CFCs , hydrochlorofluorocarbons hydrochlorofluorocarbons Compounds containing hydrogen, fluorine, chlorine, and carbon atoms. 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. Chlorofluorocarbons CFCs , hydrochlorofluorocarbons HCFCs and halons destroy the earth's protective ozone layer, which shields the earth from harmful ultraviolet UV-B rays generated from the sun.
Hydrofluorocarbons HFCs also act to warm the planet. Man-made compounds such as chlorofluorocarbons CFCs , hydrofluorocarbons HCFCs and halons destroy ozone in the upper atmosphere stratosphere. The stratospheric ozone layer makes life possible by shielding the earth from harmful ultraviolet UV-B rays generated from the sun. Decreased concentration of stratospheric ozone allows increased amounts of UV-B to reach the earth's surface.
Stratospheric ozone loss can result in potential harm to human health and the environment, including:. Most stratospheric ozone depletion is caused when chlorine or bromine reacts with ozone. Sherwood Rowland and Mario J. Crutzen of the Max Plank Institute for Chemistry, Mainz, another pioneer in stratospheric ozone research. That stratospheric ozone absorbs ultraviolet radiation that otherwise would reach the surface of Earth. At the time, CFCs were in wide use in refrigeration, air conditioning and aerosol spray cans.
The compounds are inert and essentially nontoxic, characteristics that made them well-suited for these applications. These same characteristics, however, also made them a danger to life on Earth. Commemorative Booklet PDF. In the s, refrigeration and air conditioning systems used compounds such as ammonia, chloromethane, propane and sulfur dioxide as refrigerants. Though effective, the compounds were toxic and flammable, and exposure to them could result in serious injury or death.
A team of chemists at Frigidaire led by Thomas Midgely Jr. The team focused their effort on compounds containing carbon and halogens such as fluorine and chlorine. Such compounds were known to be volatile and chemically inert, both important properties for the team studying their use in refrigeration. Chlorofluoromethanes are being added to the environment in steadily increasing amounts. These compounds are chemically inert and may remain in the atmosphere for years, and concentrations can be expected to reach 10 to 30 times present levels.
Photodissociation of the chlorofluoromethanes in the stratosphere produces significant amounts of chlorine atoms, and leads to the destruction of atmospheric ozone.
From an environmental standpoint, ozone is a confusing molecule. But in the stratosphere, the region of the atmosphere from 6 to 31 miles, ozone absorbs potentially damaging ultraviolet UV radiation. Without a protective ozone layer in the atmosphere, animals and plants could not exist, at least not upon land.
Lovelock had measured trichlorofluoromethane CFC in the atmosphere in amounts that suggested that practically all of the CFC ever manufactured was still present in the atmosphere. Rowland decided to devote a portion of his research to understanding the fate of CFCs in the atmosphere. Although CFCs are inert in the lower troposphere, Rowland realized that they can be broken down by UV radiation once they drift up into the stratosphere.
Each chlorine atom would react immediately with an ozone molecule, setting off a chain reaction that would destroy thousands of ozone molecules. In their paper, they estimated that if CFC use was banned immediately, ozone loss would go on for years.
If CFC production continued, however, ozone loss would be even greater. In , the National Academies of Science issued a report affirming the destructive effects of CFCs on stratospheric ozone. Congressional hearings reached similar conclusions, and states and the federal government began exploring bans on the use of CFCs in aerosol cans. When Rowland lectured on CFCs, industry groups often released statements disputing his claims. It seemed that, because of his focus on CFCs and ozone depletion, he started getting fewer invitations to speak.
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