Breathe London: Building a grassroots clean air movement with Clarity

London battles toxic air pollution, but now Breathe London pioneers a new model - engaging citizens, coordinating agencies, and deploying 400+ Clarity sensors to achieve dramatic reductions.

Breathe London Clarity Network overlayed on London skyline

Clarity Node-S sensors in the Breathe London network


London boroughs with Breathe London sensors

8.8 million

Citizens with access to real-time data

Andrew Grieve

Andrew Grieve

Senior Air Quality Analyst, Imperial College London
"The Clarity Node-S is light, it has a small solar panel, and it's reliable. We can put them anywhere. All of those things combined mean it is super easy for communities to put them up by themselves."
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London has battled poor air quality for centuries, with records of deadly air pollution events dating back to the 13th century. Major smogs in the 1940s and 1950s led to the implementation of the UK's Clean Air Act in 1956. But while air quality improved dramatically, London still exceeds World Health Organization limits for key pollutants like nitrogen dioxide (NO2) and fine particulate matter (PM2.5).

Recent research indicates that in 2019 alone, air pollution contributed to the equivalent of over 4,000 early deaths in London. The health impacts of pollution exposure are wide-ranging, including increased risk of respiratory disease, cardiovascular disease, adverse birth outcomes, and neurological disorders. Children, the elderly, economically disadvantaged groups and those with existing health conditions are among the most vulnerable.

To combat air pollution, London has implemented one of the world's first Ultra Low Emission Zones (ULEZ). Effective since 2019, the ULEZ creates a central London area where vehicles must meet strict emissions standards or face daily charges. Early data indicates ULEZ has reduced NO2 and PM2.5 within the zone. 

Traditionally, ambient air quality monitoring has been conducted by local authorities using expensive reference-grade instruments housed in large roadside cabinets. While critical for regulatory reporting and research, these networks provide limited spatial coverage and little opportunity for community involvement.

With a vision to supplement London's reference monitoring and empower citizens, the Greater London Authority (GLA) partnered with Imperial College London's Environmental Research Group (ERG) to fund the Breathe London network of low-cost sensors in 2021. Leveraging the Clarity Node-S, Breathe London provides Londoners with hyperlocal air pollution data while promoting education, civic engagement, and policy decision-making. 

A Grassroots Network, From the Ground Up

Unlike many community air quality monitoring initiatives which take a top-down approach, Breathe London is intentional in enabling community-led projects. As Andrew Grieve, Senior Air Quality Analyst at the Environmental Research Group, explains:

Because we can put them almost anywhere, small sensors like the Node-S allow us to work directly with communities building a monitoring network that reflects their needs."

— Andrew Grieve, Senior Air Quality Analyst, Imperial College London

The team distributes Node-S devices through the innovative Community Programme, funded by Bloomberg Philanthropies, through which local groups are encouraged to share their concerns and objectives and apply for a Node-S device. Working together, Breathe London and communities determine optimal locations to install Clarity Node-S sensors, which measure PM2.5 and NO2 and run on solar power. Local groups manage the devices day-to-day while Breathe London provides training, data quality assurance, technical support, and a platform to share results.

Sadiq Khan, Mayor of London inspects a Clarity Node-S

I am delighted that Londoners will now have access to real-time, accurate air quality data for their area from more than 400 monitoring sites. This will improve awareness and help people reduce their exposure to polluted air. and better target efforts on improving air quality at a local level."

— Sadiq Khan, Mayor of London

This grassroots approach ensures each Node-S device is sited based on community priorities. Clarity devices have been installed everywhere from schools, hospitals, and parks to busy roads, market stalls, and bus stops. As of 2023, the network has grown to over 400 Nodes across all 33 London boroughs.

Empowering Communities Through Data

For many groups, joining Breathe London is their first foray into air quality monitoring. The ability to easily obtain local pollution data is often a catalyst for community organizing and civic participation.

Mums for Lungs, a community group and recipient of the first wave of Node-S devices.

Take the case of Clean Air 4 Schools, a group of parents at William Patten Primary School in the London borough of Hackney. After learning their school playground exceeded NO2 limits, the group installed a Breathe London Node-S in 2021. Access to real-time monitoring data enabled compelling outreach campaigns, driving concrete policy changes by Hackney Council that improved air quality for William Patten and surrounding schools.

As Sally Newsom of Clean Air 4 Schools describes, “Hyperlocal pollution data is vital to assess the air quality, to help spread awareness, and to start making change. As soon as people understand the air they're breathing, they can start to make real positive change.”

Air data from William Patten Primary School in the London borough of Hackney

Improving London's Air, From the Ground Up

Beyond community empowerment, Breathe London is generating data to inform urban planning decisions and policies for cleaner air. As Dr. Laura Jane Smith, a respiratory consultant at King’s College London explains, hyperlocal monitoring helps officials understand “the influence of air pollution on health and then we can put things in place to account for that.”

Above: The Breathe London network of Clarity Node-S devices has grown to over 400 monitors across all 33 London boroughs.

By interfacing with London's existing air quality reference network, Breathe London data is robust enough for research applications while remaining accessible to the public.

The network has informed analyses of pollution exposure inequalities as well as spatial variability of pollution from traffic, airports, industry, and wood burning. Outcomes help target interventions including expanding low-emission zones, deploying green infrastructure, limiting wood burning, and more.

The Role of Clarity Sensing-as-a-Service Node-S

A key enabler of the Breathe London network is the Clarity Node-S. The Node-S measures NO2 and PM2.5, two priority pollutants for health. Its compact size and solar panel enable installation virtually anywhere to provide hyperlocal air quality data.

A Clarity Node-S installed at William Patten

Clarity's Sensing-as-a-Service model has been invaluable in supporting the large-scale Breathe London network. Clarity hosts a cloud-based data platform to ingest, process, and visualize measurements. Users can access air quality data through a dashboard and API. The dashboard also provides tools to manage devices and configure alerts, crucial for managing a network of this scale. If any nodes are damaged or need to be replaced, Clarity swiftly ships free replacement devices to minimize data gaps.

Device management on the Clarity dashboard

Crucially, ERG developed proprietary algorithms that correct raw sensor measurements based on data from London's network of reference monitors. As Timothy Baker, Deputy Manager of ERG's Measurement Team, explains:

We use our reference network with collocated Node-S devices to make estimates of the interactions between the pollutants. This also helps us to make adjustments for the weather conditions like relative humidity, how damp is the air, how hot is the air."

— Timothy Baker, Deputy Manager of ERG's Measurement Team

This unique "transfer of value" from the reference network enables Breathe London to provide enhanced data quality and reliability compared to sensor networks in other cities. Today, all Breathe London Node-S devices are collocated with London Air reference monitors before calibration is applied and the devices are deployed.

A Model for Community-Led Air Quality Monitoring

With over 400 sensors and counting, Breathe London has become a globally recognized model for community air quality monitoring. Breathe London also provides a model for the Breathe Cities Network, an initiative by C40 Cities and Mayor of London Sadiq Khan to expand community air quality monitoring globally.

Having proven that we can achieve the data quality that's required to really answer questions, I think the next stage is to take this process outside of London and go national and international with it."

— Timothy Baker, Deputy Manager of ERG's Measurement Team

The Breathe Cities Network aims to empower citizens worldwide with hyperlocal air quality insights. By embracing affordable sensor networks like Breathe London, C40 cities can generate the granular data needed to target interventions, evaluate progress, and engage communities for cleaner air. Clarity's end-to-end Sensing-as-a-Service solution simplifies large-scale community monitoring. With turnkey hardware, connectivity, data management, and support, cities like London can quickly deploy hundreds of sensors with citizens steering site locations. The Breathe London model demonstrates the immense value of democratized, hyperlocal air quality data for C40 cities seeking to improve public health.

By combining reference monitoring with affordable, easy-to-use sensors, Breathe London has engaged everyday citizens in improving their local air quality. The initiative provides a model for urban communities worldwide to take air monitoring into their own hands, empowering impact from the ground up.

As Sally Newsome of Clean Air 4 Schools says, "Affordable, accessible tech like the Clarity Node is a total game changer. It's giving power to the people and I love that, it's really exciting."

With special thanks to Dr. Mohammed Mead, Dr. Gary Fuller, Dr. Ben Barratt, Dr. David Green, Timothy Baker, Andrew Grieve and Hima Chouhan at Imperial College London

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