6.4 Acid Deposition

Question 1

How is acid rain formed?

Answer 1

Rain is naturally acidic (pH 5.6)
- Caused by carbon dioxide in the air forming carbonic acid

HOWEVER:
When sulfur and nitrogen dissolve in the rain they form sulfuric and nitric acid and can have a very low pH.

Question 2

Acid deposition can be either w__ or d__ :

Answer 2

Acid deposition can be either WET or DRY

Question 3

Pollutants can be either p____ or s____

Answer 3

Pollutants can be either PRIMARY or SECONDARY

Question 4

What are primary pollutants?

Answer 4

Primary pollutants - those directly emitted by a factory or vehicle

- SO2 - sulfur dioxide
- NO and NO2, usually identified as NOx

Question 5

What are secondary pollutants?

Answer 5

Secondary pollutants - primary pollutants react with other substances in the atmosphere and create different pollutants

- H2SO3 - sulfurous acid
- H2SO4 - sulfuric acid
- HNO3 - nitric acid

Question 6

What are some of the effects of Acid deposition on Terrestrial ecosystems?

Answer 6

SOIL:

• Leaching of calcium, magnesium and potassium leading to a loss of soil fertility
• Inhibition of decomposition by bacteria and fungi and disappearance of earthworms and molluscs

LICHENS:

• These are particularly sensitive to sulphur dioxide
• Tables of lichen indicator species are used to estimate pollution levels

CONIFEROUS TREES:

• Acid deposition causes yellowing of needles and buds due to a loss of chlorophyll and damage in the form of lesions as well as thinning of the waxy cuticle. These effects allow pathogens and insect pests to gain entry to the trees.
• Decreased soil pH leads to leaching of essential nutrients meaning reduced availability and lower productivity.

Question 7

What are some of the effects of Acid deposition on Freshwater ecosystems?

Answer 7

1. Below ph4.5 trout do not produce the enzyme which breaks down the outer coating of eggs. The larvae therefore do NOT hatch, preventing successful reproduction
2. A decreased soil pH makes aluminium ions more soluble and they are leached into rivers. Aluminium causes fish to produce excess sticky mucus on their gills, clogging them up and making gas exchange difficult
   - -> Aluminium can also prevent fish from regulating the amount of salt and water in their bodies and can result in death

Question 8

The effects of acid deposition tend to be ______

Answer 8

REGIONAL, rather than global as with ozone depletion and the greenhouse effect, as before the pollutants are spread over very long distances, they return to the Earth’s surface as dry or wet deposition.

Question 9

Why are the effects of acid deposition particularly great in non-limestone areas? (eg. granite)

Answer 9

They do not have a buffering effect and the soils are much more sensitive to acid deposition.

Question 10

How can Acid deposition be reduced?

Answer 10

1. Most efforts to reduce acid deposition concentrate on reducing emissions of sulphur dioxide and nitrogen oxides for example by decreasing fossil fuel consumption through the use of alternative energy sources, decreasing consumer demand for electricity through energy saving measures and decreasing car use and developing more efficient cars
2. Fuel desulphurisation –> pre-combustion technique where sulphur is removed from coal before burning
3. Catalytic converters on car exhausts. (Catalyses the conversion of NOx to harmless nitrogen and oxygen which are then emitted in the exhaust gases).

Question 11

How are acidified lakes treated?

Answer 11

Acidified water bodies can be treated with lime

• -> This is a short term solution where the effects can be limited due to the flow of water
• -> Neutralises acidity, increases calcium levels and precipitates aluminium out of solution

HOWEVER:
- Large amounts of limestone are needed, which is very expensive and the process can be slow