NEW DELHI: Widespread bursting of firecrackers beyond the time window permitted by Supreme Court on Diwali night drove Delhi’s air quality deeper into the ‘very poor’ category on Tuesday.
The surge of toxic smoke, laden with pollutants and heavy metals, caused the city’s average hourly PM2.5 levels to touch 675 micrograms/cubic metre at midnight, the highest since 2021 for Diwali night, when it had stood at 728.
However, a rise in wind speed from 6am onwards and above-normal temperatures, along with negligible impact of stubble burning, prevented a further spike in pollution during the day.
Delhi’s 24-hour average AQI on Diwali day stood at 345 in the ‘very poor’ category at 4pm — the highest Diwali day reading since 2021, when it had reached 382. On Tuesday, it had risen marginally to 351 — higher than last year’s post-Diwali reading of 339 (on Nov 1) but lower than the level recorded in 2023 (358).
AQI past 350, no GRAP-III yet
The worst post-Diwali air quality on record was in 2021, when the AQI spiked to 462 (‘severe’) on Nov 5.
After a gap of five years, the Supreme Court had allowed the bursting of green crackers, which release 30% less particulate matter than conventional crackers, from 6am to 7am and 8pm to 10pm on Oct 19 and 20, respectively. However, crackers were burst till well past midnight, with people also opting for conventional crackers due to their easy availability. A sharp rise in PM2.5 levels across several stations in the city within a gap of a few hours shows that the crackers were used.
Delhi Pollution Control Commission’s real-time air quality data showed that the hourly PM2.5 concentration at Nehru Nagar in Lajpat Nagar rose from 679 micrograms per cubic metre at 9pm to 1,763 micrograms per cubic metre at 10pm on Monday. Several stations recorded a similar spike within a matter of a few hours. The AQI remained in the higher end of the ‘very poor’ to ‘severe’ category in some parts of the city.
Anumita Roychowdhury, executive director, research and advocacy, Centre for Science and Environment, said Delhi-NCR experienced the season’s first smog episode on Monday night due to the concentrated bursting of crackers.
“Pollution levels have hit very poor to severe levels at this onset of the winter when it’s still much warmer. The particulate levels have increased steadily since early Oct. But on Oct 20, the levels increased by nearly eight times between afternoon and night, causing very high exposures. This has happened even when the contribution of farm fires was less than 1-2%,” said Roychowdhury. She added that the coming months will require much stronger systemic action to control emissions from sources and not just temporary emergency measures that have short-lived impacts.
As winds remained calm during the night, it caused an accumulation of pollutants. However, winds picked up from 6am onwards, leading to dispersion. “The hourly particulate matter spiked from 9pm on Monday and saw an increasing trend until 5am on Tuesday and then a sharp decline as the sun came out,” said Gufran Beig, founder of the System of Air Quality and Weather Forecasting and Research (SAFAR) and chair professor at the National Institute of Advanced Studies (NIAS).
According to the India Meteorological Department, the city witnessed shallow fog with visibility dipping to 600 metres at Palam between 3.30am and 5am on Tuesday as winds were calm. From 6am onwards, an average wind speed of up to 10kmph was recorded.
Even though the city’s average AQI surpassed 350 on Tuesday, the Commission for Air Quality Management did not impose stage III of the Graded Response Action Plan. A CAQM source said, “Last year, Supreme Court directed that Stage III (Severe) of Grap be imposed at AQI levels above 350 and Stage IV (Severe Plus) when the AQI goes beyond 400. However, there are no such directions this time. So, we will use thresholds as per our schedule — triggering Stages III and IV at 400 and 450, respectively.”
The Air Quality Early Warning System for Delhi (EWS), which functions under the Union ministry of earth sciences, initially predicted that AQI would touch ‘severe’ on Tuesday and Wednesday. In its updated bulletin on Tuesday, EWS said AQI is likely to remain in the ‘very poor’ category from Wednesday till Friday.