Breathe Easy? Assessing if London's ULEZ Expansion is Really Cutting Air Pollution

 

Breathe Easy? Assessing if London's ULEZ Expansion is Really Cutting Air Pollution: A Complete Guide

London is facing a serious challenge with its toxic air, and things have reached a crucial point. Since the Ultra Low Emission Zone (ULEZ) was expanded to cover all boroughs in August 2023, the city has become the largest low-emission zone in the world. Mayor Sadiq Khan has framed this bold initiative as a vital step to tackle a public health crisis, pointing out that air pollution is responsible for about 4,000 premature deaths each year in the capital. 

However, while the policy aims to penalize the most polluting vehicles, there's a heated debate about how effective it really is in practice. For those living and working on the outskirts of the city—from commercial fleets to private hire vehicles—the financial impact is immediate. Take, for example, a driver from a Taxis Hemel operator; they now have to ensure their fleet meets ULEZ standards if they want to cross into North-West London, which adds a new layer of costs that simply didn’t exist three years ago. This blog post dives into the latest data to tackle the crucial question: Is the expanded ULEZ genuinely improving London’s air quality, or is it merely a pricey tax on drivers?

The Evidence of Success: What the Data Shows

According to the latest updates from City Hall, the initiative is exceeding even the most optimistic expectations. A review of the first six months after the expansion shows a significant drop in harmful emissions. In outer London, which was previously unprotected, nitrogen oxide (NOx) emissions from cars are now estimated to be 13 percent lower than they would have been without this scheme. For vans, the reduction is around 7 percent. 

What’s even more noteworthy is the effect on fine particulate matter (PM2.5), those tiny particles that can get deep into our lungs and bloodstream. The expansion has resulted in an estimated 22 percent decrease in PM2.5 exhaust emissions from cars in outer London. To give you an idea of the impact, this reduction is like taking 200,000 cars off the road for a whole year. This data indicates that the "stick" approach of charging non-compliant vehicles £12.50 a day is successfully encouraging a change in behavior.

A Tale of Two Pollutants: The Science of Unintended Consequences

The story of unqualified success gets a bit more complicated when we take a closer look at the science behind it. A recent study published in Atmospheric Environment reveals that while the Ultra Low Emission Zone (ULEZ) has been a standout example of cutting down on certain pollutants, it might be unintentionally boosting others. The research shows that the policy has successfully reduced Nitrogen Dioxide (NO2) and larger particulate matter (PM10 and PM2.5), which aligns with what City Hall has been claiming. 

However, the study also points out that these reductions in traffic emissions have resulted in a rise in ozone (O3) and "nucleation mode" particles—those ultrafine particles (UFPs) that form when fresh emissions cool and condense in the atmosphere. The health effects of these tiny particles are not as tightly regulated, but they are becoming a growing concern for environmental scientists. This means that while the air may appear cleaner by traditional standards, the chemical makeup is shifting in ways that we don’t completely grasp. For the everyday commuter, this could mean that the air feels less smoggy, but the emergence of these secondary pollutants might introduce new, unmonitored health risks.

The Compliance Shift and Financial Realities

From a logistical perspective, the expansion has truly been a remarkable success when it comes to modernizing the fleet. By late 2024, an impressive 97 percent of the vehicles you see on the roads in London are now compliant with ULEZ standards, a huge jump from just 39 percent back in 2017. This swift transformation has been supported by a £210 million scrappage scheme, which has enabled countless Londoners and businesses to upgrade their older vehicles. 

This is especially important for the private hire and airport transfer sector. Take, for instance, the route for a service like Hemel Hempstead Airport Taxis. A trip from Hemel Hempstead to Heathrow or Luton might not have needed to consider ULEZ regulations in the past, but depending on the route taken around the edges of the zone, compliance is now essential. The high compliance rate across the city shows that the vehicles in use are becoming newer and cleaner, which is definitely a win for air quality in key areas and around transport hubs.

The Criticism: Revenue vs. Results

Despite the environmental benefits, the policy is still a hot-button issue in politics. Critics highlight the heavy financial strain it places on drivers. Recent data from the Daily Mail, shared by GB News, shows that the ULEZ expansion has brought in an eye-watering £514 million in daily charges and penalties since it started, with Transport for London (TfL) pulling in a record £219 million just in 2025. Detractors, including Shadow Transport Secretary Richard Holden, argue that the initiative seems more focused on generating revenue than on public health, labeling it an "anti-driver obsession." Conservative MP Bob Blackman has pointed out that the expansion has had a "minimal impact" on air quality in outer London, while it disproportionately burdens working-class drivers who can't afford to upgrade their vehicles. Yet, these political arguments are becoming harder to reconcile with the solid data showing significant drops in NO2 levels in outer London boroughs like Sutton, Merton, and Croydon.

Also read: Do Airlines Supply Their Own Jet Fuel? The Truth About Airport Refueling

The Verdict: A Qualified Success

So, will London’s expanded ULEZ actually help reduce air pollution? The answer is yes, but it comes with some caveats. The evidence clearly shows that the ULEZ expansion is effectively cutting down on harmful pollutants like Nitrogen Dioxide and exhaust PM2.5. In fact, London’s air quality is improving faster than in the rest of England, and the city is on track to meet legal pollution limits by 2025—a goal that once seemed like it would take nearly 200 years to achieve. 

That said, there’s still work to be done. The increase in ultrafine particles and ozone levels, driven by changes in atmospheric chemistry, suggests that we might just be swapping one form of pollution for another. Plus, the success of this initiative hinges on a balanced approach. As Manish Kharel, General Manager of Lime in London, pointed out, the ULEZ acts as the "stick" to encourage people to ditch their cars, but now the city needs to provide the "carrot"—like improved cycling paths and better public transport options—to truly offer viable alternatives.

For commuters coming in from places like Hemel or other areas in the home counties, the message is clear: the age of the diesel car in London is coming to an end. While the air quality is getting better, the cost of entering the city—whether it’s in a new electric vehicle or through an expanding public transport system—is likely to remain a significant aspect of life in London for the foreseeable future.