Ozone is a molecule that contains three oxygen atoms. It is much less prevalent than atmospheric oxygen, and is most concentrated in an area of the stratosphere from about nine to 18 miles above the Earth’s surface. This region is referred to as the ozone layer. The ozone layer performs a very valuable service for living organisms on Earth, by filtering out a portion of the sun’s UVB radiation. Without the ozone layer, life on Earth, as we know it, would not exist.
In the mid-1970s it was discovered that chemicals called chlorofluorocarbons (CFCs) were destroying the ozone layer. At that time, CFCs were widely used as propellants in spray cans, as well as coolants in refrigerators and air conditioners. The thinning of the ozone layer results in more UVB radiation reaching the Earth’s surface, and higher levels of UVB radiation have disastrous effects on all living organisms. In humans, UVB radiation causes skin cancer, cataracts, and suppression of the immune system. For example, it is estimated that a 10% decrease in stratospheric ozone will result in 300,000 more cases of skin cancer each year. It can also kill small crustaceans, larval fish, and phytoplankton, which is the basis for the aquatic food chain. In plants, it can damage leaves, stunt growth, cause mutations and interfere with photosynthesis.
In addition to CFCs, natural events like volcanic eruptions can also destroy ozone. In a volcanic eruption, huge numbers of sulfate droplets are propelled into the stratosphere where they provide surface area for ozone-depleting reactions to occur. When Mount Pinatubo erupted in 1992, it resulted in the destruction of 70% of the ozone layer over an area the size of North America.
The example of global cooperation to stop the depletion of the ozone layer is perhaps our most outstanding environmental success story to date. From 1987 to 1992, governments of the world banded together for a common goal to dramatically reduce the production of ozone-depleting agents by signing agreements and implementing regulations. The results have been encouraging, as the ozone hole of 1997 and 1998 had shrunk about 9% by 2001. The battle is not over yet, though. Because CFCs take several years to reach the stratosphere, and because once there, they can last 75 to 100 years, it will likely take another 100 to 200 years for the ozone thinning to completely recover.
In the mean time, we need to continue to take measures to even further reduce the release of ozone-depleting agents into the atmosphere by finding substitutes for CFCs. Although we have begun this research, there is still a long way to go. From a human health standpoint, possibly the best thing we can do in the interim is use sunscreen and wear quality sunglasses that reduce the penetration of UVB radiation.
Chiras, D., Natural Resource Conservation– 10th Edition