Natural forces can alter the amount of ozone. Remember, ozone is very unstable. It reacts easily with other atoms, and will easily donate that free oxygen atom O 1 to nitrogen gas N 2 , hydrogen gas H 2 , or chlorine Cl. These atoms have always existed in the stratosphere, and they are released from a wide variety of sources volcanoes, oceans, etc. Scientists have discovered that ozone levels change as part of natural cycles on Earth.
Ozone levels vary slightly with seasonal changes winter to summer as an example , wind circulation patterns, and solar cycles. If a large volcano erupts, it can send enough material into the stratosphere to increase the breakdown of ozone.
But in the early s, scientists found some startling evidence that humans were contributing to the destruction of ozone. Many technological advances of the time included chemicals containing chlorofluorocarbons CFCs for short. CFCs contain a chlorine, fluorine, and carbon atoms that are bound together.
CFCs are stable. The relative heights of atmospheric layers. Also view an animation 1. The formation of ozone, also animated. Ozone is extremely valuable since it absorbs a range of ultraviolet energy. When an ozone molecule absorbs even low-energy ultraviolet radiation, it splits into an ordinary oxygen molecule and a free oxygen atom. Usually this free oxygen atom quickly re-joins with an oxygen molecule to form another ozone molecule. Because of this "ozone-oxygen cycle," harmful ultraviolet radiation is continuously converted into heat.
Natural reactions other than the "ozone-oxygen cycle" described above also affect the concentration of ozone in the stratosphere. Because ozone and free oxygen atoms are highly unstable, they react very easily with nitrogen, hydrogen, chlorine, and bromine compounds that are found naturally in Earth's atmosphere released from both land and ocean sources.
For example, single chlorine atoms can convert ozone into oxygen molecules and this ozone loss balances the production of ozone by high-energy ultraviolet rays striking oxygen molecules. In addition to the natural ozone balance, scientists have found that ozone levels change periodically as part of regular natural cycles such as the changing seasons, winds, and long time scale sun variations. Moreover, volcanic eruptions may inject materials into the stratosphere that can lead to increased destruction of ozone.
Over the Earth's lifetime, natural processes have regulated the balance of ozone in the stratosphere. Although ozone depleting substances, they are less potent at destroying stratospheric ozone than chlorofluorocarbons CFCs.
They have been introduced as temporary replacements for CFCs and are also greenhouse gases. See ozone depleting substance. HCFCs , carbon tetrachloride carbon tetrachloride A compound consisting of one carbon atom and four chlorine atoms. Carbon tetrachloride was widely used as a raw material in many industrial uses, including the production of chlorofluorocarbons CFCs , and as a solvent. Solvent use ended when it was discovered to be carcinogenic. It is also used as a catalyst to deliver chlorine ions to certain processes.
Its ozone depletion potential is 1. Methyl chloroform is used as an industrial solvent. Its ozone depletion potential is 0. ODS that release bromine include halons halons Compounds, also known as bromofluorocarbons, that contain bromine, fluorine, and carbon. They are generally used as fire extinguishing agents and cause ozone depletion. Bromine is many times more effective at destroying stratospheric ozone than chlorine. Methyl Bromide is an effective pesticide used to fumigate soil and many agricultural products.
Because it contains bromine, it depletes stratospheric ozone and has an ozone depletion potential of 0. Production of methyl bromide was phased out on December 31, , except for allowable exemptions. In the s, concerns about the effects of ozone-depleting substances ODS ODS A compound that contributes to stratospheric ozone depletion. Gaseous CFCs can deplete the ozone layer when they slowly rise into the stratosphere, are broken down by strong ultraviolet radiation, release chlorine atoms, and then react with ozone molecules.
See Ozone Depleting Substance. Aerosols are emitted naturally e. There is no connection between particulate aerosols and pressurized products also called aerosols. See below propellants. However, global production of CFCs and other ODS continued to grow rapidly as new uses were found for these chemicals in refrigeration, fire suppression, foam insulation, and other applications.
Some natural processes, such as large volcanic eruptions, can have an indirect effect on ozone levels. For example, Mt. Pinatubo's eruption did not increase stratospheric chlorine concentrations, but it did produce large amounts of tiny particles called aerosols aerosols Small particles or liquid droplets in the atmosphere that can absorb or reflect sunlight depending on their composition. These aerosols increase chlorine's effectiveness at destroying ozone.
The aerosols in the stratosphere create a surface on which CFC-based chlorine can destroy ozone. However, the effect from volcanoes is short-lived. Not all chlorine and bromine sources contribute to ozone layer depletion. For example, researchers have found that chlorine from swimming pools, industrial plants, sea salt, and volcanoes does not reach the stratosphere.
In contrast, ODS are very stable and do not dissolve in rain. Thus, there are no natural processes that remove the ODS from the lower atmosphere. One example of ozone depletion is the annual ozone "hole" over Antarctica that has occurred during the Antarctic spring since the early s. This is not really a hole through the ozone layer, but rather a large area of the stratosphere with extremely low amounts of ozone. Ozone depletion is not limited to the area over the South Pole.
Research has shown that ozone depletion occurs over the latitudes that include North America, Europe, Asia, and much of Africa, Australia, and South America.
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