More than 50% of particulate matter (PM) related to non-exhaust emissions (NEE) from cars is generated by vehicle braking systems. This is particularly due to the wear of discs and friction materials used to produce brake pads. The European Commission has recently imposed legal limits on emissions from auto braking systems [1]. The regulation describes a brake emissions level below 7 mg/km/M1vehicle, which is lower than the current average emissions. Challenges related to the environmental impact caused by NEE are leading the automotive industry to choose composite materials with low friction wear and high stability. RAICAM Industrie S.R.L. [2], a company specialized in the design and production of brake pads, is studying the release of particulate matter (PM10 and PM2.5) from automobile braking systems.

The study aims to conduct a chemical-physical analysis of PM emissions from three categories of brake pads: Low Steel (LS), Non-Asbestos Organic (NAO), and a Low Steel formula with a Low Organic Content (LOC). PM10 and PM2.5 are collected on glass fiber filters following the 'WLTP-Euro7' dynamometer bench test. The wear behaviour of the three categories of pads and the type of binder used are evaluated. Scanning electron microscopy (SEM-EDS) with backscattered electrons was used to perform PM characterization, analysing its chemical composition and morphology. The number and size distribution of emitted particles were also taken into account. The obtained results were compared to the chemical analysis of material detached from the worn surface of the pads [3] using SEM-EDS and X-ray diffraction (XRD). The study indicates that LS pads produce higher PM emissions compared to LOC and NAO [4]. SEM-EDS and XRD analyses reveal the presence of iron oxide and metallic iron in all families, which results from both steel fiber wear (LS and LOC) and cast iron disc (LS, LOC and NAO). This observation leads to hypotheses about the non-negligible contribution of PM derived from the disc [5]. Further investigations are currently being conducted at Raicam Industrie S.r.l.