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

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.

Atmospheric mercury in the southern hemisphere – Part 1: Trend and inter-annual variations of atmospheric mercury at Cape Point, South Africa, in 2007–2017, and on Amsterdam Island in 2012–2017

“…An upward trend was surprising because manual mercury measurements at the same site in 1995 -2004 showed a downward trend. Downward trends of atmospheric mercury concentrations and of mercury wet deposition have also been reported for many sites in the northern hemisphere (Temme et al, 2007;Cole et al, 2014;Steffen et al, 2015;Weigelt et al, 2015;Weiss-Penzias et al, 2016;Marumoto et al, 2019) but Cape Point has been the only station in the southern hemisphere with a long enough mercury concentration record to calculate trends. The northern hemispheric downward trend has been attributed to decreasing emissions from the North Atlantic Ocean due to decreasing mercury concentrations in subsurface water (Soerensen et al, 2012) and more recently to decreasing global anthropogenic emissions mainly due to the decline of mercury release from commercial products and the changes of Hg 0 /Hg 2+ speciation in flue gas of coal-fired utilities after implementation of NOx and SO2 emission controls (Zhang et al, 2016).…”

Mercury biogeochemical cycling: A synthesis of recent scientific advances

“…Many studies show that ambient atmospheric Hg concentrations are declining (Martin et al, 2017;Marumoto et al, 2019;Navrátil et al, 2018;Zhang et al, 2016), though this appears not to be the case universally (Fu et al, 2015;Martin et al, 2017). Declining Hg will, in general, mean declining ecosystem impacts, but the timing and spatial aspects of those changes are uncertain because atmospheric impacts to the surface are complex.…”

A New Monitoring Effort for Asia: The Asia Pacific Mercury Monitoring Network (APMMN)

“…Lulin, Taiwan since measurements began in 2006. Marumoto et al [35] measured decreasing GEM trends at Cape Hedo, Okinawa, Japan, but no significant annual trends in either GOM or PBM 2.5 . For deposition, Fu et al [10] reported recent wet deposition rates in China from measurements and other studies.…”