Bengaluru: Firecrackers were the main source of fine particulate matter (PM2.5), a major air pollutant, on the day after Diwali in Delhi as per data published online by the Indian Institute of Tropical Meteorology’s Air Quality Warning and Integrated Decision Support System for Emissions for Delhi.They contributed around 71% of all the PM2.5 in the national capital on November 9. Most of north India including Delhi celebrated Diwali on Sunday, November 8. The celebrations were marked by citizens flouting the Supreme Court’s order on bursting firecrackers only from 8 to 10 p.m. at night.Diwali darknessThe data is part of the source apportionment results released by Pune IITM, which operates the Air Quality Warning and Integrated Decision Support System for Emissions for Delhi. Source apportionment is a scientific technique used to identify and quantify the specific sources of air pollution (such as particulate matter) measured at a monitoring station.Also read: Before the Firecrackers, Delhi Was Already Choking: Fourth Worst Diwali in a DecadeThe IITM’s source apportionment data shows that firecrackers contributed only 5.6% of PM2.5 levels in Delhi on November 5. This percentage, however, increased and varied over the next two days: 9.3% on November 6 and 5.6% on November 7. It then jumped to 43.4% on November 8, the day of Diwali.Firecrackers contributed the highest (71%) to total fine particulate matter levels in the city on November 9. The next highest contributor to PM2.5 on the day, vehicle emissions, were far behind, at only 6.9%.The percentage of firecrackers in PM2.5 levels fell to 29.8% on November 10 (Tuesday).Source: Air Quality Warning and Integrated Decision Support System for Emissions, Delhi. Indian Institute of Tropical Meteorology.Data for all days was based on a 24-hour average, except for November 10 (Tuesday) which has been collected only from 1 a.m. to 9 a.m., IITM scientist Sachin Ghude told The Wire.A firstThis is the first time that the IITM has looked at firecrackers separately as a source in its source apportionment study, said Ghude, who is a scientist at the IITM Pune and heads the DSS and Air Quality Warning and Integrated Decision Support System for Emissions (AIRWISE). His team wanted to see how much of PM2.5 is coming from stubble burning and how much is from firecrackers separately because this coincides with the peak stubble burning period historically, he told The Wire.Such high levels of PM2.5 from firecrackers is a health problem, he added.“It’s not good for health,” Ghude told The Wire. “Lead and aluminium [content] was significantly high.”Lead is the dominant priority among the selected toxic elements by measured mass concentration, as it peaked at 20.788 µg/m³ at nighttime, he added.The permissible limits for lead in ambient air in India, as set by the Central Pollution Control Board under the National Ambient Air Quality Standards (NAAQS), is 1.0 µg/m³ over 24 hours.Source: Air Quality Warning and Integrated Decision Support System for Emissions, Delhi. Indian Institute of Tropical Meteorology.PM2.5 or fine particulate matter are fine particles less than 2.5 micrometers in diameter which are usually released when fossil fuels are burned, and are also a component of dust.Firecrackers release high levels of PM2.5 because they traditionally comprise of a mixture of black powder or gunpowder (which contains potassium nitrate, sulphur and charcoal), metal fuels (aluminium, magnesium, titanium) and colouring agents (such as barium, strontium, copper and sodium).Also read: Delhi’s Missing Diwali-Night Pollution Data Released: PM2.5 Crosses 3,700; Politicians Cling to SuperstitionIn low wind dispersion areas (as New Delhi often is during winter), the chemicals released by firecrackers can often persist in the atmosphere, studies mention.“In the IGB [Indo-Gangetic Basin], these spikes are amplified by stagnant post-monsoon weather, trapping pollutants and creating multiday haze episodes. The health implications are severe like exposure to such pollution levels elevates risks of respiratory emergencies (asthma, COPD exacerbations), cardiovascular events, and premature mortality, particularly among children, the elderly, and those with pre-existing conditions,” a recent study on Diwali pollution in India in the journal Scientific Reports mentioned.