India's Air Pollution Crisis | 01 Jul 2025

Source: TH 

Why in News? 

A recent study revealed that secondary pollutants, particularly ammonium sulphate (sulphur dioxide (SO₂) + ammonia (NH₃)), contribute to nearly one-third of India’s PM2.5 pollution highlighting the urgent need for air pollution controls. 

• Over 60% of SO₂ emissions in India come from coal-fired power plants, yet only 8% have installed mandatory Flue Gas Desulphurisation (FGD) systems, key to controlling secondary PM2.5 pollution. 

What are Key Facts Regarding Air Pollution? 

• About: Air pollution is caused by chemical, physical, or biological substances including noise that disturb the air’s natural composition, mainly from combustion, vehicles, industries, and fires. 
  • Key pollutants like PM, CO, O₃, NO₂, and SO₂ are associated with serious respiratory diseases and higher mortality rates. 
• Types of Pollutants: They are divided into two types based on how they exist in the environment after being released. 
  • Primary Pollutants: They remain in the same form as they were released into the environment, such as DDT, plastic, carbon monoxide (CO), carbon dioxide (CO₂), and oxides of nitrogen and sulphur. 
  • Secondary Pollutants: They are produced through reactions between primary pollutants. For instance, peroxyacetyl nitrate (PAN) is formed by the interaction of nitrogen oxides and hydrocarbons. 

• Particulate Pollutants: Particulate pollutants (also called particulate matter or PM) are tiny solid or liquid particles suspended in the air that can be harmful to human health and the environment. 
  • PM10: Particles with a diameter of 10 micrometers or less. E.g., dust, pollen, mold etc. 
  • PM2.5: Particles with a diameter of 2.5 micrometers or less. E.g., Vehicle emissions, industrial processes, power plants etc.  
• Measures Taken to Control Air Pollution:  
  • National Clean Air Programme 
  • Graded Response Action Plan (for Delhi) 
  • New Commission for Air Quality Management 
  • System of Air Quality and Weather Forecasting and Research (SAFAR) Portal 

What is Flue Gas Desulphurisation (FGD)? 

• About: Flue Gas Desulphurisation (FGD) is a process that removes sulphur dioxide (SO₂) from flue gas emitted during the combustion of fossil fuels like coal and oil. 
  • It is mainly used in coal-fired power plants, using reagents such as limestone (CaCO₃), lime (CaO), and ammonia (NH₃). 
• Purpose: Coal contains sulphur, and its combustion releases SO₂, causing acid rain. FGD cleans exhaust gases, preventing acid rain and protecting crops, infrastructure, soil, and aquatic ecosystems. 
• Types: FGD systems are mainly of three main types: 
  • Dry Sorbent Injection: It involves using limestone to remove SO₂ before it reaches dust control systems and is known for its simplicity and dry operation. 
  • Wet Limestone System: It is ideal for large-scale applications, offering high SO₂ removal efficiency and producing useful gypsum as a byproduct. 
  • Seawater-Based System: It uses alkaline seawater to cut SO₂ emissions by 70–95%, suitable where emission standards are relaxed and initial costs are low.