Crackers account for 71% of Delhi’s PM2.5 on Diwali night: Data

Why in the News

For the first time, an official source apportionment estimate for Delhi’s air includes firecracker emissions, and it puts their share of PM2.5 at 71.1% in the hours after Diwali night. The assessment by the Indian Institute of Tropical Meteorology (IITM), Pune, rests on real time data. The estimate is indirect and covers only an eight hour window each day.

What is source apportionment, and how was this estimate made?

1. What it is: Source apportionment works out how much each source, such as vehicles, biomass burning or dust, adds to air pollution. It is like splitting a shared electricity bill appliance by appliance.
2. Pollutant measured: The estimate covers PM2.5, fine particles of 2.5 micrometres or less that enter deep into the lungs.
3. New laboratory: The Advanced Atmospheric Chemistry and Aerosol Toxicity Analysis Laboratory (AATAL) opened at IITM’s Delhi branch on October 24. It analyses the chemical composition of gases and aerosols (airborne particles), including PM2.5, metals and toxic elements.
4. Integrated system: AATAL is linked to IITM’s Air Quality Warning and Integrated Decision Support System for Emissions (AIRWISE), which combines air quality forecasts, observations and source apportionment information.
5. The takeaway: Delhi now has an official figure for a source earlier debated without measurement, which helps plan targeted interventions.

What did the assessment find?

1. Diwali night share: Firecrackers contributed 71.1% of Delhi’s PM2.5 in the study hours of November 9, just after the celebrations wound down.
2. Build up before Diwali: The firecracker share in the same hours was 5.6% two days earlier and 43.4% on the night before Diwali.
3. Regular sources displaced: Before Diwali night, secondary organic aerosols (particles formed in the air from gases) and biofuel burning led. Their shares fell sharply on Diwali night.
4. Lingering effect: Firecrackers remained the top contributor a day later, at 29.8% in the study hours, followed by secondary organic aerosols and transport emissions. Delhi’s Air Quality Index (AQI) was 299, in the “Poor” category.
5. Peaks at monitoring stations: PM2.5 peaked at 4,985 micrograms per cubic metre in Jahangirpuri and 2,808 in Nehru Nagar in the early hours after Diwali night.

Why is the estimate uncertain?

1. Indirect estimation: No real time measurement of firecracker aerosols exists, so their impact is estimated indirectly. IITM says it used the best available source profiles and established methods.
2. Episodic source: Firecracker emissions come in bursts, unlike continuous sources such as vehicles. Their concentration shifts with the timing and intensity of bursting, wind speed and atmospheric mixing.
3. Boundary layer height: The height of the planetary boundary layer (the lowest layer of the atmosphere) decides whether pollutants disperse or accumulate close to the ground.
4. Tracer overlap: Potassium is the common chemical marker (tracer) for fireworks, but biomass burning, including crop residue and wood, also releases it. A study this year found the two mixing into a “complex, chemically evolved haze”.
5. Variation across locations: A 2022 study of two Delhi sites about 15 km apart found substantial differences in fireworks related elements.

Challenges

1. Limited window: The estimate covers only 1 am to 9 am for each date, not the full day’s contribution.
2. Chemical overlap with age: Separating firecracker particles from other smoke gets harder as pollutants age and mix in the atmosphere.
3. Enforcement in one night: Curbs on bursting firecrackers are hard to police across an entire city within a few hours.

Way Forward

1. Full day estimates: IITM should extend the apportionment from the eight hour window to the full day.
2. More measurement sites: Add chemical analysis at several locations, since firecracker impact differs across the city.
3. Advance warnings: Delhi’s agencies should use AIRWISE forecasts to time curbs before Diwali night.

Conclusion

Firecrackers now have a measured place in Delhi’s official pollution accounts, with stated limits on how far the figure can be read. Whether next season’s curbs are planned on this evidence is what to watch.

Key numbers

1. Leading shares before Diwali night: Secondary organic aerosols 20.8%, mixed or unresolved biofuel burning 18.1%.
2. Other shares before Diwali night: Waste burning 11.6%, secondary inorganic aerosols 10.3%, vehicles 8.8%.
3. Shares on Diwali night: Vehicles 6.9%, secondary inorganic aerosols 5%, secondary organic aerosols 4.5%, waste burning 1.1%.
4. Time of the PM2.5 peaks: 3 am on November 9, at both stations.

Matching Previous Year Question

“[2016] In the cities of our country, which among the following atmospheric gases are normally considered in calculating the value of Air Quality Index? 1. Carbon dioxide 2. Carbon monoxide 3. Nitrogen dioxide 4. Sulfur dioxide 5. Methane Select the correct answer using the code given below. (a) 1, 2 and 3 only (b) 2, 3 and 4 only (c) 1, 4 and 5 only (d) 1, 2, 3, 4 and 5 ANSWER: (b)”