For the first time, IITM Pune’s air-quality decision-support system has treated firecrackers as a separate pollution source. It attributes about 71% of Delhi’s fine-particle pollution on the day after Diwali to fireworks, with airborne lead peaking at about 20 times the national standard. Separately, hourly data released by Delhi’s pollution board show PM2.5 readings of more than 3,700 micrograms per cubic metre on Diwali night, readings that were absent from the central database.
Every year, the argument after Diwali is the same. How much of the smoke over Delhi comes from fireworks, and how much from vehicles, industry, dust and crop burning? This year, two sets of numbers released on 10 November give an unusually detailed answer, and raise awkward questions about how pollution data are recorded.
Separating the sources
The Indian Institute of Tropical Meteorology (IITM) in Pune runs a decision-support system for Delhi’s air quality, known as AIRWISE. It estimates the share of PM2.5, particles smaller than 2.5 micrometres, that comes from different sources. This method, called source apportionment, combines inventories of emissions with models of how pollutants move and transform in the atmosphere. It produces estimates, not direct chemical measurements.
According to The Wire, this year was the first time IITM modelled firecrackers as a distinct source. The results, provided by Sachin Ghude, the IITM scientist who heads the system, show a sharp spike. Firecrackers’ estimated share of Delhi’s PM2.5 was:
- 5–7 November: between 5.6% and 9.3% a day.
- 8 November (Diwali): 43.4%.
- 9 November: about 71%, with vehicle exhaust next at 6.9%.
- 10 November: 29.8%, for 1 am to 9 am only.
The 9 November peak reflects the timing of the celebrations. Most fireworks are set off late on Diwali night, which falls in the early hours of the next calendar day. Calm, cold night air then traps the smoke near the ground.
Metals in the smoke
Fireworks owe their colours and sparkle to metal salts and powders. Ghude told The Wire that “lead and aluminium [content] was significantly high”. Airborne lead peaked at night at about 20.8 micrograms per cubic metre. India’s national ambient standard for lead is 1.0 µg/m³ averaged over 24 hours. An hourly peak cannot be compared directly with a 24-hour standard, but the size of the gap is striking. Lead is a neurotoxin with no known safe level of exposure, and children are the most vulnerable. “It’s not good for health,” Ghude said. The station and exact time of the peak were not given.
The readings that went missing
The second set of numbers concerns what the official record did not show. According to Business Today, citing an analysis first published by the Hindustan Times, the Delhi Pollution Control Committee (DPCC) released hourly readings for Diwali night on the evening of 9 November. Its data show:
- Peak: PM2.5 of 3,744 µg/m³ at Mundka at 2 am on 9 November.
- Other stations: 3,023 at JNU, 3,008 at NSUT West Campus and 2,908 at Mandir Marg.
- Breadth: eleven stations above 2,000 µg/m³.
For comparison, India’s 24-hour PM2.5 standard is 60 µg/m³, and the World Health Organization’s guideline is 15.
In the central database maintained by the Central Pollution Control Board (CPCB), 125 station-hours were missing. Every one of the corresponding DPCC readings was above 1,000 µg/m³. Where both databases had a value, the figures matched. At 1 am, 36 of Delhi’s 59 stations had no PM2.5 reading in CPCB’s records, and the highest CPCB reading of the night was 1,000. An unnamed official attributed the gaps to “technical glitches”.
Why the gaps matter, and why they don’t change the AQI much
Recalculated with the missing readings, Delhi’s 24-hour Air Quality Index to 9 am on 9 November rises from the published 370 to about 384, according to the Hindustan Times analysis reported by Business Today. The difference looks modest because of how the index works. The AQI is capped at 500, which hourly PM2.5 reaches at about 420 µg/m³, so readings in the thousands add little to the headline number.
This is precisely why the raw data matter. The AQI is designed to communicate a health category, not the true scale of an extreme event. Exposure during the peak hours of Diwali night was far worse than any “severe” label conveys. Complete hourly records are needed for health studies, for enforcing time limits on fireworks and for judging whether “green” crackers make any difference. The Wire reports that the Supreme Court had allowed fireworks only between 8 pm and 10 pm. The readings in the small hours suggest that the window was widely ignored.
The limits of the evidence
Both data sets need careful handling:
- Source apportionment: AIRWISE figures are model outputs. A different figure attributed to firecrackers, “80%” in a Times of India headline, could not be checked because the page was blocked, and NSH uses IITM’s figures.
- Provisional data: the DPCC readings have not been quality-assured.
- Lead: the reading is a single reported peak, not a 24-hour average.
None of this changes the central finding. On the night after Diwali, fireworks overwhelmed every other source of pollution in the capital.
The Hyderabad parallel
The problem is not confined to Delhi. As NSH reported on 10 November, the CPCB’s citywide AQI for Hyderabad reached 315 on Diwali night. The Telangana pollution board published no data, and its University of Hyderabad station was offline at the peak. In Andhra Pradesh, the state board’s bulletin showed air quality worsening in all 17 monitored cities, with Visakhapatnam at 264. Incomplete records during the worst hours appear to be a national pattern, not a single city’s glitch.
What happens next
Delhi has been under Stage III of its Graded Response Action Plan since 6 November, according to Business Standard. Lasting change will depend on enforcing time and product rules for fireworks, and on publishing complete, timely data from every monitoring station.
