Naoki Kaneyasu (Senior Research Scientist), Global Environment Study Group, the Research Institute for Environmental Management Technology (Director: Hiroaki Tao) of the National Institute of Advanced Industrial Science and Technology (AIST) (President: Tamotu Nomakuchi), Akinori Takami (Chief) and Kei Sato (Senior Researcher), Asian Atmosphere Section, Asian Environmental Research Group of the National Institute for Environment Studies (NIES) (President: Shinichiro Ohgaki), and Masahiko Hayashi (Professor) and Keiichiro Hara (Assistant Professor), Department of Earth System Science, Faculty of Science, Fukuoka University (President: Takuya Eto), jointly clarified that the concentration of fine aerosols (PM_2.5) in northern Kyushu in the spring of 2009 is due almost entirely to the influx of air pollutants from other areas.

With the rapid economic development in East Asia, there is concern about an increase in air pollutants transported to Japan, which is located leeward of the westerlies.  In the spring of 2009, we started year-round observations to monitor the concentration of PM_2.5 in Fukuoka City, the major city in northern Kyushu with a population of approximately 1,440,000, and on Fukue Island, one of the Goto Islands located approximately 190 km west of Fukuoka City with a population of approximately 40,000.  We further analyzed the composition of particulate matters in the atmosphere collected between early and mid April.  From the measurements, we found that the concentrations of PM_2.5 in Fukuoka City and Fukue Island fluctuated synchronously, with about 12 hour delay in Fukuoka City.  In addition, PM_2.5 concentrations on Fukue Island were the same as, or slightly higher than, those in Fukuoka City during the events (Fig. 1).

On Fukue Island, monthly average PM_2.5 concentration in April was also higher than that in Fukuoka City.  These indicate that in northern Kyushu, even in a large city, PM_2.5 concentration during the spring of 2009 was subject to regional pollution caused by the transport of PM_2.5 from the other area.  In order to lay the foundations for future measures to decrease PM_2.5 concentrations, it is important to promote measures against the emission sources, not only in Japan but also in East Asia, through international cooperation.

Figure 1: Time series of PM2.5 concentrations on Fukue Island, one of the Goto Islands, and in Fukuoka City from early to mid April of 2009

The achievement of the Environmental Air Quality Standard for particles of 10 μm or less in diameter in the atmosphere (suspended particulate matters: SPM) has improved considerably in Japan since 2000 by virtue of various legal regulations and technological measures addressing emissions from automobiles and industrial activities.  On the other hand, the National Ambient Air Quality Standard for much smaller particles, PM_2.5, was established in the US on the basis of long-term epidemiological survey on their health effects in 1997.  The health effects of PM_2.5 have also been studied in Japan, which recently set up the Environmental Air Quality Standard for PM_2.5 on September 9, 2009.  As such, studies on the composition, origin, secondary formation, and transformation of PM_2.5 are essential to formulate and promote measures against PM_2.5 pollution.

Particulate matters originating in East Asia will supposedly increase in the near future, and there is much concern about their influence on Japan, which is located on the leeward side of the westerlies.  Judging from the occurrence of high-concentration ozone in northern Kyushu in May 2007, we are at a point where trace components in the atmosphere transported from East Asia have to be regarded as air pollutants that directly affect the achievement of the domestic Environmental Air Quality Standards.

AIST has been conducting research on the diffusion, transport, and transformation of particulate matters in the atmosphere to contribute to the formulation of policies for prevention of air pollution.  In November 2008, a project on the influence of particulate matters in the atmosphere on plants and humans (Grants-in-Aid for Scientific Research: Impact of aerosol on plants and humans in East Asia) sponsored by the Ministry of Education, Culture, Sports, Science and Technology (http://www.tuat.ac.jp/~aerosol/index.html) was inaugurated.  As one of the groups involved in this project, our research team installed automatic measurement instruments at the Observatory of Atmospheric Environment in Fukue Island and at Fukuoka University in Fukuoka City in the spring of 2009, and started to monitor the concentrations of PM_2.5 and black carbon particles every hour throughout the year.  At the same time, we also measured the same items at the atmospheric observatory of NIES at Cape Hedo on the main island of Okinawa.  Additionally, in early to mid April of 2009, we intensively observed and analyzed the concentration and composition of particulate matters harmful to the human health such as polycyclic aromatic hydrocarbons and heavy metals.

During the two weeks in early to mid April, a time when transport events are frequently observed, we found that time series of PM_2.5 concentrations (Fig. 1) on Fukue Island and in Fukuoka City shared almost identical fluctuations and levels.  In particular, a prominent transport event was observed on April 8, with an hourly average concentration of 90 μg/m³ on Fukue Island.  While, in leeward Fukuoka City, a maximum concentration of 80 μg/m³ was recorded 12 hours later.  The daily average concentrations were 72.6 μg/m³ and 60.7 μg/m³ on Fukue Island and in Fukuoka City, respectively (The environmental standard is a daily average concentration of 35 μg/m³).  In another transport event from the late evening of April 5 to early morning of April 6, the maximum concentration in Fukuoka City was observed 8 hours after that on Fukue Island (The maximum concentrations were 72.7 μg/m³ and 73.6 μg/m³ in Fukuoka City and on Fukue Island, respectively.).  In detail, the mechanism of the short–time-span transport event of April 5 - 6 was different from that of the long-time-span transport event centered on April 8.  The former occurred behind a cold front, whereas the latter occurred in a current on the margin of a migratory anticyclone.  We also observed an event on April 16 that increased the concentration only on Fukue Island.

From an intensive observation conducted in the same period, we found that sulfate particles accounted for the largest portion of the high-concentration PM_2.5, followed by particulate organics.  Sulfate particles are formed through the oxidization of sulfur dioxide in the atmosphere, which is emitted from the combustion of sulfur-containing substances such as coal.  Figure 2 shows the daily average concentrations of non-seasalt sulfate in Total Suspended Particulates including PM_2.5.  In the period with increased concentrations centered on April 8, the concentrations were higher on Fukue Island than in Fukuoka City.

Figure 2: Comparison of daily average concentrations of non-seasalt sulfate (non-seasalt SO42-) in total suspended particulates (TSP) from early to mid April of 2009 on Fukue Island and in Fukuoka City (The collection of TSP began in Fukuoka City 9 hours after it had started on Fukue Island.)

As described above, on Fukue Island, for which the emission of air pollutants is far less than that for Fukuoka City, the maximum concentrations during the transport events appeared earlier than in Fukuoka City.  Furthermore, the concentrations of pollutants during the transport events were higher on Fukue Island than that in Fukuoka City.  These two observations indicate that the influence of Fukuoka City on the fluctuation of PM_2.5 concentrations on Fukue Island in the spring is relatively small, and that the concentration levels and fluctuations at the two sites reflect transport from the Asian Continent.

In addition, we compared the monthly average PM_2.5 concentrations at the two observation sites (Fig. 3).  We found that the concentrations during the period up to June when the rainy season ends (essentially, the period under the influence of the Asian continental air mass) are 8–15 μg/m³ higher than those during the summer, and that differences in concentration between Fukue Island and Fukuoka City are quite small.  We also found that the average concentration in April is higher on Fukue Island than in Fukuoka City.

To summarize, the springtime high PM_2.5 concentration in northern Kyushu is subject to regional pollution caused by the influx of aerosols from other areas, even in such a large city as Fukuoka.  This finding indicates the importance of efforts through international cooperation to promote measures against the emission sources within East Asia as well as in Japan.

Figure 3: Comparison of monthly average PM2.5 concentrations between Fukue Island and Fukuoka City during the first six months of FY2009

NIES is currently analyzing polycyclic aromatic hydrocarbons collected during the same period.  As of October 2009, we are conducting intensive ground-based observations and analyses, in concert with airborne measurements of air pollutants by a research group at Tokyo University of Agriculture and Technology.  The data obtained by this research will be used in an epidemiological survey to be conducted in the same area by the University of Tsukuba, in order to advance research on the health effects of PM_2.5 and harmful components.