Ozone breaks down in the ozone layer in the following major ways:
- N2O* encounters water vapor, and can no longer help form ozone.
- Ozone absorbs UV-C or UV-B and most of it will break back down to oxygen.
- Ozone has a natural half-life, and decays spontaneously with time and temperature back to oxygen.
- Ozone encounters water vapor, and forms hydrogen peroxide.
- Ozone encounters a photocatalyst (like CFC, HCFC, Halon), and is converted back to oxygen.
CFCs, HCFCs, and Halon:
The ozone layer is destroyed by CFC's, chlorofluorocarbons, that are used as a propellant in aerosol cans, and refrigerants in older cars and refrigerators. When Chlorofluorocarbons (Freon and other CFCs) and Bromofluorocarbons (Halons) they became popular refrigerants and fire fighting agents. As the compounds were inert and thought to pose no damage to health or the environment they were handed without much consideration for losses. As a consequence the concentrations of these materials built up in the atmosphere. However (there's always a however) when the materials reached the stratosphere the were acted on by ultraviolet radiation and broke down releasing chlorine and bromine into the ozone layer. The ozone layer is the earth's ultraviolet shield. The chemistry is such that the chlorine and bromine attack the ozone, reducing it to ordinary oxygen which as no shielding effect from UV-B. The complex chemical reactions allow the chlorine and bromine to interact again and again with ozone molecules, until they eventually leave the ozone layer bonded to some other compound. Since the Montreal Protocol was developed to control and ban the use of these compounds the ozone layer has improved. But due to the long-lasting impact the problem will not be resolved totally for many years.
The ozone layer is strongly negatively affected by the presence of water vapor. Not only does it suppress the formation of ozone, but it provides another decay path. Whenever there is large quantities of anomalous stuff associated with an ozone hole (clouds, NOx, more), it is compounds that are daughters of the suppression of ozone by water vapor. Water vapor carried in some part by high altitude aircraft (which also reduce the oxygen locally from which ozone is made).
Depletion of available oxygen:
Ozone is formed from oxygen. Processes / actions that reduce the viable plant life that make oxygen, are depleting ozone. Ozone is not "leaving the Earth", it is not being harvested by aliens, or being sprayed into deep space. Ozone is unstable (it decays with time, back into oxygen), it will attack any other molecule that is not protected by fluorine, and it breaks down when UV-B or more energetic light hits it. Our ozone layer depends on UV-C from the Sun to make some new "fresh" ozone each day, some survives all night long. Contaminants, as described above, decrease the equilibrium ozone concentration. Allowing more UV-B to arrive at Earth's surface, and damage us and our food sources.
The ozone hole size as a measure of overall ozone depletion:
Some of the ozone hole is natural. Some of the depletion of ozone is due to "natural factors". Man-made chemicals seem to be concentrated in regions of low ozone concentration, and these have been otherwise shown to destroy ozone. Man also dumps water vapor high in the atmosphere, and water vapor also destroys ozone. Assessing the damage we have done to the ozone layer will be hard to do without more data. We had a record sized ozone hole (2006) and we have not decreased too much percentage-wise since then (2008). But we simply don't know how much we are responsible for. Does it matter? We are not required to feel guilty. We are stewards. This is our home. We know what we have to do to help Nature repair the damage (and any damage is reversible, hopefully without eliminating Man first). When CFCs are present in the stratosphere they reacted on by ultra violet light to release a chloride ion. The ion breaks down an ozone molecule to create an oxygen molecule and ionic oxygen. The ionic oxygen releases more chloride ions to break down more ozone and CFCs
The end result is the ozone is converted to oxygen quicker than natural processes can replace it Ozone depletion may be occurring because of the inadvertent actions of Man. It appears that water vapor in the upper atmosphere and compounds like CFCs have increased due to the actions of Man. It depletes every year at the pole, when it is winter at the pole. Ozone decays with time, and there is no UV-C from the Sun to make more when that pole is having winter. Not sure it is being entirely destroyed. Ozone has even been found on Mars, and it has almost no free oxygen. Mostly likely candidates for the thinning of the ozone layers are:
- water vapor
Chlorine and chlorine-based compounds, create a surface on which ozone can be broken apart or destroyed. This is mainly why CFC's (chlorofluorocarbons) were banned by law, because they destroyed ozone. Note that the prefix chloro is in chlorofluorocarbons, meaning that the reason ozone was destroyed by CFC's was due to the fact that CFC's were chlorine-based compounds. because they made a hole in it. Chlorofluorocarbons are the main cause of global warming. It's kind of like if you burnt a hole in a piece of paper it can't be fixed.
Ultra Violet Rays:
The sun's ultra violet rays are also damaging the ozone layer
from the outside because the ozone layer protects us from the sun's
harmful rays while we are depleting the ozone layer from the inside
by releasing carbon dioxide and other ozone depleting substances
into the atmosphere.
Chlorine atoms break away from the CFCs and destroy the ozone molecules. This allows harmful UV radiation to reach the earth.