Paris (AFP) - The mayors of Paris, London and Seoul on Wednesday launched an initiative to rate the most polluting vehicles in a bid to keep them off the roads of their cities.
The aim of the "Air'volution" scheme is to help drivers avoid buying the most harmful diesel vans and cars.
Speaking at a press conference in Paris, London Mayor Sadiq Khan said respiratory problems caused by emissions led to 9,000 deaths a year in his city.
"It is imperative that we do something," Khan said.
He said the index of vehicles would be the "first of its type in the world".
Major car manufacturers have been invited to participate in the scheme, but Paris mayor Anne Hidalgo admitted that trust "needed to be rebuilt" after the scandal over emissions test cheating that embroiled Volkswagen and has also drawn in French giant Renault.
"This must be a co-production with car manufacturers and it is work that must be a win-win situation," Hidalgo said.
French automakers' association CCFA said it supported the initiative.
"The improvement of air quality remains a major challenge in the development of the car of tomorrow," CCFA said in a statement.
The mayor of the South Korean capital, Park Won-Soon, said his city had slashed harmful emissions by converting 7,500 buses to operate on gas rather than diesel.
On the day that Britain triggered the formal process to leave the European Union, Khan said the scheme was a reminder that big cities in Europe "simply must continue to work together".