May 3, 2004
NASA Satellites and Balloons Catch the Fast Pollution “Train”
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.
###
Contacts:
Gretchen Cook-Anderson
Headquarters, Washington
Phone: 202/358-0836
Rob Gutro
Goddard Space Flight Center,
Greenbelt, Md.
Phone: 301/286-4044
Mike Mewhinney
Ames Research Center,
Moffett Field, Calif.
Phone: 650/604-3937
Harvey Leifert
American Geophysical Union
Phone: 202/777-7507 |
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Riding the Pollution Train
The red arrows on this globe trace the fast track of ozone pollution
from Asia as it contributes to the highest ozone episodes found in the
South Atlantic. Asian smog with moderate amounts of ozone moves south
into the Indian Ocean. Repeatedly, every few weeks, when this ozone can
be swept upwards by tall rainclouds, it can then move eastward rapidly
across Central Africa (upper arrow). The long red path is shown to end
at Ascension Island, but actually a large patch of ozone fills much of
the South Atlantic. Additionally, lightning and vegetation burning over
Africa could add highly visible ”pollution peak” features,
but these obvious nearby African sources tell only half the story of
the Atlantic ozone episodes. CREDIT: NASA, MODIS image
NASA Sensors Find Pollution Hiding in the SHADOZ of the Atlantic
Ocean
Scientists from NASA and 10 tropical countries used balloon-borne ozonesonde
sensors in the SHADOZ (Southern Hemisphere Additional Ozonesondes) Project,
and found that ozone ”piles up” over the south Atlantic Ocean
due to natural circulation patterns and that pollution (low-level ozone)
from Africa and South America streams into the pile-up region, making
the ozone even more concentrated. This graphic shows how pollution can
move with winds blowing from South America pushing pollution into the
middle Atlantic, and easterly winds from Africa also blowing pollution
into the mid-Atlantic, where atmospheric motions are already dumping
ozone. In fact, these easterly winds derive ozone from much further away,
in the Central Indian Ocean. The winds do vary in time, corresponding
to weather patterns in Africa and its neighboring oceans. CREDIT: NASA
GSFC, Barbara Summey
Pollution Event Spans Nearly One-Third of the Globe
Upper Image: This image from NASA’s TRMM satellite shows the pathway
(blue line) of an ozone pollution event, from its origins in Asia. Along
the way it passes through regions of lightning. Lightning is associated
with natural increases in ozone values in the upper air. The intensity
of strikes is coded with colored dots (cool to warm ”intense” values)
which appear mostly over South America and Central Africa, Wind streamlines
at 25,000 feet are also depicted by the circular and wavy lines. The
combination of natural lightning-enhanced ozone with air pollution from
Asia is reflected by the ”hot” red- and yellow-colored features
in the center of the lower ozone map.
Lower Image: The orange swath in the lower map indicates an extended
plume of ozone pollution detected by the TOMS instrument. High levels
of ozone pollution extend from South Asia all the way to the coast of
Brazil. Some ozone is also formed in South America and Africa, due to
lightning and burning. CREDIT: NASA Ames/MSFC/GSFC
An Ozonesonde and Balloon
Anne Thompson (NASA, left) and Agnes Phahlane (South African Weather
Service, right) prepare to launch a balloon carrying an ozonesonde, a
sensor that measures ozone. CREDIT: NASA |
