Improved Mechanistic Modeling on Reproducing Particle-Bound Mercury in the Marine Atmosphere

Mercury (Hg) is a neurotoxic pollutant that is ubiquitous on the planet and receives global concern because of its adverse health effects. Particle-bound HgP formation in the atmosphere stems mainly from the adsorption of reactive gaseous HgII on aerosol particles, particularly sea salt aerosol. However, the observed comparable abundance of HgP over HgII in the marine atmosphere has not been reproduced by traditional statistics-based schemes, which were constructed by continental observations. This study incorporated an improved mechanistic scheme in an atmospheric chemical transport model to simulate SSA-bound HgP cycling processes in the marine atmosphere. Results show that a widely used statistics-based scheme could reproduce atmospheric HgP concentrations over continents but failed to reproduce the concentrations over the ocean. The HgP concentrations particularly relative abundance of HgP over HgII in the marine atmosphere could be successfully reproduced by the process-based scheme. Accordingly, a new global atmospheric Hg cycling budget was constructed, manifesting mainly in the atmospheric burden of 4 Mg, dry deposition of 160 Mg yr–1, and wet deposition of 1410 Mg yr–1 for SSA-bound HgP. The new insight on the global atmospheric Hg budget sheds light on the re-examination of Hg deposition risks in the ocean owing to a transition from previously recognized gaseous HgII deposition to unrecognized particulate HgP deposition over the ocean.