At London Climate Action Week this year, Breathe Cities marks two years since it was announced by Mayor of London and C40 Co-Chair Sadiq Khan and Michael R. Bloomberg, the United Nations Secretary-General’s Special Envoy on Climate Ambition and Solutions and Founder of Bloomberg Philanthropies. Since then, the initiative, delivered by C40 Cities, the Clean Air Fund and Bloomberg Philanthropies, has been working with city governments and communities around the world to clean the air, cut carbon emissions and improve public health.
The global initiative draws inspiration from pilots in London and Warsaw. The Breathe London citywide air quality monitoring programme put real-time data into the hands of Londoners. Over 450 sensors at its peak were installed at schools, hospitals, cultural venues and other key locations, while a dedicated Community Programme provided low-cost monitors to 60 community groups across 24 boroughs. Together, these efforts created a detailed picture of air quality across the capital and cultivated a network of residents using data to advocate for healthier, greener spaces. Its recently announced next phase will see Breathe London maintain a monitoring network of approximately 350 sensors, with 10 new monitors installed in and around Oxford Street to track the effects of the planned pedestrianisation scheme, as well as a new programme of public engagement.
This community-driven, data-led model helped lay the groundwork for what became Breathe Cities. The initiative now supports a cohort of 14 cities across five continents, collectively home to 77 million people. To date, more than 1,000 air quality sensors have been installed in the cities, providing governments and communities with vital information to identify pollution hotspots, take action and raise awareness.
To help drive impact beyond the core cohort, Breathe Cities has also engaged with 62 cities globally (including the 14 Breathe Cities), offering opportunities to exchange lessons, share tools and collaborate across borders. While every city faces its own unique challenges, the initiative is helping to create a shared foundation for faster, more coordinated action on air quality.
Elsewhere, cities in the Breathe Cities network are adapting this blueprint to their own contexts:
- In Nairobi, 50 sensors are being installed at schools and health facilities, forming the backbone of the city’s first-ever government-owned air quality monitoring network.
- Warsaw introduced a Clean Air Zone in 2024, covering 37 square kilometres of the city centre which could halve traffic-related pollution this decade. A Breathe Cities-supported campaign helped raise awareness and reached nearly half a million people.
- In Paris, the low-emission zone has expanded citywide, along with infrastructure that encourages walking and cycling. Efforts like this have helped to halve harmful particle and nitrogen dioxide levels in the Paris region since 2005. The initiative is also supporting research into ultrafine particles and awareness-raising among schools.
- Milan is building out 750 kilometres of cycling infrastructure by 2035, while also piloting a pedestrianised zone in its famous fashion district. Air quality workshops are also being delivered to students and teachers across the city.
- In Rio de Janeiro, the programme is helping to establish a Low Emission District and expand inclusive pedestrian and cycling routes. These efforts are being complemented by a plan to electrify 20% of the city’s bus fleet by 2030 and raise public awareness around toxic air.
Two years on from its announcement, Breathe Cities is demonstrating the power of cities working together for greater, faster action. By sharing knowledge, scaling solutions, and supporting city-led ambition, the initiative is helping to build a future where clean air is the standard, not the exception.
