Source apportionment of air pollution in Delhi reveals that no single sector is overwhelmingly responsible. How should this inform multi-sectoral policy design for achieving NCAP targets?

The CAQM's Supreme Court-mandated report by 33 domain experts, based on a meta-analysis of source apportionment studies (2015–2025), confirms PM2.5 as Delhi's dominant pollutant but attributes it to no single villain [1]. This diffused profile demands that NCAP shift from episodic, sector-blaming action to a calibrated multi-sectoral portfolio.

A diffused and diagnostic source profile

• Winter PM2.5 shares: secondary particulates 27%, transport 23%, biomass burning 20%, dust 15%, industry and thermal power 9% — no source exceeds one-third [1].
• The largest share is not directly emitted: secondary particulates form from gaseous precursors (SO₂, NOₓ, NH₃), so particulate-only controls miss the biggest contributor [1].
• The report also highlights transboundary movement of pollutants across the airshed, alongside local emissions [1].
• Urgency persists: 2025 was Delhi's cleanest year since 2018, yet PM10 (198 µg/m³) and PM2.5 (97 µg/m³) stayed far above NAAQS [3].

Implications for policy design

• Proportionate simultaneity: allocate NCAP effort roughly in proportion to source shares; disproportionate political focus on stubble burning (20%) cannot deliver the targeted 40% PM10 reduction/NAAQS compliance by 2025-26 [4].
• Precursor-led regulation: emission norms for NOₓ, SO₂ and ammonia across thermal power, industry and agriculture, to attack secondary particulates at source [1].
• Airshed governance, not municipal boundaries: use CAQM's statutory mandate to coordinate Delhi, Haryana, Punjab, Rajasthan and Uttar Pradesh as one unit [2].
• Year-round structural action over emergency GRAP curbs — public transport expansion, construction-dust protocols, clean cooking fuel.
• Evidence infrastructure: the 46 additional monitoring stations approved for the region should feed periodic, city-specific apportionment to redirect funds [1].

Delhi's air is a shared commons polluted by many small hands, and its remedy must be equally distributed. A precursor-focused, airshed-wide and continuously monitored NCAP — with citizens as participants rather than only sufferers — can convert marginal annual gains into durable compliance, giving substance to the right to clean air under Article 21.