---
title: "Short note: Acid rain causes and impacts"
subject: "Technology, Environment and Society"
chapter: 5
key: "semester_7/technology_environment_and_society:acid-rain"
source: https://www.bctengineer.com/q/semester_7/technology_environment_and_society/acid-rain
site: BCT Engineering
---

# Short note: Acid rain causes and impacts

Technology, Environment and Society · Chapter 5: Water and Air Pollution

- Asked in: 2082 Baisakh, 4 marks; 2080 Bhadra, 4 marks (asked 2 times)
- Video: [Acid Rain | Environmental Chemistry | Chemistry | FuseSchool](https://www.youtube.com/watch?v=Nf8cuvl62Vc) — FuseSchool - Global Education
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/technology_environment_and_society/acid-rain
- Whole chapter: https://www.bctengineer.com/md/semester_7/technology_environment_and_society/chapter-5

## Question

Write a short note on acid rain: causes and impacts (consequences).

## Short answer

Acid rain has pH below about 5.6 and forms when sulphur dioxide and nitrogen oxides react with water vapour to produce sulphuric and nitric acids. Main causes are coal and oil burning, vehicles and industry. It damages aquatic life, forests, crops and buildings, and harms health. Control includes scrubbers, low-sulphur fuels, catalytic converters and renewable energy.

## Answer

**Acid rain** is rain, snow, fog or dust that is more acidic than normal, with **pH below about 5.6**. (Normal rain is slightly acidic, pH ≈ 5.6, because of dissolved CO₂.) It forms when sulphur dioxide and nitrogen oxides in the air react with water vapour to form sulphuric and nitric acids.

#### Causes
- **Sulphur dioxide (SO₂)** – from burning coal and oil in thermal power plants, industries, brick kilns, smelting of ores.
- **Nitrogen oxides (NOₓ)** – from vehicle exhaust, power plants and high-temperature combustion.
- **Natural sources** – volcanoes, lightning, decaying vegetation (smaller share).

**Formation (simplified):**
- SO₂ + H₂O + O₂ → H₂SO₄ (sulphuric acid)
- NOₓ + H₂O + O₂ → HNO₃ (nitric acid)

These acids fall as **wet deposition** (rain, snow) or **dry deposition** (acidic gases and particles), sometimes hundreds of kilometres away from the source.

#### Impacts (consequences)
1. **Aquatic life** – lakes and rivers become acidic; fish eggs and insects die; aluminium released from soil is toxic to fish.
2. **Forests and crops** – leaves damaged, nutrients (Ca, Mg) washed out of soil, trees weakened (e.g. forest dieback in Europe).
3. **Soil** – loss of fertility and of useful microbes.
4. **Buildings and monuments** – marble and limestone corrode (e.g. Taj Mahal yellowing; risk to stone temples); metals rust faster.
5. **Human health** – the SO₂ and NOₓ gases that cause acid rain (and the sulphate and nitrate particles they form) also cause asthma and bronchitis; acidic water can leach lead and copper from pipes.

**Control:** low-sulphur fuels, flue gas desulphurisation (scrubbers), catalytic converters in vehicles, more renewable energy, and liming of acidified lakes.

## Check yourself

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

1. Acid rain has pH below about:
   A. 5.6
   B. 7
   C. 8.5
   D. 3
   Answer: A. Normal rain is pH ~5.6 due to dissolved CO2. (Key point: pH of acid rain)

2. Which acids form acid rain?
   A. Acetic only
   B. Sulphuric and nitric acids
   C. Hydrochloric and citric
   D. Carbonic only
   Answer: B. SO2 and NOx give H2SO4 and HNO3. (Key point: Formation)

3. How does acid rain harm fish?
   A. Heats lakes
   B. Adds nitrate only
   C. Acidifies water and releases toxic aluminium from soil
   D. Adds oxygen
   Answer: C. Aluminium released from soil is toxic. (Key point: Impact on aquatic life)

## Related in Technology, Environment and Society

- [Deforestation: causes and consequences](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Adeforestation-consequences) — Technology, Environment and Society, chapter 6, asked 2×
- [Short note: Causes and impacts of climate change](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Aclimate-change-causes-impacts) — Technology, Environment and Society, chapter 6, asked 2×
- [Global environmental issues: causes and consequences](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Aglobal-env-issues-causes) — Technology, Environment and Society, chapter 4
- [Causes and impacts of World War I and II](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Aworld-wars-causes-impacts) — Technology, Environment and Society, chapter 3
- [Water pollution: sources, causes and impacts](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Awater-pollution-sources-impacts) — Technology, Environment and Society, chapter 5
- [Climate change causes, impacts and solutions for LDC](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Acc-solution-ldc) — Technology, Environment and Society, chapter 6

## Related in other subjects

- [Short note: Acid rain](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aacid-rain) — Engineering Chemistry, chapter 3, asked 2×
- [NO₂ and SO₂ sources; role in acid rain](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ano2-so2-acid-rain) — Engineering Chemistry, chapter 3
- [Acid rain; sources and control of CO and SO₂](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aacid-rain-co-so2) — Engineering Chemistry, chapter 3
- [Global warming: meaning, causes, consequences](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aglobal-warming-causes-consequences) — Engineering Chemistry, chapter 3