Abstract
Brake-related airborne particulate matter contributes to urban emissions in the transport sector. Recent research demonstrated a clear dependence of the number of ultra-fine particles on the disc brake temperature. Above the so-called transition temperature, the number of ultra-fine particles increases dramatically (several magnitudes). As for exhaust emissions, part of the emissions released during braking can be in the volatile fraction. For this reason, a disc brake test stand specifically designed for aerosol research was equipped with three different aerosol sampling instruments: (i) a standard cascade impactor, (ii) a cascade impactor operating at high temperature with a heated sampling line, and (iii) a standard cascade impactor with a thermodenuder. Tests with a brake assembly representative of European passenger vehicles were executed, and the concentration of released airborne particles was determined. The results showed a decrease by several magnitudes in the concentration (in the size range of below 200 nm) using the cascade impactor operating at 180 °C with the sampling line heated to 200 °C. A further decrease in the concentration of airborne particles with size fractions below 200 nm was measured using a standard cascade impactor with a thermodenuder heated to 300 °C.
Highlights
Aerosols generated by car disc brake systems contribute considerably to emissions in urban areas [1].Studies from field tests, dedicated laboratory tests in disc brake dynamometers, and pin-on-disc tribometers reveal a wide spectrum of aerosol ranges from above 10 μm to below 6 nm [2,3,4].recent research shows that the size of disc brake aerosols can be reduced to 1 nm [5].Disc brakes typically consist of two pads that are pressed against the rotor to stop the vehicle by mechanical friction
We considered that the HT ELPI+ began 7 cm after the end of the heated sampling line (HSL); this meant that the main decrease in temperature occurred within 7 cm of the end of the HSL (200–180 ◦ C)
Special attention is given to the volatile fraction of disc brake aerosols in this study
Summary
Aerosols generated by car disc brake systems contribute considerably to emissions in urban areas [1].Studies from field tests, dedicated laboratory tests in disc brake dynamometers, and pin-on-disc tribometers reveal a wide spectrum of aerosol ranges from above 10 μm to below 6 nm [2,3,4].recent research shows that the size of disc brake aerosols can be reduced to 1 nm [5].Disc brakes typically consist of two pads that are pressed against the rotor to stop the vehicle by mechanical friction. Aerosols generated by car disc brake systems contribute considerably to emissions in urban areas [1]. There is a critical brake material temperature at which the ultrafine particle emission rate rises stepwise by 10 times for railway brake operations [6] and by four to six orders of magnitude in the case of passenger car friction brake operations. This was demonstrated at the pin-on-disc level where Nosko et al [7] found a transition temperature of 168–189 ◦ C measured in the disc material. Wahlström et al [10] found that the ultrafine number increased by several magnitudes when the pin temperature approached
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