Secondary pollutants, especially ammonium sulphate, constitute a third of PM2.5 pollution
Relevance
- GS Paper III: Environmental Pollution and Degradation
What are Secondary Pollutants?
- Definition: Pollutants not emitted directly but formed in the atmosphere through chemical reactions between primary pollutants and other atmospheric constituents.
- Example:
- Ammonium sulphate (NH₄)₂SO₄ – formed by reaction of sulphur dioxide (SO₂) and ammonia (NH₃).
- Ammonium nitrate – another significant secondary PM2.5 component.
Key Findings (CREA Study, 2024)
- Ammonium sulphate accounts for ~34% of India’s PM2.5 mass.
- Nationwide average concentration: 11.9 µg/m³.
- Main source of SO₂: Coal-fired thermal power plants (>60% of SO₂ emissions).
- Concentration gradient:
- Within 10 km of coal plants: 15 µg/m³
- Beyond 10 km: 6 µg/m³ (2.5 times less)
- PM2.5 share due to ammonium sulphate:
- Near coal plants: 36%
- Elsewhere: 23%
- NCAP Cities (130):
- Ammonium sulphate share in PM2.5: 20%–43%
- 30% share in 114 cities out of 130
Implications
- Health Hazards:
- Penetrates deep into lungs → respiratory, cardiovascular, and neurological disorders.
- Environmental Impact:
- Contributes to acid rain, visibility reduction, and ecosystem damage.
- Spatial Reach:
- Due to the transboundary nature of air pollution, ammonium sulphate is found even in cities far from emission sources.
Policy & Regulatory Challenges
- FGD (Flue Gas Desulphurisation):
- Mandatory for coal plants.
- Only 8% of plants have installed FGD systems.
- Government reportedly considering relaxing the FGD mandate.
- NCAP Target: Reduce air pollution by 20–30% by 2025–26 in identified cities.
Way Forward
- Enforce FGD Installation
- Strengthen compliance among coal-fired thermal power plants.
- Efficient Fertilizer Use
- Promote balanced fertilization, urea inhibitors, and bio-fertilizers to reduce ammonia emissions.
- Regulatory Compliance Across Sectors
- Ensure strict implementation of SO₂ and NH₃ emission norms in industry, transport, and agriculture.
- Strengthen NCAP
- Include secondary pollutant tracking and expand monitoring infrastructure.
- Regional and Cross-Sectoral Approach
- Address transboundary pollution via inter-state coordination and integrated air-shed management.
Conclusion
The challenge of PM2.5 pollution in India cannot be addressed without tackling the rise of secondary pollutants like ammonium sulphate. Ensuring strict adherence to emission norms, technological upgrades in coal power plants, and sector-wide accountability are essential for effective air quality management and safeguarding public health.
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