UPSC Prelims 2011 Q2: Environment & Ecology – Pollution & Waste Management
Consider the following:
1. Carbon dioxide
2. Oxides of Nitrogen
3. Oxides of Sulphur
Which of the above is/are the emission/emissions from coal combustion at thermal power plants?
- (a) 1 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (d) 1, 2 and 3
Explanation
Emissions from coal combustion at thermal power plants
Burning coal releases gases depending on what the coal contains and how completely it burns.
| Gas | Released? | Source in coal |
|---|---|---|
| 1. Carbon dioxide | Yes | From the carbon in coal, the main combustion product |
| 2. Oxides of Nitrogen | Yes | From nitrogen in the air and in coal, reacting at high flame temperature |
| 3. Oxides of Sulphur | Yes | From sulphur impurities present in most coal |
Why this matters:
| Pollutant | Main environmental effect |
|---|---|
| CO₂ | Greenhouse gas, drives global warming |
| SO₂ / SO₃ | Causes acid rain; needs Flue Gas Desulphurisation (FGD) to control |
| NOx | Causes acid rain and smog; also a greenhouse gas |
This is why thermal power plants are fitted with FGD units and electrostatic precipitators, and why coal quality (ash and sulphur content) matters.
Answer: (d) 1, 2 and 3.
Why each option is right or wrong
- (a) Incorrect. Coal combustion also releases oxides of nitrogen and sulphur, not just carbon dioxide.
- (b) Incorrect. Carbon dioxide is also released; it is in fact the largest-volume emission.
- (c) Incorrect. Oxides of nitrogen are released too, not just carbon dioxide and sulphur oxides.
- (d) CORRECT. Coal combustion releases CO₂, NOx and SOx together.
Key point
Coal combustion at thermal plants releases CO₂ (from carbon), NOx (from nitrogen) and SOx (from sulphur impurities) — all three.
Remember
Coal burning: CO₂, NOx and SOx, all three.
Common mistakes
- Assuming only carbon dioxide comes from burning carbon-based coal.
- Forgetting that air itself supplies nitrogen that becomes NOx at high temperature.
- Not knowing coal naturally contains sulphur impurities, which become SOx.
Exam tip
Burning anything with air at high temperature makes CO₂ and NOx; impurities in the fuel decide the rest. Coal has sulphur, so SOx follows too.
Sources
- Environment (Protection) Rules, 1986, Schedule I (emission standards for thermal power plants)
- NCERT Class XI Chemistry — Environmental Chemistry (air pollutants: oxides of carbon, nitrogen and sulphur)