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Microplastics, road dust, and biological particles drive hazardous urban ice fog formation
Summary
Researchers collected and sublimed ice fog crystals in Fairbanks, Alaska, and found that road dust (66–69%) and tire wear microplastics (13–16%) were the dominant ice-nucleating particles — the first field evidence of microplastics driving hazardous ice fog formation, with biological particles such as lichens contributing an additional 6–10%.
Ice fog is common across high latitudes, with hazardous visibility reductions causing automobile accidents and aviation delays, yet the particles responsible for nucleating ice fog crystals remain a mystery. During winter in Fairbanks, Alaska, ice fog crystals were collected and sublimed, leaving behind residual particles likely corresponding to the ice nucleating particles (INPs). Non-exhaust vehicular emissions were the dominant source of ice fog residual particles, in the forms of road dust (66–69%, by number) and microplastics (e.g., tire wear, 13–16%). Biological particles (e.g., lichens) comprised 6–10%, highlighting their importance as INPs in wintertime urban and boreal environments. These observations demonstrate microplastics acting as INPs in the urban atmosphere, corroborating previous laboratory experiments. The observation of road dust reveals an unintended air quality impact of gravel application for traction on roads. Therefore, developing methods and policies to reduce road wear aerosol may mitigate hazardous ice fog formation.