Acid Rain

Seite 1

Causes of Acid Rain

The burning of fossil fuels also produces nitrous oxides and sulfur dioxides

These dissolve in water vapour in the atmosphere and react with water to form acids

This water vapour condenses into clouds and will then fall as acid rain

Oxides of nitrogen + water → Nitric acid

Sulfur dioxide + Water → Sulfuric acid

Seite 2

Harms of Acid Rain and other Atmospheric Pollution

Acid rain:

Increases the rate of weathering - Damaging buildings made of limestone or marble

Increases the rate of corrosion of metals

Makes soil acidic - Some crops find it hard to grow

Makes lakes acidic - Prevent fish eggs hatching

Kills fish and insects - Especially conifer trees

Nitrous oxides:

Cause respiratory diseases - Such as bronchitis

Cause smog - When they react with other chemicals in the presence of sunlight

Incomplete combustion of fossil fuels:

Releases carbon monoxide - Which reduces the amount of oxygen the blood can carry

Releases particulate carbon - Which settles on objects and makes them dirty

Seite 3

Reducing Acid Rain

The amount of sulfur dioxide given off by a power station can be reduced by:

Removing sulfur from the fossil fuels themselves

Removing sulfur dioxide from the flue gases emitted by coal-burning power stations. This is known as desulfurisation by wet scrubbing.

Wet scrubbing involves the removal of sulfur dioxide from flue gases before it escapes from the power station chimney.

Two methods are employed:

Spraying the flue gases with seawater droplets which neutralise the sulfur dioxide

Using calcium oxide mixed with water to form an alkaline slurry. When mixed with air and sprayed with the slurry, the sulfur dioxide in the flue gases forms solid calcium sulphate. This solid is removed allowing cleaned gases to escape.