GTE: PEM Tropics B

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The NASA Pacific Exploratory Mission in the central and eastern regions of the tropical Pacific Ocean basin (PEM-Tropics B) scheduled for the March/April 1999 time period will comprise the second of two planned Pacific Exploratory Missions in the central and eastern regions of the tropical Pacific Ocean basin. PEM-Tropics B 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 Mission to Planet Earth (OMTPE).

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 Mission to Planet Earth.

NASA has important and unique capabilities with which to study possible changes in the chemistry of the troposphere. The GTE has provided a scientific management structure for bringing these capabilities to bear in the most effective manner. The major thrust of the GTE has been to utilize NASA's DC-8 and P-3B aircraft that have been based at the NASA Ames Research Center and the NASA Wallops Flight Facility, respectively, to carry multi-instrument payloads into regions of the global troposphere where natural processes and/or human impacts are believed to be particularly significant in effecting chemical composition changes and/or where the troposphere is still relatively unimpacted. Previous missions conducted by the GTE have provided valuable data in such change-sensitive environments as the Amazon rain forest in Brazil, the tropical South Atlantic Ocean, the Alaskan tundra, the northern Canadian wetlands, and the western Pacific Ocean just off the Asian continent.

In August -October, 1996 the GTE PEM-Tropics A mission utilized both the NASA DC-8 and P-3B aircraft in a coordinated project to study the chemistry of the troposphere over the central and eastern Pacific Ocean with a focus on the tropics. This relatively unexplored region of the troposphere was expected to be and, in many places, was found to be a very clean air region of the world, possibly the cleanest on earth. It proved to be an outstanding "laboratory" for studying the role of nitrogen oxides in tropospheric ozone formation and loss and of sulfur compounds in aerosol formation, problems that have important climate implications. It yielded important new information on chemical changes that are affecting the oxidizing power of the global troposphere and, therefore, the rate at which the global atmosphere can cleanse itself of pollutants emitted into it by human activities. Data from the PEM-Tropics A mission have been released to the public, and the PEM-Tropics A Science Team submitted papers for publication of some key results early in October 1997.

The tropical South Pacific region, while still quite clean, was found, however, to be experiencing significant burdens of pollutants at elevated altitudes south of the South Pacific Convergence Zone. These pollutants appear, from preliminary analysis, to have originated from biomass burning on land masses to the west of the impacted areas. A major objective of PEM-Tropics B (see scientific objectives) is to study the tropical Pacific atmosphere during a season when biomass burning impacts should be significantly less than during the PEM-Tropics A experiment. PEM-Tropics B is presently scheduled to begin aircraft integration in the mid-January with deployment March through April time frame of 1999 and will utilize the DC-8 and P-3B aircraft.

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