Low Emission Zones: Cleaner Air, But What Comes Next?

Low Emission Zones (LEZ) or Ultra Low Emission Zones (ULEZ) are town planning tools to tackle air pollution from vehicles[1]. The primary types of pollution of concern are Nitrogen Dioxide (NO2), and fine particulate matter which are designated as PM10 or PM2.5 for particles smaller than 10 microns (0.01 mm) or 2.5 microns (0.0025 mm) respectively. But why do we need to tackle air pollution?

The tragic death of nine-year-old Ella Adoo-Kissi-Debrah in London in 2013 made the reality of vehicular air pollution more relatable and helped bring about changes in our perception of its impact. At her 2020 inquest, the coroner concluded that she died from asthma contributed to by excessive air pollution, with traffic emissions identified as the principal source of her exposure: the first time traffic pollution was specifically cited on a death certificate[3]. Hers is unlikely to be the only such death; she is only the first to be formally recognised as such. Studies have estimated the number of deaths linked to air pollution in the UK at around 30,000 for 2025[4]. This follows earlier reports by Public Health England of 28,000 to 36,000 deaths per year due to air pollution (all sources)[2].

Expanding on the effects of pollution, Nitrogen Dioxide is a product of combustion and can irritate airways, worsen asthma and reduce our defences against lung infections; it is also associated with reduced lung development in children. Particulate matter can also be a product of combustion but also comes from road, tyre and brake wear. Estimates vary for different sizes of particulates but around 20-30% are tailpipe emissions; the proportion from combustion will reduce with the shift to electric vehicles. The smaller particulate matter (PM2.5) is small enough to pass through the lungs and can increase the risk of asthma attacks, lung cancer and heart disease. The larger particular matter (PM10) can cause irritation of the eyes, nose and throat[2].

There is no “safe level” of air pollution although there are legal limits to some pollutants. The UK legal limit for NO2 is for an annual mean concentration of 40 µg/m³ (micrograms per cubic metre), alongside an hourly limit where concentrations above 200 µg/m³ cannot occur more than 18 times in a single year. The World Health Organisation (WHO) recommends limiting the annual mean concentration to 10 µg/m³. For PM10, the average concentration is limited to 40 µg/m³, with a daily limit of 50 µg/m³ not to be exceeded more than 35 times in a year, and for PM2.5 the limit is 20 µg/m³, with Scotland setting a more stringent 10 µg/m³ objective.[5]

(U)LEZ schemes have been implemented in many cities around the world to tackle air pollution, each with their own local nuances. Different approaches to their implementation have been adopted: one is to charge the most polluting vehicles a fee to enter the zone and another is an outright ban of these vehicles with punitive charges. London has adopted the former while Glasgow the latter.

The development and implementation of the London and Glasgow (U)LEZ schemes are outlined below followed by a discussion of the relative merits of each approach from an environmental, economic and social perspective. This can be a divisive topic and your views are welcome in the comment section, whether on the concept of a LEZ as a solution to air pollution, the method of implementation and enforcement, or any other issues.

The London ULEZ

Before the ULEZ, London’s initial road charging scheme was introduced in 2003 as a response to traffic congestion in a 21 km² area in central London. A daily charge was levied to enter the central zone with the intent of encouraging a switch from driving to public transport, walking and cycling. During the first year traffic within the zone fell by about 16%, congestion by around 30%, and average car speeds increased by more than 20%. It generated substantial revenue ring-fenced for investment in London's transport system, with early spending concentrated on the bus network, road safety, walking, cycling and safer routes to schools. In its first full year, after running costs, it generated around £90m net revenue. The scheme went on to generate more than £2bn in net income between 2003 and 2020.

It became increasingly apparent that London's transport problems were about more than simply congestion and that air pollution posed a major public health risk. In response, the Ultra Low Emission Zone (ULEZ) was introduced in central London in April 2019 (the congestion charging zone), expanding to inner London in 2021 and Greater London in 2023. It now covers around 1,500 km² and nine million people.

Unlike the blanket Congestion Charge, it was based on vehicle emissions standards, targeting older, more polluting petrol and diesel cars and vans. (A separate Low Emission Zone (LEZ), was introduced earlier, in 2008, targeting heavier commercial vehicles). Drivers pay a daily charge, currently £12.50, to enter the ULEZ if their car does not meet the following criteria:

• Petrol: Euro 4 standard (typically vehicles registered from 2006 onwards)
• Diesel: Euro 6 standard (typically vehicles registered from 2015 onwards)

The congestion charge remains in place in central London during peak times in addition to the ULEZ charge.

The Glasgow LEZ

Glasgow’s Low Emission Zone (LEZ) was implemented as an air-quality measure for the city centre, rather than a city-wide scheme and, as such, covers a much smaller geographical area compared with London. The current zone covers only about one square mile of Glasgow city centre, bounded by the M8 to North and West, the River Clyde to the South and the High Street/Saltmarket to the East.

The LEZ, which forbids non-compliant vehicles from entering, came into effect on 31 May 2022, with enforcement beginning on 1 June 2023 after a statutory one-year grace period. Similar to the London ULEZ, cars may enter the LEZ if they comply with the following requirements:

• Petrol: Euro 4 standard (typically registered from 2006 onwards)
• Diesel: Euro 6 standard (typically registered from 2015 onwards)

Drivers of non-compliant vehicles are issued with a Penalty Charge Notice. For the first infringement the penalty charge is £60(reduced by 50% for payment within 14 days) with the penalty doubling for each subsequent infringement to a maximum of £480 for cars and light goods vehicles.

The complete ban implemented in Glasgow reflects a fundamentally different approach from London. In London drivers can pollute for a fee while Glasgow's LEZ is focused purely on its purpose to improve air quality in the city centre.

Separately, Glasgow first introduced a LEZ in 2018 targeting the bus fleet, the biggest source of particulate pollution in the city centre.

The table below compares the London and Glasgow schemes.

	London ULEZ	Glasgow LEZ
Introduced	2019	2022
Full current extent	Greater London(from 2023)	Glasgow city centre
Basic mechanism	Daily charge	Exclusion + penalty
Petrol threshold	Euro 4	Euro 4
Diesel threshold	Euro 6	Euro 6
Main objective	Air quality + transport policy	Air quality
Revenue	Significant	Relatively small

Comparison between London & Glasgow (U)LEZ

Impact on Air Pollution Levels

Before going into the figures, it is important to recognise that changes in air pollution levels cannot be fully attributed to the introduction of the (U)LEZ schemes. There are various factors at play which compound the picture. Vehicle standards, such as those used to set the limits for entry to the low emission zones, are already changing the make-up of the vehicle fleet. As older cars are scrapped, the proportion of cleaner, less polluting cars increases without the additional incentives of the (U)LEZ. There are also some shifts in the way people travel. Perhaps more so in London than Glasgow, where there is a slight shift to public transport and active travel options. In addition, post COVID-19, more people in both cities are working from home for a portion of the week, hence reducing city centre travel. The data analysis for London attempts to correct for this through modelling by comparing changes in areas remote from the ULEZ in order to isolate the ULEZ effect. The Glasgow data looks at measured data without any correction, comparing changes year on year.

The results presented below should therefore be treated as evidence of the combined effect of the LEZ, changes in the make-up of the vehicle fleet, and changes to travel patterns rather than attributing all the reduction of emissions solely to the enforcement regime.

London

The London-wide Ultra Low Emission Zone One Year Report presents an assessment of the impact of the ULEZ through its implementation stages, ultimately to cover all Greater London[6]. In the first year of operation, roadside NO2 concentrations in outer London were on average up to 4.8 per cent lower than would have been expected without the London-wide ULEZ expansion.

Transport for London (TfL) estimates that, cumulatively across all phases of ULEZ from 2019-24, NOx emissions were 24% lower, while PM₂.₅ exhaust emissions were 29% lower in 2024 than they would otherwise have without the ULEZ. For the most recent figures, all monitoring points in Greater London recorded NO2 levels below the 40 µg/m³ compared with a third exceeding this limit only five years ago. Only 1% of monitored neighbourhoods met the stricter WHO recommended level of 10 µg/m³, so there remains work to be done.

Figure 1: Trend of Annual Mean NO2 levels in Central, Inner and Outer London. Solid lines represent roadside trends, dashed lines represent the urban background trends.

Glasgow

The early evidence in Glasgow is encouraging. The city council’s 2025 air-quality assessment, covering the first full calendar year of enforcement, found a 20% reduction in average NO₂ concentrations from 2022 (pre-LEZ) within the LEZ[7]. No exceedances of the 40 µg/m³ target limit were recorded across all 27 monitoring stations within the LEZ. Reductions varied from negligible to 40% at different locations in the city centre depending on the baseline conditions. The average reduction in NO2 for parts of the city outside the LEZ was 15%, which may be partly as a result of the LEZ accelerating reduction in the number of non-compliant vehicles in the city as a whole.

There is no discernable reduction in particulate matter pollution as a result of the LEZ introduction, although target levels have consistently been achieved throughout the city centre. Particulate pollution has reduced significantly over the last few decades, mostly as a result of improving vehicle standards and transition to electric vehicles (EVs), especially in the bus fleet. The majority of the remaining vehicular particulate pollution comes from non-combustion sources such as road, tyre and brake wear. This comes from all vehicles, including EVs, and reducing emissions from these sources is technically difficult. Most EVs are heavier than equivalent petrol or diesel cars and can therefore produce more particulates from tyre and road wear. On the other hand regenerative braking employed by most EVs reduces brake wear emissions.


Figure 2: Trend of Annual Mean NO2 levels measured on Hope Street by Central Station in Glasgow. Years are calendar. LEZ enforcement commenced part way through 2023.

It is difficult to compare the efficacy of the two schemes directly due to different methods of reporting, historical context (such as prior initiatives), and severity of the air pollution problem. Through a combination of measures over several years both cities have been effective at bringing annual mean NO2 levels below minimum legal standards. Neither city has achieved the more desirable WHO guideline levels although Glasgow’s monitored locations are generally closer to it, perhaps due to its relatively smaller geographic area with fewer overlapping hot spots.

Revenue

London

The London ULEZ has raised almost £1.2bn (gross) since launch in 2019, which has been reinvested in transport after running costs. The table below shows the step change in revenue as the scheme expanded first to Inner London then to the whole of London in 2023. It is also worth noting the slight drop in revenue in the years following introduction to the whole of London. This reflects the change in the vehicle fleet from around 85% compliant vehicles in 2023 to 97% in 2026. This trend is expected to continue with a negligible surplus expected as early as 2027.

Around £500m of surplus revenue (after costs of establishing and operating the system) has been invested in transport schemes, primarily the Superloop express orbital bus routes connecting outer town centres, a clean air scrappage scheme and active travel paths. These are mostly positive investments to improve long term sustainable travel within the city.

Glasgow

Unlike London, Glasgow's LEZ has generated relatively little net revenue. In its first year, 2023/24, more than £980,000 was raised in fines, and around £757,000 in 2024/25. The operating costs were £614,000 in 2024/25, resulting in a net revenue of £141,000. For 2025/26, income dropped again to £513,873 which has been reported as being less than the operating costs.

This highlights an important difference between Glasgow and London schemes. Glasgow's LEZ was not designed as a revenue-raising scheme, while in London, it is a key objective. When there is net revenue available after costs, it will be used for projects which contribute towards meeting air quality objectives or contribute towards emissions reduction targets. This raises the question of whether a modest revenue stream could have been used to support measures that further reduce emissions, such as public transport or the Avenues Project.

Society, equity and inclusion

Interventions such as (U)LEZ do not affect all proportionally. Considering the London ULEZ, the daily charge is unaffordable to many; these same people are also least able to afford a newer, compliant car to avoid the charge. A demographic particularly badly hit is night workers, who will pay two daily charges for a single shift which straddles two days. This includes key workers in the health and care sectors, cleaning staff and the night time entertainment sector, many of whom also earn lower wages. Public transport options are often limited or non-existent leaving little option but driving or using taxis.

Turning to Glasgow, affordability of a daily charge is a moot point, and the LEZ effectively forced people living within the zone to dispose of their cars if they did not meet the emissions standards. For those living and working within the LEZ this may not be too serious an inconvenience given the size of the area but it would be significant for people working further afield. As the LEZ prevents those from outside entering with non-compliant vehicles and, as with London, those working unsociable hours are worse affected.

Both schemes had a scrappage scheme to support owners of non-compliant cars to scrap them and replace them with newer, compliant cars. In Glasgow, the scheme is strictly means tested and is only available for households receiving certain benefits, while the London scheme was open to all, but is now closed. Both schemes give/gave £2000 in return for scrapping a non-compliant vehicle. This does not go far towards a replacement car.

The greatest relative financial burden is therefore carried by lower earners, who are more likely to be adversely affected by air pollution. London's charging model creates a distinction between people who can afford to change their vehicle or pay the charge and those for whom neither option is readily available. In Glasgow the distinction is between people who can afford to change their vehicle and those who need to find alternative methods to go into the city centre, whether for work, education, access to services or for leisure. This raises an important equity question: should access to cleaner urban air depend partly on an individual's ability to pay?

Next Steps

It is difficult to conclude on how effective the two emission charging schemes are at reducing air pollution and whether one is significantly better than the other. Through a combination of tools over several years both Glasgow and London have been effective at bringing annual mean NO2 levels below minimum legal standards. There is still, however, some way to go before reaching the more desirable WHO recommended levels. Evidence shows that there are fewer older, more polluting vehicles on the road, which means further reductions in pollution concentrations will be marginal at best for the current schemes, as is reflected in diminishing revenue from daily charges or penalties.

This begs the question: what next for (U)LEZ? Should the schemes be wound down, having achieved their primary purpose? Should they continue with a stricter target to bring NO2 levels down to less than 10 micrograms per cubic metre while also improving levels of particulate pollution? In the Glasgow case, should the geographic extents be increased to cover the whole city or further to the Glasgow City Region, including surrounding towns such as Paisley and East Kilbride?

The easy part has been done; the next stage will be more difficult: as exhaust emissions decline, the challenge changes and the remaining pollution becomes harder to tackle. Future air-quality policy will need to address not only the combustion engine but also the pollution generated by the movement of vehicles themselves.

Limited options remain for local planners to tackle conditions in the most polluted areas. They include:

• Allow progressively improved emission standards to do their work and monitor the results. At a local level, this is effectively the “do nothing” base case. Over time this will see an increase in the proportion of petrol cars complying with Euro 6 standards followed by a growing number of vehicles compliant with Euro 7 standards. See below for more on vehicle emission standards.
• Implement stricter emission standards in the (U)LEZ area to accelerate the drop off of the most polluting vehicles from the fleet. The criteria would align with emission standards and should be planned for long term implementation, starting with Euro 6 standards for petrol vehicles, which would see a further 25% reduction in NO2 emissions per km, then progressing to Euro 7 standards. This would need to be a longer term plan.
• Adopt a non-emissions based congestion charge such as in central London, perhaps limited to peak times, to discourage non-essential journeys.
• Limit certain streets to EVs only. This will reduce combustion related emissions but have a lower impact on particulates.
• Encourage more people out of their cars through attractive alternatives such as affordable efficient public transport and active travel incentives. This will require a combination of hard infrastructure investment to reduce journey times for public transport and provide safe routes for cycling and walking, and financial support to ensure public transport service levels remain high at off-peak times. London has maintained relatively steady levels of public transport use over the past decade, while Glasgow has seen a decline, which illustrates the challenge of using this as a tool to reduce air pollution.
• Change infrastructure to remove traffic from pollution hotspots. This may include measures to re-route through traffic away from hotspots, introduce one-way systems, bus gates, lane reductions or pedestrianised areas. This would represent a longer term strategy which requires careful modelling and analysis to ensure it doesn’t simply move the problem around.

All of these options apart from the first require a degree of investment and political commitment at the local level. At a national level, introduction of stricter vehicle emission standards such as the planned Euro 7 standards will contribute to pollution reduction measures. This next level of vehicle standards has yet to be fully implemented by manufacturers. For new types of cars and light commercial vehicles, Euro 7 requirements apply from November 2026, followed by all new vehicles of these categories from November 2027. Expanding on the scope of previous emission standards, Euro 7 also covers non-tailpipe emissions such as from tyre and brake wear. It sets limits for PM10 from braking of 7mg/km for ICE/hybrid cars and 3mg/km for EVs and also establishes limits on tyre abrasion rates This will reduce particulate pollution. Realistically it will be 5-10 years before the majority of vehicles in use comply with this standard. Introducing the standard as the basis for emission charging or enforcement may be politically challenging before there is significant adoption.

To return to the beginning: why do we need to tackle air pollution? From the Royal College of Physicians’ report: “A toxic burden on the most vulnerable people: Air pollution is harmful to everyone, but the most deprived communities – who typically contribute least to emissions – disproportionately experience its effects and suffer the worst health outcomes”.[4]

Progress has been made. Now we plan for the next chapter and the ultimate objective of safe clean air for all.

Notes :

[1] Low and Ultra Low Emission Zones are terms used by different schemes, often meaning the exact same emission levels. For the schemes in this article, Glasgow uses the term "LEZ" while London uses "ULEZ". The abbreviation (U)LEZ has been used throughout unless in reference to a specific scheme.

[2] Health Matters: Air Pollution, Public Health England, November 2018.

[3] Science Vs, How Toxic is the Air You Breathe, Transcript:Science Vs Air Pollution Transcript ; Podcast: Science Vs Podcast Episode: How Toxic is the Air You Breathe 

[4] Royal College of Physicians article, June 2025 "Air pollution linked to 30,000 UK deaths in 2025 and costs the economy and NHS billions", coinciding with the release of their report "A breath of fresh air: responding to the health challenges of modern air pollution".

[5] The Air Quality Standards Regulations, 2010, Schedule 2. 

[6] London-wide Ultra Low Emission Zone One Year Report, Mayor of London, March 2025.

[7] Air Quality Annual Progress Report, Glasgow City Council, August 2026.

Further Reading

If this is your first time visiting this blog, I recommend you go to the About this Blog page, which sets out the scope and aims of the blog and includes some guidance on navigation. It contains links to pages on the blog's key themes, including a page on Travel & Transportation. You can also explore articles using the tags at the top of the article.

Older posts with some relevance to this article include:

• Electric Cars (2012) - an old post about EV trials by Glasgow City Council. A footnote has been added to emphasise some parts of the article that are now incorrect.
• Testing Times (2013) - another old post on the emission testing scandal from 2013.