The Brake Emissions Task Force met on 3 June 2021 to discuss PN measurement approaches. Participants reviewed PM specifications with final comments due by 10 June. RV and AJ presented LINK’s brake PN measurement experience, emphasizing the sampling plane location following EPA Method 1A, flexible hoses for particle transfer, and transfer efficiency results. Most brake systems exhibit multimodal particle size distributions with peaks at approximately 10 nm, 50–100 nm, and 500 nm, with an additional peak at 1.5–2.0 µm not considered crucial for PN concentration. A consensus was reached that large particles shall not be considered for PN measurement. Discussion covered total PN versus Solid PN, with volatiles showing low concentrations across cycles. The next meeting was scheduled for 10 June 2021.

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.