Air quality is a major public health issue over the world. Rail transportation is rightfully considered as one of the greener and more CO2-efficient mobility solution. However, many studies have evidenced bad air quality in confined railway stations leading to major concerns regarding particles from non-exhaust emissions (Querol et al., 2012; Martins et al., 2015). In addition to particles, Volatile Organic Compound (VOC) emissions are also expected to worsen air quality (Yang et al., 2023), although much less investigations have been carried out. The objectives of the presented works were (i) to characterize VOC emissions of a railway braking system from two braking benches: a 1:1-scale bench at Alstom Flertex facilities and a reduced scale bench at LaMcube laboratory; (ii) to evidence relationships between VOC emissions, brake materials, and braking conditions. Different braking conditions were tested like the initial speed and temperature and the force applied to the system. The two benches were instrumented to control braking parameters and to measure VOCs and particles (not reported here) emissions, both online and offline. VOC characterization instruments include an online Photo-Ionization Detector (PID, for total VOCs) and sampling on Tenax followed by gas chromatography mass spectrometry and DNPH (dinitrophenyl hydrazine) cartridges analyzed by liquid chromatography (for speciated VOCs and carbonyls, respectively). The methodology for VOCs measurements will be first presented, including the advantages and the drawbacks of the two setups and the associated limitations. The results pinpointed a number of identified and quantified VOCs. The potential origin of these compounds (brake pad, side emissions from lubricant or else, ambient air) was carefully looked at, with particular attention to the chemical composition of the organic brake pad. Possible relationships between VOC emissions, braking system and particles will be discussed. This work represents one of the first comprehensive analysis on VOC emissions from railway brake systems. Acknowledgements: The present work takes place within the BREAQ project funded by the French government as part of the PIA, Invest for the Future Plan, now integrated into France 2030, and operated by ADEME, the French ecological transition agency. References V. Martins, T. Moreno, M. C. Minguillón, F. Amato, E. de Miguel, M. Capdevila, X. Querol, Exposure to airborne particulate matter in the subway system, Sci. Tot. Environ. 511, 711–722 (2015) X. Querol, T. Moreno, A. Karanasiou, C. Reche, A. Alastuey, M. Viana, O. Font, J. Gil, E. De Miguel, M. Capdevila, Variability of levels and composition of PM 10 and PM 2.5 in the Barcelona metro system. Atmos. Chem. Phys. 12, 5055-5076 (2012) J. Yang, X. Fan, H. Zhang, W. Zheng, T. Ye, A review on characteristics and mitigation strategies of indoor air quality in underground subway stations, Sci. Tot. Environ. 869, 15 April 2023, 161781 (2023)

Ms. Raafa Al Kaderi, PhD student, IMT Nord Europe; Dr. Asma Grira, Post-doc, IMT Nord Europe; Ing. Marina Jamar, Engineer, IMT Nord Europe; Dr. Laurent Alleman, Assistant Professor, IMT Nord Europe; Dr. Esperanza Perdrix, Assistant Professor, IMT Nord Europe; Dr. Edouard Davin, Assistant Professor, Centrale Lille; Dr. Alexandre Mege-Revil, Assistant Professor, Centrale Lille; Ing. Marie-Jeanne Robert, Engineer, Alstom; Prof. Dr. Yannick Desplanques, Professor, Centrale Lille; Prof. Dr. Alexandre Tomas, Professor, IMT Nord Europe