Where the Rubber Meets the Road and Ends Up in Snow: The Hidden Effects of Tire Matter on Snowmelt and Mountain Ecosystems
Black particles from road tire wear may be an important component to the melting of snow and ice and the warming atmosphere.
Microplastic particles (<5 mm) are becoming recognized for their deleterious environmental effects, including impacts to human and animal health. Microplastics are widespread globally from pole to pole, at high elevations, on the deepest ocean floors, and in all environments in between. These particles have also been detected in human fluids and organs. A major source of airborne microplastic particles is the wear of vehicle tires. Microscopy and chemical analyses of wind-blown particles on dirty, high-elevation (2865-3690 m) snow surfaces (Figure 1) across 60,000 km2 in the Upper Colorado River Basin (UCRB), Colorado Rockies (Figure 2) revealed the presence of black carbonaceous substances intimately mixed with microplastic fibers. Identical and similar particles occur in shredded tires and in samples collected from road surfaces, leading to the hypothesis that the black particles and associated microplastic fibers in snow were derived from the wear of road tires (Figure 3). Importantly, the substance responsible for the black color of all tires is nano-size “carbon black,” an antioxidant and antiozonate additive that homogeneously permeates tire polymers and other additives.
We conducted several types of analyses to test the hypothesis and its possible significance to the Earth system. The key to documenting worn tire matter was our use of two-dimensional gas chromatography to identify hundreds of organic compounds in snow that matched those commonly found in road tires (analyses by Nick Molden, Emissions Analytics).
These findings were supported by scanning electron microscopy with energy dispersive spectroscopy (by Heather Lowers and George Breit, Geology, Geophysics, and Geochemistry Science Center) indicating that metal compositions in the black matter were consistent with metals in tires (Figure 4). Total organic carbon (by Corey Lawrence) ranged widely (8.5-22.5 wt. %). Of all organic compound types in snow samples, about half of them in each sample were organic compounds found in tires. This finding indicated a nearly uniform fallout of tire matter across the study area regardless of the amount from locally derived organic carbon.
Although our finding of black tire matter in snow is not surprising, its presence is important for several reasons. Firstly, black carbonaceous matter has a strong capacity to absorb solar radiation. This property was demonstrated for the first time for road tires by Ray Kokaly (Geology, Geophysics, and Geochemistry Science Center), who measured the reflectance spectrum of a shredded tire (Figure 5). Such extraordinary capacity to absorb sunlight can be expected to advance the onset and rate of snowmelt in UCRB, a pressing issue for the management of Colorado River water. Secondly, the toxicity of many organic compounds in tires may have deleterious effects on mountain organisms as they do on aquatic organisms from local runoff in the Pacific Northwest demonstrated by USGS colleagues at the Western Fisheries Research Center.
We estimated the mass of black carbonaceous particles produced by road tire wear by multiplying the mass of eroded tire per distance traveled measured by Emissions Analytics by vehicular distances. Under conservative assumptions of amounts of tire-wear particles emitted to the atmosphere, one of our findings was that the mass of tire matter emitted to the atmosphere in the U.S. during 2018 was approximately double an estimate made by others of the mass deposited. This finding suggests that earlier methods have underestimated the mass of tire matter emitted to the environment in the U.S. Furthermore, we concluded that the mass proportion of all atmospheric black carbonaceous matter from annual road tire wear might be as much as about 10-30% of atmospheric black carbon that includes sources such as soot from vehicle exhaust and domestic cooking. Using a separate set of values, we revised a frequently and loosely quoted estimate of 6,000 kilotonnes for the annual mass of eroded tires globally upward to 6,550 kilotonnes.
Black particles from road tire wear may thus be an important component that contributes to the melting of snow and ice elsewhere as well as to warming the atmosphere.
Black particles from road tire wear may be an important component to the melting of snow and ice and the warming atmosphere.
Microplastic particles (<5 mm) are becoming recognized for their deleterious environmental effects, including impacts to human and animal health. Microplastics are widespread globally from pole to pole, at high elevations, on the deepest ocean floors, and in all environments in between. These particles have also been detected in human fluids and organs. A major source of airborne microplastic particles is the wear of vehicle tires. Microscopy and chemical analyses of wind-blown particles on dirty, high-elevation (2865-3690 m) snow surfaces (Figure 1) across 60,000 km2 in the Upper Colorado River Basin (UCRB), Colorado Rockies (Figure 2) revealed the presence of black carbonaceous substances intimately mixed with microplastic fibers. Identical and similar particles occur in shredded tires and in samples collected from road surfaces, leading to the hypothesis that the black particles and associated microplastic fibers in snow were derived from the wear of road tires (Figure 3). Importantly, the substance responsible for the black color of all tires is nano-size “carbon black,” an antioxidant and antiozonate additive that homogeneously permeates tire polymers and other additives.
We conducted several types of analyses to test the hypothesis and its possible significance to the Earth system. The key to documenting worn tire matter was our use of two-dimensional gas chromatography to identify hundreds of organic compounds in snow that matched those commonly found in road tires (analyses by Nick Molden, Emissions Analytics).
These findings were supported by scanning electron microscopy with energy dispersive spectroscopy (by Heather Lowers and George Breit, Geology, Geophysics, and Geochemistry Science Center) indicating that metal compositions in the black matter were consistent with metals in tires (Figure 4). Total organic carbon (by Corey Lawrence) ranged widely (8.5-22.5 wt. %). Of all organic compound types in snow samples, about half of them in each sample were organic compounds found in tires. This finding indicated a nearly uniform fallout of tire matter across the study area regardless of the amount from locally derived organic carbon.
Although our finding of black tire matter in snow is not surprising, its presence is important for several reasons. Firstly, black carbonaceous matter has a strong capacity to absorb solar radiation. This property was demonstrated for the first time for road tires by Ray Kokaly (Geology, Geophysics, and Geochemistry Science Center), who measured the reflectance spectrum of a shredded tire (Figure 5). Such extraordinary capacity to absorb sunlight can be expected to advance the onset and rate of snowmelt in UCRB, a pressing issue for the management of Colorado River water. Secondly, the toxicity of many organic compounds in tires may have deleterious effects on mountain organisms as they do on aquatic organisms from local runoff in the Pacific Northwest demonstrated by USGS colleagues at the Western Fisheries Research Center.
We estimated the mass of black carbonaceous particles produced by road tire wear by multiplying the mass of eroded tire per distance traveled measured by Emissions Analytics by vehicular distances. Under conservative assumptions of amounts of tire-wear particles emitted to the atmosphere, one of our findings was that the mass of tire matter emitted to the atmosphere in the U.S. during 2018 was approximately double an estimate made by others of the mass deposited. This finding suggests that earlier methods have underestimated the mass of tire matter emitted to the environment in the U.S. Furthermore, we concluded that the mass proportion of all atmospheric black carbonaceous matter from annual road tire wear might be as much as about 10-30% of atmospheric black carbon that includes sources such as soot from vehicle exhaust and domestic cooking. Using a separate set of values, we revised a frequently and loosely quoted estimate of 6,000 kilotonnes for the annual mass of eroded tires globally upward to 6,550 kilotonnes.
Black particles from road tire wear may thus be an important component that contributes to the melting of snow and ice elsewhere as well as to warming the atmosphere.