Tens of thousands of cars and vans will face daily pollution charges of £12.50 in London as Mayor Sadiq Khan confirmed plans for a large-scale emissions zone.
The ultra-low emission zone, being brought in for central London in April 2019, will be expanded to the North and South Circular roads from October 2021, Mr Khan has announced.
It means polluting vehicles across the whole of inner London - an area 18 times greater than the central zone - will face a daily charge of £12.50 to drive in the area 24 hours a day, seven days a week all year.
Mr Khan made the announcement as he launched a new study of more than 3,000 primary school children in polluted areas of London and Luton, Bedfordshire, to test if policies to improve air quality help their health.
The charges across inner London will cover vehicles which do not meet certain emissions standards, including petrol cars that are more than 15 years old in 2021 and diesel cars that are more than six years old by that time.
The mayor also revealed plans to tighten standards for the most polluting heavy vehicles including buses, coaches and lorries across the whole of London from October 2020.
It is estimated that 100,000 cars, 35,000 vans and 3,000 lorries might be affected by the expanded zone every day, City Hall said.
Confirmation of the expanded ultra-low emissions zone (Ulez) comes after research showed the health damage from cars and vans across the UK costs £6 billion a year to the NHS and society, with the bill in London £650 million.
Officials said expanding the Ulez and stricter standards for heavy vehicles across London would result in more than 100,000 Londoners no longer living in areas exceeding legal air quality limits in 2021, and all areas in the capital are expected to see reductions in pollution.
Mr Khan said: "Tackling London's lethal air and safeguarding the health of Londoners requires bold action.
"Air pollution is a national health crisis and I refuse to stand back as thousands of Londoners breathe in air so filthy that it shortens our life expectancy, harms our lungs and worsens chronic illness.
"I promised hard-hitting measures to tackle our shameful air pollution and today City Hall is confirming the next stage of our plans to expand the ultra-low emission zone up to the North and South Circular roads."
Research into the health impacts of pollution on children will examine whether policies to improve air quality, such as London's new Ulez, are associated with improved growth of youngsters' lungs and reduced chest symptoms.
The new Children's Health in London and Luton (Chill) international study is funded by the National Institute for Health Research led by Queen Mary University of London, whose researchers along with the University of Bedfordshire are recruiting schools to take part.
Children are particularly vulnerable to traffic pollution, which can cause stunted growth of their lungs, putting them at risk of lifelong problems, and can also trigger asthma, asthma attacks and chest infections.
Professor Chris Griffiths, from Queen Mary University of London, said: "Air pollution in UK towns and cities is a major health problem, and this study is the first in the world to test the impact of targeted pollution control measures on the long-term lung growth and health of children."
He said the study would show whether low emissions zones helped improve children's lung growth and whether they should be implemented in towns and cities in the UK and globally.