First Evidence That London’s Ultra Low Emission Zone Improved Children’s Lung Health

In April 2019, London introduced far-reaching measures to curb traffic emissions and reduce the harmful air pollution that had engulfed the city centre.

The policy is known as the Ultra Low Emission Zone (ULEZ).

Five years of observations from this ‘natural experiment’ have now given scientists compelling evidence that central London’s ULEZ – along with the Toxicity Charge that came before it – substantially benefited the lung health of young people living there.

The findings offer encouraging support for comparable clean-air initiatives worldwide.

“To our knowledge, we provide the first evidence that air quality improvements following [the] introduction of a clean air zone are associated with improved lung growth trajectories in children,” the study’s authors write in their new paper, published in The Lancet Public Health.

“Decision-makers globally should consider accelerating the introduction of clean air zones to improve children's lung health.”

London’s ULEZ and air pollution

In principle, it follows that a policy of this kind could make it easier for people living in inner-city areas to breathe.

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Exposure to traffic-related air pollution is known to raise the risk of lung disease, including cancer, as well as premature death.

For children and teenagers, such exposure is also closely associated with poorer lung development. Over the rest of their lives, that can mean a greater likelihood of asthma, chronic obstructive pulmonary disease, cardiometabolic disease, and earlier death.

Official estimates indicate that, since the ULEZ began, roadside nitrogen dioxide levels – a major concern among gases produced by heavy traffic – have declined by 54 percent in central London and 27 percent across the city as a whole.

Until now, however, there has been little evidence showing how much a measure such as central London’s ULEZ genuinely changes residents’ health. That gap has left the scheme vulnerable to criticism from people worried about the costs faced by drivers.

This has been especially contentious since the zone was extended to cover the whole of Greater London.

The Ultra-Low Emissions Zone was extended to Greater London in 2023. (Transport for London)

Comparing children in London and Luton

Scientists from institutions throughout the UK tracked the lung function and lung growth of 3,414 schoolchildren, who were aged six to nine when the study began.

About half of the children lived in central London, while the remainder lived in Luton, a busy industrial town roughly 56 km away that had not introduced a clean-air zone.

During yearly visits to schools, researchers assessed lung function by asking children to forcefully breathe out for one second and then recording the volume exhaled. Doctors commonly use this test to determine how effectively a patient’s lungs are working and, for children, how well their lungs are developing.

With a population of about 225,000, Luton is plainly not the same sort of place in which to grow up as London.

Nevertheless, this study design is intended to compare children with broadly similar lifestyles in each location, leaving baseline air pollution and the ULEZ intervention as the principal differences.

Lung function and air pollution by site and year. (Wood et al., The Lancet Public Health, 2026)

ULEZ linked to improved lung growth in children

During the first year of data collection, before central London implemented the ULEZ, the average lung growth of London children was visibly reduced compared with that of their peers in Luton.

Their estimated average yearly exposure to nitrogen dioxide (NO₂) was also 18.95 μg/m³ higher than for children in Luton.

In the years after the ULEZ was introduced, however, the lungs of London children started to close the gap. On average, this lung-function measure rose 10 mL/year faster than it did in Luton.

At the same time, NO₂ levels in central London fell by 3.77 μg/m³ each year, compared with a yearly decrease of 1.77 μg/m³ in Luton.

The probability of both patterns appearing by chance is so small that the evidence strongly suggests the ULEZ was responsible.

Four years after the ULEZ began, the lung function of London children matched that of children in Luton.

Researchers further found that, as central London’s air pollution declined, the share of children with clinically impaired lung function also fell: from 14 percent before the ULEZ was launched to 9 percent five years afterwards.

Parents, pupils, and teachers reported cleaner London air, less congested traffic, and fewer problems with asthma.

As air quality improved, children in London were also four times more likely than those in Luton to begin cycling or walking to school.

Related: These Babies Grew Up With Strict Sugar Limits. Decades Later, The Results Are Dramatic.

“We already knew that the ULEZ reduced air pollution but now we know that children's lung health has improved at the same time, which is a really important finding for children and parents living in London,” says the study’s lead author, respiratory physiologist Helen Wood of Queen Mary University of London.

“However, we must not be complacent: air pollution in both London and Luton – as well as other cities across the UK – remains above WHO guideline levels, so there is still work to be done.”

The study was published in The Lancet Public Health.

This article was fact-checked and edited by Clare Watson. Although we take pride in our process, we are only human. If you notice an error, please let us know.