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Our Ozone Layer:
Past, Present & Future
April 30, 1998
I decided to investigate the environmental issue of the depletion of the ozone. Although I have heard many things about the ozone, and the hole over Antarctica, I wanted to find out more and get some real facts on ozone depletion and what we can do about it.
The ozone layer refers to the ozone within the stratosphere, where over 90% of the earth's ozone resides. The ozone layer absorbs 97-99% of the sun's ultraviolet or UV light ("The Ozone Layer"). This UV light has many damaging affects for humans, plants, and animals. In humans, exposure to UV light can increase the chances of getting skin cancer and cataracts. It also harms food crops and other plants, as well as many animals (Albritton, et al).
There are several factors influencing concentrations of ozone. Some of these are natural, which appear to cause minor fluctuations. Some of the factors are manmade and can cause major changes to the ozone layer. One natural influence is large explosive volcanoes. An eruption places aerosols and chlorine into the lower stratosphere. Although this can have major effects on localized weather patterns, the effect on global ozone is almost insignificant and only lasts 2-3 years. Stratospheric winds and greenhouse gases are also natural influences on the ozone concentration. The variations in how much UV radiation is given off from the sun also affects the ozone, but it is a negligible amount. Stratospheric chlorine is a major influence on the ozone and comes mostly from manmade halocarbons. Catalytic degradation by stratospheric chlorine leads to a 3% decrease in ozone per decade, proven by studies done from 1978-1991 ("The Ozone Layer"). I will consider the manmade problems more later when I discuss chlorofluorocarbons.
Beginning in the early 1970's, scientists discovered two potential manmade problems affecting the ozone. The first was a new breed of fast passenger planes, known as supersonic transport (SST). SST's fly high in the atmosphere, where the air is thin so they can achieve their fast speeds. Scientists suspected that reactive nitrogen compounds from the exhaust of the planes might accelerate natural chemical destruction of the ozone. The second discovery was in 1974, and concerned a popular and widely used class of chemicals known as chlorofluorocarbons. CFC's proved to be an ideal compound since their invention in the late 1920's, because they are nontoxic, nonflammable and very stable. Unfortunately, because they are so stable in the lower atmosphere, they drift up into the stratosphere and break apart when hit with the sun's high energy radiation. All this extra chlorine in the stratosphere spells trouble for the ozone. One chlorine atom can destroy 100,000 ozone molecules (Albritton, et al).
Although these discoveries were made in the early 1970's, it wasn't until 1985 that the true meaning of the destruction of the ozone was made clear. In May 1985, researchers reported finding actual holes in the ozone over Antarctica. They found that each spring, ozone concentration over Antarctica dropped below normal levels and that each year, the springtime losses grew. In 1987, the springtime hole spread across an area the size of the United States (Albritton, et al).
Ozone loss is rapid over Antarctica because of the extreme temperatures in the stratosphere. Icy cloud particles not normally present in warmer climates break apart "safe" compounds of chlorine and bromine and transform them into quick and efficient "ozone-destroying-machines." The hole is worse in the spring because at that time of the year, the sun returns to Antarctica and energizes the chemical cycle that destroys ozone (Albritton, et al).
In fact, NASA recently predicted that the rising levels of "greenhouse gases" will lead to a hole over the Arctic region not unlike the hole presently over Antarctica. The analysis projects that by the period of 2010-2019, there will be a hole over the Arctic comparable in magnitude to the one presently over Antarctica. Although these predictions do have their critics, researchers have already noticed severe drops in ozone levels in the Arctic, which they termed "half holes" (Suplee).
In 1987 the original Montreal Protocol was signed. It has been amended many times since then but it's main goal is to phase out CFC's. The latest revision scheduled a complete phase out of CFC's and related halocarbons by the year
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Ozone depletion, Ozone, Montreal Protocol, Chlorofluorocarbon, Stratosphere, Clean Air Act, Greenhouse gas, Atmosphere of Earth, Ozone depletion and climate change, Scientific Assessment of Ozone Depletion
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