PEM West A Summary

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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, and with APARE airborne sampling activities.

The international collaboration during PEM-West A, coordinated through the APARE, included the NASA sponsored PEM-West measurements (airborne and ground based); the NSF, NCAR, and NOAA sponsored MLOPEX-II ground based measurements at Mauna Loa, Hawaii; 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); 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.

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