Chlorofluorocarbons (CFCs)

Chlorofluorocarbons (CFCs) are man-made chemical compounds used as refrigerants, cleaning solvents, aerosol propellants, and blowing agents for foam packaging in many commercial applications. CFCs do not spontaneously occur in nature. They were developed by industrial chemists searching for a safer alternative to refrigerants used until the late 1920s. CFCs are non-toxic, chemically non-reactive, inflammable, and extremely stable near Earth's surface. Their apparent safety and commercial effectiveness led to widespread use, and to steadily rising concentrations of CFCs in the atmosphere, throughout the twentieth century.

CFCs are generally non-reactive in the troposphere, the lowest layer of the atmosphere, but intense ultraviolet radiation in the outer layer of the atmosphere, called the stratosphere, decomposes CFCs into component molecules and atoms of chlorine. These subcomponents initiate a chain of chemical reactions that quickly breaks down molecules of radiation-shielding ozone (O₃) in the lower stratosphere. The stratospheric ozone layer absorbs ultraviolet radiation and protects Earth's surface from destructive biological effects of intense solar radiation, including cancers and cataracts in humans.