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

ABSTRACT 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 disor- dered 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 persis- tence and environmental toxicity.