Air is what is between those ears of yours! Just kidding, air is what you breathe all day long to keep you alive. Life on Earth exists within a narrow band of space called the biosphere. The biosphere is only about 15 kilometres in depth. There are three parts to the biosphere; the lithosphere (rock and soil), the hydrosphere (water) and the atmosphere (air).
The atmosphere extends outwards from the earth's surface for several hundred kilometres and is made up of four layers. The first layer, called the troposphere, is where all our weather takes place and is the only layer of the atmosphere to support life. The troposphere has a range of about 8 to 12 kilometres in depth. Human activities like manufacturing can cause changes to the quality of this layer and to the stratosphere, the atmosphere's second layer. Factories pump a lot of pollution into these layers, not to mention automobiles. In the troposphere, the air we breathe is a complex mixture of gases. It is 78 percent nitrogen, 20 percent oxygen, 0.9 percent argon, 0.03 percent carbon dioxide and traces of other gases. Water vapour is also present in varying amounts depending on your location. In addition, there are several other gases and particles that are the result of human activities.
The quality of our air we experience is related to the composition of the gases and particles that make up our atmosphere. Air pollution from natural sources has been a feature of the earth for millions of years. Many scientists believe the extinction of the dinosaurs was caused by a large asteroid which hit the earth. The cloud of dust caused by the collision was so thick that the earth cooled and the dinosaurs could not survive in the changed environment. This became known as the Ice Age. Volcanic smoke and dust, sand and dust storms, and wild fires are all sources of "natural" air pollution.
Today, many visible effects of air pollution have been eliminated. Cleaner fuels such as natural gas are used. Manufacturing processes reduce their emissions by being more efficient in their use of energy and raw materials. Many smokestacks have dust collectors or scrubbers to reduce harmful emissions. Not all pollutants can be removed completely, but the smokestack giving off thick black smoke is nearly a thing of the past.