ENVIRONMENTAL CHEMISTRY

The term "environment" literally means "surroundings". Environmental chemistry is that branch of science which deals with the chemical phenomenon occuring in the environment i.e study of origin, transport, reaction, effect and fates of chemicalspecies in the environment. It comprises of the following four major components :-

<b>1. Atmosphere :-</b> Atmosphere is a cover of gases that extends to a height of about 1600 km above the surface of the earth and protects the lifes on the earth from the harmful radiations coming from the sun or the outer surface.

Function of the Atmosphere :-

* It contain all those gases which are essential  for the existence of life on the earth.

* It is an important carrier of water vapour which are needed for all forms of life.

* Ozone present in it absorbs the harmful ultraviolet radiations coming from the sun and thus protect life on the earth.

* It maintain heat balance of the earth by absorbing infrared radiations coming from the sun and those re-emitted from the earth. For the same reason, it controls weather and climatic conditions.

Temprature of  the atmosphere :- Differents parts of the atmosphere absorb and reflect different amount of heat of the solar radiation. Hence, temprature of the atmosphere varies from - 100*C to 1200*C

Structure or region of the atmosphere :- The atmosphere may be considered to be divided mainly into four region above the surface of the earth. These region are defined by the temprature variation with height in addition to the decrease in density and chemical composition. The names of the regions, the altitudes at which they exist, their temprature ranges and their chemical compositions.

Troposphere :- Troposphere is the most important region of the atmosphere becouse it is the domain of all living organism including animal and plants. This is the region which is greatly affected by air pollution. Further, this is the region which contains water vapour which are essential for the living organisms. 80% of the mass of the atmosphere is in this region. The temprature of this region decreases with altitude and is minimum at about 11 km. This point is called tropopause. In the next region, namely stratosphere, the temprature begins to increase. Thus, tropopause is the point of temprature inversion. The ozone present in the stratosphere absorbs the harmful ultraviolet radiation coming from the sun and thus act as an umbrella for the ultraviolet radiation for the living organism on the earth. Due to presence of ozone layer, this region is also called ozonosphere. The rise in temprature due to absorption of ultraviolet rays which is coonverted into heat. Mesosphere and thermosphere contain gases in the ionized form. These ions reflect back the rafdiowaves to the earth. This forms the basis of wireless communication.

<b> 2. Hydrosphere :-</b> It forms that part of thecenvironment which contain water in the form of sea, rivers, oceans, lakes, ponds etc. About 75% of the earth surface is covered by hydrosphere . Most of it is in the oceans and contains about 3.5% of dissolved salt . Fresh water is present in lakes or rivers or ponds which flow into them from rain or melting of snow etc.

<b>3. Lithosphere :-</b> It is the solid component of the earth consisting of soils, rocks, mountains etc. The outermost (8 - 40km) thick solid part of the earth is called the crust. The uppermost part of the earth crust contain weathered rock as well as organic matter and is called Soil. This is the most important part of lithosphere becouse we grow plants on this part. It is also a Store-house of minerals.

<b>4. Biosphere :-</b> It is that part of the lithosphere, hydrosphere and atmosphere where living organisn intereact these parts and thus live together. For ex. Green plants during photosynthesis give out oxygen which is added into the atmosphere, animal inhales oxygen and give out corbondioxide which is used by plants for photosynthesis.