Secondary particulate matter is the top cause of Delhi winter’s pollution
Yes, according to a January 2026 report by the Commission for Air Quality Management (CAQM), secondary particulate matter (PM) is the single largest contributor to Delhi’s winter air pollution, accounting for 27% of the total pollution load.
Key Findings from the 2026 CAQM Report
A meta-analysis of studies from 2015–2025 identifies the following major contributors to Delhi's winter air pollution:
- Secondary Particulate Matter (27%): These fine particles (PM2.5) are not emitted directly but form in the atmosphere through chemical reactions of precursor gases like sulfur dioxide (SO2),nitrogen oxides (πππ₯), and ammonia (ππ»3).
- Transport (23%): Identified as the largest primary source of emissions.
- Biomass Burning (20%): Includes municipal solid waste burning, residential heating, and crop residue burning.
- Dust (15%): Originates from roads, soil, and construction and demolition activities.
- Industry (9%): Includes emissions from thermal power plants and various industrial processes.
Role of Chemical Precursors
The report highlights that nearly 25% to 60% of total winter PM2.5 is composed of secondary aerosols like ammonium sulfate and ammonium nitrate. Ammonia (ππ»3), largely from agricultural activities and livestock, plays a critical role by reacting with industrial and vehicular emissions (ππ2
and ππx) to form these harmful fine particles.
Seasonal Variation
The dominance of pollutants shifts with the seasons:
- Winter: Secondary particulate matter is the top cause due to stagnant atmospheric conditions that trap pollutants.
- Summer: Dust emerges as the largest contributor at 27%, while secondary particulate matter drops to 17%.
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