Introducing Ulez was my toughest decision as Mayor of London, but we now know his surprising impact | Sadiq Khan

W.When I introduced London’s clean air zone – the ultra-low emissions zone (Ulez) – more than seven years ago, no city had tried anything like it. At the time, the plan in central London provoked fierce opposition. When I decided to expand it (first in 2021 to inner London and then again in 2023 to the entire city, making it the largest clean air zone in the world), my detractors were even louder. They claimed I had declared war on drivers in blindly pursuing a policy that might not even work. All major political parties, including mine, opposed it. However, in recent years those critics have fallen silent.

There is now a mountain of evidence showing that Ulez have dramatically reduced air pollution and improved air quality across London, and research published by Imperial College London earlier this year showed that this is already saving lives. Between 2019 (when I first introduced the Ulez) and 2024, estimated deaths associated with air pollution in the capital decreased by around 40%. But a new independent study published today by Queen Mary University of London goes even further and shows how, by helping to clean the capital’s air, Ulez are improving the lungs and lives of London’s children.

Young children are the first to feel the impact of air pollution. They breathe faster than adults and more frequently through their mouths, allowing more pollution to pass into their bodies. Their heads are also lower to the ground, meaning they are closer to vehicle exhaust fumes that spew poisonous chemicals. And, because they are still growing, prolonged exposure to air pollution can cause lasting damage to their development, leading to problems such as asthma, chronic obstructive pulmonary disease (COPD), and lung cancer when they are older.

One of the first places I visited when I was elected mayor 10 years ago was the Sir John Cass Foundation Primary School in Aldgate, now known as Aldgate School. On the roof of the school, I joined the children who were growing a garden. As they proudly showed me what they had planted, the children told me how much they loved spending time outdoors. But talking to their teachers, it was clear that they were concerned about the air the children were breathing. The school was next to one of the busiest streets in inner London and although an air quality monitor had been installed in the playground, they were unable to stop the toxic fumes from passing traffic. As a father of two daughters, I remember trying to imagine how the parents of those girls must have felt, knowing that every day their daughters were exposed to danger they could not control.

I have never forgotten that day. Because, for me, meeting those children confirmed what the fight for cleaner air is really about: not punishing motorists or making money, but protecting the lives of London’s most vulnerable people.

The Ulez has already had a surprising impact on London’s air. According to research conducted by King’s College London, Without additional measures, it would take almost two centuries to reduce levels of one of the most toxic chemicals in our air: nitrogen dioxide (NO).₂) – within legal limits. But last year we announced that we had already done it: 184 years ahead of schedule. We are now starting to see what our success means for the children of London.

The independent study published today by Queen Mary scientists is one of the most comprehensive of its kind. In it, researchers tracked the lung growth of more than 3,400 children in Luton and central London, starting in 2019 and ending five years later. The results are remarkable.

Before we introduced Ulez, London’s dirty air meant that children in the capital had significantly worse lung function than children in Luton. But, during the five-year period that Ulez was in force, children’s exposure to NO₂ it fell twice as fast in London as in Luton. And when the scientists measured lung function again at the end of the study, the young Londoners’ lungs had already caught up. This shows that reducing air pollution doesn’t just help Londoners born today: it can help children whose lungs have already been atrophied by toxic air recover, proving that it’s never too late to act. Over the course of the research, the proportion of children in London with clinically impaired lung function fell from 14% to 9%.

Introducing and expanding the Ulez involved some incredibly difficult decisions. I never took them lightly, but I knew that, as mayor, I could not stand by while Londoners, young and old, lost their lives because of a problem that was within my power to solve. For years, politicians and experts opposed to the Ulez have cynically tried to turn public health issues into a crude culture war. Today, however, it is clear that we are winning the battle against toxic air in the capital, and it is London’s children who are reaping the rewards.

Two months ago I returned to the roof garden of The Aldgate School. It had been just over 10 years since my first visit, and as I prepared to work in the garden with a group of smiling children, I felt a strange sense of deja vu. This time, however, something was different. In 2016, the playground’s air quality monitor showed that nitrogen dioxide levels in the air exceeded legal limits. But when they were measured again last year, they had fallen 48%. As a result, the children I met didn’t have to think twice about what an outdoor soccer game could mean for their health, and their parents didn’t have to worry about whether walking to school would stunt their lung growth.

• Do you have any opinions on the issues raised in this article? If you would like to submit a response of up to 300 words by email to be considered for publication in our letters section, click here.