Composition of air:
Atmospheric air comprises certain elements in a specific ratio. 99% of the Earth's atmosphere is made up of four compounds. These major components are nitrogen, oxygen, argon and carbon dioxide. The air in the atmosphere is made up of about 79% nitrogen, 20%oxygen & the remaining being noble gases & carbon dioxide. Another major component of the Earth's atmosphere is water vapor. The percentage of water vapor may range from 1-5 percent. Substances present in the air, other than these five main components are referred to as trace elements. 
Properties of air:
Air can be greatly compressed & can be expand almost indefinitely. Air have its own weight, temperature & volume. Air is under pressure as this caused by gravity & air has some velocity (speed).
AIR POLLUTION..
The causes & effects of air pollution:
The main pollutants in the air are carbon dioxide, sulfur dioxide, carbon monoxide, nitrogen oxides,methane, ground level ozone & unburned hydrocarbons.
-Most of these pollutants are formed from the combustion of fossil fuels & forest fires while some are formed by natural means like lightning & volcanic eruptions.
-Nitrogen oxides & unburned hydrocarbons react with air & sunlight to form ground level ozone & smog.
-Most methane is formed as a result of human activities such as agriculture, rearing of animals, mining & waste disposal.
-The harmful effects of atmospheric pollutants include environmental problems such as global warming & acid rain, leading to damage to health & even death.
-Global warming has caused drastic changes to Earth, such as drastic changes like floods, droughts,heat waves & the melting of polar ice caps & glaciers which leads to the flooding of many coastal countries in the world.
Prevention of air pollution:
Most of the air pollutants can be removed or reduced by some methods.
-installing catalytic converters in motor vehicles to remove nitrogen oxide, carbon monoxides & unburned hydrocarbons.
-treating acidic waste gases like sulfur dioxide & nitrogen oxides with calcium hydroxide before releasing them into atmosphere.
-burning fossil furls with less sulfur content like natural gases, using petrol & diesel with very little or no sulfur content.
-using alternative sources of energy like solar energy, wind energy, hydroelectric power & biofuel from plants.
