Composition and Structure of the atmosphere.

Atmosphere, in general, is a layer of gases that may surround a material with sufficient mass, supported by gravity. Earth’s atmosphere is up to 10,000km. However, there is no definite boundary between atmosphere and the outer space. Now, talk about the construction of space, although there is no definite boundary between layer and layer, based on the concentration of gases… Earth’s atmosphere is divided into 5 main layers:

- Troposphere: Up to 15km, which has the highest concentration of gases and also this is where we live.

- Mesosphere: up to 95/120km, this is where most meteors burn up when it goes to the atmosphere.

- Stratosphere: up to 50/60km, contains ozone layer.

- Thermosphere: up to 600km,extremely low pressure, temperature increase with height.

- Exosphere: up to 10,000km, contains many free-moving particles.

Compositions of the earth’s atmosphere:

• nitrogen (N₂: 78%),
  
• oxygen (O₂: 21%),
  
• other gases ( carbon dioxide CO₂: 0.036%, water vapour, methane, helium, krypton, argon, neon, hydrogen, nitrous oxide, iodine, carbon monoxide, ammoniac).
  

The question now is why is it so important to know what is the construction and composition of the Earth’s atmosphere? It’s not very difficult to remember these but to keep it being balance is not such a easy work. This is important because Earth’s atmosphere is such a fantastic combination, it gives us lives. Constant in line is change and every little thing that change in the atmosphere can affect the destiny of all human being. For example: Carbon dioxide (CO₂) 0.036%, needed for plants to perform photosynthesis in order to make carbon hydrates and sugar. CO₂ also keeps heat from escaping from the earth so that we won’t freeze to death. However, along with modernization and industrialization , the amount of CO₂ is increasing day by day. This means that heat is trapped in the atmosphere much more than before and results in global warming.

Another thing about the atmosphere is also important to learn about is the ozone layer. Ozone (O₃) is very unstable. It helps screen out UV-C ray (280-100nm), which is very harmful to human and UV-B which can cause cancer. The UV ray hits ozone to split it up to oxygen molecules and atom to form a oxygen-ozone cycle. The chemical equations:

- O₃ → O₂ + O

- O+ O₃→2O₂

- 3O₂ → 2O₃

However, the ozone layer depletes rapidly recently. One of the reasons is CFC gas (chlorofluorocarbons) from the refrigerators. It goes in between the oxygen-ozone cycle and this over effect make ozone decrease.

- CFCl₃ → CFCl₂ + Cl (UV rays)

- Cl + O₃ → ClO + O₂

- ClO + O₃ → Cl + 2 O₂

Another question in the lesson that needs to answer is temperature in the thermosphere can reach beyond 1200 degree Celsius but we can still freeze to death is because of the extremely low pressure and there are too little gas molecules in thermosphere. As 99.99997% mass of the atmosphere is below 100km, the temperature can be high but the chance for the molecules to reach human skin is very small. That’s the reason why we can still freeze there.

In short, through the lesson, I have had an overview of the atmosphere. As a matter of fact, I also learn the pros and cons of the change in atmosphere that can affect our live. I also learn to understand some invisible cycles that’s continuously happening to maintain conditions for life. Finally, it’s fun to know chemical equations of the ozone and ozone depletion.

Done by: Dao Thuy An (03)