April 02, 2003

Scientists using NASA satellite data have found the most intense global pollution from fires occurred during droughts caused by El Niño. The most intense fires took place in 1997- 1998 in association with the strongest El Niño event of the 20th century.

Bryan Duncan, Randall Martin, Amanda Staudt, Rosemarie Yevich and Jennifer Logan, from Harvard University, used data observed by NASA's Total Ozone Mapping Spectrometer (TOMS) satellite to quantify the amount of smoke pollution from biomass burning over 20 years.

"It's important to study biomass burning, because those fires produce as much pollution as use of fossil fuels. Most of the pollution from fires is produced in the tropics, while pollution from fossil fuel use occurs in North America, Europe and Asia," Logan said. One of the missions of NASA's Earth Science Enterprise, which partially funded the research, is to learn how the Earth system responds to natural and human-induced changes, such as droughts and worldwide fires caused by El Niño. NASA's Goddard Space Flight Center, Greenbelt, Md, developed the smoke data, the unique Aerosol Index product from the TOMS satellite.

The Harvard scientists recently published a study in the Journal of Geophysical Research - Atmospheres that describes how they combined the Aerosol Index data from TOMS with Along-Track Scanning Radiometer (ATSR) fire count data from the European Space Agency's European Remote Sensing-2 satellite.

The study assessed the effects of the 1997-1998 El Niño events on global biomass burning. They concluded biomass burning around the world was unusually high during the 1997- 1998 El Niño, greater than in any other period between 1979 and 2000. The amount of carbon monoxide emitted in 1997 and 1998 was about 30 percent higher than the amount emitted from worldwide motor vehicle and fossil fuel combustion.

"We found that fires typically produce the most pollution in Southeast Asia in March, in northern Africa in January and February, and in southern Africa and Brazil in August and September," Logan said. During the El Niño of 1997-1998, Indonesia, Mexico, and Central America experienced extreme droughts, and forest fires raged out of control.

The smoke from the fires in Mexico and Central America was blown northward in May 1998, worsening air-quality and reducing visibility over much of the eastern United States. The fires in Indonesia burned tropical forests over an area equivalent to the size of southern New England and released enormous amounts of pollutants. The team estimated the Indonesian fires produced about 170 million metric tons of carbon monoxide, which equals about one-third of the carbon monoxide annually released from fossil fuels.

Biomass burning is the combustion of both living and dead vegetation. It includes fires generated both by lightning and human activity. Humans are responsible for about 90 percent of biomass burning, with only a small percentage of natural fires contributing to the total amount of vegetation burned.

This graphic indicates the number of fires detected by the ATSR instrument from 1996 to 2000 within 100 km by 100 km (62 x 62 miles) areas on the Earth's surface. The yellow colorations indicate about 130 fires were detected during the 5-year period, while red indicates over 200 were detected. Regions of the world that experience large-scale burning during a typical year are South America, Central America, Africa, Southeast Asia, Indonesia, and Australia. CREDIT: ESA ATSR World Fire Atlas

The image indicates the amount of absorbing aerosols (tiny dark particles) in the air around the world in the last 6 months of 1997. The blue color indicates very little absorbing aerosols, and the orange to red colors indicate a high concentration of them. This is a monthly averaged Aerosol Index (number of particles in the air per 100 km (62 miles) by 125 km (77 miles) areas over the Earth's surface) as measured by the TOMS instrument. The aerosol over Indonesia was particularly high during the wildfires that raged there from September and November 1997. Burning in Africa and Brazil can also be seen. Note that the highest Aerosol Index values are usually caused by dust particles over the Sahara desert in Northern Africa (e.g., July and August 1997). CREDIT: NASA TOMS

This graph shows the distribution of mean carbon monoxide (CO) emissions from biomass burning (*1019 molecules of carbon per centimeter squared in a year). The light blue indicates the smallest number of CO emissions, while the orange and red indicate the largest (and most likely the largest concentration of fires and/or the most intense number of fires). CREDIT: Harvard University

These images depict carbon monoxide (CO) emissions by month from fires during a typical year. The red indicates the highest emissions. Fires in northern Africa typically occur in January and February during the local dry season. In March, intense burning occurs in Southeast Asia. Burning in South America and southern Africa typically occurs during June through October, the dry season. However, when there are droughts during an El Ni¤o event, small fires set by humans to clear vegetation can quickly become raging wildfires. CREDIT: Harvard University

The West Africa biomass burning season that began in November 2002 is still underway in late March 2003. This true-color Moderate Resolution Imaging Spectroradiometer (MODIS) image from the Aqua satellite on March 24, 2003, shows scores of fires (in Red) heavily concentrated in Sierra Leone, with other fires scattered across Guinea (top) and Liberia (bottom right). The high-resolution image provided above is 500 meters (3/10ths of a mile) per pixel. CREDIT: Jeff Schmaltz, MODIS Rapid Response Team, NASA GSFC