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| They were once widely used as a coolnt in refegerators and as propellant in aerosol can. | |
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The little girl frequently listened to the old man's discussion.
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| In the 1970s scientists became concerned when they discovered that chemicals called chlorofluorocarbons,long used as refrigerants and as aerosol spray propellants. | |
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| Posed a possible threat to the ozone layer. Released into the atmosphere, these chlorine-containing chemicals rise into the upper stratosphere. | |
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