Hyderabad, Nov. 9 -- It took just two hours on Diwali night for Hyderabad's air to go from unhealthy to hazardous. At around 9:30 pm on Sunday, November 8, the city's average Air Quality Index (AQI) touched 509, a hazardous level that amounts to a major public health emergency. The reading held steady until 3 am on Monday, November 9, and has been easing slowly since.

Siasat.com tracked the data from Saturday evening, November 7, the day before Diwali, to Monday, the day after the festival.

From 3 pm on November 7, Hyderabad's AQI hovered between 150 and 180, a range considered unhealthy for breathing.

The air was still unhealthy at 3 pm on Diwali day. But once the festivities began and firecrackers lit up the skies, conditions worsene...