Ozone is a trace gas that performs critical functions in the atmosphere, including blocking UV rays and contributing to the greenhouse effect. Man-made chlorofluorocarbons (CFCs) have caused a depletion of the ozone layer, leading to concerns about skin cancer. The move to ban CFCs has been slow, but progress has been made. Ozone is also created in the burning of fossil fuels, contributing to the greenhouse effect and global warming.
Ozone is one of the naturally occurring trace gases that make up our atmosphere.
The atmosphere performs three critical functions: it supplies life-giving oxygen, keeps the earth warm, and protects us from the sun’s deadly ultraviolet (UV) radiation. Most of the atmosphere is made up of nitrogen and oxygen, the air we breathe. These gases don’t hold heat, so they don’t keep us warm. They also do not protect the earth from UV rays.
For those functions one must turn to the trace gases present in the atmosphere, commonly referred to as greenhouse gases. They are: water vapour, carbon dioxide, methane, ozone and nitrous oxide.
These trace gases work like the transparent cover of a greenhouse, allowing sunlight to filter through the earth’s surface, thereby trapping the heat. Without the greenhouse effect, the earth’s temperature would plummet well below freezing every night.
Ozone is a particularly critical trace gas because it plays two roles. In the lower atmosphere it adds to greenhouse gases, keeping the earth warm. But it performs a more critical function in the upper atmosphere, where it blocks nearly all of the sun’s deadly UV rays from reaching earth.
UV rays are associated with skin cancer. The “UV index” is used in the summer months to let people know how long it is safe to be in the sun. A decrease in ozone is correlated with an increase in skin cancer. This is important because ozone has had a constant depletion rate, creating holes in the upper ozone layer.
The holes were first discovered in 1985 over Antarctica, where atmospheric circulation, temperature and other factors “draw” holes in that region. The discovery of the holes has created concern around the world.
The culprit was man-made chlorofluorocarbons (CFCs). CFCs have been released into the atmosphere for years. They are emitted in part by aerosols made with CFC propellant, refrigeration units and air conditioners. When CFCs reach the upper stratosphere, UV rays cause the gas to release free chlorine atoms. A single chlorine molecule is enough to cause the decomposition of tens of thousands of ozone molecules into simple oxygen. And again, oxygen does not filter UV rays. The danger therefore is that very small quantities of CFC gas destroy enormous quantities of ozone.
The move to ban CFCs was slow, but all major countries that produce them phased them out by the year 2000. CFCs already released will take another estimated 50 years to phase out, and CFCs will continue to be released from older products still in use. As a result, ozone levels and the hole over Antarctica continue to be monitored closely.
In addition to being a natural gas, ozone is also created in the burning of fossil fuels as a component of smog. The burning of fossil fuels also releases carbon dioxide into the air, thickening greenhouse gases, increasing the greenhouse effect and global warming.
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