Non-exhaust emissions: physical and chemical characterization of brake wear particles

Particle pollution poses a significant threat to public health. Despite the strong reduction in exhaust emissions, particles remain a concern due to the substantial contribution from non-exhaust sources including the abrasion of vehicle components such as the brakes. This study focuses on the physical and chemical characterization of particles emitted from a brake through laboratory experiments. A test chamber was designed to isolate the brake and allow accurate measurement of particle size distribution. An in-depth analysis of the chemical composition and morphology of brake wear was carried out. On-line physical investigation revealed particles ranging from 90 nm to 0.4 μm. Thermogravimetric analysis showed that the particles are composed of approximately 15% organic material (volatile compounds and solid carbon) and 85% inorganic substances. Elemental analysis identified iron, oxygen, and carbon as the predominant elements, with minor traces of copper, titanium, and barium. Further characterization using Raman spectroscopy and X-ray diffraction confirmed the coexistence of disordered carbon structures and iron oxides along with crystalline phases such as magnetite and hematite. These findings underline the chemical heterogeneity of brake wear particles, underscoring their potential for persistence and environmental toxicity.