Atmospheric pollutants from burning fuels
Burning fossil fuels emits carbon dioxide (greenhouse gas — see C9.3) plus several other pollutants that harm health and the environment.
1. Carbon monoxide CO
- Source: incomplete combustion of hydrocarbons (insufficient O₂).
- Toxic — binds to haemoglobin (~300× more strongly than O₂), reducing oxygen transport.
- Colourless, odourless — silent killer.
- Symptoms: headache, dizziness, unconsciousness, death.
Equation: 2CH₄ + 3O₂ → 2CO + 4H₂O.
2. Carbon (soot) particulates
- Also from incomplete combustion.
- Causes:
- Respiratory disease (asthma, bronchitis).
- Global dimming (block sunlight).
- Blackens buildings.
3. Sulfur dioxide SO₂
- Source: combustion of sulfur impurities in fossil fuels (especially coal, diesel).
- S + O₂ → SO₂.
- Effects:
- Acid rain (SO₂ + H₂O + ½O₂ → H₂SO₄). Damages buildings, forests, lakes.
- Respiratory problems.
4. Oxides of nitrogen NOₓ (NO, NO₂)
- Source: at high temperatures, atmospheric N₂ reacts with O₂ in car engines and power stations.
- N₂ + O₂ → 2NO (then 2NO + O₂ → 2NO₂).
- Effects:
- Acid rain (HNO₃).
- Photochemical smog.
- Respiratory problems.
Note: nitrogen does NOT come from the fuel itself but from the air drawn in for combustion.
Reducing pollutants
- Catalytic converters in cars: convert CO + NOₓ → CO₂ + N₂. (Doesn't reduce CO₂ though!)
- Desulfurisation (flue-gas scrubbing) at power stations.
- Use cleaner fuels (natural gas instead of coal).
- Improve combustion efficiency to minimise CO/soot.
- Renewable energy to avoid combustion altogether.
✦Worked example
A car emits CO, NOₓ and CO₂. Explain the source of each.
- CO: incomplete combustion of fuel.
- NOₓ: high-temperature reaction of N₂ + O₂ in the engine.
- CO₂: complete combustion of fuel.
⚠Common mistakes
- Saying NOₓ comes from the fuel — it comes from the air at high T.
- Confusing CO with CO₂. Both pollutants but with different mechanisms (toxic vs greenhouse).
- Saying acid rain is a greenhouse effect issue — it's a separate problem from SO₂ and NOₓ.
- Forgetting catalytic converters reduce some pollutants but don't eliminate all.
Links
Builds on C7.3 (combustion). Connects to C9.3 (CO₂ greenhouse effect) and C10.1 (sustainable energy).
AI-generated · claude-opus-4-7 · v3-deep-chemistry