Parameters Impacting Brake Wear Particle Emissions: A Literature Review

Abstract With the implementation by the European Union since the 1980s of strict measures to reduce emissions of air pollutants (PM10, PM2.5, NH3, CH4, O3, NOX, SOX, VOCs (volatile organic compounds), etc.), these emissions have fallen from a total of nearly 65 million tons in 1990 to around 20 million tons in 2021, according to data from the European Environment Agency. In the road transport sector, the implementation of the first European emissions standard in 1992 and the electrification of vehicles have made it possible to reduce exhaust emissions. As non-exhaust emissions increased, the European Commission introduced thresholds for braking systems for certain vehicle categories in the future Euro 7 standard. Car manufacturers are looking for solutions to reduce brake particle emissions, including the modification of the composition of the brake pads and discs. This literature review aims to present the state of the art of a set of parameters that can influence brake particle emissions. The parameters highlighted here include the raw materials and manufacturing process parameters of the brake pads, the composition of brake discs, some test parameters, and some characteristics of brake pads and discs. A brief analysis of the tribological mechanisms that could be involved in particle emissions is also described.