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Much attention is given to the consequences of airborne particles on human health and well-being. Wear is one source of airborne particles and contributions in the urban environments from wheel-to-rail contacts and disc brakes cannot be neglected. Traditionally, mechanical wear has been associated with the generation of particles of diameters of some microns. However, the research described has found ultrafine particle generation from wear processes.
Particle generation from wear was measured under controlled laboratory conditions. The wear was created through sliding contact in a tribometer (type “pin-on-disc”) with different materials and with different sliding velocities and pressures, to represent rail traffic and automobile disc braking. Particle concentrations and size distributions in the air were determined for particle diameters from 10 nm up to more than 10 µm. For most materials and conditions three particle size modes were found: one at 50-100 nm, one at a few hundred nm and one at a few µm particle diameter