Delhi‘s SO₂ pollution is being driven largely by coal-fired power plants that are no longer required to install pollution control technology, according to a new analysis by the Centre for Research on Energy and Clean Air (CREA). The report comes one year after the Indian government relaxed emission norms for most coal power plants and found that 81% of estimated sulphur dioxide (SO₂) emissions within a 300-kilometre radius of Delhi-NCR originate from plants exempted from installing Flue Gas Desulphurisation (FGD) systems.

Researchers warn that the situation could worsen as coal-fired electricity generation is expected to rise under a strengthening El Niño, increasing air pollution and associated public health risks in one of the world’s most polluted regions.

Delhi’s SO₂ pollution findings follow the Union Ministry of Environment, Forest and Climate Change’s July 2025 notification, which exempted 78% of India’s coal-fired power plants from mandatory installation of Flue Gas Desulphurization (FGD) systems.

FGDs are pollution-control technologies capable of removing up to 95% of sulphur dioxide emissions before they are released into the atmosphere.

CREA’s analysis found that around 90% of the estimated 154 kilotonnes of SO₂ emissions expected from the analysed generating units in 2025 will come from plants operating without FGD systems.

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Why Sulphur Dioxide Matters

Sulphur dioxide is a major precursor to fine particulate matter (PM2.5), one of the most harmful forms of air pollution.

• Once released into the atmosphere, SO₂ can travel hundreds of kilometres before reacting with other pollutants to form secondary PM2.5 particles.
• These particles penetrate deep into the lungs and bloodstream, surging the risk of respiratory diseases, cardiovascular illnesses, stroke, and premature deaths.
• According to a peer-reviewed study cited by CREA, the energy sector contributes up to 16% of particulate pollution across Delhi-NCR cities.

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Biggest Emitters Still Lack Pollution Controls

The report highlights significant differences between plants equipped with pollution control systems and those operating without them.

• The Mahatma Gandhi Thermal Power Plant, which has functioning FGD systems, emitted only 1,775 tonnes and 2,154 tonnes of SO₂ from two generating units despite producing nearly 3,400-4,000 million units of electricity annually.
• In comparison, the Rajpura Thermal Power Plant, operating without effective SO₂ controls, emitted an estimated 20,851 tonnes and 22,690 tonnes from two comparable units, making it the largest sulphur dioxide emitter in CREA’s assessment.

Overall, Category C plants, which are exempt from mandatory FGD installation, accounted for 125 kilotonnes of SO₂ emissions, compared with only 29 kilotonnes from Category A plants that remain subject to stricter emission requirements.

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Rising Coal Demand Could Worsen Air Quality

The report also links future air quality risks to India’s growing electricity demand.

CREA’s recent El Niño assessment projects higher coal-based power generation as reduced hydropower availability and rising temperatures increase electricity consumption. Without effective sulphur dioxide controls, additional coal generation could significantly raise SO₂ emissions across the Delhi-NCR region.

To address the issue, CREA recommends reinstating mandatory FGD installation for all coal-fired power plants, regardless of category, along with making Continuous Emission Monitoring System (CEMS) data publicly available and regularly disclosing the operational status of FGD units. According to the organization, these measures would substantially reduce sulphur dioxide emissions, limit PM2.5 formation, strengthen regulatory compliance, and improve public health as India’s reliance on coal-fired electricity continues to grow.

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