Long-Term Observation of Atmospheric Speciated Mercury during 2007–2018 at Cape Hedo, Okinawa, Japan
Kohji Marumoto,
Noriyuki Suzuki,
Yasuyuki Shibata,
Akinori Takeuchi,
Akinori Takami,
Norio Fukuzaki,
Kazuaki Kawamoto,
Akira Mizohata,
Shungo Kato,
Takashi Yamamoto,
Jingyang Chen,
Tatsuya Hattori,
Hiromitsu Nagasaka,
Mitsugu Saito
Affiliations
Kohji Marumoto
Department of Environment and Public Health, National Institute for Minamata Disease (NIMD), 4058-18, Hama, Minamata-shi, Kumamoto 867-0008, Japan
Noriyuki Suzuki
Center for Health and Environmental Risk Research, National Institute for Environmental Studies (NIES), 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506, Japan
Yasuyuki Shibata
Center for Environmental Measurement and Analysis, National Institute for Environmental Studies (NIES), 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506, Japan
Akinori Takeuchi
Center for Environmental Measurement and Analysis, National Institute for Environmental Studies (NIES), 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506, Japan
Akinori Takami
Center for Regional Environmental Research, National Institute for Environmental Studies (NIES), 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506, Japan
Norio Fukuzaki
Department of Environmental Science, Niigata Institute of Technology, 1719, Fujihashi, Kashiwazaki-shi, Niigata 945-1195, Japan
Kazuaki Kawamoto
Graduate School of Fisheries and Environmental Sciences, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki-shi, Nagasaki 852-8521, Japan
Akira Mizohata
Professor Emeritus, Osaka Prefecture University, Gakuen-cho, Naka-ku, Sakai-shi, Osaka 599-8570, Japan
Shungo Kato
Department of Applied Chemistry for Environment, Tokyo Metropolitan University, 1-1, Minami-Osawa, Hachioji-shi, Tokyo 192-0397, Japan
Takashi Yamamoto
Institute for Environmental Informatics, IDEA Consultants, Inc. 2-2-2, Hayabuchi, Tsuzuki-ku, Yokohama-shi, Kanagawa 224-0025, Japan
Jingyang Chen
Institute for Environmental Informatics, IDEA Consultants, Inc. 2-2-2, Hayabuchi, Tsuzuki-ku, Yokohama-shi, Kanagawa 224-0025, Japan
Tatsuya Hattori
Institute for Environmental Ecology, IDEA Consultants, Inc. 1334-5, Riemon, Yaizu-shi, Shizuoka 421-0212, Japan
Hiromitsu Nagasaka
Institute for Environmental Ecology, IDEA Consultants, Inc. 1334-5, Riemon, Yaizu-shi, Shizuoka 421-0212, Japan
Mitsugu Saito
Office of Mercury Management, Environmental Health Department, Ministry of the Environment Government of Japan, 1-2-2, Kasumigaseki, Chiyoda-ku, Tokyo 100-8975, Japan
The concentrations of atmospheric gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (particles with diameter smaller than 2.5 μm; PBM2.5) were continuously observed for a period of over 10 years at Cape Hedo, located on the north edge of Okinawa Island on the border of the East China Sea and the Pacific Ocean. Regional or global scale mercury (Hg) pollution affects their concentrations because no local stationary emission sources of Hg exist near the observation site. Their concentrations were lower than those at urban and suburban cities, as well as remote sites in East Asia, but were slightly higher than the background concentrations in the Northern Hemisphere. The GEM concentrations exhibited no diurnal variations and only weak seasonal variations, whereby concentrations were lower in the summer (June−August). An annual decreasing trend for GEM concentrations was observed between 2008 and 2018 at a rate of −0.0382 ± 0.0065 ng m−3 year−1 (−2.1% ± 0.36% year−1) that was the same as those in Europe and North America. Seasonal trend analysis based on daily median data at Cape Hedo showed significantly decreasing trends for all months. However, weaker decreasing trends were observed during the cold season from January to May, when air masses are easily transported from the Asian continent by westerlies and northwestern monsoons. Some GEM, GOM, and PBM2.5 pollution events were observed more frequently during the cold season. Back trajectory analysis showed that almost all these events occurred due to the substances transported from the Asian continent. These facts suggested that the decreasing trend observed at Cape Hedo was influenced by the global decreasing GEM trend, but the rates during the cold season were restrained by regional Asian outflows. On the other hand, GOM concentrations were moderately controlled by photochemical production in summer. Moreover, both GOM and PBM2.5 concentrations largely varied during the cold season due to the influence of regional transport rather than the trend of atmospheric Hg on a global scale.
