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Secondary inorganic aerosols, biomass burning within and outside Delhi, and vehicles: These contributed the most to Particulate Matter (PM) 2.5 levels in Delhi last winter, according to data from a study presented to the Delhi government this September.
The report on the real-time source apportionment study said results show the contribution of secondary inorganic aerosols, which are mostly expected to travel from far distances, to be the highest. The study, meant to understand sources of PM 2.5 in Delhi for the previous winter, was submitted to the Delhi Pollution Control Committee (DPCC) by IIT-Kanpur, IIT-Delhi and TERI.
For the winter (November 1, 2022 to March 2, 2023), the average contribution of secondary inorganic aerosols was 32%, while that of biomass burning within and outside Delhi was 24%, followed by 17% from vehicles, and 7% from coal and fly ash. Domestic sources contributed around 3%, while soil and road dust contributed 2%.
Secondary inorganic aerosols are particles like nitrate and ammonium formed in the atmosphere by the interaction of gases, with sources including power plants, decomposition of waste, vehicles, and brick kilns.
The study, which was done with data from a supersite at Sarvodaya Bal Vidyalaya, Rouse Avenue, estimated the contribution from construction and industry at the site to be 0%.
In winter, the average contribution of secondary inorganic aerosols from sources within Delhi (that is a distance of up to 30 km from the supersite) is 16%, while 84% is from outside Delhi, according to the report.
Last winter, January was found to be the most polluted in terms of average PM 2.5 levels (217 µg/m3), followed by 210 µg/m3 in November.
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The contribution of biomass burning was found to be highest in November at 36%, while in December it was 21%. The study estimated the average contribution of crop residue burning to PM 2.5 levels from November 1 to 25 to be 22%.
Last month, Environment Minister Gopal Rai had said the real-time study has been stalled after the DPCC chairman had questioned the cost of the project and its findings.
Rai said Wednesday that the study, from which data was earlier being made public on an online dashboard, would resume on Thursday.
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