Medellín in Colombia was experiencing a severe urban heat island effect. Now, new green growth is bringing temperatures down dramatically.

As restrictions on petrol-driven leaf-blowers spread across the US, neighbourhoods are getting quieter — and cleaner.

Engineers have found that almost any material can be turned into a device that continuously harvests electricity from humidity in the air.

Low-emission zones in big cities such as London reduce air pollution, especially for poorer communities.