Environmental Chemistry: Atmosphere, Troposphere, Stratosphere and Solar Formation

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Environmental Chemistry Atmosphere - Troposphere, Stratosphere, Solar Formation (Chemistry)

Table of Contents

  • Learning Outcomes


  • What is ‘Atmosphere’ ?
  • Significance of the Atmosphere
  • Composition of the Atmosphere

Evolution of the Atmosphere

  • Primitive or First Atmosphere
  • Reducing or Second Atmosphere
  • Oxidizing or Present Day Atmosphere

Structure of the Atmosphere and vertical temperature

  • Troposphere
  • Stratosphere
  • Mesosphere
  • Thermosphere
  • Exosphere

Heat budget of the earth՚s atmosphere

  • Energy budget
  • Earth՚s energy imbalance
  • Natural greenhouse effect
  • Climate sensitivity and forcing

Learning Outcomes

After studying this lesson, you shall be able to:

Structure of the Atmosphere and vertical temperature

  • Troposphere
  • Stratosphere

Structure of the Atmosphere

There are five layers of the earth՚s atmosphere based on the variation in vertical

Temperature in each layer:


  • Troposphere is closest layer to the earth՚s surface. So, the layer in which we live is troposphere.
  • It is about 18 km above the sea level at the equator and 7 km at poles.
  • 75 % of the atmospheric gases are present in this layer and almost all of the dust particles and water vapors.
  • All weather phenomenon like cloud formation, winds, rainfall, snowfall takes place in this layer.
  • The air below this layer is warmer than any other layer because it is heated from the earth surface below. The layer of air which is warm tends to rise up, and a pocket of cold air flows to cover the space, giving rise to wind movement.
  • The temperature will decrease at a rate of about 6.5 °C per km as the altitude increases.
  • The average temperature near the surface is 15°C while it is -57° C at the top. Pressure, moisture content and density of air also decrease with height thinning of air. That is why people experience breathlessness at high altitudes in mountains.
  • The troposphere ends when there is variation in temperature with height. This area, which is the top of troposphere and bottom of stratosphere, is known as tropopause.
  • The inversion of temperature beyond tropopause prevents further convection of air thereby confining most of the weather phenomenon in troposphere.
Weather Phenomenon


  • Stratosphere is the second layer of earth՚s atmosphere. It starts at the top of tropopause and is 50 km above the sea level.
  • The term stratosphere is derived from a Greek word “strata” which means arrangement in horizontal layers. Approximately 99 % of the atmosphere is located up to this height which includes almost all the gases.
  • Weather balloons and jet aircrafts fly in this region as the air present in this layer is very thin. This increases the fuel efficiency of the aircrafts.
  • The stratosphere also contains the ozone layer; at a height of about 30 km.
  • The density or thickness of ozone layer above the surface of earth is measured in Dobson Units (DU) .
  • The ozone layer is thinnest near the equator (~260 DU) and its thickness increases towards the poles, though there are seasonal fluctuations.
  • Ozone – which is a mainly formed photochemical smog – is considered to be dangerous for health if reached the ground level or near the surface of earth.
  • However, in the stratosphere, the high energy UV radiation is absorbed by the ozone layer and heats up the stratosphere. This also prevent skin cancer and damage to vegetation.
  • The ozone layer is created in the stratosphere when the oxygen molecules (O2) absorb UV radiations (240 nm) and dissociate to give atomic oxygen (O) which immediately react with another O2 molecule and results in the formation of an ozone (O3) molecule:
  • Although, the absorption of UV radiation in the stratosphere leads to dissociation of ozone molecules, the ozone layer density is maintained by the reformation of ozone:
UV Absorbption
  • As the height increases temperature in the stratosphere also increases, with the base temperature being close to − 60 °C and close to freezing at the top.
  • This is because, the top layer is hottest and bottom is coldest, the temperature stratification takes place with little or no mixing of layers.
  • The stratification has a disadvantage too. Because there is no vertical convection in the stratosphere, so dissipation and dispersion of materials do not take place.
  • Chlorofluorocarbons (CFCs) and aerosols from volcanic eruptions and meteorite impacts can stay in the stratosphere for prolonged periods of time resulting in damage to the ozone layer and alteration of global climate.
  • The periods of existence of ozone hole have also seen a considerable increase in the reported incidents of skin cancer.
Constant Temperature
  • The layer which is top of the stratosphere and bottom of mesosphere (the next layer to stratosphere) is known as stratopause.
  • Here, the temperature becomes constant with altitude till it again starts increasing in the mesosphere.


1. Ozone is present at which atmospheric layer?

a) Troposphere

b) Mesosphere

c) Thermosphere

d) Stratosphere

Answer: D

2. At what distance stratosphere is present from the sea level?

a) 50 km

b) 18 km

c) 100 km

d) 25 km

Answer: A




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