Hole in the ozone layer
The earth’s atmosphere, which includes the ozone layer, plays an important role in protecting us from ultraviolet radiation. No UVC reaches the earth, most of the UVB is absorbed into the atmosphere and the majority of UVA reaches the earth.
Ozone is a chemical (O3) that contains three molecules of oxygen. When some recently made pollutants, such as CFCs, reach the ozone layer the ozone is split and becomes oxygen (O2).
The hole in the ozone layer changes seasonally. It is always largest in winter.
Visit this site to see an animation of the ozone hole.