Plans to create an ultra-low-emission zone for vehicles entering central London have been announced by Mayor Boris Johnson.
The scheme would ensure all vehicles driving in the centre of London during working hours would be zero or low emission.
The scheme could be introduced from 2020, with Transport for London (TfL) preparing options for a public consultation.
Mayor Johnson said: "Creating the world's first big-city, ultra-low-emission zone has the potential to be a game-changing moment in the quality of life of our great capital.
"My vision is a central zone where almost all the vehicles running during working hours are either zero or low emission. This would deliver incredible benefits in air quality and stimulate the delivery and mass use of low-emission technology."
Announcing other environmental plans for the capital today, Johnson said around 900 buses would be phased out so that all London buses met European emission standards by the end of 2015.
In addition to the commitment to deliver 600 new step-on-step-off, driver-and-conductor buses, there will be another 600 conventional hybrid buses over the next three years.
There will also be steps to make construction sites low-emission zones, while TfL will look at the possibility of introducing zero-emission taxis.
Johnson also announced a £20m fund to help London boroughs to tackle local air pollution blackspots.