Pollution in the metros in Marseille: is the situation worse than elsewhere?

We take stock with AtmoSud of the air quality in the Marseille metros. (©Atmo Sud)

The National Health Security Agency (Anses) published a study on June 8 on fine particles (dangerous for the respiratory tract).

The organization recommends strengthening actions to improve air quality in metros. The level of fine particles in railway enclosures is “on average three times higher than that recommended by WHO.

So what about air quality in the Marseille metros? We put the question to Mathieu Izard, study engineer at AtmoSud, the air quality observatory in the Provence-Alpes-Côte d’Azur region.

The clues

In Marseille, the reference value for fine particles present in the air of metro stations used by AtmoSud is:

– 480 micrograms per m³ and per hour (this is a non-binding limit value. A ceiling not to be exceeded.)

The reference value set by the World Health Organization (WHO) is much stricter:

– 140 micrograms per m³ and per hour (this is a recommendation that you must try to respect. It is not binding.)

None of the metro stations meet the WHO standard

In Marseille, according to studies by AtmoSud, none of the metro stations meet the WHO standard. The times with the highest concentrations of fine particles are obviously the peak times. That is, from 7 a.m. to 9 a.m. and from 5 p.m. to 7 p.m.

The main cause would be the friction of the wheels on the tracks during braking, which pulls iron, and to the dust resuspended with each passage of the oar.

The limit value (480 micrograms per m³) is only reached in no station.

“We cannot precisely determine the impact on the health of users”, specifies Mathieu Izard. ANSES still indicates a potential risk of inflammation of the respiratory tract and heart problem.

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“Three to five times higher in the metro than in the outdoor air”

For fine particles, “we are on concentrations three to five times higher in the subways than in the outside air”, says the researcher. He adds that this varies by station.

Outdoor air quality has an impact on indoor air. Thus, the Réformé metro station, at a lower level of concentration than that of Perrier, which is located on a boulevard.

Marseille, worse than the others?

“Most territories meet WHO standards”, nuance Mathieu Izard. Indeed, metros are confined spaces, “pollutants therefore have difficulty getting out”.

He adds: “I don’t think any city is able to meet WHO standards. According to him, some old Paris metro ramps are even much more polluted.

In addition, the expert notes that “the fine particles present in the air of metros are rather large. Or, it’s the finest of them that are the most dangerous.

How to improve the situation?

Even if “there is not much to do”, the engineer is nevertheless encouraged by the work to come on the Marseilles network: “The metro trains should be completely changed between 2023 and 2024.

The frames will change braking system. And still according to the expert, this should reduce the emission of fine particles.

Another novelty which will make it possible to limit the spread of these particles from the rails to the platforms: the public authorities plan to install “landing doors”.

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The new metro ramps with screen doors. (© South Provence-Alpes-Côte d’Azur Region)

Mathieu Izard also made a point of specifying that the studies on the quality of the air in the Marseilles subways were ordered by the RTM before the State does not begin to recommend it to the various agglomerations.

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