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 Hg^P formation in the atmosphere stems mainly from the adsorption of reactive gaseous Hg^II on aerosol particles, particularly sea salt aerosol. However, the observed comparable abundance of Hg^P over Hg^II 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 Hg^P cycling processes in the marine atmosphere. Results show that a widely used statistics-based scheme could reproduce atmospheric Hg^P concentrations over continents but failed to reproduce the concentrations over the ocean. The Hg^P concentrations particularly relative abundance of Hg^P over Hg^II 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 Hg^P. 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 Hg^II deposition to unrecognized particulate Hg^P deposition over the ocean.