pollution-and-climate BOD Tap / Space to flip
pollution-and-climate Biological Oxygen Demand. Amount of dissolved O₂ used by decomposers to break down organic matter. High BOD = polluted water.
Priority topic · Spans Units 7, 8, 9
Pollution & Climate Change
Cuts across Units 7–9 (the highest-weight band). Many APES FRQ point losses come from confusing primary/secondary pollutants, point/non-point sources, bioaccumulation/biomagnification, or the two ozones.
The five most-tested distinctions
| Term | Definition | Examples |
|---|---|---|
| Primary pollutant | Emitted directly | CO, NOx, SO₂, VOCs, PM, Pb |
| Secondary pollutant | Formed in atmosphere from reactions | Tropospheric O₃, H₂SO₄, HNO₃, peroxyacyl nitrates (PANs) |
| Point source | Single, identifiable location | Factory pipe, sewage outflow |
| Non-point source | Diffuse origin | Agricultural runoff, urban stormwater, atmospheric deposition |
| Bioaccumulation | Buildup within ONE organism over time | Mercury in a single tuna\'s tissues |
| Biomagnification | Increase ACROSS trophic levels | DDT in plankton → fish → osprey (eggshell thinning) |
BOD ↔ DO
- BOD (Biological Oxygen Demand): O₂ consumed by decomposers as they break down organic matter.
- DO (Dissolved Oxygen): O₂ available for aquatic life.
- ↑ Organic pollution → ↑ BOD → ↓ DO. Healthy water has DO > 6 mg/L.
- Warmer water also holds less DO — temperature pollution is a real concern.
Eutrophication chain (memorize verbatim)
- Excess N / P input (fertilizer runoff, sewage, detergents).
- Algal bloom — rapid plant growth at the surface.
- Algae die en masse.
- Decomposer bacteria proliferate, consuming O₂ (BOD ↑, DO ↓).
- Hypoxia / anoxia → fish kill → "dead zone" (e.g., Gulf of Mexico).
Acid rain mechanism
SO₂ + H₂O + O₂ → H₂SO₄ (sulfuric acid)
NOx + H₂O → HNO₃ (nitric acid)- Sources: coal combustion (SO₂), vehicle and power-plant emissions (NOx).
- Effects: lake and soil pH drop; Al³⁺ leaches and kills fish; forests damaged; marble and limestone monuments dissolved.
- Reduced by Clean Air Act SO₂ cap-and-trade and catalytic converters.
Greenhouse gases (100-yr GWP)
| GHG | GWP | Sources |
|---|---|---|
| CO₂ | 1 (reference) | Combustion, deforestation, cement |
| CH₄ | ~28–34 | Livestock, landfills, rice paddies, fracking leaks |
| N₂O | ~265–298 | Synthetic fertilizer, combustion |
| CFCs / HFCs | 1,000s–10,000s | Legacy refrigerants, aerosols |
| Water vapor | — | Feedback, not direct forcing |
CO₂ has the largest integrated warming impact only because it is far more abundant.
The two ozones (memorize cold)
| Stratospheric ozone | Tropospheric ozone | |
|---|---|---|
| Altitude | 10–50 km | Ground level |
| Formed by | Natural UV reaction with O₂ | NOx + VOCs + sunlight (secondary pollutant) |
| Effect on humans | GOOD — UV shield | BAD — lung irritant, smog |
| Destroyed by | CFCs, halons | (Not destroyed; it IS the pollutant) |
| Policy response | Montreal Protocol (1987) | Clean Air Act NAAQS |
Example FRQs
FRQ Distinguish between bioaccumulation and biomagnification, with an example.
Answer: Bioaccumulation is the increase in toxin concentration WITHIN ONE ORGANISM over its lifetime, as it absorbs more than it excretes (e.g., mercury accumulating in a single tuna\'s tissues over years). Biomagnification is the increase in toxin concentration UP THE FOOD CHAIN — predators ingest many contaminated prey, so the concentration grows at each trophic level (DDT in plankton → small fish → larger fish → ospreys, where it caused eggshell thinning).
MCQ An algal population doubles every 3 days. Starting at 1,000 cells/L, what is the population after 12 days? (A) 4,000 (B) 8,000 (C) 16,000 (D) 32,000
Answer: C. 12 / 3 = 4 doublings. 1000 × 2⁴ = 1000 × 16 = 16,000 cells/L.
Long FRQ Make a claim about the most effective policy to reduce CO₂ emissions in the US, and justify it.
Sample answer: A carbon tax is most effective because it internalizes the previously-externalized cost of emissions, incentivizing every emitter — utilities, industries, and consumers — to reduce. Revenue can fund renewable infrastructure or be returned as a dividend to make the policy progressive. British Columbia\'s 2008 carbon tax cut emissions ~5–15% relative to the rest of Canada without harming GDP. Alternative claims (cap-and-trade, renewable subsidies, performance standards) are also acceptable if rigorously defended.
Long FRQ Explain how CFCs destroy stratospheric ozone, then explain why CO₂ and CFCs both contribute to climate change.
Answer:
Ozone destruction: UV radiation breaks Cl atoms off CFC molecules in the stratosphere. The free Cl reacts with O₃: Cl + O₃ → ClO + O₂. Then ClO + O → Cl + O₂. The Cl is regenerated, so a single Cl atom catalytically destroys ~100,000 O₃ molecules before being removed.
Climate change: Both CO₂ and CFCs absorb infrared (heat) radiation emitted by Earth\'s surface, re-emitting some of it downward and trapping heat in the lower atmosphere. CFCs are far more potent per molecule (high GWP), but CO₂ is much more abundant — so the integrated warming effect of CO₂ is largest. Both must be reduced for serious climate mitigation.
Drill flashcards
pollution-and-climate Dissolved oxygen (DO) Tap / Space to flip
pollution-and-climate O₂ available in water for aquatic life. Inversely related to BOD; higher temperature lowers DO solubility.
pollution-and-climate Eutrophication Tap / Space to flip
pollution-and-climate Nutrient enrichment (N, P) → algal bloom → algae die → bacterial decomposition spikes → O₂ depleted → fish kill.
pollution-and-climate Bioaccumulation Tap / Space to flip
pollution-and-climate Buildup of toxin (e.g., DDT, mercury) within an individual organism over its lifetime.
pollution-and-climate Biomagnification Tap / Space to flip
pollution-and-climate Toxin concentration increases up the food chain because each predator eats many prey. Top predators most affected.
pollution-and-climate Stratospheric ozone (good) Tap / Space to flip
pollution-and-climate O₃ in 12-50 km layer; absorbs UV-B and UV-C. Depleted by CFCs/halons (Antarctic ozone hole).
pollution-and-climate Tropospheric ozone (bad) Tap / Space to flip
pollution-and-climate Ground-level O₃; secondary pollutant from NOx + VOCs + sunlight. Lung irritant; component of photochemical smog.
pollution-and-climate Major greenhouse gases Tap / Space to flip
pollution-and-climate Water vapor (largest %), CO₂ (anthropogenic driver), CH₄ (~25× CO₂), N₂O (~300×), CFCs (1000s×).
pollution-and-climate Global Warming Potential (GWP) Tap / Space to flip
pollution-and-climate CO₂-equivalent warming over 100 yr. CO₂ = 1, CH₄ ≈ 25, N₂O ≈ 298, SF₆ ≈ 22,800.
pollution-and-climate CFCs · Montreal Protocol Tap / Space to flip
pollution-and-climate 1987 treaty phased out CFCs (refrigerants, aerosols). Successful — Antarctic ozone is recovering.