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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