Firecrackers accounted for 71% of Delhi’s PM2.5 on Diwali night

On Diwali night of November 9, 2021, firecrackers were responsible for 71.1% of fine particulate pollution (PM2.5) in Delhi, according to an assessment conducted by the Indian Institute of Tropical Meteorology (IITM) in Pune. This was the first-ever evaluation of firecracker emissions contributing to PM2.5 levels in India. The study found that firecrackers contributed to 43.4% of PM2.5 on the night before Diwali and only 5.6% on November 7.

Other sources like vehicular emissions, biomass-burning, waste-burning, secondary aerosols, and dust typically accounted for larger shares of PM2.5 before the Diwali celebrations.

During the study hours from 1 am to 9 am, firecracker emissions peaked at 4,985 µg/m³ in Jahangirpuri and 2,808 µg/m³ in Nehru Nagar. By contrast, vehicles, secondary inorganic aerosols, secondary organic aerosols, and waste-burning contributed 6.9%, 5%, 4.5%, and 1.1% respectively to PM2.5 levels on Diwali night. Firecrackers remained the dominant contributor of PM2.5 during the same period on Tuesday, accounting for 29.8% of pollution. Secondary organic aerosols and transport sector emissions were the next biggest contributors.

The researchers noted that firecracker emissions are episodic and can change rapidly depending on factors like timing, intensity, wind speed, atmospheric mixing, and the height of the planetary boundary layer. These challenges make it difficult to precisely quantify firecracker emissions using traditional methods. Moreover, some chemical constituents released by fireworks overlap with those from other combustion sources, further complicating the analysis.

IITM emphasized that their estimates are based on the best available source profiles, scientifically established methodologies, and accepted practices. The institute also highlighted uncertainties related to atmospheric processes, source characteristics, and observational limitations. Since firecracker emissions are only measured during the 1 am-to-9 am window, these estimates do not account for full-day contributions.

The new IITM assessment marks the first time that firecracker emissions have been specifically included in an official source-apportionment estimate. This comes after the inauguration of the Advanced Atmospheric Chemistry and Aerosol Toxicity Analysis Laboratory (AATAL) at the IITM Delhi branch, which is equipped to analyze the chemical composition of atmospheric gases and aerosols, including PM2.5 and toxic elements.