Ozone: Too Much Down Here, Not Enough Up There!
Much has been written lately about ozone and its role in protecting us from harmful ultraviolet (UV) light. This is not, however, the only case where humans and ozone interact. For example, most cities produce substantial amounts of ozone from the combination of light and common air pollutants, and that's bad!
Ozone is a toxic and unstable gas that is sometimes formed from normal oxygen. It is composed of three oxygen atoms (instead of the two in an oxygen molecule). It can be produced in several ways, usually involving light or electrical discharges. Once produced in the atmosphere it will revert back to normal oxygen in about 10 days, but not before getting involved in a complex series of chemical reactions.
Ozone is sometimes intentionally made for its strong oxidizing nature; like hydrogen peroxide, and for the same reasons, it can kill bacteria and other microorganisms. A high-voltage electrical discharge produces ozone which can then be used instead of chlorine as a disinfectant for drinking water and swimming pools . It is also produced by electric motors, and can often be detected by the characteristic sweet smell of electrical equipment. However, be forewarned: ozone is a powerful and highly toxic substance.
Ozone plays an important, but poorly understood, role in many chemical and physical processes in the atmosphere. In the lower atmosphere (troposphere), ozone is always present at low levels. In cities, it is found in much higher levels due to the action of light on concentrated pollutants. The ozone levels found in many U.S. cities (especially during summer) are often sufficient to harm human health and plants. In Fairbanks, locally produced ozone is not usually a problem because our worst pollution events occur during the dark, winter months.
In the stratosphere (the middle atmosphere from about 10-50 km or 6-30 miles up), ozone is found in much higher concentration due to the high-intensity UV light. This light energy produces sufficient ozone to offset the natural destruction mechanisms, and produces an ozone layer. One very important result: the ozone layer screens out much of the high-energy UV light. Many scientists believe that during the early evolution of the planet, life was possible only in the ponds, swamps, and seas until the protective ozone layer had been formed.
Most common air pollutants cannot reach the stratosphere because they are so reactive that they get removed in the troposphere (e.g., acid rain). However, mankind has learned to manufacture a large variety of fluorine- and chlorine-containing "chlorofluorocarbons" (CFCs). These remarkable compounds are nonflammable, nontoxic, and have chemical and physical properties that make them very suitable for refrigerants and solvents. Once released into the troposphere, they distribute themselves uniformly around the globe and over five to ten years make their way into the stratosphere. There, the high-energy UV light breaks them down, and they become involved in a complex ozone destruction cycle. It is estimated that for every atom of chlorine released into the stratosphere, 10,000 molecules of ozone are destroyed. Less ozone in the stratosphere means more UV light reaching the surface, and this translates into a higher incidence of skin cancer.
The antarctic "ozone hole" appears each spring (September-November in the southern hemisphere) when ozone levels drop to about 50 percent of their previous values. It now appears that two factors have combined to cause the antarctic ozone hole, one chemical and the other meteorological. The chemistry of these reactions appears to be very temperature sensitive, with colder temperatures favoring more ozone destruction. The meteorology acts to make the antarctic stratosphere extremely cold by isolating it from other regions of the global atmosphere (the arctic is not as isolated). However, ozone depletion has been measured over the entire globe, with greater reductions at high latitudes. A recent report indicates the existence of a smaller arctic ozone hole.
This does not mean that Alaskans are all subject to a greater risk of skin cancer, at present. During springtime, when ozone depletion is greatest, the sun is still low on the horizon. This helps absorb some of the UV light. A much more variable factor is the amount of sun exposure each of us gets. If you like to sunbathe on the beach in Mexico your risk of skin cancer will be much greater than someone who minimizes sun exposure and protects exposed skin with UV-blocking sun screens.
There's no way to get ground-level ozone up into the stratosphere, and - even during the worst Los Angeles smog - there's too little of it. We might try to replace the lost ozone by generating it with an electrical discharge. However, to fill up the ozone hole, just once, would require an amount of energy equivalent to interior Alaska's energy needs for the next 1000 years, and then we'd have to repeat the process each year!
Problems relating to ozone (too much down here, not enough up there) are not going away in the near future. Ozone depletion will become a more important concern as CFCs continue to reach the stratosphere. By being among the world's largest consumers of energy and manufactured goods, each of us is, in some small way, responsible for the ozone hole, the greenhouse effect, acid rain, and many other types of pollution. Our collective actions, purchases, and energy consumption play a major role in determining the future health of our planet. With some foresight and planning, we can revive our wounded planet and learn to keep ozone in its place.
