SYTRAL Mobilités, in collaboration with Atmo Auvergne-Rhône-Alpes, has released the results of air quality monitoring in the Lyon metro system for 2025. The data reveal a continuous downward trend in fine particles, with notable reductions compared to previous years.
At the Saxe-Gambetta station, PM10 concentrations decreased by -2.5% and PM2.5 by -7% in 2025 compared to 2024. Since 2020, the reduction has reached -58% for PM10 and over -70% for PM2.5. These improvements are partly attributed to the commissioning of new trains on line B in June 2022, which significantly reduced average concentrations, as well as the continuous operation of air purification systems installed on the platforms.
Fine particles, mainly composed of iron (70 to 91% of analyzed metals), primarily originate from train braking, which wears down brake pads and wheels. Their concentration follows traffic patterns, increasing during peak hours and decreasing during off-peak times, and dropping sharply at night and on weekends. Monitoring is conducted via a permanent station at Saxe-Gambetta, measurements aboard trains on lines A, B, and D, a classification of 38 stations, and in-depth metal analysis campaigns.
Onboard the trains, improvements are also significant between 2022 and 2025: line A shows a decrease of -60% for PM10 and -48% for PM2.5; line B, -87% for both particle types; and line D, -63% for PM10 and -61% for PM2.5.
To further enhance air quality, SYTRAL Mobilités is acting on three complementary fronts: emitting fewer particles with modern trains, capturing existing particles on platforms using filtration systems (MANN+HUMMEL, Para-PM), and deep cleaning of stations and tunnels through vacuuming. This latter method, successfully tested at Saxe-Gambetta, Foch, Vieux-Lyon, and Bellecour, reduces concentrations by up to 25% and will be extended to lines A, B, and D.
Monitoring will continue in 2026 with the maintenance of permanent measurements at Saxe-Gambetta, new onboard train measurements, and a station reclassification in the autumn.
