The leaders of four major global cities have vowed to stop the use of all diesel-powered cars and trucks by the middle of the next decade.
The domes of Les Invalides, left, and the Pantheon in Paris can be seen through a veil of smog. Photo: AFP
The mayors of Paris, Mexico City, Madrid and Athens say they are implementing the ban to improve air quality.
They say they will give incentives for alternative vehicle use and promote walking and cycling.
The commitments were made in Mexico at a biennial meeting of city leaders.
The use of diesel in transport has come under increasing scrutiny in recent years, as concerns about its impact on air quality have grown. The World Health Organization (WHO) says that around 3 million deaths every year are linked to exposure to outdoor air pollution.
Diesel engines contribute to the problem in two key ways - through the production of particulate matter (PM) and nitrogen oxides (NOx). Very fine soot PM can penetrate the lungs and can contribute to cardiovascular illness and death.
Nitrogen oxides can help form ground level ozone and this can exacerbate breathing difficulties, even for people without a history of respiratory problems.
As the evidence has mounted, environmental groups have used the courts to try and enforce clear air standards and regulations. In the UK, campaigners have recently had success in forcing the government to act more quickly.
Now, mayors from a number of major cities with well known air quality problems have decided to use their authority to clamp down on the use of diesel.
In the UK, campaigners are calling for London's mayor to commit to phase out diesel vehicles from London by 2025.
Mayor Sadiq Khan has proposed an expansion to the planned Ultra-Low Emission Zone in central London.
ClientEarth lawyer Alan Andrews said: "In the UK, London's mayor is considering bolder action than his predecessor, proposing an expansion to the planned Ultra-Low Emission Zone. This is welcome but we want him to go further and faster."
Heavy traffic is seen in Mexico City. Photo: AFP
At the C40 meeting of urban leaders in Mexico, the four mayors declared that they would ban all diesel vehicles by 2025 and "commit to doing everything in their power to incentivise the use of electric, hydrogen and hybrid vehicles".
"It is no secret that in Mexico City, we grapple with the twin problems of air pollution and traffic," said the city's mayor, Miguel Ángel Mancera.
"By expanding alternative transportation options like our Bus Rapid Transport and subway systems, while also investing in cycling infrastructure, we are working to ease congestion in our roadways and our lungs."
Paris has already taken a series of steps to cut the impact of diesel cars and trucks. Vehicles registered before 1997 have already been banned from entering the city, with restrictions increasing each year until 2020.
Once every month, the Champs-Élysées is closed to traffic, while very recently a three kilometre section of the right bank of the Seine river, that was once a two-lane motorway, has been pedestrianised.
"Our city is implementing a bold plan - we will progressively ban the most polluting vehicles from the roads, helping Paris citizens with concrete accompanying measures," said Anne Hidalgo, the city's mayor.
"Our ambition is clear and we have started to roll it out: we want to ban diesel from our city, following the model of Tokyo, which has already done the same."
Many of the measures being proposed to cut air pollution have a knock-on benefit of curbing the emissions that exacerbate global warming as well.
"The quality of the air that we breathe in our cities is directly linked to tackling climate change," said the mayor of Madrid, Manuela Carmena.
"As we reduce the greenhouse gas emissions generated in our cities, our air will become cleaner and our children, our grandparents and our neighbours will be healthier."
Many of the plans outlined by the mayors meeting in Mexico are already having a positive impact.
In Barcelona, extra journeys by publicly available bicycles have reduced the CO2 emissions by over 9000 tonnes - the equivalent of more than 21m miles driven by an average vehicle.
"And it's not just London that has this problem, we need a national network of clean air zones so that the problem is not simply pushed elsewhere."
- BBC