The winter smog is driven by a perfect storm of factors. Falling temperatures and weaker winds coincide with a spike in seasonal crop burning by farmers — compounded by already high vehicle and factory emissions, Diwali-season fireworks and construction dust. Trapped by the capital’s bowl-like geography, the pollution lingers for months.

The health impacts are severe. High concentrations of PM 2.5 raise the risk of heart attacks, cancer, respiratory diseases, strokes and dementia, local and international studies show. Almost 1.7 million deaths were attributable to air pollution in India in 2019, according to the Lancet journal. Children are particularly vulnerable, which is why the Nov. 9 protest at India Gate was organized by an advocacy group called Warrior Moms. An informal survey the group conducted across more than a dozen pharmacies recorded a substantial rise in demand for inhalers and respiratory medications in recent years, with a third of all nebulizers typically purchased for children.