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On January 23, 1978, Sweden became the first country to ban the use of aerosol sprays which use chlorofluorocarbons (CFCs) as their propellants. The ban came after research done by Frank Rowland and Mario Molina demonstrated CFCs interacted with ultraviolet light in the upper atmosphere to break the bonds of ozone molecules.

Ozone is the name for a molecule with three oxygen atoms. Ozone in the upper atmosphere absorbs ultraviolet radiation from the Sun before it reaches Earth's surface. CFCs are molecules with a central carbon atom surrounded by chlorine and fluorine atoms. They were used as refrigerants, aerosol propellants and solvents. As they were released into the atmosphere and made their way to the upper atmosphere, they would react with the ultraviolet radiation as well. This time, the ultraviolet rays would break the bonds on the chlorine atoms. The freed chlorine would collide with an ozone molecule and break off one oxygen to form oxygen gas and chlorine monoxide ions. When the chlorine monoxide finds another oxygen atom, chlorine monoxide becomes oxygen gas and ejects the chlorine. The free chlorine is free to start the process all over again and break other ozone molecules.

The loss of ozone in the atmosphere manifested itself as a 'hole' over the polar regions that allowed higher ultraviolet exposure at the surface. This prompted the banning of CFCs for most applications and restrictions on the use as refrigerants. Find out what else occurred on this day in science history.


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