AP® Environmental Science review sheet from Aim for Five (aimforfive.com/enviro/units/7/7-5)
Unit 7 · Topic 7.5
7.5 Indoor Air Pollutants
Indoor air can be more polluted than outdoor air, and people spend most of their time indoors. The main threats are smoke from cooking fires in developing countries, carbon monoxide, radon, asbestos, lead dust, VOCs like formaldehyde, and natural pollutants like mold and dust.
Key terms
- carbon monoxide
- radon
- asbestos
- formaldehyde
- volatile organic compounds (VOCs)
Cooking smoke in developing countries
Billions of people cook and heat with wood, charcoal, crop waste, dried dung or coal on open fires or simple stoves, often in poorly ventilated homes. The smoke is full of particulates and carbon monoxide. The World Health Organization estimates household air pollution causes millions of deaths a year, mostly from pneumonia, stroke, heart disease and lung disease. Women and young children, who spend the most time near the fire, are hit hardest.
Solutions include cleaner fuels such as propane or electricity, more efficient vented stoves with chimneys, solar cookers and better ventilation.
Indoor pollutants to know
| Pollutant | Source | Health effect |
|---|---|---|
| Carbon monoxide (CO) | Faulty furnaces, gas stoves and heaters, cars in attached garages | Binds to hemoglobin in blood more than 200 times as strongly as oxygen, causing headaches, dizziness and death |
| Radon (radioactive gas) | Decay of uranium in soil and rock, seeping through foundation cracks into basements | Second leading cause of lung cancer in the US after smoking |
| Asbestos | Old insulation, ceiling and floor tiles, pipe wrap | Fibers lodge in lungs, causing asbestosis, lung cancer and mesothelioma |
| Lead | Paint in homes built before 1978, and its dust | Brain and nerve damage, especially in children |
| Formaldehyde and other VOCs | Pressed-wood furniture, carpets, glues, paints, cleaners | Eye, nose and throat irritation, headaches; formaldehyde can cause cancer |
| Mold, dust, pet dander | Damp areas, poor ventilation | Allergies and asthma |
Key details
- Carbon monoxide is colorless and odorless, so you can't tell it is there. A CO detector is the main protection.
- Radon is also colorless and odorless. It is more common where the bedrock is rich in uranium, such as some granite areas. The EPA recommends fixing a home if radon is 4 picocuries per liter or higher; fixes include sealing foundation cracks and venting soil gas out from under the house with a fan and pipe.
- Asbestos is dangerous mainly when it is disturbed and fibers get into the air. Undamaged asbestos is often left in place and sealed; removal must be done by trained professionals.
- Lead paint was banned for US homes in 1978, but older homes still have it, and peeling paint and dust are the main exposure routes for children.
- 'Sick building syndrome' describes symptoms people get in tightly sealed buildings with poor ventilation and many VOC sources. Ventilation is the most general fix for indoor air.
Worked examples
Try each one yourself first, then open the solution.
- Example 1
Radon decay
Radon-222 has a half-life of 3.8 days. A sealed container holds 160 units of radon. (a) How much is left after 15.2 days? (b) Why does radon in a basement not simply disappear over a few weeks, even though its half-life is short?
Show the solutionHide the solution
- Step 1: (a) Number of half-lives = 15.2 ÷ 3.8 = 4.
- Step 2: Halve four times: 160 → 80 → 40 → 20 → 10 units. Or 160 × (½)⁴ = 160 ÷ 16 = 10.
- Step 3: (b) Radon is constantly being made underground as uranium in the soil and rock decays. Uranium has a half-life of billions of years, so it keeps producing radon, which keeps seeping into the basement. The supply is replaced as fast as it decays.
Answer: (a) 10 units. (b) Uranium in the ground keeps producing new radon, so it is continually replenished.
- Example 2
Diagnosing a household problem
Several family members get headaches, dizziness and nausea at home in winter, and they feel better at school and work. The house has an old gas furnace. What pollutant is the most likely cause, and what should the family do?
Show the solutionHide the solution
- Step 1: Symptoms that show up at home and fade away from home point to an indoor source.
- Step 2: Headaches, dizziness and nausea are classic signs of carbon monoxide poisoning, and they're worse in winter when the furnace runs and windows are shut.
- Step 3: An old or faulty gas furnace can leak CO if it burns fuel incompletely or its vent is blocked.
- Step 4: Action: get out and get fresh air, have the furnace inspected and repaired, and install CO detectors.
Answer: Carbon monoxide from the faulty furnace. Ventilate, repair the furnace, and install CO detectors.
Common mistakes
- Saying radon comes from building materials or appliances. It comes mainly from uranium decay in soil and rock beneath the building.
- Thinking you can smell carbon monoxide or radon. Both are odorless and colorless, which is why detectors and tests matter.
- Saying asbestos is dangerous just by being in a building. The risk comes from fibers released when it is damaged or disturbed.
On the exam
- Expect to match an indoor pollutant to its source and health effect. Radon → lung cancer, asbestos → mesothelioma, CO → oxygen deprivation, lead → nerve damage in children.
- For developing countries, the standard answer is particulates and CO from burning biomass indoors, with cleaner stoves or fuels as the solution.
Connected topics
Videos
Check yourself
5 questions on 7.5 Indoor Air Pollutants. Pick an answer to see if you got it, and why.
A family buys an older house. A home inspector notes the following:
• Cracks in the basement floor, which sits on rock that contains small amounts of uranium.
• A gas furnace with a rusted, partly blocked exhaust vent.
• Crumbling insulation around old pipes, installed in the 1950s.
• New pressed-wood cabinets and fresh carpet that give off a chemical smell.
Described scenario
Which pollutant is most likely to enter the house through the basement cracks?
Which finding poses the greatest risk of sudden poisoning, and why?
The chemical smell from the new cabinets and carpet most likely comes from
| Home | Foundation | Basement radon level (pCi/L) |
|---|---|---|
| 1 | Slab on sandy soil | 1.2 |
| 2 | Basement in clay soil | 4.0 |
| 3 | Cracked basement on granite bedrock | 9.6 |
| 4 | Basement with dirt crawl space | 6.2 |
Hypothetical test results from four homes in one county
The EPA recommends fixing a home if radon is 4 pCi/L or higher. Which homes should be fixed?
Which step would most effectively lower the radon level in Home 3?
0 of 5 answered