Why can the air inside a home be more polluted than the air outside?
Topic 7.5 Indoor Air Pollutants: identify the major indoor air pollutants and their sources and explain why indoor air pollution is a serious health risk.
A focused answer to APES Topic 7.5, covering the major indoor air pollutants (carbon monoxide, radon, asbestos, VOCs, particulates from biomass burning, mold, lead), their sources, why indoor air pollution is so dangerous in developing and developed countries, and how to reduce it, with a worked radon risk reasoning example.
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What this topic is asking
The College Board (Topic 7.5) wants you to identify the major indoor air pollutants and their sources and explain why indoor air pollution is a serious health risk.
The major indoor air pollutants
Radon and the developing-country burden
Reducing indoor air pollution
Why this matters
Indoor air pollution is often overlooked but causes a huge share of the world's pollution-related deaths, especially from indoor biomass burning. It links Unit 7 to biomass energy (Unit 6) and to human health (Unit 8), and the radon example is a recurring AP exam test of distinguishing a natural radioactive gas from combustion pollutants.
Try this
Q1. Identify the indoor air pollutant that is a naturally occurring radioactive gas. [1 point]
- Cue. Radon.
Q2. Explain why indoor cooking fires are a major health problem in many developing countries. [2 points]
- Cue. Burning wood, dung or charcoal indoors with poor ventilation releases high levels of particulates and carbon monoxide that accumulate in the enclosed space, exposing families, especially women and children, to serious respiratory harm.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2021 (style)4 marksSection II (FRQ). (a) Identify two indoor air pollutants and a source of each. (b) Explain why radon is a particular health concern. (c) Explain why indoor air pollution from cooking fires is a major problem in many developing countries. (d) Describe one method to reduce indoor air pollution.Show worked answer →
A 4-point FRQ on indoor air pollutants.
(a) Identify (1 point): any two with sources, for example carbon monoxide (faulty heaters and stoves), radon (uranium in soil and rock under buildings), asbestos (old insulation), formaldehyde or volatile organic compounds (furniture, paints), or particulates (indoor cooking fires).
(b) Explain (1 point): radon is a colorless, odorless radioactive gas that seeps up from the ground and accumulates indoors; long exposure is a leading cause of lung cancer.
(c) Explain (1 point): many households burn wood, dung or charcoal indoors for cooking and heating with poor ventilation, exposing families (especially women and children) to high particulate and carbon monoxide levels.
(d) Describe (1 point): improve ventilation, use cleaner cooking technology, seal foundations and test for radon, or remove asbestos safely.
Markers reward two valid pollutants with sources, the radioactive-lung-cancer point for radon, the indoor-biomass-burning explanation, and a valid reduction method.
AP 2018 (style)1 marksSection I (multiple choice). Radon, a significant indoor air pollutant, is best described as a: (A) volatile organic compound released by paint (B) naturally occurring radioactive gas that seeps from soil and rock (C) particulate produced by cooking (D) gas emitted only by faulty appliances. Justify your choice.Show worked answer →
A 1-point MCQ on indoor pollutants. The answer is (B).
Radon is a naturally occurring, colorless, odorless radioactive gas produced by the decay of uranium in soil and rock; it seeps up into buildings and accumulates, raising lung cancer risk. It is not a paint VOC (A), not a cooking particulate (C), and comes from the ground, not appliances (D). The trap is confusing radon (a radioactive gas from the ground) with combustion pollutants such as carbon monoxide.
Related dot points
- Topic 7.1 Introduction to Air Pollution: identify the major air pollutants and their sources and distinguish primary from secondary pollutants.
A focused answer to APES Topic 7.1, covering the major air pollutants, their natural and human sources, the criteria pollutants, and the distinction between primary and secondary pollutants, with a worked emissions calculation.
- Topic 7.4 Atmospheric CO2 and Particulates: describe the natural and human sources of atmospheric carbon dioxide and particulate matter and their effects.
A focused answer to APES Topic 7.4, covering the natural and human sources of atmospheric carbon dioxide and particulate matter, the difference between PM10 and PM2.5, why fine particles are most dangerous, the health and environmental effects, with a worked particulate exposure calculation.
- Topic 7.6 Reduction of Air Pollutants: describe methods used to reduce air pollution, including regulation, scrubbers, catalytic converters and cleaner fuels.
A focused answer to APES Topic 7.6, covering methods to reduce air pollution including the Clean Air Act and regulation, scrubbers and electrostatic precipitators, catalytic converters, vapor recovery, cleaner fuels and renewable energy, with a worked scrubber efficiency calculation.
- Topic 6.7 Energy from Biomass: describe how biomass and biofuels are used for energy and evaluate their benefits and drawbacks.
A focused answer to APES Topic 6.7, covering biomass and biofuels (wood, charcoal, dung, crop residues, ethanol, biodiesel), how they are used, their advantages and disadvantages, the carbon-neutrality debate, and a worked ethanol energy calculation.
- Topic 8.14 Pollution and Human Health: describe how pollutants and pathogens affect human health and how infectious diseases spread through the environment.
A focused answer to APES Topic 8.14, covering the health effects of pollutants (heavy metals, particulates, toxins), waterborne and infectious diseases (cholera, typhoid, dysentery), pathogens and disease vectors, the difference between acute and chronic effects, dysentery and access to clean water, and prevention, with a worked disease-rate reasoning example.
Sources & how we know this
- AP Environmental Science Course and Exam Description — College Board (2020)