More than two million Londoners are living in areas with illegal levels of air pollution, figures published today show.
More than 400,000 children are among those living in parts of the city which exceed the legal limits for pollution, according to the London Atmospheric Emissions Inventory.
The figures come ahead of the introduction of the ultra low emission zone (ULEZ) which will charge the most polluting cars, motorcycles and vans £12.50 a day to drive in the city centre, and £100 for lorries, buses and coaches.
Mayor of London Sadiq Khan said: "The introduction of the world's first 24-hour seven-day-a-week ultra low emission zone next week marks a watershed moment in our fight to clean up our filthy air.
"The data I've published today gives an even clearer picture of the urgent need to take action."
The research revealed there had been significant improvements in measured pollution levels.
Air pollution is down, with a 57% reduction in the number of hours recorded in which the city bust the legal limit for nitrogen dioxide so far this year compared to the same period last year.
In the first three months of 2016, 43 monitoring sites in London recorded hours exceeding their legal limit of nitrogen dioxide - with 13 going over the annual maximum of 18 hours above the cut-off.
But so far in 2019, just 10 monitoring sites have recorded breaches of the hourly limit, and none have hit the annual maximum threshold.
Officials said hourly breaches of nitrogen dioxide limits were almost exclusively due to traffic, and the improvements are likely to be down to cleaning up Transport for London buses and drivers already complying with the ULEZ.