Of the world's 10 most polluted cities, seven are located in which nation?

• A. India
• B. Russia
• C. Brazil
• D. China

Answer: (D)

This item highlights how industrial growth and energy use shape where the dirtiest urban air is found. Rankings of the world’s most polluted cities typically rely on measures of air quality—often PM2.5 or PM10 levels—summed over a year. In countries with rapid industrial expansion and heavy coal use, large cities accumulate high emissions from factories, power plants, and traffic, leading to extreme pollution in multiple urban centers. China has experienced exactly that pattern for many years, with dense populations and a concentration of smokestack industry in major cities, which is why several of the top polluted cities come from there. That pattern makes it plausible that seven of the top ten cities could be in one nation, more so than in the other listed countries, where there aren’t as many cities dominating the top of the list.