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Microplastics advance in the atmosphere and begin to interfere with ice formation in clouds, altering fundamental rain processes and expanding uncertainties about impacts on global climate and human health.
Microplastics present in the atmosphere can alter the formation of ice in clouds and, as a result, influence rain, climate modeling, and even aviation safety, according to a study led by researchers from Penn State University and published in the journal Environmental Science & Technology: Air.
In the laboratory, the team showed that these fragments act as ice nucleation particles, that is, surfaces capable of initiating the freezing of water at higher temperatures than would occur without impurities.
Microplastics in clouds and climate impact
The discovery gained relevance because microplastics have already been detected in clouds in mountainous regions of China and Japan, indicating that plastic pollution has surpassed the soil, rivers, and oceans and has begun to circulate in layers of the atmosphere directly linked to the hydrological cycle.
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In 2023, a study recorded the abundant presence of these particles in cloud water collected on Mount Tai, in eastern China, while another study identified microplastics in clouds over Mount Fuji and Mount Oyama, in Japan.
How plastic alters water freezing
In the Penn State experiment, scientists tested four types of plastic commonly found in the environment: low-density polyethylene, polypropylene, polyvinyl chloride, and polyethylene terephthalate, known by the acronym PET.
The particles were placed in small droplets of water, which were then gradually cooled to measure when ice began to form.
The goal was to understand if these residues could interfere with the microphysics of clouds, especially in so-called mixed clouds, which contain both liquid water and ice crystals at the same time.
The results indicated that contaminated droplets froze, on average, between 5 °C and 10 °C earlier than droplets without microplastics.
Under ideal atmospheric conditions, a droplet of water without “defects” tends to freeze around -38 °C.
In the case of the analyzed plastics, half of the droplets had frozen at around -22 °C in most samples.
According to the authors, this difference shows that plastic acts as a kind of physical support for ice formation, altering the point at which the transition occurs.
Effects on rain and storm formation
This mechanism helps explain why the topic is of interest to meteorology. When the water available in the cloud is distributed among a larger number of suspended particles in the air, smaller droplets are formed.
As these droplets take longer to reach a sufficient size to precipitate, the tendency is for less rain at that initial moment and greater accumulation of water within the cloud.
According to Miriam Freedman, a chemistry professor at Penn State and senior author of the study, this process can lead to episodes of more intense rain when precipitation finally occurs.
The team itself emphasized, however, that it is still not possible to accurately measure the size of this impact on the global climate or directly attribute specific extreme events to the presence of microplastics in clouds.
What the study demonstrates with certainty is the ability of these particles to interfere with ice formation, an important step within a much more complex atmospheric system.
What changes with the aging of microplastics
Another relevant point of the work involves the environmental aging of plastics.
The researchers simulated the exposure of the particles to light, ozone, and acids to verify if the passage of time would modify their behavior in the atmosphere. The effect was not uniform.
After this process, the ability to form ice decreased in samples of low-density polyethylene, polypropylene, and PET, but increased in the case of PVC.
This data contradicts the idea that wear always enhances the nucleation effect and shows that the behavior depends on the type of polymer.
Origin of microplastics and presence in the air
The presence of these residues in the air is associated with already known sources, such as tire wear, fibers released from synthetic fabrics, fragmentation of packaging, and degradation of plastic materials in urban and industrial areas.
International organizations and recent reviews indicate that microplastics circulate through soil, water, ice, and atmosphere, which expands the routes of human and environmental exposure.
Nevertheless, knowledge about the atmospheric transport of these particles and their combined effects on climate and health is still under construction.
Possible impacts on human health
In the field of health, the evidence is more cautious than what alarmist versions of the topic suggest.
The World Health Organization stated in its review on microplastics in drinking water that there are significant gaps in safely assessing the risks to human health.
More recent reviews point to potential effects such as inflammation, oxidative stress, and damage to lung tissue via inhalation.
Even so, the results still do not allow for a definitive conclusion about the exact weight of this exposure in specific diseases in the general population.
Microplastics enter the center of climate debate
Therefore, the main implication of the study is not to establish a closed scenario of atmospheric collapse.
By showing that microscopic plastic also participates in the formation of ice in clouds, the research shifts the discussion to a broader level.
This advancement places plastic pollution at the center of an agenda that until recently was dominated solely by greenhouse gases.
There is no basis, from the study, to claim that microplastics alone are creating a “lethal regime” of extreme storms.
What the data indicates is something more precise: plastic particles dispersed in the air can already alter a fundamental stage of cloud functioning.
As new measurements progress, researchers will need to better estimate the impact on rainfall distribution and cloud behavior.
Until then, the most solid data is that microscopic plastic is already involved in processes that help define when, where, and how rain forms.
