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Acid deposition 6.4 - Coggle Diagram
Acid deposition 6.4
Key points
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It can impact living systems and the built environment. The pollution management involves cross border issues hence, cooperation.
Acids contain a free H+ ion to donate. Acidity is measured with the pH scale = 1 ACID, 7 = NEUTRAL, 14 = ALKALINE. it is a log scale so pH5 is 1000x more acidic then pH2.
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Rain is naturally acidic at around pH5.6. Acid rain is defined as any precipitation with a pH lower than 5.6
Causes:
The increase has been attributed to the production of sulphur dioxide and bodies of nitrogen during the combustion of fossil fuels
Sulphur dioxide is formed when fuels containing sulphur are burnt e.g. in coal or oil - not in natural gas. Petrol + Diesel contain few sulphur compounds = don't contribute significantly to sulphur dioxide levels.
Nitrogen oxides are formed in car engines when high temps cause nitrogen from the air to combine with O2. N doesn't come from fuel
BOTH fall as Nitrates and sulphates during dry deposition. They can also be oxidised and react with water in the air to form sulphuric acid and Nitric acid = SECONDARY POLLUTANTS
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Effects
Water
Can enter directly or indirectly (runoff). It can lower the pH of water rendering it unable for organisms to survive in.
Species of phytoplankton may be sensitive to changes leading to knock on effects on the food chain and other trophic levels = some fish eggs may not hatch at bellow pH5, reproductive failure etc.
Also, decrease in soil pH leads releases Al ions which leach into water. Fish begin to produce excess mucus around the gills representing O2 uptake. The fish die from asphyxiation.
Soil
Overall increases soil acidity. Leads to leaching of calcium, potassium etc. (minerals/nutrients) in the soil = infertile soil. Also, decrease in number of earthworms, fungi and bacteria due to inability of survival below pH4.5
Coniferous trees are more threatened than deciduous trees as they don't shed their leaves at the end of the year. Trees also take up toxic Al from the soil.
Can be DIRECT = weaken tree growth, or INDIRECT =
The extent depends on the ability of the environment to neutralise the acid e.g. alkaline + acid = neutral = the buffering capacity. Hence, the larger presence of alkaline compounds means the lower the effect of acid deposition.
Management
Replace
- Switch to renewable energy sources
- Increase energy inefficiency
- Increase public transport accessibility + use
- Use electric/hybrid cars - electricity is generated with lower emissions of nitrogen oxides or sulphur dioxide
Hard to change human behaviour, takes time, change may be costly + require gov support e.g. economic incentives to act sustainably
Regulate
- Install ‘scrubbers’ on smokestacks of coal-fired power plants to remove SO2
- Catalytic converters installed on car exhausts (required in US, Canada + Europe) however, increase CO2 emissions
- Tax on pollution / Carbon tax / tradable permits
Requires enforcement, scrubber produces waste sludge needs to be disposed of, takes time to develop new technology
Restore
- Add powdered lime to acidified bodies of water
- Or to forestry plantations
- Recolonise damaged systems
Adding lime balances the acidity of acid water. It is expensive and has to be done repeatedly. It's only a short-term solution at the expense of solving the broader challenges of SO2 and NOx emissions and risks to human health. Nevertheless, it restores and allows the survival of aquatic species by improving chronically acidified surface waters.
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Regional impacts
Areas downwind of major industrial regions experience acid deposition e.g. Scandinavia experienced high acid rain in the 1980s as there was heavy industry in Western Europe. Now it is less of a threat due to less heavy industries.
Areas affected have a combination of being downwind from industrial areas or fuel petrol stations, have high rainfall and forests/lakes + thin soils.
In Scandinavia, the buffering capacity os very low as the underlying rock is granite (naturally acidic) not chalk or limestone (high buffering capacity) hence, acid deposition is very damaging