More than 200,000 tonnes of tiny plastic particles shed by car tyres and brakes are blown from roads into the oceans every year.
A new study conducted at the Norwegian Institute for Air Research suggests wind-borne microplastics are a bigger source of ocean pollution than rivers, the route that has attracted most attention to date.
Airborne transport has received much less attention than rivers because only the smallest particles can be blown by the wind and their size makes them difficult to identify as plastic. The scientists concentrated on fine tyre and brake dust as there is better data on how these are produced than tiny microplastics from other sources, such as plastic bottles and packaging.
The researchers estimated that 550,000 tonnes of particles smaller than 0.01mm are deposited each year, with almost half ending up in the ocean. About 34% of the emitted coarse tyre wear particles and 30% of the emitted coarse brake wear particles were deposited in the World Ocean.
These amounts are of similar magnitude as the total estimated direct and riverine transport of tire wear particles and fibres to the ocean.
Emissions of road microplastics are concentrated in the eastern US, Northern Europe and large urbanised areas of Eastern China, Middle East and Latin America where vehicle densities are highest.