C1aL18  Pollution Problems

Key Words

Acid rain - rain that has reacted with sulphur dioxide to form an acidic solution

Carbon Dioxide - CO2, a greenhouse gas.

Coal - a sedimentary rock formed by compressing plant material.  Used as a fuel.

Fossil fuels - fuels derived from living things that caught the sun's energy millions of years ago.

Gas -  In this context, methane, or natural gas.

Hydrocarbons - compounds consisting of hydrogen and carbon.

Global dimming - lowering of the energy coming to the Earth from the Sun, caused by pollution

Global warming - increase in average surface temperature.

Oil - crude oil, a foul sticky liquid from which petroleum products are made.

Sulphur Dioxide - SO₂, a toxic and irritating gas given off when coal is burned.

Grade E

Fossil fuels are:

• Coal,
• Oil,
• Natural Gas.

 They came from living things that lived millions of years ago.  The energy inside them is very concentrated, which makes them so useful.

When hydrocarbons are burned they produce carbon dioxide and water vapour (gas):

carbon + oxygen  ®  carbon dioxide

hydrogen + oxygen ® water vapour

Both carbon dioxide and water vapour are greenhouse gases, contributing to global warming.

In addition, most fossil fuels contain a certain amount of sulphur.  This burns to form sulphur dioxide, SO₂:

sulphur + oxygen ® sulphur dioxide

Both carbon dioxide and sulphur dioxide dissolve in water to make acid rain.

Grade C

Rainwater has a pH of about 5.5, making it slightly acidic.  This is because carbon dioxide is dissolved in the water:

carbon dioxide + water ® carbonic acid

CO₂ + H₂0 ® H₂CO₃

If sulphur dioxide dissolves we get a much stronger acid formed, sulphurous acid (NOT sulphuric acid).

sulphur dioxide + water ® sulphurous acid

SO₂ + H₂0 ® H₂SO₃

The pH is about 2, much more acidic than the carbonic acid.  This can do a lot of environmental damage.

The greenhouse gases released by burning fossil fuels are thought to cause global warming.  Carbon dioxide and water reflect infra red radiation back to the ground, so that it does not radiate into space.  This warms the ground.  As more carbon dioxide is released, this effect increases.  This could cause sea levels to rise and more extreme weather events.  There has to be a certain level of greenhouse gases, otherwise the planet would be intolerably cold.

  Acid rain does NOT cause global warming.

When fossil fuels are burned inefficiently, smoke gets emitted.  You only have to be stuck behind a school bus to see that for yourself.  The particles reduce the amount of sun-light getting to the Earth, causing lowering of temperatures, leading to global dimming. 

The Dark Ages in history are thought to be literally that; the volcano Krakatau erupted violently throwing many cubic kilometres of dust into the atmosphere.  The resultant dust reduced the light levels and temperatures considerably, leading to considerable stress on the population and the collapse of civilisation.

Grade A

A strange effect of acid rain is that many lakes are populated by larger fish.  This is thought to be die to younger fish being born that are weaker and deformed due to the lower pH of the lakes.  The older fish have less competition for food, so grow bigger.  As old fish could not reproduce easily, there have collapses in fish populations.

Dropping calcium hydroxide into lakes has increased the pH, enabling fish stocks to recover.