Air monitoring
London’s Breathe London initiative is transforming how cities tackle air pollution.
Matt Browning explains how this pioneering approach is improving lives in London – and inspiring change worldwide.
London is currently a global testbed for environmental policy.
With the ambition of achieving the best air quality of any major world city by 2050, the Mayor of London has implemented a whole suite of integrated strategies - from the Ultra Low Emission Zone (ULEZ) to electrifying the bus fleet.
However, as Matt Browning, Principal Policy and Programming Officer at the GLA, recently explained in a webinar on Envirotech Online, policy is only as effective as the data that informs it.
While London boasts a robust network of over 150 “reference-grade” monitors (the “gold standard” of expensive, stationary units used for regulatory reporting), these provide a high-level overview of historic trends across the capital.
To drive local action, the city needed something more granular: hyperlocal monitoring.
Hyperlocal monitoring allows policymakers to identify specific hotspots and, crucially, perform source apportionment.
“This allows us to pinpoint the sources and the movement of pollution through the city,” Matt notes.
“Then we can target interventions to ensure we are improving air quality and reducing personal exposure.”
This need led to the creation of Breathe London.
What began as a pilot in 2018 has evolved into a sophisticated network of low-cost stationary sensors supplementally placed alongside the reference-grade network.
By co-locating these sensors, the team can monitor validity and perform continuous calibration.
In 2024, the GLA reviewed the first phase of Breathe London and found that data alone wasn’t enough.
Participants – community groups, schools, and local partners – often struggled to interpret the numbers.
To close the gap, the team moved from the “creation phase” to the “activation phase” – positioning the GLA not just as a funder, but as a convener and knowledge partner.
To formalise this, the team developed a “Breathe London
Logic Model.”
This framework visualises the different elements of the programme, from inputs and activities, to outputs, outcomes and ultimately to impacts: a measurable reduction in personal pollution exposure across the city.
The second phase of Breathe London, delivered by a consortium including Vodafone, Global Action Plan, Airly and the University of Cambridge, introduces several technical firsts for the network.
• For the first time, the network is recording data at 60-second intervals. This high resolution allows scientists to strip out “regional background noise” and identify transient local signals, such as individual vehicle spikes or wood-burning episodes.
• By measuring ozone (O3) alongside nitrogen dioxide (NO2), the system can detect and correct any Ozone cross-sensitivity in NO2 sensor readings, adding an additional level of scrutiny to the data.
• The methodology uses “Gold” sensors co-located with reference sites for absolute calibration, alongside “Silver” sensors distributed across the network to validate these calibrations at six-month intervals. Weekly algorithm updates ensure the network remains in alignment with the reference- grade hardware.
The “insight” layer lives on the Breathe London website.
Rather than a “sea of green”, the interface displays real-time concentrations for each sensor, making pollution visible and comprehensible.
Each sensor has its own profile page where data can be custom downloaded.
Matt highlighted the importance of supporting stakeholders with additional resources.
The programme provides monthly working groups, regular webinars and training opportunities and a dedicated resource hub on the website.
One of the most exciting current applications is the Oxford Street Project.
As the iconic street undergoes pedestrianisation, the GLA plans to install 10 sensors to monitor the impact of the scheme on air quality.
By overlaying air pollution data with GDPR-compliant footfall data provided by Vodafone, the team hopes to prove a “double win”.
As vehicles are removed and the public realm improved, the hope is that air quality improves and footfall (and thus economic vitality) increases.
The success of the London model has not gone unnoticed.
A $30 million Breathe Cities programme is now replicating these learnings in 14 cities across the globe, from Rio de Janeiro to Jakarta.
The drive remains the same: providing high-resolution, granular data that gives local policymakers the confidence to design and defend health-protecting policies.
As urbanisation continues, the Breathe London initiative serves as a definitive case study in opening up environmental data.
By moving from raw numbers to actionable insights, the program ensures that the “invisible” threat of air pollution becomes visible, as well as becoming manageable.
Matt Browning is a Principal Policy and Programme Officer at the GLA with eight+ years in London’s environmental sector and an MSc in Climate Change from King’s College London.
He leads London’s WHO Air Quality Roadmap, oversees Breathe London, and manages data and EV portfolios within the Air Quality Team.
Previously, he led Lambeth’s 2017-2022 Air Quality Action Plan, delivered the RE:FIT Energy Efficiency Programme, and created Lambeth’s first Corporate Carbon Reduction Plan.
IET 36.3 May
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