Multiscale modeling of the atmospheric fate and transport of mercury

A numerical simulation of the atmospheric fate and transport of mercury (Hg ) was conducted using a multiscale approach. Two different spatial scales w ere used to simulate (1) the global cycling of atmospheric Hg and (2) the a tmospheric deposition of Hg in potentially sensitive areas. The global simu lation was conducted using an updated version of our global Hg chemical tra nsport model (CTM). The imbedded continental simulation was conducted using an updated version of the regional/continental CTM, TEAM. Simulations were conducted using 1998 meteorology and 1998/1999 emission inventories. Model simulation results show improved performance compared to earlier simulatio ns. For example, the global simulation shows background concentrations of H g species, interhemispheric gradients, and vertical gradients that are cons istent with available measurements. The comparison of simulated Hg wet depo sition fluxes with data from the Mercury Deposition Network in the United S tates shows a coefficient of determination (r(2)) of 0.75, little bias (-3% ), and an average gross error of 21%. The major remaining sources of uncert ainties, which include speciation of Hg emissions, Hg atmospheric chemistry , and dry and wet deposition processes for Hg species, are discussed.