Angad Daryani of India has invented an economical air purifier, with the potential to improve air quality for poor people in crowded cities. Existing air purification systems are very expensive, and they need constant replacement of filters. Daryani’s 160m tall devices have no filters, are inexpensive, and clean eight cubic metres of air per minute - more than enough for a small family house. Every six months you remove the container which has collected the pollution from the air. As an extra bonus, it turns out that this waste product contains valuable minerals that have been recycled to make stylish tiles, and may have other uses.