Airborne microplastics: Where they come from and where they go

A new study has found that, contrary to previous claims, the ocean is not a significant source of microplastics to the atmosphere, but rather a major sink. 

The research team used a global chemical transport model to evaluate how tiny plastic particles, known as microplastics, move around the world.

The finding challenges past assumptions about the ocean’s role in releasing plastic fragments into the air.

The journey of airborne microplastics 

Plastic debris in dust form is increasingly recognized as a worldwide contaminant. Microplastics (particles less than 5 mm in diameter) have been detected in soils, freshwater, the ocean, and even in the air that we breathe. 

Scientists warn that microscopic plastic bits pose risks for human health, since they can easily enter the respiratory system and the bloodstream. 

Once airborne, these tiny pieces can travel large distances and eventually settle in remote or sensitive regions, harming wildlife and potentially impacting human populations.

But how do these particles enter the atmosphere in the first place? The planet’s primary sources of microplastics are typically found on land, from everyday materials such as vehicle tires shedding particles on roads, or synthetic clothing fibers washed out in domestic wastewater. 

However, earlier models had suggested that there might be an additional large source at sea. Microplastics often accumulate in the oceans, carried there by rivers and other waterways. Then, once present in the marine environment, it was believed that they could be lofted into the air by sea spray or wind-driven wave action.

What is the ocean’s contribution?

Prior reports pointing to a large marine source relied on an inverse modeling technique. That method uses atmospheric measurements of particular substances and attempts to infer their origin by matching observed concentrations with predicted distributions. 

Applied to microplastics, inverse modeling suggested the ocean might contribute hundreds of millions – or even billions – of kilograms of these fragments to the air each year.

Such massive figures were then tested experimentally, with scientists using wave tanks and other controlled setups to see how vigorously wave action or bursting bubbles could transfer plastics from the water surface into the atmosphere. 

Those studies, however, hinted that only tens or hundreds of thousands of kilograms of plastic might plausibly be introduced into the air – orders of magnitude smaller than the figures derived from inverse modeling.

A global chemical transport model

In an effort to reconcile these contradictory outcomes, a group led by researchers at the Max Planck Institute for Meteorology (MPI-M) ran a global chemical transport model. This computer model simulates the movement of substances, such as microplastic particles, through the atmosphere. 

By prescribing a minor oceanic emission of microplastics – consistent with the low estimates from laboratory work – they were able to predict how microplastic concentrations should appear in the air at various locations around the globe.

The results aligned well with real-world measurements. Based on the model, the ocean in fact took up some of these airborne particles instead of emitting them in large quantities. 

The scientists learned that rather than being a source, the ocean appeared to be a sink, in which 15 percent of all airborne microplastics are deposited. 

In other words, waves, spray, and wind may occasionally lift small amounts of plastic out of the sea, but far more of the material is settling onto the water rather than emanating from it.

How airborne microplastics travel

The study also uncovered the significant influence of particle size on how microplastics travel. Larger plastic fragments drop out of the atmosphere relatively quickly, often landing in coastal areas or not far from their point of emission. 

By contrast, smaller particles can remain suspended for up to a year. That extended flight time allows them to cross entire oceans or continents and reach distant regions such as the Arctic, where they land on ice or snow.

These discoveries highlight the global character of plastic contamination, showing that microplastic dust can be widespread in places typically considered pristine. 

They also clarify that stopping microplastic pollution at its land-based sources may be the most efficient approach, as the ocean itself is neither the greatest emitter nor the root cause.

A roadmap for pollution reduction

Given that airborne microplastics reach faraway corners of the planet, the research team’s results have immediate practical value. Any broad plan to cut plastic pollution should focus on terrestrial origins: tire wear on roads, textiles shedding fibers, and insufficiently treated wastewater. 

Additionally, lessening single-use plastics and improving waste management at landfills can help limit microplastics before they disperse into the environment.

These findings show that ocean waters, already burdened by plastic accumulations, are predominantly sinks – taking in plastic particles from the air. They also emphasize that microplastics do not stay put in the environment: large ones settle nearby, while smaller ones can travel global distances. 

Future models aimed at plastic pollution will need to consider these dynamics in more detail, particularly when mapping out strategies to protect vulnerable ecosystems, reduce human exposure, and maintain cleaner oceans.

By settling this debate over whether the ocean is more of a source or a sink, scientists can now direct their attention to mitigating the true origins of airborne microplastics, thus improving targeted policies to help address this pressing environmental concern.

The study is published in the journal npj Climate and Atmospheric Science.

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