The Pacific Ocean is the only major region in the Northern
Hemisphere that is "relatively" free from direct
anthropogenic influences. In the remote regions of the northern
Pacific and in most of the southern Pacific, it should be possible to
study the biogeochemical cycles of carbon, nitrogen, ozone, sulfur,
and aerosols in an environment which, from a global perspective, is
the least perturbed by anthropogenic activities. On the other hand,
there is little doubt that long-range transport of air pollutants from
Asia and Europe and, to a lesser extent, North America is beginning to
have a significant impact on the atmosphere over a large part of the
Pacific.
Through the coordination of the International Global Atmospheric
Chemistry (IGAC) Program, the East Asia/North Pacific Regional Study
(APARE) was initiated 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. The National Aeronautics and Space Administration's Pacific
Exploratory Mission in the western Pacific (PEM-West phases A & B)
has been a major component of APARE.
The specific objectives of PEM-West were: (1) To investigate the
atmospheric chemistry of ozone (O3) and its precursors
over the northwest Pacific including examination of their natural
budgets as well as the impact of anthropogenic sources; and (2) To
investigate the atmospheric sulfur cycle over the northwest Pacific
with emphasis on the relative importance and influence of continental
versus marine sulfur sources.
The overall experiment design for the PEM-West/APARE program
encompassed two field studies positioned in time such that contrasting
meteorological regimes in the northwestern Pacific could be sampled.
The first phase of the Pacific Exploratory Mission - West, PEM-West A,
was conducted over the western Pacific region off the eastern coast of
Asia during September and October, 1991. A significant characteristics
of the lower tropospheric airflow during this time period is the
predominance of flow from mid-Pacific regions. Phase B of PEM-West was
conducted during the spring 1994, a period characterized by maximum
outflow from the Asian continent. The experimental design of PEM-West
was centered on conducting intensive airborne studies over the
northwest Pacific ocean using the NASA DC-8 aircraft which is home
based at the NASA Ames Research Center in Moffett Field, CA. During
PEM-West A, the DC-8 operated from the Yokota US Air Force Base,
Japan, the Hong Kong international airport, and the US Air force Base
in Guam. The NASA airborne component was coordinated with studies
conducted at surface sites sponsored by GTE and other collaborating
APARA agencies.
The international collaboration during PEM-West B, coordinated
through the APARE, included the NASA sponsored PEM-West measurements
(airborne and ground based); the Japanese National Institute of
Environmental Science (NIES) sponsored study-perturbation by East
Asian Continental Air Mass to Pacific Oceanic Troposphere
(PEACAMPOT-airborne and ground based measurements); the Taiwan
sponsored Climate and Air Quality Taiwan Station (CATS) (ground based
measurements); the Hong Kong Polytechnic University (HKPU) Background Air Monitoring Station (ground based
measurements); and ground based stations sponsored by the Peoples
Republic of China and Korea. Important meteorological support was also
provided by the Hong Kong Royal Observatory.