GTE: Pacific Exploratory Missions
In the vast regions of the Pacific ocean, the chemistry that
controls the composition of the atmosphere may very well represent the
last vestiges of the natural processes that were prevalent prior to
significant human influences on the global atmosphere. Yet, along the
north western rim of the Pacific are the most populated countries of
the world. The potential for these countries to emerge as major
industrial centers, with the concurrent pollution is just beginning to
be recognized. Recent evidence from satellite observations also
suggest that the southern Pacific Ocean region, while more removed
from industrial countries in the northern hemisphere, may be subject
to pollution from long range transport of biomass burning from Africa
and South America.
Early in the formative stages of the GTE program
(See GTE Implementation), ad hoc
committees convened to review the NASA Tropospheric Chemistry program
recommended as one of the major studies for the GTE Pacific
Exploratory Missions (PEM) in the Pacific region. The PEM campaigns
have to date consisted of two field missions in the north western
Pacific region, PEM-West A & B, and one mission in the south
central Pacific ocean, PEM-Tropics. (See Map
of PEM-Campaigns)
Other international components within the International Global
Atmospheric Chemistry (IGAC) Program have also recognized the
importance of the Pacific ocean region. A major study to provide early
detection and understanding of the impact of industrial and natural
emissions from the Asian continent on the north western Pacific region
was initiated in the early 1990's. This study, the East Asia/North
Pacific Regional Study (APARE), was a project within the IGAC Program.
Collaborating programs including initiatives in Taiwan, Japan, The
Peoples Republic of China, Hong Kong, and programs sponsored by the
National Atmospheric and Aeronautics Administration (NASA), the
National Oceanic and Atmospheric Administration (NOAA), and the
National Center for Atmospheric Research (NCAR).
A major component of APARE was the NASA Pacific Exploratory
Mission-West (PEM-West). The broad objective of the PEM-West/APARE
initiative is to study chemical processes and long range transport
over the northwest Pacific ocean, and to estimate the magnitude of the
human impact on the oceanic atmosphere over this region, particularly
for tropospheric and sulfur species. The joint PEM-West/APARE
initiative consisted of two major field studies conducted during two
different seasons of the year. The first phase, PEM-West (A), was
conducted in September - October, 1991, a season of the year
characterized by minimum outflow from the Asian continent. The second
phase, PEM-West(B), was conducted during February-March , 1994 a
season of the year characterized by significant outflow from the Asian
continent. Both phases of PEM-West included intensive airborne
measurements of trace gases from the NASA DC-8 aircraft coordinated
with measurements at surface sites, and during PEM-West A with
airborne measurements from a collaborating Japanese program. The
following sections of the PEM-West web page briefly describes the
experimental design for the PEM-West A
and PEM-West B phases with a brief
summary of the results from each mission.
The second field campaign in the Pacific Exploratory Missions,
PEM-Tropics, has been focussed on the south tropical Pacific region.
The field deployment phase of the PEM-Tropics mission was completed in
early October, 1996. PEM-Tropics involved the NASA DC-8 and P-3B
aircraft operating jointly from bases in Tahiti, and Easter Island,
and the P-3B operating from Christmas Island, and Guayaquil, Ecuador,
and the DC-8 from Christchurch, NZ, and Nadi, Fiji. The mission design
for PEM-Tropics is briefly described in
the following web pages.