0 to minus 38 C), ice crystals normally form around mineral dust particles from dry soils or biological particles such as be it pollen or bacteria.

Microplastics are less than 5 millimeters wide – about the size of a pencil eraser. Some are microscopic. Scientists found them in Antarctic deep seasTHE the summit of Mount Everest and fresh snow from Antarctica. Because these fragments are so small, they can be light carried in the air.

Why it matters

Ice in clouds has important effects on weather and climate, as most precipitation usually occurs it starts as ice particles.

Many cloud tops in nontropical areas around the world extend high enough in the atmosphere that cold air causes some of their moisture to freeze. Then, once the ice forms, it draws water vapor from the liquid droplets around it, and the crystals become heavy enough to fall. If ice does not develop, clouds tend to evaporate rather than produce rain or snow.

While children learn in school that water freezes at 32 F (0 C), this is not always true. Without something to nucleate on, like dust particles, water it can be overcooled in temperatures down to minus 36 F (minus 38 C) before freezing.

For freezing to occur at warmer temperatures, some kind of material that will not dissolve in water must be present in the droplet. This particle provides a surface where the first ice crystal can form. If microplastics are present, they could cause ice crystals to form, potentially increasing rain or snow.

Also the clouds affect the weather and climate in several ways. They reflect incoming sunlight away from the Earth’s surface, which has a cooling effect, and absorb some of the radiation emitted by the Earth’s surface, which has a warming effect.

The amount of reflected sunlight depends on how much liquid water versus ice does a cloud contain. If microplastics increase the presence of ice particles in clouds compared to liquid water droplets, this changing ratio could change the effect of clouds on Earth’s energy balance.

How we did our job

To see if microplastic fragments could serve as nuclei for water droplets, we used four of the most common types of plastic in the atmosphere: low-density polyethylene, polypropylene, polyvinyl chloride, and polyethylene terephthalate. Each has been tested both in a clean state and after exposure to ultraviolet light, ozone and acids. All of these are present in the atmosphere and could affect the composition of microplastics.

We suspended the microplastics in small drops of water and slowly cooled the drops to observe when they froze. We also analyzed the surfaces of the plastic fragments to determine their molecular structure, as ice nucleation could depend on the surface chemistry of the microplastics.

For most of the plastics we studied, 50% of the droplets were frozen by the time they cooled to minus 8 F (minus 22 C). These results parallel those of another recent study by Canadian scientists, who also found that some types of microplastics nucleate ice at warmer temperatures than drops without microplastics.

Exposure to ultraviolet radiation, ozone, and acids tended to reduce the ice nucleation activity on the particles. This suggests that ice nucleation is sensitive to small chemical changes on the surface of the microplastic particles. However, these plastics still nucleated ice, so they could still affect the amount of ice in the clouds.

What is not yet known

To understand how microplastics affect weather and climate, we need to know their concentrations at the altitudes where clouds form. We also need to understand the concentration of microplastics compared to other particles that could nucleate ice, such as mineral dust and biological particles, to see if microplastics are present at comparable levels. These measurements would allow us to model the impact of microplastics on cloud formation.

Plastic fragments come in many sizes and compositions. In future research, we plan to work with plastics containing additives such as plasticizers and dyes, as well as smaller plastic particles.

This article is republished from The Conversation under a Creative Commons license. Read the original article Here.