O3, sulfur dioxide (SO2), aerosols, and precipitation chemistry are carried out. In addition, networks of stations have been established for national-scale precipitation chemistry measurements by NEPA and CAMS and regional-scale measurements by RCEES and several provincial agencies.

Aerosol chemistry studies also focus primarily on urban and regional-scale environmental problems. An exception is the study of Asian dust storms that exert a large influence on the chemical and physical characteristics of aerosols and precipitation over eastern Asia and the northern Pacific Ocean. CAMS has an extensive program to study the formation and transport of dust storms. A cooperative international program, the China and America Air-Sea Experiments (CHAASE), has been conducted to study the compositions of aerosol particles and precipitation in China and Korea since 1990 (Arimoto et al. 1990, Gao et al. 1992a,b). The program involves the State Oceanographic Administration (SOA), the Korean Ocean Research and Development Institute, and the University of Rhode Island.2 In addition, as part of the WCRP Tropical Ocean and Global Atmosphere (TOGA) program (see below), compositions of rain and aerosol samples collected over the western Pacific Ocean were analyzed under bilateral projects between the U.S. National Oceanographic and Atmospheric Administration (NOAA) and the State Meteorological Administration (SMA) and between NOAA and the Chinese National Research Center for Marine Environment Forecasts at the State Oceanographic Administration (SOA).

Total O3 is measured by scientists from the CAS Institute of Atmospheric Physics at a station in Beijing and one in Yunnan Province. Ground-based remote sensing techniques for measuring stratospheric trace gases such as O3 and nitrite (NO2) are under development at CAS Anhui Institute of Optics and Fine Mechanics and Peking University. Modeling studies of the stratospheric O3 are conducted at the CAS Institute of Atmospheric Physics, SMA, CAS University of Science and Technology of China, and Peking University. In addition, chemistry models of the troposphere are also under development at some of these institutes for the study of regional and global environmental problems.

In September and October 1991, the U.S. National Aeronautics and Space Administration (NASA) conducted the first of its four planned airborne experiments over the Pacific Basin as part of what are collectively called the Pacific Exploratory Mission (PEM). Their major objectives are to investigate the budgets of tropospheric oxidants, reactive nitrogen species, and sulfur species. The first of these experiments, known as PEM-West, is coordinated through the East Asia-



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