Experts Identify Factors Driving Delhi-NCR Winter Pollution; Government Seeks Public Suggestions

By Santu Das

New Delhi: The intensification of winter air pollution in Delhi and the surrounding National Capital Region (NCR) arises not from a sudden increase in emissions alone, but from the synergistic effects of sustained emissions, regional transport of pollutants, and unfavourable meteorological conditions of the Indo-Gangetic Plain (IGP), a government report said.

The report has been prepared following series of meetings between air quality experts, coordinated by a full-time independent technical member of the Commission for Air Quality Management (CAQM) in the NCR and adjoining areas. The meetings were held on January 8, 9, 12 and 13, as per a Supreme Court directive. During the meetings, the experts shared, integrated, and analysed existing research and data from various reports, and deliberated on major sources of pollution.

The IGP covers only 18 per cent of India's land but accommodates 40 per cent of its population. This region is estimated to emit 35 per cent of country's total emissions, making it an emission hotspot.

Northern India, which includes the national capital, faces significant air pollution each winter due to multiple factors, which pose serious health hazards, particularly for the elderly and children.

Two-Phase Pollution Hit For Delhi-NCR

According to this report, winter pollution episodes in the Delhi-NCR region can be broadly divided into two phases.

The first phase typically occurs from mid-October to November, and is largely associated with emissions from agricultural residue burning in neighbouring states, along with decreasing wind speed and a low height for the planetary boundary layer (PBL), which is the Earth's lowest atmospheric layer. Pollutants generated from the agricultural residue burning are transported over long distances and contribute substantially to elevated particulate concentrations across the IGP, including Delhi.

"The second phase generally extends from December to January, and is dominated by extremely adverse meteorological conditions. Very low wind speeds, shallow mixing layers, persistent fog, and reduced solar radiation, severely limit atmospheric dispersion and enhanced secondary aerosol formation. Although emission sources remain relatively constant during this period, except for increased biomass burning for heating, the reduced atmospheric dispersion capacity leads to a pronounced buildup of pollutants, resulting in persistently poor air quality," reads the report, a copy of which was accessed by ETV Bharat.

Toxic Cocktail Of Industrial Gases

According to the report, the atmospheric chemistry within the IGP airshed significantly amplifies particulate pollution through secondary aerosol formation. Sulphur dioxide (SO2) emissions, primarily from coal combustion and brick kilns, undergo oxidation on aerosol surfaces and gas-phase reactions, with hydroxyl (OH) radicals, forming sulphuric acid (H2SO4).

Further, NOx emissions undergo photochemical and nocturnal oxidation to form nitric acid (HNO3). Both H2SO4 and HNO3 react with ammonia (NH3) from agricultural activities and human/animal excreta, to form ammonium sulfate and ammonium nitrate aerosols.

Ammonium chloride, which stays in the atmosphere for a longer time, can also form in a similar way. These acids can also react with dust to form a layer of corresponding salts on the dust particles, the report said.

Volatile organic compounds (VOCs) from vehicular emissions, biomass burning, industries and vegetation, undergo oxidation to form secondary organic aerosol (SOA), as per the report.

Unhelpful Meteorological Conditions

"Winter meteorology significantly restricts pollutant dispersion and often favours secondary aerosol formation. Calm wind conditions, reduced atmospheric mixing height, low temperatures, frequent fog formation, and diminished solar radiation collectively inhibit vertical and horizontal dilution of pollutants. These conditions promote the accumulation and persistence of particulates and gaseous pollutants near the surface," it said.

It has been recognised that Delhi-NCR’s air quality is influenced by both local sources and the transboundary effect of regional movement of pollution within the airshed. A meta-analysis of studies from 2015 to 2025 attributes PM2.5 in Delhi to a mix of primary emissions and secondary particulate formation from sources within NCR and beyond.

The most prominent primary contributors are transport, dust (road, construction and demolition), biomass burning, and industry, including thermal power plants (TPPs), as per the report.

"A small share comes under 'other sources' that include diesel generator sets, crematoria, solvents, natural sources, etc. A significant part of the overall particulate concentration in the air is contributed by secondary particulates that are formed from gases emitted by the primary sources," it stated.

CAQM Invites Public Suggestions

Following the Supreme Court's directive, the CAQM has invited suggestions from the public regarding additional actions that could be taken to address the issues identified in the report, which can be submitted till February 2.

"Pursuant to the Supreme Court's order dated January 6, a panel of identified domain experts deliberated in detail to identify the causes of worsening AQI. They unanimously finalised a report on 'Identification of the causes for worsening AQI in Delhi-NCR'. The CAQM invites the general public to share their suggestions, if any regarding the report. Suggestions may be submitted to the CAQM, latest by February 10," read the notice issued by the CAQM on Monday.

Experts Welcome Public Participation

Speaking to ETV Bharat, environmentalist B S Vohra said, "As an environmentalist, I welcome the government’s move to invite public suggestions on tackling Delhi-NCR’s air pollution crisis. While expert reports have clearly identified the causes, the real challenge lies in effective implementation and accountability."

He asserted that seasonal emergency measures are insufficient for a problem that recurs every year.

"Public participation must lead to transparent, enforceable policies, stronger inter-state coordination, and long-term solutions such as clean energy adoption, sustainable agriculture practices, improved public transport, and strict industrial regulation. Clean air is a fundamental right, and safeguarding it requires sustained political will, scientific planning, and collective responsibility," Vohra said.

Expressing similar views, environmentalist Deepak Ramesh Gaur told ETV Bharat, "This is a positive initiative in the direction towards mitigating air pollution. I welcome this step taken by the CAQM." "There is a need for ending the source of this pollution, which can only be possible through everyone's participation," he added.

Also Read:

1. Delhi-NCR Turns Into A Gas Chamber As Air Quality Slips Into ‘Severe’ Category; Dense Fog, Cold Wave Disrupt Life
2. GRAP-4 Curbs Reimposed In Delhi-NCR As Air Quality Turns 'Severe'
3. Hyderabad’s Air Quality Worsens, Matches Delhi Levels Amid Discrepancies In AQI Measurement
4. Delhi HC Asks Centre Why GST On Air Purifiers Can't Be Lowered