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A recent study found that secondary pollutants, particularly ammonium sulphate (formed from sulphur dioxide and ammonia), contribute nearly one-third of India’s PM2.5 pollution. Notably, over 60% of SO₂ emissions come from coal-fired power plants, but only 8% have installed mandatory Flue Gas Desulphurisation (FGD) systems, underlining poor compliance and rising public health risks.

Key Terms Explained

Term	Explanation
PM2.5	Fine particulate matter with a diameter ≤ 2.5 micrometers; penetrates lungs and bloodstream.
Secondary Pollutants	Formed in the atmosphere through chemical reactions between primary pollutants.
Ammonium Sulphate	A secondary pollutant formed from SO₂ and NH₃; major component of PM2.5.
Flue Gas Desulphurisation (FGD)	A technology used in power plants to remove sulphur dioxide from emissions.
SO₂ (Sulphur Dioxide)	A toxic gas emitted mainly from coal combustion; causes acid rain and respiratory issues.

Types of Pollutants

Type	Description	Examples
Primary Pollutants	Directly emitted into the atmosphere in their original form.	CO, SO₂, NOx, plastics, DDT
Secondary Pollutants	Formed by chemical reactions of primary pollutants.	Ozone, PAN, ammonium sulphate

Particulate Pollutants

Type	Particle Size	Common Sources
PM10	≤ 10 micrometers	Dust, pollen, mold
PM2.5	≤ 2.5 micrometers	Vehicle exhaust, power plants, industrial emissions

Measures Taken to Control Air Pollution

Initiative	Objective
National Clean Air Programme (NCAP)	Long-term plan to reduce PM levels by 20–30% in cities by 2024.
Graded Response Action Plan (GRAP)	Real-time pollution response system in Delhi-NCR.
Commission for Air Quality Management (CAQM)	Statutory body to coordinate air quality efforts across North India.
SAFAR Portal	Provides air quality and weather forecasts for public awareness and planning.

Flue Gas Desulphurisation (FGD)

Aspect	Details
What It Is	A process to remove SO₂ from flue gases in thermal plants.
Why Needed	Reduces acid rain, protects health, infrastructure, and environment.
Reagents Used	Limestone (CaCO₃), Lime (CaO), Ammonia (NH₃)
Types of FGD	– Dry Sorbent Injection: Simple, dry process using limestone. – Wet Limestone: Efficient SO₂ removal; produces gypsum. – Seawater-Based: Uses alkaline seawater; cost-effective where standards are relaxed.

In a Nutshell

Use the phrase: **“Power Plants S.A.F.E. – Sulphur Ammonia Form Emissions”

This helps remember:
Sulphur + Ammonia = Form Emissions (i.e., secondary PM2.5),
leading to the need for urgent FGD installation in Power Plants.

Prelims Practice Questions

1. Which of the following are secondary pollutants?
   1. Ozone
   2. Carbon Monoxide
   3. Ammonium Sulphate
   4. PAN (Peroxyacetyl Nitrate)
      Select the correct answer using the code below:
      a) 1, 3 and 4 only
      b) 1 and 2 only
      c) 2, 3 and 4 only
      d) All of the above
2. With reference to PM2.5, consider the following statements:
   1. PM2.5 particles are larger than PM10.
   2. PM2.5 can penetrate deep into lungs and enter the bloodstream.
      Which of the statements is/are correct?
      a) 1 only
      b) 2 only
      c) Both 1 and 2
      d) Neither 1 nor 2
3. Which of the following statements about Flue Gas Desulphurisation (FGD) is/are correct?
   1. FGD helps in reducing nitrogen oxide emissions.
   2. Limestone and ammonia are used in the FGD process.
   3. It is primarily used in coal-fired power plants.
      Select the correct answer using the code below:
      a) 1 and 2 only
      b) 2 and 3 only
      c) 1 and 3 only
      d) 1, 2 and 3

Mains Practice Questions

1. Discuss the significance of Flue Gas Desulphurisation (FGD) systems in combating India’s air pollution crisis. What are the challenges in their implementation?
   (GS3 – Environment)
2. Secondary pollutants now contribute a significant portion of India’s PM2.5 load. Examine the policy and technological gaps in addressing secondary air pollutants in India.
   (GS3 – Environmental Pollution)

Prelims Answers and Explanations

Q. No	Correct Answer	Explanation
1	a) 1, 3 and 4 only	Ozone, PAN, and ammonium sulphate are secondary pollutants. CO is a primary pollutant.
2	b) 2 only	PM2.5 is smaller than PM10 and can enter lungs and bloodstream, making it more harmful.
3	b) 2 and 3 only	FGD removes SO₂ (not NOx), uses limestone and ammonia, and is mainly for coal power plants.