NASA scientists announced a giant, smoggy atmospheric
brown cloud, which forms over South Asia and the Indian
Ocean, has intercontinental reach. The scientists presented
their findings today during the American Geophysical Union
Fall meeting in San Francisco.

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.

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