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Atmosphere
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Brake Wear Particle Emissions: Formation, Transport, Sampling and Prevention
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Brake Wear Particle Emissions: Formation, Transport, Sampling and Prevention

A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Air Quality".

Deadline for manuscript submissions: 30 November 2026 | Viewed by 3508

Editors

Dr. David Hesse

E-Mail Website
Guest Editor
Department of Brake Development, Volkswagen AG, 38436 Wolfsburg, Germany
Interests: brake testing; brake emissions; tribology and the fundamentals of particle formation; modeling and simulation
Dr. Sebastian Gramstat

E-Mail Website
Guest Editor
Development Brake System, AUDI AG, 85045 Ingolstadt, Germany
Interests: electric vehicle design
Dr. Frank Schiefer

E-Mail Website
Guest Editor
Institute for Particle Technology, TU Braunschweig, Schleinitzstr. 20, 36106 Braunschweig, Germany
Interests: particle-influenced contacts; tribological experiments; particle and brake emissions; data-driven hybrid modeling; simulation
Dr. Valentin Ivanov

E-Mail Website
Guest Editor
Smart Vehicle Systems, Technische Universität Ilmenau, 98693 Ilmenau, Germany
Interests: non-exhaust emissions; software defined vehicles; brake control
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Traffic-related emissions are associated with adverse effects on the environment and human health. As the tailpipe has been the biggest contributor to the overall emission level, regulations have been put in place over the past decades to limit the emissions from this source. Consequently, other sources of emissions, such as those from the friction brakes, which belong to the group of non-exhaust emissions, have become the focus of scientific research. From November 2026, Europe will be the first region to implement the Euro 7 emissions standard, which regulates non-exhaust emissions. Other regions of the world, such as China and South Korea, may also follow suit and introduce regulations on brake wear particle emissions.

To comply with potential limit values, continuing to use friction brakes with most conventional material pairings is insufficient. New approaches are needed to reduce particle formation, such as improved operating modes, new brake technologies, or low-wear material pairings. Furthermore, a better understanding of the tribological processes involved in particle formation during frictional contact is required, as these processes involve various interconnected mechanical, thermal, and chemical phenomena. Only then will it be possible to combine high safety and comfort requirements with the need to reduce emission levels.

This Special Issue aims to promote progress in the field of brake wear particle emissions, which is set to become the focus of scientific research in the future due to new emission standards. Topics covered include the tribological aspects of particle formation, airborne particle transportation, sampling, and emission prevention. New findings relating to the measurement and characterization of particles are also welcome. Studies of an experimental, simulated, or mixed nature on various scales are generally appropriate.

Dr. David Hesse
Dr. Sebastian Gramstat
Dr. Frank Schiefer
Dr. Valentin Ivanov
Guest Editors

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • brake wear particle emissions
  • particle formation
  • tribology
  • particle injection, transport and deposition
  • sampling, measurement
  • filtration and suction systems
  • regenerative braking
  • coated brake discs
  • low-wear friction pairings

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Published Papers (4 papers)

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Research

26 pages, 7844 KB  
Article
Evaluation of Active and Passive Brake Emission Mitigation Strategies in Real Driving Scenarios
by Alexander Hentschel, Miles Kunze, Patrick Habedank, Valentin Ivanov and Sebastian Gramstat
Atmosphere 2026, 17(7), 662; https://doi.org/10.3390/atmos17070662 - 30 Jun 2026
Viewed by 139
Abstract
Brake wear particles are an increasingly relevant source of traffic-related particulate emissions and are addressed by the recently introduced Euro 7 emission regulation. Airborne fractions of brake wear emissions, in particular, have been associated with adverse effects on human health and other organisms. [...] Read more.
Brake wear particles are an increasingly relevant source of traffic-related particulate emissions and are addressed by the recently introduced Euro 7 emission regulation. Airborne fractions of brake wear emissions, in particular, have been associated with adverse effects on human health and other organisms. Although several brake particle mitigation strategies have demonstrated promising results under controlled laboratory conditions, their effectiveness under variable open-road driving conditions remains insufficiently understood. This study therefore investigates the transfer of two test-bench-validated mitigation strategies to a fully instrumented passenger vehicle capable of measuring brake particle number (PN) and particulate mass (PM) emissions. The first strategy is a passive approach based on a modified brake pad–disc material pairing, while the second is an active filtration system that extracts particle-laden air directly from the brake friction zone. Both approaches were evaluated during two open-road driving cycles: a real driving emissions (RDE)-compliant cycle and a more dynamic cycle characterized by higher brake stress. Airborne particle emissions were measured over a size range from 300 nm to 10 µm. During the RDE-compliant cycle, the passive approach reduced PN and PM emissions by 44% and 94%, respectively, compared with the reference brake system. Under the higher thermal and mechanical loads of the dynamic cycle, the reductions decreased to 10% for PN and 64% for PM. The active filtration system achieved an increase in PN of 4% in RDE conditions and 11% under high-severity driving. Nevertheless, PM emissions were reduced by 23–97%, depending on its operating mode of the filtration system and the associated airflow and energy demand. For high-severity driving, the PM emissions have been reduced by 40% compared to the reference braking system. These results show that both mitigation approaches hold the potential to reduce brake particle emissions under open-road conditions, although their effectiveness depends strongly on brake load and system operation. The study extends previous laboratory-based investigations by directly comparing passive and active mitigation strategies on the same vehicle under real-world driving conditions. Full article
(This article belongs to the Special Issue Brake Wear Particle Emissions: Formation, Transport, Sampling and Prevention)
18 pages, 2587 KB  
Article
A Comparative Statistical Analysis of Two Brake Emission Test Cycles
by Sampsa Martikainen, Selina Wassermann, Michael Peter Huber, Tobias Zimmermann, Heinz Bacher, Harald Mayrhofer and Christoph Weidinger
Atmosphere 2026, 17(5), 528; https://doi.org/10.3390/atmos17050528 - 21 May 2026
Viewed by 317
Abstract
Non-exhaust emissions represent a growing share of traffic-related particulate matter and are increasingly addressed by regulatory frameworks. This study presents a comparison of two brake emission test cycles, the California Brake Dynamometer Cycle (CBDC) and Worldwide Harmonized Light Vehicles Test Procedure Braking Cycle [...] Read more.
Non-exhaust emissions represent a growing share of traffic-related particulate matter and are increasingly addressed by regulatory frameworks. This study presents a comparison of two brake emission test cycles, the California Brake Dynamometer Cycle (CBDC) and Worldwide Harmonized Light Vehicles Test Procedure Braking Cycle (WLTP-BC), the latter being formally embedded in current regulations. Firstly, we present a detailed comparison of WLTP-BC and CBDC in terms of parameters that are shown to affect or may affect braking control and particle emissions (braking torque, vehicle speed, acceleration, friction work, disc temperature, etc.). Secondly, we present a way to evaluate test system torque control quality, supplementing the friction work-based method present in United Nations Regulation (UNR) No. 179, and quantitatively assess the control quality between the cycles. CBDC was found to be the more challenging cycle to execute. However, the testbench control architecture was found to be sufficient to execute it with high fidelity. Thirdly, we present the emission results obtained from the cycles, both per kilometre driven, as well as per friction work done. We argue that the latter is better for comparing the emission results obtained from cycles with different braking profiles. Driving the CBDC resulted in higher particle mass (PM) emissions but similar particle number (PN) emissions. In light of this dataset, friction work seems to be a better predictor for PN than for PM. While this study encompasses only a single friction pair, and more tests with different brakes would be required to generalize the findings, the results highlight the importance of cycle selection in emission research, both in terms of quantifying the emissions and demands for the test system. Full article
(This article belongs to the Special Issue Brake Wear Particle Emissions: Formation, Transport, Sampling and Prevention)
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13 pages, 1825 KB  
Article
Influence of Caliper Position on Particle Emission Test Results in Heavy-Duty Brake Emission Test Systems
by Sampsa Martikainen, Michael Peter Huber, Harald Mayrhofer and Christoph Weidinger
Atmosphere 2026, 17(5), 527; https://doi.org/10.3390/atmos17050527 - 21 May 2026
Viewed by 225
Abstract
Brake wear is a major contributor to non-exhaust particulate emissions, and standardized measurement methods are currently being extended from light-duty (LD) to heavy-duty (HD) vehicles. However, differences in brake geometry and operating conditions may influence particle transport and sampling representativeness in HD brake [...] Read more.
Brake wear is a major contributor to non-exhaust particulate emissions, and standardized measurement methods are currently being extended from light-duty (LD) to heavy-duty (HD) vehicles. However, differences in brake geometry and operating conditions may influence particle transport and sampling representativeness in HD brake emission test systems. This study investigates the influence of brake caliper position on particle emissions and mixing uniformity in an HD brake emission test setup. Experiments were conducted using a dynamometer-based system with four sampling probes distributed across the sampling plane. Emissions of particulate mass (PM10, PM2.5) and particle number (solid and total particle number emissions for particles >10 nm) were measured for two caliper orientations (horizontal and vertical). Mixing quality was assessed by comparing probe-specific emission results to the plane-averaged value. The results show that the vertical orientation was associated with 34% higher PM10 and 40% higher PM2.5 emissions on average, a significant increase. Particle number emissions also increased on average, but the differences were small relative to test repeatability. The more pronounced effect on PM suggests that the caliper position mainly influences the transport and losses of larger particles, which contribute more to PM. In contrast, the uniformity of particle concentration across the sampling plane was similar for both configurations, with deviations comparable to those reported for LD systems. These findings should be considered in the interpretation of results obtained with any similar test systems, comparisons between such systems, and literary reviews. Full article
(This article belongs to the Special Issue Brake Wear Particle Emissions: Formation, Transport, Sampling and Prevention)
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28 pages, 54121 KB  
Article
Effect of Friction Material on Vehicle Brake Particle Emissions
by Marie Hoff, Yan-Ming Chen, Laurent Meunier, Christophe Bressot and Martin Morgeneyer
Atmosphere 2025, 16(9), 1075; https://doi.org/10.3390/atmos16091075 - 11 Sep 2025
Cited by 7 | Viewed by 1614
Abstract
This study focuses on the influence of different brake pad formulations on the emission of particulate matter coming from car braking systems. The brake particles were characterised using a pin-on-disc bench and some particle measuring devices such as CPC, APS, SMPS and a [...] Read more.
This study focuses on the influence of different brake pad formulations on the emission of particulate matter coming from car braking systems. The brake particles were characterised using a pin-on-disc bench and some particle measuring devices such as CPC, APS, SMPS and a PM10 sampling unit. Seven samples of brake pad materials of different compositions (1 NAO and 6 Low Steel) were tested against grey cast iron discs. The results presented in this work show differences in particle number concentration and PM10 emission factor between the different friction materials tested. Three friction materials, LS04, LS06 and NAO01, reduce particle number emissions by up to 71% and PM10 emissions by up to 57%. On the other hand, this reduction in particulate emissions goes along with a reduction of 20% to 27% in the coefficient of friction. The microscopic analyses carried out on the test parts (pins and discs) show differences between the most emissive and the least emissive friction pairs, which may explain the differences observed in particle emissions. Correlations between the emission of particles and the concentration of iron of the PM10, as well as the steel fibre content in the formulas, were found. Full article
(This article belongs to the Special Issue Brake Wear Particle Emissions: Formation, Transport, Sampling and Prevention)
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