Paris is so smog afflicted it has made public transport free and limited the days drivers are allowed on the roads in a bid to reduce traffic congestion. Paris is also one of a number of city looking to ban diesel vehicles from use by 2025 - Mayors Of Paris, Mexico City, Madrid, & Athens Move To Ban All Diesel Vehicles By 2025.
To be clear on the first commitment, this would apparently apply to all diesel vehicles — including trucks, not just cars. The idea is to improve local air quality and also to reduce greenhouse gas emissions — which is what the C40 forum was initially formed for, the idea being to give mayors working to mitigate and prevent anthropogenic climate change a place to share notes, so to speak.
The mayor of Madrid, Manuela Carmena, commented on this: “The quality of the air that we breathe in our cities is directly linked to tackling climate change. 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.”