Poor air quality poses serious health risks to humans. Industry, energy, and the transportation sector are all major contributors to poor air quality, and cities across this country breathe some of that air on Earth. The World Health Organization (WHO) estimates that 99 percent of all people breathe air that “contains high levels of pollutants.”

All but one of the world’s top 20 most polluted cities last year were in Asia, a new study shows. The majority of these cities – 13 – are in the world’s most populous country, India, where booming economic growth is fired largely by coal and where hundreds of millions live in traffic-clogged and congested megacities .