London’s Ultra Low Emission Zone cleaned up the city’s air. Then children’s lungs got bigger

In London, an Ultra Low Emission Zone requires vehicles to meet strict emissions standards or else pay a daily fee for driving through that area. 

It’s an initiative that has reduced toxic air pollution levels and spurred drivers to adopt cleaner vehicles.

And now it’s even been linked to improved lung growth in the city’s children.

Before the Ultra Low Emission Zone (ULEZ), London children had stunted lung growth, a 2018 study found. 

When exposed to air pollution, like the emissions from traffic, their lungs were smaller than they should have been—putting them at risk of asthma attacks, lung diseases, and even early death as they become adults.

But now, after five years of the ULEZ, those children’s lungs have improved, according to a major five-year study recently published in the Lancet Public Health journal. 

It’s a result that Chris Griffiths, a professor at Queen Mary University of London and lead investigator on the study, calls “astonishing.”

‘Jaw dropping’ results

The study tracked the lung development of more than 3,400 children between the ages of 6 and 9, in both London and a comparison site of Luton, another city in England with a similar mix of air pollutants but no low emissions or “clean air zone.” 

Researchers did an annual check of the children’ s lungs, tracking their growth and development over time.

Before the ULEZ, London was more polluted than Luton, and children in London had smaller lungs than their Luton counterparts. 

But after five years of the ULEZ, “extraordinarily, [the London children] just caught up,” says Griffiths.

The children’s lungs were now the same size, as measured by FEV1, or forced expiratory volume in one second, a measurement of how much breath someone can forcefully blow out in one second after taking a deep breath.

The share of Londin children with clinically impaired lung function also fell significantly, from 14%, or one in 7, before the ULEZ, to 9%, or one in 11. (In Luton, the proportion fell from 9% to 7%).  

“It was a jaw-dropping moment,” Griffiths says of the results. “There are a lot of things that damage children’s development, but you don’t hear very often about things which improve children’s development.”

A natural experiment

Traffic pollution is full of toxic emissions like nitrogen dioxide, or NO2—an air pollutant that prominently comes from combustion engines burning fuel, and which has been linked to asthma and other respiratory diseases.

After ULEZ’s implementation, the study found, London children’s exposure to NO2 fell twice as fast, and more than twice as much, compared to the children in Luton.

And as that NO2 exposure dropped, London children’s FEV1 measurements increased by 10 milliliters per year more than children in Luton.

Griffiths cautions that the results can’t specifically establish causation between the lower air pollution levels and the children’s lung development, particularly since it wasn’t a randomized trial. “You can’t randomize kids to breathe dirty or clean air,” he says.

Instead, this study was what’s called a “natural experiment,” which makes causation harder to prove. But the researchers are confident the relationship could be causal for a few reasons.

There were enough children in the study to make it statistically significant, Griffiths says.

Plus, the findings are reversible: “We showed that pollution damaged the lungs. They got smaller,” Griffiths says. “Now we’re showing that you take the pollution away, or clean it, then they get bigger.”

It also replicates other scientific findings, including research into how, when California cleaned up its smoggy air, children’s lung health improved, or when Stockholm pollution decreased, children there saw their lung capacity get better. 

This study, however, is the first to link a targeted clean air policy—a specific zone for low emissions—with those developmental improvements, Griffiths says.

‘Clean air zones deliver better health’

Air pollution is currently the top environmental cause of death. Health experts have referred to it as a pandemic: polluted air leads to some 8 million premature deaths each year. It’s also linked to other health impacts like asthma, cancer, heart disease, and more.

That makes children’s lung health crucial. Everyone’s lungs decline as they age, but if you enter adulthood with smaller, already damaged lungs, you’re more susceptible to all those health impacts. 

More and more cities are paying attention to air quality and its impacts. London has been a particularly strong example.

At the end of 2020, a London coroner made history by ruling that air pollution, along with severe asthma, were the causes of death for nine-year-old Ella Kissi-Debrah, who died in 2013. 

The coroner’s report specified that exposure to nitrogen dioxide and fine particulate matter known as PM2.5, both from traffic emissions, contributed to her death.

When London’s ULEZ was expanded in 2022, then-Mayor Sadiq Khan specifically called out the fact that kids there were growing up with “stunted lungs.” 

Though pollution levels in London have dropped, they still don’t meet the World Health Organization’s new air quality standards. And London isn’t alone: 99% of the world breathes dirty air that exceeds WHO guidelines.  

Though his study focused on London, Griffiths hopes it can be relevant for cities around the world.

“I would hope that this reinforces the message that clean air zones are a policy that deliver better health,” he says. 

It also highlights the importance of helping kids developmentally. Improvements to kids’ development leads to improvements throughout the rest of their lives.

Cleaning up air pollution is a way of “giving kids a good start,” he adds. “Conversely, if you don’t do it, then you’re damaging kids.”