We've seen that incomplete combustion makes Carbon Monoxide.

But why is this a problem?

Firstly, it is difficult to detect Carbon Monoxide because it is colourless and odourless.

More importantly, it is toxic.

It binds permanently to our red blood cells, which we need to transport Oxygen round our bodies.

Too much Carbon Monoxide means not enough Oxygen is transported and can kill us.

These days many houses have a detector in case the central heating malfunctions and starts to produce Monoxide.

We saw how Sulphur Dioxide and Nitrogen Oxides are made when fuels burn.

These gases are acidic and inhaling them is very bad for our lungs.

These gases can drift in the wind, mixing with Oxygen and water and turning into Sulphuric and Nitric Acids.

All rain is a little acidic.

Rain with a pH below 5.5 is un-naturally acidic and is usually caused this way (although volcanoes can also cause it).

Acid rain can kill plants - even entire forests.

It washes toxic compounds out of soil and into lakes that become so acidic all the fish die.

It can also dissolve buildings and statues made of limestone and marble.

Un-burned fuels and particles of soot are also bad for our lungs.

Particulate pollution from diesel engines is a real health problem.

Most people know about CO₂ causing Global Warming.

But it is thought that the many tons of particles in the atmosphere from coal and other fuels actually reflects some heat back into space.

This keeps the planet a little cooler than it would otherwise have been,

This is called Global Dimming.