The destruction of ozone can happen similarly. High energy can hit the ozone molecule, breaking it apart and some of these free O's will connect together to make oxygen. There is some equilibrium associated with this process in the atmosphere, giving us a certain ozone concentration.

Freon-related molecules in the atmosphere influence the chlorine cycle, talked about earlier. Some are concerned that Freon being heavier than the air, will stay close to the ground. It will initially, as does carbon dioxide (Lesson 6). But with time it will mix throughout the atmosphere. Remember that the chlorofluorocarbon compounds (CFCs) such as Freon 11 and 12 have very long lifetimes. To get rid of half of it would take 50 to 100 years. Once released, they stay with us for a long time mixing into the stratosphere. Once in the stratosphere, it remains there because there is minimal mixing and washing in that portion of the atmosphere.

Ultraviolet light acts on a Chlorofluorocarbon molecule in the stratosphere. It breaks the chlorine loose. When the chlorine contacts an ozone molecule, it attaches. The products are an oxygen molecule and a free chlorine to do it again. As long as it stays in the stratosphere, it will just keep forming chlorine monoxide, an oxygen molecule, and free chlorine.

Here is a simplification of how this process occurs. About all that it takes is ultraviolet energy, a chlorine source, cold temperatures, and some acid in the air (it can come from methane, which we know is produced in nature in quantity by human activity or a volcano can place acid into the atmosphere). Combining are an acidic cloud, cold temperature, the vortex, the chlorine source, and ultraviolet light. All of the ingredients to destroy the ozone are now inside that doughnut that we call the Antarctic Vortex. That is how the ozone hole is formed there.

A couple of comments on terms used and misused--Freon is DuPont's registered trademark for fluorocarbon and fluorinated hydrocarbon. Freon is a brand name for CFCs. A CFC contains only chlorine, fluorine, and carbon. We have HCFCs which contain hydrogen, chlorine, fluorine, and carbon. We also have HFC containing hydrogen, fluorine, carbon, and Halon. Halon contains bromine, fluorine, and carbon. Remember, bromine does about the same thing as chlorine. Halon is used at the computer center in their fire control system. If the fire alarm goes off, Halon rather than water is released into the room. We do not want to destroy the computer center. So we put in something that is harmless except to the ozone layer. I think that is probably a good use of it. That kind of disaster does not happen very often, and use of Halon could be reasonable even though it could be damaging to the environment in large quantities.

This vortex over the South Pole forms with the winter cooling. When the sunlight returns it provides the energy to destroy the ozone. We have an observable formation of what we call the Ozone Hole near the end of their winter.

The sun eventually warms our atmosphere, breaking up the vortex. When the vortex breaks up, ozone-poor air may be transported elsewhere. A professor friend of mine was working in South America when this happened in 1992. When Dr. Franklin from Iowa State University returned, he said: "There's something happening down there. The natives are getting sunburned. I've worked down there for 20 years, and I've never seen the people who work for me getting sunburned before. And they're getting seriously sunburned." It turned out there was terrific loss of young animals, sheep and llamas, all attributed to the Ozone Hole that moved over South America upon breaking up (Figure 14.10). It could just as easily move over Australia, or New Zealand, before mixing sufficiently with the rest of the atmosphere to minimize the harmful effects.

fig15.16 Fig. 14.10 Ozone depleted air moving over South America.

That is the situation currently. The ozone hole breakup will be a concern for many years. I get phone calls from the world's largest sheep producer in Australia, saying, "When is this thing breaking up, and can you tell if it's moving over me?" There is cause for concern as long as the Ozone Hole is there.

CFCs have a double danger. The greenhouse effect and ozone depletion. CFC 11 is probably the worst one, with CFC 12 close to it for ozone depletion (Figure 14.11). Some new things that are being developed such as 134a which doesn't have any ozone-depletion effect, and CFC 115, which has a moderate effect on the ozone but a large effect on the greenhouse. New things are being developed and tested for any greenhouse gas effect and derogatory effect on the ozone.

fig15.17 Fig. 14.11 Ozone effects of various CFC compounds.

The depletion factor for CFC 11 and 12 is 1; 113, and 115 are not as bad. The HCFCs are very low, 0.1 or 0.06 of what we had for the CFCs. Some of these new HFCs have almost no effect on the atmosphere. Of course, Halon has a terrific effect, but hopefully there won't be very much of that. We will not use it as a refrigerant, maybe just as something to extinguish fires. But 134a is used primarily in place of Freon 11 and 12.

You have seen a price change if you get your air conditioner recharged from about $15, of which $1.50 was for the Freon, to about $50. It is still $13 for the labor. The additional $37 is for the development of things that will not be so damaging to the environment. I notice they have a label on them warning, "Don't breathe it," while recharging the refrigerator. So we are still not putting these in the house. We put them in the car air conditioner and that sort of thing.

With all of this knowledge has come a few other things. By 1985 there was no doubt about the Ozone Hole being caused by people. In 1987 there was an international meeting in Montreal resulting in the Montreal Protocol which moved for eliminating the use of CFCs. Most nations agreed to no longer manufacture anything that is obligated to CFCs by 1989. By the year 2000 they will be banned. That date has been adjusted now to 2020. The HCFCs are to be banned by 2030.

I think there is already a favorable effect in that we are not seeing the Ozone Hole get worse as rapidly. Even if the use of CFCs stopped completely today, CFCs already in the atmosphere would continue to produce the damage for 50-100 years. Then things will start to return to their natural level. Some years there might be ozone depletion because of a volcano or something, but that would be just for a year.

fig15.8c Fig. 14.12 Sulfur and volcanic ash belt around the Earth.

Then those products would naturally disappear from the environment rather than staying around 50 or more years.

There are lots of ideas beginning to show up in the literature that are technological fixes for the ozone problem. One is a big curtain with huge balloons that float in the stratosphere holding a metal foil curtain with chemical properties, zinc in particular, that can purge or counteract CFCs. This would have the contradictory reaction to push the balance of ozone back the other way. Then we would not have to worry about the CFCs in the atmosphere because we would have something to counteract them.

There is some development of a second generation of the high-flying supersonic aircraft, the SST. In the 1970s there was much debate about the construction of the SST. The military, of course, had supersonic aircraft. I was involved in some upper atmospheric physics when I was associated with the military in 1970-1972. One of the studies that I became involved with was the atmospheric probing from rockets launched at the White Sands Missile Range. One thing that we did notice along with other studies we were doing is that every time we sent a rocket up through the stratosphere, it left a hole in the ozone. It was a small pinpoint hole where the rocket went through, but it did it every time. In fact, one of the scientists in Atmospheric Physics who worked with the army at that time said that he considered the entire space program just one great big exercise in atmospheric chemical modification. His whole life was studying what the rockets were doing to our atmosphere.

Based on these data, with the desire to manufacture the SST, they immediately said, "The rocket is punching a little hole in the atmosphere. The SST will be flying back and forth, painting a long, horizontal stripe, doing substantial damage to the ozone layer, at least potentially." This was the primary reason that the United States decided not to manufacture the SST. England and France did not agree. They constructed and flew them. The United States set a limit on how many flights into the United States can be made by SSTs. We have had to hold it there because in the last three or four years there have been reports of significant ozone reduction over New England and adjacent Canada. We attribute that, at least 90 percent of it, to the SST flights. The new SST generation that they are trying to design and get permission to fly would not be destructive to the ozone. For the most part, the Atlantic ozone depletion affects Europe.

We can draw a few conclusions from all of this: First, that the ozone hole is a result of man's actions. There is just no question about that. Most of the mechanisms are now well understood, and large-scale experiments such as those carried out on the Nimbus (called the TOMS experiments) have provided a global picture of what is happening. The satellites give us a very clear picture of ozone depletion.

Chemistry and dynamics have combined to make a dramatic southern ozone hole. Recent measurements show that ozone is thinning over the Northern Hemisphere, but the dynamics are not right for it to develop a big hole as occurs over the South Pole.

The other conclusion is that even with CFC manufacture being totally stopped by 1995, ozone holes will be in our future environment for another 100-200 years.

Carbon isn't the problem. I don't know what happens to the chloride part of it. There are quite a few other chloride sources that could be a problem. I know that carbon tetrachloride used to be quite common around the house and the laboratory. I don't know what the extent of it being banned is. Do you?

"No. But it's just something that I happened to think about. With a 1500 half-life, it would be around for quite a while."

I know they decided it was a real hazard to people because it was so long-lived and could be absorbed by the skin, and various things.

"From experience I know that at least 20 years ago there were tremendous fires in Brazil during the Dry Season. A lot of that has stopped and is banned, but I'm sure a lot of it is still being done."

Yes, there's still quite a bit of burning going on in South America, and I don't know if we have the same atmospheric affect from tropical plants as we do from the boreal ones that were in the study made in Russia.

"I know we don't have a lot of data on this, but when the ozone travels way off the Vortex, how often does that happen?"

Every year when the Vortex breaks up, that ozone-poor plume is going to go somewhere. So that's going to happen every time and will be a continuing hazard that we're going to have to monitor and be careful of.

Looking at it a month before it happens, you would have to say it would be random and there is no way to forecast it. As it begins to break up, we can see, just like we're having a polar outbreak in Iowa right now, and we could tell a few days before the outbreak that the polar air was going to be coming here. Well, if that had been ozone-poor air, we would have had the ozone hole over us, for example. You can tell about the same way. The concern here in Ames here is that the sheep farmers have a legitimate reason to be concerned down in Australia and New Zealand and South America, wherever they are. And many years they will have this concern that they'll be facing.

Lesson 14 Reflection
Why reflect?
Submit your answers to the following questions in the Student Notebook System.
  1. In your own words, write a short summary (< 150 words) for this lesson.
  2. What is the most valuable concept that you learned from the lesson? Why is this concept valuable to you?
  3. What concepts in the lesson are still unclear/the least clear to you?
  4. What learning strategies did you use in this lesson?