Tag Archives: ozone

Ozone on the Mend



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.


Ozone – Stratospheric or Tropospheric

What is the next word you think of if you hear the word ozone? About twenty years ago the answer would invariably have been hole, as in the “ozone hole” over the Antarctic is expanding. Currently if you hear of ozone at all, it is more likely in the form of ozone alerts which occur most commonly on hot summer afternoons in urban environments.

Ozone is another of those Dr. Jekyll, Mr. Hyde molecules. It is at the same time both beneficial and dangerously toxic. It all depends on where it is. Way up in the stratosphere, about 25 kilometers up, it protects us from deadly Ultraviolet rays from the sun, but down near the ground where we breath it is a reactive substance which damages lungs and exacerbates asthma and cardiovascular disease.

There is fairly good evidence for life arising on this planet over 3.5 billion years ago. One hypothesis is that life formed in the seas, as life on the surface of the planet was impossible due to the intense deadly Ultraviolet (UV) rays striking earth. A few billion years later and following the evolution of the chloroplast, oxygen (O2) began to accumulate in the atmosphere. In a cyclic process in the upper atmosphere the more abundant O2 is turned into Ozone (O3). This tiny bit of Ozone absorbs the dangerous UV rays and makes life possible on the surface.

Life then climbed out of the primordial soup and started building air conditioners, refrigerators, and the like which require a refrigerant to work. Compounds know as Chlorofluorocarbons (CFCs) were chosen because they were effective, non toxic and relatively stable. Bear with me here, I’ll get back to Ozone quickly.

Ozone hole over Antarctica

Ozone hole over Antarctica

It’s the stable part got that gets us in trouble. When CFCs escape the refrigerator or air conditioner, they get in the atmosphere. They are stable enough to get all the way up to the Ozone layer without falling apart. There a combination of reactions destroys the Ozone. Enough could literally wipe out life on the planet. Even small amounts of Ozone destruction lead to an increase in retinal damage and skin cancer.

And that is the story of the Ozone hole, a climatically related figure of speech referring to a lessening of the total amount of Ozone in the stratosphere. Luckily we figured this out and by an international agreement known as the Montreal Accords agreed to ban the production and use of these substances. The Ozone hole is slowly shrinking and is by about 2050 expected to be completely healed.

Now back to ground level Ozone, the Ozone we don’t want. Ozone formation at ground level where we breath is not natural. The the fault here is internal combustion engines – Cars and trucks and buses that run of gasoline or diesel.



Because engines aren’t 100 per cent efficient, some uncombusted gases escape the tail pipe. Known as volatile organic carbon (VOCs), they react with Oxygen and sunlight to produce Ozone. Luckily Ozone is unstable and degrades rapidly so if it forms in the afternoon, it is gone by the evening. Toxic ground level Ozone can be controlled by reducing the production of the VOCs. Reducing the number of cars in urban environments through mass transportation is a very effective measure. Alternately reformulating fuels to produce less VOCs works to some degree, but raises the cost. Natural gas fueled vehicles produce less VOCs and electric vehicles none.