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The objectives of this study are to identify the spatial and temporal distributions of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and fine particulate mercury (Hg P 2.5 ) in the marine boundary layer (MBL) of the Bohai Sea (BS) and Yellow Sea (YS), and to investigate the relationships between mercury species and meteorological parameters. The mean concentrations of GEM, RGM, and Hg P 2.5 were 2.03 ng m −3 , 2.5 pg m −3 , and 8.2 pg m −3 in spring, and 2.09 ng m −3 , 4.3 pg m −3 , and 8.3 pg m −3 in fall. Reactive mercury (RGM + Hg P 2.5 ) represented < 1% of total atmospheric mercury (GEM + RGM + Hg P 2.5 ), which indicated that most mercury export in the MBL was GEM and the direct outflow of reactive mercury was very small. Moreover, GEM concentrations over the BS were generally higher than those over the YS both in spring and fall. Although RGM showed a homogeneous distribution over the BS and YS both in spring and fall, the mean RGM concentration in fall was significantly higher than that in spring. In contrast, the spatial distribution of Hg P 2.5 generally reflected a gradient with high levels near the coast of China and low levels in the open sea, suggesting the significant atmospheric mercury outflow from China. Interestingly, the mean RGM concentrations during daytime were significantly higher than those during nighttime both in spring and fall, while the opposite results were observed for Hg P 2.5 . Additionally, RGM positively correlates with air temperature while negatively correlates with relative humidity. In conclusion, the elevated atmospheric mercury levels in the BS and YS compared to other open seas suggested that the human activities had a significant influence on the oceanic mercury cycle downwind of China. [ABSTRACT FROM AUTHOR]

Abstract: We determined the concentrations of gaseous element mercury (GEM) and particulate mercury (Hg P ) in the Asian marine boundary layer (MBL) during the spring and fall of 2013 and 2014 to investigate the spatial-temporal distributions of GEM and Hg P . A cascade impactor was used to collect Hg P in nine size fractions ranging from 10 μm to <0.4 μm. The concentrations of Hg P in PM 10 (hereafter referred to as HgP 10) tended to decrease from the land to the open sea both in spring and fall. The mean (±SD) concentrations of HgP 10 during spring and fall were 15.3 ± 9.1 and 15.8 ± 4.4 pg m −3 respectively, while the mean GEM concentration during the entire study period was 2.02 ± 1.08 ng m −3 (N = 12,341), which was much higher than those of other remote oceans. Moreover, the size distributions of Hg P was bi-modal during spring, and Hg P was found mainly (57%) in coarse fractions (2.1–10 μm), while Hg P was dominated by fine particles (<2.1 μm) during fall. The concentrations of GEM and HgP 10 in the Bohai Sea (BS) were generally higher than those in the Yellow Sea and East China Sea. Furthermore, the HgP 10 concentrations were slightly higher during fall than during spring except the data measured in the BS for its specific location. The average dry deposition fluxes of Hg P were calculated to be 2.77 ng m −2 d −1 during spring and 1.92 ng m −2 d −1 during fall, respectively, which were comparable to those measured at rural sites in North America, but considerably lower than those measured in urban cities in China. Additionally, compared to fine particles, coarse particles contributed more than 90% to the total dry deposition of Hg P due to higher deposition velocities. [ABSTRACT FROM AUTHOR]

The Yellow Sea in East Asia receives great Hg input from regional emissions. However, Hg cycling in this marine system is poorly investigated. In late spring and late fall 2012, we determined gaseous elemental Hg (GEM or Hg(0)) in air and dissolved gaseous Hg (DGM, mainly Hg(0)) in surface waters to explore the spatial-temporal variations of Hg(0) and further to estimate the air/sea Hg(0) flux in the Yellow Sea. The results showed that the GEM concentrations in the two cruises were similar (spring: 1.86 ± 0.40 ng m −3 ; fall: 1.84 ± 0.50 ng m −3 ) and presented similar spatial variation pattern with elevated concentrations along the coast of China and lower concentrations in the open ocean. The DGM concentrations of the two cruises were also similar with 27.0 ± 6.8 pg L −1 in the spring cruise and 28.2 ± 9.0 pg L −1 in the fall cruise and showed substantial spatial variation. The air/sea Hg(0) fluxes in the spring cruise and fall cruise were estimated to be 1.06 ± 0.86 ng m −2 h −1 and 2.53 ± 2.12 ng m −2 h −1 , respectively. The combination of this study and our previous summer cruise showed that the summer cruise presented enhanced values of GEM, DGM and air/sea Hg(0) flux. The possible reason for this trend was that high solar radiation in summer promoted Hg(0) formation in seawater, and the high wind speed during the summer cruise significantly increased Hg(0) emission from sea surface to atmosphere and subsequently enhanced the GEM levels. [ABSTRACT FROM AUTHOR]

The Yellow Sea (YS) is a potentially important receptor for enhanced anthropogenic Hg emissions from East Asia. In the past decade, high quality Hg data related to this marine system has a significant increase. Here we review the available total Hg data and then develop the first Hg mass balance to obtain insights into the sources, sinks, pathways and processes regulating the Hg cycle in the YS. The result suggests that a total of 178.9 ± 36.8 kmol Hg is held in the water column with an input of 109.7 ± 17.2 kmol year and an output of 89.7 ± 14.5 kmol year. The input mainly comes from atmospheric deposition (56.2 kmol or 51.2 % of the input) and river discharge (25.0 kmol or 22.8 % of the input). The output is dominated by Hg(0) evasion from sea surface (37.2 kmol or 41.5 % of the output) and sedimentation (33.0 kmol or 36.8 % of the output). Although the result shows an increase of Hg in the water column (~11 ± 13 % annually), the high uncertainties of the estimate suggest that this result should be considered carefully. Future mass balance development would benefit from improving the understanding of following processes: tempo-spatial variations of atmospheric Hg deposition (especially the dry deposition), riverine Hg distribution and fate in the estuary, air/sea Hg(0) exchange and the controlling factors, and the waterborne Hg scavenging as well as sedimentation in the open ocean. [ABSTRACT FROM AUTHOR]