Emission of 1.3-10 nm airborne particles from brake materials

Operation of transport vehicle brakes makes a significant contribution to airborne particulate matter in urban areas, which is subject of numerous studies due to the environmental concerns. We investigated the presence and number fractions of 1.3-10 nm airborne particles emitted from a low-metallic car brake material (LM), a non-asbestos organic car brake material (NAO) and a train brake cast iron against a cast iron. Particles were generated by a pin-on-disc machine in a sealed chamber and analyzed using a nano condensation nucleus counter, a CPC, and an FMPS. It was found that 1.3-4.4 nm particles are emitted during the friction. For the pairs with the LM and NAO, 1.3-4.4 nm particles predominate in number at temperatures above 160 degrees C. The emission of the 1.3-4.4 nm particles precedes the emission of above 4.4 nm particles. For the cast iron pair, the number of 1.3-4.4 nm particles is smaller than the number of 4.4-10 nm particles. The findings suggest that brake materials produce a significant number of 1.3-4.4 nm airborne particles, and these particles should not be neglected in environmental and tribological studies.