Non-exhaust emissions in general and brake particle emissions in particular are considered to offer huge potential in the improvement of air quality in densely populated city centers. Legislative authorities started to look into the topic of Brake Dust emissions for a post-Euro 6 regulation. Based on the recommendations of the informal working group of the "particulate measurement program" (PMP) in Europe, HORIBA developed an integrated solution to measure brake particle emissions on a brake dynamometer.

The presentation introduces some of the influencing factors on the particle number emission measurement based on the PMP method. The WLTP-Brake test cycle, dyno settings such as the drafted cooling air adjustement method and other already existing technical requirements are discussed in terms of their influence on the PN emissions. Experimental results outline some of the related challenges before an outlook on the open issues regarding Brake Dust PN is given.

Particulate pollution caused by traffic is an important socio-political issue nowadays. In addition to the engines as a source of particulate matter, non-exhaust sources of vehicles like tyre, road abrasion and the brake are moving into focus due to the improved exhaust after-treatment and electrification. Although many studies have looked into brake particle number, mass and size distribution until now, the formation of this particles and their change within the frictional contact haven't been complete revealed. However, the understanding of these mechanisms is important. This knowledge can help, for example, to identify possible reduction potentials. In order to achieve a better understanding about the mechanisms that occur between the brake pad and the brake disc, tests are carried out on a tribological brake test rig. Using a borosilicate glass disc instead of a cast iron disc, allows optical in-situ measurements with a high-speed camera equipped with a magnification lens. The microscopic system is mounted on a linear bearing and can be moved stepwise in horizontal and vertical direction. Therefor sequential observation of the entire brake pad is feasible. In addition, 3-D images provide insights into the influence of the local structure of the pad. Besides, a newly developed sampling method will be used to remove wear mass from the system and analyze it chemically. This procedure can also be applied in combination with a grey cast iron disc, which allows further validation of the described glass method. By recording of the pad surface section by section, insights about the distribution of the brake particle movement within the tribological system can be gained. Hereby it can be analyzed, whether only the location on the pad influences the occurrence of particle motion or also other influencing variables exist. For instance, the presence of primary and secondary patches, as well as deposited wear mass and the surface morphology could be important. The 3-D images in combination with the chemical analysis can shed light on the mechanisms of wear mass deposition. Therefore this study shows new findings about brake particle behavior with regard to pad location, surface structure and chemical composition. In addition, the phenomenon of deposited mass is analyzed more precisely.

This innovative project is addressing the topic, "Brake dust emissions measurement"; specifically, the further investigation of non-exhaust emissions coming from the brake system during the novel WLTP Cycle establish by the PMP Group.

Road transport is one of the most important sources of urban pollutant emissions. The upcoming trend of vehicle electrification is enhancing the non-exhaust emissions, with the brake wear particles as the most important part of it. Moreover, the health effects of PM are also proved that it is an important issue to mitigate. Hence, the need to study brake dust emissions behaviour as well as standardize a procedure and methodology to measure them has rocked.

This project aims to contribute in this new study; specifically, the main objectives are, on the one hand, to establish a measurement protocol to measure brake particles emissions during the novel WLTP cycle and, on the other hand, to understand brake wear particles behaviour (among PN and PM concentration, speed and brake temperature influence in the measurements, the impact of brake pressure conditions and pad materials on the results, etc.). Furthermore, emission measurements under standardized technical conditions to harmonize aspects of hardware, enhance the accuracy and definition of the measurement protocol.

According to the previous studies in that topic, a Sealed House for Emissions Determination (SHED) with a constant HEPA filtered airflow and a defined extraction has been used to collect the dust coming from the brake system. In addition, a brake dynamometer adapted to the aim of the project has been used, with different particles measurement equipment such as Horiba OBS-ONE PN 23 nm, Dekati HRELPI+ size distributor and eFilter (PM measurements) or PEGASOR Particle Sensor.

Along the different testing campaigns performed, interesting events has been found, for instance, the influence of the air flow rate in the SHED system to the final PN and PM concentration results or the particles emitted while the brake system is not acting (brake-off events).

In this paper, the most relevant results will be presented: the testing procedure defined for measuring brake dust emissions and the main findings about the particles behaviour. All in all, this study will help finding the conditions where the emissions events are mainly being triggered, leading to possible countermeasures that mitigate their effect.