By JONATHAN CHADWICK, ASSISTANT SCIENCE & TECHNOLOGY EDITOR
Sadiq Khan controversially expanded London's Ultra Low Emissions Zone (ULEZ) two years ago, at an estimated cost of up to £155 million.
Now, a breakthrough study suggests that fervent opposition at the time was well–judged.
Scientists at the University of Birmingham say the expansion of the ULEZ in August 2023 had no significant impact on lowering air pollution.
In addition, London still faces air pollution levels well above international health–based guidelines, according to the experts.
Campaigners are now calling for ULEZ to be scrapped altogether as it is saddling 'Londoners with mountains of debt'.
'This is just further evidence that the ULEZ expansion was about raising money rather than improving air quality,' Thomas Turrell AM, Transport & Environment spokesperson for City Hall Conservatives, told the Daily Mail.
'This is exactly what TfL's own modelling showed, but yet again, Sadiq Khan is ignoring the evidence when it doesn't suit his agenda.'
Damning figures released in 2023 showed how the ULEZ expansion generated a whopping £5.3 million in its first week alone – with millions more raked in from drivers since.
Introduced in April 2019, ULEZ allows authorities to charge diesel vehicles for being in Central London, with the aim of reducing vehicle emissions in some of the city's most polluted areas
Introduced in April 2019, ULEZ allows authorities to charge diesel and petrol vehicles £12.50/day for operating in London if they are not compliant with emissions standards.
It uses a network of cameras that snap a photo of a vehicle's plates, which searches a database to check if it is compliant, and, if not, issues a fine to the owner.
ULEZ was intended to reduce vehicle emissions in some of London's most polluted areas, but the decision to expand it to areas where traffic is less dense two years ago proved controversial.
It means the ULEZ now applies to all 32 London boroughs, covering over 1,500 square kilometres (580 sq miles) and around nine million people. The zone pushes right up to the borders of surrounding counties including Kent, Surrey, Essex and Hertfordshire.
The new University of Birmingham study focused on two harmful pollutants called nitrogen dioxide (NO2) and PM2.5 – which refers to fine particles with a diameter 2.5 micrometers or less, invisible to the naked eye.
NO2 can lead to health issues like inflamed airways while aggravating existing heart and lung diseases, while PM2.5 can enter the lungs and then the bloodstream, lodging in the heart, brain and other organs.
The team studied air quality data captured hourly at 124 sites across London following the introduction of ULEZ in April 2021, and its major expansion in August 2023.
They also created a computer model for assessing the direct impact of ULEZ on these pollutants in the Greater London area.
The team studied air quality data captured hourly at 124 sites across London following the introduction of ULEZ in April 2021, and its major expansion in August 2023
In April 2019, the Mayor of London introduced the ULEZ, an area in which drivers of more polluting vehicles must pay a daily charge of £12.50.
It aims to reduce air pollution emissions from road transport and accelerating compliance with EU air quality standards.
It previously only covered the same area of central London as the Congestion Charge, but it was expanded across all London boroughs on August 29, 2023.
ULEZ is one of several London air pollution policies introduced since 2016 like the Low Emission Zone, Low Emission Bus Zones, and bus and taxi electrification.
According to the findings, there was a 19.6 per cent reduction in NO2 at roadside sites in central London within three months of ULEZ originally being introduced in 2019.
Meanwhile, nitrogen oxides (NOx) – the wider group of toxic gases to which NO2 belongs – fell by 28.8 per cent in the same period for the same area.
However, no significant impact was detected on NO2 or NOx levels following the ULEZ expansion in August 2023.
What's more, PM2.5 pollution across the whole of London has not significantly fallen over the entire period – not just since 2023.
Unfortunately, NO2 and PM 2.5 (fine particles that can enter into our lungs) pollution in London remains well above guidelines from the World Health Organization (WHO).
Study author Professor Zongbo Shi at the University of Birmingham admits the ULEZ expansion of August 2023 has had a 'limited effect' on London air quality.
He claims this was because London drivers by that point had already largely switched to eco-friendly electric vehicles and newer petrol and diesel cars that are ULEZ-complaint.
'Commitments to expansions may have encouraged earlier transitions to cleaner vehicles, which likely explained the limited additional impacts of 2023 ULEZ expansion on air quality,' Professor Shi said.
In response to the findings, Mr Turrell refuted the assumption that improved air quality in London is due to the ULEZ.
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He told the Daily Mail: 'Air quality in outer London was already improving because of things like our amazing green spaces which he now wants to concrete over, not because of his policy of inflicting misery on millions.
'The least the Mayor could do is use the cameras to do something helpful like tackle the epidemic of car theft in our outer London boroughs.'
Councillor Colin Smith, Leader of Bromley Council, called the ULEZ a 'cynical tax raid on outer London's motorists'.
He thinks the study confirms original concerns aired in 2023 that 'an expanded ULEZ would be minimal in terms of air quality'.
'Had it been about air quality, Mayor Khan would have started where the air in London is dirtiest – in his own tube network, but no, there were no motorists to fleece there,' he told the Daily Mail.
'The reality is and was that Bromley had good air quality from the outset, amongst the very best in London, with ULEZ being an unwelcome regressive tax which remains deeply unpopular and divisive to this day.'
Overall, the study, published in npj Clean Air, concludes that the ULEZ alone is not enough to make London's air quality safe for breathing, despite promising reductions in nitrogen oxides coinciding with the first few months after its initial 2019 implementation.
The authors call for further action especially to reduce PM2.5, which not only is released from a vehicle's exhaust but also by tyres pressing against roads.
'It's important to highlight that the current ULEZ approach does not fully address significant traffic related public health issues, such as PM2.5 pollution,' said co–author Dr Suzanne Bartington.
'As a result, we need to see a modal shift to more active travel and public transport to reduce the number of vehicles on the road, which could reduce non-tailpipe-related PM2.5 emissions and improve public health.'
The authors conclude: 'Our results demonstrate the effectiveness of ULEZ policies in reducing vehicle emissions, particularly NO2 and NOX. ULEZ encourages the transition from a minority of high-polluting vehicles to cleaner alternatives. This likely generated broad societal benefits, including improvement in both physical and mental health, increased productivity, improved ecosystem services, natural capital, biodiversity, and reduced crime rates and altered tourism preferences.'
In response to the study, a spokesperson for the Mayor of London said: 'We know ULEZ has been a huge success in cleaning up London’s air.
'A lot of drivers upgraded to cleaner vehicles before ULEZ expansion was implemented. This shows the scheme working exactly as intended.
“The ULEZ One Year On Report shows that, taking all three phases into account, harmful roadside NO2 concentrations are now 24 per cent lower in outer London compared to without the ULEZ in place.
'Last month, it was confirmed that London met legal limits for NO2 for the first time in 2024, demonstrating the impact of the ULEZ and the Mayor’s other air quality policies.
'All Londoners are now breathing cleaner air – but there is still more to do, and the Mayor will keep taking action as we build a greener, fairer London for everyone.'
According to the Environmental Protection Agency, there are six major pollutants which can impact on human health and well–being.
EPA calls these pollutants 'criteria' air pollutants because it regulates them by developing human health–based and environmentally–based criteria for setting permissible levels.
Particulate matter: Particulate matter is the term for a mixture of solid particles and liquid droplets found in the air.
These particles come in many sizes and shapes and can be made up of hundreds of different chemicals.
Some are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires.
Fine particles (2.5 parts per million)are the main cause of reduced visibility (haze) in parts of the United States, including many of our treasured national parks and wilderness areas.
Carbon monoxide: Breathing air with a high concentration of CO reduces the amount of oxygen that can be transported in the blood stream to critical organs like the heart and brain.
At very high levels, which are possible indoors or in other enclosed environments, CO can cause dizziness, confusion, unconsciousness and death.
Nitrogen dioxide: Nitrogen dioxide primarily gets in the air from the burning of fuel. NO
It forms from emissions from cars, trucks and buses, power plants, and off–road equipment.
Breathing air with a high concentration of NO can irritate airways in the human respiratory system. Such exposures over short periods can aggravate respiratory diseases, particularly asthma, leading to respiratory symptoms (such as coughing, wheezing or difficulty breathing).
Sulfur dioxide: The largest source of Sulfur dioxide in the atmosphere is the burning of fossil fuels by power plants and other industrial facilities.
Short–term exposures to SO can harm the human respiratory system and make breathing difficult. Children, the elderly, and those who suffer from asthma are particularly sensitive to effects of SO.
Ground–level ozone: The ozone layer in the lower area of the lower portion of the stratosphere, approximately 12 to 19 miles above the surface of the planet (20 to 30 km).
Although ozone protects us against UV radiation, when it is found at ground level it can cause health problems for vulnerable people who suffer from lung diseases such as asthma.
It is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) – that are found in exhaust fumes – in the presence of sunlight.
Lead: Major sources of lead in the air are ore and metals processing and piston–engine aircraft operating on leaded aviation fuel.
Other sources are waste incinerators, utilities, and lead–acid battery manufacturers. The highest air concentrations of lead are usually found near lead smelters.
Depending on the level of exposure, lead can adversely affect the nervous system, kidney function, immune system, reproductive and developmental systems and the cardiovascular system.
Infants and young children are especially sensitive to even low levels of lead, which may contribute to behavioural problems, learning deficits and lowered IQ.
