Improved Model Predictions of Global Soil Mercury Volatilization Fluxes

The air-soil exchange of elemental mercury (Hg⁰) is a crucial component of the global atmospheric Hg cycle, yet current estimates of soil Hg⁰ volatilization fluxes remain highly uncertain. Previous studies have largely relied on empirical curve models, which have not been systematically validated against global-scale observational fluxes. Here, we developed a process-based bidirectional exchange model (GSEM) to predict global soil Hg⁰ emissions. The model incorporates key processes, including photochemical and non-photochemical redox reactions, soil-water partitioning, and gaseous diffusion. By constraining model outputs with global observations, we demonstrate that four mainstream empirical curve models underestimate air-soil Hg⁰ exchange fluxes, while the GSEM model offers improved performance in replicating the fluxes and yields an improved global estimate of 2272.3 Mg yr⁻¹. Emission hotspots are primarily concentrated in tropical regions such as the Amazon Basin, Central Africa, Southeast Asia, and East Asia, and the latitudinal variations in simulated fluxes closely align with global soil respiration patterns. This process-based approach significantly enhances the accuracy of air-soil Hg⁰ exchange predictions and contributes to reducing uncertainty in global Hg budget assessments.