Atmosphere

The atmosphere is the gaseous layer that surrounds the Earth. It extends from ground level to 90Km above Earth’s surface, where it slowly thins out into space. The atmosphere is made up of several different layers, separated by boundaries (–pauses) upon which there is a distinctive change in temperature and pressure.

Troposphere 0-12Km: The lowest layer which is responsible for the weather and has a temperature between 15°C to -20°C.

Tropopause

Stratosphere 12-50Km: Has the highest ozone concentration and so temperature starts to rise (-20°C to 0°C) as it traps heat.

Stratopause

Mesosphere 50-90Km: Last true distinct layer of the atmosphere, part of the atmosphere where meteroites burn upon entry and temperature goes from 0°C to -100°C at the mesopause.

Mesopause

Thermosphere 90-600Km?: Part of the atmosphere where it begins to fade out into space which has been given a boundary value of 600Km, where it turns into the exosphere.

Figure 9 Atmospheric layers (Retrieved from: http://www.ces.fau.edu/nasa/images/EarthsAtmostphere/LayersOfAtmosphere%20copy.gif Date 20/9/2015)

How did the atmosphere form?

It is important to understand that the modern atmosphere is different to the first atmosphere that formed, as the Earth has undergone changes and so to has the atmosphere response to these changes. 

The earliest atmosphere was formed from the expulsion of gases from the geosphere, it consisted of hydrogen, methane, nitrogen, water carbon monoxide and dioxide gases (http://teachertech.rice.edu/Participants/louviere/history.html retrieved 21/9/2015). As the Earth cooled, oceans formed and biological life took place. It was these early forms of life that developed the ability to photosynthesis, reducing the carbon dioxide and increasing the oxygen content of the atmosphere.

6CO₂ + 6H₂O + ϒ → C₆H₁₂O₆ + O₂

This slowly developed into the modern atmosphere which consists of 78% Nitrogen, 21% Oxygen, 0.9% Argon, 0.03% Carbon Dioxide, 0.07% Trace Gases (neon, helium, krypton and xenon).

Note that ozone isn’t included in the composition, because ozone is comprised of three oxygen atoms bonded to each other covalently (sharing electrons), therefore it is included in the overall oxygen composition. This differs to oxygen gas which is two oxygen atoms bonded covalently and this is the type of oxygen we require for respiration. NB ozone is the covalently bonded molecule of three oxygen atoms.

Various forms of oxygen bonding (Retrieved from: https://www.ucar.edu/learn/images/3oxygen.gif Date 19/9/2015).

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How is the ozone being affected?

The ozone is being affected on two levels:

1.    The troposphere where ozone is being formed.

2.    The stratosphere where the ozone is being depleted.

The stratosphere is where the ideal ozone layer is (see earlier) as it formed naturally there, so the earth evolved with respect to stratospheric ozone. Because the troposphere is the lowest layer production of ozone insulates the earth more, keeping in heat and toxic gases.

Ozone in the troposphere is formed from the reaction of carbon monoxide and oxygen, this in turn depletes the troposphere of oxygen and replaces it with less ideal carbon dioxide and ozone gases.

CO + O₂ → CO₂ + O₃

The stratosphere is where the ozone layer is situated naturally and deflects ultraviolet waves preventing them from reaching the Earth’s surface in harmful amounts. Therefore reducing the amount of ozone present in the stratosphere is harmful, which is what hydrofluorocarbons and the sunlight’s gamma rays do.

CFCl₃ + O₃ + ϒ → CFCl₂ + ClO^- + O₂ + β⁺

So the ozone is being removed from where it is needed and added to where it is not.

This is creating serious issues with regards to weather patterns, due to an increase in temperatures amongst layers and has resulted in a change to how air currents flow as temperature affects the density of the molecules and so the pressure is affected. Therefore a change in air flow has resulted in seasonal weathering becoming more extreme i.e. highest snowfalls are being record across America and Europe as is highest temperatures on records.

What does this mean for us?

With the atmosphere changing and so to weather systems we must start to look at ways in which we can limit the future damage to the troposphere and stratosphere. This will limit the severity of future weather systems however it would be naive to think that the weather will return back to how it was as the damage has been done and cannot be undone.

Therefore we must learn to adapt to the conditions and for future worse conditions.