CAQM Report on Delhi Winter Air Pollution

Jan. 23, 2026

Why in the News?

A recent synthesis report by the Commission for Air Quality Management has identified secondary particulate matter as the single largest contributor to Delhi’s winter air pollution.

What’s in Today’s Article?

Delhi’s Air Pollution (Background, Key Findings of CAQM Report, Secondary Particulate Matter, Ammonia, Policy Implications)

Background: Understanding Delhi’s Air Pollution Challenge

Delhi and the National Capital Region (NCR) experience severe air pollution every winter due to a combination of meteorological, geographical, and emission-related factors.
Low wind speeds, temperature inversion, and high moisture levels trap pollutants close to the ground, leading to persistent smog episodes.
Over the years, multiple studies have attempted to identify dominant pollution sources, but variations in methodology often led to conflicting conclusions, complicating policy responses.
To address this gap, the Commission for Air Quality Management (CAQM) undertook a meta-analysis of existing scientific studies to present a consolidated and evidence-based assessment of pollution sources affecting Delhi during the winter months.

Key Findings of the CAQM Meta-Analysis

The CAQM synthesis report presents a clear source-wise contribution to winter air pollution in Delhi:

The report clarifies that no new pollution sources have been identified.
Instead, it harmonises findings from earlier studies that used differing analytical techniques, thereby offering a unified scientific basis for policymaking.

Secondary Particulate Matter as the Dominant Pollutant

Secondary particulate matter is not emitted directly from sources such as vehicles or factories.
Instead, it forms in the atmosphere through chemical reactions involving primary pollutants like sulphur dioxide (SO₂), nitrogen oxides (NOx), and ammonia (NH₃).
These reactions lead to the formation of sulphates and nitrates, which together constitute nearly 25-60% of PM2.5 concentrations during winter.
Fine particles of this nature are especially harmful as they penetrate deep into the lungs and bloodstream, aggravating respiratory, cardiovascular, and ophthalmic diseases.
The CAQM report emphasises that focusing solely on visible emission sources may be insufficient without addressing these secondary chemical processes.

Role of Ammonia in Pollution Formation

Ammonia plays a critical enabling role in the formation of secondary particulate matter.
Studies cited in the report indicate that nearly 80% of ammonia emissions in India originate from agricultural activities, particularly fertiliser use and livestock excreta.
In the atmosphere, ammonia reacts with sulphuric and nitric acids, formed from SO₂ and NOx emissions, to produce ammonium sulphate and ammonium nitrate aerosols.
These compounds significantly increase PM2.5 levels during winter, underscoring the rural-urban linkage in Delhi’s air pollution problem.

Transport, Biomass Burning, and Dust Contributions

Transport emissions remain the second-largest contributor, reflecting the high vehicle density, fossil fuel use, and congestion in Delhi-NCR.
Biomass burning, including crop residue burning in neighbouring States and municipal waste burning, contributes one-fifth of winter pollution, particularly during peak burning periods.
Dust pollution arises from unpaved roads, construction activities, and resuspension of settled particles.
Although often overlooked, dust contributes substantially to particulate load, especially under stagnant winter conditions.

Policy Implications and Future Studies

It highlights the need for multi-sectoral interventions, including agriculture, transport, energy, and waste management.
It calls for integrated emission inventories and updated source apportionment studies, with 2026 as the proposed base year.
The findings will support improved Air Quality Early Warning Systems and Decision Support Systems, which had earlier faced limitations in forecasting pollution spikes accurately.

A more science-driven approach is expected to improve both preventive and responsive policy measures.

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