That charge is in effect in the same zones at the same time as the T Charge, though it applies to almost all vehicles and costs £11.50 pounds per day ($15).
From this point onwards, vehicles driving through the centre of the capital are required to meet minimum exhaust emission standards or risk a £10 emissions fee - known as the Toxicity Charge, or T-charge.
Speaking to Sky News, Khan said: "We don't make a profit from the T-charge - it's costing us". Research by King College London found that 9,500 people die each year in the capital due to poor air quality.
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Shaun Bailey, conservative environment spokesman at the London Assembly, told BBC News: "As an asthmatic I'm well aware of how critical an issue this is for London but we need policies that actually deliver progress".
In a move that will affect some fresh produce suppliers in the capital, drivers of the most polluting vehicles now have to pay nearly twice as much to enter the centre of London.
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. Effectively, owners of the most polluting cars will pay about £21.50 or $28 per day to drive in central London.