Diwali, derived from the word “Deepavali,” meaning “a row of lights,” is typically celebrated by socializing and exchanging gifts. The dates of the festival are based on the Hindu lunar calendar, typically falling in late October or early November. Shoppers crowded markets to buy flowers, lanterns and candles.

New Delhi and its metropolitan region — home to more than 30 million people — routinely ranks among the world’s most polluted cities during winter.