The “ozone layer” is a concentration of ozone (O3) molecules in the “stratosphere.” Stratospheric ozone is important because it blocks a significant portion of the sun's ultraviolet (UV) radiation from reaching the Earth’s surface. Overexposure to UV rays can lead to skin cancer, cataracts, and weakened immune systems. Increased UV exposure can also damage plants – including important food crops and can even have dangerous effects on marine animal reproductive health. Without stratospheric ozone protecting us from Ultraviolet radiation, life on Earth would not exist. But why would we say “without stratospheric ozone?” Is it going somewhere?

The Ozone "Hole"
Scientific data has shown that the ozone layer is being destroyed. It turns out that an unintentional side-effect of some industrial chemicals commonly used as cleaners and refrigerants - Chlorofluorocarbons (CFCs) - also do a terrific job destroying ozone. The family of chemicals commonly called CFCs were used widely as refrigerants, insulating foams, and cleaning solvents because they were extremely chemically stable, relatively non-toxic compounds that were safer to use than the chemicals they replaced. What was not known at the time was that when CFCs reach the stratosphere, the ultraviolet radiation from the sun causes them to become unstable, break apart and release chlorine atoms, which readily react with ozone. This starts a continual chemical cycle that wreaks havoc on the ozone layer. One chlorine atom can break apart more than 100,000 ozone molecules.

Although we have focused on CFCs because of their wide-spread use, there are other chemicals that damage the ozone layer. Collectively these are referred to as “Ozone Depleting Compounds” (ODC) or “Ozone Depleting Substances” (ODS) and include: methyl bromide, which is used as a pesticide, halons, which are a class of chemicals commonly used in fire extinguishers, and methyl chloroform, which is used as an industrial solvent. As methyl bromide and halons are broken apart, they release bromine atoms, which are 40 times more destructive to ozone molecules than chlorine.

In the 1980s, a team of scientists that comprised the British Antarctic Survey found a “hole” in the ozone layer above Antarctica. Discovery of the link between CFCs and the “ozone hole” in 1986 led to an international pact called the “Montreal Protocol.” This treaty was organized by participating nations and a commitment was made to reduce the use of CFCs and other ozone-depleting substances. The treaty was later amended banning all CFC production after 1995 in all developed countries. Today, over 160 countries have signed the treaty. CFCs are no longer produced in the U.S., but the other ozone depleting substances are still widely used.

Impacts of depletion of stratospheric (good) ozone
When vented to the ambient air, Ozone Deplting Compounds (ODC) can rise some 20 miles above the Earth's surface to the stratospheric ozone layer. Once in the stratosphere, these compounds are powerful ozone depleters and consume the ozone layer that screens the earth from the sun's harmful ultraviolet (UV-B) radiation.

To date, the stratospheric ozone layer above Antarctica has suffered the most thinning, acquiring the name "the Antarctic ozone hole." Thinning of the stratospheric ozone level has occurred to a much lesser degree over North America, Europe and other populated areas. According to health scientists, continued destruction of the ozone layer and the consequent increase in the level of ultraviolet radiation reaching the earth's surface could result in:

• 1.6 million additional cases of cataracts per year.
• 300,000 cases of skin cancer per year.
• A decrease in the human immune defense system.
• A decrease in crop productivity.
• A decline in the population of microscopic plankton, the primary building block supporting the global food chain, which includes humans.
• An increased formation of ground-level ozone, or smog. As explained in a previous section, exposure to smog contributes to lung disorders, such as asthma and leads to permanent lung damage