NASA satellites and balloons spot airborne pollution 'train'

05/03/04

NASA scientists discovered pollution could catch an airborne "express train," or wind current, from Asia all the way to the southern Atlantic Ocean.

Scientists believe during certain seasons, as much as half of the ozone pollution above the Atlantic Ocean may be speeding down a "train" track of air from the Indian Ocean. As it rolls along, it picks up more smog from air peppered with thunderstorms that bring it up from the Earth's surface.

Bob Chatfield, a scientist at NASA's Ames Research Center, Moffett Field, Calif. said, "Man-made pollution from Asia can flow southward, get caught up into clouds, and then move steadily and rapidly westward across Africa and the Atlantic, reaching as far as Brazil."

Chatfield and Anne Thompson, a scientist at NASA's Goddard Spaceflight Center, Greenbelt, Md., used data from two satellites and a series of balloon-borne sensors to spot situations when near-surface smog could "catch the train" westward several times annually from January to April.

During those periods of exceptionally high ozone in the South Atlantic, especially during late winter, researchers noticed Indian Ocean pollution follows a similar westward route, wafted by winds in the upper air. They found the pollution eventually piles up in the South Atlantic. "We've always had some difficulty explaining all that ozone," Thompson admitted.

Seasonal episodes of unusually high ozone levels over the South Atlantic seem to begin with pollution sources thousands of miles away in southern Asia," Chatfield said. Winds are known to transport ozone and pollutants thousands of miles away from their original sources.

Clearly defined individual layers of ozone in the tropical South Atlantic were traced to lightning sources over nearby continents. In addition to ozone peaks associated with lightning, high levels of ozone pollution came from those spots in the Sahel area of North Africa where vegetation burned. However, even outside these areas, there was extra ozone pollution brought by the Asian "express train."

The scientists pinpointed these using the joint NASA-Japan Tropical Rainfall Measuring Mission satellite to see fires and lightning strikes, both of which promote ozone in the lower atmosphere. Researchers also identified large areas of ozone smog moving high over Africa using the Total Ozone Mapping Spectrometer satellite instrument.

The scientists confirmed the movement of the smog by using sensors on balloons in the Southern Hemisphere Additional Ozonesondes (SHADOZ) network. A computer model helped track the ozone train seen along the way by the SHADOZ balloon and satellite sensors. The scientists recreated the movement of the ozone from the Indian Ocean region to the Southern Atlantic Ocean.

Their research results appear in an article in a recent issue of the American Geophysical Union's Geophysical Research Letters.

Source: Eurekalert & others

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