A new study shows that London’s Ultra Low Emission Zone (ULEZ) has delivered a significant drop in roadside nitrogen dioxide (NO2), but experts say it should be accompanied by greater use of public transport and active travel.
The research from the University of Birmingham found that NO2 levels in central London fell 19.6% within three months of ULEZ’s introduction in April 2019, while nitrogen oxides (NOx) dropped 28.8%.
However, following the 2023 expansion, the study detected no significant additional reduction, and NO2 and PM2.5 pollution remain well above WHO guidelines across the city.
High compliance among vehicles is a key factor: non-compliant vehicles fell from 39% before 2019, to 27% three months after, and just 7% by 2023, limiting further gains. Three months later, this figure had fallen further to 4.2%.
Professor Zongbo Shi said the ‘anticipation effect’ of the expansion encouraged earlier adoption of cleaner vehicles, reducing the measurable impact of the 2023 rollout. He added, ‘ULEZ is an important step, but it is not enough on its own.’
Dr Suzanne Bartington highlighted the ongoing risks from PM2.5 pollution and stressed the need for a ‘modal shift’ to public transport and active travel to improve urban air quality and public health.
