---
title: "Short note: SO2 emission and impact"
subject: "Energy Environment and Society"
chapter: 4
key: "semester_7/energy_environment_and_society:so2-emission-impact"
source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/so2-emission-impact
site: BCT Engineering
---

# Short note: SO2 emission and impact

Energy Environment and Society · Chapter 4: Environmental Impact of Energy sources

- Asked in: 2071 Shrawan, 2 marks
- Video: [Sulfur Oxides (SOx) Generation and Environmental Impacts](https://www.youtube.com/watch?v=ObG88Rq7SRg) — Future Energy & Technology
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/so2-emission-impact
- Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-4

## Question

Write a short note on SO2 emission and its impact.

## Short answer

SO₂ is a pungent gas from burning sulphur-containing fuels like coal and diesel. It irritates eyes and lungs, causes acid rain that damages ecosystems and buildings, forms PM2.5, and harms vegetation. Control includes low-sulphur fuel, flue gas desulphurisation, and switching to clean energy.

## Answer

**Sulphur dioxide (SO₂)** is a colourless gas with a pungent smell, produced when fuels that contain sulphur (coal, heavy fuel oil, diesel) are burned: S + O₂ → SO₂.

#### Sources
- Coal-fired power plants (largest source), industries, brick kilns using coal, and metal smelting.
- Diesel and heavy-oil vehicles and ships; volcanic eruptions (natural).

#### Impact
- **Human health:** irritation of eyes, throat and lungs, cough, asthma attacks, bronchitis, and reduced lung function; harms children and elderly most.
- **Acid rain:** SO₂ oxidises to SO₃ and with water forms sulphuric acid (SO₂ + ½O₂ → SO₃; SO₃ + H₂O → H₂SO₄). This acidifies lakes and soil, kills fish and forests, and damages buildings, monuments (marble) and metals.
- **Particulate formation:** sulphate aerosols form fine particles (PM2.5) and haze.
- **Vegetation:** damages leaves and reduces crop yield.
- **Climate:** sulphate aerosols have a slight cooling effect.

#### Control
Use low-sulphur fuel, flue gas desulphurisation (limestone scrubber: SO₂ + CaCO₃ → CaSO₃ + CO₂), fluidised bed combustion, and switch to clean energy such as hydropower and solar.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How is SO2 produced?
   A. Incomplete combustion of carbon
   B. Burning fuels containing sulphur, such as coal and heavy oil
   C. Reaction of NOx in sunlight
   D. Decay of dung in digesters
   Answer: B. S + O2 -> SO2; coal power plants are the largest source. (Key point: Source of SO2)

2. How does SO2 cause acid rain?
   A. It reacts with CO to form carbonic acid
   B. It forms ozone in sunlight
   C. It oxidises to SO3 which with water forms sulphuric acid
   D. It dissolves directly to form nitric acid
   Answer: C. SO2 + 1/2 O2 -> SO3; SO3 + H2O -> H2SO4. (Key point: Acid rain)

3. Which method removes SO2 from flue gas?
   A. Catalytic converter for CO
   B. Using leaded petrol
   C. Increasing stack temperature only
   D. Limestone scrubber (flue gas desulphurisation)
   Answer: D. SO2 + CaCO3 -> CaSO3 + CO2; low-sulphur fuel also helps. (Key point: Control)

## Related in Energy Environment and Society

- [Emission hazards and health impact](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aemission-hazard-health-impact) — Energy Environment and Society, chapter 4, asked 2×