8.5 Acid deposition

Acid deposition

• Acid deposition: the process by which acid-forming pollutants are deposited on the earth’s surface.
• Increased industrialization have led to rapidly increasing emission of nitrogen and sulfur dioxides which cause acid rain, most prevalent form of acid deposition

Acid rain

• Pure water has pH of 7.0. Rainwater is acidic due to presence of dissolved carbon dioxide which forms weak carbonic acid. Typical pH is 5.6
• Acid deposition is formed when nitrogen or sulfur oxides dissolve in water to form HNO₃, HNO₂, H₂SO₄ and H₂SO₃
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• The sources of nitrogen and sulfur are:
  • Volcanic eruptions
  • Decomposition of vegetation
  • Combustion of fossil fuels
• Go over nitrogen and sulfur cycles which form the acids

Pre- and post-combustion technologies

Pre-combustion methods: refer to techniques used on fuels before their combustion

Post-combustion methods: focus on several complementary technologies to remove sulfur dioxide, nitrogen oxides and other gases from combustion gases before they are released into the atmosphere.