Tens of thousands of children in a quarter of all London's schools are exposed to illegal levels of air pollution that can cause permanent damage to their health, a study has found.
Pupils at 802 of the capital's schools, including a third of nurseries, are routinely breathing in toxic air that increases their chances of developing conditions such as asthma.
The report also shows that London's poor are far more likely to be living in areas affected by air pollution linked to 9,000 early deaths every year in the capital.
It is one of many places hit by the UK's air quality crisis, which has caused the Government to be issued with a "final warning" by the European Commission for repeated breaches of legal limits.
London mayor Sadiq Khan, who commissioned the report, vowed to tackle air pollution, which is also linked to heart and lung diseases.
He said: "It is an outrage that more than 800 schools, nurseries and other educational facilities in the capital are in areas breaching legal air pollution limits.
"We know air pollution is permanently affecting children's lung development - resulting in smaller lungs for life.
"I refuse to stand by when our children are being exposed to dangerously polluted air, putting them at greater risk of serious health conditions when we know it's within our power to tackle the problem."
Among the measures he plans to introduce are air quality audits to help schools identify ways to protect their children from "filthy air", much of which is come from traffic fumes.
Mr Khan has already announced the introduction of a £10 "toxicity charge" for drivers of some of the oldest and most polluting cars in central London from October.
He also suggested that he could go further by banning certain cars from the streets, warning "nothing is off the table".
The latest research shows that 802 of the capital's 3,261 nurseries, primaries, secondary schools and colleges in 2013 were within 150 metres of nitrogen dioxide levels that breached the EU limit.
The number of schools affected nearly doubled from 2010 when it was 433.
London is not the only city affected by the air quality crisis.
Birmingham, Derby, Leeds, Nottingham and Southampton are also planning to charge for the highest polluting vehicles to enter clean air zones.