· Carbon monoxide - a colorless and odorless poison, it is a gas produced when fuel is not completely burned in engines, furnaces and space heaters. A major source of this is the vehicles.
· Carbon Dioxide - a product by normal combustion. Although it is not a serious pollutant, it is believed that the continuous build up of this gas in the atmosphere would cause a "green house effect" by reducing the flow of heat from earth back into the space, thus causing the warming of the earth.
· Sulfur dioxide - one of the most dangerous of all air pollutants. The major sources of these pollutants are factories and electric power plants that use sulfur-containing coal or oil as fuel. In the air, some sulfur dioxide is converted to sulfuric acid, which is then deposited into the earth's surface, usually by rain. This acid rain has caused damage to the environment in many parts of
the world.
· Nitrogen oxides - are mildly poisonous brown gases. These are produced in automobile engines and other devices where combustion takes place. During thunderstorms, heat energy that has been released by lightning causes nitrogen and oxygen in the air to react to form nitrogen oxides. Gas ranges are a major source of nitrogen oxides. These oxides dissolve in water to form acid rain.
· Hydrocarbon pollutant - produced by unburned fuel and is emitted mostly by motor vehicles. This also contributes to smog.
· Particulate matter - tiny liquid or solid particles in the air. Particulate matter includes smoke, dust, and soot, which may contain toxic substances like asbestos, fluorides, lead, and mercury. Tobacco smoke is one of the major sources of particulate matter.
· Chlorofluorocarbons (CFC's) - are synthetic substances that have has a variety of industrial uses. It is believed that CFC's can also contribute to a "greenhouse effect" resulting in the warming of earth. Some scientists also believe that CFC's are destroying ozone that absorbs potentially harmful ultraviolet radiation from the sun.
· Radon - is a naturally occurring radioactive gas formed in varying concentrations in the ground. The waste products of radon enters building from the ground, in place where there is a high concentration of radon, dangerous level of this gas may accumulate in building where there is poor ventilation.
· Methane – is a colourless and odourless gas. it is produced from decaying matter and the decay of rubbish in landfills. It is an important greenhouse gas.
