When London introduced its Ultra Low Emission Zone — a daily charge for drivers of more polluting vehicles entering the capital — critics questioned whether the policy would deliver real health benefits. Now, a landmark study has provided compelling evidence that it is working where it matters most: in children's lungs.
Research from Queen Mary University of London, published in The Lancet Public Health, tracked 3,400 schoolchildren before and after the ULEZ came into force. The results were striking: the proportion of children in London with impaired lung function fell from 14% to just 9% — a 36% reduction — over the study period.
Perhaps most remarkably, London's children, who had previously shown significantly smaller lungs than their peers in nearby Luton (a city outside the zone), have now caught up entirely. By the end of the study, their lung size and function were comparable to those of Luton children.
Breathing the Difference
Before the ULEZ, children growing up in London were breathing air that was measurably damaging their lung development. Air pollution — particularly fine particles and nitrogen dioxide from diesel engines — stunts lung growth in children, leaving them with smaller, less efficient respiratory systems that can impact health for decades.
The ULEZ began as a central London zone in 2019 and expanded significantly in subsequent years, charging daily fees to vehicles that don't meet modern emission standards. Traffic in affected areas became measurably cleaner almost immediately after implementation.
"We already knew that the ULEZ reduced air pollution, but now we know that children's lung health has improved at the same time, which is a really important finding," said lead author Dr. Helen Wood, a research fellow at Queen Mary University of London.
Catching Up
The research team monitored children in London schools and compared them to children in Luton — a city of similar demographics outside the ULEZ. Before the zone was introduced, London's children showed significantly worse lung function. After the ULEZ expanded, that gap closed completely.
The drop from 14% to 9% in impaired lung function represents tens of thousands of children who are now growing up with healthier respiratory systems. Lung capacity developed during childhood largely determines respiratory health in adulthood, meaning the benefits of this improvement will compound over entire lifetimes.
"It feels like it's a very important advance," said Professor Peter Johnson, national clinical director for cancer at NHS England, commenting on the broader evidence base linking clean air policy to health outcomes.
Why This Matters
Urban air pollution is one of the leading environmental health risks globally, linked not only to lung disease but also to heart disease, cognitive development, and premature mortality. Children are especially vulnerable: their lungs are still developing, they breathe more air relative to their body weight, and they spend more time outdoors near traffic.
Policies that reduce vehicle emissions have long been championed by public health advocates, but real-world evidence demonstrating measurable improvements in children's health has historically been difficult to obtain. This study, with its large cohort and clear pre/post design, provides some of the strongest evidence yet that clean-air zones work.
A Model for Cities Worldwide
London's ULEZ has been controversial since its inception. But the accumulating evidence — now including this Lancet study — paints a clear picture: cleaner air translates directly into healthier children.
Cities around the world are watching. As governments debate how to reduce vehicle emissions, London's experience provides both a template and a proof of concept. Dr. Wood cautioned that air quality in London and Luton still exceeds safe guideline levels, meaning further action is needed. But the direction of travel is unmistakably positive — and the lungs of London's children are the proof.
