When it comes to automotive pollution, the focus is almost always on exhaust fumes. Yet a growing share of urban pollution comes from another source, brake and tire wear. It is from there that microplastics and metal particles are released that end up in the air and settle on soil, plants and surfaces.
A new study conducted by an international team involving the University of Siena, the National Institute of Geophysics and Volcanology, and Trent University has tried to measure just such emissions, focusing on one of the most critical contexts possible: a major urban artery with very high traffic.
Lichens become natural powerhouses
The research took place in Toronto, along Highway 401, one of the busiest roads in North America. Here researchers took a novel approach: using lichens as monitoring tools. These organisms absorb substances directly from the air and, by accumulating them over time, offer an accurate snapshot of air quality.
Therefore, they were transplanted at different distances from the road, along a corridor of about 150 meters. In this way, it was possible to observe how the concentration of microplastics and metals changes as one moves away from the emission source.
Pollution falls rapidly with distance
The results show a very clear trend. The amount of microplastics from tire wear decreases exponentially as early as the first few meters from the roadway. Even more obvious is the behavior of metallic particulate matter: about 35 meters from the road there is a 70% reduction.
It is a figure that confirms how areas immediately adjacent to traffic are the most exposed. Sidewalks, bike lanes and urban spaces close to major thoroughfares thus become prime accumulation areas for these particles. Another interesting element concerns the strong correlation between brake dust and tire-generated dust. The two sources do not act separately, but contribute together to build a complex mix of contaminants.
A mix not to be underestimated
The particles released from tire wear are not simply plastic. They contain chemical additives and can carry potentially toxic metals. This makes them particularly relevant from an environmental and health perspective, because they can be inhaled or deposited in soils and water.
The study also highlights an innovative aspect: these particles are associated with magnetic signals, which allows them to be tracked using specific techniques. An approach that expands monitoring possibilities and allows for more precise maps of pollutant dispersion.
The issue of friction emissions is also beginning to enter European regulation. The new Euro 7 standards will include specific limits for emissions generated by brakes and tires for the first time, marking a change in perspective from the past.
This is a necessary shift, especially considering that the spread of electric vehicles, while reducing exhaust, does not eliminate these types of emissions. On the contrary, the increased weight of vehicles may contribute to increased tire wear.
Upcoming challenges
Research perspectives go beyond urban monitoring. Researchers also intend to apply these methodologies to the study of cultural heritage contamination, to understand the extent to which microplastics contribute to the degradation of historic surfaces and materials. It is a step that expands the picture: traffic pollution not only affects air quality, but can also have direct effects on cultural heritage.
The good news is that the concentration of these particles falls rapidly with distance. The bad is that in cities, where space is limited and traffic is heavy, this distance is often not there.The result is widespread exposure that calls into question not only vehicle technology, but also the way we design and organize urban spaces.
