Maintaining Air Quality

This topic covers the composition of dry air, common atmospheric pollutants and their sources, harmful effects on health and the environment, methods to reduce pollution, the importance of the ozone layer, the carbon cycle, and the impact of greenhouse gases on climate change.

1. Volume Composition of Dry Air
  • 🔹 Dry air is a mixture of gases: approximately 78% nitrogen (N₂), 21% oxygen (O₂), and small amounts of argon (Ar), carbon dioxide (CO₂), and other noble gases.
2. Common Atmospheric Pollutants
  • 🔹 Carbon Monoxide (CO): A toxic, colourless, odourless gas formed from incomplete combustion of fuels. It binds to haemoglobin and reduces oxygen transport, potentially causing death.
  • 🔹 Methane (CH₄): A greenhouse gas released from decay of organic matter and livestock farming. Contributes to global warming.
  • 🔹 Nitrogen Oxides (NO and NO₂): Formed by lightning and high-temperature engines. Contribute to acid rain and respiratory issues.
  • 🔹 Sulfur Dioxide (SO₂): Released from burning fossil fuels and volcanic activity. Dissolves in water to form acid rain.
  • 🔹 Ozone (O₃, ground-level): Formed from reactions involving unburnt hydrocarbons and nitrogen oxides under sunlight. Causes eye irritation and breathing difficulties.
  • 🔹 Unburnt Hydrocarbons: From vehicle exhausts, contributing to photochemical smog.
3. Sources of Pollutants
  • 🔹 Incomplete combustion in car engines and industrial processes (CO, unburnt hydrocarbons).
  • 🔹 Lightning and engine combustion (NOx).
  • 🔹 Burning fossil fuels and volcanic eruptions (SO₂).
4. Reactions to Mitigate Pollutants
  • 🔹 Catalytic Converters: Convert harmful gases to safer ones: CO and unburnt hydrocarbons oxidised to CO₂ and H₂O; NOx reduced to N₂.
  • 🔹 Flue Gas Desulfurisation: SO₂ is removed from emissions by reacting with calcium carbonate (CaCO₃) or calcium oxide (CaO) to form calcium sulfite (CaSO₃), which is then oxidised to calcium sulfate (CaSO₄).
5. Effects on Health and Environment
  • 🔹 CO: Interferes with oxygen transport in blood.
  • 🔹 NOx and SO₂: Cause acid rain, damaging crops, aquatic life, and buildings.
  • 🔹 O₃ and hydrocarbons: Lead to smog, causing respiratory problems.
  • 🔹 Methane and CO₂: Trap heat, contributing to climate change and extreme weather.
6. Importance of the Ozone Layer

🔹 Ozone in the stratosphere absorbs harmful UV radiation. CFCs break down ozone by releasing chlorine radicals, leading to ozone depletion and increased UV exposure on Earth.

7. The Carbon Cycle
  • 🔹 Photosynthesis: Removes CO₂ from atmosphere.
  • 🔹 Respiration and Combustion: Release CO₂ into the atmosphere.
  • 🔹 Decomposition: Returns carbon to the environment.
8. Greenhouse Gases
  • 🔹 Carbon Dioxide (CO₂) and Methane (CH₄) are key greenhouse gases that trap heat in Earth’s atmosphere.
  • 🔹 Human activities (e.g., burning fuels, agriculture) increase their levels.
9. Potential Effects of Increased Greenhouse Gases
  • 🔹 Global warming and rising temperatures.
  • 🔹 More frequent extreme weather events.
  • 🔹 Melting polar ice caps and rising sea levels.

  • Oxidation of CO in catalytic converter: 2CO(g) + O₂(g) → 2CO₂(g)
  • CO and NO reaction in catalytic converter: 2NO(g) + 2CO(g) → N₂(g) + 2CO₂(g)
  • Oxidation of unburned hydrocarbon in catalytic converter: 2C₈H₁₈(g) + 25O₂(g) → 16CO₂(g) + 18H₂O(g)
  • Flue gas desulfuration: SO₂(g) + CaCO₃(s) → CaSO₃(s) + CO₂(g)
  • Flue gas desulfuration: CaO(s) + SO₂(g) → CaSO₃(s)
  • Oxidation of CaSO₃: 2CaSO₃(s) + O₂(g) → 2CaSO₄(s)
  • Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
  • Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

  • ⚠️ Thinking air is mostly oxygen – nitrogen is the major component.
  • ⚠️ Believing carbon monoxide is safe because it’s colourless and odourless.
  • ⚠️ Confusing the 'ozone hole' problem with global warming – they involve different processes and gases.
  • ⚠️ Assuming acid rain only affects plants – it also damages buildings and aquatic ecosystems.
  • ⚠️ Mistaking ground-level ozone (pollutant) for protective ozone in the stratosphere.

  • 👉 Remember the correct percentages of gases in dry air.
  • 👉 Link each pollutant to its source, effect, and control method.
  • 👉 Use balanced equations when asked to describe pollutant removal reactions.
  • 👉 Differentiate between good ozone (upper atmosphere) and bad ozone (smog).
  • 👉 Use correct scientific terms when explaining greenhouse effect and carbon cycle.

📚 Further Understanding

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