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CLOUDS SHIELD POLLUTANTS GOING OUT TO SEA
NASA scientists have the first evidence more regional pollution
lurks in clouds than in clear skies off the Asian coastline. This
finding has implications for space-based attempts to monitor global
pollution and for other populated regions around the
world.
Scientists estimate that roughly two-thirds of Asian pollution
from the Pacific Rim flows to the western, North Pacific Ocean
under cloudy conditions. They based the study on direct
measurements taken in and around clouds by aircraft instruments
during the Transport and Chemical Evolution over the Pacific
(TRACE-P) field experiment.
NASA's P-3B aircraft flies along the Asian
coastline sampling pollution near clouds during the TRACE-P field
experiment. Scientists used pollution measurements in and around
clouds over the Asian-Pacific region to determine the link between
clouds and pollution.
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"The idea that clouds can be associated with pollution transport
is not new, but the TRACE-P observations provide the first evidence
of a cloud-pollution link over a large region," said Jim Crawford,
the TRACE-P deputy mission scientist at NASA Langley Research
Center.
Scientists measured 32 percent more carbon monoxide, an
indicator of pollution, in cloudy regions of the lower atmosphere
(troposphere) and 15 percent more in the upper troposphere as
compared to pollution levels in clear skies. Scientists also
found a similar relationship between clouds and other pollutants
such as the greenhouse gases carbon dioxide and methane.
"Larger concentrations of pollution are being transported away
from Asia under the cover of clouds than we expected," Crawford
said. "This information is critical for interpreting pollution
measurements from space."
The scientists think clouds could mask pollution from spacecraft
sensors, so current predictions based on satellite observations
alone could underestimate pollution levels. Researchers say they
will need additional information from field studies that combine
observations from satellites, aircraft and ground stations to
determine the extent that clouds impact spacecraft-based
measurements. The Journal of Geophysical
Research-Atmospheres recently published a paper on the
study.
Although the Asian-Pacific region was the focus of the study,
scientists believe the relationship between clouds and pollution
could also exist downstream from other populated regions of the
world. The North American-North Atlantic and the
African-South Atlantic regions are examples of areas where people
can contribute to regional pollution.
Human activities, such as the burning of fossil fuels for
household heating and industrial uses, and the burning of
vegetation, called biomass burning, produce air pollution. Cold air
masses or cold fronts flow eastward across Asia and lift the warm,
polluted air mass in front of them.
The lifting caused by cold fronts, which are dominant during the
springtime in Asia, induce cloud formation in the warm air mass.
Thus the mechanism for cloud formation and the export of pollution
is the same, leading to a link between clouds and pollution.
NASA's Earth Science Enterprise funded this research in an
effort to better understand and protect our home planet. TRACE-P,
conducted from March to April 2001, is part of the long series of
NASA Global Troposphere Experiments (GTE). The aim of GTE is to
develop a better understanding of worldwide chemistry of the
troposphere and to provide information that will allow scientists
to more accurately understand how to use satellite observations for
global air quality studies.
For information about
this research on the Internet, visit:
www-gte.larc.nasa.gov
For information about
NASA on the Internet, visit:
www.nasa.gov
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