How Do Chlorofluorocarbons Harm The Ozone Layer?

Earth enjoys many advantages among the planets in the solar system, from its moderate temperatures and the existence of water and oxygen to its layer of ozone molecules that protect its inhabitants from the sun's harmful energy. The advent of chlorofluorocarbons, or CFCs, threatened the ozone layer and the survival of Earth dwellers. Manufacturers thought the chemicals were the panacea to their manufacturing headaches because CFCs emitted no odors, were stable, were not flammable or toxic and could be manufactured cheaply. Little did these manufacturers know that their hopes would be dashed only decades later.

A layer of ozone envelops the Earth and keeps damaging ultraviolet, or UV, radiation from reaching living things on the planet's surface. The ozone layer exists mainly in the stratosphere, a layer of the atmosphere that reaches from 10 to 50 kilometers (about 6 to 30 miles) above the Earth's surface. UV radiation causes various harmful effects in humans, including skin cancer and cataracts, a clouding of the lens of the eye. Ozone comprises three atoms of oxygen bonded together chemically, while oxygen in its usual form is diatomic, meaning that it contains two chemically bonded atoms of oxygen. Ozone molecules absorb UV rays, using this energy to separate an oxygen atom from the ozone molecule. This uses up the energy of the UV ray and renders it harmless to living things. Of the three types of UV radiation, UVB is the most harmful because it reaches the furthest, even beneath the ocean's surface.

Chlorofluorocarbons, or CFCs, are compounds made up of combinations of the elements chlorine, fluorine and carbon; aerosols, refrigerants and foams contain CFCs. When these CFCs enter the air, they rise up into the atmosphere to meet up with and destroy ozone molecules. First used in 1928, CFCs have since become more common as various other CFC compounds were created. Some of the better-known CFCs are the Freon compounds, which were used as cooling ingredients in refrigerators and air conditioners but have since been phased out of production in the United States. The U.S. government still permits the use of Freon in appliances and vehicles as long as supplies are available. Environmentally friendly compounds have mostly replaced Freon as refrigerants.

When the sun's UV rays come in contact with CFCs, the chlorine atoms come loose. These chlorine atoms wander around the atmosphere until they meet up with ozone molecules. The chlorine atom and one of the oxygen atoms of ozone combine, leaving behind diatomic, or molecular, oxygen. When a free oxygen atom contacts this chlorine-oxygen compound, the two oxygen atoms combine to form molecular oxygen, and the chlorine goes off to devastate more ozone molecules. Molecular oxygen, unlike ozone molecules, cannot keep UV rays from reaching the Earth's surface. The U.S. Environmental Protection Agency estimates that one atom of chlorine can destroy as many as 100,000 molecules of ozone. In 1974, M. J. Molina and F. S. Rowland published a paper outlining how CFCs broke down ozone molecules in the atmosphere.

CFCs get released into the atmosphere because of leaks in equipment. Because CFCs are stable compounds and do not dissolve in water, they tend to stick around for long periods of time, from decades to hundreds of years. Generally, ozone is constantly being formed and destroyed, but the total amount of ozone in the atmosphere should essentially remain at a stable number. CFCs upset this balance, removing ozone faster than it can be replaced.

UVB rays break down DNA, the molecule that stores the genetic material of all living things. Organisms can repair some of this damage themselves, but the unrepaired DNA causes cancers to form and results in other mutant effects such as missing or extra limbs in animals. In 1978, after the publication of several studies concerning the effects of CFCs on the ozone layer, the United States decided to ban CFCs used in aerosols, with several other countries following suit.