London's Ultra Low Emissions Zone (ULEZ) came into force on Monday in the centre of the capital.
Starting this week, owners of vehicles which do not meet certain emissions standards must pay a daily charge of £12.50 in the zone, which operates 24 hours a day, every day of the year.
The zone currently operates in central London – covering the same area as the congestion charge – but will expand to the North and South Circular Roads in October 2021.
Mayor of London Sadiq Khan said: "Our toxic air is an invisible killer responsible for one of the biggest national health emergencies of our generation.
"This is also about social justice – people in the most deprived parts of London, who are least likely to own a car, suffer the worst effects of harmful air pollution.
"I will not stand by and watch children grow up with underdeveloped lungs in our city."
Green Party London Assembly Member Caroline Russell, also welcomed the ULEZ on behalf of the Assembly and said the zone is important to "drive out polluting vehicles from choking our city".
But Gareth Bacon, the leader of the GLA Conservatives, criticised Mr Khan for launching the ULEZ in central London 17 months earlier than previously planned.
It was originally scheduled for September 2020.
Mr Bacon said: "Sadiq Khan's decision to bring forward the roll-out of the initiative by a year has caught small businesses and charities on the hop and given them insufficient time to prepare for the change.
"The damage caused by the early introduction of the central ULEZ will pale into insignificance compared to the impact of its extension to the North and South Circulars in 2021.
"This punitive move will hit the very poorest Londoners hardest and questions have been asked about whether the Mayor's blanket approach is the best way to deal with this grave problem."
What do you need to know about the ULEZ?
Heavier vehicles – lorries weighing more than 3.5 tonnes, and buses and coaches weighing more than five tonnes – will have to pay £100 per day when driving in the zone.
Some discounts apply for residents living in the zone, vehicles registered with a 'disabled' or 'disabled passenger vehicles' tax class and minibuses not used for business purposes.
Whether or not vehicles are eligible depends on their emissions, according to standards covering vehicles sold in the European Union that set limits for air polluting nitrogen oxides and particulate matter from engines.
It is likely that anyone who owns a motorcycle built before 2007, a car built before 2005 and a light van built before 2006 will have to pay the ULEZ charge.
You can use the Transport for London (TfL) checker tool to determine your vehicle's emission standard status.
Drivers who forget to pay the ULEZ will be fined £169, reduced to £80 if paid within 14 days.
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