Factors influencing air quality in underground railway enclosures

Several factors explain the variation in the quality of the air breathed in these spaces:

• Attendance at places (the higher the attendance at a station, the more the air quality is impacted)
• The depth of the station (the deeper the station is located, the more difficult the air exchanges are, particularly if the ventilation system is not optimal and the less the air is of good quality)
• Ventilation
• The metro or RER trains that run there (the equipment used is not the same from one line to another
• Train running frequency
• The age of the station (the first metro stations were built at the beginning of the 20th century, while others are much more recent)

Particles: the majority pollutant

Compared to the outside air, nitrogen dioxide is found in lower concentrations and ozone is almost absent from these enclosures.

Particles, on the other hand, represent the most present pollutant, for two main reasons:

• The movement of trains, and above all, the braking system. A situation all the more marked as the station is very busy.
• The resuspension of particles deposited on the ground by the passage of trains and the movements of passengers.

Due to these two elements, particle concentrations remain higher on platforms, in the immediate vicinity of trains, than in other station spaces, such as corridors.

Evolution of PM10 concentrations over one day on the RER C platform at Avenue Foch station over the period from April 2018 to December 2022. 

The dark blue line represents the average evolution, the blue surface the evolution of concentrations for a given hour. At night, when stations are closed to the public, high levels can occasionally be measured on the platforms. They are generally linked to work on the tracks.

Available data

As part of its partnership with Île-de-France Mobility, Airparif has published a first map of particle pollution on 44 metro, RER and Transilien platforms in underground or mixed stations (both underground and in the air). free). The 44 station platforms present air pollution levels which vary greatly from one station to another, and from one time of the day to another. Of the 44 stations, 3 (all underground) have high levels of air pollution compared to the thresholds recommended by the National Agency for Food, Environmental and Occupational Health Safety (ANSES). ). For more information, see thededicated news.

Airparif has also worked in partnership with SNCF Gares & Connexions since 2016. Thus, a major measurement campaign was carried out between September 2016 and September 2018 at 25 stations on the Transilien network, with Airparif and the Railway Testing Agency (AEF). 

This partnership also made it possible to implement continuous measurements carried out by Airparif on the RER C platform at Avenue Foch station. This station was chosen according to its typology, its traffic, its attendance and the level of dust. Continuous and live measurements are accessible online.