Scientists warn that London’s Ultra Low-Emissions Zone (LEZ) has had little impact on the city’s pollution levels. 

Researchers from Imperial College London say the controversial scheme – which was last month expanded and made 18 times bigger – is not effective on its own.  

They examined pollutants levels over a period of 12 weeks starting in March 2019 and ending after Sadiq Khan, Mayor of London, launched the ULEZ.

Researchers found that the NO2 levels had dropped by just 3 percentage points over time. There were also ‘insignificant drops’ in O3 levels. These can be harmful to the lungs and cause damage to the brain.

Surprisingly, some areas in the capital have seen their air quality worsen despite having the ULEZ.

These new findings show that the ULEZ – which costs drivers a whopping £12.50/day – is ‘not a silver bullet’ in tackling air pollution.

This comes just a month after London’s ULEZ area was widened so that it covers all roads within the North Circular, catching 130,000 more drivers.

Comparing with a prior analysis done by the Greater London Authority the results show that the ULEZ has a lower impact on air pollution than previous analyses. 

The Greater London Authority said ULEZ had caused a 29 per cent reduction in roadside NO2 concentrations in central London from July to September 2019 and a 37 per cent reduction from January to February 2020. 

ULEZ will cover central London from 2019, but under the new plans it was extended massively to all of inner London two years later

ULEZ covers central London beginning in 2019, but it has been expanded massively to inner London under new plans two years later.

ULEZ now stretches to cover an area surrounded by the North and South Circular roads. The ULEZ is separate from the Low Emission Zone (LEZ), which implemented tougher emissions standards for heavy diesel vehicles from March 1, 2021

The ULEZ is now extended to encompass an area bordered by the North Circular and South Circular roads. The ULEZ can be separated from the Low Emission zone (LEZ), which has stricter emission standards in place for heavy diesel engines starting on March 1, 2021

What is the ULEZ? 

The ULEZ is a new area that requires drivers to pay a fee daily for their more polluting vehicle. It was established by London’s Mayor in April 2019.

This project aims at reducing air pollution from roads and speeding up compliance with EU standards for air quality. 

The Congestion Charge was previously limited to the same central London area as it did the Congestion Charge. 

However, since October 25, it has included all the North Circular roads to try and improve air quality. 

The ULEZ is among several London policies to reduce air pollution that were introduced in 2016, including the Low Emission Zone and Low Emission Bus Zones. 

ULEZ, which was launched in April 2019, allows local authorities to assess diesel vehicles for their presence in Central London. It is intended to decrease vehicle emissions in the worst-affected areas of London. 

The zone was expanded from Central London up to, but not including, the North and South Circular Roads from October 25, 2021 – although three in five motorists weren’t aware of the expansion, a recent poll found. 

Drivers of vehicles that do not comply face being landed with a £12.50-a-day charge, but the new study suggests the zone isn’t as effective as hoped. 

Dr Marc Stettler from Imperial’s Department of Civil and Environmental Engineering and Centre for Transport Studies said that a ULEZ alone isn’t an effective strategy for improving air quality. 

“The London case shows that this combination works well when it is accompanied by a wider range of policies to reduce emission across different sectors, such as bus retrofitting and support for active public transport. 

In response to the study, a spokesperson for the Mayor of London called the study ‘very misleading’, saying ULEZ ‘has had a significant and positive effect on London’s air pollution’.

A spokesperson cited the previous peered-reviewed Greater London Authority research which showed a NO2 decrease of 37% compared to a scenario without ULEZ. 

The Ultra Low Emission Zone in London is now 18 times larger due to the October expansion, meaning any drivers whose cars do not meet standards will face a £12.50 charge

The Ultra Low Emission Zone in London is now 18 times larger due to the October expansion, meaning any drivers whose cars do not meet standards will face a £12.50 charge


PM can be described as a combination of liquid droplets and solid particles found in the atmosphere.

They are created from a variety of sources, including traffic, construction sites, unpaved roads, fields, smokestacks or fires.

The reactions between chemicals like sulfur dioxide or nitrogen oxides are responsible for most particles that form in the atmosphere. 

Some PM such as dust or soot or smoke can’t be seen naked eye. 

The size of other PM can be only detected by an electron microscope. 

PM2.5 – of diameters that are generally 2.5 micrometers and smaller – differ from PM10 – 10 micrometers and smaller.

Source: US EPA 

‘The ULEZ has already helped cut toxic roadside nitrogen dioxide pollution by nearly half and led to reductions that are five times greater than the national average,’ said Shirley Rodrigues, Deputy Mayor for Environment and Energy.

‘But pollution isn’t just a central London problem, which is why the expansion of ULEZ will benefit Londoners across the whole of the city and is a crucial step in London’s green recovery from this pandemic.’ 

For the study, the Imperial researchers used publicly available air quality data from the London Air Quality Network, which shows air quality around the city based on roadside and non-roadside (‘background’) sensor readings. 

The site was used by researchers to measure changes in pollution over a period of 12 weeks, starting February 25, 2019, just before the ULEZ was implemented, and ending May 20, 2019, once it had been in place. 

After controlling for weather fluctuations, they used statistical analysis for quantifying and identifying changes in pollution. 

It was found that there had been a drop in the number of Londoners in areas where NO2 levels were illegally high between 2016-2020. Other reductions in air pollution in London have also occurred, with the exception of the April 2019 implementation. 

These researchers also discovered that air quality improvements were greatest before the ULEZ was implemented in 2019. 


Londoners are scathing about Sadiq Khan, London’s Mayor. They claim that they have to travel five miles to get around the ULEZ to avoid being “taxed to recycling.”

Local residents in Richmond claim that their waste center has been taken into the zone of ultra-low emissions after it was expanded on Monday.

It means residents living in the town and driving older vehicles face a £12.50 charge if they want to take their recycling to the local tip.

Read more: London drivers blast Mayor over new ULEZ scheme  

Around the time the ULEZ was implemented, they observed changes in the levels of O2 and NO2 at 75% and 24% of the monitored sites respectively. 

There were many changes in the air quality at these locations. At some places, pollution even worsened. Relative changes ranged from -9 percent to 6 cents for nitrogen dioxide to -5 percentage to 4 procent for ozone to -6 percentage to 4 percent respectively for PM2.5.

The lining of your lungs can be inflamed by NO2, which can lead to lower immunity against lung infections and worsening respiratory conditions. 

Particulate matter or PM can cause brain damage and is found in a wide range of places, such as vehicle exhausts, industrial sites, and construction sites.  

Researchers suggest other cities should not consider these programs without considering other options. 

They include the phasing-out of petrol and diesel cars, increasing charging points for electric vehicle, planting trees, and creating more cycleways. 

Dr Stettler stated that similar schemes had been implemented in other cities, such as Birmingham, Glasgow, and London, but at a lower scale. 

Clean air zones are being implemented in many other cities. We could help to shape their policies by sharing our insights.

Particulate matter, or PM, comes from a variety of sources, including vehicle exhausts. Some PM, such as dust, dirt, soot, or smoke, is large or dark enough to be seen with the naked eye

There are many sources of particulate matter (or PM), including car exhausts. Particulate matter, also known as dust, dirt and soot or smoke can be visible with the naked eye in some cases.

“Cities that are considering policies to combat air pollution should not assume that ULEZs will solve the problem alone. They contribute marginally to cleaner air.

“This applies especially to pollutants from other places that are blown into cities by the wind, like particulate matter or ozone.    

Air pollution caused 40,000 deaths in the UK, according to 2016 study by the Royal College of Physicians – around 4,000 of which were in Greater London. 

Outdoor air pollution is responsible for approximately 4.2 million deaths annually worldwide. 

This study is published in Environmental Research Letters today.  

How much and will I get hit by Ulez? 

Following the expansion of London’s Ultra Low-Emission Zone, more motorists will now be subject to a daily cost. These are the 12 most important questions to ask about this scheme

Which vehicles will be affected by this?  It depends how much nitrogen dioxide it emits, which is generally linked to its age. Diesel cars are the most compliant, as they were registered in large numbers after September 2015. Most compliant petrol cars were first registered after 2005.

How do I verify the vehicle’s status?  Transport for London is urging people to use its online checker by visiting 

How much is it to have a vehicle that does not comply with the law?  The daily fee is £12.50 for cars, motorcycles and vans up to 3.5 tonnes. Heavier vehicles, including lorries, buses and coaches, are charged £100.

How do I know if charges are applicable?  All day, every day of the year except on Christmas Day. 

What is Ultra Low Emission Zone? There is an area within London where older and more polluting cars are subject to a daily charge.

What have you noticed?  It was previously limited to central London. But it was expanded on Monday to cover 18 percent of the city.

How do we define the boundaries of our new world?  All areas of the North and South Circular Roads have been included in the Ulez.

What has this person done and how did they do it?  Sadiq Khan, London’s mayor, has implemented the change in an effort to improve air quality.

How fast do I need to pay?  After the trip, you have till midnight to complete the third day.

– How do I do it?  TfL allows you to pay online, via the app Pay to Drive London, and by telephone. The option to set up automatic billing allows drivers to be charged every month.

– What happens if my payment is not received?  You could be handed a Penalty Charge Notice for £160, reduced to £80 if paid within a fortnight.

What happens to the money?  TfL claims that the money it gets from the Ulez goes to improving London’s transportation network as well as air quality. The TfL insists that it does not make any profit from this scheme.