--- title: "Classification and sources of air pollutants" subject: "Environment and Pollution Control" chapter: 1 key: "semester_7/environment_and_pollution_control:air-pollutants-classification-sources" source: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/air-pollutants-classification-sources site: BCT Engineering --- # Classification and sources of air pollutants Environment and Pollution Control · Chapter 1: Air pollution - Asked in: year not given, 5 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_7/environment_and_pollution_control/air-pollutants-classification-sources - Whole chapter: https://www.bctengineer.com/md/semester_7/environment_and_pollution_control/chapter-1 ## Question Define air pollution. Classify air pollutants and explain with examples the natural and anthropogenic sources of air pollution. ## Short answer Air pollution is the presence of harmful substances in outdoor air. Pollutants are classified as primary (emitted directly, e.g. SO2, CO, fly ash) and secondary (formed in the atmosphere, e.g. ozone, PAN). Natural sources include volcanoes, forest fires and dust storms; anthropogenic sources include fuel combustion, vehicles, industry, agriculture and domestic burning. ## Answer Air pollution is the presence in the outdoor atmosphere of one or more substances (gases, particles, vapours) in quantities and for durations that are harmful to human health, plants, animals, materials or the environment. #### Classification of pollutants - **Primary pollutants** are emitted directly from a source, e.g. $\text{SO}_2$, CO, NO, hydrocarbons, fly ash, soot. - **Secondary pollutants** are formed in the atmosphere by reactions between primary pollutants, e.g. ozone, PAN, sulphuric acid mist, $\text{NO}_2$ from NO. | Basis | Types | Examples | |---|---|---| | Physical state | Particulate | Dust, fume, smoke, mist, fly ash | | Physical state | Gaseous | $\text{SO}_2$, $\text{NO}_x$, CO, $\text{CO}_2$, $\text{O}_3$, VOCs | | Origin | Natural / anthropogenic | Volcano / vehicles | | Source geometry | Point / line / area | Chimney / highway / city | #### Natural sources - Volcanic eruptions (ash, $\text{SO}_2$, $\text{H}_2\text{S}$) - Forest fires (smoke, CO, $\text{CO}_2$) - Dust storms, sea spray, pollen and spores - Decay of organic matter (methane, $\text{H}_2\text{S}$) and lightning (NO) #### Anthropogenic (man-made) sources - **Combustion of fuels** in power plants, industries and homes: $\text{SO}_2$, $\text{NO}_x$, fly ash, CO. - **Transport:** CO, hydrocarbons, $\text{NO}_x$, lead (where leaded fuel is used), PM from diesel engines. - **Industrial processes:** cement, brick kilns, steel, chemical plants, mining (dust, fumes, acid gases). - **Agriculture and waste:** burning of crop residue, open burning of waste, methane and ammonia. - **Domestic:** cooking with biomass, kerosene and coal. Anthropogenic sources are the main concern because they are concentrated in cities and are continuous. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which pollutant is a secondary pollutant? A. SO2 from a chimney B. Ozone formed by reactions in the atmosphere C. Fly ash D. CO from a petrol engine Answer: B. Secondary pollutants such as ozone and PAN are formed in the air by reactions between primary pollutants, not emitted directly. (Key point: Primary vs secondary pollutants) 2. According to the answer, air pollution exists when substances in the outdoor air are present: A. In any quantity at all B. Only if they are of human origin C. In quantities and durations harmful to health, plants, animals, materials or the environment D. Only when visible as smoke Answer: C. Air pollution is defined by harmful quantity and duration, regardless of whether the source is natural or visible. (Key point: Definition of air pollution) 3. Which set contains only natural sources of air pollution? A. Volcanoes, forest fires, dust storms B. Brick kilns, vehicles, volcanoes C. Crop residue burning, pollen, cement plants D. Lightning, power plants, sea spray Answer: A. Volcanic eruptions, forest fires and dust storms are natural; kilns, vehicles, power plants and cement plants are man-made. (Key point: Natural sources) 4. Why are anthropogenic sources the main concern? A. They emit gases that natural sources never emit B. They are concentrated in cities and are continuous C. They are always larger in total than natural sources worldwide D. They only emit primary pollutants Answer: B. Man-made emissions are concentrated where people live and occur continuously, so exposure is high. (Key point: Why anthropogenic sources matter most) ## Related in Environment and Pollution Control - [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 - [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 - [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 - [Sources and effects of SO2, NOx and CO](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Agaseous-pollutants-so2-nox-co) — Environment and Pollution Control, chapter 1 - [Hazardous waste: definition and classification](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Ahazardous-waste-definition-classification) — Environment and Pollution Control, chapter 5 ## Related in other subjects - [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 - [Classification of air pollutants; sources, effects](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aair-pollutants-classified) — 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 - [Water pollution, pollutants and adverse effects](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awater-pollutants-effects) — Engineering Chemistry, chapter 3