More than a billion Indians celebrated Diwali on Saturday amid twin concerns of a resurgence in coronavirus infections and rising air pollution that is enveloping the country’s north in a cloud of thick toxic smog. Diwali, the Hindu festival of lights, is typically celebrated by socializing and exchanging gifts with friends and family, and lighting oil lamps or candles to symbolize a victory of light over darkness. Fireworks are also a major part of the celebrations.