GTE: PEM Tropics B
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.