ULEZ is a charging scheme designed to reduce harmful vehicle emissions by discouraging the use of the oldest, most polluting cars, vans and motorcycles within Greater London.
Since its phased introduction (starting in central London in 2019 and expanded to cover the whole city by August 2023), the evidence shows significant improvements in air quality metrics attributed to the policy.
Reports from the Greater London Authority and City Hall indicate that ULEZ has reduced key pollutants compared with a hypothetical scenario in which the scheme did not exist. For example, nitrogen dioxide (NO₂) - a gas linked with asthma and cardiovascular problems - is estimated to be about 27% lower across London, with larger reductions (over 50%) in central areas that were regulated the longest. Meanwhile, particulate matter from vehicle exhausts has also fallen substantially - around 31% lower in outer London than it would have been without the ULEZ expansion.
These improvements represent not just statistical changes but real public health gains: cleaner air reduces the burden of respiratory diseases, heart conditions, and long-term morbidity linked to pollution exposure. Independent evidence also suggests that air quality monitoring sites across London are reporting better conditions than before the policy, and even areas just outside the capital have seen pollution benefits.
However, it’s important to recognise that London’s air quality still exceeds World Health Organisation guidelines in many places, particularly for NO₂ and fine particulate matter - meaning ULEZ is effective but not sufficient on its own to solve all urban air pollution issues.
The context of air quality in early 2026 has been shaped by exceptionally persistent rainfall across the UK, including southern England - with reports indicating rain every day so far this year.
Rain plays a complex role in air quality. On one hand, precipitation scavenges particles and gases from the air, a process known as wet deposition, which can temporarily improve local air quality, by removing airborne pollutants such as particulates and NO₂. Frequent rainfall can wash out particulates, leading to lower concentrations near the ground than might otherwise occur. Thus, during prolonged wet spells like those in early 2026, some monitoring sites might register better short-term air quality, simply because rain is physically clearing pollutants from the atmosphere.
On the other hand, persistent wet conditions can also hinder pollutant dispersion. When skies remain cloudy and atmospheric conditions are stable, pollutants emitted between rain events (e.g., from vehicles, heating systems and industry) can accumulate at lower heights rather than dispersing vertically. In such scenarios, especially if wind speeds are low, concentrations of certain pollutants can remain elevated once rain subsides or in areas sheltered from stronger airflow. This effect can complicate interpretations of air quality trends if rainfall is not accounted for in analysis.
As we are nearing the end of the second year of this new policy being in place, it will be interesting to see how the air quality will have improved, and how the unprecedented weather could have played a role in this. It is expected that the City of London will produce an updated report in March 2026.