New evidence reveals that all Londoners are now breathing cleaner air following the first year of the expanded Ultra Low Emission Zone (ULEZ)

1. Roadside Nitrogen Dioxide (NO2) levels, a toxic gas that exacerbates asthma, impedes lung development, and raises the risk of lung cancer, have decreased by a record 27% across the entire capital [1].
2. Particle emissions (PM 2.5) from vehicle exhausts, are 31% lower in outer London in 2024 than they would have been without the ULEZ expansion. [2]
3. The environmental impact of ULEZ has been substantial, with carbon emissions equivalent to nearly three million one-way passenger trips between Heathrow and New York saved [3]
4. Air quality has improved at 99% of air quality monitoring sites across London since 2019, and London’s air quality is improving at a faster rate than the rest of England [4, 5]

In London, around 4,000 premature deaths per year were previously attributed to toxic air [6]. Air pollution increases the risk of developing asthma, lung cancer, heart disease and stroke, and there is growing evidence that air pollution exposure increases the risk of developing dementia [7]. 

In April 2019, the Mayor of London launched the world’s first 24-hour Ultra Low Emission Zone (ULEZ) in central London. The zone was expanded across inner London in 2021, and finally to cover the whole capital In August 2023, bringing the air quality and associated health benefits to the five million people living in outer London.

A new City Hall report, extensively reviewed by an independent advisory group of experts* shows that the ULEZ has led to substantial improvements in air quality in outer London and across the capital. [1]

Particle emissions (PM2.5) from vehicle exhausts are estimated to be 31% lower in outer London in 2024 than they would have been without the ULEZ expansion. Alongside NO2 and PM2.5 reductions, NOx (Nitrogen Oxides) emissions from cars and vans are also estimated to be 14 per cent lower in outer London. [2]

The biggest reductions in NO2 levels have been in central London (54%) but there have also been substantial reductions in inner London (29%) and outer London (24%) [1].

The boroughs that have seen the biggest reductions in NOx emissions due to the ULEZ expansion are Sutton, Merton, Croydon, Harrow and Bromley, where harmful emissions are estimated to be around 15 per cent lower in 2024 than would be expected without the expansion to outer London, which covers a large area of around 1250km2.

Thanks to all phases of the ULEZ, NOx emissions from road transport are estimated to be 36 per cent lower across London in 2024, a saving of around 3400 tonnes - the equivalent of approximately one year of emissions from all passenger car trips in Los Angeles [8]. 

The report also shows that the ULEZ has led to savings in carbon emissions.

Cumulatively between 2019 and 2024, the equivalent of nearly three million one-way passenger trips between Heathrow and New York has been saved in carbon due to ULEZ as a whole [3]. 

Deprived communities are seeing some of the biggest benefits. For some of the most deprived communities living near London’s busiest roads, there was an estimated 80 per cent reduction in people exposed to illegal levels of pollution in 2023 – this increases to 82 per cent in outer London, compared to a scenario without the ULEZ [9]. 

Data from the report [2], alongside independent analysis [10] has found that the ULEZ expansion has not impacted footfall or retail and leisure spending in either outer London or London as a whole [8]. Visitor footfall in outer London increased by almost 2 per cent in the year after the London-wide ULEZ expansion.

The Mayor of London, Sadiq Khan, said: “When I was first elected, evidence showed it would take 193 years to bring London's air pollution within legal limits if the current efforts continued. However, due to our transformative policies we are now close to achieving it this year. Today’s report shows that ULEZ works, driving down levels of pollution, taking old polluting cars off our roads and bringing cleaner air to millions more Londoners. 

“The decision to expand the ULEZ was not something I took lightly, but this report shows it was the right one for the health of all Londoners. It has been crucial to protect the health of Londoners, support children's lung growth, and reduce the risk of people developing asthma, lung cancer and a host of other health issues related to air pollution.   

“With boroughs in outer London seeing some of the biggest reductions in harmful emissions and London’s deprived communities also seeing greater benefits, this report shows why expanding ULEZ London-wide was so important. 

“Thanks to ULEZ and our other policies, all Londoners are now breathing substantially cleaner air - but there is still more to do, and I promise to keep taking action as we build a greener, fairer London for everyone.”    

TfL data also shows that Londoners have continued to upgrade their vehicles to cleaner models with 96.7 per cent of vehicles seen driving in London now ULEZ compliant, up from 91.6 per cent in June 2023 and 39 per cent in February 2017, when changes associated with the ULEZ began. Van compliance in outer London is over 90 per cent for the first time (90.7 per cent). In February 2017, just 12 per cent of vans met the ULEZ standards, demonstrating the schemes’ impact on reducing the number of more polluting older vans driving in London. [2]

The data also shows there were nearly 100,000 fewer non-compliant vehicles detected in London on an average day in September 2024 compared to June 2023, when the Mayor announced his plans to extend the ULEZ to outer London - a 58 per cent reduction in non-compliant vehicles. This has been aided by the Mayor’s scrappage scheme, which provided around £200m to support Londoners to switch to cleaner vehicles. The scrappage schemes that supported the introduction of the ULEZ to central London, and the expansion to inner London, were successful in removing 15,232 older and more polluting vehicles from London's roads. Over 54,700 further applications were approved before the scheme closed in September 2024, including over 400 vehicles donated to humanitarian and medical efforts in Ukraine. A ULEZ scrappage scheme evaluation report to be published shortly will set out the full impact of the scheme, including the total numbers of vehicles scrapped, replaced and donated. 

The ULEZ is the centrepiece of a range of measures the Mayor and TfL is implementing to tackle London’s toxic air, including putting a record number of 1900 zero-emission buses on the roads. Since 2019, air quality has improved in 99 per cent of air quality monitoring sites included in the analysis (8) across London, thanks to these measures and wider transport policies, with 80 per cent of monitoring locations showing average NO2 concentration reductions of more than 10 µg/m3, which is a quarter of the legally permitted annual NO2 concentration.   

London’s air quality is improving at a faster rate compared to the rest of England (2017-2024). This is particularly notable in outer London where concentrations have improved more rapidly over recent years and are now similar to the rest of England average, which has historically been lower than London [9].  

Dr Maria Neira, Director, Department of Environment, Climate Change and Health at the World Health Organization: "Improving air quality through initiatives like the Ultra Low Emission Zone in London is crucial for protecting public health and reducing the burden of disease. Cleaner air leads to healthier communities, lower rates of respiratory and cardiovascular illnesses, and a better quality of life for all residents. The World Health Organization commends the efforts of cities like London in implementing measures to reduce emissions from vehicles and improve air quality, which ultimately contribute to a healthier and more sustainable urban environment."

Anne Hidalgo, Mayor of Paris, said: “Reducing car traffic is one of our greatest opportunities to address the climate emergency. Under the leadership of Mayor Khan, London is showing us what safer, healthier, and greener communities look like, and the results of London's clean air zone speaks for itself. I commend Mayor Khan for his commitment, leadership and vision to addressing the climate crisis and protecting the lives and health of city residents. London is demonstrating once again that cities lead the fight against climate change.”

Rosamund Adoo-Kissi-Debrah CBE, Global Heath Advocate and Founder of the Ella Roberta Foundation said: “I am delighted that the latest analysis since the expansion of ULEZ to outer London shows that air pollution has reduced.  My daughter Ella died from emissions from the South Circular Road close to where we live, and I will not stop until everyone in London can breathe safe, clean air, regardless of where they live in the city.  People’s health, particularly children’s, should always be prioritised by society, and I look forward to hearing what further plans the Mayor has to continue to clean up the air for all Londoners.  ULEZ was an important step, but there is so much more to do, and I will ensure that politicians and decision-makers are held to account, and do all they can to protect people’s health and clean up the air we breathe."

Christina Calderato, TfL’s Director of Strategy, said: “Bold and ambitious environmental schemes like the ULEZ are pivotal to making tangible long-term air quality improvements to tackle a public health crisis, as shown in this new report. Everyone in the capital is now breathing cleaner air because of ULEZ. Harmful NO2 concentrations are 27 per cent lower across the city than if there had been no ULEZ. There’s less PM2.5 exhaust emissions and NOx pollutants from cars and vans in outer London - an even greater reduction than reported in the first six months of ULEZ showing the continued success of the scheme.  

“It is great to see it making a real difference to the air Londoners breathe, and together with our efforts to decarbonise the public transport network, will see generations to come reaping the benefits of a greener, cleaner London.” 

Dr Gary Fuller, Imperial College London, and Chair of the ULEZ Advisory Group, said: “Each phase of the ULEZ has led to clear improvements in the air pollution next to London’s roads. This is good news for the current and future health of Londoners, as well as those who travel to London for work or leisure.   

“The analysis in this report benefited from an international advisory group of scientists, all with experience in assessing the impacts of urban clean air policies. We worked with the Mayor’s team to stress-test key parts of the analysis and concluded that the core methodology used in this report, and in previous ULEZ reports, was appropriate and robust. The ULEZ is one of over 300 such schemes across the UK and Europe, and many cities are looking to London's ULEZ results to inform their own plan.”

Jemima Hartshorn, Director, Mums for Lungs said: “Today is a good day for children, and all of us: Air pollution has been reduced due to the pioneering measures of our Mayor and we are so glad about that. But air pollution across the country and even London remains too high. Hopefully, the national Government will learn from this success and support Mayors and councils in stopping pollution from diesel and wood burning making us sick.”

Larissa Lockwood, Director of Policy and Campaigns at Global Action Plan said: “Clean air is a health and social justice issue. This report shows that bold, pro-environment policies can be successful – both in terms of health benefits and electoral success. We celebrate the air quality improvements from ULEZ, urge the Mayor to continue cleaning up the air in London and hope that other political leaders across the UK and the world will be inspired to implement bold measures to tackle air pollution.”

Izzy Romilly, Sustainable Transport Manager at Possible said: “The largest clean air zone in the world has been a triumph. We’ve slashed pollution, and we’ve protected the lungs of the most vulnerable Londoners, with the biggest benefits being felt in areas of highest deprivation. Now, national government and leaders around the world should learn the lessons of ULEZ and show the same ambition to clean up toxic air. Here in London, these findings should give the Mayor the courage to go further and faster on tackling harmful emissions. We need to see more action on transport and traffic, a serious tax on SUVs, and a diesel phase out by 2030."

Jane Burston, CEO at Clean Air Fund said: “The new data shows how the ULEZ is making a real difference to the quality of the air Londoners breathe. It's especially encouraging to see that the communities living near the busiest roads are seeing substantial benefits one year on. London's progress provides an inspiring blueprint for others, including those in our Breathe Cities initiative, by showing how tackling air pollution can improve lives, boost public health and address the climate crisis.”

Barbara Stoll, Senior Director at Clean Cities Campaign said: “Despite fierce opposition - even from the government of the time - the Mayor stood firm, and the results speak for themselves. The ULEZ shows that when city leaders have vision and determination, they can reduce inequities and transform urban life for the better. We urge the Mayor to continue his leadership in championing healthy, climate-friendly transport and to stay committed to making London the world’s first truly electric-vehicle-ready global city.”

Michael Solomon Williams from Campaign for Better Transport said: “This report shows that clean air zones work and other cities should take encouragement from London’s experience. Reducing the harmful effects of road transport and ensuring there are good public transport, walking and cycling options are key to creating healthier, happier communities.”

Livi Elsmore, Campaign Manager, Healthy Air Coalition said: "Over a year on from the expansion of the Ultra Low Emission Zone (ULEZ) in London, we are delighted to see significant progress made in cleaning up the capital’s air to protect the health of everyone who lives and works in the capital, and future generations of Londoners.

“Contributing to as many as 4,000 deaths each year in London, air pollution poses the greatest environmental threat to our health. Measures like the ULEZ are among the most effective tools we have to tackle toxic air and protect public health.

“And the impact of ULEZ is now clear: toxic nitrogen dioxide emissions are 27% lower than they would be without the scheme.

“We call on the Mayor of London to continue showing leadership through building a pathway for London to meet the air pollution levels recommended by the WHO, meet London’s transport targets, and take concerted action on unnecessary wood burning in the capital.”

Henry Gregg, Director of External Affairs, Asthma + Lung UK said: "A year on it’s great to see the ULEZ expansion is having a positive impact on improving the capital’s air quality and helping protect the lung health of millions of people, every day. Expanding ULEZ reduced the number of polluting vehicles on the road and is helping every Londoner, regardless of age, ethnicity or background, breathe cleaner air. Air pollution is a public health emergency that affects us all – particularly the estimated 585,000 people in Greater London who have asthma or Chronic Obstructive Pulmonary Disease (COPD). Air pollution can worsen the symptoms of people with existing lung conditions, such as breathlessness, wheezing and coughing, and potentially lead to life-threating asthma attacks or serious flare-ups. In some cases it can lead to hospitalisation and even death – up to 4,000 early deaths a year in the capital are linked to air pollution. Unfairly, it is often those living in the most deprived communities who are affected the most by breathing in toxic air. There are no safe levels of air pollution and the government must commit to an ambitious Clean Air Act, which could protect people, wherever they live, from the dangers of polluted air.”

Yvonne Aki-Sawyerr OBE, Mayor of Freetown and Co-Chair of C40 Cities: "Clean air is not a privilege, it’s a fundamental right. The success of London’s clean air zone serves as a powerful testament to the impact of bold action in protecting public health, especially for our most vulnerable communities. As his fellow Co-Chair of C40 Cities, I am proud to stand alongside him, and I urge leaders everywhere to take note of these transformative policies."

Giuseppe Sala, Mayor of Milan: "The impact of London’s clean air zone is clear: better air, fewer emissions, and a healthier future for all Londoners. Milan supports and celebrates this achievement, as we work on similar policies to protect the health of our residents and make our cities greener and more liveable for all." 

Martin Lutz, formerly Berlin City Government, and member of the ULEZ Advisory Group, said: “With the latest step of extending the ULEZ to the whole city, London has set a global benchmark for how access restrictions for high emission vehicles can effectively reduce air pollution from cars.    

“This one year report makes a very strong case for the success and health benefits of the ULEZ for Londoners, thanks to the wealth of data and measurements that have been painstakingly collected over the years of the zone's gradual expansion.”   

Ludo Vandenthoren, Mutualités Libres (a Belgian mutual health insurance firm), and member of the ULEZ Advisory Group, said: "It was an honour to work on this project alongside experts in the field. The GLA and TfL, with their commitment to the citizens of London, demonstrated great receptiveness to the feedback we provided. We were able to contribute information on the socio-economic aspects and health effects of air quality, offer input on the statistical methodology specific to this topic, and share valuable references for their reports. I am particularly proud that the study from the Belgian Independent Health Insurance Funds on air quality is seen as an inspiring model for their own approach. The London ULEZ is an ambitious initiative that will undoubtedly inspire other cities."  

Professor David Carslaw, University of York, and member of the ULEZ Advisory Group, said: “This report represents a detailed evaluation of the emissions and air quality impacts of the London ULEZ. London and its surrounding areas are fortunate in having one of the world’s most comprehensive air quality networks, which provides a strong basis for the evaluation of the air quality impacts of the ULEZ as it has expanded in recent years. The results show the benefits of the ULEZ are widely distributed and have accelerated the improvement in London’s air quality.”  

Dr Chinthika Piyasena, Consultant Neonatologist in London said: “As a Londoner and clinician, I’ve long advocated for bold action on air pollution because the science is clear: toxic air harms babies before they even take their first breath. Nitrogen dioxide exposure has been linked to an increased risk of stillbirth, babies being born too early or too small, and even impacts brain development. So a year after the full expansion of ULEZ, it’s incredible to see real progress in reducing this pollutant. Every step we take towards cleaner air, is a step toward healthier pregnancies, healthier babies and a healthier future for all Londoners.”   

Simon Birkett, Founder and Director of Clean Air in London said: "I have campaigned for low emission zones since April 2006 - almost two years before the first phase was implemented in London. I was also the first to call for an inner London low emission zone. It is particularly pleasing therefore that the Mayor’s One-Year report on ULEZ expansion - the ninth phase of low and ultra-low emission zones in London - has shown again that these big solutions work. In fact, together with related measures such as cleaner buses and taxis, they have almost single handedly helped London to slash nitrogen dioxide (“NO2”) concentrations by 2/3 near busy roads, and nearly comply with legal limits and the WHO’s 2005 air quality guideline of 40 micrograms per cubic metre ("mg/m3") by 2025, probably ahead of smaller UK cities.” 

Professor Kevin Fenton, London Regional Director, Office for Health Improvement and Disparities and Regional Director of Public Health, NHS London said: “As well as reducing air pollution in outer London, this report also shows that ULEZ and its expansions continue to have a positive impact on air quality across the city. Londoners are now benefiting from improved air quality, and this is particularly true for those communities who live in more deprived areas of London.  

"In a city where over 480,000 Londoners have a diagnosis of asthma and are more vulnerable to the impacts of air pollution, a 27% reduction in harmful roadside NO2 concentrations across the whole city will bring about invaluable health benefits. And I’m optimistic that Londoners will continue to benefit from better air quality, and subsequently, better health, due to the ULEZ and its expansions.”

Chris Streather, Medical Director and Chief Clinical Information Officer, NHS England London, said: “It’s encouraging to see that all Londoners have experienced a significant improvement in air quality, and this reduction in pollutants directly contributes to better health outcomes.

“Vital initiatives like the ULEZ create a healthier urban environment, reducing the risks of respiratory conditions such as asthma and lung cancer, and ultimately lessen the burden on our health system.”