May 13, 2003
NASA Finds Soot Has Impact on Global Climate
A team of researchers, led by NASA and Columbia University scientists,
found airborne, microscopic, black-carbon (soot) particles are even
more plentiful around the world, and contribute more to climate change,
than was previously assumed by the Intergovernmental Panel of Climate
Change (IPCC).
The researchers concluded if these soot particles are not reduced,
at least as rapidly as light-colored pollutants, the world could warm
more quickly.
The findings appear in the latest issue of the Proceedings of the
National Academy of Sciences. It is authored by Makiko Sato, James
Hansen and others from NASA's Goddard Institute for Space Studies (GISS)
and Columbia University, New York; Oleg Dubovik, Brent Holben and Mian
Chin of NASA's Goddard Space Flight Center, Greenbelt, Md.; and Tica
Novakov, Lawrence Berkeley National Laboratory, Berkeley, Calif.
Sato, Hansen and colleagues used global atmospheric measurements taken
by the Aerosol Robotic Network (AERONET). AERONET is a global network
of more than 100 sun photometers that measure the amount of sunlight
absorbed by aerosols (fine particles in the air) at wavelengths from
ultraviolet to infrared. The scientists compared the AERONET data with
Chin's global-aerosol computer model and GISS climate model, both of
which included sources of soot aerosols consistent with the estimates
of the IPCC.
The researchers found the amount of sunlight absorbed by soot was
two-to-four times larger than previously assumed. This larger absorption
is due in part to the way the tiny carbon particles are incorporated
inside other larger particles: absorption is increased by light rays
bouncing around inside the larger particle.
According to the researchers, the larger absorption is attributable
also to previous underestimates of the amount of soot in the atmosphere.
The net result is soot contributes about twice as much to warming the
world as had been estimated by the IPCC.
Black carbon or soot is generated from traffic, industrial pollution,
outdoor fires and household burning of coal and biomass fuels. Soot
is a product of incomplete combustion, especially of diesel fuels,
biofuels, coal and outdoor biomass burning. Emissions are large in
areas where cooking and heating are done with wood, field residue,
cow dung and coal, at a low temperature that does not allow for complete
combustion. The resulting soot particles absorb sunlight, just as dark
pavement becomes hotter than light pavement.
Both soot and the light-colored tiny particles, most of which are
sulfates, pose problems for air quality around the world. Efforts are
beginning to reduce the sulfate aerosols to address air quality issues.
"There is a pitfall, however, in reducing sulfate emissions without
simultaneously reducing black carbon emissions," Hansen said. Since
soot is black, it absorbs heat and causes warming. Sulfate aerosols
are white, reflect sunlight, and cause cooling. At present, the warming
and cooling effects of the dark and light particles partially balance.
This research continues observations of global climate change. It
was funded by NASA's Earth Science Enterprise. The Enterprise is dedicated
to understanding the Earth as an integrated system and applying Earth
System Science to improve prediction of climate, weather, and natural
hazards using the unique vantage point of space.
For information the about the AERONET program on the Internet, visit:
http://aeronet.gsfc.nasa.gov/
For information about NASA and Earth Science initiatives on the Internet,
visit:
http://www.nasa.gov
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Contact:
Robert J. Gutro
Goddard Space Flight Center
301-286-4044
Rgutro@pop900.gsfc.nasa.gov |
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Soot Particle Under a Microscope
IMAGE CREDIT: D.M. Smith, University of Denver
Size of a Soot Particle
Soot particles are measured in micrometers (µm), and are smaller
than the diameter of a human hair. IMAGE CREDIT: NASA
Spotting Airborne Soot
Some climate computer models indicate soot by using colors, such as
yellow and orange. Darker colors indicate more soot. IMAGE CREDIT:
NASA
Burning and Soot
Outdoor biomass burning, including forest fires and the burning of
fields in the tropics, is a large source of soot. IMAGE CREDIT: NASA/GSFC
Carbon Dioxide from Fossil Fuels
Diesel engines are a major soot source in developed countries, especially
trucks and buses. IMAGE CREDIT: NASA/GSFC
Soot Generated from a Smokestack
CREDIT: Energy Information Admin., U.S. Dept. of Energy
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