NASA Satellites Track Asia-Atlantic Smog Train

GREENBELT, Maryland, May 5, 2004 (ENS) - Scientists with the National Aeronautics and Space Administration (NASA) have found that ground level air pollution created in one region of the world can be swept up by air currents and travel halfway around the globe. The pollution appears to catch an airborne wind current from Asia to the southern Atlantic Ocean.

From January to April, 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 thunderstorms that bring it up from the Earth's surface.

Bob Chatfield, a scientist at NASA's Ames Research Center at Moffett Field, California 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 in Greenbelt, 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 said.

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.

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 locations in the Sahel area of North Africa where vegetation burned.

Even outside these areas, the scientists found there was extra ozone pollution brought by what they called 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 the American Geophysical Union publication "Geophysical Research Letters."