1.0 INTRODUCTION
The NASA Transport and Chemical Evolution over
the Pacific (TRACE-P)
scheduled for early spring 2001 will comprise the third of three
planned Pacific Exploratory Missions in the central and western
regions of the Pacific Ocean basin. TRACE-P will be conducted as
part of NASA's Global Tropospheric
Experiment (GTE). The GTE is an ongoing element of the Tropospheric
Chemistry Program, a Research and Analysis (R&A) program within
the Science Division of NASA's Office
for Earth Science Enterprise.
The long-range goal of the GTE is to contribute
substantially to scientific understanding of human impacts on the
chemistry of the global troposphere. Changes in chemical composition
of the troposphere on a global scale have been well documented
during the last two decades and have given rise to considerable
concern that these chemical changes in the troposphere, which are
expected to increase as population increases and economic activity
expands, will lead to changes in the earth's climate. The connection
between atmospheric chemical composition change and climate change
is a major focus of NASA's Earth Science Enterprise Office.
NASA has unique capabilities with which to study
changes in the chemistry of the global troposphere. The GTE has
provided a scientific management structure for bringing these capabilities
to bear in an effective manner. The major thrust of the GTE to
date has been to utilize NASA's DC-8 and P-3B aircraft,
based at the NASA Dryden Flight
Research Center (DFRC) and the NASA
Wallops Flight Facility (WFF), respectively, to carry multi-instrument
payloads into regions of the troposphere where natural processes
and/or human impacts are believed to be particularly significant
in controlling chemical composition. Previous
GTE missions have obtained data in diverse environments, such
as the Amazon rain forest in Brazil, the tropical South Atlantic
Ocean, the Alaskan tundra, the northern Canadian wetlands, the
western Pacific Ocean just off the Asian continent, and the tropical
Pacific Ocean.
In 1991 and 1994, the GTE utilized the NASA DC-8
aircraft in two measurement campaigns, named the Pacific
Exploratory Mission in the West A and B (PEM-WEST A and B).
These experiments were exploratory in nature and had a variety
of objectives, one of which was to detect and study the Asian plume
in times of strong and weak outflow. They revealed significant
seasonal and geographic effects in the chemistry and transport
of air emerging from Asia. Data from the PEM-WEST A and B missions
have been released to the public and key results published in special
sections of JGR-Atmospheres in January 1996 for PEM-West
A and December 1997 for PEM-West B.
In the years since these earlier experiments were
conducted, interest has increased in the question of the origin,
chemistry, and fate of the pollution plume emerging from Asia,
which is rapidly growing in both population and economic activity.
The Pacific Basin is a part of the world where the air quality
is still less polluted by human activities than is, for example,
the North Atlantic Basin, but it will be impacted by the pollution
plume emerging from Asia. Energy use in eastern Asia has increased
by 5% per year during the last decade, and this rate of increase
will likely continue for the next two decades. Combustion of fossil
fuels is the main source of energy in Eastern Asia. Emission of
nitrogen oxides from combustion sources there is expected to increase
almost five-fold from 1990 to 2020, resulting in substantial impacts.
Experiments conducted along the West Coast of North America have
already found enhanced combustion tracers in numerous air masses
undergoing rapid transport from the west.
The NASA GTE will conduct TRACE-P in
the early spring of 2001. It will be a comprehensive experiment
that will utilize both the DC-8 and the P-3B with the appropriate
instrument payloads to examine the chemical composition, transport,
and chemical evolution of air as it moves from Asia out across
the Pacific Ocean. TRACE-P will take full advantage of recent improvements
in instrumentation. The strong focus on two major scientific objectives
- chemistry of the air emerging from Asia and the chemical evolution
of that air as it moves away from Asia - will enable a deeper understanding
of these phenomena than was possible from the PEM-West missions.
The use of two aircraft will allow for coordinated flight plans
tailored to the two major objectives
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