Curbing the dust pollution

Every driver knows that brake pads need to be replaced periodically because they wear out. But where do the resulting fragments go? Some deposit on wheel rims – turning them black – and on the roadside. However, that’s only half the story: about 50% of the particles generated by disc–pad wear are released into the atmosphere, contributing to fine dust pollution (PM10, PM2.5, and others) we breathe every day.

Many might assume this is negligible. It is not. The amount of dust produced by brake wear is comparable to that from exhaust gases, which have been drastically reduced in recent decades thanks to improved fuels and engines. Therefore, to reduce overall particulate emissions into the air, the problem must be tackled on several fronts, including brake dust.

The issue has been known for decades. The European Union had already set the goal of reducing emissions by about 50% by 2020. In this context, the pioneering Rebrake project was launched, funded with €2 million and carried out in collaboration between the Department of Industrial Engineering (DII) of the University of Trento, Brembo N.V. (a world leader in braking systems), and the Royal Institute of Technology (KTH) in Stockholm. The project focused on improving the characteristics of brake pads and, above all, brake discs. Typically made of cast iron, the discs proved less polluting when subjected to a specific hardening heat treatment that significantly reduced emissions.

In subsequent years, other European projects followed. Lowbrasys expanded the collaboration network to several companies and research centers across Europe, adopting a holistic approach: improving braking system performance, developing local dust-capturing systems, and implementing strategies to optimize driving styles, thereby reducing brake wear. Other projects, again involving the DII and Brembo, continued along this line, while many more have been conducted worldwide.

Today, the situation has reached a turning point. The European Union has introduced the Euro 7 regulation, which will take effect in December 2026. This will require car manufacturers to limit brake particulate emissions to a maximum of 7 mg/km, decreasing to 3 mg/km after 2035. Based on research results, companies are focusing on several strategies:

• Improving disc performance through surface engineering treatments or cast iron enhancement, continuing the Rebrake approach while keeping production costs under control.
  
• Using optimized pads, such as NAO or other “green” compounds, which reduce emissions but currently provide lower braking performance, especially for European market standards.
  
• Implementing dust capture and collection systems, possibly combined with redesigned braking systems (e.g., a return to drum brakes), while avoiding performance penalties or excessive cost increases.
  
• Promoting electric mobility: these vehicles also brake, but they benefit from deceleration through the motor during certain phases, reducing the use of mechanical brakes.
  

Research continues at the DII, and deadlines are approaching. Updates and results will be shared on DII News.

Figures and captions:

Fig.1: Wear fragments from the braking system deposited on a car rim. The fragments appear comparatively large and black due to their high iron oxide content.

Fig.2: Wear fragments from the braking system released into the atmosphere (collected using special filters). The fragments are comparatively small.