London's ULEZ restores children's lung capacity, study finds

A study of London schoolchildren has found something that seemed almost too straightforward to be true: when you remove the most polluting vehicles from a city's streets, children's lungs actually grow bigger and work better. Researchers from Queen Mary University of London tracked 1,664 children aged six to nine in the capital from 2018 to 2022, measuring their lung capacity before and after the ultra-low emission zone came into force in 2019. They compared these children to 1,750 peers in Luton, a town with similar traffic patterns but no clean air restrictions, which served as a control group. The results were unambiguous. Before the zone was introduced, London children had significantly smaller lungs than their counterparts in Luton. Within five years, that gap had closed. The London children's lungs had grown to match those of the Luton children—a reversal of a problem that had plagued the city for decades.

The damage from traffic pollution had been well documented. Previous research showed that by age eight or nine, children growing up in London's most polluted areas had 5 to 10 percent less lung capacity than children elsewhere. That deficit was not merely a statistical curiosity. Scientists understood it as a marker of deeper harm: exposure to nitrogen dioxide and other traffic pollutants was stunting development in ways that would follow these children into adulthood, increasing their risk of asthma, chronic obstructive pulmonary disease, heart disease, and premature death. The Ulez policy, introduced by Mayor Sadiq Khan in 2019, was justified partly on these health grounds, but at the time it lacked hard evidence. Researchers saw an opportunity to test whether the policy actually worked.

The mechanism was straightforward. Within five years of the zone's introduction, London children's exposure to nitrogen dioxide fell twice as fast and twice as much as exposure among children in Luton. The improvements in air quality correlated strongly with improvements in lung function. The children's bodies had responded to cleaner air by growing as they should have all along. Chris Griffiths, a professor of primary care at Oxford and QMUL and one of the study's senior authors, framed the finding as validation of an approach that had faced considerable criticism. "Traffic pollution in cities damages children's health and development," he said. "We provide the strongest evidence yet on how these harms can be prevented. Ambitious clean-air zones should be considered a priority for cities globally with traffic-related air pollution."

The political dimension of the study was unavoidable. The Ulez had been contentious from the start—motorists complained about the restrictions, and opponents had sought to frame the policy as an overreach. Khan, writing in response to the study, acknowledged the difficulty of the decisions involved. "I never took them lightly, but I knew that – as mayor – I could not stand by while Londoners young and old lost their lives to a problem it was within my power to solve," he wrote. He also pushed back against what he called attempts to turn public health into a culture war, suggesting that the evidence now showed the policy was working. The health minister, Karin Smyth, called the study "a powerful reminder of the impact that air quality has on children's lung health."

Not everyone was entirely convinced. Stephen Burgess, a professor of biostatistics at Cambridge who was not involved in the research, raised a methodological concern: it was not entirely clear that the improvements were solely attributable to the Ulez, as opposed to other factors such as reduced traffic during the Covid pandemic, which would have lowered pollution levels across the board. "Nevertheless, the finding is important because lung function in childhood is an important measure of health, and the study provides encouraging evidence that changes in the urban environment may benefit children's lung development," he said. The caveat was fair, but it did not diminish the core observation: children in London had measurably healthier lungs after the zone was introduced. The study now stands as evidence that clean-air policies, however politically fraught, can produce tangible benefits in the bodies of the young people who breathe the air they are meant to protect.