--- title: "Indoor air pollutants and their sources" subject: "Environment and Pollution Control" chapter: 3 key: "semester_7/environment_and_pollution_control:indoor-air-pollutants-sources" source: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/indoor-air-pollutants-sources site: BCT Engineering --- # Indoor air pollutants and their sources Environment and Pollution Control · Chapter 3: Indoor Air Quality - Asked in: year not given, 6 marks - Video: [Indoor air pollutants| Atmospheric pollution| AP Environmental science| Khan Academy](https://www.youtube.com/watch?v=nqRPRwO79kg) — Khan Academy - 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/indoor-air-pollutants-sources - Whole chapter: https://www.bctengineer.com/md/semester_7/environment_and_pollution_control/chapter-3 ## Question List the major indoor air pollutants and describe their sources and health effects in homes and offices. ## Short answer Major indoor pollutants include CO, PM, NO2, radon, formaldehyde/VOCs, biological agents, asbestos/lead, tobacco smoke and CO2. Sources are combustion appliances, building materials, occupant activities, outdoor air and HVAC systems; effects range from respiratory irritation and asthma to cancer and poisoning. ## Answer Indoor air is often more polluted than outdoor air because people spend 80-90% of their time indoors and pollutants build up where ventilation is poor. | Pollutant | Main sources | Health effects | |---|---|---| | Carbon monoxide | Faulty stoves, heaters, attached garages, tobacco | Headache, dizziness, death at high levels | | Particulate matter (PM2.5/PM10) | Biomass/coal cooking, tobacco smoke, candles, dust | Respiratory infection, asthma, COPD, heart disease | | Nitrogen dioxide | Gas stoves and heaters, kerosene lamps | Lung irritation, reduced resistance to infection | | Radon | Soil gas from rock entering through cracks in floors; building materials | Lung cancer (second leading cause after smoking) | | Formaldehyde and other VOCs | Plywood, particle board, paints, adhesives, carpets, cleaning products | Eye and throat irritation, headache, cancer risk | | Biological agents | Mould, dust mites, bacteria, pollen, pets, damp walls | Allergy, asthma, infections (e.g. Legionella from cooling towers) | | Asbestos and lead | Old insulation, roofing sheets, old paint | Asbestosis, lung cancer, lead poisoning | | Environmental tobacco smoke | Cigarettes | Lung cancer, heart disease, respiratory illness in children | | Carbon dioxide | Human breathing, combustion | Drowsiness and poor concentration at high levels (> 1000 ppm indicates poor ventilation) | #### Classification of sources - **Building materials and furnishings:** formaldehyde, asbestos, radon, VOCs. - **Combustion:** cooking and heating appliances. - **Occupants and activities:** CO$_2$, bio-effluents, smoking, cleaning, hobbies. - **Outdoor air entering the building:** vehicle exhaust, pollen, dust. - **HVAC systems:** contaminated ducts, filters and humidifiers. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why can indoor air be more polluted than outdoor air? A. Indoor air has no ventilation at all B. People spend 80-90% of time indoors and pollutants build up where ventilation is poor C. Outdoor air is always clean D. Indoor sources emit only CO2 Answer: B. Poor ventilation lets pollutants accumulate while people spend most of their time indoors. (Key point: Why indoor air is worse) 2. Radon enters buildings mainly from: A. Gas stoves B. Soil gas and rock through cracks in floors, and building materials C. Tobacco smoke D. Photocopiers Answer: B. Radon comes from soil gas and rock and causes lung cancer. (Key point: Radon) 3. Formaldehyde and VOCs indoors come mainly from: A. Plywood, particle board, paints, adhesives, carpets B. Biomass cooking only C. Human breathing D. Mould Answer: A. Building materials and furnishings off-gas formaldehyde and VOCs. (Key point: Formaldehyde sources) 4. CO2 above about 1000 ppm indoors indicates: A. Gas leak B. Radon presence C. Poor ventilation D. Asbestos Answer: C. CO2 comes from occupants breathing, so a high level shows inadequate fresh air. (Key point: CO2 as indicator) ## Related in Environment and Pollution Control - [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 - [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 - [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 - [Control strategies for indoor air quality](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Aindoor-air-control-strategies) — Environment and Pollution Control, chapter 3 - [Household smoke pollution and effects on residents](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Ahousehold-smoke-pollution-effects) — Environment and Pollution Control, chapter 3 ## Related in other subjects - [Health impacts of indoor air pollutants](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aindoor-air-pollutants-health) — Energy Environment and Society, chapter 4 - [Classification of air pollutants; sources, effects](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aair-pollutants-classified) — Engineering Chemistry, chapter 3 - [Reducing indoor air pollutants](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aindoor-air-pollutant-reduction) — Energy Environment and Society, chapter 4 - [Air pollutants: effects and remedies](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aair-pollutants-effects) — Engineering Chemistry, chapter 3