Secondary particulate matter and Delhi winter pollution

Study commissioned by the Commission for Air Quality Management (CAQM) for the National Capital Region.

Prepared following Supreme Court directions (January 6) to identify major causes of worsening AQI.

It is a meta-analysis (synthesis of existing studies), not a fresh field study.

Secondary particulate matter: 27% (largest contributor)

Transport emissions: 23%

Biomass burning: 20%

• Includes crop residue burning and municipal solid waste burning

Dust: 15%

Industry: 9%

Primary particulate matter is directly emitted (e.g., NOx, SO₂, VOCs).

Secondary particulate matter forms in the atmosphere due to chemical reactions involving:

• Sulphur dioxide (SO₂)

• Nitrogen oxides (NOx)

• Ammonia (NH₃)

SO₂ (primarily from coal combustion and brick kilns) → oxidised to sulphuric acid (H₂SO₄)

NOx → oxidised to nitric acid (HNO₃)

H₂SO₄ + NH₃ → ammonium sulphate aerosols

HNO₃ + NH₃ → ammonium nitrate aerosols

Ammonia plays a key enabling role in secondary PM formation.

25%–60% of PM2.5 consists of sulphates and nitrates formed this way.

Nearly 80% of ammonia over India comes from fertilisers and livestock excreta.

“The total NH3 emission in India is found to be 10.54 Tg in 2022, where synthetic fertilizer application and livestock excreta are the dominant contributors with 4.9 Tg per year and 3.2 Tg per year respectively,”

CAQM acknowledged variation in methodologies across earlier studies.

A new emissions inventory and source apportionment study is planned with:

• Automotive Research Association of India

• Indian Institute of Technology Delhi

• The Energy Resources Institute

• Indian Institute of Tropical Meteorology

Base year: 2026

In late 2024, CAQM suspended the Decision Support System (DSS) due to poor forecasting accuracy for sudden AQI deterioration.

Commission for Air Quality Management is a statutory body.

Established under the Commission for Air Quality Management in National Capital Region and Adjoining Areas Act 2021.

Objective: To address air pollution issues impacting Delhi-NCR and adjoining areas.

Better coordination, research, identification, and resolution of air quality problems.

Prevention and control of air pollution affecting:

• National Capital Territory (NCT) of Delhi

• NCR and adjoining areas

Ensures inter-state coordination on air quality management.

Covers:

• Delhi

• Punjab

• Haryana

• Rajasthan

• Uttar Pradesh

Focus on sources that impact air quality of Delhi-NCR, even if located outside Delhi.

Restrict or prohibit activities influencing air quality.

Conduct investigations and research on environmental pollution.

Prepare codes, guidelines, and standards for air pollution control.

Issue binding directions, including:

• Inspections

• Regulations

• Compliance orders

All orders and directions of CAQM are legally binding.

Directly accountable to Parliament.

Chairperson

• Government official of rank of Secretary or Chief Secretary.

• Tenure: 3 years or till 70 years of age, whichever is earlier.

Ex-officio members (5)

• Chief Secretaries or Environment Secretaries of:

  • Delhi

  • Punjab

  • Haryana

  • Rajasthan

  • Uttar Pradesh

Full-time members

• Three technical members.

Non-government members

• Three members from NGOs.

Technical representation from institutions

• Central Pollution Control Board

• Indian Space Research Organisation

• NITI Aayog

Statement 1 is incorrect: secondary PM forms in the atmosphere, not emitted directly.

Statements 2 and 3 are correct.