Improved model for mercury emission, transport and deposition

Most regional models that have been developed to study the behaviour of mercury (Hg) in the environment do not include detailed treatment of natural (i.e. non-anthropogenic) Hg emissions. We have developed a Hg emission model including natural sources; incorporated it into the CMAQ-Hg model (US EPA) and used it to study the behaviour of Hg in the atmosphere. Our natural Hg emission model uses an algorithm based on meteorology to calculate the emission from vegetation, soil and water using Hg concentrations in soil and water. Using our new model, we carried out simulations for the months of May to September 2000 inclusive on a domain covering eastern North America containing 75 by 70 grid cells at a resolution of 36 km. The simulated daily average natural Hg emission flux varied between 1.8 and 3.7 ng m−2 h−1, with the maximum occurring in July. The simulation found that the total natural emission averaged across the domain is about twice the anthropogenic emission. Hg concentration in the air and wet deposition amounts were higher in the eastern part of the domain than in the western part and reflected both local sources and transport. We report for the first time comparisons of hourly and daily Hg concentrations measured by CAMNet monitoring stations with model simulations done at the same timescales. The correlation coefficients (R) between modelled daily average total gaseous Hg concentrations and measurements for Point Petre, Egbert and Burnt Island are between 0.74 and 0.82. Neglecting natural emissions led to poorer correlations (between 0.22 and 0.51), indicating the importance of including an accurate and detailed treatment of natural Hg emissions in atmospheric Hg models.