For most of November, Delhi has been blanketed by dense smog. Doctors in the capital declared the crisis a public healthy emergency, while the chief minister, Arvind Kejriwal, called it a “gas chamber.” Since the beginning of the month, average pollution levels in the city have exceeded 10 times the World Health Organization-recommended 24-hour levels. At its worst, pollution levels were nearly 40 times this number.

But pollution is not just a Delhi problem. Indian cities are consistently ranked among Asia’s most polluted, according to WHO. Per the WHO’s 2016 database, 10 of the world’s most polluted cities, in terms of fine particulate matter, are in India.

Particulate matter pollution is the single largest environmental health risk across the world. These particles led to 4.2 million premature deaths in 2015-2016-more deaths than from malaria, tuberculosis and HIV-AIDS combined. A recent study from the Energy Policy Institute at University of Chicago (EPIC), on the impact of prolonged exposure to particulates, finds that…