#25 Paris, France

Air pollution -- tiny particles and droplets of acid, organic chemicals, metals and dust -- kills about 1.3 million people worldwide every year. But if there's a tangerine lining to fine-particulate pollution, it's the dazzling sunsets that can form when light bounces off it. The World Health Organization compiled levels of urban outdoor air pollution from 1,100 cities in 91 countries. If the air quality in these locales doesn't take your breath away, their saffron sunsets just might.

The sun sets over rooftops in the Montmartre district in Paris, one of the most romantic and polluted cities in the world.