Clouds develop when water vapor, an unseen gas present in the atmosphere, adheres to minuscule airborne particles like dust, transforming into liquid droplets or ice crystals.
A recent study reveals that microplastic particles can similarly influence this process, leading to the formation of ice crystals at temperatures ranging from 5 to 10 degrees Celsius (9 to 18 degrees Fahrenheit) higher than those required for droplets that lack microplastics.
This finding indicates that airborne microplastics may alter weather patterns and climate by facilitating cloud formation under conditions where it would not typically occur.
As atmospheric chemists, we investigate how various particle types initiate ice formation upon contact with liquid water—a process known as nucleation that is perpetually occurring in the atmosphere.
Clouds can consist of either liquid water droplets, ice particles, or a combination of both. In higher altitudes where temperatures range from 0 to minus 38 degrees Celsius (32 to minus 36 degrees Fahrenheit), ice crystals generally form around mineral dust from arid soils or biological entities like pollen and bacteria.
Microplastics are tiny fragments measuring less than 5 millimeters—similar in size to a pencil eraser—with some being microscopic. These particles have been discovered in remote locations such as the deep seas of Antarctica, atop Mount Everest, and within fresh Antarctic snow.
Due to their small size, they can be easily carried through the air. Clouds play a crucial role in Earth’s intricate weather system, influencing precipitation patterns, temperature variations, and overall climate conditions.
Why it matters
The significance of ice in clouds lies in its crucial role in influencing weather patterns and climate, as most precipitation usually begins as ice particles.
In many non-tropical regions across the globe, the tops of clouds rise high enough into the atmosphere for cold air to freeze some of their moisture. O
nce ice crystals form, they attract water vapor from nearby liquid droplets, eventually becoming heavy enough to precipitate. If ice does not form, clouds are more likely to dissipate instead of producing rain or snow. While it’s commonly taught that water freezes at 32°F (0°C), this is not always accurate.
In the absence of nucleation sites like dust particles, water can remain supercooled and resist freezing at temperatures as low as -36°F (-38°C). For ice to form at higher temperatures, there must be a substance that is insoluble in water within the droplet.
This substance serves as a nucleus for the initial formation of ice crystals. The presence of microplastics could facilitate this process, potentially leading to an increase in precipitation such as rain or snow.
Additionally, clouds influence weather and climate through various mechanisms. They can reflect sunlight away from the Earth’s surface, contributing to cooling, while also absorbing some of the radiation emitted by the Earth, which leads to warming.
The degree of sunlight reflection is influenced by the ratio of liquid water to ice present in a cloud. If microplastics enhance the quantity of ice particles relative to liquid droplets in clouds, this alteration could impact how clouds interact with Earth’s energy balance.
The approach we took to complete our tasks.
To investigate if microplastic particles can act as nuclei for the formation of water droplets, we examined four common types of plastics found in the atmosphere: low-density polyethylene, polypropylene, polyvinyl chloride, and polyethylene terephthalate.
Each type was evaluated in both its original form and after being subjected to ultraviolet light, ozone, and acidic conditions. These environmental factors are known to influence the characteristics of microplastics.
We suspended the plastic fragments in tiny water droplets and gradually lowered the temperature to see at what point they would freeze. Additionally, we scrutinized the surfaces of the plastic particles to analyze their molecular structure, as the chemistry of these surfaces may play a role in ice nucleation.
To investigate if microplastic particles can act as nuclei for the formation of water droplets, we examined four common types of plastics found in the atmosphere: low-density polyethylene, polypropylene, polyvinyl chloride, and polyethylene terephthalate.
Each type was evaluated in both its original form and after being subjected to ultraviolet light, ozone, and acidic conditions. These environmental factors are known to influence the characteristics of microplastics.
We suspended the plastic fragments in tiny water droplets and gradually lowered the temperature to see at what point they would freeze. Additionally, we scrutinized the surfaces of the plastic particles to analyze their molecular structure, as the chemistry of these surfaces may play a role in ice nucleation.
What still isn’t known
In order to grasp the influence of microplastics on weather and climate, it is essential to determine their concentrations at the altitudes where clouds develop.
Additionally, we must compare these concentrations of microplastics with those of other particles that can initiate ice formation, like mineral dust and biological substances, to assess if microplastics are present in similar amounts. Collecting this data will enable us to model how microplastics affect cloud development.
Plastic debris varies widely in size and composition. Future studies will focus on plastics that include additives such as plasticizers and colorants, along with smaller plastic particles.