in Order to reduce the emission of fine particulate matter in the streets of Paris, the ile-de-france are invited to abandon the car in favour of public transport. But what to do when the platforms of metro and RER are also invaded by this pollution? The authorities care about the poor air quality of the transport network underground in the Île-de-France. The braking system of trains, which causes a massive concentration of fine particles in the air, is directly responsible for this. "The paradox is that we are told that "it is very polluted at the surface, take the underground", but one is likely to find the pollution in the metro", lamented the president of the region Île-de-France, Valérie Pécresse, in march 2018.

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The gare de Avenue-Foch, RER C), hosts since Monday, an experiment aimed at improving the quality of the air breathed in by the users. Six machines designed by Air liquide have been installed on the docks, with the function to filter the air, according to the process of"ionization positive". After having sucked in the polluted air via a ventilation system, the machine retains the bad particles, and rejects that of the air "clean". Three sensors are installed next to the machines by Air liquide, SNCF and the association monitoring the air quality in the Ile-de-France (Airparif) will measure the effectiveness of the system. Next Friday, the station Alexandre-Dumas, on line 2 of the metro, will be the subject of an experiment similar, conducted this time by the company Suez.

These initiatives more widely in the project "Innovating for the air of our stations," launched in march 2018, by the region Ile-de-France. Valérie Pécresse, announced "one million euros to be able to clean up the air in the stations, metro stations, so that the agents of the RATP, but also the travelers can travel in good conditions". The challenge is of size. Almost 1.5 million passengers in the île de france, 12% of the regional population, are exposed every day to levels of pollution are considerable. In the stations Aubert, Franklin Roosevelt and the Châtelet, "50% of concentrations of PM10" (particles in suspension whose diameter is smaller than 10 micrometers) are more than ten times higher than thresholds recommended by the WHO, according to the data of the plan for the air in the Île-de-France.

For its part, the national Agency health safety of food, environment and labour (ANSES) said in 2015 that "the concentrations of mass" of the particles suspended in the air in the underground stations were "significantly higher than those measured in the outdoor air, even in the vicinity of road traffic". In April 2018, the RATP has set up a monitoring system allowing users to view real-time data relating to the quality of the air in some stations in paris.