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Worldwide monitoring has shown that stratospheric ozone has declined for at least two decades, with losses of about 10 percent in the winter and spring and 5 percent in the summer and autumn in such diverse locations as Europe, North America, and Australia.Researchers now find depletion over the North Pole as well, and the problem seems to be getting worse each year.Instead, they began with basic questions about the nature of Earth's atmosphere—its composition, density, and temperature distribution.
In the absence of this gaseous shield in the stratosphere, the harmful radiation has a perfect portal through which to strike Earth.
Although a combination of weather conditions and CFC chemistry conspire to create the thinnest ozone levels in the sky above the South Pole, CFCs are mainly released at northern latitudes—mostly from Europe, Russia, Japan, and North America—and play a leading role in lowering ozone concentrations around the globe.
These compounds play crucial roles in such phenomena as urban smog, the loss of stratospheric ozone, and the global removal of atmospheric impurities.
Scientists had not detected free radicals because they reside in the atmosphere at concentrations well below the part-per-million level that state-of-the-art equipment in 1948 could detect.
Like many lines of scientific inquiry, research leading to the prediction and discovery of global ozone depletion and the damaging effects of CFCs followed a path full of twists and turns.
Investigators did not set our to determine whether human activity affects our environment nor did they know much about chemical pollutants.But in attempting to further analyze the composition of the atmosphere, researchers at the turn of the century faced a major stumbling block: virtually all gases, except for molecular nitrogen and oxygen, exist in such minute concentrations that available equipment could not detect them. During the 1880s, scientists had begun perfecting a new, highly precise method of identifying a compound by recording a special kind of chemical fingerprint—the particular pattern of wavelengths of light it emits or absorbs. By the 1950s, researchers had identified 14 atmospheric chemical constituents.Despite this progress, researchers were still missing a major piece of the atmospheric puzzle.According to a United Nations report, the annual dose of harmful ultraviolet radiation striking the northern hemisphere rose by 5 percent during the past decade.During the past 40 years, the world has seen an alarming increase in the incidence of malignant skin cancer; the rate today is tenfold higher than in the 1950s.Yet it has dramatically different effects depending upon its location.Near Earth's surface, where ozone comes into direct contact with life forms, it primarily displays a destructive side.All of the compounds detected possessed an even number of electrons, a characteristic which typically gives chemical stability.Other less common compounds with an odd number of electrons—known as free radicals—readily undergo chemical reactions and do not survive for long.Such research spurred advances on two fronts: a substantial increase in the precision and accuracy of measurements of atmospheric gases and a striking decrease in the minimum concentration of a compound that must be present to be detected.As a result, the number of atmospheric compounds identified by scientists has increased from 14 in the early 1950s to more than 3,000 today.