Report

NanoWear – nanoparticles from wear of tyres and pavement

Reseach area: Sustainable transport
Year: 2009
VTI-code: R660
Price: 160 kr

 
VTI rapport 660 (75 pages + 4 Appendices including 9 pages, 3 227 kB, written in Swedish with an English summary)

Particles from road and tyre wear have in recent years come into focus as they constitute an important and relatively unexplored contribution to air particulate pollution. Especially during winter and spring, wear particles contribute to violations of the environmental quality standard for inhalable particles in road and street environments. Mechanically generated wear particles are relatively coarse (> 0.5 microns) compared with combustion particles from vehicle exhaust, but in controlled trials in VTI's road simulator in the project WearTox, a fraction of ultra fine (<100 nm) particles (approximately 30–50 nm ) were formed from tyre and pavement wear. As these particles are morphologically different from the coarser mineral particles the hypothesis was that the particles emanated from the tyres rather than the road surface. To test this hypothesis, the present project was initiated. The project has been implemented using the VTI's road simulator and various particle instruments. Wear particles from nine different tyres wearing the same road pavement were studied. Particle concentrations, size distributions, elemental composition and PAH content was studied.

The results clearly show that the nanoparticles of size 30–50 nm occur only from tests with studded tyres. One of the two tested unstudded Nordic winter tyres produced an even finer particle fraction (<10 nm), while the other tyre of the same type resulted in no nanoparticles. Tests with summer tyres do not result in the formation of nanoparticles. The exact source of the nano particles has, despite comparisons with both elemental composition and PAH content in tyres and pavement materials, not clearly been established. It is clear that the fine particles contain higher relative concentrations of sulphur, which is present at relatively high levels in both bitumen and tyres suggesting that either one or both of these sources dominate in the finer particle fractions. It is unclear whether the ultrafine particles formed when testing studded tyres in the road simulator also occur in real traffic. As they appear in the same size fractions as exhaust particles but in lower concentrations, they might be difficult to identify.

The PAH composition of inhalable particle fractions differs between both individual tyres and tyre types. However, the PAH content of the tyre materials and pavement bitumen has poor correlation to that of the particle samples. PAH composition is likely to be affected by frictional heat in the trials so that a match might not be expected. Wolfram from studded tyre studs has been detected in relatively high concentrations of particulate samples. Emission factors were calculated and are for coarse particles of the same magnitude as the emission factors calculated for real traffic. The emission factors for ultrafine particles of studded tyres are roughly ten times lower than that of vehicle exhaust. Unstudded Nordic winter tyres and especially summer tyres have consistently lower particle emission factors.

The results of this project show that studded tyres, and maybe also unstudded Nordic winter tyres, in a laboratory environment during wear, produce particles considerably smaller than normally associated with wear particles. If this is true also for real traffic situations, the results are important for how wear particles are considered in relation to exhaust particles, where normally wear particles are assigned to the coarser part of the inhalable fraction (PM10-2,5). If wear between road surface and tyres also generates nanoparticles this might also affect the assessment of health effects from the different traffic related sources.

Author(s)
Blomqvist, Göran

Gustafsson, Mats

Hjort, Mattias


Brorström-Lundén, Eva
Dahl, Andreas
Gudmundsson, Anders
Johansson, Christer
Jonsson, Per
Swietlicki, Erik

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