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Protective Ozone

Most ozone is concentrated in the stratosphere, (27k jpeg) at about 25 km in altitude, and is considered to be "good ozone."In this region, ozone acts as a shield to protect Earth's surface by absorbing harmful ultraviolet radiation. Without this shield, we would be more susceptible to skin cancer, cataracts, and impaired immune systems.A 1 % decrease in total column ozone causes the amount of transmitted UV radiation, in the spectral region that damages deoxyribonucleic acid (DNA), to increase by about 2 %. Although good ozone only represents a tiny fraction of the atmosphere, it is crucial for life on Earth.

The proportion of good and bad ozone in the atmosphere depends on the balance between processes that create ozone and those that destroy it. An upset in this balance can have serious consequences for life on Earth, and scientists are finding evidence that the balance has changed.Concentrations within the protective ozone shield are decreasing, while levels in the air we breathe are increasing.

Ozone amounts in the stratosphere are small, rarely exceeding 10 parts per million by volume.Ozone is measured in Dobson Units. (40k jpeg) One Dobson Unit (DU) corresponds to 2.69 x 10E16 molecules per square centimeter, which is equivalent to the amount of gas in one square centimeter at 1 atmosphere of pressure.Average ozone levels are 300 DU, which would be equivalent to a layer three millimeters thick if compressed to the planet's surface. Levels may range from less than 100 DU to over 500 DU globally.

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Last updated: Apr 06, 2016 05:58 PM ET