1On winter mornings, a thick grey haze hangs over the city, hiding the tops of the tallest buildings.
2Doctors warn that dirty air causes breathing problems, especially for young children and elderly people.
3The city council has created low emission zones where old, polluting cars are no longer welcome.
4Buses now run on electricity, and hundreds of new bicycle lanes cross the whole city centre.
5Large factories outside the city must install modern filters to catch harmful particles before they escape.
6Sensors on street lamps measure the air quality and send the results to a public website.
7Parents can check this website each morning before deciding how their children should travel to school.
8Since the new rules began, the number of smoggy days has fallen by almost twenty percent.
9Clean air is not a luxury for the few; it is a basic right for every citizen.
10The city still has far to go, but the sky is slowly turning blue again.