The $219 million question: Can ULEZ deliver on clean air?

A review of local air-quality monitors reveals that many parts of London still exceed legal nitrogen-dioxide limits,questioning the mayor's assertion that the Ultra Low Emission Zone has secured city-wide compliance.

The figures compiled by the charity Asthma + Lung UK and the Healthy Air Coalition show that more than half of London's boroughs still record annual average NO2 concentrations above the 40 μg per cubic metre threshold.

18 monitoring sites tell a different story

At least 18 monitoring sites, including one in central Romford and several in the City of London where ULEZ has operated for seven years, posted averages well over the legal ceiling, with some locations approaching double the permissible level.

These discrepancies stem from the way Defra aggregates data: it treats London as a single region based on readings from 15 Automatic Urban and Rural Network (AURN) stations , while each borough runs a denser network of automatic monitoors and manual diffusion tubes that capture local variations more accurately.

Experts call for urgent alignment of monitoring approaches

Experts such as Professor Frank Kelly of Imperial College London argue that the borough monitors are technically comparable to the AURN stations and therefore provide a reliable picture of pollution hotspots that Defra's modelling disregards.

The result is a picture of a city where, despite record ULEZ revenues of £219 million last year, many residents - especially the 12 million people in the UK living with lung conditions - continue to breathe air that exceeds the legal limit for NO2.

A wider issue: the UK's legal NO2 limit

The debate also highlights a wider issue : the UK's legal NO2 limit of 40 μg/m³ is four times higher than the World Health Organization's recommendation, a gap that Labour's 2024 manifesto aimed to close with a new Clean Air Act, although no concrete steps have been announced yet.

ULEZ's future efficacy hangs in the balance

As the city grapples with the dual challenge of reducing emissions and ensuring transparent, trustworthy data, the future efficacy of ULEZ and related traffic-calming measures will likely hinge on integrating local monitoring data into national reporting frameworks .