Secondary Particulate Matter Tops Delhi Winter PM2.5 Load at 27%: CAQM Findings

An expert report prepared following a Supreme Court order in the M.C. Mehta vs. Union of India case presents findings on Delhi’s winter PM2.5 sources. The report identifies secondary particulate matter as the top contributor to winter PM2.5 and lists sector-wise contributions, trends since 2016, transboundary share, and recommendations.

CAQM Expert Report on Delhi Winter PM2.5 Load :

Dimension	Key Details
Largest contributor to Delhi winter PM2.5	Secondary particulate matter contributes 27%
Secondary particulate matter	Fine particles formed in the atmosphere through chemical reactions of precursor gases
Precursor gases listed	SO₂, NOx, NH₃ and VOCs
Example of Aerosol	Ammonium nitrate and ammonium sulphate aerosols
Other major winter contributors	Transport 23%; biomass burning 20%; dust 15%; industry including thermal power plants 9%
Dust sub-sources	Road, soil, and construction & demolition sources
Trends	Gradual decline and stable trends are noted in both PM2.5 and PM10 concentrations in Delhi since 2016
Compliance status with NAAQS	There is still a huge gap to meet the annual National Ambient Air Quality Standards (NAAQS)
Transboundary share (PM2.5)	Around two-thirds of Delhi’s PM2.5 originates outside Delhi
Seasonality: winter peak drivers	Pollution peaks during winter mainly due to low wind speed, shallow planetary boundary layer and atmospheric stagnation which traps pollutants
Infrastructure	Augmenting waste-to-energy plants, installing barrier-free toll systems, and rationalizing the Environment Compensation Charge
Transport reforms	Phasing out polluting vehicles, expanding electric/CNG public transport and zero-emission mobility, and addressing congestion with traffic management
Governance	Mandates implementing mandatory annual action plans for NCR states to ensure accountability