Seven years have passed since the introduction of London’s Ultra Low Emission Zone (Ulez), and researchers are now shifting their focus from pollution readings to the effects of cleaner air on residents’ health. Their findings especially portray noticeable benefits for children’s lung development.
The Ulez was established in April 2019 with a goal to reduce traffic pollution and safeguard the well-being of London’s citizens. Up until now, its impact was evaluated mainly through roadside monitors, exhaust emissions, and fluctuating vehicle counts. However, recent research provides a more tangible insight by assessing the improvements in people’s health due to cleaner air.
A five-year study was conducted involving over 3,400 primary school students from London and Luton. Led by Queen Mary University of London, the researchers selected children aged six to nine from schools within or bordering the original central London Ulez. They were compared with children in Luton, a similar urban area lacking a clean-air zone.
These children underwent annual lung-function tests between 2018 and 2022, allowing scientists to compare how their lungs developed pre and post Ulez implementation. Before the scheme was enforced, the London children had lower lung capacity and were exposed to higher levels of nitrogen dioxide (NO₂), a harmful pollutant strongly associated with vehicle exhausts. However, after 2019, NO₂ levels dropped faster in London, and the children’s lungs experienced a more rapid growth.
One key measure was FEV₁, which gauges the amount of air a person can force out in one second after taking a deep breath. Initially, the average FEV₁ among the London children was about 38ml lower. However, over the subsequent four years, the annual growth was approximately 10ml greater than that among children in Luton. As a result, by the end of the study, this difference had almost disappeared.
Another measure, forced vital capacity (FVC), also showed faster improvement among London children, although that gap had not entirely closed. Prof Chris Griffiths, one of the study’s senior authors at Queen Mary University of London, expressed astonishment at the speed of the improvement. He stated that this shows an ambitious clean air zone can significantly reduce pollution levels, quickly restoring children’s stunted lung growth.
Prof Anna Hansell, of the University of Leicester, who wasn’t involved in the research, asserted that the improved lung function would likely provide lifelong health benefits. However, she cautioned that an observational study could not confirm that every difference between the London and Luton children resulted from Ulez.
The findings represent a substantial development in the assessment of the Ulez effects. Previously, debates on Ulez revolved around the decline in emissions, the shift to cleaner vehicles, and pollution monitoring results. Now, researchers are starting to compile evidence on what these changes could mean for the people breathing the cleaner air.
Children represent an especially revealing group because their developing lungs are vulnerable to traffic pollution. Poor lung growth during childhood can persist into adulthood and heighten the risk of respiratory and cardiovascular diseases later in life.
The recent findings also build on earlier research from the same study suggesting that Ulez influenced some children’s travel habits. 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. This was in contrast to just 20% of children in Luton. The shift toward active travel was especially pronounced among children who lived further from school.
For Rosamund Adoo-Kissi-Debrah, the distressing impact of London’s polluted air was palpably clear. Her nine-year-old daughter, Ella, tragically passed away following an asthma attack in 2013 after years of exposure to high pollution levels near their Lewisham home. In 2020, Ella became the first person in the UK to have air pollution declared as a cause of death.
After the release of this new research, Adoo-Kissi-Debrah spoke to the BBC, stating that the initial steps toward improving London’s air through Ulez have clearly been worth it, while emphasizing the need for further action.
Since the Ulez was initiated, London has demonstrated significant progress on reducing nitrogen dioxide levels. In 2024, for the first time, the capital passed the government’s national compliance assessment for the legal annual NO₂ limit. However, some individual monitoring sites have continued to record concentrations above that level, and the UK limits are considerably weaker than WHO guidelines.
Initially covering central London, Ulez expanded to inner London in 2021 and across the capital in August 2023. The policy has sparked political debates over the £12.50 daily charge imposed on drivers of older, more polluting vehicles. Critics argue that this cost could disproportionately affect lower-income households and businesses.
Despite the controversy, the evidence of falling pollution levels 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. Furthermore, population-weighted NO₂ exposure dropped by 41% between 2019 and 2024. Also, the exposure to PM2.5 – tiny particles capable of entering the lungs and bloodstream – fell by 28%. These broader reductions cannot be exclusively attributed to Ulez, as other clean-air policies have been implemented over the same period.
Some of the most significant improvements have been observed in communities that historically suffered from 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 about 80% lower than it would have been without Ulez.
Evidence of wider health effects has also started 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, it is believed to have contributed to the overall improvement.
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.”
