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This article throws light upon the five main zones or regions of atmosphere. The zones are: 1. Troposphere 2. Stratosphere 3. Mesosphere 4. Ionosphere 5. Anthrosphere.
Zone of Atmosphere # 1. Troposphere (Tropos Meaning Turning):
Troposphere is the region nearest to the earth’s surface and extends up to an altitude of 11 km.
It is the most important zone for organisms and is composed of O2, N2, CO2, H2O and particulate matter.
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Temperature ranges from 14°C to -56°C in troposphere. The top of troposphere is called tropopause.
The change of temperature with height is known as lapse rate. The decrease of temperature with increasing altitude in the troposphere is called positive lapse rate. The transition from positive lapse rate to negative lapse rate at the tropopause marks the temperature inversion.
Zone of Atmosphere # 2. Stratosphere:
The region above the tropopause is known as stratosphere (11 km to 50 km with temperature range from -56°C to -2°C). In this zone, the temperature-altitude curve shows a warming trend with increasing altitude, i.e., it exhibits a negative lapse rate.
Ozone in stratosphere acts as a protective shield for life on earth from injurious effects of sun’s ultraviolet rays and at the same time, supplies the heat source for partitioning the quiescent stratosphere from the turbulent troposphere.
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The region above the stratosphere (>50 km) is called stratopause. Because of the absorption of ultraviolet radiation, stratosphere is heated up and this causes temperature inversion which limits vertical mixing of pollutants. This is the reason why smog is seen to hang in industrialized areas. The smog spreads horizontally very fast but very slowly vertically.
Zone of Atmosphere # 3. Mesosphere:
Mesosphere is the region above stratopause that extends from 50 km to 85 km. In this zone, temperature again decreases (from -2°C to -92°C) with height, that is, it exhibits a positive lapse rate. Important components are O2 and NO 2+. The region above the mesosphere is called mesopause.
Zone of Atmosphere # 4. Ionosphere or Thermosphere:
Thermosphere is the region (85 km to 500 km, temperature ranges from -92°C to 1200°C) above mesopause, where temperature rises rapidly with increasing altitude, exhibiting a negative lapse rate. The gases present in this region (O2 and NO) absorb solar radiation and undergo ionisation.
The region above the stratosphere, in the altitude range of 50 km to 100 km, is called ionosphere. In this region, O2+, O+, NO+ and electrons exist at significant levels. Atmosphere above the ionosphere is called exosphere or outer space. It extends up to 32190 km from the earth’s surface. It lacks atmosphere and consists of only H and He.
Zone of Atmosphere # 5. Anthrosphere:
Anthrosphere constitutes the fifth sphere of the environment along with the geosphere, hydrosphere, atmosphere and biosphere. It consists of things humans construct and use.
