The introduction of London's Ultra Low Emission Zone (ULEZ) has been strongly associated with improved lung growth in children, according to a five-year study of more than 3,400 children.

The study, led by Queen Mary University of London in collaboration with Imperial College London and universities in the UK and US, found that improvements in air quality following the introduction of the ULEZ were linked to accelerated lung growth among children living in London.

Published in The Lancet Public Health, the study followed more than 3,400 children aged six to nine from 84 primary schools across London and Luton between 2018 and 2022. Luton was used as a comparison site because it had similar exposure to traffic-related pollutants but did not have a clean air zone.

Researchers found that children's exposure to nitrogen dioxide (NO₂), a key indicator of exhaust pollution, fell more than twice as much and twice as quickly in London as in Luton following the introduction of the ULEZ.

As NO₂ exposure declined, London children's lung function increased by an average of 10ml per year more than children in Luton. After five years, lung function was comparable between the two groups, suggesting that the London children's lung growth had accelerated enough to catch up with their peers in Luton.

The proportion of London children with clinically impaired lung function also fell from 14% to 9% over the study period, compared with a reduction from 9% to 7% in Luton.

Professor Chris Griffiths, Professor of Primary Care at the University of Oxford and Queen Mary University of London, and joint senior author, said the research provided “the strongest evidence yet” of how the health impacts of traffic pollution on children can be prevented.

The researchers say the findings provide the first evidence that clean air zones can benefit children's lung development, strengthening the case for ambitious clean air policies in cities affected by traffic-related air pollution.