In India, a thick blanket of toxic air pollution has covered the city of New Delhi, prompting a public health emergency. In some parts of the city, air quality readings reached the maximum score that instruments can measure—999—with a score above 100 considered unsafe by India’s government. The pollution is so bad, Delhi’s chief minister called the city a “gas chamber.” A recent study by the medical journal Lancet found air pollution kills a half a million Indians prematurely each year.