Air pollution doesn't stay put. Sulfur and nitrogen oxides from a Midwest power plant can drift hundreds of miles and fall as acid rain on a forest or lake in another state or country — pollution without borders. And ironically, the air that's often most dangerous is the air inside your home, where radon seeps from the ground and chemicals off-gas from furniture, sometimes at higher concentrations than outdoors. This lesson covers three pollution problems that don't fit the smokestack image: acid deposition that travels, indoor air that concentrates, and noise that stresses bodies without leaving a residue. Each has clear causes, effects, and solutions the exam expects you to know.
Acid deposition forms when sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) — primary pollutants from burning fossil fuels (especially coal) — react with water, oxygen, and other compounds in the atmosphere to form sulfuric acid (H₂SO₄) and nitric acid (HNO₃). These fall as wet deposition (acid rain, snow, fog) or dry deposition (acidic particles), often far downwind of the source.
Normal rain is slightly acidic (pH ~5.6 due to dissolved CO₂). Acid rain is more acidic (often pH 4–5). Recall the pH scale is logarithmic — each unit is a 10× change in acidity (pH 4 is 10× more acidic than pH 5).
[DIAGRAM: Acid deposition pathway. Coal plant emits SO₂ and NOₓ → carried downwind → react with water/O₂ in atmosphere → H₂SO₄ and HNO₃ → fall as acid rain/snow (wet) or acidic particles (dry) on distant forests, lakes, and buildings.]
Effects of acid deposition: - Acidifies lakes and streams — killing fish and aquatic organisms (especially at low pH); some organisms' eggs/young are most sensitive. - Leaches nutrients (calcium, magnesium) from soil and mobilizes toxic aluminum, harming tree roots. - Damages forests (especially high-elevation). - Corrodes buildings, statues, and monuments (limestone/marble dissolve). - Buffering capacity: areas with limestone bedrock/soils neutralize acid better; areas with granite bedrock (thin soils) are more vulnerable.
Solutions: reduce SO₂/NOₓ emissions via scrubbers, low-sulfur coal, catalytic converters, switching to cleaner fuels/renewables, and policy — the Clean Air Act's SO₂ cap-and-trade program notably reduced US acid rain. Liming acidified lakes is a temporary fix.
Indoor air is often more polluted than outdoor air, and people spend most of their time indoors. Major indoor pollutants:
| Pollutant | Source | Effect |
|---|---|---|
| Radon | Radioactive gas from uranium decay in soil/rock, seeps into basements | Leading cause of lung cancer among nonsmokers |
| Carbon monoxide (CO) | Faulty furnaces, stoves, generators | Binds hemoglobin; can be fatal |
| VOCs / formaldehyde | Paints, glues, furniture, carpets, cleaners | Irritation, headaches, possible carcinogen |
| Asbestos | Old insulation, tiles | Lung disease, mesothelioma (when fibers disturbed) |
| Secondhand smoke | Tobacco | Respiratory illness, cancer |
| Mold, particulates | Damp areas, cooking, dust | Allergies, respiratory problems |
In developing countries, indoor smoke from cooking/heating with biomass or coal over open fires is a major killer. Sick building syndrome describes clusters of symptoms (headache, irritation, fatigue) linked to poorly ventilated buildings with pollutant buildup.
Solutions: ventilation, radon testing and mitigation (sub-slab depressurization), CO detectors, low-VOC products, removing/sealing asbestos, cleaner cookstoves.
Noise pollution is unwanted or harmful sound (traffic, industry, aircraft, construction). Effects: hearing loss (prolonged loud exposure), stress, sleep disruption, elevated blood pressure, and impacts on wildlife (interferes with communication, navigation, breeding — e.g., ship noise and marine mammals). Measured in decibels (dB) — also a logarithmic scale. Solutions: sound barriers, quieter technology, zoning, hearing protection.
Acid rain (SO₂/NOₓ → sulfuric/nitric acid, downwind effects, buffering, cap-and-trade solution) is a reliably tested topic. Indoor air pollutants — especially radon (lung cancer) — and their sources/solutions are common MC. Noise pollution is a smaller but testable topic, especially its wildlife impacts.
Which two primary pollutants cause acid rain, and what acids do they form?
Solution: Sulfur dioxide (SO₂) forms sulfuric acid (H₂SO₄), and nitrogen oxides (NOₓ) form nitric acid (HNO₃), when they react with water and oxygen in the atmosphere.
Interpretation: SO₂ → sulfuric acid; NOₓ → nitric acid.
A lake's pH drops from 6 to 4 due to acid rain. How much more acidic is it, and what's one biological effect?
Solution: The pH scale is logarithmic, so a drop of 2 units = 10 × 10 = 100 times more acidic. Effect: fish and aquatic organisms (especially eggs and juveniles) die as acidity rises; leached aluminum adds toxicity.
Interpretation: Each pH unit = 10×; two units = 100×.
Two lakes receive equal acid rain. Lake A sits on limestone; Lake B on granite. Predict which is more harmed and why.
Solution: Lake B (granite) is more harmed. Limestone around Lake A neutralizes (buffers) the acid, keeping pH stable, whereas granite has little buffering capacity, so Lake B's pH drops and aquatic life suffers.
Interpretation: Limestone buffers acid; granite doesn't → granite regions are more vulnerable.
Explain the source and health risk of radon, and one mitigation method.
Solution: Radon is a radioactive gas produced by the decay of uranium in soil and rock; it seeps into homes (especially basements) through cracks in the foundation. It is the leading cause of lung cancer among nonsmokers. Mitigation: testing and sub-slab depressurization / improved ventilation to vent radon outside before it accumulates.
Interpretation: Radon = natural radioactive soil gas → lung cancer → fix with venting/ventilation.
10 × 10 = 100 times.(B) Scrubber.
Formation/transport: Coal combustion emits SO₂ and NOₓ, which travel downwind and react with water/oxygen to form sulfuric (H₂SO₄) and nitric (HNO₃) acids, falling as wet or dry deposition far from the source. Effects (two): acidifies lakes (kills fish), leaches soil nutrients and mobilizes aluminum, damages forests, corrodes buildings. Solutions: technology — scrubbers on smokestacks (remove SO₂); policy — Clean Air Act SO₂ cap-and-trade / low-sulfur fuel standards.
Limestone buffers/neutralizes acid, keeping pH stable; granite has little buffering capacity, so acid rain lowers the lakes' pH and harms aquatic life. Action: reduce upwind SO₂/NOₓ emissions (scrubbers/policy); temporarily lime the acidified lakes.
FRQ rubric (10 pts): - (a) 1 pt SO₂/NOₓ emitted and react with water/O₂ in the atmosphere; 1 pt form sulfuric and nitric acid that deposit downwind. (2) - (b) 1 pt granite lacks buffering capacity; 1 pt limestone neutralizes acid, so granite lakes acidify more. (2) - (c) 1 pt radon = radioactive gas from uranium decay in soil/rock seeping into homes; 1 pt risk = lung cancer; 1 pt mitigation (venting/sub-slab depressurization, ventilation, sealing foundation). (3) - (d) 1 pt technology (scrubbers, low-sulfur coal, catalytic converters, switch to renewables) + justification; 1 pt policy (Clean Air Act standards/cap-and-trade, emission limits) + justification; 1 pt both plausibly reduce SO₂/NOₓ. (3)
Coal-fired power plants upwind of a mountainous, granite-bedrock region cause acid deposition. Lakes are acidifying and fish are declining. Meanwhile, nearby homes report elevated indoor radon.
(a) Explain how the power plants' emissions become acid rain, naming the acids formed. (2 pts) (b) Explain why the granite region is especially vulnerable compared to a limestone region. (2 pts) (c) Explain the source and health risk of the indoor radon and one mitigation. (3 pts) (d) Propose two solutions to reduce the acid deposition (one technology, one policy) and justify each. (3 pts)
MC:
1. (B) SO₂ and NOₓ.
2. (C) 2 units → 10 × 10 = 100 times.
3. (B) Limestone.
4. (B) Leading cause of lung cancer in nonsmokers.
5. (B) VOCs/formaldehyde.
6. (B) Lowering pH and mobilizing toxic aluminum.
7. (B) SO₂ cap-and-trade program.
8. (B) Interfering with communication, navigation, and breeding.
9. (B) Poorly ventilated buildings with pollutant buildup.
10. (B) Scrubber.
Formation/transport: Coal combustion emits SO₂ and NOₓ, which travel downwind and react with water/oxygen to form sulfuric (H₂SO₄) and nitric (HNO₃) acids, falling as wet or dry deposition far from the source. Effects (two): acidifies lakes (kills fish), leaches soil nutrients and mobilizes aluminum, damages forests, corrodes buildings. Solutions: technology — scrubbers on smokestacks (remove SO₂); policy — Clean Air Act SO₂ cap-and-trade / low-sulfur fuel standards.
Limestone buffers/neutralizes acid, keeping pH stable; granite has little buffering capacity, so acid rain lowers the lakes' pH and harms aquatic life. Action: reduce upwind SO₂/NOₓ emissions (scrubbers/policy); temporarily lime the acidified lakes.
FRQ rubric (10 pts): - (a) 1 pt SO₂/NOₓ emitted and react with water/O₂ in the atmosphere; 1 pt form sulfuric and nitric acid that deposit downwind. (2) - (b) 1 pt granite lacks buffering capacity; 1 pt limestone neutralizes acid, so granite lakes acidify more. (2) - (c) 1 pt radon = radioactive gas from uranium decay in soil/rock seeping into homes; 1 pt risk = lung cancer; 1 pt mitigation (venting/sub-slab depressurization, ventilation, sealing foundation). (3) - (d) 1 pt technology (scrubbers, low-sulfur coal, catalytic converters, switch to renewables) + justification; 1 pt policy (Clean Air Act standards/cap-and-trade, emission limits) + justification; 1 pt both plausibly reduce SO₂/NOₓ. (3)
⭐ Exam strategy: Acid rain = SO₂ + NOₓ → sulfuric + nitric acid, traveling downwind; limestone buffers, granite doesn't. For indoor air, radon (soil→lung cancer) is the star. And remember pH and decibels are both logarithmic — one unit is a tenfold change.
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