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NASA
Data Track Pollution Over India
NASA's Terra
spacecraft
Data from the Multi-angle Imaging Spectroradiometer (MISR)
instrument on NASA's Terra spacecraft have been used in a
groundbreaking new university study that examines the
concentration, distribution and composition of aerosol pollution
over the Indian subcontinent. The study documents the region's
very high levels of natural and human-produced pollutants, and
uncovered surprising seasonal shifts in the source of the
pollution.
Larry Di Girolamo and postdoctoral scientist Sagnik Dey of
the University of Illinois, Champaign, used a decade's worth of
MISR data to comprehensively analyze aerosol pollution over the
Indian subcontinent. This densely populated region has poor air
quality and lacks on-the-ground pollution monitoring sites. The
study was published recently in the Journal of Geophysical
Research.
Aerosols — tiny particles suspended in the air — are
produced both by natural sources, such as dust and pollen carried
on the wind, and by human activities, such as soot and other
hydrocarbons released from the burning of fossil fuels. They can
affect the environment and human health, causing a range of
respiratory problems. Aerosol pollution levels can be measured on
the ground, but only the most developed countries have widespread sensor data.
Since standard satellite imaging cannot measure aerosols
over land, Di Girolamo and Dey used NASA's MISR, developed and
managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif.
MISR's unique multi-view design allows researchers to
differentiate surface variability from the atmosphere so they can
observe and quantitatively measure particles in the air. MISR not
only measures the amount of aerosols, but can also distinguish
between natural and human-produced particles.
The scientists found very high levels of both natural and
human-produced aerosol pollutants. The level of atmospheric
pollution across most of the country was two to five times higher
than World Health Organization guidelines.
But the study also revealed some surprising trends. For
example, the researchers noticed consistent seasonal shifts in
human-produced versus natural aerosols. Before monsoon season
begins, the winds over the Indian subcontinent shift, blowing
inland instead of out to sea. These winds carry immense amounts of
dust from Africa and the Arabian Peninsula to India, degrading air quality.
"Just before the rains come, the air gets really
polluted, and for a long time everyone blamed the dust," Di
Girolamo said, "but MISR has shown that not only is there an
influx of dust, there's also a massive buildup of man-made
pollutants that's hidden within the dust."
During monsoon season, rains wash some of the dust and soot
from the air, but other human-produced pollutants continue to
build up. After monsoon season, dust transport is reduced, but
human-produced pollutant levels skyrocket, as biomass burning and
the use of diesel-fueled transportation soar. During winter,
seaward-blowing breezes disperse all the pollutants across the
subcontinent and out to sea, where they remain
until the pre-monsoon winds blow again.
"We desperately needed these observations to help
validate our atmospheric models," said Di Girolamo.
"We're finding that in a complex area like India, we have a
long way to go. But these observations help give us some guidance."
As MISR continues to collect worldwide aerosol data, Di
Girolamo says atmospheric scientists will continue to refine
models for India and other areas and begin to propose new
regulatory measures. The MISR data may also reveal trends in
aerosol concentration over time, which can be compared with
climate and health data. Source: NASA - National Aeronautics
and Space Administration |
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