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Oxides of sulphur and nitrogen as pollutants

Short answer

SO2 and NOx are air pollutants because they form acid rain (H2SO4, HNO3), cause respiratory diseases (asthma, bronchitis), contribute to photochemical smog, damage plants and materials, and N2O is a greenhouse gas that also depletes ozone.

Why are the oxides of sulphur and nitrogen assumed as air pollutants?

Oxides of sulphur (SO₂, SO₃) and nitrogen (NO, NO₂, N₂O) are major air pollutants because:

  1. Sources are large: SO₂ is produced by burning coal and oil, smelting of sulphide ores and brick kilns; NOx by vehicle engines and power plants (N₂ + O₂ → 2NO at high temperature).
  2. Acid rain: they form H₂SO₄ and HNO₃ in the air (2SO₂ + O₂ + 2H₂O → 2H₂SO₄; 4NO₂ + O₂ + 2H₂O → 4HNO₃), which acidify lakes and soils and damage forests and buildings.
  3. Health effects: they irritate the eyes, throat and lungs, causing asthma, bronchitis and reduced lung function; NO₂ is toxic.
  4. Smog: NO₂ with hydrocarbons in sunlight forms photochemical smog and ground-level ozone; SO₂ with smoke forms classical smog.
  5. Damage to plants and materials: they bleach leaves and corrode metals, stone, paper and textiles.
  6. N₂O is also a greenhouse gas and depletes ozone in the stratosphere.

✓ Answer checked by Claude Opus 5.5 (high effort)

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