Drivers of older, more polluting vehicles now have to pay almost twice as much to drive in central London.
Mayor Sadiq Khan's £10 T-Charge, which mainly applies to diesel and petrol vehicles registered before 2006, has come into force.
It covers the same area as the existing congestion charge zone, bumping up the cost to £21.50 for those affected.
Opponents said the scheme would "disproportionately penalise London's poorest drivers".
The measure is the latest attempt by Mr Khan to improve air quality in the capital and, according to the mayor's office, will affect 34,000 motorists a month.
Speaking on the Today programme, Mr Khan said: "We've got a health crisis in London caused by the poor quality air.
"Roughly speaking each year more than 9,000 Londoners die prematurely because of the poor quality air - children in our city whose lungs are underdeveloped, with adults who suffer from conditions such as asthma, dementia and strokes directly caused by poor quality air."
However, Simon Birkett, from the campaign group Clean Air London, does not believe the move goes far enough.
"The mayor has pledged in his manifesto to restore London's air quality to legal and safe limits and that means he has to do a whole lot more.
"We want him to take steps which are bigger, stronger and smarter."
Mr Khan has described the introduction of the T-Charge as "part of a package of measures" being undertaken.
Many people have taken to social media to express their views on the new levy.
Daniel McGuiness said on Twitter: "T-Charge, it's a start but there's still a long way to go in tackling the public health emergency that is our filthy air. #CleanAir".
T-Charge, it’s a start but there’s still a long way to go in tackling the public health emergency that is our filthy air. #CleanAir— Daniel McGuinness (@dannymcg) October 23, 2017
While David Smith said: "With the introduction of the new T-Charge, it'll be the poorest who will be paying the most... again."
With the introduction of the new ‘T-Charge’ it’ll be the poorest who will be paying the most...again— David P-Smith (@david_p_s) October 23, 2017
What is changing?
From Monday 23 October, there is a £10 daily fee for those who drive more polluting vehicles in the congestion charging zone, on top of the existing £11.50 congestion charge.
Vehicles that do not comply with the Euro IV exhaust standard must pay the £10 charge.
The standard defines emissions limits for cars, vans, buses, coaches and lorries. Most vehicles registered before 2006 are likely to exceed these limits.
The zone will operate between 07:00 and 18:00, Monday to Friday.
You can find out if your car is affected with TfL's T-Charge checker.
The T-Charge is the first of a series of new rates being introduced in London.
It is due to be replaced by a stricter Ultra-Low Emission Zone in 2020, although Mr Khan is consulting on bringing this forward to 2019.
This will mean diesel cars registered before September 2015 and petrol cars registered before 2006 will face a £12.50 charge in addition to the £11.50 congestion charge.
The mayor hopes to expand the area covered for cars and vans up to the North and South Circular roads in 2021.
City authorities in Birmingham, Leeds, Southampton, Derby and Nottingham have also been advised to impose charges for some polluting diesel vehicles by 2020, the Department for Environment, Food and Rural Affairs (Defra) said.
To tackle air pollution, Oxford City Council and Oxfordshire County Council proposed a ban on petrol and diesel cars in the city centre from 2020.
Paris, Grenoble and Lyon introduced an emission sticker scheme in January which splits vehicles into six different groups depending on their Euro Emissions standard.
Vehicles deemed too polluting - which includes petrol and diesel-powered cars registered before 1997 - are not granted a sticker, banning them from driving in the city during certain times.
Sue Terpilowski, from the Federation of Small Businesses, said: "The introduction of the T-Charge comes at a time when small and micro-businesses in London are already facing astonishingly high property, employment and logistics costs.
"There is a fear that this will be the final straw that closes businesses and takes jobs."
Shaun Bailey, Conservative environment spokesman at the London Assembly, said: "As an asthmatic I'm well aware of how critical an issue this is for London but we need policies that actually deliver progress.
"By boasting about a policy that so disproportionately penalises London's poorest drivers and puts jobs at risk, the mayor is simply blowing more smoke into the capital's already polluted atmosphere."
Friends of the Earth air pollution campaigner Jenny Bates said: "Clearly, the last thing individuals want is a new charge for moving around, but the grim reality is that nearly 10,000 early deaths are caused in London each year by the capital's toxic air, so the mayor is right to try to dissuade drivers bringing the oldest, dirtiest vehicles into central London.
"It's only one small step towards clean air though - we urgently need a programme of meaningful financial assistance to help drivers of the dirtiest vehicles switch to something cleaner, and bold policies to cut traffic overall."
The mayor is also seeking new powers to ban wood burning in the most polluted areas of the capital.
When asked if wood-burning stoves would be banned entirely, Mr Khan told the Today programme the problem was with the material that was being burnt and a lack of maintenance rather than the stoves themselves.