Text Size

Related Links

For more information contact:

David E. Steitz
Headquarters, Washington
(Phone: 202/358-1730)

Robert J. Gutro
Goddard Space Flight Center
(Phone: 301/286-4044)

Mary Tobin
Columbia University
(Phone: 845/365-8607)

Allan Chen
Lawrence Berkeley National Laboratory
(Phone: 510/486-4210)


Viewable Images


Story Archives

The Top Story Archive listing can be found by clicking on this link.

All stories found on a Top Story page or the front page of this site have been archived from most to least current on this page.

For a list of recent press releases, click here.

May 13, 2003 - (date of web publication)



Image of microscopic soot particle

Image 1

Soot Particle Under a Microscope

Credit: D.M. Smith, University of Denver

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.


Soot particle comparison to diameter of human hair

Image 2

Size of a Soot Particle

Soot particles are measured in micrometers (um), and are smaller than the diameter of a human hair. Credit: NASA

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.


Global image indicating airborne soot

Image 3

Spotting Airborne Soot

Some climate computer models indicate soot by using colors, such as yellow and orange. Darker colors indicate more soot. Credit: NASA

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


Photos of forest fire and billowing smoke

Image 4

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
fires and household burning of coal and iomass 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.



Photo of automobile traffic

Image 5

Carbon Dioxide from Fossil Fuels

Diesel engines are a major soot source in developed countries, especially trucks and buses. Credit: NASA/GSFC

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 ithout 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.


Photo of smokestack

Image 6

Soot generated from a smokestack
Credit: Energy Information Admin., U.S. Dept. of Energy

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.





Back to Top