Indoor air pollutants are gases and particles inside buildings that harm health—think carbon monoxide (an asphyxiant), particulates like asbestos/dust/smoke, radon-222 (a radioactive gas from uranium decay), mold, VOCs and formaldehyde from furniture/insulation/carpet, and lead paint (CED keywords). They come from natural sources (radon, mold), human-made materials (off-gassing VOCs, insulation), and combustion (CO, NOx, SO2, tobacco smoke). Why care? Short-term exposure can cause headaches, respiratory irritation, or carbon monoxide poisoning; long-term exposure raises risks like radon-induced lung cancer (the second leading cause in the U.S.) and chronic respiratory disease. For the AP exam, you should be able to identify these pollutants, their sources, and effects (STB-2.E / STB-2.F). Review the Topic 7.5 study guide for targeted facts and practice identifying examples (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj). For broader Unit 7 review and extra practice questions, see the unit page (https://library.fiveable.me/ap-environmental-science/unit-7) and practice set (https://library.fiveable.me/practice/ap-environmental-science).

“Asphyxiant” means a substance that prevents tissues from getting enough oxygen. Carbon monoxide (CO) is called an asphyxiant because it binds to hemoglobin in your red blood cells much more strongly than oxygen does. When CO binds, it forms carboxyhemoglobin and cuts the blood’s ability to carry O2, causing tissue hypoxia (low oxygen) even if the air looks fine. CO is odorless and comes from indoor combustion sources (faulty heaters, car exhaust in attached garages, gas stoves), so people can be poisoned before they notice symptoms like headache, dizziness, or nausea. On the AP CED, CO is listed as an indoor asphyxiant (EK STB-2.E.1) under indoor air pollutants—know its source and health effect for the exam. For a quick topic review check the Indoor Air Pollutants study guide (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and find practice questions at (https://library.fiveable.me/practice/ap-environmental-science).

Natural indoor pollutants come from the environment or biological processes; human-made ones come from building materials, products, or activities. Examples from the CED: natural = radon-222 (a radioactive gas from uranium decay that can seep up through basements and is the 2nd leading cause of lung cancer), mold, and dust (EK STB-2.E.4; STB-2.F.1–2). Human-made = insulation fibers/asbestos, VOCs off-gassing from furniture, formaldehyde from building materials and carpeting, and lead in paint (EK STB-2.E.5). Combustion-related indoor pollutants (a mix of sources) include carbon monoxide (an asphyxiant), NOx, SO2, particulates, and tobacco smoke (EK STB-2.E.1, E.3, E.6). For the AP exam, be ready to ID types (asphyxiants, particulates, VOCs) and link sources to health effects (e.g., radon → lung cancer). Review the Topic 7.5 study guide (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).

VOCs are volatile organic compounds—basically carbon-containing chemicals that easily evaporate into the air at room temperature. In homes they “off-gas” from things like furniture, paneling, carpets, paints, and some cleaners (this is listed in the CED: EK STB-2.E.5). Common examples include formaldehyde and compounds in solvents. They’re indoor air pollutants because you breathe them in; short-term exposure can irritate eyes, nose, and throat or cause headaches, while long-term exposure can increase risk of chronic problems. To reduce VOCs: increase ventilation (open windows, use exhaust fans), buy low-VOC or labeled products, let new furniture or paint off-gas outdoors before bringing them inside, and store solvents in sealed containers. On the AP exam you should be able to identify VOCs as human-made indoor pollutants and give sources and basic health effects (see EK STB-2.E.3–5). For a focused review, check the Topic 7.5 study guide (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj); for more unit review see (https://library.fiveable.me/ap-environmental-science/unit-7) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).

Radon-222 is a radioactive gas formed when uranium in rock and soil decays. It’s odorless and invisible, so you don’t notice it as it moves. Gas in the pore spaces of soil migrates upward (because gases move from higher to lower pressure) and can seep into homes through foundation gaps, basement floor cracks, utility openings, or poorly sealed crawl spaces. Radon can also dissolve in groundwater and enter indoor air when that water is used (wells, showers). (CED: EK STB-2.E.7; STB-2.F.1.) Long-term exposure increases lung cancer risk—radon is the second leading cause of lung cancer in the U.S. (STB-2.F.2). For AP review, focus on radon as a natural indoor pollutant, its soil/groundwater pathways, and health effects. For a clear study guide and practice questions, see Fiveable’s topic page (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and the Unit 7 overview (https://library.fiveable.me/ap-environmental-science/unit-7).

Particulate indoor air pollutants are tiny solid or liquid particles you breathe in. The CED specifically lists asbestos, dust, and smoke as particulates (EK STB-2.E.2). Other common examples include: tobacco smoke (combustion particulates), soot from wood or gas stoves, pet dander, pollen tracked indoors, and fine particulate matter (PM2.5) from cooking or candles. Asbestos fibers are especially important on the AP: they’re a particulate that causes lung problems when disturbed (EK STB-2.E.3–2.E.6). Natural sources that contribute particulates indoors include dust and pollen; human-made/combustion sources include smoking, fireplaces, and poorly vented stoves (EK STB-2.E.3–2.E.6). For AP prep, memorize the CED list and examples so you can ID particulates on multiple-choice or FRQs (STB-2.E/STB-2.F). For a focused review, see the Topic 7.5 study guide (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and more unit resources (https://library.fiveable.me/ap-environmental-science/unit-7).

Radon-222 is dangerous because, even though it’s natural (it comes from uranium in rocks/soil—EK STB-2.E.7), it’s a radioactive gas that emits alpha particles when it decays. If radon seeps into homes through basement cracks or groundwater (EK STB-2.F.1), those alpha particles can damage lung tissue and DNA when you inhale radon daughters. Over time that damage raises your risk of radon-induced lung cancer—it’s the second-leading cause of lung cancer in the U.S. (EK STB-2.F.2). The key risks are (1) you can’t smell or see radon, and (2) it accumulates indoors to higher concentrations than outdoors. For the AP exam, remember radon as a common natural indoor pollutant and a health risk from soil infiltration. For review and practice on indoor air pollutants, check the Topic 7.5 study guide (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).

Combustion pollutants get into homes mainly when things that burn (gas stoves, furnaces, water heaters, fireplaces, wood stoves, candles, tobacco, or vehicle exhaust from attached garages) release gases and particles indoors. Many common pathways: - Unvented or poorly vented appliances (gas stoves, space heaters) release carbon monoxide (CO—a colorless, odorless asphyxiant) and nitrogen oxides (NOx) directly into living spaces. - Cracked or clogged chimneys and flues let smoke and combustion gases backdraft into rooms. - Air infiltration: gaps, vents, windows, and HVAC systems can bring in outdoor combustion pollution (like vehicle NOx and particulates) or distribute indoor emissions. - Indoor smoking and wood-burning produce particulates and soot that linger on surfaces and in dust. On the AP exam you should be able to identify CO and NOx as common combustion indoor pollutants (STB-2.E, EK STB-2.E.1 and EK STB-2.E.6). For more review, see the Topic 7.5 study guide (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).

Formaldehyde is a common indoor air pollutant that “off-gasses” from building materials, pressed-wood furniture, upholstery, and carpeting—it’s listed in the CED as a human-made indoor pollutant (STB-2.E.5). Many manufactured wood products (plywood, particleboard) and some adhesives contain formaldehyde resins that slowly release gas, especially when new or warm. Short-term exposure can irritate eyes, nose, throat and worsen respiratory symptoms; long-term exposure is linked to increased cancer risk, so it’s an AP-relevant example of a VOC/formaldehyde source to know. To reduce exposure: ventilate, buy low- or no-formaldehyde products (CARB- or “no added formaldehyde” labels), and let new furniture or carpets air out. For quick review, see the Topic 7.5 study guide on Fiveable (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and practice questions for Unit 7 (https://library.fiveable.me/ap-environmental-science/unit-7).

Good question—yes, lead-based paint was banned for residential use in the U.S. in 1978, but it’s still a problem because many older homes and buildings still have that paint on walls, trim, windows, and doors. As paint ages, it can chip or create lead-containing dust (an indoor particulate), and renovations or friction (like opening old windows) release more dust. Kids are most at risk because they ingest dust or paint chips; lead causes neurological and developmental damage. Lead also persists in soil near old buildings and is expensive to remove safely—so presence, not legality, makes it an indoor pollutant today. For APES, remember lead is listed under human-made indoor pollutants in the CED (STB-2.E.5) and is an example of a particulate source from building materials. For a quick review, see the Topic 7.5 study guide (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and practice questions at (https://library.fiveable.me/practice/ap-environmental-science).

Even though radon is a gas, it’s radioactive—that’s the key. Radon-222 comes from uranium decay in soil and rock (EK STB-2.E.7). When you breathe air with radon, its atoms decay in your lungs and emit ionizing radiation (mainly alpha particles). Those particles don’t travel far, but they deposit lots of energy into lung tissue and can damage DNA, raising lung-cancer risk. Because radon can seep into many homes through basements, foundation cracks, or well water (EK STB-2.F.1), chronic low-level exposure is widespread; that’s why it’s the second leading cause of lung cancer in the U.S. (EK STB-2.F.2), especially for smokers. The AP exam expects you to link “naturally occurring radioactive gas” + inhalation pathway to health effects (radon → lung cancer). Test homes with a radon kit and use mitigation (venting, sealing) if levels are high. For a quick review, see the Topic 7.5 study guide (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and more practice at (https://library.fiveable.me/practice/ap-environmental-science).

Memorize these main indoor-air pollution sources for the AP exam (matches CED EKs): - Combustion sources: carbon monoxide (CO, an asphyxiant), nitrogen oxides (NOx), sulfur dioxide (SO2), particulates, and tobacco smoke (from stoves, heaters, fireplaces, cigarettes). - Particulates: asbestos, household dust, and smoke. - Natural sources: radon-222 (from uranium decay in some soils/rocks entering basements through foundation cracks or well water), mold, and dust. - Human-made/off-gassing: volatile organic compounds (VOCs) from furniture, paneling, carpets; formaldehyde from building materials/upholstery; lead from old paint. You’ll be asked to identify these (STB-2.E) and describe effects like radon-linked lung cancer (STB-2.F). Review the Topic 7.5 study guide on Fiveable for quick drills (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and practice questions (https://library.fiveable.me/practice/ap-environmental-science).

Think by categories—it’s way easier than memorizing a long list. From the CED, learn these groups and 1–2 examples each: - Asphyxiant: carbon monoxide (CO). - Particulates: asbestos, dust, smoke. - Natural sources: radon (radon-222 → lung cancer), mold, dust. - Human-made: insulation, VOCs (off-gassing from furniture/paneling/carpets), formaldehyde, lead paint. - Combustion products: CO, nitrogen oxides (NOx), sulfur dioxide (SO2), particulates, tobacco smoke. Study tips: make 5 flashcards (one per category) with examples and health effects (radon → 2nd leading cause of lung cancer). Use a single mnemonic: “CARP-M” = CO, Asbestos/Particulates, Radon/Mold, Pharmaceuticals? (replace with human-made VOCs/formaldehyde), Methane—then map correctly to categories—or just memorize the five category headers and plug examples in. Practice with MCQs and FRQ-style prompts so you can identify pollutants by source/effect (Topic 7.5 appears on the multiple-choice and may show up in free-response). Review the topic study guide (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj), unit overview (https://library.fiveable.me/ap-environmental-science/unit-7), and practice problems (https://library.fiveable.me/practice/ap-environmental-science).

Radon-222 is a naturally occurring radioactive gas produced by uranium decay in some soils and rocks. It moves up through the soil and can enter homes through basements, foundation cracks, gaps around pipes, or in well water (CED EK STB-2.E.4 and STB-2.F.1). Once trapped in enclosed spaces it can accumulate to high concentrations. When you breathe radon decay products, they emit alpha particles that damage lung tissue—long-term exposure increases your risk of radon-induced lung cancer (the second leading cause of lung cancer in the U.S., CED STB-2.F.2). For AP exam relevance, radon is a key natural indoor air pollutant to know and explain in short-answer or multiple-choice questions (Topic 7.5). For more review and practice, see the Topic 7.5 study guide (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj), the Unit 7 overview (https://library.fiveable.me/ap-environmental-science/unit-7), and practice questions (https://library.fiveable.me/practice/ap-environmental-science).

Mold and dust count as natural indoor air pollutants because the CED classifies them as naturally occurring particulates and common natural indoor pollutants (EK STB-2.E.2 and EK STB-2.E.4). Mold is a fungus that grows where moisture and organic material exist (basements, bathrooms); it releases spores into the air that are inhaled. Dust is a mix of tiny particles—skin cells, pollen, soil, textile fibers, dust-mite waste—that stays suspended as particulates. Both are non-manmade sources that degrade indoor air quality and can trigger asthma, allergies, and respiratory irritation (connects to STB-2.F health effects). For the exam, you should be able to identify them as natural-source particulates and explain health impacts. If you want a quick review tied to the AP framework, check the Topic 7.5 study guide on Fiveable (https://library.fiveable.me/ap-environmental-science/unit-7/indoor-air-pollutants/study-guide/y1B4lwSL0xpAcpSCHRjj) and practice related questions at (https://library.fiveable.me/practice/ap-environmental-science).