The expert report was prepared following a Supreme Court order related to the M.C. Mehta vs. Union of India case.

Key findings of the Report

• Secondary Particulate Matter: Largest contributor (27%) to Delhi’s winter pollution. 
  • Secondary Particulate Matter are fine particles formed in the atmosphere through chemical reactions of precursor gases like SO₂, NOx, NH₃ and VOCs, e.g., ammonium nitrate and ammonium sulphate aerosols.
• Other Major Winter Contributors: Transport is the largest primary source at 23%, followed by biomass burning (20%). 
  • Dust accounts for 15% (comprising road, soil, and construction & demolition sources), while industry including thermal power plants contributes 9%.
• Trends in PM2.5 and PM10: A gradual decline and stable trends are noted in both PM2.5 and PM10 concentrations in Delhi since 2016
  • However, there is still a huge gap to meet the annual National Ambient Air Quality Standards (NAAQS).
• Transboundary Pollution: Around two-thirds of Delhi’s PM2.5 originates outside Delhi.
• Seasonality: Pollution peaks during winter mainly due to low wind speed, shallow planetary boundary layer and atmospheric stagnation which traps pollutants, rather than sudden emission spikes.