A five-year study tracking more than 3,400 children aged 6 to 9 across 84 primary schools has found that ULEZ children lung growth accelerated after London introduced its Ultra Low Emission Zone, with the share of central London children with impaired lung capacity falling from 14 per cent to 9 per cent over the study period.
The findings, published in The Lancet Public Health, were produced by researchers from Queen Mary University of London working alongside teams from Imperial College London and the Universities of Bedfordshire, Oxford, Cambridge and Edinburgh, as well as the University of Southern California, according to Medical Xpress. The breadth of that collaboration reflects how seriously the research community has treated this question: can cleaning up urban air actually reverse damage to developing lungs, or does it merely slow the harm?
How the ULEZ children lung growth study was designed
The researchers used a comparison that gave the study much of its credibility. Children in central London were tracked alongside a similar group in Luton, where no clean-air zone was in place. That pairing created a natural experiment: two groups of children, developing at the same time, but in environments where pollution was falling at different rates.
Nitrogen dioxide levels (closely tied to vehicle exhaust) fell roughly twice as fast in London as in Luton. Central London saw a reduction of around 3.8 micrograms per cubic metre per year, against 1.8 micrograms in Luton. Both cities improved, but not equally.
Lung function followed the same pattern. Scientists measured how much air each child could forcefully exhale in one second, a standard test of lung capacity. Before the ULEZ came into effect, London children were growing lung capacity more slowly than those in Luton. As pollution fell, the gap closed. London children’s lung function grew by an average of 233 millilitres per year, against 223 millilitres in Luton. After four years, the difference had vanished entirely: London children had caught up.
The Luton data adds useful texture. The BBC reports that in Luton, the proportion of children whose lung capacity was deemed clinically impaired fell from 9 per cent to 7 per cent over the same period, a meaningful improvement in its own right, and a reminder that broader trends in vehicle emissions benefited both cities. The London numbers moved further and faster, but Luton was not standing still.
Why lung development in childhood matters beyond the numbers
Lungs are not fully formed at birth. They keep growing through childhood and into early adulthood, and what happens during those years shapes respiratory health across a lifetime. Children whose lungs do not develop fully carry higher lifetime risks of asthma and other conditions. That is the context that makes this study’s core finding consequential: it is the first to connect a clean-air zone directly to faster lung growth measured in children’s bodies, not merely in pollution readings.
The Science Media Centre notes the study drew on 84 primary schools across London and Luton over five years. That scale is part of what makes the findings hard to dismiss. With more than 3,400 children tracked, the researchers had enough statistical power to detect changes that would be invisible in a smaller sample.
Political and legal headwinds have not gone away
None of this landed in a neutral political environment. The ULEZ restricts or charges drivers of more polluting vehicles, and it has attracted sustained opposition. Cameras have been vandalised or stolen, according to the Metropolitan Police. The 2023 expansion of the zone across all London boroughs was challenged in court by several local councils, and only proceeded after the High Court let it stand.
The study does not resolve those arguments. Costs, fairness and enforcement remain contested. What it does is add a measurable health outcome to the ledger: five percentage points fewer children with impaired lung function in central London over four years. Policymakers in other cities watching London’s experiment now have that figure to weigh alongside the objections.
