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Long-Term Observation of Atmospheric Speciated Mercury during 2007–2018 at Cape Hedo, Okinawa, Japan

1
Department of Environment and Public Health, National Institute for Minamata Disease (NIMD), 4058-18, Hama, Minamata-shi, Kumamoto 867-0008, Japan
2
Center for Health and Environmental Risk Research, National Institute for Environmental Studies (NIES), 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506, Japan
3
Center for Environmental Measurement and Analysis, National Institute for Environmental Studies (NIES), 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506, Japan
4
Center for Regional Environmental Research, National Institute for Environmental Studies (NIES), 16-2, Onogawa, Tsukuba-shi, Ibaraki 305-8506, Japan
5
Department of Environmental Science, Niigata Institute of Technology, 1719, Fujihashi, Kashiwazaki-shi, Niigata 945-1195, Japan
6
Graduate School of Fisheries and Environmental Sciences, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki-shi, Nagasaki 852-8521, Japan
7
Professor Emeritus, Osaka Prefecture University, Gakuen-cho, Naka-ku, Sakai-shi, Osaka 599-8570, Japan
8
Department of Applied Chemistry for Environment, Tokyo Metropolitan University, 1-1, Minami-Osawa, Hachioji-shi, Tokyo 192-0397, Japan
9
Institute for Environmental Informatics, IDEA Consultants, Inc. 2-2-2, Hayabuchi, Tsuzuki-ku, Yokohama-shi, Kanagawa 224-0025, Japan
10
Institute for Environmental Ecology, IDEA Consultants, Inc. 1334-5, Riemon, Yaizu-shi, Shizuoka 421-0212, Japan
11
Office of Mercury Management, Environmental Health Department, Ministry of the Environment Government of Japan, 1-2-2, Kasumigaseki, Chiyoda-ku, Tokyo 100-8975, Japan
*
Author to whom correspondence should be addressed.
Atmosphere 2019, 10(7), 362; https://doi.org/10.3390/atmos10070362
Received: 31 May 2019 / Revised: 21 June 2019 / Accepted: 26 June 2019 / Published: 30 June 2019
(This article belongs to the Special Issue Atmospheric Mercury in Asia)
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Abstract

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. View Full-Text
Keywords: atmospheric Hg; speciation; long-term observation; annual trend; Japan; East Asia atmospheric Hg; speciation; long-term observation; annual trend; Japan; East Asia
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Marumoto, K.; Suzuki, N.; Shibata, Y.; Takeuchi, A.; Takami, A.; Fukuzaki, N.; Kawamoto, K.; Mizohata, A.; Kato, S.; Yamamoto, T.; Chen, J.; Hattori, T.; Nagasaka, H.; Saito, M. Long-Term Observation of Atmospheric Speciated Mercury during 2007–2018 at Cape Hedo, Okinawa, Japan. Atmosphere 2019, 10, 362.

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