A new charge for the most-polluting vehicles comes into effect today, with those entering central London facing a daily payment of £21.50.
Those driving older, more polluting petrol and the dirtiest diesel vehicles will pay the new T-Charge of £10 plus the Congestion Charge (C-Charge) of £11.50.
The Mayor of London Sadiq Khan said the move was a "major milestone" in tackling the thousands of early deaths caused by London's "lethal air".
The charge is applicable to Pre-Euro 4 vehicles every weekday between 7am-6pm.
These are typically vehicles registered before 2006, but Transport for London suggests anyone who has a vehicle registered before 2008 should check to see if it is eligible for the charge.
The Mayor of London Sadiq Khan launched the T-Charge to tackle London's air-pollution and prepare Londoners for the early introduction of the Ultra-Low Emission Zone, which he is proposing to introduce as early as April 2019.