Stratosphere

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The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler higher up and warmer farther down. The border of the troposphere and stratosphere, the tropopause, is marked by where this inversion begins, which in terms of atmospheric thermodynamics is the equilibrium level. The stratosphere is situated between about 10 km (6 miles) and 50 km (31 miles) altitude above the surface at moderate latitudes, while at the poles it starts at about 8 km (5 miles) altitude.

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Ozone and temperature

Within this layer, temperature increases as altitude increases (see temperature inversion); the top of the stratosphere has a temperature of about 270 K (−3°C or 29.6°F), just slightly below the freezing point of water.[1] The stratosphere is layered in temperature because ozone (O3) here absorbs high energy UVB and UVC energy waves from the Sun and is broken down into monoatomic oxygen (O) and diatomic oxygen (O2). Monoatomic oxygen is found prevalent in the upper stratosphere due to the bombardment of UV light and the destruction of both ozone and diatomic oxygen. The mid stratosphere has less UV light passing through it, O and O2 are able to combine, and is where the majority of natural ozone is produced. It is when these two forms of oxygen recombine to form ozone that they release the heat found in the stratosphere. The lower stratosphere receives very low amounts of UVC, thus monoatomic oxygen is not found here and ozone is not formed (with heat as the byproduct). This vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere. The top of the stratosphere is called the stratopause, above which the temperature decreases with height.

Methane (CH4) while it is not a direct cause of ozone destruction in the stratosphere, does lead to the formation of compounds that do destroy ozone. Monoatomic oxygen (O), in the upper stratosphere, reacts with methane (CH4) to form a hydroxyl anion (OH-). This hydroxyl anion is then able to interact with non-soluble compounds like chlorofluorocarbons and UV light break off chlorine anions (Cl-). These chlorine anions break off an oxygen atom from the ozone molecule, creating an oxygen molecule (O2) and a hypochlorite molecule (ClO-). The hypochlorite molecule then reacts with a monoatomic oxygen creating another oxygen molecule and another chlorine anion, thereby preventing the reaction of a monoatomic oxygen with O2 to create natural ozone.

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