The atmosphere surrounding the Earth is a mixture of gases. In some places, human activities have added other gases to the atmosphere, which are called pollutants.
The Earth is surrounded by a mixture of gases called the atmosphere. The main gases in the atmosphere, and their approximate percentages in dry air are: nitrogen 78%, oxygen 21% and argon 1%. The atmosphere also contains a small but important amount of carbon dioxide, approximately 0.04%, and tiny amounts of a few other gases. In addition to these, air also contains water vapour. The percentage of water vapour varies from one location to another, and according to weather conditions. This is why the percentages of other gases are usually quoted for dry air.
Pollutants in Air
Human activities produce a number of gases that are released into the atmosphere. Most of these pollutant gases are produced by the burning of fuels. The burning of fuels releases a large amount of carbon dioxide into the atmosphere. This is thought to cause global warming. Other pollutant gases that are released when fuels are burned include carbon monoxide, nitrogen oxides and sulfur dioxide. The incomplete combustion of fuels also releases small particles of solids, such as carbon, into the air. This makes buildings dirty and affects the lungs.
The Effects of Pollutants
Some of these pollutants are directly harmful to humans. For example, carbon monoxide is toxic, and if breathed in, can cause death. Other pollutants are harmful to the environment, so cause harm to humans indirectly. For example, sulfur dioxide causes acid rain that can damage or kill trees and crops.
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