The Environment November 1982

Trouble in the Stratosphere

Dangerous sunlight and altered climates may result from pollution of the upper atmosphere
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ON SEPTEMBER 26, 1974, a headline on the front page of The New York Times announced: “Tests Show Aerosol Gases May Pose Threat to Earth.” The trouble, the story said, began with synthesized chemicals called fluorocarbons. Some scientists believed that these manmade substances would destroy a large part of the atmosphere’s ozone layer. The results would likely be dire. No longer adequately shielded by ozone from the harshest of the sun’s ultraviolet radiation, human beings might suffer an epidemic of skin cancers. No one could say what might happen to the plants and animals of the earth, but it seemed clear that an altered ozone layer would mean a greatly altered planet.

Looking back eight years afterward, a scientist involved in research on ozone remarked, “An abstract scientific theory made the front page of The New York Times, and six months later it was a subplot on the Archie Bunker show.” The fluorocarbon theory proposed that global catastrophe could have a homely, even

frivolous source, and perhaps that is why the story traveled very widely. Practically everyone in the industrialized world used fluorocarbons, which had long been thought to rank among the safest of manmade chemicals. Colorless, nearly odorless, fluorocarbons are present in virtually every modern system of refrigeration. They are used as solvents and as foaming agents for making such items as disposable coffee cups and rigid insulation. In 1974, fluorocarbons propelled the contents from half of the roughly 2 billion aerosol cans being sold in America. The headlines focused on this last application. Was the world really going to end with the hissing of cans of deodorant? In contemplation of like questions, many commentators in America could not restrain their mordant glee. The prospects were just too wonderfully ironic. In the early days of the alarm, some scientists went before Congress and on the basis of meager evidence drew the worst of imaginable conclusions. One, for example, said that the continued production of fluorocarbons “could drive life on earth back to where it was hundreds of millions of years ago.” Hyperbole was rampant.

In this case, however, excessive zeal in relating bad news probably had some salutary effects. The notoriety of the fluorocarbon theory promoted investigation of the stratosphere, an atmospheric region that is very important to life on earth but that scientists had just begun to explore. The alarm also caused many Americans to stop buying aerosols, and by 1978, when Congress banned the use of fluorocarbons in all but a few sorts of spray cans, American industry had already substituted other propellants. Worldwide production of fluorocarbons had been doubling roughly every seven years. After the alarm, production began to decline, and has remained at a level some 18 percent below that of 1974. If there had been no general fright, production of the chemicals would certainly have grown far more quickly than knowledge about their effects on ozone. As it turned out, a margin of safety was probably bought, albeit at the expense of a thriving industry.

Scary stories often create, for a little while, a comforting illusion that the world has only one problem. Then they tend to disappear. By the end of the 1970s, news about the ozone layer had all but vanished from the popular press, but the effects of manmade chemicals onozone are still worth worrying about. However, the scientific issues have become increasingly complex and ambiguous. One of the authorities on the ozone layer, a chemist from Harvard named Michael McElroy, described the general problem in this way: “The atmosphere is the air shared by the entire living system, inhaled and exhaled on a planetary scale, and we are doing things to it which are readily detectable but the effects of which are very hard to predict.”

PHOTOGRAPHS OF EARTH taken from outer space have lost their novelty, but, like a psychoanalysis, they have irreversibly altered the view. An extraterrestrial picture taken as the sun appears over the limb of the earth reveals the earth as a dark, convex semicircle and, above it, space as a dark, concave one; in between is a shining sliver, a fingernail paring of light, which is the atmosphere. Seemingly huge and inexhaustible, it is in fact quite small.

Some ozone turns up in the lowest section of the atmosphere. There, it’s a manmade constituent of urban smog, an especially nasty one, which has a corrosive effect on the lungs. Higher up, however, in the stratosphere, which is the second layer of the atmosphere, ozone is beneficent. Oxygen exists in abundance in the atmosphere because of biological activity on the planet below. In the stratosphere, sunlight creates ozone out of oxygen. Stratospheric ozone is, therefore, a product of biological activity, and it also protects that activity by absorbing most of the sun’s ultraviolet radiation. Life could not have evolved on earth as it did without the layer of ozone above, and vice versa. The system is a lovely wheellife leads to ozone, ozone leads to lifeand perhaps a fragile one.

The ozone layer isn’t very far away; the stratosphere begins ten miles up and extends to a height of about thirty miles. While the ozone layer can be pictured as a shield, encircling the earth and absorbing the blows of ultraviolet radiation, it is hardly as sturdy as the term “shield” implies. This shield’s thickness varies greatly with both time and place: the lower the latitude, the thinner the column of ozone above, and there’s more of it in the spring than at any other time of the year.

Overall, the shield is very thin. The ozone in it represents about a hundred parts per billion of the total atmosphere. Were the ozone layer distributed uniformly around the earth and squeezed until it reached the pressure of the air at sea level, it would make a girdle only one eighth of an inch thick. Moreover, the molecules of ozone that make up the shield behave in an unstable fashion. They react with many other sorts of molecules, and, in reacting, turn into something else.

In the natural state of things, the shield of ozone is constantly broken down by chemical reactions and constantly recreated by one simple process, which begins with solar photons splitting oxygen atoms in two. An enormous amount of solar energyabout ten times as much energy as the human world consumes in a yeargoes into making the stratosphere’s annual ration of ozone. So for all practical purposes, the supply of ozone remains fixed. Ingenious mankind can’t significantly acid to the ozone layer. According to the theories of ozone depletion, however, mankind can accelerate the destruction of ozone and create someday a new balance of forcesand with it a dangerously thinner version of the thin ozone shield.

Not much that is sent from the earth into the air escapes the atmosphere. Most substances, in fact, don’t get beyond the lowest region, which cleanses itself efficiently, returning airborne substances to earth in rain. Fluorocarbons, however, are inert, which means that they don’t react with other chemicals. This property, which makes them safe inside homes, and thus has delighted industrial chemists, causes them eventually to escape the lower atmosphere and to travel intact to the stratosphere. There the fierce, relatively unfiltered sunlight breaks them into several different chemicals. One of these, atomic chlorine, belongs to a class of substances vividly named “free radicals,” and laboratory experiments have shown that atomic chlorine will act as a catalyst in transformations that destroy ozone. According to present atmospheric theory, one fluorocarbon molecule can end up destroying 100,000 molecules of ozone.

The scientists who propounded or endorsed this theory felt especially alarmed because their calculations suggested that it would take a long timenow thought to be on the order of fifty yearsfor a fluorocarbon molecule to make the round trip from release in the biosphere to eventual return to earth. Fluorocarbons could thus become the source of an awful problem. Industrycould continue to load up the atmosphere with these chemicals, and the ill effects could be disguised for many years.

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