The evolution of Breathe London

The Breathe London network started with a pilot scheme back in 2018. The project was convened by C40 Cities and the Mayor of London, with funding from the Children’s Investment Fund Foundation and Clean Air Fund.

The pilot scheme aimed to better understand the exposure of Londoners by testing the reliability and accuracy of a lower-cost stationary sensor network and providing hyperlocal data to the public.

Delivered by a consortium of experts led by the Environmental Defense Fund, 100 sensors were deployed across the city for a period of 2 years.

Data from the pilot scheme can be found here on the Breathe London Pilot website and further details can be found in the Breathe London Technical Report (Pilot Phase).

Following the success of the pilot scheme, the Mayor of London and Bloomberg Philanthropies launched a new four-year project with Imperial College London to establish the next phase of Breathe London, providing over 100 new air quality sensors at priority locations including schools and hospitals. The new sensors, provided by Clarity, were also installed at numerous sites from London’s well established reference air quality monitoring network, providing ongoing calibration improving the accuracy of the network.

As part of this partnership, the Breathe London Community programme was established, distributing an additional 60 sensors for community groups. Selected groups, ranging from parents and residents associations to running clubs and local campaign groups, were given a sensor to host in their local community, empowering them to monitor local air pollution. With support from Imperial College London and The Social Innovation Partnership, communities also benefited from a dedicated engagement program. Sensors were also installed in six cultural institutions including the Science Museum and the Serpentine Gallery.

For the first time, Londoners were also able to “buy in” to the network at a low cost and host sensors at locations of their choice. This revolutionised Londoners’ access to reliable data for schools, charities, businesses, individuals, NHS trusts and boroughs, and expanded the footprint of the network to over 450 locations at its peak.

With the Breathe London model firmly established, the network has evolved into a collaborative, community focussed air quality monitoring network.

In June 2025 at London Climate Action Week, the Mayor of London and Bloomberg Philanthropies renewed their commitment to the program with a new phase of public engagement, including working groups for schools, hospitals, community groups, and local authorities, annual webinars and on-site training sessions.

This phase is being delivered by a consortium of leading experts, convened by Vodafone, including Global Action Plan, Airly, Ricardo, Scotswold Ltd, Cambridge Environmental Research Consultants, and the University of Cambridge.

The consortium will deliver at least 146 sensors, including 10 on and around Oxford Street to monitor the impacts of the newly announced pedestrianisation scheme.

The new programme introduces an innovative approach to data calibration and data processing, with one minute measurements, ozone monitoring and ‘gold sensors’.

Vodafone brings the ability to scale the sensor network with its access to infrastructure (street furniture, retail stores, etc.) and with additional data and insights gleaned from the telecom network (e.g., rainfall and footfall) that can inform pollution prediction and exposure studies.

Global Action Plan brings an enhanced engagement programme including working groups for schools, hospitals, community groups, and local authorities, annual webinars, and on-site training sessions.

Please see our about page for more information on the consortium and here for more information on calibration.

The Breathe London Community Programme, supported by Bloomberg Philanthropies and Clean Air Fund, continues to be delivered by Imperial College London and The Social Innovation Partnership, working closely with the consortium, focused on empowering local communities and advocates.

In Phase 2, Breathe London is working to ensure robust air quality data is accessible for all Londoners.

At COP26, Mayor Khan called for the creation of Breathe Cities to build upon the success of Breathe London and help more cities around the world take action on air pollution. Launched in 2023 by Michael R. Bloomberg and Mayor Khan, Breathe Cities is an initiative delivered by Clean Air Fund, C40 Cities and Bloomberg Philanthropies to clean the air, cut carbon emissions, and enhance public health in cities around the world.

Today, 14 cities across five continents are benefitting from support to expand air quality data, build evidence-led policies, engage local communities, and share knowledge globally. Through this tailored approach, the initiative aims to reduce pollution on average across participating cities by 30% by 2030. Further information can be found on the Breathe Cities website.