The Pacific coast of East Asia, like Europe and North America, is a region in which human activities impose a heavy load on the atmosphere. Air pollutants released from this region are known to affect not only the Asian continent but also a large area of the Pacific. Moreover, emissions of SO₂ and NO_X, which in western Europe and North America have been decreasing or at least remaining steady since 1980, are still growing in Asia and will likely continue to do so in the 21st century. Although the Pacific coast of East Asia has a significant influence on regional and global environments, the atmospheric chemistry of this area has not been thoroughly or systematically monitored and thus is not fully understood. Scientific data on the pollutants transported from Asia to Japan and the Pacific Ocean are very important in analyzing the present status of the atmosphere of this area and in developing international cooperation on air pollution controls.

Experimental methods

The atmosphere was sampled from an aircraft (either a Cessna 404 or a Fairchild Swearingen SA-226 [Merlin-IV]). Ambient air was introduced into analyzers from a glass manifold connected to a 9.5-mm Teflon tube that led from an inlet set either on the nose of the Cessna or on a window forward of the engine air intake of the Merlin. Aerosols were collected on Fluoropore filters with a high-volume sampler (Kimoto) through a 25-mm stainless steel tube set either on the copilot's window on the Cessna 404 or on the window forward of the engine air intake of the Merlin.

Sulfur dioxide was measured on board with a TECO Model 43S pulse fluorescence SO₂ monitor. A nitrogen oxide analyzer based on the NO2 chemiluminescence method, which itself is based on the reaction of NO + O₃ Æ NO₂*, was modified for use in aircraft observations. The main modifications were the introduction of the sample air intake method (800 SCCM) using a mass flow meter, a method to generate ozone for reaction from pure oxygen, and reduction of the absolute pressure of the reactor (from 5.7 to 5.2 kPa) to improve the efficiency of the chemiluminescence. A metallic molybdenum reducing agent (with a reaction temperature of 320C) supported on a carrier was used to convert NO_X to NO. In the experiment in February 1999, the position of the converter was changed to make it possible to measure NO_Y in place of NO_X. The resulting data were stored in a TEAC DR-F3 digital data recorder at 10 s intervals. PAN in air was collected by a U-shaped trap packed with

0.2 g Teflon beads and chilled with granulated dry ice. Each aerosol sample filter was divided into 2 equal parts in our laboratory, and each part underwent ultrasonic extraction in 10 mL of distilled water. Cations and anions in the extracted solutions were analyzed by ion chromatography. The ambient temperature and relative humidity were measured with a Väisala HMP 133Y thermometer-hygrometer.

PEACAMPOT campaign

The National Institute for Environmental Studies (NIES) created the "Perturbation by the East Asian Continental Air Mass to the Pacific Oceanic Troposphere" (PEACAMPOT) program as part of its "Study on Transport and Changes in Qualities of Acidic and Oxidizing Substances in East Asia" project, which is funded by the Japan Environment Agency, for promoting comprehensive studies of the global environment. NIES has been chemically monitoring the atmosphere over East Asia in cooperation with other institutes under international programs.

Aircraft and intensive ground-based observations were started in 1991 as a five-year project under an initiative taken by NIES. Figure 1 shows the area covered by PEACAM-POT.

Figure 1. Observation area for PEACAMPOT campaign. A: North of the Sea of Japan, B: southwest of the Sea of Japan, C: East China Sea, D: Yellow Sea, E: west of Yaku Island.

In 1991, observations were made as part of an international research project based on the IGAC/APARE program, in cooperation with the PEM-West program of NASA (USA). In 1992, we conducted aerial observations over the Sea of Japan off the San'in Region of Japan and over the East China Sea off the southern coast of Cheju Island, Korea. These were made at four different altitudes to measure the vertical distribution of pollutants more thoroughly than in the previous year. At the same time, we made intensive ground-based observations in the Oki Islands and in the Happo-one Mountains, Japan.

In 1993, we made our observations in concert with Phase B of PEM-West. Aerial observations were made in early spring. Intensive ground-based observations were conducted in the Oki Islands and in the Happo-one Mountains. At the same time, the Korean Institute of Science and Technology (KIST) conducted intensive ground-based observations on Cheju Island and gave us their data.

In 1994, intensive aerial and ground-based observations were conducted in and over Yaku Island, Japan, with the same objective as before. Yaku Island is an area where valuable nature has been preserved, hence Yaku Island became a World Heritage Area. Nevertheless, it is being jeopardized by environmental degradation, especially the decline of forests. Thus, it was a matter of great interest to learn how the atmospheric pollutants transported from Asia affect the natural environment of the island.

In 1995, the final year of the project, observations focused mainly on the influence of slightly polluted areas in northeastern Asia. We made both ground-based and aerial observations in the northern Sea of Japan. The main objective was to see how air masses are transported not from areas with large-scale pollution sources, such as China and Korea, but from areas with few pollution sources, such as eastern Russia.

All data have been compiled and published as data books [Hatakeyama, 1993, 1994, 1995, 1996a, 1996b] and data CDs [Hatakeyama, 1997, 1998]. We drew four main conclusions:

1. The air over the seas between Japan and the Asian continent is strongly affected by anthropogenic emissions, given the vertical distribution of PAN (Figure 2). The vertical gradient in pollutant concentrations was reported to be gentle over a polluted continent [Meyrahn et al., 1984; central Europe] but steep over clean oceans [Singh and Salas, 1983]. The slope in Figure 2 is similar to that reported for the polluted continent.
2. A high concentration of SO2 was transported over the western part of the Sea of Japan via the Korean peninsula. This distance is very short.
3. The concentration of sulfate was higher over the East China Sea, where air pollutants spent a relatively long time and were oxidized well.
4. The air mass transported from northern Eurasia was less polluted than that from other areas mentioned above. Findings 2-4 are already reported [Hatakeyama et al., 1995].

Figure 2. Vertical distribution of PAN over the seas between Japan and the Asian continent. Horizontal bars show 1 standard deviation. Adapted from data in Watanabe et al. [1998] and Hatakeyama [1998].

PEACAMPOT II campaign

From 1996 to 1998, the second phase of PEACAMPOT (PEACAMPOT II) was conducted as part of a project of the Global Environment Research Fund of the Environment Agency of Japan called "Studies on the Development of a Comprehensive Model of Atmosphere and Soil and an International Cooperative Field Survey to Clarify the Budget of Environment-Acidifying Substances in East Asia." The target area was confined to the northern East China Sea to determine the transport of air pollutants from central China. Samples were taken in almost the same area as before (Figure 3). Ground-based observations were made on Fukue Island.

Figure 3. Flight plans for PEACAMPOT II.

On 2 February 1999, we found very high concentrations of SO₂ over the observation area (Figure 4). SO₂ was high not only at low altitude (~300 m) but also at high altitude (~2300 m). NO_X, aldehydes, gaseous HCl, and gaseous HNO3 showed very similar variations. Sulfate and ammonium showed similar variations (data not shown). Thus, it can be said that the air sampled on that day was highly polluted and well mixed. The vertical distribution of the PAN/NOY ratio also clearly showed the mixing of air (Figure 5). On 4 and 6 February, the ratio showed a remarkable difference between upper and lower altitudes. In contrast, it showed little dependence on altitude on 2 February, which indicates that the air was thoroughly mixed within the lower troposphere.

Figure 4. Altitude of measurements and concentrations of SO2 and ozone measured on 2 February 1999.

Figure 5. Vertical distribution of PAN/NOY ratio.

A low pressure system originating near Taiwan passed over this area very quickly on 1 February, and the weather was very windy on 2 February. The system moved along the southern coast of Japan to reach the northwest Pacific; it would have caused mixing. Uno et al. [1998] pointed out that just such a weather pattern should cause a large-scale, long-range transport of polluted air. The results of 2 February support this contention very well. Thus, we found one more path for the long-range transport of an air mass from Asia in addition to the three transport patterns we found in PEACAMPOT [Hatakeyama et al., 1997] (findings 2-4 of the previous section). This other path is from central China (around Shanghai) via the northern East China Sea to Japan.

Acknowledgments

The members of PEACAMPOT II science team were K. Muranao, H. Mukai, and F. Sakamaki (National Institute for Environmental Studies); H. Bandow (Osaka Prefecture University); and Y. Komazaki and S. Tanaka (Keio University). Their contribution is gratefully acknowledged.

References

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