Which cities face most, least air pollution according to new WHO data

Story highlights

  • 9 out of 10 people in the world breathe air that is highly polluted, a new report says
  • Air pollution is found in the home and outdoors
  • About 7 million people die each year because of this pollution, the WHO says

(CNN)Nine out of every 10 people on the planet breathe air that contains high levels of pollut