The director general of the World Health Organization has said air pollution is "one of the most pernicious threats" facing global public health today and is on a much bigger scale than HIV or Ebola.

Dr Margaret Chan told the Today programme that poor air quality was having a disproportionate impact on the young.

She said indoor and outdoor pollution was linked to the deaths of hundreds of thousands of children each year.

A week of coverage by BBC News looking at ways to cut air pollution.