A major source for airborne microplastic particles is road-tire wear. Microscopy and chemical analyses of wind-blown particles on dirty, high-elevation (2865-3690 m) snow surfaces in the Colorado Rocky Mountains revealed the presence of black carbonaceous 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 nano-size carbon black, a tire additive that homogeneously permeates tire polymers and other additives and that strongly absorbs solar radiation .
The key to documentation of worn tire matter was the identification in two-dimensional gas chromatography by Emissions Analytics of many organic compounds in snow common to those in road tires. The mass of black carbonaceous particles produced by road-tire wear may be estimated by multiplying measured mass of eroded tire-per-distance traveled by vehicular distances. The eroded tire mass from moving vehicles used for these estimates was measured by Emissions Analytics.
Under assumptions of amounts of tire-wear particles emitted to the atmosphere, the mass proportion of atmospheric black carbonaceous matter from annual road-tire wear might be as much as about 10-30% of atmospheric black carbon, such as soot from vehicle exhaust and domestic cooking. Black particles from road-tire wear may thus be an important component that contributes to melting of snow and ice as well as to warming the atmosphere. The potential toxicity of organic compounds in black-tire matter is another concern for the health of organisms in mountain ecosystems. A revised estimate for the annual mass of eroded tires globally is 6550 kilotonnes.
Citation:
Reynolds, R. L., Molden, N., Kokaly, R. F., Lowers, H., Breit, G. N., Goldstein, H. L., Williams, E. K., Lawrence, C. R., & Derry, J. (2024). Microplastic and Associated Black Particles from Road-tire Wear: Implications for Radiative Effects across the Cryosphere and in the Atmosphere. Journal of Geophysical Research: Atmospheres, 129, e2024JD041116, https://doi.org/10.1029/2024JD041116