Shades of grey—tire characteristics and road surface influence tire and road wear particle (TRWP) abundance and physicochemical properties

Abstract

There is mounting evidence that tire wear particles can harm natural systems, but worldwide trends in car weight and car usage, mean emissions are set to increase. To control tire wear emissions and help understand fate and transport, detailed characterisation of the particles, and the relationship between road surface properties and emission profiles is needed. This study deployed a suite of experiments utilising the advanced road simulator of the Swedish National Road and Transport Research Institute to compare seasonal tire types from three brands. An extraction method was developed for a coarse (>30 µm) fraction of tire and road wear particles (TRWP), and a comprehensive physicochemical characterisation scheme applied to both TRWP and tire-tread, including microscopy, energy-dispersive X-ray spectroscopy and pyrolysis-GC/MS. Road simulator dusts and hand-picked TRWP showed differences in shape, numbers, and mass between tire types and brands, and between asphalt and cement concrete road surfaces. Contrary to accepted perceptions, tactile analyses revealed that firm-elastic TRWP comprised only a minor proportion of TRWP. Fragile and chemically distinct tire-road-derived particles, termed here sub-elastic TRWP, comprised 39–100% of TRWP. This finding raises urgent questions about overall TRWP classification and identification features, resistance to weathering, and environmental fate. At the same time, differences in TRWP generation between tire formulations, and road surfaces, show potential for controlling emissions to reduce global impacts.

Contribution of Road Vehicle Tyre Wear to Microplastics and Ambient Air Pollution

“…A recent laboratory study could detect two separate types of tyre wear particles, denoted as firm elastic and sub-elastic, where the sub-elastic type was characterised by the commonly seen cigar shape and embedded mineral grains, while the firm-elastic type was more irregular and knobbly and with superficial mineral encrustations. In the laboratory, the sub-elastic type was vastly more common than the firm-elastic type [149]. The average aspect ratio of particles collected from roadside or tunnel samples is around 1.65 [76,102].…”

Measures to Reduce the Discharge of tire Wear into the Environment

“…Other options include (bicycle) sharing services and very well-functioning and well- Probably the most efficient way to bring emissions down is to reduce the number of kilometres driven by vehicles [22]. Wilkinson et al [91] states that the strongest driver of car mobility is the convenience of driving. Promoting sustainable initiatives is the way forward.…”