Data published by the City of London showed that expanding the Ultra Low Emission Zone (ULEZ) was associated with a significant reduction in air pollution, while a subsequent study provided evidence of improved lung function among children. These findings follow years of political debate over imposing a daily charge on vehicles that do not meet modern emissions standards.
The ULEZ imposes a daily charge of £12.50 on non-compliant vehicles and operates around the clock. The zone was established in 2019 during Sadiq Khan’s tenure as Mayor of London, after Boris Johnson had announced it in 2015 when he held the same office. Initially, the zone was limited to central London, then expanded in 2021 and 2023 to cover all of Greater London, which is home to approximately 9 million people.
Widespread reductions in vehicle pollutants
The report compares actual pollution levels with what would have been expected if the ULEZ had not been implemented. According to this comparison, nitrogen dioxide (NO2) fell by 27% in outer London, while concentrations of fine particulate matter, PM2.5, declined by 31%. Total nitrogen oxides, including NO and NO2, fell by 14%.
The reduction was greater in central London, where NO2 levels fell by 54%. In addition, 99% of air-quality monitoring devices across London recorded a decrease in pollution. This result is particularly significant in deprived areas, where the proportion of residents exposed to pollution levels exceeding legal limits fell by 80%.
Before the period covered by the report, toxic air pollution was attributed to approximately 4,000 deaths annually in London. The source indicates that a reduction of about one-third in the most dangerous pollutants could mean saving more than 1,000 lives each year, but this figure remains an estimate based on the relationship between pollution levels and deaths, rather than a directly verified death toll reported in the study.
Additional evidence from children’s lung function
A study by Queen Mary University of London added a direct health dimension to the air-quality findings. Researchers compared children’s lung function in London before and after the zone was implemented, and also compared it with that of children in the nearby city of Luton, which does not operate a comparable low-emission zone.
Before the ULEZ was implemented, lung function among children in Luton was clearly better than that of their peers in London, amid the capital’s higher pollution levels. Four years after the zone began, lung function among children in London had caught up with levels in Luton. Both cities improved, but the improvement was faster in London. The proportion of children with clinically weak lung function also fell from 14% to 9% in London, and from 9% to 7% in Luton.
The article also cites an earlier estimate by King’s College London in 2019, which concluded that London would have needed 193 years to reach the legal limits for nitrogen dioxide without additional action. The city reached that threshold last year, 184 years earlier than the previous projection, according to the source.
What changed in practice?
The policy did not rely on the charge alone. Between June 2023 and September 2024, the number of non-compliant vehicles on London’s roads fell by 58%. A £200 million scrappage scheme, partly allocated to support people on low incomes, also helped remove 15,232 older vehicles from service.
The ULEZ differs from the congestion charge zone in central London: the former aims to reduce pollution by restricting the most polluting vehicles, while the latter aims to reduce traffic, with an indirect effect on air quality. ULEZ rules are also not a blanket ban, as most petrol cars made within the last 20 years and most diesel cars made within the last 10 years comply, in addition to exemptions for certain delivery vehicles, buses and others.
The policy was implemented alongside the growing prevalence of electric cars in the United Kingdom; electric cars accounted for nearly three out of every ten cars sold in 2024, according to the article. The availability of less-polluting alternatives makes compliance with policies like these easier, while the spread of electric vehicles itself may benefit from restrictions imposed on higher-emission cars.
The policy was also associated with a reduction in carbon emissions equivalent, over five years, to the emissions generated by approximately 3 million individual flights between London and New York, according to the estimate cited in the source.
Why does this example matter?
London offers a practical case of a policy targeting emissions at their source, with measurable results in air quality, health and vehicle-use behavior. The experience also shows that the impact of charges depends on a combination of factors, including the scope of implementation, its continuity, the presence of support programs for lower-income groups, and the availability of alternative transport and less-polluting vehicles.
Nevertheless, the findings do not eliminate the political and social debate over the policy’s cost and the distribution of its burdens. Some conclusions in the article, such as linking the reduction in pollution to a specific number of lives saved, are interpretive estimates rather than direct measurements of individual health outcomes. The report and the lung-function study should therefore be read as evidence of improvement in specific indicators, not as proof that all health improvements in London resulted from the ULEZ alone.