The fires that raged across southern Africa this August and September produced a thick "river of smoke" that observers compared with the aftermath of the Kuwaiti oil fires in 1991. NASA-supported studies currently underway on the event will contribute to improved air pollution policies in the region and a better understanding of its impact on climate change.
"Every year African biomass burning greatly exceeds the scale of the fires seen this year in the western United States," says Robert Swap of the University of Virginia, one of the organizers of the Southern African Regional Science Initiative (SAFARI 2000) field campaign. "But the southern African fire season we just observed may turn out to be an extreme one even by African standards. It was amazing how quickly this region went up in flames."
The intensive SAFARI 2000 six-week field campaign was planned to coincide with the dry-season fires. The experiment included observations from NASA's Terra and Landsat 7 spacecraft, research aircraft including NASA's ER-2 high-altitude jet, and several ground stations. Over 200 scientists from around the world participated in the campaign, which ended Sept. 25.
This year the southern African fire season peaked in late August and early September. The region is subject to some of the highest levels of biomass burning in the world. SAFARI 2000 planners tracked the changing location of fires with daily satellite maps provided by researchers at NASA's Goddard Space Flight Center (Greenbelt, Md.). The heaviest burning was in western Zambia, southern Angola, northern Namibia, and northern Botswana. Some of the blazes had fire fronts 20 miles long that lasted for days.
The thick haze layer from these fires produced between Aug. 23 and Sept. 7 was heavier than campaign participants had seen in previous field studies in the Amazon Basin and during the Kuwati oil fires.
"We observed a river of smoke that moved from northwest to southeast over the subcontinent, causing heavy haze and reduced visibility over Botswana and South Africa for about ten days in early September," says SAFARI 2000 organizer Harold Annegarn of the University of the Witwatersrand, Johannesburg.
According to veteran pilot Ken Broda, who flew NASA's ER-2 above the haze layer, "this was probably the worst in-flight visibility I've seen anywhere, even during the oil fires following the Persian Gulf war. From the ER-2's altitude of 60,000 feet, where normal visibility can stretch 60 miles, I couldn't clearly see the city of Johannesburg until I was directly overhead."
With instruments on the ground, in the air, and in space, scientists were able to sample the chemistry and measure the thickness of the smoke plumes, map the movements of the haze layer, and investigate how the smoke and fine aerosol particles affect clouds.
"For the first time we were able to track this annual haze from its source and determine what happens to the aerosols in the haze," says Annegarn. "The measurements we have now of carbon transport in the haze, both as gases and particles, will add important pieces to balancing global carbon budgets."
Studies by research aircraft flying inside the pall of haze revealed several surprises. Aircraft encountered puzzling layers of extremely clean air sandwiched between polluted layers.
"The pollution in the region is often very stratified with height in the atmosphere," says Peter Hobbs of the University of Washington, principal investigator for the experiments onboard the university's Convair-580 aircraft. "Regions of heavy pollution were separated by a very thin - just a few hundred feet deep - layer of almost pristine air."
The haze aerosols sampled were also more heat-absorbing than expected, which means the haze layer may have a significant warming influence on the region's atmosphere. "The aerosol in the region was surprisingly absorbing," says Hobbs. "Such aerosols may well add to the greenhouse warming effect, particularly in the mid-troposphere. Most aerosols are thought to offset that warming by scattering incoming solar radiation back into space."
The thick haze also contained high levels of ozone, a component of smog, that frequently reached levels similar to those found during air pollution alerts in major U.S. cities. Making the first balloon-borne measurements of ozone during the height of a southern African burning season, NASA Goddard scientist Anne Thompson found that the impact of the haze may be greater on climate change than on human health.
"Ozone levels in U.S. urban centers may be more unhealthy at the ground, but the ozone profiles we took in Zambia show that much of the ozone here is in the middle and upper troposphere where ozone's 'badness' is its effect as a greenhouse gas," says Thompson.
New air quality data collected during the campaign will also help governments in the region develop future environmental policies. Annegarn and other South African scientists are working to distinguish the industrial sources of air pollution from natural sources such as emissions from vegetation and soils.
"With the SAFARI 2000 data we now have the first comprehensive measurements of aerosols from the major industrial sources in southern Africa," said Annegarn. "Together with the detailed chemical analyses of these sources gathered during the campaign, we can now evaluate the relative importance of industrial emissions in the region's air pollution, which will contribute to the development of both national and regional air quality management policies."
U.S. participation in the SAFARI 2000 campaign was sponsored by NASA's Earth Observing System (EOS) project, a suite of spacecraft and interdisciplinary science investigations dedicated to advancing our knowledge of global change. EOS is managed by Goddard Space Flight Center for NASA's Earth Science Enterprise. A key objective of this year's campaign was to acquire measurements for validating new data products from NASA's Terra spacecraft.
More information on the SAFARI 2000 project is available at: http://safari.gecp.virginia.edu/
Materials provided by NASA/Goddard Space Flight Center--EOS Project Science Office. Note: Content may be edited for style and length.
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