Air quality metro

Improving air quality, a key innovation priority for Keolis

Air quality metro
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PostedNOV. 23, 2022
Words byKeolis
Keolis is innovating every day to promote a sustainable alternative to car use in all regions and to continue reducing its environmental impact.

Air pollution, a challenge for the environment and public health

Fine particles from natural and industrial sources alter the air we breathe. Every year, air pollution is responsible for 48,000 premature deaths in France and more than nine million worldwide. While transportation contributes to this phenomenon (for example, through fuel combustion and abrasion of tires and braking systems), the massive shift towards shared and motorless mobility is making it possible to reduce the impact of transport on air quality. For this reason, Keolis intends to develop alternative forms of mobility and limit its own emissions while controlling the air quality of its underground metro stations and trains. These major challenges are also opportunities to innovate in the service of passengers.

© Jacek Dylag
© Jacek Dylag



of harmful emissions are linked to private cars in urban areas


out of 4 French people live in areas served by one or more stations connected to a transport network

Limiting particle emissions as much as possible

To limit emissions and thus improve air quality, Keolis is accelerating its energy transition plan by bringing an increasing number of electric- and hydrogen-powered buses into service on its networks while also helping its drivers to reduce their fuel consumption through eco-driving training. At the same time, the Group supports the development of new forms of mobility in all regions such as on-demand transportation, bicycles, and carpooling, and encourages the use of public transportation with digital nudges. New technical processes are also being introduced or studied to limit particle emissions, such as replacing mechanical brakes with electronic brakes in metro systems and injecting hydrogen into the diesel engines of buses.

In Denmark, Keolis uses solar panels on the roof of its buses to promote "green mobility".
In Denmark, Keolis uses solar panels on the roof of its buses to promote "green mobility".

Precise measurement of air quality in the metro

Keolis is also working to keep air pollution in metro stations below the levels prescribed by the World Health Organization and to ensure that passengers enjoy good air quality during their journey, notably following the example of Rennes, where air quality in stations is particularly good.

To do this, precise and regular measurements are required in underground rail facilities. To this end, Keolis carried out six voluntary measurement campaigns between 2004 and 2015. In 2020, this led to a partnership with the French National Institute for Industrial Environments and Risks (INERIS), which publishes a standardized measurement protocol. Together with several mobility authorities, Keolis is committed to taking a shared approach aimed at obtaining new objective and comparable data on fine particles in all underground stations and trains. Analysis of this data in the Group's data labs will provide a better understanding of the factors that impact air quality on a daily basis. In the long run, this approach will enable the Group to establish a tailored air quality treatment process for all its networks. 

Subway station

In order to keep the level of pollution in metro stations below the levels recommended by the World Health Organization, Keolis is working to establish a common air quality treatment process for all its networks.

Capture, vacuum, restore: innovative tools for reducing the pollution index

What kind of innovations are available to help reduce the pollution index in stations? Eric Callé, Keolis' Director of Innovation and Industrialization, emphasized the importance of partnerships during a program on the online media platform Maddyness to mark World Car-Free Day: "We have to work as an ecosystem with startups, research laboratories and universities to find the right solutions together". To measure the impact of solutions to improve air quality, Keolis is working with the startup Bioteos, which has developed an air purification solution based on filtering microalgae.

Maddyness videos are available at the end of the article. 

Eric Callé

Eric Callé

Director of Innovation and Industrialization at Keolis

"We have to work as an ecosystem with startups, research laboratories and universities to find the right solutions together."

The Group has also identified three main challenges related to air quality in stations and is working with mobility authorities to introduce new solutions: 

- Limiting fine particle emissions, for example by partially replacing mechanical brakes with electronic brakes and by training drivers in eco-driving 

- Capturing pollutants at the source by installing a suction device connected directly to vehicle braking systems, allowing dust to be channeled into a vacuum cleaner 

- Treating air in stations with new systems for filtering the air and removing fine particles. Using fans to blow air through filters could help to reduce fine particle pollution by nearly 30%.

All of these projects will be developed once the results of the initial tests have been validated, as Antonia Höög, Keolis' CSR Director, pointed out during the Maddyness conference.

Keolis is developing three types of solutions to improve air quality in stations
Antonia Höög

Antonia Höög

CSR Director at Keolis

"Thanks to our international dimension, we can work with local players and then widely roll out the initiatives that have worked best."

Watch both parts of the Maddyness conference right here:

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