Science in Antarctica

Measuring the Ozone

Atmospheric scientists from the University of Wyoming at Laramie are in McMurdo to send up balloons carrying equipment that measures the ozone layer.

In the dim light of a cold Antarctic morning, Bruno Nardi, Jason Gonzales, Russ Ashendon, and Bill Bellon carefully fill a large, delicate plastic balloon (it looks like a thin white garbage bag) with helium, then hang on until the wind lifts the balloon into the air. The balloon billows gracefully into the sky. It will travel a distance of up to 100 miles, and will rise to 20 miles, up into the stratosphere. Immediately, the team returns to the lab, where they begin collecting data over a computer. The device attached to the balloon measures pressure, altitude, rise rate, temperature and level of ozone.

The Wyoming researchers are part of a whole group of scientists who have been monitoring the depletion of the ozone layer for some time. According to Bruno, every year the ozone hole opens over the Antarctic, getting bigger and bigger until the end of October, then it starts naturally healing, or closing up, as the air over Antarctica mixes with more ozone rich air from mid latitudes. By December, there is almost no noticeable ozone hole over the Antarctic. But, even though the hole heals itself each season, there is still an overall global depletion of ozone each year, and that is significant.

The ozone is an atmospheric layer made up of molecules that are themselves made of three combined atoms of oxygen (O3). The ozone layer protects the earth from ultraviolet light. Ultraviolet light is high frequency, low wavelength light that has been shown to cause increases in skin cancer, and is related to global climate changes. UV light has also been shown to actually damage DNA in hampsters, frogs and humans.

Under ideal circumstances, when ultraviolet light hits the ozone layer, the ozone layer absorbs it, protecting the earth from its harmful rays. This process also breaks the ozone molecule apart into an oxygen molecule (O2) and a single oxygen atom (O). Ideally, then, the ozone molecule recombines--so the net destruction and net production of ozone is equal.

The hole in the ozone is created when chlorine atoms (Cl) enter the scene. Most of the chlorine atoms in the stratosphere come from chlorofluorocarbons. These come from freon, which is used in refrigeration, from aerosol cans, and from the making of styrofoam. Chlorofluorocarbons (CFCs) themselves are not bad or harmful, they are inert, but in the upper atmosphere they can be released into harmful forms. The most harmful form is a bare chlorine atom. Crystals in polar stratospheric clouds, or any other "surface area" in the atmosphere, can serve as a platform upon which these "ozone super killers" do their work.

What happens is that under the right circumstances (sunlight and very cold temperatures) a chlorine atom gets released and breaks up ozone molecules, creating an oxygen molecule (O2) and an extra oxygen atom. The chlorine atom then takes up the extra oxygen atom to make chlorine monoxide (ClO). ClO will then re-release chlorine atoms, so that, says Bruno, the chlorine atoms will go on to break up many ozone molecules before they cycle out of the system. Chlorine monoxide is known as the "smoking gun" in ozone research. If a scientist sees that molecule, he or she knows that ozone is being destroyed.

The Wyoming researchers are not necessarily discovering anything new about the ozone, but their monitoring has shown them that the ozone hole over the Antarctic, which represents about 3 percent of the world's total ozone, is reduced by about 60 percent each austral spring, and that since 1993, this rate has been relatively stable.

In 1987 United States and other industrial nations agreed to reduce the production of CFCs under the Montreal Protocol on Substances that Deplete the Ozone Layer. In 1990 the same nations agreed to phase out production of CFCs by the turn of the century. Despite this, however, scientists think that the amount of chlorine in the atmosphere will peak during the first decade of the next century. As a result, the hole in the ozone over Antarctica may double over the next few decades.

For more information on the Wyoming scientists and their ozone research click HERE.

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