The ozone layer
A thin band of ozone high in the atmosphere that absorbs most of the Sun's harmful ultraviolet light; CFCs ate holes in it.
What the paper can ask
- Lies mainly 15 to 35 km up; ozone peaks at 8 to 15 parts per million; blocks nearly all UV-C and most UV-B.
- Discovered 1913 by Charles Fabry and Henri Buisson; Sydney Chapman described the ozone-oxygen cycle in 1930.
- CFCs and other halogen compounds destroy ozone; global ozone fell about 4 percent after the late 1970s; the Antarctic hole was announced in 1985.
- The 2022 assessment projects recovery to 1980 levels around 2040 for most of the world and 2066 over Antarctica.
Why exams ask
Which layer of the atmosphere holds it, which gases destroy it, the treaties that saved it and World Ozone Day (16 September) are asked.
The full story
Ozone (O3) collects in a layer 15 to 35 km above the ground, where ultraviolet light splits oxygen molecules and the atoms recombine into ozone. The layer absorbs almost all UV-C and most UV-B, the rays that cause sunburn and skin cancer. It was discovered in 1913 by the French physicists Fabry and Buisson.