Breathe London is a groundbreaking air quality monitoring initiative that has deployed hundreds of low-cost sensors across the capital to create the world's most detailed picture of urban air pollution at the neighbourhood level. The project represents a step change from traditional air quality monitoring, which relies on a relatively small number of expensive reference stations, by providing hyper-local, real-time data that reveals pollution patterns at individual streets, schools, and community spaces.
The initiative combines two complementary data sources. A permanent network of fixed sensors, installed across London boroughs, provides continuous monitoring of key pollutants including nitrogen dioxide, particulate matter (PM2.5 and PM10), and ozone. This is supplemented by mobile measurement campaigns using Google Street View vehicles equipped with scientific-grade air quality instruments, which have mapped pollution levels on thousands of London streets.
Machine learning algorithms validate and calibrate the sensor data, ensuring that readings from low-cost devices are accurate and comparable with reference-grade measurements. The resulting dataset is made publicly available through a real-time dashboard and open API, empowering researchers, journalists, community groups, and policymakers to access and analyse air quality information for any location in the city.
Breath London's data has already had tangible policy impact. It has informed the expansion of London's Ultra Low Emission Zone, supported the introduction of School Street closures that restrict traffic near school gates during drop-off and pick-up times, and influenced planning decisions for new developments in pollution-affected areas. Over 200 schools now have dedicated sensors providing parents, teachers, and pupils with real-time information about the air they breathe.
The project has become an international reference model for cities seeking granular, affordable, and scalable air quality intelligence, demonstrating how sensor technology and data science can transform environmental governance and public health protection.