Tyre Wear Emissions
When you buy new tyres for your vehicle, have you ever wondered where the rubber from the old ones went?
As vehicles travel along the road surface, particles are created as the tyre abrades against the road surface. The particles created are suspended in the atmosphere and are small enough to enter your lungs. Tyre wear is a growing problem because the number of tyres in use is increasing. In Britain, over 47 million tyres were disposed of during 2005. That’s about 100,000 worn tyres a day (Used Tyre Group, 2007). Estimates calculated within the UK suggest 140g of tyre wear-derived particles are released per metre of road per year (Environment Agency, 1999). Research has suggested tyre wear contributions to be 11% of the total particle mass depending on sampling location (Stocker and Carruthers, 2007). Tyre wear particles also pollute soil and watercourses situated close to roads.
Tyres are a complex mixture of very different materials including heavy metals and carcinogenic substances. Organic compounds make up a large fraction of the particulate mass released through tyre wear. Organic compounds found within tyre material include: polycyclic aromatic hydrocarbons, benzothiazoles, toluene, styrene, methylethenylbenzenes, methyloctene, butadiene polymers, ethylbenzene, limonene, xylenes, ethylmethylbenzenes and dimethylcyclohexenes (Rogge et al., 1993). Particles released through tyre wear also contain metals such as zinc, copper, cadmium, magnesium, sodium, calcium, iron and antimony. Around 20% of the total zinc concentrations within aerosol samples in inner cities are thought to originate from tyre particles (Fauser et al., 2002). In 1999, as a result of tyre wear, 10,000-11,000 metric tons of zinc was released into the US environment (Councell et al. 2004).
Tyre wear rates are affected by a number of factors. A selection of factors are given below:
- Higher speeds- increase the mechanical stress exerted on the tyre.
- Hard braking- increases the tyre abrasion against the road surface.
- Tyre pressure- under and over inflation changes the tyres' surface area.
- Tyre fitting and maintenance - misalignment causes uneven wear to tyres.
- Vehicle weight- overloading vehicles increase pressure on the tyres.
Tyre manufacturers are working to reduce the effect of tyre wear particles.
Find out how you could reduce your non-exhaust emissions