Every borough in London had levels of toxic air that passed World Health Organisation guidelines - with almost all exceeding the UK's less stringent legal limit.

Mayor of London Sadiq Khan today released the figures he tried to justify the “difficult decision” to expand the Ultra Low Emission Zone (ULEZ).

City Hall data for 2021 shows that just five London boroughs had air below the legal limit for levels of potentially deadly nitrogen dioxide (NO2), but every single one was above the guideline set by the World Health Organisation (WHO).

Only Bexley and Harrow in the capital's 33 boroughs have not installed air quality monitors, so figures for whether they exceed the legal limit have not been published.

The new data released by City Hall shows that in Brent, Croydon and Merton, NO2 levels were above the legal limits at more than a quarter (25%) of the locations monitored.

Here is a breakdown of the findings from boroughs across north, east, south and west London:


Brent is among one of the worst offenders in exceeding the legal limit for nitrogen dioxide of 40 µg/m3, with the level passed at 26% of its testing locations.

A total of 13% of Barnet locations had testing sites above the limit, and 10% of Enfield's .

Camden and Haringey were also over the limit, with unlawful levels at 9% and 8% respectively at their test sites.

However, Islington had no sites where NO2 exceeded the legal limit, although it is still over the WHO guideline of 10 µg/m3.


The figures in east London are lower compared to north and south London.

Redbridge has the highest percentage of locations where toxic air exceeding the legal limit, with 9%.

The number of sites with illegal levels in both Hackney and Havering was lower, at 8%.

In Waltham Forest the number was 5%, Tower Hamlets' was 4% and Barking and Dagenham's 3%.

Newham has not exceeded the legal limit, although it was still above the WHO guideline for nitrogen dioxide of 10 µg/m3.


Within south London, the majority of boroughs have greatly exceeded the legal limit for toxic air.

Merton is the worst offender, with air at 27% of sites higher than the limit, followed by Croydon, where a quarter breached it.

Lambeth totalled 15% of sites above the limit, in Richmond this was 13%, Wandsworth had 12% and both Greenwich and Southwark had 11%.

Kingston Upton Thames exceeded the limit at 8% of test sites, Sutton at 4% and Bromley at 3%.

However Lewisham did not exceed the legal limit, although it is still over the WHO guideline for nitrogen dioxide of 10 µg/m3.


Hammersmith and Fulham had the most sites where air measured above the legal limit for toxic air in west London - 20% or one in five.

Limits were breached at 10% of Ealing locations and 4% of Hounslow's.

Hillingdon had none over the legal limit, although all were still above the WHO guideline for nitrogen dioxide of 10 µg/m3.


The City of London still had 7% of testing sites above the legal limit for toxic air. But none of Westminster's exceeded the limit, although all were still over the WHO guideline for nitrogen dioxide of 10 µg/m3.

What has the Mayor of London said?

Mr Khan says that the figures show action needs to be taken to reduce pollution, claiming there are 4,000 premature deaths a year due to toxic air.

He said: “This data is yet more shocking proof that London’s air quality has been in serious breach of the recognised global standard - and it’s a problem in every single part of the capital.   

“I have made tackling toxic air pollution a priority since I was first elected in 2016, and we have made huge progress since then. However, I am determined to do all I can to ensure that children now and the next generation of Londoners can grow up breathing cleaner air – wherever they live in the capital.

 “This is why I made the difficult decision to expand the ULEZ London-wide - to help save lives and to give all Londoners the right to breathe cleaner air.”