The air is always around us but we pay it little attention. It contains 78% nitrogen, 20% oxygen and 0.04% carbon dioxide and is essential for our lives.
Yet we do not seem to be too bothered about it and go on pumping all sorts of nasty things into it.
The atmosphere is a complex thing, which we do not realise is important to us. Recently we have begun to realise just how important one part of it is to us, the ozone layer.
Ozone is a molecule made up of three oxygen atoms:
The oxygen molecules present in air has only 2 oxygen atoms in it. So what is so different about ozone?
If you go up to 12-30 miles above the Earth's surface you find a layer of air which contains small amounts of ozone gas. The ozone molecules absorb the ultraviolet (UV) rays that are emitted from the Sun and which are dangerous to all living things. UV rays can increase the risk of cancers forming, such as skin cancer.
So ozone gives us a protective blanket high above us that reduces the amount of UV rays that get through to the Earth's surface. Therefore ozone helps protect us.
However the atmosphere's protective effect is under threat from things we do.
CFC's are "Chloro-fluoro-carbons" to their friends. Although nowadays they don't have many friends.
We thought that they were great molecules at one time. They used to do useful things like running cool machines such as 'fridges' and air-conditioning units. They were in aerosols and polystyrene foam.
However, we now know that they break up ozone molecules and so destroy the layer that protects us from UV rays from the Sun. Not a good idea!
In the last few years we have realised that there are huge holes in the ozone layer near the North and South poles - and they have grown! As more nasty UV rays flood through more people are developing skin cancer.
CFC's have been banned in many countries and alternatives are used instead, but these can be expensive.
This diagram shows renewable and fossil fuels:
We all burn fossil fuels. We do it directly by burning coal or driving cars. We also indirectly burn fossil fuels when we use electricity generated using them.
Our cars and power stations are responsible for most of the fossil fuel burning. The gases released include carbon dioxide, sulphur dioxide and oxides of nitrogen (NO2, NO3, etc.). Up in the atmosphere these gases are dissolved in water and cause acid rain.
The gases also mess up the atmosphere. The extra carbon dioxide causes the greenhouse effect.
Not only do our cars burn a fossil fuel but the older "4 star" petrol contains the element lead.
This leaded petrol was used because it made engines run smoothly. But when it was burned it released the lead into the air. When breathed in it could damage our nervous system. Not nice.
Thankfully, more modern engines can burn "lead-free" petrol and so there will be less lead in the air.