Janice Brahney and colleagues at Utah State University collected rain and dust samples over 14 months at 11 remote sites in national parks and wilderness areas across the western US.
They found microplastic in 98% of samples, making up about 4% of the dust particles collected. Scaling up, they estimated that more than 1,000 tonnes of microplastic, equivalent to 120–300 million plastic bottles, are deposited on protected lands in the western US every year. Much of it was fibres from clothing and fragments from packaging, carried long distances by wind.
The study matters because it showed plastic pollution reaches places with no local sources, moving through the atmosphere much like other pollutants.
The estimate is for one region; global atmospheric deposition is much less well quantified.