The challenge
Air pollution from vehicles was harming Londoners' health.
The case
London introduced its Ultra Low Emission Zone in central London in 2019, charging older, more polluting vehicles a daily fee, and expanded it to cover all of Greater London by 2023. The share of compliant vehicles rose sharply as people replaced older cars. Independent studies found the 2019 central zone reduced nitrogen dioxide in central London, with some benefit across the city, but one found no detectable effect from the 2023 expansion and no significant effect on fine particles (PM2.5). The expansion was politically contentious, especially in outer boroughs. Tong and colleagues estimated the 2019 zone cut nitrogen dioxide by 19.6% at central London roadside sites in the first three months, while the 2023 expansion had no detectable effect.
Why the results were mixed
Charging the dirtiest vehicles quickly changed the vehicle fleet. How big the air-quality benefit was depends on the comparison used, and expansion showed the need for support such as scrappage grants.
Sources
- Hajmohammadi, H., & Heydecker, B. (2022). Evaluation of air quality effects of the London ultra-low emission zone by state-space modelling. Atmospheric Pollution Research.
- Tong, Z., et al. (2025). Further improvement in London's air quality demands more than the Ultra Low Emission Zone policy.
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