The first simultaneous and continuous underway measurements of atmospheric gaseous elemental mercury, carbon dioxide and methane in the marine boundary layer: Results of cruise study in the Sea of Japan in May 2018

This paper presents the results of the first simultaneous measurements of gaseous elemental mercury (GEM) and greenhouse gases (CH4 and CO2) in the marine boundary layer over the Sea of Japan. Continuous underway measurements of atmospheric GEM, CH4 and CO2 concentrations were carried out aboard the R/V Akademik M. A. Lavrentiev from 4 to May 26, 2018. GEM concentrations (range: 0.4-1.6 ng/m3; mean +/- standard deviation (SD): 1.0 +/- 0.2 ng/m3; N = 938) were lower than both the atmospheric background and previously observed values in this area. Concentrations of CH4 (range: 1922.6-2010.6 ppb; mean +/- SD: 1942.2 +/- 10.8 ppb) and CO2 (range: 408.9-436.1 ppm; mean +/- SD: 412.5 +/- 2.5 ppm) were higher than both the average global atmospheric concentrations in May, and the average annual values. Concentration-weighted trajectory (CWT) analysis highlighted the Korean peninsula, northeastern China, southern Primorsky Krai (Russia) and the southwestern coast of Hokkaido (Japan) as potential source areas influencing atmospheric GEM, CH4 and CO2 concentrations during the cruise. Vertical distribution of the CWT values for all the measured gaseous species identified the lower atmosphere up to 1000 m as source layer. The same layer was also characterized by lower CWT values for CH4 and CO2, which were associated with atmospheric transport from the central part of the Sea of Japan. With increasing altitude, the CWT values for GEM and CH4 decreased, while the CO2 values began to rise from 2000 m reflecting the respiration of terrestrial ecosystems and, possibly, atmospheric transport from fires in western Russia. The study shows potential source regions influencing GEM, CH4 and CO2 concentrations in the atmosphere over the Sea of Japan in May 2018.