PM from Brakes Greater Threat than from ICE

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Source: Graz University of Technology post

“We have a problem, and nobody knows how big it is,” says TU Graz researcher Peter Fischer. But one thing is certain: brakes cause more particulate matter (PM) emissions than internal combustion engines (ICE) via their exhaust gases. Nevertheless, there is a shortage of basic knowledge and legal regulations.”

The braking process rubs off mass from brake discs and pads. This abrasion passes into th environment as fine dust – and is virtually unexplored.

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Exhaust from exhaust pipes is becoming less and becoming cleaner, and it is no longer an issue in e-mobility anyway. So far, so reassuring. These emissions from combustion engines have been a well-known, publicly very present issue for years, for which there have been strict EU-wide guidelines since 2017/2018 with the Euro 6 emissions standard, which has led to a significant improvement. However, there are other particulate emissions from motorized traffic that are harmful to health and the environment and about which very little is known: particulate emissions from the abrasion of brake discs and brake pads.

Quantitatively ahead of exhaust emissions

Fischer, head of the Institute of Automotive Engineering at TU Graz explains: “Calculated both on a per-mile basis and over the entire vehicle life cycle, this abraded mass far exceeds that of the PM that a diesel vehicle can emit through the exhaust pipe within all standards and limits. This can be estimated relatively easily using the measured loss of mass of the four brake discs and eight brake shoes with corresponding brake pads and the replacement intervals.”

And yet these emissions, which like the abrasion of tires and road surfaces are classified as non-exhaust particle emissions, lead a shadowy existence – not only in the public perception, but also in research, politics and industry.

Test cycle with values too good to be true

There is a lack of basic knowledge, a lack of measurement methods and a lack of legal regulations – still. This is because the EU intends to enshrine relevant legislation presumably between 2025 and 2027.

Environmental organizations, industry and EU policy makers are already holding initial talks on this. In the framework of the Particle Measurement Program (PMP) of the Economic Commission for Europe UNECE, work is currently being done on the recommendation for legislation, on the test procedure and test set-up (on the test bench only).

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Accordingly, brake PM is to be regulated based on measurement data from so-called WLTP test cycles (WLTP stands for “worldwide harmonized light-duty vehicles test procedure”). However, these cycles on the chassis dynamometer are far removed from real-world driving behavior and deliver values that are far too good overall.

“Our fear is – to put it bluntly – that a driving cycle will be tinkered with in a way that doesn’t match real-world driving and produces low emissions. Especially for mountainous areas, where brakes get extremely hot and other chemical reactions take place, legislation based on these facts would do little to improve the emissions situation,” says Fischer.

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