Why in news?

The Union Environment Ministry has defended its recent order revising SO₂ emission norms for thermal power plants.

It clarified that exempting many coal- and lignite-based plants from mandatory flue gas desulphurization retrofits was based on evidence, emission trends, and sustainability needs.

The ministry stated there was no significant difference in ambient SO₂ levels between cities with or without such technology, countering claims of regulatory dilution.

What’s in Today’s Article?

• Sulphur dioxide: A Significant Air Pollutant 
• India and Sulphur dioxide Emission
• Key Highlights of the Revised SO₂ Norms

Sulphur dioxide: A Significant Air Pollutant

• Sulphur dioxide (SO₂) is a major air pollutant primarily released from coal-fired power plants and other fossil fuel combustion.
• It poses serious health and environmental risks. As a respiratory irritant, SO₂ can trigger asthma, bronchitis, and other lung diseases.
• It is also a precursor to PM2.5, fine particulate matter linked to heart attacks, strokes, and premature death.
• Beyond human health, SO₂ contributes to acid rain, harming soil quality, aquatic ecosystems, and plant life.
• Its combined direct and indirect effects make SO₂ control vital for public health, environmental protection, and climate resilience.

India and Sulphur Dioxide Emission

• India is the world's largest emitter of sulfur dioxide (SO2), primarily due to its heavy reliance on coal for power generation.
  • In 2022, India was the world’s largest emitter of sulphur dioxide (SO₂), contributing over 20% of global anthropogenic emissions due to its coal-heavy power sector.
  • India topped SO₂ emissions from electricity generation at 6,807 kilotonnes, far ahead of countries like Turkey, Indonesia, South Africa, and Saudi Arabia.
• While SO2 levels have shown a declining trend, they remain high in certain regions like the Indo-Gangetic Plain, central and eastern India.

The Revised SO₂ Norms

• The Union Environment Ministry has defended its order revising sulphur dioxide (SO₂) emission norms for thermal power plants, countering claims of regulatory dilution.
• The ministry cited research from IIT Delhi, NEERI, and others, noting no major public health concern from current ambient SO₂ levels and highlighting that sulfate aerosols from SO₂ contribute minimally to PM2.5 pollution.
• FGD systems, which cut sulphur dioxide (SO₂) emissions from coal plants, were made mandatory in 2015.
• Yet, only 8% of India’s 180 coal plants have installed them so far, with delays attributed to high costs and limited availability.
• Rationale Behind the Policy Shift
  • According to the Ministry, India’s ambient SO₂ levels have been declining, with 2023 measurements across 492 cities showing compliance in all but two.
  • Indian coal naturally has low sulphur content, leading to relatively lower SO₂ emissions.
  • Studies have found no major difference in SO₂ concentrations between cities with and without FGD-fitted plants.
  • The Ministry noted that eliminating all SO₂ emissions would only marginally improve particulate matter (PM2.5) levels, while retrofitting all plants would cost around ₹2.54 lakh crore — a disproportionately high investment for limited environmental benefit.
• Key Highlights of the Revised SO₂ Norms
  • Category A Plants (11% of Total Units): Located within 10 km of Delhi-NCR or cities with over 1 million population. Must comply with SO₂ norms by end-2027.
  • Category B Plants (11% of Total Units): Located within 10 km of critically polluted areas or non-compliant cities. Norms apply case-by-case based on expert committee recommendations.
  • Category C Plants (78% of Total Units): Located outside A and B zones. Fully exempted from SO₂ norms but must meet stack height criteria.
  • Plants Retiring Before 2030: Exempt from SO₂ norms if they submit an undertaking. Those operating beyond 2030 must pay ₹0.40 per unit as compensation.
  • Scientific Basis: Revision backed by studies from IIT Delhi, NEERI, and CPCB, showing no significant difference in SO₂ levels between areas with and without FGD retrofits.
  • Cost Consideration: Estimated ₹2.54 lakh crore required for FGD retrofitting across India, prompting focus on high-impact areas only.

Global Standards Context

• The Ministry also highlighted that India’s annual SO₂ standard (50 micrograms/cubic metre) is stricter than those of countries like Japan and Australia.
• Given these factors, the revised norms aim to balance public health priorities with economic and operational realities, focusing regulatory efforts where they are most needed.