Microplastic and Associated Black Particles From Road‐Tire Wear: Implications for Radiative Effects Across the Cryosphere and in the Atmosphere

• Published in: Journal of geophysical research. Atmospheres Vol. 129; no. 19
• Main Authors: Reynolds, Richard L., Molden, Nick, Kokaly, Raymond F., Lowers, Heather, Breit, George N., Goldstein, Harland L., Williams, Elizabeth K., Lawrence, Corey R., Derry, Jeff
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 16-10-2024
• Subjects: Additives; Air pollution; Atmosphere; Black carbon; Carbon; Carbon black; Chemical analysis; Color; Cryosphere; Distance; Elevation; Environmental effects; Gas chromatography; Hydrocarbon combustion; Hydrocarbons; Light; microplastic particles; Microplastics; Microscopy; Mixtures; Mountains; nanoplastic particles; Organic compounds; Particulate matter; Particulates; Plastic debris; Plastic pollution; Polymers; River basins; Roads; road‐tire wear; Snow; Snow and ice; Snowmelt; Tires; Wear; Wear particles; Wear rate; Rocky Mountains; United States > US; Colorado
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2024JD041116

The environmental effects of airborne micro‐ and nano‐size plastic particles are poorly understood. Microscopy and chemical analyses of atmospherically deposited particles on snow surfaces at high elevation (2,865–3,690 m) in the Upper Colorado River basin (UCRB; Colorado Rocky Mountains) revealed the presence of black substances intimately associated with microplastic fibers, particles interpreted to have originated as tire matter. Identical and similar particles occur in shredded tires and road‐surface samples. The substance responsible for the black color of all tires is carbon black, a graphitic light‐absorbing tire additive produced by hydrocarbon combustion that homogeneously permeates the mixture of tire polymers and other additives. Such black tire matter may thus exert radiative effects closely similar to those of black carbon. The presence in snow of many organic compound types common to tires, measured by two‐dimensional gas chromatography, suggests that atmospherically deposited black road‐tire‐wear matter is among the light‐absorbing particulates that advance the onset and rate of snow melt in the UCRB. The mass of road‐tire‐wear particles shed from vehicles may be estimated by multiplying measured amounts of eroded tire‐per‐distance traveled by vehicular distances. Under a combination of measurements and assumptions about the amounts and radiative properties of atmospheric tire‐wear particles, the radiative effects of these particles might add about 10%–30% to those effects from black carbon, an estimate ripe for revision. On regional and global scales, the amounts and effects of emitted and deposited tire‐wear matter likely vary by factors of geographic source, transport pathway, and depositional setting.
Plain Language Summary
A major source for airborne microplastic particles is road‐tire wear. Microscopy and chemical analyses of wind‐blown particles on dirty, high‐elevation (2,865–3,690 m) snow surfaces in the Colorado Rocky Mountains revealed the presence of black substances intimately mixed with microplastics, particles interpreted as tire matter. Identical and similar particles occur in shredded tires and in samples collected from road surfaces. The black substance responsible for the black color of all tire particles is carbon black that homogeneously permeates the mixture of tire polymers and other additives. The mass of particles produced by road‐tire wear may be estimated by multiplying measured amounts of eroded tire‐per‐distance traveled by vehicular travel distances. Under assumptions of amounts of tire‐wear matter emitted to the atmosphere, their presence as light‐absorbing particles likely contribute to melting of snow and ice as well as to warming the atmosphere.
Key Points
Light absorbing particles, as blackened microplastic matter from road‐tire wear, occur in snow of the Colorado Rocky Mountains (2013–2021)
The mass of road‐tire‐wear particles annually generated is estimated to be 6,550 kt, of which about 655–1,965 kt might become airborne
The results are relevant to radiation modeling of snow and ice surfaces as well as the atmosphere