London's Clean Air Zone Rebuilt Children's Lungs. Will Other Cities Follow?

In February 2013, a nine-year-old girl from Lewisham died of an asthma attack. Ella Adoo-Kissi-Debrah had been relatively healthy until just before her seventh birthday, when a persistent cough turned into a diagnosis of asthma and, over the next two years, more than 30 emergency hospital admissions. No doctor treating her ever mentioned air pollution as a possible trigger. It took her mother, Dr Rosamund Adoo-Kissi-Debrah, years of campaigning and a second inquest before a coroner finally reached a different conclusion. Ella died of asthma contributed to by exposure to excessive air pollution. She lived a few hundred metres from the South Circular, one of London's busiest and most congested roads, and is still the first person in the world to have air pollution listed as a cause of death on their death certificate.

Ella's case is why London's Ultra Low Emission Zone (ULEZ) exists in the form it does. It is also why last week's news matters so much. A study published in The Lancet Public Health has found that after the ULEZ came into force, London children's stunted lung growth caught up with, and matched, that of children living outside the zone. It is the first study to show that a clean air policy can measurably reverse, not just slow, the damage traffic pollution does to developing lungs. Twelve years after a coroner first drew the link between traffic fumes and a child's death in London, there is now hard evidence that taking those fumes away helps children's lungs recover.

What the study actually found

The findings come from the Children's Health in London and Luton (CHILL) study, led by researchers at Queen Mary University of London alongside teams from Imperial College London and the Universities of Bedfordshire, Oxford, Cambridge, Edinburgh and Southern California, and funded by the National Institute for Health and Care Research.

Between 2018 and 2022, researchers followed more than 3,400 children aged six to nine across 84 primary schools, roughly half inside London's central ULEZ and half in Luton. Each child was tested once a year using spirometry, the standard measure of how much air the lungs can forcibly exhale. At the start, the gap between the two groups was stark. London's children had noticeably smaller lungs than their peers in Luton, echoing what the same research group had already found in earlier work on London's air.

However, what happened in the five years that followed is the part that really matters. As the ULEZ took effect, children's exposure to nitrogen dioxide, the pollutant most closely tied to exhaust fumes, fell twice as fast and by more than twice as much in London as it did in Luton. Lung growth in London sped up right alongside it, and by the end of the study, lung function in the two groups was effectively the same.

The share of children with clinically impaired lung function fell from 14% to 9% in London over the study period, against a smaller fall from 9% to 7% in Luton. As Dr Helen Wood, the study's lead author, said, “We already knew that the ULEZ reduced air pollution, but now we know that children’s lung health has improved at the same time.”

The policy behind the numbers.

ULEZ itself is a fairly simple mechanism. Since the Mayor of London launched it on 8 April 2019, drivers of vehicles that fail to meet emissions standards, broadly pre-2015 diesels and pre-2006 petrol cars, have had to pay a daily charge to drive within the zone. £12.50 for cars, vans and motorcycles, and £100 for heavier vehicles such as lorries and coaches, 24 hours a day, every day except Christmas.

What has changed is its geography. The zone started out covering the same area as London's congestion charge zone, expanded to the North and South Circular roads in October 2021, and then to the whole of Greater London in August 2023. City Hall now says more than 97% of vehicles driving in London on an average day already meet ULEZ standards, meaning most drivers barely notice it day to day. That expansion was also, it's worth remembering, one of the most fiercely contested pieces of environmental policy in recent London politics, sparking sustained backlash from motorists in outer boroughs and becoming a defining issue in the 2023 Uxbridge and South Ruislip by election.

These CHILL results land right in the middle of that unresolved argument, giving the clearest health evidence yet for a policy that has mostly been fought over on cost and convenience grounds rather than what it actually does to children's bodies.

Not job done.

Despite the good news, it is crucial to understand that there is still work to be done. After five years of falling pollution, air quality in both London and Luton, and in most UK cities, still sits above World Health Organization guideline levels. As Dr Wood put it, the fact that children's lungs can recover is significant, but it doesn't mean the underlying problem is solved.

Zoom out from London and the situation appears worse. Government figures show average roadside nitrogen dioxide across the UK was still 20.4 µg/m3 in 2025, exactly double the WHO's guideline of 10 µg/m3. And cities such as Manchester, Sheffield, Bradford and Newcastle, none of which has anything like a ULEZ, breached the WHO's daily NO2 limit on well over half the days in 2025, according to analysis of Defra's own monitoring network.

Ella Adoo-Kissi-Debrah's coroner made three recommendations in 2021. Legally binding pollution limits in line with WHO guidance, better public awareness of air pollution as a health risk, and training for doctors and nurses to flag it as an asthma trigger. More than five years on, only some of that has happened. The lungs of London's children are proof the policy works, but whether it reaches the children who need it most is still an open question.

What it means beyond London.

Other cities weighing up their own low emission or congestion charging schemes often face fierce local opposition. Clean air zones have typically been judged on air quality data alone. The CHILL study adds a harder, more human outcome to that ledger, measurable improvement in children's physical development, within a timeframe and the public can actually see and feel.

For membership bodies working across health, transport, planning and environment, the lesson from CHILL is less about ULEZ specifically and more about the value of long term, outcome-based evidence on one hand, and the value of seeking long-term outcomes outweighing immediate costs on the other. Policies designed to cut emissions are increasingly being asked to prove their worth in other terms too, whether that's child health, productivity or public support, and associations are well placed to help members track that evidence, translate it for boards, and make the case that environmental and social outcomes can be delivered together rather than traded off against each other. They are equally well placed to drive sustained positive change, across pollution, climate change, and other impacts.

This is one of the core goals of Climate Action for Associations (CAFA), the global resource and network dedicated to net zero and sustainability for the membership sector. By joining our free membership, you can access the frameworks and support to guide your members into becoming leaders. Join us today.