For the first time, pollution mapping in the Paris metro and RER was carried out at the initiative of the transport organizing authority, Ile-de-France Mobilités (IDFM), with the support of Airparif. Made public on Monday January 22, it revealed high levels of pollution in at least three stations.

The question is often raised, without ever being resolved. Is the air in the Paris metro dangerous for your health? The concentration of fine particles, produced when trains brake, can cause respiratory difficulties or illnesses, particularly in vulnerable people. In spring 2023, the Paris public prosecutor’s office opened an investigation for “endangering others” targeting the Régie Autonome des Transports Parisiens (RATP), suspected by the Respire association of concealing from its users an abnormally high level of fine particles .

To have reliable data, IDFM decided to carry out a large-scale study, with the support of Airparif, by asking RATP and the Société nationale des chemins de fer français (SNCF) to take measures for at least one week, seven days a week, twenty-four hours a day. In certain stations, measurements were taken continuously throughout the 2015-2022 period by the RATP and SNCF measurement network.

As a result, three stations display a concentration of fine PM10 particles exceeding 480 micrograms per cubic meter of air (µg/m3), i.e. the maximum threshold recommended by the National Health Security Agency (ANSES) from one hour of exposure. No figures on PM2.5 particles, which are finer and more harmful, have been communicated.

Precise mapping expected in June

The threshold for PM10 is established by ANSES with regard to the exposure time in railway enclosures. The World Health Organization (WHO) recommends a maximum threshold of 140 µg/m3, but this relates to outdoor exposure.

The stations concerned are Belleville, Jaurès and Oberkampf, all located in eastern Paris. Among the other stations studied, thirty-one display a “medium level” of concentration of fine PM10 particles, that is to say between 140 and 480 µg/m3, and ten a “low level”, that is to say -say less than 140 µg/m3.

Another study carried out for the television show “Vert de rage” in 2023, but contested by the RATP, also came to the conclusion that the Belleville station was the most polluted.

“The work communicated by Airparif and IDFM does not reflect the exposure of travelers or employees,” says Sophie Mazoué, director of sustainable development and corporate social responsibility for the RATP group. According to her, no user or employee stays on a platform for an hour, and data should also be available on the trains.

This will be the case in June: IDFM has promised to establish a precise map of the 397 metro and RER stations as well as the lines. “The particles are not the same in the trains and on the platforms. In general, it is a little lower in the trains because the air is ventilated. We will have the verification in June,” said the general director of IDFM, Laurent Probst.

Renewal of fans

At this stage, the very limited scientific literature on air quality in the metro prevents us from issuing a clear opinion on the consequences for health. ANSES suggested the risk of “inflammation of the airways, particularly in sensitive populations, such as asthmatics,” or “effects on autonomic cardiac function.” She rejected “the increased risk of lung cancer or myocardial infarction.”

In the meantime, IDFM intends to ask RATP and SNCF operators to deploy an action plan to improve air quality in the most polluted stations. “The Belleville station will benefit from the renewal of a fan from 2024,” promised IDFM. Jaurès will see his fan reinforced this year; in Oberkampf, a new fan has been operating since the end of 2023 and two additional structures will be built this year. “These three stations will go at least orange, if not green,” Mr. Probst wants to believe.

IDFM also asked to deploy “as quickly as possible a system which reduces emissions of fine particles generated when trains brake”, particularly on the RER A and 1, 2, 3, 4, 5 and 9 metro lines. . At this stage, only the latest generation MP14 metros, deployed on lines 4, 11 and 14, have electromagnetic braking, which does not emit fine particles.