Home >> Science & Nature >> Science

Ultraviolet and Photochemical Effects on the Stratosphere

Without the chemical processes taking place high in the stratosphere, life on Earth wouldn't be possible. Hovering between five and 30 miles above the surface, the stratosphere becomes warmer the higher up you go. The most important part of the stratosphere is the ozone layer, a thin zone full of a specific oxygen compound. The ozone layer protects life at the surface from harmful ultraviolet radiation. The creation and destruction of ozone is influenced both by solar radiation levels and human industrial activity. The stratosphere is the laboratory in which all of these chemical reactions take place.

Ozone Production
- Ozone is an unstable molecule composed of three oxygen atoms. Normally, oxygen is a diatomic compound, meaning it occurs as two atoms joined together. In the stratosphere, ultraviolet radiation from the sun breaks the bond between oxygen atoms. These free atoms then combine with diatomic oxygen molecules, forming ozone. The newly created ozone molecule has a short life, as the same ultraviolet radiation that helped create it also destroys it. The whole cycle is self-sustaining and maintains a constant amount of ozone in the stratosphere.
Chlorofluorocarbons
- Chlorofluorocarbons, or CFCs, are used in industrial and residential processes. They're cheap, stable and have a low toxicity compared to other chemicals that perform the same functions. However, their stability has had unintended consequences. CFCs released into the air eventually make their way into the stratosphere. Once above Earth's weather, ultraviolet radiation acts on CFCs, breaking them down into numerous other substances.
CFCs and Ozone
- Four chemicals in the stratosphere are known to contribute to the depletion of ozone: nitric oxide, hydroxyl, chlorine and bromine. Each of these chemicals intrudes on the natural reaction between UV radiation and ozone. A single chlorine atom can destroy up to 100,000 ozone atoms. These chemicals upset the delicate balance of ozone destruction and creation. Fortunately, governments and manufacturers are increasingly agreeing to phase out the most destructive of these chemicals, although restoring the stratosphere's natural chemical processes will take time.
Natural Aerosols
- According to the U.S. Environmental Protection Agency, volcanoes and wildfires produce chlorine, which survives intact all the way into the stratosphere. Volcanoes also generate substances known as aerosols, which increase the effectiveness of chlorine in destroying the ozone. However, neither natural chlorine nor volcanic aerosols compare to the amount of harmful chemicals released into the air by human activity, especially heavy industry and automobiles.

Science