Sadiq Khan has called for urgent action on pollution following a report that shows every London hospital is surrounded by toxic air.
The two main air pollutants of concern, nitrogen dioxide (NO2) and fine particulate matter (PM2.5), reach levels that fail strict World Health Organisation (WHO) guidelines at all 291 hospitals and medical centres in the capital, according to analysis released by City Hall.
The Mayor described the figures, based on the latest London Atmospheric Emissions Inventory, as "unacceptable" for "vulnerable Londoners when they are most unwell".
"We know toxic air pollution stunts the growth of children’s lungs and worsens chronic illnesses such as asthma, lung and heart disease," he said.
Khan said he did not want to delay in taking action for "a moment longer than necessary".
Last month he unveiled a raft of radical proposals to tackle air pollution, including a daily £2 "clean air charge" and a ‘boundary charge’ for drivers entering the capital in a vehicle registered outside London.
The analysis, which uses data from 2019, shows that 26 of the 291 hospitals measured breach the UK's legal limit for PM2.5.
The WHO revised its air quality guidelines last year to tighten the limit on PM2.5, which is viewed by experts as the most deadly.
It cut the recommended limit on PM2.5 from 10 micrograms per cubic metre (µg/m3) to 5µg/m3, while in the UK the legal limit is 40µg/m3.
Mat Shaw, chief executive of Great Ormond Street Hospital, said staff there see "first-hand the impact of air pollution on the children and families".
"The children we see have the right to clean air, particularly when coming to hospital," he added.
Rosamund Adoo-Kissi-Debrah’s daughter Ella was nine when she died from an asthma attack in 2013 after being exposed to severe air pollution from living 25 metres from the South Circular in Lewisham, south-east London.
Last week she urged political leaders at London Assembly’s environment committee to tackle air pollution to stop the next generation being victims of future pandemics.
Adoo-Kissi-Debrah pointed to the role air pollution played in the pandemic, calling for it to be part of the terms of reference in the future Covid-19 public inquiry.