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.
The mission of NASA’s Earth Science Enterprise is to develop a
scientific understanding of the Earth system and its response
to natural or human-induced changes to enable improved
prediction capability for climate, weather, and natural
hazards.
For images and information about this research on the Internet,
visit:
http://www.gsfc.nasa.gov/topstory/2004/0426pollutiontrain.html
For information about NASA on the Internet, visit:
