Study: London’s ULEZ Linked to Improved Child Lung Health
Traffic-related air pollution is a major risk factor for lung disease, respiratory conditions, cardiovascular disease and, ultimately, premature mortality.
To mitigate these risks, clean air zones as a form of public health intervention have become a fixture in many cities across the UK, including Bristol, Manchester and Birmingham, as well as across Europe in Paris, Madrid and beyond.
Perhaps one of the most infamous and comprehensive clean air zones is in London, where the Ultra Low Emission Zone (ULEZ) has been in place since April 2019 under Mayor of London Sadiq Khan.
A study published in The Lancet Public Health, led by teams at Queen Mary University of London and Imperial College London, has provided evidence that the ULEZ has positively affected children's lung growth and function in the city.
“Traffic pollution in cities damages children’s health and development,” says Chris Griffiths, the study’s joint senior author and a Professor of Primary Care at the University of Oxford and Queen Mary University of London.
“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.”
A major study
Examining more than 3,400 primary school children in London and Luton, the study – known as Children's Health in London and Luton (CHILL) – established a baseline for lung performance in 2018 before the introduction of ULEZ. The lung capacity and performance of the participating children were then tested annually across five years.
While initial baseline results suggested that London-based children had smaller, less-developed lungs than those in Luton, lung capacity reached near-identical levels by the end of the study.
Within five years of ULEZ's launch, London children's exposure to NO2 fell twice as fast and twice as much as in Luton, and their lung capacity grew an extra 10ml per year faster than Luton children's – closing the gap entirely by year five.
- 3,400+ primary school children in London and Luton were tracked over the five-year study.
- 10ml - the additional lung capacity growth per year London children gained compared to Luton children as NO2 exposure fell, closing the gap entirely by year five.
- 14% to 9% - the drop in London children with clinically impaired lung function over the study period (versus 9% - 7% in Luton).
- 2x - London children's NO2 exposure fell twice as fast and twice as much as in Luton over the five years.
Clinically impaired lung function also dropped further in London (14% to 9%) than in Luton (9% to 7%).
Luton was chosen as the comparator site because it is geographically distant enough to avoid ULEZ spillover effects, yet shares London's population demographics, pollutant source mix and established long-term air quality monitoring, while having no low emission zone plans of its own.
Minister of Health of the UK Goverment, Karin Smyth, says: "This study is a powerful reminder of the impact that air quality has on children's lung health, and will help to improve our understanding of how reductions in air pollution can restore normal lung growth among children, reduce the risk of respiratory illnesses in adulthood and support our goal to give every child the best start in life.”
A growing body of evidence
The results follow another research study by Imperial College London researchers published in June 2026, which found air pollution-related deaths have significantly declined in London following the implementation of stricter emissions policies.
The independent analysis found that deaths from poor air quality fell by around 40% between 2019 and 2024.
Speaking at the time of the study’s publication, Jane Burston, CEO of the Clean Air Fund, said: “A 40% reduction in deaths linked to air pollution in just five years is a remarkable public health achievement.
“This research adds to a growing body of evidence that clean air measures, like London’s ULEZ, save lives. This progress reflects ongoing efforts by city leaders, civil society organisations, and communities that have pushed for ambitious action.”
Pollution levels remain too high
However, the authors of the latest study say significant work remains to be done, with air pollution levels in London and across other UK cities remaining above World Health Organisation (WHO) guidelines.
Despite air quality improving dramatically since 2019, London’s average PM2.5 level – fine-particulate air pollution – is around double the WHO’s guideline levels.
