India emits the highest amount of sulphur dioxide (SO₂) in the world and is the second-largest emitter of ammonia (NH₃), according to a new analysis by the Centre for Research on Energy and Clean Air. The report warns that these gases are forming toxic secondary pollutants, particularly ammonium sulfate, which accounts for nearly one-third of India’s deadly PM2.5 air pollution.
Published on Friday, the report by Manoj Kumar and Rosa Giriens examines air quality data across 130 Indian cities under the National Clean Air Programme (NCAP). While NCAP focuses largely on PM10, the findings suggest that secondary particles are a major but overlooked source of PM2.5 across India.
The CREA analysis finds that cities with the highest concentrations of ammonium sulfate – a compound formed when SO₂ reacts with ammonia in the atmosphere – include Patna (22.5 µg/m³), Muzaffarpur (21.7 µg/m³), Kolkata (21.7 µg/m³), Howrah (21.7 µg/m³), and Varanasi (21.6 µg/m³).
In contrast, cities with the lowest concentrations are Srinagar (3.9 µg/m³), Thoothukudi (5.9 µg/m³), Madurai (6.2 µg/m³), Trichy (6.7 µg/m³), and Kohima (6.9 µg/m³).
The analysis identifies SO₂ emissions from coal-fired thermal power plants (TPPs) as the biggest contributor to ammonium sulfate formation, with these plants accounting for over 60 percent of India’s SO₂ output. This makes the installation of flue gas desulfurisation (FGD) systems at TPPs a critical intervention.
However, Newslaundry had earlier reported on the union power ministry seeking repeated extensions on the implementation of FGD systems.
The analysis suggests that ammonium sulfate concentration is 2.5 times higher within 10 km of coal-fired thermal power plants (15 µg/m³) compared to areas beyond 10 km (6 µg/m³). While the contribution to PM2.5 is 36 percent near TPPs, it remains significant at 23 percent in other areas, indicating both local and transboundary impacts of SO₂ emissions.
According to the analysis, NCAP currently prioritises PM10 and primary pollutant sources, but the new findings suggest the urgent need to shift the focus toward controlling emissions of precursor gases such as sulphur dioxide and ammonia, which lead to the more harmful and widely prevalent secondary PM2.5.
“The current NCAP primarily focuses on reducing PM10 and addresses coarse dust and visible pollution. However, PM2.5 is far more toxic to human health because it penetrates deeper into the lungs and enters the bloodstream, increasing the risk of heart disease, lung disorders, and premature death. Despite this, PM2.5 has not received adequate focus in many clean air action plans, and the role of precursor gases in forming PM2.5 has been largely overlooked,” the analysis stated.
Kumar is also one of the experts guiding Newslaundry’s campaign to tackle air pollution.
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