This is one of the main recommendations of the public authorities during pollution peaks in urban areas: favor public transport over the car. However, the levels of particle concentration are on average three times higher in the various French metros than in the urban ambient air, warns the National Health Security Agency (Anses) in an expert report published on Wednesday June 8. Also, ANSES insists on the need to reduce this pollution to limit the exposure of users and proposes new indicators with concentrations not to be exceeded. The agency had been seized in August 2019 by the general directorate of health in order to establish “guideline values for indoor air associated with user exposure in underground railway enclosures ».
Air quality in the metro is one of the blind spots of anti-pollution policies. Unlike ambient air, it is not regulated and therefore very little monitored. However, it is a public health issue. Several million people use underground transport every day in the conurbations of Paris, Marseille, Lyon, Lille, Toulouse, Rennes and Rouen. The Ile-de-France network, one of the busiest in the world, is used by around 5 million travelers per day. And by 2030, with the Grand Paris Express, Ile-de-France should have sixty-eight stations and 200 kilometers of additional lines, mainly underground.
Air quality measurements in underground railway enclosures, introduced only at the beginning of the 2000s, reveal concentrations of particles “very superior” (about three times) to those measured outside in an urban background. By particles, we mean PM10, greater than 10 micrograms per cubic meter (µg/m3) and PM2.5 (less than 2.5 µg/m3), the most dangerous to health because they penetrate deeper into the body. The Respire association has been carrying out measurement campaigns on the Ile-de-France network for several years. In March 2021, she filed a complaint against the RATP for “aggravated deception” and “unintentional injuries” after finding peaks of up to 500 µg/m3 at the Auber RER station, ten times more than the alert threshold for a pollution peak.
Concentrations not to be exceeded
However, is it more dangerous to breathe particles in suspension in the metro for a few minutes a day while waiting for your train on the platform or to inhale the exhaust gases stuck in your vehicle and the traffic jams on the ring road? Not easy to settle the question scientifically. The sources of particle emissions in the metro are clearly identified: the wear of materials due to the braking of trains and contact between the rolling stock and the railway, or even the resuspension of dust linked to the passage of trains .
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