Secondary Pollutants Now a Major Contributor to India’s PM2.5 Burden

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• A recent study has revealed that Secondary Pollutants are responsible for nearly one-third of India’s fine particulate matter (PM2.5) pollution.

Understanding Secondary PM2.5 Pollution in India

• Particulate matter smaller than 2.5 microns (PM2.5) is one of the most hazardous components of air pollution, responsible for serious respiratory and cardiovascular diseases. 
• Traditionally, primary pollutants such as soot and dust from burning fossil fuels have been considered the chief contributors to PM2.5 levels. 
• However, new research highlights the rising significance of secondary pollutants, especially ammonium sulphate, as key components of India’s air pollution challenge.

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Primary and Secondary Pollutants: A Distinction

• Primary pollutants originate directly from emission sources such as vehicle exhaust, coal-fired power plants, and biomass burning. 
• In contrast, secondary pollutants are formed when primary pollutants react with each other or with atmospheric elements like water vapour and sunlight. 
• These reactions lead to the formation of complex particles like ammonium sulphate and ammonium nitrate, which can be equally or more harmful.

Key Findings of the CREA Study

• According to a study by the Centre for Research on Energy and Clean Air (CREA), secondary pollutants, especially ammonium sulphate, constitute up to 34% of India’s PM2.5 mass. 
• This widespread presence was identified using satellite-based imagery and atmospheric modelling.
• Nationwide Impact:
  • The average ammonium sulphate concentration across India was found to be 11.9 μg/m³.
  • These concentrations are not limited to cities near pollution hotspots, but extend nationwide due to the transboundary nature of air pollution.
• Coal Plants as a Major Source:
  • Over 60% of India’s sulphur dioxide (SO₂) emissions, the precursor to ammonium sulphate, are linked to coal-fired thermal power plants. These facilities become the primary driver of secondary PM2.5 formation.
• Higher Concentration near Coal Plants:
  • Within 10 km of coal power plants, ammonium sulphate concentrations were 2.5 times higher (15 μg/m³) compared to areas beyond that range (6 μg/m³). 
  • Near these plants, it accounts for 36% of PM2.5 pollution, whereas even distant areas reported a significant 23% contribution.

Status of Emission Control Measures

• Although it is mandatory for Indian coal thermal plants to install Flue Gas Desulphurisation (FGD) systems to reduce SO₂ emissions, compliance has been poor; only about 8% of such plants have installed the required units. 
• Further, reports suggest that the government is contemplating rolling back this requirement, which could severely undermine efforts to reduce secondary PM2.5.

Impact Across NCAP Cities

• The findings are particularly significant for the 130 cities identified under the National Clean Air Programme (NCAP). 
• These cities are mandated to reduce pollution by 20-30% by 2025-26, but face an uphill task given the high concentration of secondary pollutants.
• Concentration Levels:
  • PM2.5 levels due to ammonium sulphate in these cities ranged from 3.9 to 22.5 μg/m³.
• Widespread Presence:
  • In 114 out of the 130 NCAP cities, ammonium sulphate made up more than 30% of the total PM2.5 burden.
• Combined Effect:
  • Including ammonium nitrate, secondary pollutants could constitute up to 50% of PM2.5 pollution in urban areas.

Strategies for Mitigation

• To address the growing burden of secondary pollutants, a multipronged strategy is required:
• Strict Implementation of Emission Norms:
  • Enforcement of FGD installation in coal power plants must be non-negotiable. Regulatory rollback would be counterproductive to public health goals.
• Agricultural and Industrial Reforms:
  • Efficient fertiliser management can reduce ammonia emissions, which are a key reactant in forming secondary particles.
• Source-Specific Action:
  • Pollution mitigation efforts must target both direct emission sources and precursor gases like SO₂ and NH₃.
• Transboundary Cooperation:
  • Given the dispersal nature of secondary pollutants, regional coordination between states is essential for effective air quality management.
• Real-Time Monitoring and Research:
  • Investments in air quality monitoring infrastructure and continuous data-driven research are needed to identify evolving patterns in pollution dynamics.

Source : TH