The Brake Emissions Task Force held its 34th session on 10 June 2021. Discussions covered particle number measurement approaches, with JARI presenting findings on their PN measurement system, including residence time of approximately 4.6 seconds and recommendations for a 10 nm CPC. Ford presented PN measurement experience, noting high variability in repeatability tests and ultrafine particles in some braking events. The group acknowledged that lack of dilution and instrument saturation may have influenced measurements. An interlaboratory study was expected to provide more robust data on total and solid PN measurements.