Spatial-temporal distributions of gaseous element mercury and particulate mercury in the Asian marine boundary layer

We determined the concentrations of gaseous element mercury (GEM) and particulate mercury (HgP) 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 HgP. A cascade impactor was used to collect HgP in nine size fractions ranging from 10 μm to <0.4 μm. The concentrations of HgP in PM10 (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 HgP was bi-modal during spring, and HgP was found mainly (57%) in coarse fractions (2.1-10 μm), while HgP 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 HgP 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 HgP due to higher deposition velocities.