Ozone on the Mend

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ozreact

For once I can bring good [environmental] news to this column. The Ozone hole is shrinking! This is a result of what may be the most successful international treaty ever to address a dire environmental threat. First a little background and then the details.

Ozone is an allotrope of the element Oxygen. Allotrope is the name given to substances made of the same element which have different atomic arrangements. Diamonds and graphite are perhaps the best know substances which are allotropes, in this case of carbon. The stuff which comprises 21% of the atmosphere, the stuff that aerobic organisms such as we human beings need to live is also an allotrope of Oxygen. It’s the most common form so it is just called Oxygen, but it is more formally Dioxygen. It’s chemical formula is O2, whereas the formula of Ozone is O3.

Ozone is created in the upper atmosphere via the reaction of dioxygen. The process of the conversion of Dioxygen to Ozone absorbs significant amounts Ultraviolet light. If this light were not absorbed in the process it would continue to the surface and make life on earth impossible. What little Ultraviolet light does make it to the surface of earth is responsible for the most common form of cancer – skin cancer.

OK, that is a little dense, to recap simply, life would not exist on the surface of the planet without a proper amount of Ozone in the upper atmosphere.

In the early 1970s scientists showed in laboratory studies that certain man made compounds known as chlorofluorocarbons (CFC) react with Ozone and suggested that if these compounds are released to the atmosphere they could cause the depletion of Ozone in the stratosphere (upper atmosphere.) Subsequent measurements of the amount of Ozone showed that in fact the CFCs were going up to the stratosphere and Ozone was being depleted. And the depletion correlated precisely with the concentration of CFCs.

For complex meteorologic reasons, the depletion was the most severe during the spring over the north and south poles. The depletion was so great as to constitute a “hole in the Ozone layer.” Whereas the reduction of Ozone amounted to a few percent at the equator, it got as high as 90% or more at the poles.

In the late 1980s world leaders met in Montreal and agreed to a treaty, thenceforth called the Montreal Protocol which would phase out the use of CFCs and similar compounds, the majority of which were used as refrigerants. New compounds that did not deplete Ozone were gradually developed and put in to service, but it was a decades long process to find the right compounds and modify the refrigerator compressors to work with the new compounds.

Recent measurements now show that it worked! Reductions in the production and release of CFCs has slowed the degradation of stratospheric Ozone and in fact the “holes” have begun to heal. Besides the fact that life on the planet can go on unimpeded by damaging ultraviolet light, it shows that the world community can come to agreements that affect all of us.

One thought on “Ozone on the Mend

  1. Steve Zimmer

    In 1975 & 76, I had a high school student researching the effects of freon (I don’t recall which freon she use; it was provided to us in pressured cans from a local company) upon ozone. She showed that ozone concentration would decrease in the presence of the freon. I took her to the International science fair in City in ’75 as an exhibitor. In ’76, she continued her study by proposing that in a steady state system, it was impossible to completely impossible to totally destroy ozone. She set up an aquarium with a Hg light inside to generate ozone. The setup had a constant flow of oxygen into the aquarium and then to a Cary-14 UV spectrophotometer to monitor the ozone level. Regardless of the amount of freon introduced, the level of ozone never dropped below a certain level. I cannot what the percentage was, but it was a significant value. I took her to the International Science in Denver in ’76 as an exhibitor. I had other students continue to study ozone depletion by other pollutants (nitrogen, sulfur & phosphorus oxides) but they did not have the success the first study had.

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