Air is one of the most important natural resources. Air is necessary for all living organisms for their respiratory process. The organisms which live on the land (called terrestrial organisms) get oxygen needed for respiration from the air. A healthy man breaths 22000 times a day and takes in about 16 kg of air.
Air is invisible, colorless, odorless and tasteless. Air has mass and it exerts pressure.
Air is not a single gas. It is a mixture of many gases, water vapor and other particulate matter. The actual composition of air varies from place to place. Near the earth’s surface, air mainly consists of nitrogen and oxygen, carbon dioxide and water vapor. Of all the components of air, carbon dioxide (CO2) has the highest solubility in water.
The actual average composition of the air near the earth’s surface (atmosphere) is given below in table: The percentage of almost all the gases except carbon dioxide, remain nearly constant. The proportions of carbon dioxide(CO2), water vapor (H2O(v)) and dust/smoke particles in the air keep changing from time to time and place to place. For example, the air around an industrial area contains more carbon dioxide.