RESEARCH AND/OR ENGINEERING QUESTIONS/OBJECTIVE Increasing levels of particulate matter in urban areas is a growing global concern due to the negative impact on human health. Accordingly, the next EURO 7 emissions standard will extend its scope to regulate non-exhaust emissions which contribute significantly to traffic-related PM10 emissions. The objective of this study is to provide a comprehensive analysis of the methods used for characterizing brake particles in the recent literature. Through a systematic review it identifies the prevailing standards, types of tests, and sensors used in the field providing, statistical data related to each category. METHODOLOGY A systematic literature search was performed on the Engineering Village website by entering the keywords brake, wear, friction, particle, emission, and airborne. The search was limited to a set time frame (2017-2022) and to Q1 journals which are considered the most prestigious and influential in their respective fields. Altogether, 175 papers were identified and subsequently screened to select those related to brake wear particle emissions. The remaining 74 papers were analysed and data was extracted to obtain the statistics regarding: brake standards, text type, and sensors for measuring brake wear particles. RESULTS This review analysed 74 studies on brake particle emissions. Regarding the testing standards mentioned in the articles, the statistics show that there is no predominant standard due to the lack of consensus among researchers. Tribometers and dynamometric benches were found to be the most widely used equipment, accounting for 54% and 45% of the total, respectively. A wide variety of test configurations and testing conditions were also identified. Considering that after the publication of the reviewed papers the European Commission has established a method that provides comprehensive instructions for performing measurements, the test conditions are no longer open to discussion. However, the devices necessary to capture PM10 particles also significantly affect the results. Electrical Low-Pressure Impactors (ELPI), Engine Exhaust Particle Sizers (EEPS), Optical Particle Sizers (OPS) and Condensation Particle Counters (CPC) were identified as the most common sensors used to evaluate brake particle emission.   LIMITATIONS OF THIS STUDY The limitations of the study include its time frame (2017-2022) and focus on Q1 journals. These limitations should be considered when interpreting the results of the review and planning future research in this field. WHAT DOES THE PAPER OFFER THAT IS NEW IN THE FIELD IN COMPARISON TO OTHER WORKS OF THE AUTHOR? To the best of the authors knowledge, this is the first systematic review providing an overview of the current state of the art in particle measurement testing for braking systems. It highlights the methods, techniques and sensors commonly used in the field today. This review can assist researchers determine the most appropriate and effective particle collection system. CONCLUSION The study reveals a lack of consensus among the scientific community regarding the characterization of brake wear particle emissions, and highlights the current state of the art. Based on the findings, the authors conclude that accurate particle measurements require the use of multiple sensors. An impactor should be utilized to capture and filter particles based on their size, followed by additional sensors for particle sizing and counting.

Mr. Sergio Fernández, PhD Student, Mondragon Unibertsitatea; Dr. Iñigo Llavori, Researcher/Lecturer, Mondragon Unibertsitatea; Dr. Andrea Aguinagalde, Researcher/Lecturer, Mondragon Unibertsitatea; Dr. Josu Eguia, Researcher/Lecturer, Mondragon Unibertsitatea; Mr. Asier Rodríguez, Innovation Projects Manager – Product Development, EDERTEK S. Coop.; Mr. Ricardo Labrador, Product Development Director, EDERTEK S. Coop.; Dr. Alaitz Zabala, Researcher/Lecturer, Mondragon Unibertsitatea