UPSC Prelims 2024 Q90: Environment & Ecology – Pollution & Waste Management
- (a) Locomotives using fossil fuels
- (b) Ships using fossil fuels
- (c) Extraction of metals from ores
- (d) Power plants using fossil fuels
Answer: (d) Power plants using fossil fuels
Explanation
Largest Source of Sulphur Dioxide (SO2) Emissions
| Source | SO2 Contribution | Notes |
|---|---|---|
| Power plants using fossil fuels | Largest source (~73% of US SO2 emissions per EPA) | Especially coal-fired power plants. Coal contains sulphur compounds that oxidize to SO2 during combustion. A major source of acid rain and particulate pollution. |
| Locomotives using fossil fuels | Small fraction | Diesel locomotives emit SO2 but contribution is minor compared to power plants |
| Ships using fossil fuels | Significant but smaller | Heavy fuel oil (bunker fuel) in ships has high sulphur content, but total volume is less than power generation |
| Extraction of metals from ores | Significant in specific contexts | Smelting (especially copper, zinc, lead) releases SO2 when sulphide ores are roasted. But globally/nationally, power plants are larger overall. |
According to the US Environmental Protection Agency (EPA), coal-fired power plants are the single largest source of SO2 emissions.
Answer: (d) Power plants using fossil fuels.
Why each option is right or wrong
- (a) Incorrect. Locomotives (trains) using fossil fuels are a minor source of SO2. They contribute far less than coal-fired power plants which are the dominant source.
- (b) Incorrect. Ships using heavy fuel oil do emit significant SO2 (prompting IMO Sulphur Cap regulations in 2020 limiting marine fuel sulphur to 0.5%), but ships are not the largest source overall - power plants exceed ship emissions.
- (c) Incorrect. Metal extraction (ore smelting) does produce SO2 (especially copper and zinc smelting) and can be a major local source, but globally per EPA data, power plants using fossil fuels are the largest source.
- (d) CORRECT. According to the US Environmental Protection Agency, power plants using fossil fuels (especially coal-fired plants) are the largest source of sulphur dioxide emissions. Coal combustion releases sulphur compounds as SO2.
Key point
Largest SO2 source = Power plants using fossil fuels (especially coal). Coal contains sulphur compounds - combustion converts them to SO2. Per EPA, power plants account for the majority of SO2 emissions. Causes acid rain.
Remember
According to EPA, power plants using fossil fuels (primarily coal-fired power plants) are the largest source of sulphur dioxide (SO2) emissions. Coal combustion releases sulphur as SO2.
Common mistakes
- Thinking metal smelting is the largest SO2 source - while ore smelting (especially copper) is a major local source, power plants (coal combustion) are the largest overall source nationally and globally.
- Overlooking the sulphur content in coal - coal naturally contains sulphur (0.5-4% by weight), which is released as SO2 during combustion in power plants.
- Confusing SO2 sources with CO2 sources - both are primarily from fossil fuel combustion, but SO2 reduction policies focus specifically on coal power plants.
Exam tip
SO2 = mainly from COAL combustion in power plants. Coal has high sulphur content. SO2 causes: acid rain + particulate matter + respiratory diseases. Clean Air Act (USA) specifically targeted SO2 from power plants. Ships addressed by IMO Sulphur Cap (2020).
Sources
- US Environmental Protection Agency (EPA) - Sulphur Dioxide Basics
- NCERT Class 12 Biology - Chapter 16: Environmental Issues (Air Pollution)