Ozone: A Greenhouse Gas
Ozone is a gas that can be found in the Earth's upper atmosphere and at ground level. Depending on its location in the atmosphere, however, it can be good or bad for people's health. The troposphere, the air closest to the Earth's surface, contains the ground-level and so-called "bad" ozone which is a pollutant that is a significant health risk to many. It also damages trees, crops and other vegetation. The stratosphere, the air secondary to the Troposphere, contains the "good" ozone which can extend upward from approximately 6 to 30 miles. The ozone in the stratosphere protects life on Earth from the sun's harmful ultraviolet (UV) rays. However, this natural shield has been gradually depleted by man-made chemicals like chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCFC's), carbon tetrachloride and methyl chloroform. These Ozone Depletion Substances (ODS's) are a group of manufactured chemicals containing chlorine and bromine. These chemicals destroy the stratospheric ozone layer due to their ability to float upward through the lower atmosphere where they are safe and nontoxic, into the stratosphere where they become potent and dangerous. Overall, the ozone layer is a region of the Earth's stratosphere that absorbs the majority of the Sun's UV radiation, as briefly stated before. It contains high levels of ozone in comparison to the other parts of the Earth's atmosphere, but it is still very small relative to other gases in the stratosphere, such as exhaust gases.
The Main Ozone-Depleting Substances (ODS's)
- Chlorofluorocarbons (CFC's)
- Chlorofluorocarbons are the most used ODS and they are responsible for over 80% of stratospheric ozone depletion.
- It is used as a coolant in refrigerators, freezers and air conditioners in buildings and cars manufactured before 1995.
- CFC can be found in industrial solvents, dry-cleaning agents and hospital sterilizers.
- They are also used in foam products such as soft-foam padding, such as cushions and mattresses, and firmer foam products like home insulation.
- Halons are used in some fire extinguishers, in cases where materials and equipment would be destroyed by water or other fire extinguisher chemicals. In British Columbia, halons' cause more damage to the ozone layer than CFC's do from car air conditioners!
- Methyl Chloroform
- Methyl Chloroform is used mainly in the industry world for vapor degreasing, some aerosols, cold cleaning, adhesives and chemical processing.
- Carbon Tetrachloride
- Carbon Tetrachloride is used in solvents and some fire extinguishers.
- Hydrochlorofluorocarbons (HCFC's)
- HCFC's have become major, “transitional” substitutes for CFC's. They are less harmful to stratospheric ozone than CFC's are, but HCFC's still cause damage to the ozone layer and are potent greenhouse gases.