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Satellite data reveal immense pollution pool over Bihar, India
James E. Kloeppel, Physical Sciences Editor
217 244-1073; kloeppel@uiuc.edu
1/27/05
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CHAMPAIGN, Ill.
— Scientists studying satellite data have discovered an immense
wintertime pool of pollution over the northern Indian state of Bihar.
Blanketing around 100 million people, primarily in the Ganges Valley,
the pollution levels are about five times larger than those typically
found over Los Angeles.
The discovery was made by researchers analyzing four years of data collected
by the Multi-angle Imaging Spectro-Radiometer (MISR) onboard the Terra
satellite. Lofted into orbit on Dec. 18, 1999, Terra is the flagship
of NASA’s Earth Observing System Program.
“This study is the most comprehensive and detailed examination
of industrial, smoke and other air pollution particles over the Indian
subcontinent to date, and reveals how topography, meteorology and human
activity help determine where these particles are concentrated,”
said Larry Di Girolamo, a professor of atmospheric
sciences at the University of Illinois at Urbana-Champaign and a
co-investigator on the MISR mission.
“MISR is the first instrument to make high-resolution, multi-angle
radiometric measurements of Earth from space,” Di Girolamo said.
“By measuring reflected sunlight at nine angles, we can accurately
determine the amount of particulate matter, including that generated
from man-made pollution, in the atmosphere.”
While high pollution levels were found over much of India, a concentrated
pool of particles was discovered over Bihar, a largely rural area with
a high population density. A large source contributing to the Bihar
pollution pool is the inefficient burning of a variety of biofuels during
cooking and other domestic use. Particles in the smoke remain close
to the ground, trapped by valley walls, and unable to mix upward because
of a high-pressure system that dominates the region during winter.
“The result is a pollution episode that can affect both human
health and local climate,” Di Girolamo said. “The airborne
particles can damage delicate lung tissue, and by altering the radiative
heating profile of the atmosphere, the particles may change temperature
and precipitation patterns.”
Prior to the MISR study, atmospheric models had predicted a tongue of
pollution extending across the middle of India. The MISR observations,
however, show the pollution lies much farther north.
“These models are very important to us, as they are used to forecast
pollution episodes and climate change,” Di Girolamo said. “The
fact that model results don’t match the MISR observations suggests
there are problems in the models or the model inputs that need to be
fixed.”
The role of airborne particles remains one of the largest uncertainties
in atmospheric modeling. In addition to modifying local climate, the
particles can interact with clouds and change the cloud properties.
This is particularly important, since clouds have the greatest radiative
forcing on the climate system.
“The Bihar pollution pool must be having a tremendous impact on
the local climate and the health of the approximately 100 million people
that reside within this pool.” Di Girolamo said. “Our long-term
goal is to better predict the occurrence of these pollution episodes
and their impact on public health and local climate.”
The work, funded by NASA, involved collaborators from Illinois, the
Jet Propulsion Laboratory, the National Center for Atmospheric Research
and Scripps Institution of Oceanography. The researchers published their
findings in the December issue of the journal Geophysical Research Letters.
