Characteristics of mercury speciation in seawater and emission flux of gaseous mercury in the Bohai Sea and Yellow Sea.

Four cruises were performed in the Bohai Sea (BS) and Yellow Sea (YS) to ascertain the levels and distributions of gaseous elemental mercury (GEM), dissolved gaseous mercury (DGM), methylmercury (MeHg), and total mercury (THg) during 2012 and 2014. Their concentrations and Hg flux exhibited clear spatial-temporal distributions. The GEM level over the BS in spring (2.71 ± 0.49 ng m) was significantly higher than that in fall (1.98 ± 0.91 ng m). Air masses with elevated GEM mainly originated from northern China. During the two cruises in 2012 over the BS, the mean DGM concentration in spring (35.7 ± 4.6 pg l) was comparable to that in fall (32.4 ± 4.6 pg l). During the spring cruise of 2014, the mean DGM concentration in the BS (52.8 ± 12.5 pg l) was comparable to that in the YS (52.4 ± 14.1 pg l), while during the fall cruise of 2014, it was significantly lower in the BS (26.7 ± 14.4 pg l) than in the YS (57.2 ± 17.9 pg l). DGM represents a small portion of unfiltered THg in the BS (3.95%) and YS (5.12%). The MeHg and MeHg% values were higher in nearshore areas than in open sea, indicating higher productivity in coastal regions. The Hg flux in the YS (4.56 ng m h) was about twice that in the BS. The annual emission Hg fluxes from the BS and YS were 2.71 and 23.68 tons yr, respectively.