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

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

Wang, Chunjie / Wang, Zhangwei / Ci, Zhijia / Zhang, Xiaoshan / Tang, Xiong

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 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 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.

Highlights • Spatial-temporal distributions of GEM and Hg^P in the Asian MBL were discussed. • Size distributions of Hg^P were bi-modal in spring and uni-modal in fall. • The coarse mode was dominant in spring while the fine mode was dominant in fall. • The coarse particles contributed more than 90% to the total dry deposition of Hg^P.