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Ozone layer

The ozone layer (O3) is in the stratosphere, about 25 km high, and acts as a filter for ultraviolet rays, preventing them from reaching the earth's surface and damaging the health of living beings.

The ozone layer began to thin out when, starting in the 1970s, CFCs (chlorofluorocarbons) began to be released from aerosols, solvents, refrigerants, and fertilizers. CFCs, by the action of solar radiation, release chlorine and bromine in the stratosphere, which react with ozone and decompose it. This caused that in the 80s, in the Antarctic area (South Pole) it decreased significantly, originating the well-known hole in the ozone layer. It is not really a hole, but a decrease in the thickness of the ozone layer.

In the 90s the emission of CFCs was banned and you can already see how it is increasing its thickness again.

Why does the ozone hole occur in Antarctica?

The depletion of the ozone layer is produced by the presence in the stratosphere of CFCs (chlorofluorocarbons) and nitrogen oxides. Chlorine from CFCs reacts with ozone (O3) to form chlorine oxides, capturing oxygen atoms, and preventing the ozone layer from regenerating.
Cl + O3  → Cl2O + O2
The special atmospheric conditions of Antarctica have favored the ozone layer to decrease its thickness by more than 50%, allowing the entry of ultraviolet radiation. This ultraviolet radiation is the cause of some diseases in humans (such as skin cancer, visual problems, deficiencies in the immune system, etc.), and mutations in animals and plants.
The hole in the ozone layer becomes larger in September, when the temperature is very low (southern hemisphere) and sunlight begins to appear over the horizon (south pole), when chemical reactions begin to destroy ozone. In October, this ozone destruction stops, and the hole shrinks. From October to December, the hole moves towards mid-latitudes.

Evolution and solutions

Since the 1990s, the use of CFCs and other chemicals that damage the ozone layer has been discontinued and, until seven years later, a decrease in CFCs in the troposphere could not be observed. Although there is already an improvement and the ozone layer is gaining thickness, due to the long life that CFCs have in the atmosphere, it is believed that it will not reach its natural situation until the year 2070.

Cartoons about the hole in the Ozone layer: Ozzy Ozone (part 1 and part 2).

Answer in your notebook

9.4.- What is the cause of the depletion of the ozone layer?