Researchers have discovered that smoke and smog move in different ways through the atmosphere. A series of unusual events several years ago created a blanket of pollution over the Indian Ocean. In the second half of 1997, smoke from Indonesian fires remained stagnant over Southeast Asia while smog, which is tropospheric, low-level ozone, spread more rapidly across the Indian Ocean toward India.

This situation was exacerbated by El Nino, which had already increased the thickness of smog over the region. At the same time, additional smog from African fires streamed over the Indian Ocean and combined with the smog from Indonesia, creating an aerial canopy of pollutants.

Researchers tracked the pollution 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, globally," said Anne Thompson, NASA Earth Scientist at Goddard Space Flight Center, Greenbelt, MD. "The extreme pollution generated during the Indonesian fires was the first time we saw smoke move more slowly and in different directions from where smog moved." Although TOMS has been observing the atmosphere since 1978, new air-quality technologies added in 1997 enabled scientists to see the divergence of smoke and smog for the first time.

The different movement occurred because the pollutants were in different layers of the atmosphere. Heavier smoke particles stayed close to the region of the fires while smog moved more quickly and spread over a large area. "Typically, smog is seen coming from Africa because much more burning occurs there, but in 1997 the Indonesian plume was thicker due to the fires there," Thompson added.

Between July and November 1997, the emissions from the Indonesian fires caused considerable air pollution throughout the Southeast Asian region, including Indonesia, Malaysia, and Singapore. Hazardous particles found in smoke caused air-quality and health problems throughout the region including asthma, upper respiratory infections, decreased lung function, and eye and skin irritation.

Before the fires began in 1997, the El Nino and changing atmospheric patterns over the Indian Ocean, a pattern called the Indian Ocean Dipole, caused the ozone column to thicken, indicating that climatic factors play a major role. When scientists went back and looked at the 1980s El Nino events, they noticed the same behavior.

"However, we can detect no trend in smog ozone during the 1980s in the tropics, even though burning may have increased," said Thompson. "In some regions of the tropics, rising ozone precedes the burning period and in other regions, ozone levels don't rise as much as we would expect during the local burning season. Clearly, factors other than biomass burning exert a strong influence on tropical tropospheric ozone."

Since 1978, TOMS has eyed upper and lower level ozone in Earth's atmosphere. Since upper-level ozone in the stratosphere over the tropics is uniform, TOMS can subtract it out from its readings and calculate the smog in a "column" of atmosphere that stretches from the surface to the tropopause, more than 40,000 feet high.

A paper titled "Tropospheric Ozone and Biomass Burning," by Goddard's Anne Thompson and researchers at the University of Maryland; Science Systems and Applications, Inc.; and Hokkaido University of Japan, explaining the divergence of the pollutants, appears in the March 16 issue of Science.

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.

Note: If no author is given, the source is cited instead.

• Air Quality
• Air Pollution
• Pollution
• Environmental Science
• Environmental Issues
• Wildfires

• Tropospheric ozone
• Inversion (meteorology)
• Nitrogen oxide
• Smoke
• Smog
• Automobile emissions control