Better insight into the fate and transport of tyre and road grit
It is now possible to use a model to map the distribution and concentrations of particulate matter from tyres and road wear anywhere across the globe. This is important for taking precautionary measures and, in the long term, for developing legislation and regulations. The model can be applied to both water and soil.
To this end, Deltares worked with The Tire Industry Project (TIP), part of the World Business Council for Sustainable Development. TIP are working to make the production and use of car tyres more sustainable.
TRWP (Tire-and Road Wear Particles) are particles generated by friction between tyres and the road surface whilst driving. These particles subsequently end up in atmosphere, water and soil. It is important to track and map the fate and transport of particles as they move through the environment. This provides an answer to the question of whether there is a problem and how serious it is. Ultimately, this also shows what measures can be taken. However, until now, there was no reliable method available to map the routes and quantities. This was particularly true of the dispersion and concentration in runoff rainwater that eventually ends up in waterways. This model now generates essential information to map these routes as well.
Monitoring and forecasting globally using a mass balance model
Using the so-called mass balance model, it is possible to track the particles at a reasonable scale and thus predict how they move through catchment areas. The model is designed to utilise global and local datasets and open-source modelling frameworks, such as the Copernicus ERA5 climate dataset and Deltares’ Wflow and Delft3D model for hydrology in river basins. This modelling approach has been validated using field measurements from river basins on three different continents. The Seine in France (Europe), Chesapeake Bay in the United States (America) and the Yodo River in Japan (Asia).
The results of applying the model to the three aforementioned catchment areas show significant differences in the amount of TRWP that ultimately reaches surface water. The amounts that ultimately reach estuaries vary from 2% to 18%, depending on factors such as the size of the catchment area, the degree of urbanisation, the climate and the rainwater management infrastructure. The study further indicates that factors such as improvements in rainwater collection and treatment systems can reduce the transport of TRWP to surface waters by up to half, underlining the value of infrastructure-based mitigation measures.
Having a robust, reproducible model for TRWP transport and fate that can be applied worldwide is essential for advancing both scientific understanding and practical solutions.
Nicolas Tissier, Director of Research at TIP
"Our role at TIP is to support rigorous, transparent science that helps researchers, policymakers, and industry make evidence-based decisions. By making this model open access, we aim to support broader collaboration across the scientific community around TRWP in the environment, and to enable the development of more effective mitigation strategies.”
Still room for improvement
The study also highlights limitations, such as the lack of highly detailed local data and uncertainties surrounding TRWP materials. There should be more monitoring campaigns focusing on TRWP in soil, water and sediment, as well as on tyres and road materials. Standardisation of measurement methods is also mentioned; this can reduce uncertainty and improve the accuracy of the models.
“Despite many scientific knowledge gaps and uncertainties, this model illustrates that state-of-the-art open data and software can greatly enhance our understanding of the environmental transport of TRWP and the options to act” says Jos van Gils, who lead the development of the model on behalf of Deltares.
The model is a refinement of previous work by TIP and Deltares and extends the modelling approach to a global scale. The next phase of development has already been initiated, with the aim of compiling a global mass balance and making the model accessible to users outside the scientific community.
