Real-Time Air Quality Monitoring
Air quality monitoring is based primarily on maintaining hygiene and cleanliness standards in RATP spaces—for both passengers and staff.
With the support of Île-de-France Mobilités, RATP has been conducting continuous air quality measurements since 1997 (year-round, 24/7) using reference-grade equipment. These measurements currently take place at five key stations:
- Auber (RER line A)
- Châtelet-les-Halles (RER line A)
- Nation (RER line A)
- Franklin D. Roosevelt (Metro line 1)
- Saint-Germain-des-Prés (Metro line 4 – temporarily replacing Châtelet station on Metro line 4 during renovation works)
These five stations are among the most heavily frequented in the Île-de-France region. You can view continuous air quality measurements for each of them.
In addition, one-off measurements are regularly carried out across the entire network.
Key Figure
For over 25 years, RATP has been working—together with Île-de-France Mobilités (IDFM), ANSES, Inéris, and Airparif—to monitor, assess, and provide expertise on air quality within the underground network.
Airparif, a leading authority on air quality, published a report in July 2022 evaluating the air quality monitoring and information system in underground stations operated by RATP on behalf of Île-de-France Mobilités. In its report, Airparif highlights that the air quality measurement system implemented by RATP for Île-de-France Mobilités over the past 25 years is “the most comprehensive in the world”, notably because it includes the monitoring of multiple air quality parameters (PM10 particles, fine PM2.5 particles, nitrogen oxides (NOx), and carbon dioxide (CO₂)).
According to an international comparison conducted by Airparif, the network operated by RATP ranks among the top five least polluted transit networks in terms of PM2.5 and PM10 levels.
Furthermore, to date, there is no legal or regulatory standard for assessing air quality in underground railway environments. However, in 2022, ANSES issued general recommendations, which RATP is actively working to follow, taking into account passengers’ exposure times.
RATP actions plan
Beyond air quality monitoring across its network, RATP’s air quality improvement plan relies on several key levers:
- Strengthening and modernizing station ventilation systems to improve indoor air renewal. A major €57 million investment plan—funded by Île-de-France Mobilités—has already been launched for the 2021–2024 period.
- Deploying electric braking systems on new trains and testing new materials for mechanical braking.
- Gradual phase-out of combustion engines in maintenance operations.
- Testing various technological solutions to improve air treatment in stations (such as filtration, particle capture, and fixation systems).
- Conducting epidemiological studies on RATP staff exposure to air pollutants.
What about other rail networks?
RATP actively engages in discussions about air quality with other international rail networks (such as Stockholm and London) through the International Association of Public Transport (UITP).
In addition, a summary of studies conducted on other French networks (Lyon, Toulouse, Rennes, Lille) shows air quality levels comparable to those recorded in Paris. In Toulouse and Lyon, peak hourly PM10 levels range between 200 and 500 µg/m³. In London, occasional measurements have shown concentrations ranging from 500 to 1,120 µg/m³.
