Red alert! 'recycled' ozone adds to health hazards in Zambia

December 10, 2001

Researchers analyzing harmful low-level ozone or "smog" over the African country of Zambia measured high amounts of pollution throughout the burning season in the year 2000, and discovered that the pollution is "recycled" from other southern African countries.

Anne Thompson, an Atmospheric Chemist from the NASA Goddard Space Flight Center, Greenbelt, Md., led the study of ozone transport in Zambia during the Southern African Regional Science Initiative (SAFARI 2000) last year.

Ozone measurements from balloons launched over Zambia in September 2000 by Thompson, Jacquie Witte of Science Systems and Applications, Inc., and Agnes Phahlane of the South African Weather Service showed multiple ozone pollution layers generated by the burning of vegetation throughout the country.

In the capital city of Lusaka, smoke from charcoal production adds to pollution from agricultural burning, covering Lusaka with a continuous blanket of haze every August and September. Along with the haze, the balloon data showed that ground-level ozone over Lusaka exceeded .90 parts per million (ppm) during the daytime, "Equivalent to a 'Code Red Ozone Day' in U.S. cities," Thompson said.

The balloon data showed that there is a layer of even higher ozone on top of the surface smog. That higher layer moves in from all over southern and central Africa. Spinning counterclockwise around a semi-permanent high-pressure system, pollution from fires over Zimbabwe, Angola, DR Congo, and Botswana is swept over the Indian Ocean then "recycled" back over Zambia. "This trans-boundary ozone pollution is similar to that in the United States, except that instead of pollution moving from one state to another, it moves from country to country over Africa," Witte said. Some of the pollutants also seep out to the eastern Atlantic as well as the Indian Ocean.

During SAFARI-2000, Thompson and her colleagues also tracked pollution over southern Africa using data from NASA's Earth Probe Total Ozone Mapping Spectrometer (TOMS) satellite instrument. "TOMS is the only satellite instrument that follows both smoke and smog," Thompson noted.

Because ozone in the stratosphere over the tropics is uniform, researchers subtract it from total amount of ozone that TOMS reads from the surface to the upper atmosphere. This enables them to calculate the smog in a "column" of atmosphere that stretches from the surface to the tropopause, more than 40,000 feet high. The TOMS satellite clearly shows tropospheric, or low-level ozone accumulating over the Indian and Atlantic Oceans because of the counter-clockwise movement of air over central and southern Africa.

High concentrations of ozone near ground level can be harmful to people, animals, and plant life. Ozone can irritate your respiratory system, aggravate asthma, and contribute to chronic lung diseases like emphysema and bronchitis. Harmful ozone levels, such as those in Lusaka, can also reduce the immune system's ability to fight off bacterial infections in the respiratory system, and may cause permanent lung damage.

SAFARI 2000 is focused on investigating the coupled land-atmosphere processes associated with the emission, transport, transformation, deposition and impact of southern African aerosols such as ozone, and trace gases. During the last 2 years, NASA was a major participant in several SAFARI 2000 field campaigns, providing satellite, airborne, and ground-based observations and scientific analyses. TOMS has been following ozone in Earth's atmosphere since 1978.
Anne Thompson will be making this presentation at the American Geophysical Union fall meeting in San Francisco, Calif. on Thursday, December 13 at 11:35am, PT in Room MC 123.

This research was conducted by NASA's Earth Science Enterprise; a long-term research effort dedicated to studying how human-induced and natural change affects our global environment. More information is available on the Internet at: or

NASA/Goddard Space Flight Center

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