Structure and composition of the atmosphere

What is the atmosphere?

• Thin layer of gases surrounding the earth, held in place by gravity

How is it essential to life on earth?

Provides a vital support system:

• Source of gases for natural processes

• Absorbs electromagnetic radiation from the sun

• Delays escape of infrared energy

• Creates moving air which distributes heat and water vapour

• Provides winds over the oceans, creating water currents

• Creates pressure which allows liquid to exist

• Source of gases for human exploitation

What is the composition of the atmosphere?

• Nitrogen- 78%

• Oxygen- 21%

• Carbon dioxide- 0.04%

• (Combined) rare gases- 1%

• Ozone- 0.000007%

Dynamic equilibrium in the atmosphere

Natural processes are in a state of balance

• DE in the atmosphere maintains the composition so that it only changes over very long timescales

• Photosynthesis and aerobic respiration are particularly important processes, roughly balancing eachother

• However, the rates at which they occur varies over different timescales so the concentration of each gas fluctuates around a mean concentration

Layers in the atmosphere

TRuST METH

• Troposphere

• Stratosphere

• Mesosphere

• Thermosphere

A change in temperature with distance is called a temperature gradient.

The atmosphere is divided into layers based on:

• Change in atmospheric pressure

• Change in temperature

• Chemical composition

Atmospheric pressure

• Controls the ease with which water molecules can evaporate and escape from the water surface

• If atmospheric pressure was much lower there would be no liquid water on Earth

• Pressure decreases with altitude

Changes with altitude

Troposphere:

• Temperature declines with increasing altitude in the troposphere due to heating by IR radiation from the ground

• Also contains much more water vapour than other layers, and lots of dust particles

Stratosphere:

• Temperature increases with altitude

• More ozone found in the stratosphere where UV light interacts with oxygen

• Suns UV heats the stratosphere

Mesosphere:

• Temperature decreases with altitude due to fewer air particles and radiative emissions such as CO2

Thermosphere:

• Temperature increase with altitude due to solar activity, our particles are not as well mixed in this layer

Stratospheric ozone layer

• Protects us from incoming UV radiation

• Ozone molecules which absorb UV later re-radiate energy as heat, warming the stratosphere

• Doesn’t contribute to global warming and climate change

Tropospheric ozone

• Ground level (tropospheric) ozone is created by chemical reactions between oxides of nitrogen and volatile organic compounds

• The combination of these chemicals in the presence of sunlight form ozone

• Ozone in the troposphere is considered a greenhouse gas, and may contribute to global warming

Graph of temperature of different altitudes showing layers

How does the atmosphere support life?

• Gases for natural processes

• Gases for human exploitation

• Transport of water vapour

• Absorption of EM radiation from the sun

• Delaying escape of IR energy

• Heat distribution

• Ocean currents

1) Gases from natural processes

• Nitrogen > DNA and protein synthesis

• Carbon dioxide> photosynthesis and natural greenhouse effect

• Oxygen> aerobic respiration

• Water> biological solvent

• All carbohydrates, lipids and proteins contain C,H,O and N

2) Gases for human exploitation

• Humans extract a variety of industrially important gases

• Nitrogen, oxygen, carbon dioxide

• Also and inert gases such as argon, neon, krypton (they wont undergo chemical reactions with many materials)

• Helium> balloons, blimps, coding in high tech manufacturing

• CO2> fire extinguisher

• Nitrogen> fertiliser manufacturing

• Ozone> water sterilisation, treatment, purification

• Oxygen> steel, iron purification, breathing gases, cutting and welding, rocket fuel, sewage treatment

3) Transport of water vapour

• Winds transport water vapour to areas that would otherwise get little or no precipitation

4) Absorption of electromagnetic radiation from the sun

• Lots of UV light that passes through upper atmosphere is prevented from reaching earth’s surface by the various forms of oxygen present in the stratosphere

  • O, O2 and O3> monoatomic, diatomic, triatomic

  • The 3 form is dispersed layer in the stratosphere known and the ozone layer

  • This absorbs / utilises UV light, producing a dynamic equilibrium of chemical reactions which form and destroy ozone

5) Delaying escape of infrared energy

• Most incoming visible light is absorbed, converted to heat and re-emitted as IR energy

• Naturally occurring atmospheric gases absorb this infrared energy, convert it to heat and increase the temperature of the atmosphere

• This raises earths temperature in 2 ways:

  • Warm atmosphere emits infrared energy which is absorbed by earths surface

  • Warm atmosphere reduces heat loss by conduction from land and oceans

6) Heat distribution

• Most energy that is absorbed from the sun is absorbed by the surface in tropical regions

• Warm surface heats atmosphere above, this heat is distributed to higher latitudes by warm winds

7) Ocean currents

• Winds blowing over the oceans create currents that distribute heat by carrying warm water from tropical areas to higher latitudes

  • e.g. North Atlantic Conveyor

• These currents can also distribute dissolved nutrients