World Health Organization releases list of world's most polluted cities

Zabol, Iran, has replaced New Delhi as the world's most polluted city in terms of PM 2.5. India, however, is still home to 10 of the 20 cities with the unhealthiest air. Four Chinese cities also made the list. Global air pollution grew 8 percent in the last five years, with the bulk of the increase (and associated health effects) in the world's poorest cities. Mashable