---
title: "Classification of air pollutants; sources, effects"
subject: "Engineering Chemistry"
chapter: 3
key: "semester_2/engineering_chemistry:air-pollutants-classified"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/air-pollutants-classified
site: BCT Engineering
---

# Classification of air pollutants; sources, effects

Engineering Chemistry · Chapter 3: Environmental Chemistry

- Asked in: 2072 Magh, 1+3 marks
- Video: [Air Pollution | Classification of Air Pollutants | Effect of Air Pollution | Environmental Science](https://www.youtube.com/watch?v=jscG31gMKMI) — Gautam Varde
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/air-pollutants-classified
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-3

## Question

How are air pollutants classified? State four common air pollutants, their sources and effects on the human and environment.

## Short answer

Air pollutants are classified by origin (primary or secondary), physical state (gaseous or particulate), and source (natural or man-made). Common ones: CO from incomplete combustion causes carboxyhaemoglobin; SO₂ from coal burning leads to acid rain and respiratory illness; NOx from vehicles contributes to smog and acid rain; particulate matter from construction and vehicles triggers asthma and lung cancer.

## Answer

#### Classification of air pollutants
1. **By origin:** *primary pollutants* are emitted directly (CO, SO₂, NO, soot); *secondary pollutants* form in the air by reaction of primary ones (O₃, PAN, H₂SO₄ mist, NO₂).
2. **By physical state:** *gaseous* (CO, SO₂, NOx, hydrocarbons) and *particulate* (dust, smoke, fumes, fly ash, aerosols).
3. **By source:** natural (volcanoes, dust storms, forest fire) and man-made (vehicles, industries).

#### Common air pollutants (any four)
| Pollutant | Main sources | Effects |
|---|---|---|
| Carbon monoxide (CO) | Incomplete combustion in vehicles, wood and coal fires | Combines with haemoglobin (carboxyhaemoglobin), reducing O₂ transport; headache, death |
| Sulphur dioxide (SO₂) | Burning coal and oil, smelters, brick kilns | Respiratory diseases; acid rain; damages plants |
| Oxides of nitrogen (NOx) | Vehicles, power plants, high temperature combustion | Lung irritation; photochemical smog; acid rain |
| Hydrocarbons / VOCs | Vehicle exhaust, solvents, evaporation of petrol | Photochemical smog; some are carcinogenic |
| Particulate matter (dust, smoke, PM₁₀, PM₂.₅) | Brick kilns, construction, vehicles, burning of waste and forests | Asthma, bronchitis, lung cancer; reduced visibility |
| Lead | Leaded petrol, batteries | Damages brain and nerves, especially in children |

## Check yourself

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

1. Which is a secondary pollutant?
   A. CO emitted by vehicles
   B. O3, PAN or H2SO4 mist formed by reactions in air
   C. SO2 from smelters
   D. Soot
   Answer: B. Secondary pollutants form in the air; primary ones are emitted directly. (Key point: Primary vs secondary)

2. How are pollutants classified by physical state?
   A. Organic and inorganic
   B. Primary and secondary
   C. Gaseous and particulate
   D. Natural and man-made
   Answer: C. By physical state: gaseous or particulate. (Key point: Physical state)

3. Why is CO poisonous?
   A. It reacts with lung tissue to form acid
   B. It makes blood too thick to flow
   C. It destroys ozone in the lungs
   D. It combines with haemoglobin to form carboxyhaemoglobin, reducing O2 transport
   Answer: D. CO binds haemoglobin, so less oxygen is carried. (Key point: CO effect)

4. CO in air comes mainly from
   A. Incomplete combustion in vehicles and wood/coal fires
   B. Complete combustion of LPG
   C. Photosynthesis
   D. Evaporation of water
   Answer: A. Incomplete combustion gives CO. (Key point: CO source)

## Related in Engineering Chemistry

- [Air pollutants: effects and remedies](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aair-pollutants-effects) — Engineering Chemistry, chapter 3
- [Air pollution, pollutants, sources and remedies](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aair-pollution-sources-remedies) — Engineering Chemistry, chapter 3
- [Water pollution, pollutants and adverse effects](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awater-pollutants-effects) — Engineering Chemistry, chapter 3
- [Water pollutants, sources; oxides making water acidic](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awater-pollutants-acidic) — Engineering Chemistry, chapter 3
- [Soil pollutants, effects and remedies](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Asoil-pollutants-effects-remedies) — Engineering Chemistry, chapter 3, asked 5×
- [Water pollutants, harmful effects, control measures](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awater-pollutants-effects-measures) — Engineering Chemistry, chapter 3

## Related in other subjects

- [Classification and sources of air pollutants](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Aair-pollutants-classification-sources) — Environment and Pollution Control, chapter 1
- [Particulate pollutants: sources and effects](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Aparticulate-pollutants-sources-effects) — Environment and Pollution Control, chapter 1
- [Indoor air pollutants and their sources](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Aindoor-air-pollutants-sources) — Environment and Pollution Control, chapter 3
- [Water pollution: sources and effects](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Awater-pollution-sources-effects) — Environment and Pollution Control, chapter 4