The National Health Security Agency was commissioned in 2019 by the public authorities to carry out a study on the feasibility of developing “guide values ​​for indoor air” in “underground railway enclosures” (EFS). Seven cities in France have underground networks: Lille, Lyon, Marseille, Paris, Rennes, Rouen and Toulouse.

The rate of particles in the air is “on average three times higher than in urban outdoor air”, due to friction with the tracks, especially during braking. The dust is also regularly resuspended in the air as the trains pass.

But after reviewing the available data, ANSES considers that it cannot define such “VGAI”, based solely on health criteria, because “the body of specific epidemiological and toxicological studies is too limited to be able to draw conclusions firm on the possible health effects of the exposure of users to air pollution from EFS”.

But she notes that the existing data “suggests the possibility” of cardio-respiratory effects.

The agency therefore proposes instead of VGAI, air quality “indicators”, determined in particular according to the respective durations of journeys on the different networks and which “integrate exposures over a day in different environments – at the home, at work and in transport”.

The accumulation of these particle concentrations should comply with the exposure standards set by a 2008 European directive on air quality and if possible those of the WHO, stricter than EU regulations and tightened in 2021 to take into account account the most recent knowledge on the health impact of air pollution.

In addition, the agency recommends strengthening air quality measurements in these underground networks, which are not yet widespread.

– New braking systems –

On the Parisian network “there are only three stations which are well instrumented”, notes Eric Vial, director of risk assessment at ANSES. And these measurements are carried out by fixed sensors on the platforms, while it would also be necessary to regularly study corridors and trains, underlines the opinion.

The available measurements suggest that European regulations are “generally respected,” explains Marion Keirsbulck of ANSES, who stresses that “this is much less the case” for WHO values.

To improve the situation, it is necessary to continue the measures taken by the operators and “to tackle the emission of these particles, by replacing rolling stock, changing braking systems and improving ventilation” in particular, continues Eric Vial.

And a more systematic and expanded monitoring of air quality would then make it possible to check “if these actions are bearing fruit”.

The air quality in the Paris metro has already given rise to legal action. The Respire association filed a complaint against the RATP in March 2021 for “aggravated deception” and “involuntary injuries”, questioning the levels of air pollution.

Ile-de-France Mobilités (IDFM) launched an action plan at the end of May to improve air quality in metro and RER stations. New measurement points are planned, in particular on ultra-fine particles, the results of which will be public like those already carried out.

The RATP “is extremely mobilized” on the subject, betting in particular on “technological improvement” to reduce emissions at the source, insists Sophie Mazoué, responsible for sustainable development at the Parisian management.

Tests have thus been launched in the RER on new brake linings, whose preliminary “very promising” results on the test bench have shown a 90% reduction in particle emissions, explains the manager. Investments of 57 million euros are also planned for ventilation, with experiments in “electrostatic filtration” and “particle trapping systems” stations.

According to the authorities, air pollution is responsible for some 40,000 premature deaths per year in France.