Exploring the Ozone

Remember the children’s story of Chicken Little who was hit on the head by a falling acorn, and assumed the sky was falling. Her outrageous reaction and her fervent activism got the entire farmyard, and eventually the whole countryside to take totally unnecessary protective actions.

The Greens have “alerted” all of us to the alarming possibility that we are destroying the earth’s ozone layer, and threatening all life on earth.

An interesting premise. Let’s examine this acorn more closely.

Ozone is an unstable molecule formed when free oxygen atoms are released in an oxygen-rich atmosphere. That fresh smell following a thunder storm is the ozone created by the electric bolts we call lightning. O3 – ozone is a molecule consisting of three oxygen atoms, unlike O2, oxygen – which consists of two oxygen atoms. Free oxygen atoms cannot exist by themselves. They immediately combine to form O2, oxygen. When free atoms of oxygen are released in an oxygen atmosphere, one of two things happens: they either combine with each other to form more O2, or they combine with O2 to form O3 – ozone. Because ozone is naturally unstable, over time it will decay, losing one of the oxygen atoms. The free oxygen atoms so formed combine with themselves to form O2.

In our atmosphere, most ozone is created when normal oxygen molecules are split apart by the action of ultraviolet light in normal sunshine. In the process, the ultraviolet is absorbed, so that it never reaches the Earth’s surface – hence the “protection”. Of course, this occurs near the top of the atmosphere where the ultraviolet first encounters the oxygen. Strictly speaking, therefore, it is not ozone that forms a protective layer, but rather ozone is formed as a consequence of the “protective” process, where O2 splits into oxygen atoms while absorbing the ultraviolet. Of course, all the ozone that is created also absorbs ultraviolet – hence the “protective ozone layer”.

As mentioned earlier, ozone decays naturally. It is broken apart faster in the presence of CFCs (refrigerants and propellants), oxides of nitrogen (auto emissions, power plants, forest fires, and volcanoes), and methane (agriculture and volcanoes). The chemistry is a bit complicated, but the bottom line is that when these gases are present mixed with ozone, more of the ozone decays than when these gases are not present. Thus, ozone that drifts into the lower atmosphere tends to be destroyed. The opposite is also true. When these man-made gases drift into the upper atmosphere they increase the natural decay rate of the ozone.

When ozone molecules break up spontaneously at the top of the atmosphere, new ozone is created immediately by the sun’s ultraviolet light. Studies on how long this process takes indicate that ozone regenerates fast enough to preclude significant ultraviolet effects at the earth’s surface. Put another way, when a ray of ultraviolet sunlight manages to slip past the initial clumping of ozone, because an O3 molecule happens not to be there, it runs smack into a regular old oxygen molecule and splits it apart, getting absorbed in the process and, by the way, generating replacement ozone.

This process is not an absolute. Some ultraviolet always reaches the Earth’s surface. Since the thickness of the ozone varies continuously, the amount of ultraviolet at any spot on the Earth’s surface also changes continuously, not to mention the effects of clouds, water vapor, smog, etc.

The Earth is tilted 23 degrees to the ecliptic, which means that the Earth’s axis forms a 23 degree angle to the plane formed by the Earth’s orbit around the Sun. As the Earth moves along its orbital path, at mid-summer in the northern hemisphere the north pole is tilted to its maximum towards the Sun. Six months later it is tilted to its maximum away from the Sun. In between the tilt is parallel. What this means at the poles is that the sun never sets in the summer; it just goes round and round the horizon, reaching a height of 23 degrees at mid-summer. At the Autumnal Equinox, the sun rolls on the horizon, and then it begins to move below the horizon, until it reaches a maximum amount of 23 degrees below at mid-winter. It then ascends again, reaching the horizon at Spring Equinox, and repeats the cycle all over again. In simple terms, this amounts to three months of direct sunlight, three months of twilight, three months of darkness, and three more months of twilight. Remember what happens to ozone when it is left by itself: it decays away; it becomes plain oxygen.

So let’s put this acorn together.

For three Summer months the Sun’s ultraviolet light generates and maintains a distinct ozone layer atop the Earth’s oxygen atmosphere. Then follows nine months of twilight and night and twilight again, during which – as they say – the “Sun don’t shine”. But the ozone continues to decay…so guess what? The “ozone layer” gets really thin up there. A thinning of the ozone layer – a “hole” – appears above the polar region. Always has – always will.

The “hole” is an artifact of the polar night. The effect is enhanced by the presence of CFCs, nitrogen oxides, and methane; but it is not caused by these agents.

Buildup of CFCs, nitrogen oxides, and methane may inevitably result in an overall thinning of the ozone layer, but the amount of these substances that would cause immediate dissolution of each ozone molecule the moment it forms would wreck direct havoc on our atmosphere long before reaching the point of totally preventing the formation of an ozone layer. Ozone layer thinning caused by “normal industrial amounts” of CFCs will be insignificant, especially when compared to the effects of volcanic eruptions combined with summer methane production from northern hemisphere agriculture (you know – cows!).

Prof. S. Fred Singer who is on leave from the University of Virginia, directs the Washington-based Science & Environmental Policy Project. He recently served as chief scientist of the Department of Transportation and earlier as the first director of the U.S. weather satellite program. Some of his scientific accomplishments relate to the ozone issue: He devised the ozone monitor used in satellites and was the first to publish on ozone destruction by anthropogenic methane. Dr. Singer has written extensively on the ozone issue for both professional and popular audiences. He points out several times that if one were to take the worst case scenario for ozone depletion and subsequent increase in ultraviolet activity at the Earth’s surface, it would produce a total change in ultraviolet levels roughly equivalent to moving from New York City to Miami.

It was the Austral Summer, 1981. I was at the Geographic South Pole – Amundson-Scott Station they call it. I was in charge of south polar atmospheric monitoring for the National Science Foundation. Part of my duties was to measure the ozone layer from the surface using a Dobson Meter, a device that generates a relative measure of the thickness of the ozone at the top of the atmosphere. During this period, I was able to coordinate my measurements with measurements made simultaneously from the Nimbus 7 polar orbiting satellite. For the first time in history we were able to establish an absolute measure of the ozone layer thickness. This was pretty heady stuff.

During the Summer, Amundsen-Scott Station has a relatively high number of visitors. Among others, we hosted a group of senators and their assistants, and a group of news people. One of these was Dale Van Atta, who was there representing Pulitzer Prize winner and investigative reporter Jack Anderson. Dale came out to my lab looking for something out of the ordinary. In my capacity as a uniformed officer with NOAA, I did not want to contribute directly to his mischief, but I did tell him about our ozone measuring success. I also pointed him towards a female scientist working at McMurdo Station. This lady was especially attractive, and I had learned during a visit there, that she was hugely upset that the thousand male occupants of the station insisted on viewing her as a female instead of a scientist. I thought she might have a thing or two to say to Dale Van Atta.

It turned out that essentially everyone in Antarctica had heard about our linking the ground and satellite measurements of the ozone thinning. In other words, the hole was no longer just an hypothesis – we had actually established its existence. As I said, it was pretty heady stuff. It was this acorn that the lady scientist chose to drop on Mr. Van Atta. Apparently, with tongue in cheek she painted a dramatic picture for him of ultraviolet poisoning, widespread environmental damage, massive human cancers. And sure enough, shortly after he returned to the United States, the story broke in the New York Times.

In reaction, Congress passed legislation financing massive new atmospheric research. For the first time in their professional lives, atmospheric scientists had sufficient funds. These guys weren’t stupid. They used the money well. And when the furor began to die down, NASA sent a plane into the high arctic during the polar spring, and guess what they found: another hole. Acorns were falling everywhere. And, of course, Congress appropriated more money.

I should add that along with the money, under pressure from the Greens and their sympathizers, Congress legislated a phase out of CFCs and certain other chemicals that were thought to be the root cause of the hole. With the “discovery” of the hole in the Arctic, Congress accelerated the phase out of CFCs, to the delight of those same forces and, of course, the commercial interests who benefited from the phase in of the replacement technologies and chemicals.

All good things must end. Eventually, in the late 1990s, NASA announced that recent research had produced a surprising result: the ozone layer was repairing itself much more quickly than had been expected. The picnic was over.

And from the acorn grew a mighty oak that reached to the sky.