Environmental Engineering Reference
In-Depth Information
Ozone Depletion
The ozone layer shields the Earth from the harmful effects of UV radiation. Ozone becomes depleted when the
natural balance of production and destruction of ozone in the stratosphere is skewed toward destruction. Peri-
odically occuring natural phenomena can create a temporary decrease of ozone. Of immediate importance are
man-made chemical compounds released in the atmosphere that can cause ozone depletion. These compounds
contain halogens (chlorine, bromine, iodine, and fluorine) and are known as
ozone-depleting substances,
such
as chlorofluorcarbons (CFCs).
The global awareness and concern of ozone depletion started in 1985 with the discovery of a thinning of the
ozone layer above the Antarctic by British scientists Joesph Farman, Brian Gardiner, and Jonathan Shanklin.
Further research revealed that this thinning is twofold: First, overall levels of ozone in Antarctica have dropped
30 percent since the 1970s. This depletion continues at a rate of about 3 percent per year. The second depletion
has been commonly described as the
ozone hole.
The ozone hole is not technically a "hole" devoid of ozone; it
is an area of seasonal depletion over Antarctica that, once formed, tends to travel northward toward the equator
and may linger over landmasses such as Australia, New Zealand, South America, and South Africa. When
present, this ozone hole increases the UVB levels in affected areas by 3 percent to 10 percent, and in some
years, by as much as 20 percent. The severe depletion of ozone above the Antarctic occurs because of special
weather conditions. Very low temperature in the Antarctic winter months of below -78°C create ice clouds
called
polar stratospheric clouds (PSCs).
Consolidation of greenhouse gases in these clouds helps drive
