World’s most and least polluted countries

TonyV3112 / Shutterstock.com

The silent killer

Air pollution is a far bigger killer than many people realise, causing more than three million premature deaths worldwide every year. Global pollution levels are on the rise, and while some countries are blazing a trail in tackling it, others have done little to stop it ruining lives. Here are the 20 most polluted and 20 least polluted nations, based on World Health Organization figures on levels of tiny pollutant particles in their cities.