Context:
A recent study by the Centre for Research on Energy and Clean Air (CREA) highlights that nearly one-third of India’s PM2.5 air pollution originates from secondary pollutants, with ammonium sulphate emerging as a major contributor. The findings underline critical gaps in India’s air pollution control strategy, particularly the underestimation of secondary particulate formation.
Key Highlights:
Scientific Basis / Formation Mechanism:
- Secondary pollutants are not emitted directly but are formed in the atmosphere through chemical reactions.
- Ammonium sulphate [(NH₄)₂SO₄] is formed by reactions between:
- Sulphur dioxide (SO₂)
- Ammonia (NH₃)
Sources of Precursors:
- Over 60% of SO₂ emissions in India come from coal-fired thermal power plants.
- Agricultural activities and fertiliser use are major sources of ammonia emissions.
Magnitude and Distribution:
- Secondary pollutants contribute nearly 34% of PM2.5 nationally.
- Ammonium sulphate concentrations are:
- 11.9 µg/m³ (national average)
- 15 µg/m³ within 10 km of coal plants, contributing 36% of PM2.5
- Levels are 2.5 times higher near coal plants, yet the pollutant spreads widely due to trans-boundary movement.
NCAP Cities Impact:
- In 130 NCAP cities, ammonium sulphate contributes 20%–43% of PM2.5.
- 114 out of 130 cities report more than 30% PM2.5 composed of ammonium sulphate.
Regulatory Gaps:
- Only 8% of coal power plants have installed Flue Gas Desulphurisation (FGD) units despite legal mandates.
- The government is reportedly considering scrapping the FGD mandate, raising concerns over policy rollback.
Relevant Prelims Points:
- Issue: Rising contribution of secondary pollutants to PM2.5 pollution.
- Causes:
- High SO₂ emissions from coal-based power plants.
- Ammonia emissions from agriculture.
- Weak enforcement of emission control norms.
- Government Initiatives:
- National Clean Air Programme (NCAP) (does not adequately address secondary pollutants).
- Benefits of Addressing Secondary Pollution:
- Significant reduction in fine particulate concentration.
- Improved public health outcomes.
- Challenges & Impact:
- Policy focus remains on primary pollutants.
- Regulatory delays in installing FGD systems.
- Increased health risks from prolonged PM2.5 exposure.
- Difficulty in controlling pollutants formed post-emission.
Relevant Mains Points:
- Conceptual Clarity:
- PM2.5: Fine particulate matter (<2.5 µm) that penetrates deep into lungs and bloodstream.
- Secondary Pollutants: Formed in the atmosphere from primary pollutants.
- Ammonium Sulphate: Dominant secondary aerosol formed from SO₂ and NH₃.
- FGD: Technology to remove SO₂ from flue gases in thermal power plants.
- Environmental and Health Implications:
- Secondary pollutants worsen chronic respiratory and cardiovascular diseases.
- Spread across regions due to trans-boundary pollution, affecting cities far from emission sources.
- Governance and Policy Concerns:
- Weak enforcement of environmental compliance.
- Inadequate integration of scientific evidence into policy decisions.
- Risk of undermining India’s air quality and climate commitments.
- Way Forward:
- Strict enforcement of mandatory FGD installation in all thermal power plants.
- Efficient fertiliser management to reduce ammonia emissions.
- Penal action against violators of emission norms.
- Regional cooperation to tackle trans-boundary pollution.
- Investment in real-time monitoring of PM2.5 components and precursor gases.
- Explicit inclusion of secondary pollutants in air quality policy frameworks.