For Release: Oct. 30, 1996
Headquarters, Washington, DC
Catherine E. Watson
Langley Rsearch Center, Hampton, VA
Release No. 96-170
A NASA research team has found high concentrations of ozone, comparable to urban pollution levels, in a region of traditionally clean air. The pollution in the tropical South Atlantic has been linked to intense, seasonal biomass burning in South America and Africa, providing convincing evidence that human activities are extending their impact further, and in more diverse ways.
"Most people don't realize that over a hundred thousand square miles of vegetation are burned each year in southern Africa, an area larger than that burned in South America," said Dr. Jack Fishman of NASA's Langley Research Center.
The new research findings are reported today in a special issue of the Journal of Geophysical Research. The Transport and Chemistry near the Equator over the Atlantic (TRACE-A) experiment was spearheaded by NASA, the Brazilian Space Agency (INPE) and scientists in South Africa. "The purpose of our mission," said Fishman, the TRACE-A mission scientist, "was to understand how much each continent contributed to the observed pollution pool and to gain an understanding of the unusual chemistry taking place in the atmosphere so far removed from the origin of the pollution."
According to Fishman, the biomass burning pollutants drift over the tropical South Atlantic Ocean, where the wind pattern traps them. Chemical processes, driven by very bright sunlight, then produce a smog similar to what is found in industrialized areas of the world. Eventually, the plumes of ozone and other pollutants produced by those chemical processes extend to the far reaches of the Indian Ocean, with some evidence that traces are seen as far away as Australia.
"As a result of TRACE-A, our understanding of the atmospheric chemistry of the entire Southern Hemisphere is greatly improved," Fishman added. "And we now realize that the composition of the atmosphere in what was once thought to be one of the cleanest regions in the world has also been greatly altered by human activity."
Most of the earth's ozone is found in a layer in the stratosphere, which begins about 20 miles above the surface. It is produced by the interaction of sunlight with oxygen and other gases that occur naturally in the upper atmosphere. The stratospheric ozone layer provides a shield from harmful ultraviolet radiation from the sun. In the lower atmosphere, however, ozone is a toxic gas that has long been known to exist in harmful amounts over highly populated, heavily industrialized regions. Its occurrence in large amounts in remote parts of the atmosphere has been much rarer, however.
More than 300 scientists from 14 nations participated in TRACE-A and its concurrent counterpart, the Southern African Fire-Atmosphere Research Initiative (SAFARI). Their work has shed new light on the impact and extent of human activities on the atmosphere and has provided data that will help to understand the links that may exist between the chemical makeup of the atmosphere and the earth's climate.
The major element of the NASA contribution to TRACE-A was a DC-8 aircraft specially instrumented for very sensitive measurements of ozone and the gases that produce it in the atmosphere. The DC-8 could measure a wide variety of trace gases down to the parts per trillion level (one-millionth of a part per million). During TRACE-A, the DC-8 flew more than 70,000 miles, probing the air over South America, southern Africa and the vast expanses of the South Atlantic and Indian Oceans. On board the DC-8, a dozen scientists and their support crews from several NASA centers and U.S. universities operated sophisticated instruments, inlcuding airborne lasers to measure ozone and smoke particles above and below the aircraft.
TRACE-A also utilized an operational satellite to map the large-scale distribution of ozone and biomass burning patterns. In addition, a series of ozonesonde (ozone sensors launched aboard weather balloons) and enhanced weather measurements provided information about the transport of the various trace gases and the physical processes responsible for their observed distributions in the atmosphere. Computer models also were used to integrate the results and help to interpret them.
A data illustration is available.
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