The Ozone Layer
The Solar SpectrumTo understand the importance of ozone in the atmosphere, we first must understand the nature of the energy that comes to us from the sun. The sun and other stars are very hot and so radiate energy. Specifically, we call this energy electromagnetic energy.
We can characterize electromagnetic radiation according to its wavelength. Remember that the energy of the radiation is inversely proportional to the wavelength.
Molecular FiltersConsider the figure at right. The magenta filter blocks some wavelength of light, the cyan and yellow filter block others. When the 3 filters are combined, all wavelengths of visible light are blocked and the color appears black.
The atmosphere consists of many molecular and atomic filters that each block a certain range of wavelengths of light. With the combined effect of all of these, most of the harmful radiation from the sun is blocked before it reaches the plants and animals on the surface of the Earth.
Ozone in the StratosphereOzone has a low concentration throughout the atmosphere but there is a region in the stratosphere where its concentration is higher than anywhere else. About 90% of the ozone in the atmosphere is located within a band centered at 25 km above the surface.
Ozone's concentration within the ozone layer is 0.2 to 0.4 ppm. Typical concentrations in unpolluted air closer to the surface is 0.03 ppm.
The ozone in the ozone layer absorbs 97-99% of all the ultraviolet light that passes into the stratosphere.
The Ozone HoleUntil recently, the concentration of ozone in the stratosphere was nearly constant. However, man-make chemicals such as the FREON used in refrigerators and air conditioners destroy it.
Over the course of the winter, reactive molecules build up in stratospheric clouds over the poles. The light and heat of the early spring causes these molecules to combine with ozone, resulting in a hole in the ozone layer.
UV radiation can reach the Earth's surface under this hole in the protective ozone layer.
International treaties are now limiting the amount of ozone-damaging chemicals that are released.