Despite Supreme Court enforcing a two-hour window, revelers burst crackers until late night.
Fireworks on Diwali night played an "overwhelming" role in the rapid deterioration of air quality in Delhi-NCR, a Centre for Science and Environment (CSE) report showed today.
CSE experts analyzed real-time data for the Delhi-NCR region to show bursting of crackers "ushered in the season's first severe pollution peak."
The report said air was much cleaner before Diwali in 2019 as compared to 2018, which "shows the overwhelming role of firecrackers in building the severe peak on Diwali night".
"From a very clean afternoon, the change to severe pollution levels after 10 pm at (Diwali) night was drastic. There was a 10-fold jump in PM2.5 concentrations between 5pm and 1am due to bursting of firecrackers. The peak level during 1am to 3am was quite similar to the peak levels observed in 2018," the report said.
This has undone the comparatively cleaner trend achieved so far from September 15 to October 27, the CSE said.
PM2.5 is tiny particulate matter with a diameter of equal to or less than 2.5 microns that can enter deep into the lungs and even the bloodstream.
"The air quality data indicates that the concentrated bursting of crackers after 10pm at night had spiralled the pollution curve to nearly the same severe level that was observed during the previous Diwali night," it said.
"This happened despite the 2019 Diwali being warmer and windier than in 2018. This temporarily undid the comparatively better air quality gains of this season due to favorable weather, on-going pollution control action and preventive emergency measures," it said.
Despite Supreme Court enforcing a two-hour window - from 8pm to 10 pm, revelers burst crackers until late on Diwali night.
The top court had also ordered that only green firecrackers, said to cause 30 per cent less pollution, can be manufactured and sold, but a Delhi Pollution Control Committee (DPCC) official said a large number of illegal crackers were burst on Diwali.
"While harsher winter conditions are yet to set in and the weather during the period of analysis (September 15 to October 27) has remained relatively favorable, including a delayed monsoon, several ongoing systemic actions and preventive emergency measures had also contributed to prevent an early onset of very poor and severe pollution in Delhi-NCR. The scenario has changed on Diwali night," said Anumita Roychowdhury, executive director-research and advocacy, CSE.
The CSE also said "poor'' and "very poor'' days this season have started to occur only after October 10. But during 2018, there were more such days, starting as early as September 26.
Nearly all cities and towns had experienced severe pollution days before Diwali.
"This year, only Ghaziabad has experienced the season's first 24-hour average severe pollution on Diwali day. However, there is early indication that air quality in the post-Diwali days could deteriorate to severe category," it said.
Mr Roy said it was absolutely necessary that action was now stepped up to ensure that Delhi-NCR do not plunge into a prolonged smog episode this winter.