As of Wednesday, New Delhi’s PM 2.5 concentration – a measure of pollutants in the air – was more than 40 times the World Health Organization’s annualized guideline level, according to Swiss air quality monitoring company IQAir. The sharp deterioration in air quality this week comes following celebrations for Diwali, the Hindu festival of lights, which traditionally involves the widespread use of firecrackers which release sulfur oxides and nitrogen oxides into the air, as well as harmful heavy metals. In 2020, authorities enacted a complete ban on making, selling or using firecrackers in New Delhi, citing hazardous pollution levels. India is also desperate to fuel its booming economy and meet the energy needs of its 1.4 billion people. On Wednesday, three Indian cities, including New Delhi, were ranked among the world’s most polluted, according to air quality tracker IQAir.