Secondary Pollutant

Published on 12 Nov 2025

• A recent study from the Centre for Research on Energy and Clean Air (CREA) reveals that secondary pollutants are responsible for nearly one-third of India's fine particulate matter (PM2.5) pollution.

• Primary pollutants are released directly from sources like cars and factories. 

• When these pollutants rise into the atmosphere and react with other gases and water vapor, they form more complex and harmful particles known as secondary pollutants.

• The study identifies ammonium sulphate, which forms from the reaction between sulphur dioxide (from coal plants) and ammonia, as a major secondary pollutant. 

• This one compound accounts for about 34% of India's PM2.5.

• The primary source of the pollution-causing sulphur dioxide is coal-fired power plants. 

• Although it is mandatory for these plants to install flue gas desulphurisation (FGD) systems to clean their emissions, only about 8% of Indian plants have done so.

Keywords:

Secondary Pollutant Air pollution Centre for Research on Energy and Clean Air CREA particulate matter PM2.5 ammonium sulphate coal-fired power plants flue gas desulphurisation FGD