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**Summary:**

A study by the Centre for Research on Energy and Clean Air (CREA) reveals that secondary pollutants, particularly ammonium sulphate, contribute significantly to India’s PM2.5 pollution, accounting for approximately one-third of the total. The ammonium sulphate results from the reaction of sulphur dioxide (SO2) and ammonia (NH3) in the atmosphere, with coal-fired power plants being a major source of SO2. The study highlights the trans-boundary nature of this pollution, impacting areas both near and far from emission sources. It emphasizes the need for stricter implementation of flue gas desulphurisation (FGD) systems in coal plants and better pollution control measures across all sectors to combat secondary PM2.5 pollution.

**News Article:**

**Secondary Pollutants Account for a Third of India’s PM2.5 Pollution, Study Finds**

**New Delhi, June 28, 2025** – A new study by the Centre for Research on Energy and Clean Air (CREA) has revealed that secondary pollutants, particularly ammonium sulphate, are responsible for nearly one-third of India’s hazardous PM2.5 pollution. The study, released today, highlights the significant contribution of atmospheric reactions, specifically the combination of sulphur dioxide (SO2) and ammonia (NH3), to the country’s air quality crisis.

Ammonium sulphate, a secondary pollutant, forms when SO2 emitted primarily from coal-fired thermal power plants reacts with ammonia in the atmosphere. The CREA analysis, using satellite data and modelling, found a nationwide average concentration of 11.9 μg/m3 of ammonium sulphate, making up about 34% of PM2.5 mass.

“This widespread presence of ammonium sulphate is a concern in both big and small cities, due to its ability to travel across borders via air,” said a CREA representative.

The report emphasizes the need for urgent action, particularly the implementation of flue gas desulphurisation (FGD) systems in coal-fired power plants. While mandatory, only a small fraction (8%) of Indian plants have installed these systems, raising concerns about regulatory enforcement. Concentrations of ammonium sulphate are significantly higher near coal plants.

Across the 130 cities under the National Clean Air Programme (NCAP), ammonium sulphate contributes between 20% and 43% of PM2.5 levels. The study warns that alongside SO2 reduction, comprehensive pollution control measures are needed across all sectors to tackle the increasing problem of secondary PM2.5 pollution.

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