Marylebone in central London has some of the worst air pollution levels in the country due to its congested roads.
But the 60,000 commuters passing through the railway station every day will now breathe air that is 95% cleaner.
Four new filtering chambers have been fitted in the station to create clean air zones.
The units suck in dirty air at the top, which is passed through three big filters inside to remove particulate matter and nitrogen oxide from the air.
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