What can cities do when air pollution soars and what works?

Reducing speed limits, banning home wood-burning and providing free transport are just some of the approaches taken

Earlier in January the London mayor and other organisations issued the first pollution warning of the year. These warnings follow the UK government index.

They are designed to protect vulnerable people, but they do this by asking those people who experience most harm to avoid doing things outdoors. They do not ask the polluters to reduce their emissions.