Magazine article Science News

Ozone Layer Succumbs to Assault

Magazine article Science News

Ozone Layer Succumbs to Assault

Article excerpt

The global ozone layer is even more vulnerable to chemical pollutants than previously thought, a group of 80 researchers concluded last week after finishing a major study of the atmosphere. The new findings raise concern that ozone levels over the globe's populous middle latitudes could decline even faster than earlier estimates had warned.

"We have a remarkably different picture of this than we had before the mission," says James G. Anderson of Harvard University, the project scientist for the study, which involved observations by both aircraft and satellites.

Anderson and his colleagues embarked on the NASA-led project last October to examine the ozone layer both inside the Arctic region and over the more temperate parts of the Northern Hemisphere. The researchers set out to analyze the potential for severe ozone losses in the Arctic as well as to explain a disturbing ozone erosion occurring over much of the globe since 1970.

Data from the study indicate that chemical pollution destroyed significant amounts of ozone over the Arctic this winter and will most likely cause even larger depletions in the far north in coming years.

Even more important, the mission reveals that the atmosphere cannot defend itself against chlorine and bromine pollution as well as scientists had thought, says Anderson. Measurements made by NASA's high-altitude ER-2 plane overturned the long-held idea that chlorine and bromine play a minor role in controlling ozone concentrations above the middle latitudes.

Scientists had believed that natural chemical cycles involving nitrogen and hydrogen controlled the stratospheric ozone amounts in this part of Earth's atmosphere. But the ER-2 observations detected much lower levels of nitrogen oxides ([NO.sub.x]) than scientists expected, suggesting they had overemphasized the importance of the nitrogen cycle. The measurements also showed higher-than-anticipated levels of chlorine monoxide (CIO), known to play a key role in destroying ozone in the polar regions.

These observations directly support laboratory experiments that suggest nitrogen chemicals undergo so-called heterogenous reactions on the surface of atmospheric sulfate particles. When incorporated into computer models, such reactions lead to lower-than-expected levels of [NO.sub.x] and higher-than-expected levels of CIO -- the same relationship discovered by the ER-2.

Scientists now seek a consistent theory to explain the observed ozone loss over the middle latitudes. Although not proof, the new data indicate that heterogeneous reactions reduce the importance of the nitrogen cycle, allowing the chlorine and bromine cycles to destroy ozone there. …

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