A cyclist on a road shrouded in smog in Delhi, India, the day after Diwali. Toxic air is estimated to kill more than one million Indians each year. Ruhani Kaur / Bloomberg
A cyclist on a road shrouded in smog in Delhi, India, the day after Diwali. Toxic air is estimated to kill more than one million Indians each year. Ruhani Kaur / Bloomberg

Why Delhi-dwellers are breathing in the equivalent of 40 cigarettes a day