Fact Check: ULEZ expansion has a negligible effect on air quality

The claim:

Sadiq Khan: "By expanding the ULEZ, 5 million more people in Greater London will be able to breathe cleaner air."

Analysis:

This is misleading. The ULEZ expansion will have a negligible effect on air quality, according to the Mayor's own independent impact assessment.

The annual mean concentration of nitrogen oxides (NO₂) in outer London will drop only by 0.3µg/m3, from 20.2 to 19.9, a negligible change.

There will be no measurable effect on particulates (PM2.5), one of the most harmful forms of air pollution, which remains at 10.1µg/m3 regardless of whether the ULEZ expansion is implemented or not.

Academic research has also found the existing ULEZ delivered only small improvements in air quality, in the context of a longer-term downward trend in London's air pollution levels (Ma et al, 2021).