It is no longer mandatory to wear a mask in the metro, even if, given the proximity between passengers, it remains highly recommended to avoid catching all sorts of germs. On the other hand, more and more voices are being raised against the abnormally high level of PM10 fine particle pollution in the stations. Is there a risk to the health of users and workers in the underground network? Should you wear an anti-pollution mask on the Metro?
Is Parisian Metro air more polluted than outside?
A 2019 study by Franch Respire association shows that the amount of fine particles is up to ten times higher in the corridors and tunnels of public transports Paris metropolis than outside. These measurements were carried out in partnership with the RATP (Parisian Metro company) autonomous union and a CNRS researcher, Jean-Baptiste Renard. RATP comapny contested these results "measured with portable devices which are not the official/reference ones placed in 3 Parisian stations".
Particles come from two sources. On the one hand, the polluted air from the streets is ventilated into the stations. On the other hand, the trains themselves create brake pad dust when braking and friction between the wheels (or tires) and the rails. We're not even talking about maintenance work. It is estimated that around 450 tons of material are emitted in this way each year in the metro.
Respire association, whose reports point to alarming levels of pollution in Parisian stations, has already filed complaints for "aggravated deception and unintentional injuries".
In May 2023, an investigation by journalists from the show “ Green with rage » measured the concentration of fine particles with a diameter less than 2.5 micrometers (PM2.5) – the most dangerous because they penetrate the deepest into our lungs and blood – on average at 24 micrograms per cubic meter (μg/m³) in the metro and RER stations in the Paris region, with peaks at more than 100 μg/m³. The threshold not to be exceeded according to the WHO is 5 μg/m³ for annual exposure, and 15 μg/m³ for daily exposure.
On Jan 22nd 2024, it was the turn of Ile de France Mobilité (IDFM), the managing company of the Grand Paris area transport network, to unveil a map of air pollution in the underground transport network showing a very high concentration of fine PM10 particles in the Belleville, Jaurès and Oberkampf stations as shown in the map below. Surprisingly, It only refers to the coarsest particles (10µm) which do not penetrate deep into the respiratory tract. PM2.5 are not taken into account in the study.
Air as polluted as in Beijing or New Delhi…
Want a pollution fix? Take the subway! The latest figures show pollution levels in some stations comparable to those in cities like Beijing or New Delhi, known for their very poor air quality. For the Respire association, the RATP's measurement system is insufficient: "Three sensors for a network of more than 300 stations, with huge disparities, are not representative of reality. A more developed monitoring network is needed."
Aware of the problem, Île-de-France Mobilités has already invested 57 million euros with the RATP to improve or renew the ventilation systems in the metro and RER (suburb trains). The problem is that ventilation introduces polluted air from outside. It would have to be filtered to be efficient.
In addition to the millions of daily users, the 26,000 employees of public transports are also affected: drivers, security agents, controllers, maintenance workers as well as the 8,000 workers responsible for maintaining the network.
Where do these subway particles come from?
A lot of particles come from when train brake pads. The responsibility lies with the friction between the brake pads and the wheels or brake discs but also between the wheels. Brake pads are a mixture of resins, metals and minerals . " If we zoom in on these surfaces, which appear smooth, we see that they are rough. When they rub, this slows down their movement, but at the same time generates particles , explains Martin Morgeneyer, a teacher-researcher at the University of Technology of Compiègne (France).
The toxicity of these metal particles present in confined railway spaces would be greater than that of particles in urban outdoor air.
Danger is linked to exposure duration
Professor Bruno Crestani, a pulmonologist at Bichat Hospital in Paris and president of the Breathing Foundation, puts things into perspective by saying that we must first look at the duration of exposure to pollutants. On average, a user spends 36 minutes in the Parisian metro. "The health impact of short-term exposure to fine particles has not been demonstrated. The probability of there being a toxic effect of this pollution on users is really very low." On the other hand, he states that this air pollution in the metro could have an impact on the health of those who work there.
The technologies are ready but not RATP
Wabtec, an American company, seems to have developed a very interesting solution. This railway equipment specialist has developed a new brake technology called " Green friction " , whose composition, kept secret, would reduce PM2.5 fine particles by 85%, and PM10 by 90%. An experiment took place in 2021 on but since one train line but nothing has progressed for a deployment. The system is in fact more expensive than the classic system…
Which anti-pollution mask to wear in the Metro?
Wearing an FFP2/N95 mask as Frogmask can fully protect users and underground professionals. FFP2/N95 filter blocks fine particles up to 0.4µm. Mask breathability allows to be worn for long hours without being more bothered than with a classic paper mask but with a better seal.
With its two nosebands, one on the filter and the other on the mask, exhaled air does not rise up the nose and therefore prevent from fogging glasses even indoors.
What are the alternatives?
If you have the possibility and you do not live too far from your work, bike commuting is a very virtuous solution. This practice is becoming more and more widespread for a multitude of good reasons: speed, Metro card saving or exercising to feel more fit. Let's go to work by bike!
