Air Pollution

Secondary Pollutants constitute up to third of PM2.5 Pollution

Prelims Only | Enviro & Biodiversity | Mains Paper 3: Conservation, Environmental Pollution & Degradation, Eia

Why in the News?

A recent study by the Centre for Research on Energy and Clean Air (CREA) highlights that secondary pollutants, particularly ammonium sulphate, are responsible for nearly one-third of India’s PM2.5 pollution.

What are Primary Air Pollutants?

  • Definition: Primary air pollutants are directly released into the atmosphere from specific sources like vehicles, coal plants, industries, and biomass burning.
  • Natural and Man-made Origins: They arise from both natural events, such as dust storms, and human activities like fuel combustion.
  • Key Examples:
    • Carbon monoxide (CO) – from incomplete fuel combustion in vehicles and stoves.
    • Sulphur dioxide (SO₂) – from burning sulphur-rich coal, especially in power plants.
    • Nitrogen oxides (NOₓ) – from high-temperature fuel combustion in vehicles and factories.
    • Particulate Matter (PM) – includes soot, dust, smoke, and other visible particles.
    • Volatile Organic Compounds (VOCs) – released from fuel fumes and industrial solvents.
  • Impact: These pollutants are immediately harmful to health and easier to trace to their sources.

About Secondary Air Pollutants:

  • Definition: Secondary pollutants form in the atmosphere through chemical reactions involving primary pollutants and environmental agents like sunlight and water vapour.
  • Formation Factors: Their creation depends on weather, sunlight, and existing pollutants, making them more complex.
  • Key Examples:
    • Ammonium sulphate and nitrate – from SO₂ and NH₃ reacting in the air.
    • Ground-level ozone (O₃) – formed when NOₓ and VOCs react under sunlight.
    • Acid rain components – such as sulfuric and nitric acids.
    • Photochemical smog – a mix of toxic secondary pollutants in urban air.
  • Impact: They contribute heavily to PM2.5 pollution and have long-lasting, widespread effects.

Highlights from CREA’s Study:

  • Ammonium Sulphate Share: This secondary pollutant accounts for 34% of India’s PM2.5, averaging 11.9 μg/m³ nationwide.
  • Source Link: It forms from SO₂ (mainly from coal plants) reacting with ammonia from fertilisers and waste.
  • FGD Compliance: Only 8% of India’s coal plants have installed flue gas desulphurisation (FGD) units, despite regulations.
  • High Exposure Zones: Within 10 km of coal plants, ammonium sulphate levels are 2.5 times higher than in distant areas.
  • NCAP City Impact: In 130 cities, it contributes 20–43% of PM2.5; in 114 cities, the share exceeds 30%.
  • Other Contributors: Ammonium nitrate and similar secondary compounds form up to 50% of PM2.5 in many places.
  • Policy Suggestions: The study urges rapid FGD rollout, fertiliser reform, and strict pollution control enforcement.
[UPSC 2013] Photochemical smog is a resultant of the reaction among-

Options: (a) NO 2 , O 3 and peroxyacetyl nitrate in the presence of sunlight * (b) CO 2 , O 2 , and peroxyacetyl nitrate in the presence of sunlight (c) CO, CO 2 , and NO 2 at low temperature (d) high concentration of NO 2 , O 3 and CO in the evening

 

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