NSF PR 99-40 - June 8, 1999
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Massive Pollution Documented over Indian Ocean
An international group of scientists has documented
widespread pollution covering about 10 million square
kilometers of the tropical Indian Ocean -- roughly
the same area as the continental United States. This
finding by scientists participating in the Indian
Ocean Experiment (INDOEX) raises serious questions
about what impact the extensive pollution is having
on climate processes and on marine life in the ocean
below.
INDOEX, a $25 million project, sponsored in part by
the National Science Foundation, is investigating
how tiny pollutant particles called aerosols are transported
through the atmosphere, and their resulting effect
on climate. The project is coordinated by the Center
for Clouds, Chemistry and Climate (C4) at the Scripps
Institution of Oceanography, a National Science Foundation
(NSF) Science and Technology Center at the University
of California, San Diego. Paul J. Crutzen, director
of the Max Planck Institute for Chemistry and a 1995
Nobel laureate in chemistry and V. Ramanathan, director
of C4 at the Scripps Institution of Oceanography,
serve as co-chief scientists.
"Aerosols affect the amount of solar radiation that
is absorbed and reflected back to space by the atmosphere,”
explained Jay Fein, program director in NSF’s division
of atmospheric sciences. “They can also change the
composition of clouds, thereby altering the amount
of solar radiation they absorb and reflect back to
space. Aerosol - cloud - radiation processes are highly
complex and not well understood. In fact, the effect
of aerosols on our atmosphere’s radiation balance
is one of the largest sources of uncertainty in predicting
future climate. INDOEX was designed to reduce this
uncertainty."
Ramanathan said the team of scientists was shocked
by the extent of pollution they encountered during
the six-week field experiment that began in early
February and continued through the end of March 1999.
The INDOEX scientists reported finding a dense, brown
haze of pollution extending from the ocean surface
to altitudes of one to three kilometers. The haze
layer covered much of the research area almost continually
during the six-week experiment. The affected area
includes most of the northern Indian Ocean, including
the Arabian Sea, much of the Bay of Bengal, and spills
over into the equatorial Indian Ocean to about 5 degrees
south of the equator.
The haze is caused by high concentrations of small
particles known as aerosols that are usually less
than a few micrometers in diameter. Comprised primarily
of soot, sulfates, nitrates, organic particles, fly
ash and mineral dust, the particles often reduced
visibility over the open ocean to less than 10 kilometers,
a range typically found near polluted regions of the
United States and Europe. The haze layer also contains
relatively high concentrations of gases, including
carbon monoxide, various organic compounds, and sulfur
dioxide, providing conclusive evidence that the haze
layer is caused by pollution.
Asia and the Indian subcontinent, which together have
a population of more than 2 billion people, emit large
quantities of pollutants that can be carried to the
Indian Ocean during the northern hemisphere winter
by monsoon winds from the northeast. Preliminary results
indicate that aerosols in the polluted region scatter
the incoming solar radiation and reduce the amount
of energy absorbed by the ocean surface by as much
as 10 percent.
"If you cut the amount of sunlight going into the ocean,
you will also impact the amount of moisture evaporating
from the sea surface either regionally or globally
and, consequently, the amount of rainfall that will
be generated," Ramanathan said. "So the entire hydrological
cycle is being perturbed." A reduction in the amount
of sunlight reaching the ocean surface can also have
a detrimental effect on plant life that depends on
photosynthesis, including plankton, which provides
a key link in the marine food chain.
One of the primary goals of INDOEX is to determine
the role that aerosols play in global climate change.
Early results indicate that the pollutants play a
dual role in that they have both warming and cooling
effects. The tiny particles produce a cooling effect
in that they scatter sunlight back to space. By acting
as seeds for cloud condensation, they also produce
an indirect cooling effect by increasing both the
longevity and reflectivity, or albedo, of clouds.
The pollutants have a warming effect, however, in
that they absorb a large amount of sunlight. The airborne
particles over the northern Indian Ocean are unusually
dark because they contain large amounts of soot and
other materials from incompletely burned fuels and
wastes. Dark aerosols lead to the increased absorption
of solar radiation. "The soot contributes a substantial
amount of heating of the atmosphere, but it also reduces
the amount of sunlight reaching the ocean," Ramanathan
said. "So, it is just too early to say at this point
whether the net effect is one of cooling or warming."
The dark airborne particles over the Indian Ocean appear
to be markedly different from those over North America
and Europe, where advanced pollution control technologies
remove much of the dark material and yield particles
that are relatively brighter. Thus, the impact on
climate processes of pollution particles stemming
from Asia appears to be fundamentally different from
those originating in the United States and Europe.
The measurements taken in the Indian Ocean are also
important because they characterize emissions from
the rapidly emerging economies in this region. Emissions
of pollutants are expected to increase over the Indian
Ocean and in other parts of the globe as similar economies
grow.
The INDOEX scientists were surprised to find that such
a dense pollution layer in the Indian Ocean was caused
by sources at least a thousand or more kilometers
away. They suggest that the pollution events observed
in INDOEX may be symptomatic of large-scale pollution
transport that may be occurring in other regions of
Earth.
INDOEX was also funded by the U.S. Department of Energy,
the National Oceanic and Atmospheric Administration,
and NASA.
Editors: B-roll is available from the Scripps
Institution of Oceanography. Contact Cindy Clark at
cclark@ucsd.edu or (619) 534-3624.
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