The scientists discussed the massive cloud's sources, global movement and its implications. The brown cloud is a moving, persistent air mass characterized by a mixed-particle haze. It also contains other pollution, such as ozone.

"Ozone is a triple-threat player in the global environment. There are three very different ways ozone affects our lives," said Robert Chatfield, a scientist at NASA's Ames Research Center, Moffett Field, Calif. "A protective layer of good ozone, high in the atmosphere, shields us from deadly ultraviolet light that comes from the sun. Second, bad or smog ozone near the surface of Earth can burn our lungs and damage crops. In our study, we are looking at a third major effect of ozone, that it can warm the planet, because it is a powerful greenhouse gas," Chatfield said.

"We found both brown cloud pollution and natural processes can contribute to unhealthy levels of ozone in the troposphere where we live and breathe. Some ozone from the brown cloud rises to high enough altitudes to spread over the global atmosphere," Chatfield explained. Ozone from the Earth's protective stratospheric layer, produced by natural processes, can migrate down to contribute to concentrations in the lower atmosphere, according to the scientists.

The researchers studied the intercontinental smog ozone processes associated with the brown cloud over South Asia. They used a NASA technique that combines data acquired by satellites with ozone data measured by instruments on special weather balloons.

The ozone-monitoring instrument on NASA's Aura satellite is providing data about the brown cloud. "The beautiful, high- detail images from this instrument promise to help us sort out our major questions about how much of the tropospheric ozone is from pollution and how much is from natural factors," Chatfield said.

Analysis shows ozone in the lower atmosphere over the Indian Ocean comes from the intensely developed industrial- agricultural areas in the region. The southern pollutant buildup has long-range effects, often traveling across Africa, further than the brown cloud of particles, according to researchers.

To access technical information about the brown cloud study on the Web, visit:

http://geo.arc.nasa.gov/sgg/chatfield/recentRes.html

For information and images related to this story on the Web, visit:

http://www.nasa.gov/vision/earth/environment/brown_cloud.html

For information about NASA and agency programs on the Internet, visit:

http://www.nasa.gov