London clean-air zone linked to recovery in children’s lung growth

London’s clean-air policy shows signs of reversing damage

A major study has found that children’s lungs in London grew bigger and stronger after the most polluting vehicles were pushed out of the city centre under the ultra-low emission zone, or Ulez. The research suggests that pollution damage to lung development is not only measurable in childhood but can also be reduced when air quality improves.

Reporting in the Guardian Business section, the study examined London schoolchildren before and after Ulez was introduced and found a restoration in lung capacity that had previously been held back by exposure to dirty air. The researchers said the results offer a strong argument for clean-air policy, particularly in large cities where traffic emissions remain a persistent health threat. For the original report, see the Guardian’s coverage of the London Ulez study.

What the researchers measured

The work was carried out by researchers at Queen Mary University of London, who saw Ulez as a real-world opportunity to test whether cleaner traffic conditions could alter children’s lung development. Before the policy came into force, the team recruited 1,664 children aged six to nine in London and 1,750 in Luton, which was used as a control because it had a similar mix of traffic pollutants but no clean-air zone.

The children were monitored through annual school visits from 2018 to 2022. The researchers tracked their size and health and compared lung growth over time as air quality changed in the capital. The pattern was clear: early measurements showed children in London had significantly smaller lungs than children in Luton. After Ulez began, the London children’s lung size and function improved until they were comparable with the children in the control town.

The study also found a strong relationship between the health gains and cleaner air. Within five years of Ulez starting, London children’s exposure to nitrogen dioxide fell twice as fast and twice as much as that of children in Luton.

Why the findings matter for child health

The significance of the results extends beyond London’s roads and traffic rules. Earlier research had already shown that children living in the most polluted parts of London could have 5 to 10 percent less lung capacity by the age of eight or nine than their peers elsewhere. Scientists linked that effect to exposure to nitrogen dioxide, one of the main pollutants associated with traffic.

That loss of lung capacity matters because childhood lung development has long-term consequences. The source report notes that the impairment can leave people at higher risk in adulthood of asthma, chronic obstructive pulmonary disease, cardiovascular disease, metabolic disease and even premature death. The new findings matter because they suggest some of that harm can be prevented, or at least reduced, when traffic pollution is cut.

Chris Griffiths, professor of primary care at the University of Oxford and Queen Mary University of London and the study’s joint senior author, said traffic pollution in cities damages children’s health and development. He described the findings as the strongest evidence yet on how those harms can be prevented and said ambitious clean-air zones should be considered a priority for cities around the world.

Political backing and public debate around Ulez

Ulez was introduced in 2019 after London mayor Sadiq Khan explicitly cited the health of Londoners as a reason for the policy. At the time, the scheme was widely seen as sensible in principle, but the evidence base for its health benefits was not yet established. This study is being presented as a major piece of that evidence.

Khan argued in the Guardian that introducing and later expanding Ulez involved difficult choices. He said he did not take those decisions lightly, but believed he could not stand by while Londoners young and old suffered and died from a problem that was within his power to address. He also said opponents had tried to turn a public health question into a culture war, and that London was now winning the fight against toxic air.

The research arrives in a context where Ulez has been criticised by some motorists as a financial burden. The authors say their findings vindicate the policy by showing that cleaner air is not just an abstract environmental goal but something with measurable effects on child health.

What experts say happens next

The study, published in Lancet Public Health, was welcomed by the health minister, Karin Smyth, who called it a powerful reminder of how air quality affects children’s lungs. She said the results should improve understanding of how lower pollution can restore normal lung growth in children, reduce the risk of respiratory illness in adulthood and support the broader goal of giving every child the best start in life.

Not all outside researchers were ready to give Ulez sole credit. Stephen Burgess, a professor of biostatistics at the University of Cambridge who was not involved in the study, said it was not fully clear that the changes observed were entirely caused by Ulez, because other factors such as the Covid pandemic’s effect on pollution levels may also have played a part. Even so, he said the findings were important because childhood lung function is a meaningful measure of health and because the study offers encouraging evidence that changes in the urban environment can benefit children’s lung development.

Taken together, the results strengthen the case that cleaner traffic policy can produce health gains that are visible in schoolchildren within a few years. For cities weighing similar measures, the London experience now offers something more concrete than theory: evidence that cleaner air can help children breathe more freely as they grow.