The Particle Measurement Programme Informal Working Group (PMP-IWG) coordinated a global interlaboratory study (ILS) on brake wear particle emissions with the participation of 16 testing facilities. Two articles present the main outcomes of the ILS: (I) Particulate matter mass (PM), and (II) Particle Number (PN) emissions. The test matrix covered a wide variety of brake systems and configurations. The tested disc brakes were found to emit PM2.5 and PM10 that varied between 0.8–4.0 mg/km and 2.2–9.5 mg/km per brake, respectively, depending on the type of brake and the applied testing load. The drum brake emitted much lower PM due to its enclosed nature. Almost 37–45% of the emitted PM falls in the fine particle size with this fraction being higher for the drum brake. On the other hand, almost 50–65% of the total brake mass loss falls in particle sizes larger than 10 μm or gets lost before being measured. The most important loss mechanisms for PM in the proposed layout are being discussed. Finally, the PM measurement variability and lab-to-lab reproducibility are investigated.

The Particle Measurement Programme (PMP) informal working group co-ordinated a global interlaboratory study (ILS) on brake wear particle emissions with the participation of 16 laboratories in 2021. Two articles present the results of the ILS: (I) particulate matter mass (PM) and (II) particle number (PN) emissions. The test matrix covered different brake systems, including ECE and NAO pad materials with grey cast iron discs and a drum brake. Regarding PN, the study measured the total particle number from approximately 10 nm to 2.5 µm (TPN). Some testing facilities measured solid particle number emissions (SPN) in parallel. The mean TPN concentrations ranged from 9.1 × 10⁸ #/km/brake to 1.1 × 10¹⁰ #/km/brake. TPN and SPN emission levels were comparable, except for one lab that measured very high volatile particle emissions for one brake system. The minimum and maximum SPN emissions for a given brake differed by a factor of 2.5 ± 0.5, comparable to data from exhaust SPN ILS measurements. This article provides an overview of lessons learned and subsequent measures incorporated in an upcoming global technical regulation to reduce measurement variability when sampling and measuring brake particle emissions for light-duty vehicles up to 3.5 t.

The relative contribution of brake emissions to traffic-induced ambient Particulate Matter (PM) concentrations has increased over the last decade. Nowadays, vehicles’ brakes are recognised as an important source of non-exhaust emissions. Up to now, no standardised method for measuring brake particle emissions exists. For that reason, the Particle Measurement Programme (PMP) group has been working on the development of a commonly accepted method for sampling and measuring brake particle emissions. The applied braking cycle is an integral part of the overall methodology. In this article, we present the results of an interlaboratory study exploring the capacity of existing dynamometer setups to accurately execute the novel Worldwide Harmonised Light-Duty Vehicles Test Procedure (WLTP)–brake cycle. The measurements took place at eight locations in Europe and the United States. Having several dynamometers available enabled the coordination and execution of the intended exercise, to determine the sources of variability and provide recommendations for the correct application of the WLTP–brake cycle on the dyno. A systematic testing schedule was applied, followed by a thorough statistical analysis of the essential parameters according to the ISO 5725 standards series. The application of different control programmes influenced the correct replication of the cycle. Speed control turned out to be more accurate and precise than deceleration control. A crucial output of this interlaboratory study was the quantification of standard deviations for repeatability (between repeats), sample effect (between tests), laboratory effect (between facilities), and total reproducibility. Three critical aspects of the statistical analysis were: (i) The use of methods for heterogeneous materials; (ii) robust algorithms to reduce the artificial increase in variability from values with significant deviation from the normal distribution; and (iii) the reliance on the graphical representation of results for ease of understanding. Even if the study of brake emissions remained out of the scope of the current exercise, useful conclusions are drawn from the analysis of the temperature profile of the WLTP–brake cycle. Urban braking events are generally correlated to lower disc temperature. Other parameters affecting the brake temperature profile include the correct application of soak times, the temperature measurement method, the proper conditioning of incoming cooling air and the adjustment of the cooling airspeed.

The stringency of vehicle exhaust emissions regulations resulted in a significant decrease in exhaust particulate matter (PM) emissions over the years. Non-exhaust particles (i.e., from brakes and tyres) account for almost half or more of road transport-induced ambient PM. Even with the internal combustion engine ban in 2035, electrified vehicles will still emit PM from brake and tyre wear. Consequently, non-exhaust PM emissions cannot decrease significantly without any regulatory measures. Because independent research carried out under different methods is not readily comparable, a Global Technical Regulation (GTR), which sets the procedures and boundaries of testing brake wear particle emissions, is currently under development. This overview describes the particle number (PN) measurement setup based on the well-known exhaust emissions PN methodology. We provide the technical requirements and the expected maximum losses. In addition, we estimate the effect of particle losses on the differences between different setups for typical size distributions observed during brake testing. Finally, we compare brake testing PN specifications to those of exhaust PN.

Vehicles’ exhaust particulate matter (PM) emissions have significantly decreased over the years. On the other hand, non-exhaust emissions, i.e., particle emissions from brakes and tires, have increased due to the increase in the vehicle fleet, traffic congestion, and the distance traveled. As a result, regulatory bodies are investigating the possibility of mitigating non-exhaust emissions. The Euro 7 proposal introduces specific emission limits for both brakes and tires for the first time in a regulation worldwide. The methodology for brake particle emissions sampling and measurement builds on the work of the Particle Measurement Programme (PMP) informal working group of the United Nations Economic Commission for Europe (UNECE). The recently adopted Global Technical Regulation (GTR) on brakes from light-duty vehicles up to 3.5 t prescribes the technical details. In this paper, we present the technical specifications for the measurements of PM. We also evaluate the penetrations for two cases with two setups for minimum and maximum particle losses. This study, using aerosol engineering calculations, estimates the maximum expected differences between the two setups, both of which are compliant with the GTR. This study also discusses the mass ratios of PM_2.5 and PM₁₀ as a function of the mass median diameters.

While light-duty vehicles already have a test cycle under Global Technical Regulation 24 to characterize brake wear emissions as part of Euro 7, heavy-duty vehicles, also covered by Euro 7, still lack a harmonized test cycle for this purpose. This study presents the development of the Worldwide Harmonized Heavy Duty Brake Cycle (WHBC), a novel test cycle representing real-world HDV braking behavior across urban, rural, and motorway conditions. A large, globally sourced dataset of vehicle activity and existing cycles was analyzed via brake-event extraction and statistical characterization using empirical cumulative distribution functions of key brake metrics. The resulting cycle comprises 246 brake events over 271 km and 5:39 h. An analysis of parasitic losses based on a European heavy-duty CO₂ monitoring database indicates that roughly 73% of kinetic energy dissipation must be absorbed by the brakes. Dynamometer testing confirmed the feasibility and repeatability of the cycle as well as providing first insights into particle measurements. The WHBC offers a technically sound, broadly representative basis for the ongoing development of a harmonized regulatory test procedure for heavy-duty brake particle emissions.