The Envelope of air held around the earth by its magnetic force, gravity or geomagnetism, is called the atmosphere.
What is air? Air is a mechanical mixture of different gases surrounding the earth. The specific composition of air and the radiation from the sun make the atmosphere peculiar for the earth and its inhabitants.
The air density in the atmosphere decreased by increasing altitude and more than 90% of air by mass is found within a range of about 30 Km from ground level. According to recent investigations certain electrically charged particles called ions, are found along with various gases, dust particles and water- vapour in the atmosphere.
Water vapour found in the atmosphere is called as humidity. It enters into atmosphere due to transpiration and vaporization processes occurring due to high temperature and speed of wind. Roots of some plants such as epiphytes (like Orchid), mosses, lichens and even hanging roots of banyan trees absorb humidity of air to meet their excessive water demands.
Humidity of air also plays important roles in keeping up the heat balance on earth as it can also absorb Ultraviolet radiations of the sun. Accumulation of gases like NO2, CO2, SO2 contribute in the Acid Deposition in the environment and causes acid rain. As we know, acidic water of rain has pH lesser than 7 and can corrode walls of monuments by reacting with their plaster.
The importance of the study of atmosphere has increased since last few decades. It is due to following facts-
1. Air of atmosphere helps in the operation of different natural phenomena like water cycle, origin of wind, formation of clouds, rain fall and snow fall etc.
2. Oxygen of atmosphere helps in the respiration of all organisms and Carbon dioxide helps in the process of photosynthesis. Other gases of atmosphere like nitrogen, organ and helium are isolated for industrial purposes.
3. The ozone layer of atmosphere checks harmful ultraviolet radiations against reaching to the earth. The ultraviolet radiations are very harmful to life as they cause skin cancer, cataract in eyes, burning of leaves of plants and death of smaller organisms etc. if these radiations are allowed to reach to the earth.
4. Atmosphere helps in the flying of birds and in aviation. It also acts as a medium for the transmission of sound waves.
5. The study of atmosphere helps in the forecasting about future changes in the weather conditions that often cause extreme events like natural disasters.
6. The advanced knowledge gained through the study of atmosphere helps in the advanced management and preparedness against natural disasters.
