Managing acid deposition at Higher Level: The same statement as SL, with different real cases: Sudbury, Ontario's coal phase-out, China's scrubbers and the US-Canada Air Quality Agreement. At HL, weigh the law (treaties, emission limits) against the economics (cap-and-trade, who pays for scrubbers and liming).
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- Evaluate a strategy: strength, limitation, judgement.
- Use all three levels of the model.
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Stop it, catch it, fix it: Acid deposition is managed with the pollution management model.
Three levels of management
- Alter human activity: make less SO₂ and NOₓ in the first place.
- Control the release: catch the gases at the chimney or exhaust, by technology and by law.
- Clean up and restore: repair the soils, lakes, forests and people already harmed.
- The higher the level, the more it tackles the root cause; clean-up treats only the effects.
- The best plans use all three levels at once.
Remember it as: Stop it, catch it, fix it.
Alter human activity
- Renewables instead of coal
- Low-sulfur fuel
- Public transport
Control the release
- Scrubbers
- Catalytic converters
- Laws, cap-and-trade, treaties
Clean up and restore
- Lime lakes and soils
- Restock fish, replant trees
- Healthcare
Real example: Sudbury used all three levels. Its smelters changed their process and captured sulfur dioxide to sell as sulfuric acid, and the city limed and replanted the bare land around them.
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The surest way to stop acid rain is to stop making the gases. That means changing the fuel, or burning less of it, before anything reaches the chimney.
Before burning: alter human activity
- Switch to alternative energy: wind, solar, hydro, nuclear, or gas instead of coal.
- Use low-sulfur coal and oil, or wash the coal to remove sulfur before burning.
- Save energy: efficient buildings and machines burn less fuel.
- Fewer cars: public transport, cycling, walking, car-sharing.
- Education campaigns change what people choose and value.
Strengths
- Tackles the root cause
- Cuts SO₂, NOₓ and CO₂ together
- No damage to repair later
Limitations
- Big, costly changes
- Needs political will
- People may resist changing habits
Real example: Ontario, in Canada, closed its coal power stations one by one, ending with the last in 2014. Its electricity now comes mainly from nuclear and hydro power, which release no sulfur dioxide.
Catch it at the source: If the fuel is still burnt, the gases can be removed before they escape: in the furnace, the chimney or the exhaust pipe.
Controlling the release
- Scrubbers (flue-gas desulfurisation): limestone slurry absorbs SO₂ from the smoke; about 90% removed.
- The scrubber turns SO₂ into gypsum, which is sold to make plasterboard.
- Catalytic converters on vehicles turn NOₓ back into nitrogen and oxygen.
- Low-NOₓ burners and cooler furnaces make less NOₓ in power stations.
- Catalytic converters are for exhausts: they do not clean a smelter's or power station's SO₂.
Strengths
- Very effective: most SO₂ or NOₓ removed
- Keeps existing power and cars running
- Easy to require by law
Limitations
- Expensive to fit and run
- CO₂ still released
- Converters need mined platinum metals
Real example: from the mid-2000s China required its coal power stations to fit scrubbers. Between 2007 and 2016 the country's sulfur dioxide emissions fell by about 75%.
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Technology works only if someone makes polluters use it. That is the job of laws, and of agreements between countries.
Laws and agreements
- Emission limits set by law, with monitoring and fines.
- Cap-and-trade: a cap on total SO₂; firms that cut more can sell their spare permits.
- Acid rain crosses borders, so countries need international agreements.
- CLRTAP (1979) was the first; its 1985 Helsinki Protocol cut sulfur by at least 30% of 1980 levels by 1993.
- Later protocols added NOₓ (Sofia, 1988) and more cuts (Gothenburg, 1999).
Real example: acid rain from US power stations fell on Canada's lakes, so in 1991 the two countries signed the Air Quality Agreement, with targets for sulfur dioxide and nitrogen oxides.
Repair the damage: Even when emissions fall, acid soils and lakes take decades to recover. Restoration speeds this up, but it treats the symptoms.
Clean-up and restoration
- Liming: add powdered limestone to lakes, rivers or soils to neutralise the acid.
- CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂: the acid is used up, so the pH rises.
- Add fertiliser or wood ash to replace leached nutrients.
- Restock fish; replant forests, using acid-tolerant plants to bind the soil.
- Healthcare treats people with asthma and bronchitis.
- Cheap and quick, but short-term: it must be repeated and does not stop the acid.
Real example: between 1978 and 2011 Sudbury limed 3,435 hectares of bare, acid land, and its regreening programme has planted more than 10 million trees and shrubs.
Not a cure: Liming must be repeated every few years, costs money, and quarrying the limestone damages other land. It works best once emissions have been cut.
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How this comes up: Paper 2: short Section A parts that evaluate one strategy for a pollutant on a graph, or name a restoration method.
Graphs show nitrogen oxides and sulfur dioxide in a coastal city on wet and dry days. Both come mostly from traffic and an oil-fired power station.
Evaluate a strategy to manage the effects of one of these pollutants.
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A one-mark part asks for a way to repair the damage.
A lake in the Adirondack Mountains lost its trout to acid deposition.
State one method that could be used to restore this ecosystem.
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See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.