The zone, which charges drivers of some polluting older vehicles £12.50, will be pushed to the boundaries of the M25 on Tuesday.
Along with Greater London residents, it means those living in the home counties near the outer border who need to cross it for work or leisure will also be affected.
Heathrow will be inside the area, so if they have an older car, passengers or their friends and relatives will be charged £12.50 to reach the airport, then another £5 entry fee plus a parking charge of a minimum £5.
Road signs near the airport have been erected to warn drivers they’re entering the Ulez zone. Failure to pay in three days can lead to a £180 fine, reduced to £90 if paid within 14 days.
Mayor Sadiq Khan has said the scheme is the "right one to save lives" as studies show pollution costs the city’s health care system up to £3.7 billion a year.
City Hall has introduced a £160 million scrappage scheme, which provides drivers with grants to replace non-compliant vehicles with less polluting models. Mr Khan said: "I’ve continued to listen to Londoners’ concerns and every single Londoner with a non-Ulez compliant vehicle is now eligible for financial support."
He has also repeatedly criticised the Government for not supporting London’s scrappage scheme.
Six of the seven Tory-run boroughs bordering the capital have refused to let TfL install Ulez warning signs.