London’s Ulez linked to healthier lung growth in children

When London introduced its Ultra Low Emission Zone (Ulez) in April 2019, the aim was to cut traffic pollution and protect the health of the people breathing it. For years, evidence of its impact has largely come from roadside monitors, exhaust emissions and changing vehicle numbers. Seven years on, researchers are increasingly able to measure something more tangible: what cleaner air appears to be doing to people’s bodies.

The latest findings come from a five-year study involving more than 3,400 primary school children in London and Luton. Researchers led by Queen Mary University of London recruited children aged six to nine from schools within or bordering the original central London Ulez and compared them with children in Luton, a similar urban area without a comparable clean-air zone.

The children underwent annual lung-function tests between 2018 and 2022, allowing scientists to compare how their lungs developed before and after Ulez was introduced.

Before the scheme came into force, the London children had lower lung capacity than those in Luton and were exposed to higher levels of nitrogen dioxide (NO₂), a harmful pollutant strongly associated with vehicle exhausts. After 2019, however, NO₂ levels fell faster in London while the children’s lungs grew more rapidly.

One key measure was FEV₁, the amount of air a person can forcibly breathe out in one second after taking a deep breath. At the beginning of the study, average FEV₁ was around 38ml lower among the London children. Over the following four years, annual growth was around 10ml greater than among children in Luton and, by the end of the study, the difference had effectively disappeared.

A second measure, forced vital capacity (FVC), also improved faster among London children, although that gap had not completely closed.

Prof Chris Griffiths, one of the study’s senior authors at Queen Mary University of London, told the BBC he was “absolutely stunned” by the speed of the improvement.

“This shows an ambitious clean air zone can drive pollution levels down, rapidly restoring children’s stunted lung growth,” he said.

Prof Anna Hansell, of the University of Leicester, who was not involved in the research, said the improved lung function was “likely to have lifelong benefits for their health”, while cautioning that an observational study cannot prove that every difference between the London and Luton children was caused by Ulez.

The findings mark a significant development in how the effects of the scheme can be assessed. Until relatively recently, most arguments over Ulez revolved around how far emissions had fallen, whether drivers were switching to cleaner vehicles and what pollution monitors were recording. Researchers are now beginning to build evidence of what those changes could mean for the people exposed to the air itself.

Children are an especially revealing group because developing lungs are vulnerable to traffic pollution. Poor lung growth during childhood can persist into adulthood and is associated with increased risk of respiratory and cardiovascular disease later in life.

The latest findings also follow earlier research from the same study suggesting that Ulez changed the way some children travelled. Researchers found that 42% of London children who had previously been driven to school switched to walking, cycling or public transport after the zone was introduced, compared with 20% of children in Luton. The shift towards active travel was particularly pronounced among children who lived further from school.

For Rosamund Adoo-Kissi-Debrah, the consequences of London’s polluted air had already been devastatingly clear. Her nine-year-old daughter, Ella, died following an asthma attack in 2013 after years of exposure to high levels of pollution near the family’s home in Lewisham. In 2020, Ella became the first person in the UK to have air pollution listed as a cause of death.

This shows an ambitious clean air zone can drive pollution levels down, rapidly restoring children’s stunted lung growth

Her mother has since campaigned for legally enforceable clean-air standards aligned with World Health Organization recommendations through the campaign known as Ella’s Law.

Speaking to the BBC following publication of the new research, Adoo-Kissi-Debrah said the first steps towards improving London’s air through Ulez had “clearly been worth it”, while emphasising that further action was still needed.

London has made substantial progress on nitrogen dioxide since Ulez began. The capital passed the government’s national compliance assessment for the legal annual NO₂ limit for the first time in 2024, although some individual monitoring sites have continued to record concentrations above that level and UK limits remain considerably weaker than WHO guidelines. UK regulations allow an annual average of up to 40 µg/m³, compared with the WHO guideline of 10 µg/m³.

Initially covering central London, Ulez expanded to inner London in 2021 and across the capital in August 2023. The policy has been politically contentious, particularly over the £12.50 daily charge levied on drivers of older, more polluting vehicles, with critics arguing that the cost could fall disproportionately on lower-income households and businesses.

Against that debate, the evidence of falling pollution has become increasingly substantial. City Hall estimates that roadside NO₂ concentrations across London in 2024 were 27% lower than they would have been without Ulez and its expansions. Across the capital more broadly, population-weighted NO₂ exposure fell by 41% between 2019 and 2024, while exposure to PM2.5 – tiny particles capable of entering the lungs and bloodstream – fell by 28%. Those wider reductions cannot be credited to Ulez alone, as other clean-air policies and changes took place over the same period.

Some of the largest gains have been recorded in communities that historically breathed London’s dirtiest air. City Hall analysis estimated that among some of the most deprived communities near busy roads, the number of people exposed to illegal pollution levels was around 80% lower than it would have been without Ulez.

Evidence of wider health effects is also beginning to emerge. A 2026 Imperial College London study found that the introduction of the earlier T-Charge and Ulez was associated with significant reductions in cardiovascular and all-cause emergency hospital admissions, although the reduction in respiratory admissions was not statistically significant.

Separate analysis estimates that the number of deaths attributable to air pollution across London fell by around 40% between 2019 and 2024. Researchers again stress that the decline cannot be attributed solely to Ulez, but taken alongside the emerging evidence on hospital admissions and children’s lungs, it suggests that London’s cleaner air is beginning to show up in more than pollution monitors.

“Traffic pollution in cities damages children’s health and development,” Griffiths told the Guardian. “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.”

Main image: iStock / dusanpetkovic