2. Gwalior, India - 176 µg/m3 of PM 2.5

Gwalior, a historic city about 200 miles south of New Delhi, is the Indian city with the worst air pollution both in terms of PM 2.5 and 10, according to the WHO. The Times of India attributes Gwalior's bad air pollution to coal-powered plants, cars, and inefficient energy use in buildings.