London’s Clean‑Air Zone Helps Children’s Lungs Grow Better

London introduced its Ultra Low Emission Zone (Ulez) in April 2019 to cut traffic pollution and protect the health of people who breathe the city’s air. Seven years later, scientists are moving beyond simple pollution readings to ask a deeper question: what is cleaner air doing to people’s bodies? The answer is striking, especially for children.

Researchers from Queen Mary University of London led a five‑year study that followed more than 3,400 primary‑school children in London and Luton. The children were aged six to nine and came from schools that were inside or next to the original Ulez boundary, as well as from a comparable urban area in Luton that did not have a clean‑air zone. The study began in 2018, before Ulez was in force, and continued through 2022.

Each year the children underwent lung‑function tests. These tests measured how much air they could forcefully exhale in one second (FEV ₁) and the total amount of air they could exhale after a deep breath (forced vital capacity, or FVC). By comparing the growth of these measures over time, scientists could see whether the children’s lungs were developing normally or whether pollution was slowing their growth.

Before Ulez started, London children already had lower lung capacity than their Luton peers. They also lived in areas with higher levels of nitrogen dioxide (NO₂), a harmful pollutant that comes mainly from car exhaust. After Ulez was introduced, NO₂ levels fell faster in London, and the children’s lungs grew more quickly.

At the start of the study, the average FEV ₁ of London children was about 38 ml lower than that of Luton children. Over the next four years, London children’s FEV ₁ grew about 10 ml more per year than Luton children’s. By the end of the study, the difference had essentially disappeared. FVC also improved faster in London, although the gap had not closed completely.

“This shows an ambitious clean‑air zone can drive pollution levels down, rapidly restoring children’s stunted lung growth,” said Prof Chris Griffiths, one of the study’s senior authors at Queen Mary University of London.

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

The study also found that Ulez changed how some children travelled. Forty‑two percent 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 percent in Luton. The shift was strongest among children who lived farther from school.

London has made substantial progress on nitrogen dioxide since Ulez began. In 2024, the capital passed the government’s national compliance assessment for the legal annual NO₂ limit for the first time. Some monitoring sites still record concentrations above that level, and UK limits remain weaker than World Health Organization (WHO) guidelines. The UK allows an annual average of up to 40 µg/m³, while the WHO guideline is 10 µg/m³.

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 that can enter 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.

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.

Her mother has since campaigned for legally enforceable clean‑air standards aligned with WHO recommendations through the campaign known as Ella’s Law. Speaking to the BBC after the new research was published, Adoo‑Kissi‑Debrah said the first steps toward improving London’s air through Ulez had “clearly been worth it,” while emphasising that further action was still needed.

Traffic pollution in cities damages children’s health and development. The study provides the strongest evidence yet on how these harms can be prevented. Ambitious clean‑air zones should be considered a priority for cities worldwide with traffic‑related air pollution.

“Traffic pollution in cities damages children’s health and development,” said Griffiths. “We provide the strongest evidence yet on how these harms can be prevented.”